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Bridge Engineering – Types of Bridges

Bridge Engineering –Types of Bridges

 

Over the last several thousand years, bridges have served one of the most important roles in the development of our earliest civilizations, spreading of knowledge, local and worldwide trade, and the rise of transportation.

Initially made out of most simple materials and designs, bridges soon evolved and enabled carrying of wide deckings and spanning of large distances over rivers, gorges, inaccessible terrain, strongly elevated surfaces and pre-built city infrastructures.

Starting with 13th century BC Greek Bronze Age, stone arched bridges quickly spread all around the world, eventually leading to the rise of the use of steel, iron and other materials in bridges that can span kilometers.

To be able to serve various roles, carry different types of weight, and span terrains of various sizes and complexities, bridges can strongly vary in their appearance, carrying capacity, type of structural elements, the presence of movable sections, construction materials and more.

Bridges by Structure

The core structure of the bridge determines how it distributes the internal forces of tension, compression, torsion, bending, and sheer . While all bridges need to handle all those forces at all times, various types of bridges will dedicate more of their capacity to better handle specific types of forces. The handling of those forces can be centralized in only a few notable structure members (such as with cable or cable-stayed bridge where forces are distributed in a distinct shape or placement) or be distributed via truss across the almost entire structure of the bridge.

Arch Bridges

Arch bridges – use arch as a main structural component (arch is always located below the bridge, never above it). With the help of mid-span piers, they can be made with one or more arches, depending on what kind of load and stress forces they must endure. The core component of the bridge is its abutments and pillars, which have to be built strong because they will carry the weight of the entire bridge structure and forces they convey.

Galena Creek Bridge, a cathedral arch bridge

Arch bridges can only be fixed, but they can support any decking fiction, including transport of pedestrians, light or heavy rail, vehicles and even be used as water-carrying aqueducts. The most popular materials for the construction of arch bridges are masonry stone, concrete, timber, wrought iron, cast iron and structural steel.

Examples of arch bridge are “Old Bridge” in Mostar, Bosnia, and Herzegovina, and The Hell Gate Bridge in New York. The oldest stone arch bridge ever is Greek Arkadiko Bridge which is over 3 thousand years old. The longest stone arch bridge is Solkan Bridge in Slovenia with an impressive span of 220 meters.

Beam Bridges

Beam bridges – employ the simplest of forms – one or several horizontal beams that can either simply span the area between abutments or relieve some of the pressure on structural piers. The core force that impacts beam bridges is the transformation of vertical force into shear and flexural load that is transferred to the support structures (abutments or mid-bridge piers).

Rio Grande in Las Cruces bridge

Because of their simplicity, they were the oldest bridges known to man. Initially built by simply dropping wooden logs over short rivers or ditches, this type of bridge started being used extensively with the arrival of metalworks, steel boxes, and pre-stressed construction concrete. Beam bridges today are separated into girder bridges, plate girder bridges, box girder bridges and simple beam bridges.

Individual decking of the segmented beam bridge can be of the same length, variable lengths, inclined or V-shaped. The most famous example of beam bridge is Lake Pontchartrain Causeway in southern Louisiana that is 23.83 miles (38.35 km) long.

Lake Pontchartrain Causeway bridge

Truss Bridges

Truss bridges – is a very popular bridge design that uses a diagonal mesh of most often triangle-shaped posts above the bridge to distribute forces across almost entire bridge structure. Individual elements of this structure (usually straight beams) can endure dynamic forces of tension and compression, but by distributing those loads across entire structure, entire bridge can handle much stronger forces and heavier loads than other types of bridges.

Common types of truss bridges

The two most common truss designs are the king posts (two diagonal posts supported by single vertical post in the center) and queen posts (two diagonal posts, two vertical posts and horizontal post that connect two vertical posts at the top). Many other types of the truss are in use – Allan, Bailey, Baltimore, Bollman, Bowstring, Brown, Howe, Lattice, Lenticular, Pennsylvania, Pratt, and others.

 

Admiral T.J. Lopez Bridge

Truss bridges were introduced very long ago, immediately becoming one of the most popular bridge types thanks to their incredible resilience and economic builds that require a very small amount of material for construction. The most common build materials used for truss bridge construction are timber, iron, steel, reinforced concrete and prestressed concrete. The truss bridges can be both fixed and moveable.

Cantilever Bridges

Cantilever bridges – are somewhat similar in appearance to arch bridges, but they support their load, not through a vertical bracing but trough diagonal bracing with horizontal beams that are being supported only on one end. The vast majority of cantilever bridges use one pair of continuous spans that are placed between two piers, with beams meeting on the center over the obstacle that bridge spans (river, uneven terrain, or others). Cantilever bridge can also use mid-bridge pears are their foundation from which they span in both directions toward other piers and abutments.

Howrah Bridge, Kolkata

The size and weight capacity of the cantilever bridge impact the number of segments it uses. Simple pedestrian crossings over very short distances can use simple cantilever beam, but larger distances can use either two beams coming out of both abutments or multiple center piers. Cantilever bridges cannot span very large distances. They can be bare or use truss formation both below and above the bridge, and most popular constriction material are structural steel, iron, and prestressed concrete.

Same of the most famous cantilever bridges in the world are Quebec Bridge in Canada, Forth Bridge in Scotland and Tokyo Gate bridge in Japan.

Tokyo Gate bridge in Japan

Tied Arch Bridges

Tied arch bridges – are similar in design to arch bridges, but they transfer the weight of the bridge and traffic load to the top chord that is connected to the bottom cords in bridge foundation. The bottom tying cord can be reinforced decking itself or a separate deck-independent structure that interfaces with tie-rods.

Generic tied-arch bridge with a movable support on the right side

They are often called bowstring arches or bowstring bridges and can be created in several variations, including shouldered tied-arch, multi-span discrete tied-arches, multi-span continuous tied-arches, single tied-arch per span and others. However, there is a precise differentiation between tied arch bridges and bowstring arch bridges – the latter use diagonally shaped members who create a structure that transfer forces similar to in truss bridges.

Tied arch bridges can be visually very stunning, but they bring with them costly maintenance and repair.

The Fort Pitt Bridge is a tied-arch bridge. The arches terminate atop slender raised piers and are tied by the road deck structure

Suspension Bridges

Suspension bridges – utilize spreading ropes or cables from the vertical suspenders to hold the weight of bridge deck and traffic. Able to suspend decking over large spans, this type of bridge is today very popular all around the world.

View of the Chain Bridge invented by James Finley Esq.” (1810) by William Strickland. Finley’s Chain Bridge at Falls of Schuylkill (1808) had two spans, 100 feet and 200 feet

Originally made even in ancient times with materials such as ropes or vines, with decking’s of wood planks or bamboo, the modern variants use a wide array of materials such as steel wire that is either braided into rope or forged or cast into chain links. Because only abutments and piers (one or more) are fixed to the ground, the majority of the bridge structure can be very flexible and can often dramatically respond to the forces of wind, earthquake or even vibration of on-foot or vehicle traffic.

Some of the most famous examples of suspension bridges are Golden Gate Bridge in San Francisco, Akashi Kaikyō Bridge in Japan, and Brooklyn Bridge in New York City.

Akashi Kaikyō Bridge in Japan

Cable-Stayed Bridges

Cable-stayed bridges – use deck cables that are directly connected to one or more vertical columns (called towers or pylons) that can be erected near abutments or in the middle of the span of the bridge structure. Cables are usually connected to columns in two ways – harp design (each cable is attached to the different point of the column, creating the harp-like “strings” and “fan” designs (all cables connect to one point at the top of the column). This is a very different type of cable-driven suspension than in suspension bridges, where decking is held with vertical suspenders that go up to main support cable.

Suspension bridge

Cable-stayed bridge, fan design

Originally constructed and popularized in the 16th century, today cable-stayed bridges are a popular design that is often used for spanning medium to long distances that are longer than those of cantilever bridges but shorter than the longest suspension bridges. The most common build materials are steel or concrete pylons, post-tensioned concrete box girders and steel rope. These bridges can support almost every type of decking (only not including heavy rail) and are used extensively all around the world in several construction variations.

The famous Brooklyn Bridge is a suspension bridge, but it also has elements of cable-stayed design.

Brooklyn Bridge

Fixed or Moveable Types

The vast majority of all bridges in the world are fixed in place, without any moving parts that forces them to remain in place until they are demolished or fall due to unforeseen stress or disrepair. However, some spaces are in need of multi-purpose bridges which can either have movable parts or can be completely moved from one location to another. Even though these bridges are rare, they serve an important function that makes them highly desirable.

Fixed Bridges

Fixed – Majority of bridges constructed all around the world and throughout our history are fixed, with no moveable parts to provide higher clearance for river/sea transport that is flowing below them. They are designed to stay where they are made to the time they are deemed unusable due to their age, disrepair or are demolished. Use of certain materials or certain construction techniques can instantly force bridge to be forever fixed. This is most obvious with bridges made out of construction masonry, suspension and cable-stayed bridges where a large section of decking surface is suspended in the air by the complicated network of cables and other material.

Small and elevated bridges like Bridge of Sighs, ancient stone aqueducts of Rome such as Pont du Gard, large medieval multi-arched Charles Bridge, and magnificent Golden Gate Bridge are all examples of bridges that are fixed.

Temporary Bridges

Temporary bridges – Temporary bridges are made from basic modular components that can be moved by medium or light machinery. They are usually used in military engineering or in circumstances when fixed bridges are repaired, and can be so modular that they can be extended to span larger distances or even reinforced to support heightened loads. The vast majority of temporary bridges are not intended to be used for prolonged periods of time on single locations, although in some cases they may become a permanent part of the road network due to various factors.

 

The simples and cheapest temporary bridges are crane-fitted decking made out of construction wood that can facilitate passenger passage across small spans (such as ditches). As the spans go longer and loads are heightened, prefabricated bridges made out of steel and iron have to be used. The most capable temporary bridges can span even distances of 100m using reinforced truss structure that can facilitate even heavy loads.

Moveable Bridges

Moveable bridges – Moveable bridges are a compromise between the strength, carrying capacity and durability of fixed bridges, and the flexibility and modularity of the temporary bridges. Their core functionality is providing safe passage of various types of loads (from passenger to heavy freight), but with the ability to move out of the way of the boats or other kinds of under-deck traffic which would otherwise not be capable of fitting under the main body of the bridge.

Movable Bridge in Chicago, USA

Most commonly, movable bridges are made with simple truss or tied arch design and are spanning rivers with little to medium clearance under their main decks. When the need arises, they can either lift their entire deck sharply in the air or sway the deck structure to the side, opening the waterway for unrestricted passage of ships. While the majority of the moveable bridges are small to medium size, large bridges also exist.

The most famous moveable bridge in the world is London Tower Bridge, whose clearance below the decking rises from 8.6m to 42.5m when opened.

Types by Use

When thinking about bridges, everyone’s first thought are structures that facilitate easy passenger and car traffic across bodies of water or unfriendly terrain. However, bridges can be versatile and can support many different types of use. Additionally, some bridges are designed in such way to support multiple types of use, combining, for example, multiple car traffic lanes and pedestrian or bicycle passageways (such as a present on the famous Brooklyn Bridge in New York City).

Pedestrian Bridges

Pedestrian bridges – The oldest bridges ever made were designed to facilitate passenger travel over small bodies of water or unfriendly terrain. Today, they are usually made in urban environments or in terrain where car transport is inaccessible (such as rough mountainous terrain, forests, swamps, etc.). Since on-the foot or bicycle passenger traffic does not strain the bridges with much weight, designs of those bridges can be made to be more extravagant, elegant, sleek and better integrated with the urban environment or created with cheaper or less durable materials. Many modern pedestrian-only bridges are made out of modern material, while some tourist pedestrian bridges feature more exoteric designs that even include transparent polymers in the decking, enabling users unrestricted view to the area below the bridge.

Charles Bridge as viewed from Petřínská rozhledna

While the majority of modern pedestrian bridges were made from the start to facilitate only on-foot access (such as Venice’s Ponte Vecchio and Rialto bridge), other bridges can be transformed from other purposes to pedestrian-only function (such as Prague’s historic Charles bridge).

Car Traffic

Car Traffic – This is the most common usage of the bridge, with two or more lanes designed to carry car and truck traffic of various intensities. Modern large bridges usually feature multiple lanes that facilitate travel in a single direction, and while the majority of bridges have a single decking dedicated to car traffic, some can even have an additional deck, enabling each deck to be focused on providing travel in a single direction.

Double-decked Bridges

Double-decked bridges – Multi-purpose bridges that provide an enhanced flow of traffic across bodies of water or rough terrain. Most often they have a large number of car lanes, and sometimes have dedicated area for train tracks. For example, in addition to multiple car lanes on the main decking, famous Brooklyn Bridge in NYC features an isolated bicycle path.

Train Bridges

Train bridges – Bridges made specifically to carry one or multiple lanes of train tracks, although in some cases train tracks can also be placed beside different deck type, or on different decking elevation. After car bridges, train bridges are the second-most-common type of bridges.

Cikurutug Bridge, Indonesia

First train bridges started being constructed during the early years of European Industrial Revolution as means of enabling faster shipment of freight between ore mines and ironworks factories. With the appearance of safe passenger locomotives and cars, the rapid expansion of railway networks all around Europe, US and Asia brought the need for building thousands of railway bridges of various sizes and spans.

Pipeline Bridges

Pipeline Bridges – Less common as a standalone bridge type, pipeline bridges are constructed to carry pipelines across water or inaccessible terrains. Pipelines can carry water, air, gas and communication cables. In modern times, pipeline networks are usually incorporated in the structure of existing or newly built bridges that also house regular decking that facilitates pedestrian, car or railway transport.

A pipeline bridge carrying the Trans-Alaska Pipeline

Pipeline bridges are usually very lightweight and can be supported only with the basic suspension bridge construction designs. In many cases, they are also equipped with walkways, but they are almost exclusively dedicated for maintenance purposes and are not intended for public use.

Aqueducts

Aqueducts – are ancient bridge-like structures that are part of the larger viaduct networks intended to carry water from water-rich areas to sometimes very distant dry cities. Because of the need to maintain a low but constant drop of elevation of the main water-carrying passageway, aqueducts are very precisely created structures that sometimes need to reach very high elevations and maintain rigid structure while spanning large distances. The largest aqueducts are made of stone and can have multiple tiers of arched bridges created one on top of each other.

 

The aqueduct at Querétaro city

The modern equivalent of the ancient aqueduct bridges are pipeline bridges, but while the viaduct network used natural force of gravity to push water toward the desired destination, modern pipeline networks use electric pumps to propel water and other material.

Commercial Bridges

Commercial bridges – These are bridges that host commercial buildings such as restaurants and shops. Most commonly used in medieval bridges created in urban environments where they took advantage of the constant flow of pedestrian traffic, today these kinds of bridges are rarely constructed with a notable amount of them being found in modern India. Slovakia’s city of Bratislava is a home of a car passageway bridge with a large tower that hosts a restaurant on top of it.

Medieval bridges are much more commonly known for their commercial applications. Italy is home to two of the best known commercial bridges in the world – the famous multi-tiered Ponte Vecchio in the city center of Florence, and brilliant white Rialto Bridge that spans the scenic Grand Canal in Venice. Both feature numerous shops that offer tourist memorabilia and jewelry.

Types by Materials

The core function of the bridge is to span a stable decking intended for the transport of pedestrians, cars or trains while enduring weight of its core structure, the weight of the traffic, and the natural forces that slowly but surely erode its durability. Various materials can help bridge designers to achieve their goal, and provide stable and long-lasting bridges that require varying levels of maintenance (and in cases of historic bridges, restorations). Here is the breakdown of all the common types of materials that are used in historical and modern bridge building:

Natural Materials

Bridges of natural materials – The first bridges ever made were constructed from unprocessed natural materials, starting from simple wooden logs that were placed across small rivers or ditches, to the large rope-tied bridges that are constructed over large canyons and mountain ranges in inhospitable areas of Asia.

Wood

Wood (Wooden bridges) – Wood is an excellent material that can be used for the creation of small to medium-sized bridges that are best suited for pedestrian or low-weight car transport. In modern times, wooden bridges are most commonly found for spanning short distances or being used to transport people, cars, and livestock over rough terrain or small rivers in Covered Bridges.

Stone

Stone (Stone bridges) – Stone is an excellent long-lasting natural material that can be used for the construction of bridges that can last for centuries. Stone pieces can even be used to construct very large bridge structures that don’t even use concrete – such as in Pont du Gard aqueduct in southern France that uses the weight of individual stones to make an entire 48.8 m high and 275 m structure stable for two thousand years.

Concrete and Steel

Concrete and Steel bridges – Durable, long-lasting and highly versatile modern materials that are today used for the creation of countless types of bridge designs. Coupled with the presence of cables and other modern materials, these types of bridges represent the majority of all the bridges that are currently in public pedestrian, car, and train transport use today.

Advanced Materials

Bridges of advanced materials – As decades go on, modern industry enables bridge builders to gain access to wide array of advanced materials that offer noticeable advantages over traditional construction processes.

 

 

 

High Tech for Hard Hats

High Tech for Hard Hats

 

A Caterpillar dozer can weigh up to100 tons of steel, powered by over 800 horsepower behind a 12-foot wide blade. It moves dirt—tons of it—literally leveling hills, making roadways, sites for campuses, skyscrapers. Armored dozers have been used in war, destroying berms that were made to guard against the U.S. invasion of Iraq in 2003. Nothing in their way stood a chance. It was the modern-day rendition of Hannibal’s elephants. You’d expect the operator of anything so potentially devastating to be paying very close attention to where the machine is heading. But look at a modern construction site, and you would probably see the operator absorbed in his Android tablet.

Relax. He’s not watching videos on Hulu. What he’s watching can greatly accelerate the pace of a construction project, reduce use of materials, and provide precision from a machine that belies its size.

The tablet in question (a TD250) is like one you might buy, except it can withstand the bumps and grinds of a construction site—the shock, vibration, and rough terrain. “An iPad just won’t cut it,” says Martin Wagener, expert of Trimble’s precise positioning on dozers (his official title is Worldwide Product Implementation manager, Civil Engineering at Trimble). The specially-ruggedized Android tablet ($3K replacement cost) can be seen in bright sunlight. It can also take a wider range of temperature extremes.

“One is made for watching videos in my living room,” says Martin. “The other is made for work.”

A Trimble TD250, left, is part of the retrofit Earthworks system for dozers. It is displayed at Dimensions 2018, Trimble’s bi-annual user meeting. Picture it rigidly mounted inside the dozer cabin.

 

A properly outfitted dozer, with sensors on its blade, is relaying its exact position and orientation to the tablet 20 times a second to the TD250 tablet as it scrapes the ground. Let’s combine what the blade is seeing to the graded surface model (the final product) and the operator will know exactly if the blade is digging too deep, not enough, or if it is on the right path—and let the operator make adjustments.

“We don’t expect dozer operators to take classes to have to learn how to use Earthworks,” says Martin. Indeed, the Earthwork app does seem to be drop-dead easy to use.

 

The perfect pit. Excavator bucket position being precisely controlled by Trimble Earthworks for Utah-based Rock Structures; the company has said the Earthworks system prevented over digging and reduced spending on fill-in material. (Picture courtesy of Trimble.)

 

A more evolved version of the Trimble Earthworks system will be able to control the blade by itself, rather than rely totally on a human operator.

Trimble Earthworks for dozers was introduced last year. More recent is Earthworks for excavators. Sensors on the bucket and arm of the excavator feed into the tablet, which shows the digging against the construction model.

“I can control a grade to within 3/10 of an inch,” one operator is quoted as saying in a Trimble case history. The software is said to prevent the bucket from exceeding the limits of the dig, as governed by the 3D construction model. Machine operators who used to over dig can now dig more precisely. The same excavation says their newfound ability to dig as needed but not a shovelful more has helped save cost of material. “We use half the gravel to fill in the hole now as we did before,” he says.

Guiding a giant machine to move one pebble without touching the one next to it involves a sequence of technologies. Satellite data (GPS) provide the position, in this case to the sensors on the earthmovers, for the right street address. Triangulation between cell towers will put the excavator buckets and dozer blades within feet of the target. Zeroing in on the final fractions of an inch comes with lasers and IMUs (inertial measuring units). An IMU—now commonly found in smart phones—can tell where they are even without a signal.

Super precise positioning seems to be Trimble’s forte. The company, founded by Charley Trimble in 1978, has prided itself as being the surveyor’s favorite, its line of sight surveying equipment the gold standard of the industry. The company has reinvented itself with each wave of technological advances, embracing lasers, point clouds, drones and design software. It’s acquisition of SketchUp alone has vaulted it to the lead in number of 3D CAD users. Whatever can be used to locate precisely on Earth—whether the technology uses satellites, cell towers, lasers or IMUs—count on Trimble to be on top of it.

 

Sensors on the dozer blade provide XYZ position, plus rotation on all 3 axes.

Source: www.engineering.com

The extension of the BIM domain

The extension of the BIM domain

 

The BIM (Building Information Model), we hear a lot about it and we think we know what it is. It’s about Building, therefore construction, about Information, therefore data, and Modeling, that is design, therefore appearance.

At least that’s the only thing this acronym tells us.

As for going beyond the raw meaning of the acronym, it is a very different matter. But what exactly is it about? Is BIM really new to start with?

Wikipedia, which can be taken at face value because it has so many observers on the lookout for the slightest failure, tells us this: “Architect Phil Bernstein, a consultant at Autodesk, was the first to use the term BIM for “Building Information Modelling.”

It therefore appears that the term was originally used in the field of architecture. But would it be possible that we did BIM before BIM without knowing it?

This is quite possible because, any religious consideration aside, it is not the name that creates the thing.

Mechanical design disciplines have long been modelling 3D objects to mimic reality by representing static and dynamic properties and doing BIM without saying it. The faithful 3D representation of reality, associated with what is called PLM (Product Lifecycle Management) is very similar to what is called BIM. Purists will tell me no, but all the basics were already there.

The BIM concept is therefore not new, far from it. What is new is the extension of its domain. No one knows exactly where the boundaries of this field lie at the moment, for two reasons: no one has explored them yet, and would have they done so, they would change every day.

The BIM is at the hinge of two worlds. The real world and the digital world. Your computer is also at the crossroads of two worlds. A vinyl record, which is not new, is also at the hinge of two worlds, it is both a material and totally immaterial object since it is capable of reproducing music. Magic.

If we are only at the beginning in the field of BIM in architecture and infrastructure, it is easy to imagine where BIM will take us. It will lead us into a parallel world, that of a digital world that no longer represents reality, but reproduces it.

We are only in the early stages. We are currently ecstatic when we see a digital model on a computer screen, but these are only simplified objects, modelled in 3D, static, to which we have attached some poor properties. The future is not there, the future is in the complete digital reproduction of the real world not as it is at a particular moment, but as it will be at all times in the future (and was in the past). A building is a living thing, it gets old, it gets damaged, it is sometimes rebuilt (not yet by itself but we will come to it, yes it will…). It is this life of buildings and infrastructures that in the future we will reproduce electronically with all the necessary realism so that we can no longer distinguish between the real and the artificial.

Some video games have already made good progress in this direction. And in video games there are characters. There will naturally be some in the BIM in architecture and city planning. Autodesk software, for example, that simulates crowd movements, will be integrated into these building models, but much more than that, we will reproduce the way human beings work, their thinking, their behaviour, their mistakes, too, to make them live in this artificial world. This already exists in an embryonic way in some video games. Humanoid robotics will join the BIM.

Finally, digital artificial reality will be far superior to reality since, in addition to visually and functionally reproducing it, it will add databases that are missing from reality. A piece of furniture does not know how big it is. A piece of furniture in the world of BIM and artificial reality will know this. BIM will bring intelligence to objects.

It is ultimately a very natural evolution of Humanity. Equipping yourself with increasingly efficient tools is a story that began in prehistoric times. But the characteristic of the digital age is that tools no longer transform only the real but also the representation that we have made of them. I wouldn’t teach anyone who has a teenager at home, that is, on their computer, by saying that the real world, for a teenager, is a vague and strange concept whose necessity they don’t really understand. I’m not sorry about that. In my youth, I would have liked to have lived in this double world.

We will not lack BIM managers. They already have the (two) feet firmly anchored in this second world.

Finally, I’ll let Confucius speak, him who was already responding to critics of BIM 2500 years ago:

When you do something, know that you will have against you, those who would like to do the same thing, those who wanted the opposite, and the vast majority of those who did not want to do anything.

 

Written by Patrick EMIN – www.Linkedin.com

Why does it cost between $25-$39 million to construct a kilometer of high speed rail in the European Union?

Why does it cost between $25-$39 million to construct a kilometer of high speed rail in the European Union?

 

This $25–39 million per km figure appears to be derived from a 2014 World Bank report that compared the construction cost of Chinese high-speed rail (HSR) projects to comparable European ones. In the same report, Chinese HSR costs ranged from $17–21 million per km, or roughly 30–50% less expensive.

The best way to understand where these numbers are coming from is to dig into the major cost elements of your typical high-speed rail project. Here is a table from that report that looks at the cost breakdown of typical Chinese HSR projects at various speeds:

Source: World Bank — High-Speed Railways in China: A Look at Construction Costs (Page 4)

We will go through each of the categories above to explain how and where the cost differences may be coming from:

  • Land acquisition and resettlement — HSR lines need to be pretty straight to accommodate high-velocity rolling stock and land usage rights along this path need to be acquired. Since property rights are weaker / less developed in China, it is fairly straightforward and thus relatively inexpensive to acquire these land usage rights. This also often involves displacement of existing populations and in China project planners factor in resettlement costs — mainly in the form of building new housing for displaced farming families.
  • Civil works — As one can imagine, there is a ton of civil engineering and construction involved in high-speed rail projects. Unlike regular rail, high-speed rail lines need to be straight. To achieve this, you are often forced to build lots of raised viaducts or bore tunnels in hilly/mountainous areas. This was the biggest area of cost for Chinese HSR projects, a combination of (mostly) labor and raw materials (e.g. cement, steel, gravel, stones etc.).
  • Track — Self-explanatory.
  • Signaling and communications — Specialized systems to manage the entire system and make sure trains don’t crash into each other. Lots of signaling equipment, network equipment, fiber optic lines and software.
  • Electrification — HSR trains are electric and draw power from the electrified track.
  • Rolling stock — The high-speed trains themselves.
  • Buildings including stations — Train stations and related intermodal links (e.g. local metro, bus station, taxi and airport).
  • Other costs — Sometimes (but not always) capitalized interest is included in the total project cost.

 

 

The main reasons why European projects were more expensive most likely boiled down to a few key factors:

  • Higher labor costs — Labor is the largest cost item in civil works and track-laying. European labor is several times more expensive than Chinese labor.
  • Higher land acquisition costs — Stronger property rights in European Union countries means that project planners need to shell out more cash to acquire land along the line’s path. Paying more for the land is not necessarily a terrible outcome, as it represents an internal transfer of wealth from the public to landowners along the track’s path hoot necessarily good either). However, the bigger issue here are delays that it may cause in the construction phase if certain holdouts — leveraging their property rights — refuse to acquiesce (better eminent domain law/process can alleviate this). Longer construction periods translate into higher build and financing costs. To illustrate this point: The Chinese HSR projects usually took 3 to 4 years to complete once construction began while European projects took 2 to 3 years longer.
  • Differences in economies of scale — The sheer scale of Chinese HSR allowed for significant standardization in process, technology, materiasl procurement and design. For example, raised viaducts were preferred in China to “minimize resettlement and the use of fertile land as well as to reduce environmental impacts” (page 5, World Bank Report). Following this, there were a massive number of viaducts that needed to fabricated and attached. So each section was built to standardized specifications (24 or 32 meters, weighing between 750 and 800 tons) and special machinery was invented to lay the viaduct quickly and efficiently.

 

There were differences in other categories as well, but much smaller in impact:

  • Train stations — One thing you will notice about most new Chinese train stations (exception being “mega” stations in Tier I transportation hub cities like Beijing or Wuhan) is that they look quite similar in layout and design. This was done on purpose. Since they were building so many train stations at the same time, many of the designs were standardized from station to station which saved cost. Meanwhile you will notice that many of the European stations are quite unique in design. Basically, Europeans paid more for aesthetics, which while subjective is not necessarily a bad thing either.
  • More expensive rolling stock — France (Alstom), Germany (Siemens) and China (CRRC) used mainly domestically manufactured trains for their networks. Chinese trains are less expensive, reflecting lower embedded labor costs as well as greater economies of scale in manufacturing.
  • Raw materials — Another embedded cost item is materials cost (cement, steel and other raw materials), but since these are commodities, I do not think the cost difference would be that significant.

It is also possible that there were differences in terrain that increased the civil engineering requirements (e.g. bridges and tunnels), but you could really only assess this by looking at the detailed topography on an individual line basis.

What is a two-way slab?

What is a two-way slab?

 

A Two-Way Slab “TWS” is simply a slab carrying loads in both directions (length and width) to its supports (Beams or Columns). This is because it’s length to width ratio is (Long/Short) not big enough for loads to travel in the short direction only (width).

Theoretically speaking:

Loads are lazy, they travel in the shortest path possible, they like to spend the least effort.

Slabs have 4 supports to transfer its loads to (2 in each direction).

  • Slab: A structural element that has large width and length compared to its thickness. Designed to carry whatever loads the building is meant to carry, and transfer it to its the supporting elements.
  • Loads: Slab’s own weight, Slab covering and finish, live loads (people, furniture, machines…etc) etc.
  • Supports: Beams or Columns that the Slab is resting on at its 4 edges (could be on . The slab transfers its loads to the supports > Supports transfer its loads to the foundations on the ground > Foundations transfer all these loads to the grounds below the building.

That being said, let’s assume a (10 x 2) Rectangular Slab (width=2m and length=10m) the ratio is large enough (Long/Short = 10/2 = 5) in this case all the loads will travel much faster through the Short Direction which is the 2m width to the nearest supports.

This makes a One Way Slab “OWS”. On this slab loads will not travel in the Long Direction (the 10m length). The slab will carry 100% of the loads to half of its supports through one direction only. (supports on the other direction will not receive any loads from the slab, therefore these slabs can have 2 supports only at the short direction).

  1. The Length is larger than Double the Width (Long/Short > 2)
  2. 100% of the Loads Travel in the Short Direction only.
  3. Only the 2 Supports on this Short Direction will carry the slab and 100% of its the loads.
  4. We need Reinforcement (steel bars or other) in this direction only to resist the straining actions caused by loads traveling through this direction to the supports.
  5. We will study and design based on one direction only.
  6. Slab thickness is design based on short direction only.

Now assume a (5 x 5) Square Slab with ratio (Long/Short = 5/5 =1), in this case loads will travel in both directions equally, since Long=Short they will spend almost equal effort. Each direction will carry 50% of the loads to its supports.

This makes a Two Way Slab “TWS”. In this case all 4 supports are working and they receive almost equal loads from the slab. (The Slab must be supported from all directions).

  1. The Length is equal to the Width (Long/Short = 1)
  2. Loads Travel in Both Directions. 50% of the total loads through each direction.
  3. All supports (2 pairs in each direction) will carry half of the slab and its loads.
  4. We need equal reinforcement in both directions.
  5. We will study two directions, but since they are equal, we can design one direction and apply the same to the other.
  6. Slab thickness is design based on either direction, since they are equal.

If we have something in between the above two cases, assume a (4×6) Rectangular slab (width=4m, length=6m) Which direction will the loads travel through?

The ratio is (Long/Short = 6/4 = 1.5) which is smaller than double the width (1.5 < 2) which means this a “TWS” as well.

The number we compare to the length to width ratio (2) might be different depending on the Application and the Code we are following (which is based on studies and experiments), but here we assume that the breakpoint is the length being over or under double the width.

So this is also a “TWS” where we predict loads travel in both directions, but will each direction carry 50% of the loads? We know that one direction is shorter than the other, therefore more of our loads will prefer to travel through the easier-shorter direction, and less will travel through the longer direction. Supports will receive a percentage of the Slab loads based on the distance it has to travel.

  1. The Length is smaller than Double the Width (Long/Short <2)
  2. Loads Travel in Both Directions. The short direction transfers a larger percentage of the loads, the long direction transfers a smaller percentage of the loads.
  3. All support (2 pairs in each direction) will carry the slab, but each pair will receive different percentage of the loads.
  4. We need more reinforcement in the short direction (larger percentage of loads > larger bending moment) than we need in the long direction (smaller percentage of loads > smaller bending moment)
  5. We will study and design each direction separately (different loads, different bending moments, different reinforcement)
  6. Slab thickness is designed based on the worst case, the larger straining actions we calculate from the Short or Long direction (most probably the short direction)

Can drones be utilized in construction for creating accurate BIM models?

Can drones be utilized in construction for creating accurate BIM models?

 

Not many years ago, people who thought they were being constantly watched by someone or something were labeled paranoids. But that is not the case right now; times have changed and we live in a world where there are flying cameras watching over human activities. We have seen these flying cameras during sports events, concerts and even during some wedding receptions.

You could call it a plane without a pilot or a flying remote controlled toy camera but how do we define them in a surveying and engineering context? When technically elaborating, they may be identified as tools that capture beneficial digital data and images from a different perspective. These systematic images captured are then used to create a 3D model, point cloud or a Digital Terrain Model (DTM). The DTM statistics are extremely useful for the generation of 3D renderings of any location in a described area and they could come handy for engineers working in various fields like geodesy & surveying, geophysics, and geography.

All this cumulatively contribute to elevated efficiency levels during the different phases of construction engineering. Construction is a one of a kind industry, where even such small gains in efficiency and flexibility can reap billions of savings. With that in mind it’s no real surprise that the engineers are slowly embracing the so called “Drone Revolution”. Now, UAVs are starting to dominate all the 4 stages of Architectural engineering, namely; pre-construction stage, construction stage, post construction stage and finally and most significantly the ongoing safety maintenance stage.

Pre-construction Stage

During preconstruction stage, the project is in its budding stage and the whole design is nourished slowly and carefully by the architects. The paramount activity during this stage is land survey documentation. Drones can provide us with precise and speedy overviews of large sites and high risk areas thereby ensuring that the documentation of land condition is precise. This data can further be used for scheduling and planning of the construction activities which are to happen in the location.

In conventional point cloud methods, there are possibilities of uneven topography due to certain occlusions in the sight, but the bird’s eye vision advantage of drones ensure generation of data across an entire region with the identical consistency in accuracy and density and this data can be even used to create a Building Information Model (BIM) which clearly shows how exactly our building is going to look like after the whole construction process is done, which is very beneficial from the designer’s point of view.

Construction Stage

During the construction stage, there are innumerable difficulties to be dealt with. One such difficulty is the proper documentation of the project progress schedule. Usually there would be a site manager traversing around the site capturing photographs at random points and then preparing the whole site report based on these limited photographs. Needless to say the report would be defective and insufficient. But with the introduction of UAVs into the construction industry, a series of high definition aerial shots and videos can be easily captured so as to get a better insight to the progress that has occurred without actually being on-site. The real time data acquired by light detecting sensors mounted on the Drones can help create point clouds or Building Information Models (BIMs) which can be directly fed into Autodesk’s program line such as BIM, Inventor, AutoCAD and Revit for early damage detection procedures, quality management exercises and other asset evaluation techniques. The point clouds or Building Information Models (BIM models) can be further used to retrieve relevant information at the wish and will.

Post Construction Stage

The post construction stage can be just as problematic as the construction stage. Evaluation of high rise buildings and other complex structures are often a tedious task with the naked eye. Inspecting a building roof using UAV multi – rotor system is an economical and secure way than by using conventional methods. Like laser systems, drones can also be used to capture aerial thermal images to locate the potential hot and cold spots in a building but their 4K quality gives them an upper hand over the low quality laser scanned images. This aesthetic dominance the drones have over conventional laser methodologies are certainly a boon while considering a marketing angle as well. There’s undeniably no better way to advertise a new project than a top to down view from a bird’s eye point of view. An engaging walk through project video is a delightful way to introduce key personnel to the project and get them on board.

Ongoing Safety and Maintenance Stage

The role of UAVs in implementing a safe and secure work atmosphere is the one salient feature that stands out and this simply is the reason why drones have become a household name for safety inspectors in large construction sites. Often in multi-million projects, the officer in charge may not always be around and this is where the live video coverage of the drones strike gold. The live feeds can be accessed by the superiors easily even from a remote location, thereby enabling routine asset inspections, fatigue and damage evaluations and condition surveys at all times. Keeping in mind all this, it is no wonder that UAVs are nicknamed the new onsite “BOSS”.

As researches have demonstrated, in the coming years we are undoubtedly to witness drones spearheading the construction industry. With our eyes and ears virtually in the sky, it’s already quite effortless to identify the contradictions in the ongoing process and in addition to that we can know how aesthetically appealing the buildings are coming up. The control and planning aspects of the construction process have also witnessed considerable changes which were practically unfeasible a few years back. The money and time saved with the support of drones are going to be immeasurable in the future. In short,

Drones can be used for:

  1. Land survey and site inspection during pre-construction stage
  2. Building Information Modeling (BIM) and Point cloud scanning
  3. Marketing and promotional photography during and after construction
  4. Monitoring and tracking onsite activities thereby ensuring accurate work flow
  5. Ensuring routine asset inspections and safety measures at all times

Thus, it is safe to claim that the notion of ‘technology integrated construction’ have advanced by leaps and bounds with the intervention of drones into the construction industry!

 

Source: http://www.advenser.com/blog/

HOW IS 5D BIM TRANSFORMING CONSTRUCTION INDUSTRY

HOW IS 5D BIM TRANSFORMING CONSTRUCTION INDUSTRY

 

BIM is currently the making new revelations in the industry, and changing its practices from information sharing to design coordination and from construction management to construction scheduling and cost planning. To general contractors and construction companies, 4D BIM and 5D BIM remain vital functional aspects and utilities of BIM platforms such as Autodesk Revit or BDS.

What is 5D BIM; Definition

5D BIM can essentially be called as the information sharing in full collaboration as in BIM Level 2 for the physical and functional aspect of BIM. While it can also be said to have an additional dimension to the native 4D construction sequencing models – a dimension time along with costs in Common Data Environment (CDE) of BIM.

Cost planning and estimation with 5D BIM modeling involves more project teams of engineers, sub-contractors and stakeholders. It eliminates the concept of working in isolation. The collaborative modeling of Revit BIM platforms also facilitates quick and automatic generation of quantities, accurate design data fetching and BOQs and BOMs when connected with the cost estimation software. It thus opens avenues for the engineers and consultants towards efficient design, timelines and costs.

5D BIM accelerates pre-construction stages

Another major area where 5D BIM has a very profound impact is helping project managers. Estimating accurate quantity takeoffs, measurements, and costs is the most time-consuming process and error-prone task. Up until now, these processes were done manual by calculating the quantity requirements from the blueprints. But with BIM the process has transformed and increased the productivity for contractors as well as quantity surveyors.

5D streamlines the decision making of a building construction project for the owners and chief contractor. They get the ability to see through the changes in CDE of the design models change done by other stakeholders and design teams. The impacts of design changes and its corresponding changes in costs on each model estimates can be envisioned which helps staying on budgets.

Benefits of 5D BIM

A survey by, McKinsey&Company says that, “75% of companies invested in 5D BIM experiences a positive ROI.”

5D BIM technology offers savings on time by subtracting paper trails, down on overhead costs, rowers etc. and facilitates shorter project cycles. Consequently, governments across the UK, Finland & Singapore have mandated BIM for all public infrastructure projects.

The Virtual Design and Construction capabilities of BIM provide a better understanding of building construction project horizon. Specific designs, construction simulation, topography based sequencing, and cost estimation and logical phasing brings a more coherent approach in the over project execution.
Whole of the project team develops an understanding of the proposed design by staying on same page throughout the project tenure, assumptions made, and cost factors. The team then can have brief BIM meetings for the scope, cost, and schedule which directly have an impact on the time saving factor.

Also the data that is fed in real-time will continuously update the model accordingly so that the alternative designs can also be explored. It shortens the project design development cycle and drives more efficiency in designing output. The “what-if” scenarios can also be evaluated objectively and any economical solution will never be missed out.

Furthermore, all the project stakeholders can visualize the building design way before construction breaks the ground and transparency stays onboard all the time. The cloud isn’t only used to back up your phone.

Future of 5D BIM 

5D BIM, in coming times, will essentially drive the construction industry to new heights. With cloud technology, all the project information will be made accessible to all the team, irrespective of their location and time zones. Construction is soaring and cloud technology is equally popular in the industry as much BIM. About 1/3rd of the construction companies use cloud data and information management and sharing today.

Additionally, there are upcoming technologies like Augmented and Virtual reality transforming to mixed reality where holographic displays of the building design model are seen in layered devices. It will particularly help the building construction project in facility construction, maintenance and operations.

Looking at these disruptions, one thing is sure that 5D BIM is growing and will serve as an important link between designing and construction as well as the designs and operations and maintenance stages. There is no stopping now. Coming times for the construction industry are transitional and there will be several profound impacts on the growth as well as efficiency in practices.

 

Source: https://www.wooloo.org

Types and Causes of Concrete Deterioration

Types and Causes of Concrete Deterioration

 

The exceptional durability of portland cement concrete is a major reason why it is the world’s most widely used construction material. But material limitations, design and construction practices, and severe exposure conditions can cause concrete to deteriorate, which may result in aesthetic, functional, or structural problems.
Concrete can deteriorate for a variety of reasons, and concrete damage is often the result of a combination of factors. The following summary discusses potential causes of concrete deterioration and the factors that influence them.

1. CORROSION OF EMBEDDED METALS

Corrosion of reinforcing steel and other embedded metals is the leading cause of deterioration in concrete. When steel corrodes, the resulting rust occupies a greater volume than the steel. This expansion creates tensile stresses in the concrete, which can eventually cause cracking, delamination, and spalling (Figs. 1 and 2).
Fig. 1. Corrosion of reinforcing steel is the most common cause of concrete deterioration.
Fig. 2. The expansion of corroding steel creates tensile stresses in the concrete, which can cause cracking,
delamination, and spalling.
Steel corrodes because it is not a naturally occurring material.Rather, iron ore is smelted and refined to produce steel. The production steps that transform iron ore into steel add energy to the metal. Steel, like most metals except gold and platinum, is thermodynamically unstable under normal atmospheric conditions and will release energy and revert back to its natural state — iron oxide, or rust. This process is called corrosion.
For corrosion to occur, four elements must be present: There must be at least two metals (or two locations on a single  metal) at different energy levels, an electrolyte, and a metallic connection. In reinforced concrete, the rebar may have many separate areas at different energy levels. Concrete acts as the electrolyte, and the metallic connection is provided by wire ties, chair supports, or the rebar itself.

a – Concrete and the Passivating Layer

Although steel’s natural tendency is to undergo corrosion reactions, the alkaline environment of concrete (pH of 12 to 13) provides steel with corrosion protection. At the high pH, a thin oxide layer forms on the steel and prevents metal atoms from dissolving. This passive film does not actually stop corrosion; it reduces the corrosion rate to an insignificant level. For steel in concrete, the passive corrosion rate is typically 0.1 μm per year.
Without the passive film, the steel would corrode at rates at least 1,000 times higher (ACI 222 2001). Because of  concrete’s inherent protection, reinforcing steel does not corrode in the majority of concrete elements and structures.
However, corrosion can occur when the passivating layer is destroyed. The destruction of the passivating layer occurs when the alkalinity of the concrete is reduced or when the chloride concentration in concrete is increased to a certain  level.

b – The Role of Chloride Ions

Exposure of reinforced concrete to chloride ions is the primary cause of premature corrosion of steel reinforcement. The intrusion of chloride ions, present in deicing salts and seawater, into reinforced concrete can cause steel corrosion if oxygen and moisture are also available to sustain the reaction (Fig. 3). Chlorides dissolved in water can permeate
through sound concrete or reach the steel through cracks.
Fig. 3. Deicing salts are a major cause of corrosion of reinforcing steel in concrete.
Chloride-containing admixtures can also cause corrosion. No other contaminant is documented as extensively in the literature as a cause of corrosion of metals in concrete than chloride ions. The mechanism by which chlorides promote corrosion is not entirely understood, but the most popular theory is that chloride ions penetrate the protective oxide  film easier than do other ions, leaving the steel vulnerable to corrosion.

c – Carbonation

Carbonation occurs when carbon dioxide from the air penetrates the concrete and reacts with hydroxides, such as  calcium hydroxide, to form carbonates. In the reaction with calcium hydroxide, calcium carbonate is formed:
Ca(OH)2 + CO2 → CaCO3 + H2O
This reaction reduces the pH of the pore solution to as low as 8.5, at which level the passive film on the steel is not stable. Carbonation is generally a slow process. In high-quality concrete, it has been estimated that carbonation will proceed at a rate up to 1.0 mm (0.04 in.) per year. The amount of carbonation is significantly increased in concrete with a high water-to-cement ratio, low cement content, short curing period, low strength, and highly permeable or porous paste.
Carbonation is highly dependent on the relative humidity of the concrete. The highest rates of carbonation occur when the relative humidity is maintained between 50% and 75%. Below 25% relative humidity, the degree of carbonation that takes place is considered insignificant. Above 75% relative humidity, moisture in the pores restricts CO2 penetration (ACI 201 1992).
Carbonation-induced corrosion often occurs on areas of building facades that are exposed to rainfall, shaded from sunlight, and have low concrete cover over the reinforcing steel (Fig. 5).
Fig. 4. Carbonation-induced corrosion often occurs on building facades with shallow concrete cover.

d – Dissimilar Metal Corrosion

When two different metals, such as aluminum and steel, are in contact within concrete, corrosion can occur because each metal has a unique electrochemical potential. A familiar type of dissimilar metal corrosion occurs in an ordinary flashlight battery. The zinc case and carbon rod are the two metals, and the moist paste acts as the electrolyte. When the carbon and zinc are connected by a wire, current flows. In reinforced concrete, dissimilar metal corrosion can occur in balconies where embedded aluminum railings are in contact with the reinforcing steel.
Below is a list of metals in order of electrochemical activity:
Zinc / Aluminum / Steel / Iron / Nickel / Tin / Lead / Brass / Copper / Bronze / Stainless Steel / Gold
When the metals are in contact in an active electrolyte, the less active metal (lower number) in the series corrodes.

2. FREEZE-THAW DETERIORATION

 

When water freezes, it expands about 9%. As the water in moist concrete freezes, it produces pressure in the  capillaries and pores of the concrete. If the pressure exceeds the tensile strength of the concrete, the cavity will dilate and rupture. The accumulative effect of successive freeze-thaw cycles and disruption of paste and aggregate can eventually cause significant expansion and cracking, scaling, and crumbling of the concrete (Fig. 5).
The resistance of concrete to freezing and thawing in a moist condition is significantly improved by the use of  intentionally entrained air. Entrained air voids act as empty chambers in the paste for the freezing and migrating water to enter, thus relieving the pressure in the capillaries and pores and preventing damage to the concrete.
Concrete with low permeability is also better able resist the penetration of water and, as a result, performs better when
exposed to freeze-thaw cycles. The permeability of concrete is directly related to its water-to-cement ratio—the lower the water-to-cement ratio, the lower the permeability of the concrete.

Fig 5. Freeze-thaw cycles can cause scaling of concrete surfaces

a – Deicer Scaling

Deicing chemicals used for snow and ice removal, such as sodium chloride, can aggravate freeze-thaw deterioration. The additional problem caused by deicers is believed to be a buildup of osmotic and hydraulic pressures in excess of the normal hydraulic pressures produced when water in concrete freezes. In addition, because salt absorbs moisture, it keeps the concrete more saturated, increasing the potential for freeze-thaw deterioration. However, properly designed and placed air-entrained concrete can withstand deicers for many years.
In the absence of freezing, sodium chloride has little to no chemical effect on concrete. Weak solutions of calcium chloride generally have little chemical effect on concrete, but studies have shown that concentrated calcium chloride solutions can chemically attack concrete. Magnesium chloride deicers have come under recent criticism for aggravating scaling. One study found that magnesium chloride, magnesium acetate, magnesium nitrate, and calcium chloride are more damaging to concrete than sodium chloride (Cody, Cody, Spry, and Gan 1996). Deicers containing ammonium nitrate and ammonium sulfate should be prohibited because they rapidly attack and disintegrate concrete.

b – Aggregate Expansion

 

Some aggregates may absorb so much water (to critical saturation) that they cannot accommodate the expansion and
hydraulic pressure that occurs during the freezing of water. The result is expansion of the aggregate and possible disintegration of the concrete if enough of the offending particles are present. If a problem particle is near the surface of the concrete, it can cause a popout.
D-cracking is a form of freeze-thaw deterioration that has been observed in some pavements after three or more years of service. Due to the natural accumulation of water in the base and subbase of pavements, the aggregate may  eventually become saturated. Then with freezing and thawing cycles, cracking of the concrete starts in the saturated aggregate at the bottom of the slab and progresses upward until it reaches the wearing surface. D-cracking usually starts near pavement joints.
Aggregate freeze-thaw problems can often be reduced by either selecting aggregates that perform better in freeze-thaw cycles or, where marginal aggregates must be used, reducing the maximum particle size.
Fig 6. D-cracking is a form of freeze-thaw deterioration that has been observed in some pavements after three or more
years of service.

3. CHEMICAL ATTACK

Concrete performs well when exposed to various atmospheric conditions, water, soil, and many other chemical exposures. However, some chemical environments can deteriorate even high-quality concrete.  Concrete is rarely, if ever, attacked by solid, dry chemicals. To produce significant attack on concrete, aggressive chemicals must be in solution and above some minimum concentration.

a – Acids

In general, portland cement concrete does not have good resistance to acids. In fact, no hydraulic cement concrete, regardless of its composition, will hold up for long if exposed to a solution with a pH of 3 or lower. However, some weak acids can be tolerated, particularly if the exposure is occasional.
Acids react with the calcium hydroxide of the hydrated portland cement. In most cases, the chemical reaction forms water-soluble calcium compounds, which are then leached away by aqueous solutions (ACI 201 1992).
The products of combustion of many fuels contain sulfurous gases which combine with moisture to form sulfuric acid. Also, certain bacteria convert sewage into sulfuric acid. Sulfuric acid is particularly aggressive to concrete because the calcium sulfate formed from the acid reaction will also deteriorate concrete via sulfate attack (Fig. 7).
Fig. 7. Bacteria in sewage systems can produce sulfuric acid, which aggressively attacks concrete
In addition to individual organic and mineral acids which may attack concrete, acid-containing or acid-producing substances, such as acidic industrial wastes, silage, fruit juices, and sour milk, will also cause damage.
Animal wastes contain substances which may oxidize in air to form acids which attack concrete. The saponification reaction between animal fats and the hydration products of portland cement consumes these hydration products, producing salts and alcohols, in a reaction analogous to that of acids. Acid rain, which often has a pH of 4 to 4.5, can slightly etch concrete, usually without affecting the performance of the exposed surface.
Any water that contains bicarbonate ion also contains free carbon dioxide, a part of which can dissolve calcium carbonate unless saturation already exists. This part is called the “aggressive carbon dioxide.” Water with aggressive carbon dioxide acts by acid reaction and can attack concrete and other portland cement products whether or not they are carbonated.
Calcium-absorptive acidic soil can attack concrete, especially porous concrete. Even slightly acidic solutions that are lime-deficient can attack concrete by dissolving calcium from the paste, leaving behind a deteriorated paste consisting primarily of silica gel.
To prevent deterioration from acid attack, portland cement concrete generally must be protected from acidic environments with surface protective treatments. Unlike limestone and dolomitic aggregates, siliceous aggregates are acid-resistant and are sometimes specified to improve the chemical resistance of concrete, especially with the use of chemical-resistant cement. Properly cured concrete with reduced permeability experience a slightly lower rate of attack from acids.

b – Salts and Alkalis

The chlorides and nitrates of ammonium, magnesium, aluminum, and iron all cause concrete deterioration, with those of ammonium producing the most damage. Most ammonium salts are destructive because, in the alkaline environment of concrete, they release ammonia gas and hydrogen ions. These are replaced by dissolving calcium hydroxide from the concrete. The result is a leaching action, much like acid attack. Strong alkalies (over 20 percent) can also cause concrete disintegration (ACI 515 1979).

c – Sulfate Attack

Naturally occurring sulfates of sodium, potassium, calcium, or magnesium are sometimes found in soil or dissolved in ground-water. Sulfates can attack concrete by reacting with hydrated compounds in the hardened cement. These reactions can induce sufficient pressure to disrupt the cement paste, resulting in loss of cohesion and strength.
Calcium sulfate attacks calcium aluminate hydrate and forms ettringite. Sodium sulfate reacts with calcium hydroxide and calcium aluminate hydrate forming ettringite and gypsum. Magnesium sulfate attacks in a manner similar to sodium sulfate and forms ettringite, gypsum, and brucite (magnesium hydroxide). Brucite forms primarily on the concrete surface, consumes calcium hydroxide, lowers the pH of the pore solution, and then decomposes the calcium silicate hydrates.
Environmental conditions have a great influence on sulfate attack. The attack is greater in concrete exposed to wet/dry
cycling (Fig. 8). When water evaporates, sulfates can accumulate at the concrete surface, increasing in concentration
and their potential for causing deterioration.
Fig 8. The bases of these concrete posts have suffered from sulfate attack
Porous concrete is susceptible to weathering caused by salt crystallization. Examples of salts known to cause  weathering of field concrete include sodium carbonate and sodium sulfate (laboratory studies have also related saturated solutions of calcium chloride and other salts to concrete deterioration). Under drying conditions, salt solutions can rise to the surface by capillary action and, as a result of surface evaporation, the solution phase
becomes supersaturated and salt crystallization occurs, sometimes generating pressures large enough to cause cracking and scaling (Mehta 2000).
Sulfate attack is a particular problem in arid areas, such as the Northern Great Plains and parts of the Western United States. Seawater also contains sulfates but is not as severe an exposure as sulfates in groundwater.

4.  ALKALI-AGGREGATE REACTIVITY

In most concrete, aggregates are more or less chemically inert. However, some aggregates react with the alkali  hydroxides in concrete, causing expansion and cracking over a period of years. This alkali-aggregate reactivity has two forms—alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). ASR is of more concern than ACR because  aggregates containing reactive silica materials are more common.

a – Alkali-Silica Reactivity

Aggregates containing certain forms of silica will react with alkali hydroxide in concrete to form a gel that swells as it draws water from the surrounding cement paste or the environment. In absorbing water, these gels can swell and induce enough expansive pressure to damage concrete:
1. Alkalies + Reactive Silica → Gel Reaction Product
2. Gel Reaction Product + Moisture → Expansion
Typical indicators of alkali-silica reactivity are map (random pattern) cracking and, in advanced cases, closed joints and spalled concrete surfaces (Fig. 9). Cracking usually appears in areas with a frequent supply of moisture, such as close to the waterline in piers, from the ground behind retaining walls, near joints and free edges in pavements, or in piers or columns subject to wick action.
Because sufficient moisture is needed to promote destructive expansion, alkali-silica reactivity can be significantly reduced by keeping the concrete as dry as possible. The reactivity can be virtually stopped if the internal relative humidity of the concrete is kept below 80%. In most cases, however, this condition is difficult to achieve and maintain. Warm seawater, due to the presence of dissolved alkalies, can particularly aggravate alkali-silica reactivity.
Fig. 9. Typical indicators of alkali-silica reactivity are map cracking and, in advanced cases, closed joints and spalled
concrete surfaces

b – Alkali-Carbonate Reactivity

 

Reactions observed with certain dolomitic rocks are associated with alkali-carbonate reaction (ACR). Dedolomitization, or the breaking down of dolomite, is normally associated with expansive alkali-carbonate reactivity. This reaction and subsequent crystallization of brucite may cause considerable expansion.
The deterioration caused by alkali-carbonate reaction is similar to that caused by alkali-silica reaction (Fig. 10); however, alkali-carbonate reaction is relatively rare because aggregates susceptible to this reaction are less common and are usually unsuitable for use in concrete for other reasons, such as strength potential.
Fig. 10. Map cracking pattern caused by alkali-carbonate reactivity.

5. ABRASION/EROSION

Abrasion damage occurs when the surface of concrete is unable to resist wear caused by rubbing and friction. As the  outer paste of concrete wears, the fine and coarse aggregate are exposed and abrasion and impact will cause  additional degradation that is related to aggregate-to-paste bond strength and hardness of the aggregate.
Although wind-borne particles can cause abrasion of concrete, the two most damaging forms of abrasion occur on vehicular traffic surfaces and in hydraulic structures, such as dams, spillways, and tunnels.

a – Traffic Surfaces

Abrasion of floors and pavements may result from production operations or vehicular traffic. Many industrial floors are subjected to abrasion by steel or hard rubber wheeled traffic, which can cause significant rutting.
Tire chains and studded snow tires cause considerable wear to concrete surfaces (Fig. 11). In the case of tire chains, wear is caused by flailing and scuffing as the rotating tire brings the metal in contact with the concrete surface.
Fig 11. Tire chains and studded snow tires can cause considerable wear to concrete surfaces

b – Hydraulic Structures

 

Abrasion damage in hydraulic structures is caused by the abrasive effects of waterborne silt, sand, gravel, rocks, ice, and other debris impinging on the concrete surface. Although high-quality concrete can resist high water velocities for many years with little or no damage, the concrete may not withstand the abrasive action of debris grinding or repeatedly impacting on its surface.
In such cases, abrasion erosion ranging from a few millimeters (inches) to several meters (feet) can result, depending on flow conditions. Spillway aprons, stilling basins, sluiceways, drainage conduits or culverts, and tunnel linings are particularly susceptible to abrasion erosion. Abrasion erosion is readily recognized by its smooth, worn appearance, which is distinguished from the small holes and pits formed by cavitation erosion.
As is the case with traffic wear, abrasion damage in hydraulic structures can be reduced by using strong concrete with hard aggregates. Cavitation is the formation of bubbles or cavities in a liquid. In hydraulic structures, the liquid is water and the cavities are filled with water vapor and air. The cavities form where the local pressure drops to a value that will cause the water to vaporize at the prevailing fluid temperature. Cavitation damage is produced when the vapor cavities collapse, causing very high instantaneous pressures that impact on the concrete surfaces, causing pitting, noise, and vibration.

6. FIRE/HEAT

 

Concrete performs exceptionally well at the temperatures encountered in almost all applications. But when exposed to fire or unusually high temperatures, concrete can lose strength and stiffness (Fig. 12).
Fig. 12. When exposed to fire or unusually high temperatures, concrete can lose strength and stiffness
Numerous studies have found the following general trends:
• Concrete that undergoes thermal cycling suffers greater loss of strength than concrete that is held at a constant temperature, although much of the strength loss occurs in the first few cycles. This is attributed to incompatible dimensional changes between the cement paste and the aggregate.

• Concrete that is under design load while heated loses less strength than unloaded concrete, the theory being that

imposed compressive stresses inhibit development of cracks that would be free to develop in unrestrained concrete.
• Concrete that is allowed to cool before testing loses more compressive strength than concrete that is tested hot. Concrete loses more strength when quickly cooled (quenched) from high temperatures than when it is allowed to cool
gradually.
• Concrete containing limestone and calcareous aggregates performs better at high temperatures than concrete containing siliceous aggregates (Abrams 1956). One study showed no difference in the performance of dolostone and limestone (Carette 1982). Another study showed the following relative aggregate performance, from best to worst: firebrick, expanded shale, limestone, gravel, sandstone and expanded slag.
• Proportional strength loss is independent of compressive strength of concrete.
• Concrete with a higher aggregate-cement ratio suffers less reduction in compressive strength; however, the opposite is true for modulus of elasticity. The lower the water-cement ratio, the less loss of elastic modulus.
• If residual water in the concrete is not allowed to evaporate, compressive strength is greatly reduced. If heated too quickly, concrete can spall as the moisture tries to escape.

7. RESTRAINT TO VOLUME CHANGES

Concrete changes slightly in volume for various reasons, the most common causes being fluctuations in moisture content and temperature. Restraint to volume changes, especially contraction, can cause cracking if the tensile stresses that develop exceed the tensile strength of the concrete.

a – Plastic Shrinkage Cracking

When water evaporates from the surface of freshly placed concrete faster than it is replaced by bleed water, the surface concrete shrinks. Due to the restraint provided by the concrete below the drying surface layer, tensile stresses develop in the weak, stiffening plastic concrete, resulting in shallow cracks of varying depth (Fig. 12). These cracks are often fairly wide at the surface.
Fig. 13. Plastic shrinkage cracks can occur when water evaporates from the surface faster than it is replaced by bleedwater
Plastic shrinkage cracks can be prevented by taking measures to prevent rapid water loss from the concrete surface. Fog nozzles, plastic sheeting, windbreaks, and sunshades can all be used to prevent excessive evaporation.

 

b – Drying Shrinkage Cracking

 

Because almost all concrete is mixed with more water than is needed to hydrate the cement, much of the remaining water evaporates, causing the concrete to shrink. Restraint to shrinkage, provided by the subgrade, reinforcement, or another part of the structure, causes tensile stresses to develop in the hardened concrete. Restraint to drying shrinkage is the most common cause of concrete cracking.
In many applications, drying shrinkage cracking is inevitable. Therefore, control joints are placed in concrete to predetermine the location of drying shrinkage cracks. Drying shrinkage can be limited by keeping the water content of concrete as low as possible and maximizing the coarse aggregate content.

c – Thermal Cracking

 

Concrete expands when heated and contracts when cooled. An average value for the thermal expansion of concrete is about 10 millionths per degree Celcius (5.5 millionths per degree Fahrenheit). This amounts to a length change of 5 mm for 10 m of concrete ( 2 ⁄ 3 in. for 100 ft of concrete) subjected to a rise or fall of 50°C (90°F).
Thermal expansion and contraction of concrete varies with factors such as aggregate type, cement content, water-cement ratio, temperature range, concrete age, and relative humidity. Of these, aggregate type has the greatest influence.
Designers should give special consideration to structures in which some portions of the structure are exposed to temperature changes, while other portions are partially or completely protected. Allowing for movement by using properly designed expansion or isolation joints and correct detailing will help minimize the effects of temperature variations.

 

Free Global DEM Data Sources – Digital Elevation Models

Free topography Data Sources – Digital Elevation Models

 

1. Space Shuttle Radar Topography Mission (SRTM)

NASA only needed 11 days to capture Shuttle Radar Topography Mission (SRTM) 30-meter digital elevation model. Back in February 2000, the Space Shuttle Endeavour launched with the SRTM payload.

Using two radar antennas and a single pass, it collected sufficient data to generate a digital elevation model using a technique known as interferometric synthetic aperture radar (inSAR). C-Band penetrated canopy cover to the ground better but SRTM still struggled in sloping regions with foreshortening, layover and shadow.

In late 2014, the United States government released the highest resolution SRTM DEM to the public. This 1-arc second global digital elevation model has a spatial resolution of about 30 meters. Also, it covers most of the world with absolute vertical height accuracy of less than 16m.
Below, shaded relief images of deeply eroded volcanic terrain in northeast Tanzania demonstrate the improved nature of the highest-resolution SRTM data now being released. The image at left has data samples spaced every 90 meters (295 feet); the image at right has samples spaced every 30 meters (98 feet).

 

2. ASTER Global Digital Elevation Model

ASTER GDEM is an easy-to-use, highly accurate DEM covering all the land on earth, and available to all users regardless of size or location of their target areas.
Anyone can easily use the ASTER GDEM to display a bird’s-eye-view map or run a flight simulation, and this should realize visually sophisticated maps. By utilizing the ASTER GDEM as a platform, institutions specialized in disaster monitoring, hydrology, energy, environmental monitoring etc. can perform more advanced analysis.

The ASTER Global Digital Elevation Model (ASTER GDEM) is a joint product developed and made available to the public by the Ministry of Economy, Trade, and Industry (METI) of Japan and the United States National Aeronautics and Space Administration (NASA).  It is generated from data collected from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), a spaceborne earth observing optical instrument.

The first version of the ASTER GDEM, released in June 2009, was generated using stereo-pair images collected by the ASTER instrument onboard Terra. ASTER GDEM coverage spans from 83 degrees north latitude to 83 degrees south, encompassing 99 percent of Earth’s landmass.

The improved GDEM V2 (released October 17, 2011) adds 260,000 additional stereo-pairs, improving coverage and reducing the occurrence of artifacts. The refined production algorithm provides improved spatial resolution, increased horizontal and vertical accuracy, and superior water body coverage and detection. The ASTER GDEM V2 maintains the GeoTIFF format and the same gridding and tile structure as V1, with 30-meter postings and 1 x 1 degree tiles.

Version 2 shows significant improvements over the previous release. However, users are advised that the data contains anomalies and artifacts that will impede effectiveness for use in certain applications. The data are provided “as is,” and neither NASA nor METI/Japan Space Systems (J-spacesystems) will be responsible for any damages resulting from use of the data.

3. JAXA’s Global ALOS 3D World

 

ALOS World 3D is a 30-meter resolution digital surface model (DSM) captured by the Japan Aerospace Exploration Agency’s (JAXA). Recently, this DSM has been made available to the public.

The neat thing about is that it is the most precise global-scale elevation data now. It uses the Advanced Land Observing Satellite “DAICHI” (ALOS) based on stereo mapping from PRISM.

JAXA has been processing about 100 digital 3D maps per month as part of our engineering validation activities of DAICHI so for. As we conducted research and development for full automatic and mass processing map compilations, we now have a perspective to process 150,000 maps per month. By applying our research and development results, we will start the 3D map processing in March 2014 to complete the global 3D map in March 2016. JAXA will commission the compiling work and service provision to NTT DATA Corporation and Remote Sensing Technology Center (RESTEC), Japan.

In order to popularize the utilization of the 3D map data, JAXA will also prepare global digital elevation model (DEM) with lower spatial resolution (of about 30 meters under our current plan) to publish it as soon as it is ready. Its use will be free of charge. We expect that data from Japan will become the base map for all global digital 3D maps, and contribute to the expansion of satellite data utilizations and the industrial promotion, science and research activities as well as the Group on Earth Observations.

4. Light Detection and Ranging (LiDAR)

 

You might think that finding LiDAR is a shot in the dark.

But it’s not anymore.

Slowly and steadily, we are moving towards a global LiDAR map.

With Open Topography topping the list at #1, we’ve put together a list of some of the 6 best LiDAR data sources available online for free.

Because nothing beats LiDAR for spatial accuracy. After you filter ground returns, you can build an impressive DEM from LiDAR.

And if you still can’t find anything in the link above, try your local or regional government. If you tell them what you are using it for, they sometimes hand out LiDAR for free.

 

Top 3D Rendering Software 2018

Top 3D Rendering Software  2018

 

With the advent of the digital era, rendering software has undergone a plethora of changes. The demand from users of 3D rendering software coupled with technological advancements has influenced the industry to progress over the years. The need has helped the industry revolutionize renderings that are life-like and realistic, thus appealing to clients seeking such services.

One outstanding feature is the active rendering plug-ins that come with the software. The feature has presented a wide array of options for users that can sometimes make it chaotic to use especially for those new to it. Designers and architects often stick to the 3D rendering software they used while in school and update their knowledge with any new updated versions of the software.

Nevertheless, you may be new to the industry or just seeking to expand your tech/software savvy to new visualization heights. It is essential to narrow down your search to what’s best suited for your needs.

Here is a collection of rendering software considered as popular in the industry:

V-Ray

 

V-Ray 3D rendering software is considered as top tier by most of its users. It was developed by the Chaos Group to provide you with the most realistic visualization features. Its latest version (VRay 3.6) was launched in late 2017 with improvements that make its predecessors (version 3.4 and 3.5) look inferior. The improvements are based on the quality of realistic visualization and speeds in rendering.

Pre-loaded final textures like hair, fur, and grass cut rendering time by almost 50% making total rendering time even faster. Adaptive lights algorithm is one of the accelerated lens effects enhanced in VRay. It allows you to adjust glare and bloom of light which will make your final render realistic. Otherwise, it is compatible with various plug-ins such as Cinema 4D, Autodesk Revit, 3DS Max and Google Sketch-up among others.

A review from most users suggests that the engine contains a wide variety of options which could make it difficult to use. The best solution to the problem is to use online tutorials to learn from.

 

Maxwell Render

 

Next Limit Technologies developed Maxwell in Madrid, Spain. You might have heard that it is too slow for rendering images. It may be true as it takes a long time to render extraordinarily sharp and realistic visuals. The rendering software uses a unique lighting engine called “unbiased rendering” responsible for using real-life modeling techniques, unlike other rendering software which uses tricks and shortcuts and results in fewer quality images.

 

The tradeoff in best quality images is the long rendering time the engine takes. Why not be patient for the best quality images? Besides, why not wait for greatness? The stand-alone software is mostly used in the film and animation industry.

Octane Render

 

Octane Render is the newcomer to the industry and has a couple of tricks above its sleeve. Developed by Refractive Software Ltd and OTOY, it is classified as a real-time 3D unbiased rendering application; it’s the first commercially available unbiased renderer to work on the Graphics Processing Unit (GPU). This attribute helps the render engine use the power of your graphics card to facilitate most of its render calculations. So the better your graphics card, the better the rendering speeds.

 

On the contrary, Octane does not have a wealth of resources like VRay and Mental Ray, but its unique dependence on the GPU qualifies it to be among the popular rendering software. As it is new to the game, you may not find many tutorial videos online, and its most significant downside is that it will only work with NVIDIA cards. Sorry ATI card users.

Cinema 4D

 

Cinema 4D brings something different to the table. It is not just a 3D rendering software but also includes animation and motion graphics capabilities. MAXON Computer GmbH developed the application in Germany. It is capable of the typical 3D modeling applications and an added advantage of procedural and polygonal/subd (Catmull–Clark subdivision surface) modeling.

Cinema 4D works as the best ArchiCAD or Vectorworks add-on, especially if you’re an architect on the row for defiance in sticking by ArchiCAD. The programs work seamlessly.

Modo

 

 

Modo makes a name in mainstream listings among famous rendering giants like Mental Ray and VRay for its wholesomeness. It makes a list because of its ability to model and render from the same application. No more cumbersome imports or exports which require you to switch between different halves of the same rendering software.

Out of all renderers with preview capabilities, Modo leads the day with the fastest processing time. It gives fast and quality realistic scenes, unlike other engines which compromise quality while giving you a preview. Its major drawback is that it does not have too many control features.

3DS Max

 

3DS Max was formerly known as 3D Studio and Studio Max. The software was developed and produced by Autodesk Media and Entertainment. It may not necessarily be the most acclaimed rendering software but certainly earned its place amongst the most popular. 3DS Max also comes with an onboard renderer that can work with a 3D modeling software. It interfaces well with AutoCAD and Revit, which are Autodesk products.

Note that Revit also has rendering capabilities but is limited in its results and flexibility. This is where 3Ds saves the day by allowing an import and satisfactorily manipulates textures intuitively to render visuals of the best quality.

Honorable Mention: Mental Ray (development discontinued ?)

Developed by Mental Images (owned by the renowned NVIDIA graphics card maker), Mental Ray earns its closest comparison to V-Ray from most of its users in terms of quality of render images towards realistic effects. Although personal preferences between the two engines may differ, what is apparent is that Mental Ray is a friendlier rendering engine. It may not match the level of realism V-Ray is capable of, but its simplicity to use qualifies it to be considered as a top-tier renderer.

Developed in 2007, the main aim was to produce a universal rendering engine that can be used by designers, architects, and artists. Its usefulness is mainly pegged on its versatility and ease of use especially advantageous to architects. There is a lot to learn about any rendering software, but Mental Ray doubles up as the best for first-time users.

 

Lumion

 

Lumion is a 3D rendering software that has been developed to integrate with CAD software. Its ease of use makes it suitable for designers and architects who want to render in-house. In addition, Lumion renders in real-time, making it an ideal tool to develop the look and feel of a product.

To enhance your renders, this 3D rendering software includes an extensive library of skies, water, grass, materials, plants, people, trees and other assets. Impressively, Lumion can handle landscapes populated with thousands of these assets.

The large feature-set makes this 3D rendering software an excellent addition to any architect’s toolbox.

LuxRender

 

LuxRender is an unbiased/biased 3D rendering software that is available under an OpenSource license. On a wide range of features, LuxRender can compete with commercial rendering solutions: The materials used are physically based, thus enabling photorealistic results.

Even complex phenomena like subsurface scattering and volumetrics are supported by LuxRender. To help minimize the overall render time, users can choose to render in biased mode. To the same end, instanced objects may be used in this 3D rendering software.

Because of LuxRender’s impressive range of features, it is an excellent 3D rendering software for special effects and architectural visualization.

 

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