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:
Land survey and site inspection during pre-construction stage
Building Information Modeling (BIM) and Point cloud scanning
Marketing and promotional photography during and after construction
Monitoring and tracking onsite activities thereby ensuring accurate work flow
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!
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.
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.
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.
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.
Design of Concrete Retaining Wall as per BS 8110:2005
Retaining walls provide lateral support to vertical slopes of soil. They retain soil which would otherwise collapse into a more natural shape. The retained soil is sometimes referred to as backfill.Retaining walls can be constructed of many different materials and with a variety of building techniques.
All advice or information from the British Cement Association and/or The Concrete Centre is intended for those who will evaluate the significance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted by the BCA, TCC or their subcontractors, suppliers or advisors. Users should note that all TCC software and publications are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.
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.
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.
The best apps for architects can be hard to find when you are working on sketches, with project owners, or managing a team. That is why we looked for the best apps for architects so you would not have to.
On our search for the top apps for architects, we found a wide range of apps: architecture calculators, architecture prioritization apps, architecture drawing apps, and more.
Here is a list of the top apps for architects that we found:
Best Apps For Architects
For Architecture Calculators
Concept App by Fast + Epp
Stemming from clients’ desire to assess project feasibility before putting pencil to paper, structural engineers at Fast + Epphave developed CONCEPT – a free iPhone app that allows architects and engineers to calculate member depths and browse project photos for structural expressions.
CONCEPT’s depth calculator uses typical span-to-depth ratios for common steel, concrete, and wood members. The user simply indicates if the information they’re inputting is a roof or floor, with the internal calculator determining an approximate depth. Additional information is provided to qualify the load assumptions and tributary areas.
Users are able to share search and calculation results by emailing them to co-workers and clients for discussion prior to the first design charrette.
Paul Fast, the Partner of Fast + Epp states “Concept is a free app because we wanted to make it readily accessible to as many architects and designers as possible. We’re confident this is going to be a really useful tool.
For Floor Plans
Magicplan
Magicplan is the post-PC floor plan creation technology for everyone, and it is particularly helpful for architects. Its augmented reality features let you create a floor plan simply by taking pictures. With Magicplan, you can easily generate complete work estimates, furnish a home, or plan your next DIY project.
For Drafting
Scala Architectural And Engineering Scale
Scala Architectural and Engineering Scale provides a new way to measure printed drawings on the go and at your desk. It includes standard imperial architectural, metric architectural, and engineering scales in a handy app. You can also create custom variable scales in case your drawings aren’t to a known scale.
For Architecture Prioritization
Priority Matrix
Priority Matrix is a prioritization app that helps architect firms manage resources, increase visibility, and track progress of all of their projects.
Within Priority Matrix, you can use the tool to:
Visualize your team’s workload by using the platform to view how work is distributed across your team. This means that you can tell which members of your team have the most on their plate, and which members you can assign more work to.
Determine which items are of high priority so you and your team can focus on what matters most.
Keep track of tasks by inputting tasks into Priority Matrix along with notes, screenshots, and a due date. In addition, you can delegate tasks through the app, and communicate any questions or comments under the task to keep things organized.
Generate Simple Reports like visual Gantt charts, or a report to show how many tasks were completed yesterday by specific members of your team.
Store files, including those large CAD files so everything is in one place.
Keep clients in the loop, using the read-only feature to send project owners project updates; you can even send them over your Gantt-chart.
For Architecture Jobs and Recruitment
Design & Construct
Even though Design & Construct is not an app, we felt it was necessary to include it because it should be a tool on your list to meet your recruiting needs.
Design & Construct is a leading Australian-based recruitment agency, providing a specialized approach to recruitment in the Architecture and Construction industry.
By working with a specialist recruiter, you can be sure to know about the best opportunities as they rise. A recruiter has the technical insights into Australia’s architecture jobs market, meaning they know what employers are looking for. Whether it’s architecture, interior design, landscape design, or urban planning roles, specialists will have the contacts.
As their company states, “Tailored recruitment is at the heart of Design & Construct, and the key reason why 95% of clients return to us and 97% are happy to refer us to their most trusted industry contacts.”
For File Sharing
FileCloud
FileCloud is a file sharing, sync and mobile access solution. FileCloud has many capabilities, including:
File Remote Access and Sharing which allows businesses to create their own, branded file sharing, sync, and mobile access solution for their employees, customers and partners.
File Sync, allowing for effortless file synchronization across users computers, smart phones and tablets, so everyone can work together anywhere from any device.
Endpoint Backup and DLP, creating secure backup and Data Leak Prevention (monitor, prevent and fix) across all your user’s devices (Computers, Mobile Phones/Tablets).
In addition, FileCloud offers deployment flexibility where users can self-host on their premise, host in the cloud, or create a hybrid solution.
For Presentation
GRAPHISOFT BIMx
GRAPHISOFT BIMx is an award-winning communication and presentation app.
BIMx features virtual reality (VR) functionality. This enhanced functionality provides architectural and interior design firms an immersive way to share their projects. BIMx with Google CardboardTM viewer allows users to navigate through an ARCHICAD model in virtual 3D with a simple turn of the head.
For Creating 3-D Models
Shapr3D
Shapr3D is the world’s first professional 3D modeling tool designed specifically for iPad Pro.
Shapr3D is the only truly mobile CAD app. It offers you a quick but precise way to create 3D models from scratch. You can easily create 2D sketches and turn them into 3D models using various tools.
The program is mostly used by engineers, industrial designers, product designers, 3D hobbyists, and architects.
Famous users include Patrick Jouin (one of France’s most acclaimed designers), Rodrigo Otazu (who designs jewelery for Madonna, Bruno Mars, Lady Gaga and Swarowksi), and Claas Kuhnen (industrial design professor at Wayne State University).
Architecture Sketching Apps
Archisketch
Archisketch is a scale-aware sketching program ideal for architects, interior and landscape designers, product designers, design students, or anyone working with design on an iPad. Inspired by the tradition of sketching on a tracing pad, Archisketch brings sketching and the early stages of a design process into the modern era on an iPad.
Archisketch helps architects and designers visualize, capture, and explore their ideas using layers, symbols, colors, dimension guidelines, 2D grids, isometric and axonometric 3D grids, and even smart one and two-point perspectives for 3D. When finished, drawings can be printed to scale directly from the iPad up to A1 size, or exported to PDF, which can be included in a CAD application, or even uploaded to the Photos App or the Adobe Creative Cloud.
SmartDraw
With SmartDraw, you get the power of CAD software without the CAD hassles.
SmartDraw gives you powerful tools and a broad selection of architectural templates to help you plan your next office, building or home project.
First, you choose a template and add symbols from the thousands included. You can draw your plan using any scale selected from the standard architectural, civil engineering, mechanical engineering, and metric scale, or you can even define your own custom scale.
In the program, you can import DXF or Visio files, add annotation layers, print to scale, change sizing by just typing in dimensions, and more.
For Experience Tracking Apps
My AXP
Reporting hours for the Architectural Experience Program™ (AXP™) has never been easier, thanks to NCARB’s My AXP mobile app! Licensure candidates can log hours, submit experience reports to supervisors, review their progress, and more. And it is available for free on Apple and Android devices.
For Home Remodeling and Design
Houzz
Houzz is a platform for home remodeling and design, providing people with everything they need to improve their homes from start to finish. From decorating a small room to building a custom home and everything in between, Houzz connects millions of homeowners, home design enthusiasts, and home improvement professionals across the country and around the world.
With the largest residential design database in the world and a vibrant community empowered by technology, Houzz is the easiest way for people to find inspiration, get advice, buy products and hire the professionals they need to help turn their ideas into reality.
The Houzz app is reimagining the home shopping experience, with unique features that are changing the way people shop for and design their homes, including:
View in my room lets app users virtually place and see over 9 million products from the Houzz Shop in their own homes before they buy
Sketch makes it easy for homeowners and home professionals to communicate ideas and collaborate directly on any of the more than 14 million photos on Houzz, or images from their own library and around the web, by adding measurements, notes, stickers, Houzz Shop products, and more. Additionally, the tool can be used to create mood boards and floor plans. Sketch allows for real-time collaboration, where multiple people can simultaneously annotate the same photo.
Visual Match is a visual recognition tool that makes it easy for people to discover and buy on Houzz the types of products and materials that inspire them in photos. Available for desktop and in the Houzz app for iPhone, iPad, and Android, Visual Match applies deep learning technology to scan the more than 14 million photos on Houzz to identify furniture and decor in living spaces and surface visually similar inventory from the Houzz Shop.
Plaans
Plaans is a documentation tool for architects, engineers, surveyors, facility managers, interior designers, and many more.
The app provides a wide range of features to support the whole documentation process – from photos, voice memos, and notes, to measurements and sketches. It will always remember, where and from what direction you took a photo and at what exact position you took a note or recorded a voice memo.
Additionally, Plaans exports your data in a well-organized file and folder structure to make sure nothing gets lost and you can access your data fast and easy. For efficient teamwork, you can compile the documentation data as a ZIP file within Plaans and send it by e-mail. With that being said, Plaans automatically generates interactive plans you can view in any internet browser and easily deploy them for colleagues and clients for subsequent processing.
For Stress Management
Stop, Breathe, and Think
The architecture industry is a stressful industry to be in at times. The good thing about living in a world full of apps is that there are companies who have created apps to help you take some time and relax.
Stop, Breathe,and Think is great because it generates meditations that you can do after plugging in how you feel into the app (for example, stressed out, angry, excited). The meditations are short enough that you can pull in a quick one during your lunch, or at the end of your work day.
For travel
Trip Advisor
Trying to plan a vacation to de-stress? Trying to find a hotel to stay at when you have to check out a site? Trip advisor will take away the stress that comes from searching.
With Trip Advisor, not only can you read reviews for hotels, restaurants, and attractions, but Trip Advisor will compare prices of hotels that you can stay at when you are away, saving you a lot of clicks.
Expedia
Like Trip Advisor, if you are planning on going on a vacation or a business trip, Expedia will save you a ton of clicks so that you can find the least expensive airfare, hotels, car rentals and more when flying to your destination. This way, you will spend less time to make your arrangements and spend less of your hard earned money when you travel.
For Architecture Fashion
Warby Parker
If you spend a lot of time outdoors or on the field, you know that you always need the right pair of shades in order to keep your eyes safe from the rays. Just because you are working, does not mean you cannot be hip on the field.
Warby Parker sells prescription eyeglasses and sunglasses starting at $95 ($175 for prescription sunglasses), which you can order online, in store, or over the phone (888.492.7297, 9a.m.–9p.m. ET).
The great thing about Warby Parker is that they allow you try on sunglasses before you buy them with their home try onsystem where you select five frames to test out for five days and then they ship them to you for free! They also offer a 30-day no-questions-asked return or exchange policy for all their eyewear — so there is no pressure.
Another great thing about Warby Parker is that they accept flexible spending account (FSA) dollars affiliated with major credit cards, or you can apply for reimbursement if you have an out-of-network benefit included in your insurance plan.
Used in conjunction, these apps will save you time (and money) and resources in order to get everything done efficiently and hopefully make you and your team’s job a little easier.
Written by ANDY LI – 3D architectural renderings, Animation and multimedia Product Manager in Fancy Digital Technology Co., Ltd.
Construction Equipment Earthwork & Soil Compaction
1.Cable Excavator
Cable excavators are large earthmoving machines used for heavy excavation of materials with the use of cables or wire ropes. Almost obsolete, cable excavators were once used in mining and some construction applications and usually consisted of a variety of attachments that could transform it into a backhoe, skimmer, dragline, and more. Aside from a few companies that still manufacture them, cable excavators have been replaced by hydraulic excavators due to their cheaper costs, easier operation and faster mobility.
2. Hydraulic excavators (slewing excavators)
A hydraulic excavator (digger) is a large vehicle that is designed for excavation and demolition purposes. Hydraulic excavators consist of a chassis, boom, and bucket, and move via tracks or wheels. They range in size and function, an example of which is the similar but smaller “mini excavator.” All versions are generally designed for the same purposes. Hydraulic excavators weigh between 3,000 and 2 million pounds and their speed ranges between 19 HP and 4,500 HP.
3.Backhoe excavators
Backhoe is another widely used equipment which is suitable for multiple purposes. The name itself telling that the hoe arrangement is provided on the back side of vehicle while loading bucket is provided in the front.
This is well useful for excavating trenches below the machine level and using front bucket loading, unloading and lifting of materials can be done.
4. Bulldozers (dozers)
A bulldozer is a crawler (continuous tracked tractor) equipped with a substantial metal plate (known as a blade) used to push large quantities of soil, sand, rubble, or other such material during construction or conversion work and typically equipped at the rear with a claw-like device (known as a ripper) to loosen densely compacted materials.
Bulldozers can be found on a wide range of sites, mines and quarries, military bases, heavy industry factories, engineering projects and farms.
5. Scrapers
Scraper, in engineering, machine for moving earth over short distances (up to about two miles) over relatively smooth areas. Either self-propelled or towed, it consists of a wagon with a gate having a bladed bottom. The blade scrapes up earth as the wagon pushes forward and forces the excavated material into the wagon. When the wagon is filled, the gate is closed, and the material is carried to the place of disposal. The scraper is the dominant tool in highway construction.
6. Graders
Grader, in excavation, precision finishing vehicle for final shaping of surfaces on which pavement will be placed. Between its front and rear wheels a grader carries a broad mechanically or hydraulically controlled blade that can be extended from either side. Either end of the blade can be raised or lowered. Graders may be used for shallow ditching, but most models are used to assist other earth-moving equipment and to smooth roads, fills, and cuts.
7. Compactors
A compactor is a machine or mechanism used to reduce the size of material such as waste material or bio mass through compaction. A trash compactor is often used by a home or business to reduce the volume of trash it produces.
The popular RC-spreadsheets package version 4 was issued following the amendment to the UK National Annex to Eurocode 2 in December 2009. These Excel spreadsheets are intended as aids for design to both Eurocode 2 and BS 8110-1:1997.
Version 4B.2 provides updates to Version 4B.1 that reflect developments and improvements particularly with respect to punching shear, column design and pilecap design as well as applying bug fixes.
What does RC Spreadsheets do? For the experienced engineer, the spreadsheets allow the rapid production of clear and accurate design calculations. For post-graduates and new engineers they encourage understanding of concrete design and help the gaining of experience by studying ‘what if’ scenarios. The individual user is able to answer their own questions by chasing through the cells to understand the logic used.
Since their release in January 2000, the RC Spreadsheets have proved to be enormously popular. They are written for engineers by engineers. The original spreadsheets have evolved and been added to and the usefulness and robustness of the product have been enhanced by users feedback. If you have any comments please let us know.
Mineral-producing bacteria have been found that could help mend micro-cracking in concrete. Dr Henk Jonkers, a micro-biologist at Delft University, talked to Ingenia about research developments in producing bioconcrete that could bring benefits for civil engineering projects.
Self-healing concrete could solve the problem of concrete structures deteriorating well before the end of their service
life. Concrete is still one of the main materials used in the construction industry, from the foundation of buildings to the structure of bridges and underground parking lots.
Traditional concrete has a flaw, it tends to crack when subjected to tension. A healing agent that works when bacteria embedded in the concrete convert nutrients into limestone has been under development at the Civil Engineering and Geosciences Faculty in Delft since 2006.
The project is part of a wider programme to study the self-healing potential of plastics, polymers, composites, asphalt and metals as well as concrete. Dr Henk Jonkers, a microbiologist who specialises in the behaviour of bacteria in the environment, has developed self-healing concrete in the laboratory and full-scale outdoor testing will start in 2011. The
first self-healing concrete products (successful research results permitting) are expected to hit the market in two years’
time and are expected to increase the lifespan of many civil engineering structures.
Jonkers has worked closely with civil and structural engineers to learn about the properties of concrete and steel reinforcement, and develop the concrete. “For a biologist to work with civil engineers to incorporate living matter into
structural concrete material is in itself a great innovation,” he says.
WHY THE NEED ?
Concrete will continue to be the most important building material for infrastructure but most concrete structures are
prone to cracking. Tiny cracks on the surface of the concrete make the whole structure vulnerable because water seeps in to degrade the concrete and corrode the steel reinforcement, greatly reducing the lifespan of a structure.
Concrete can withstand compressive forces very well but not tensile forces. When it is subjected to tension it starts to crack, which is why it is reinforced with steel; to withstand the tensile forces.
Structures built in a high water environment, such as underground basements and marine structures, are particularly vulnerable to corrosion of steel reinforcement. Motorway bridges are also vulnerable because salts used to de-ice the roads penetrate into the cracks in the structures and can accelerate the corrosion of steel reinforcement. In many civil engineering structures tensile forces can lead to cracks and these can occur relatively soon after the structure is built.
Repair of conventional concrete structures usually involves applying a concrete mortar which is bonded to the damaged surface. Sometimes, the mortar needs to be keyed into the existing structure with metal pins to ensure that it
does not fall away. Repairs can be particularly time consuming and expensive because it is often very difficult to gain
access to the structure to make repairs, especially if they are underground or at a great height.
Self-healing concrete is a product that will biologically produce limestone to heal cracks that appear on the surface of concrete structures. Specially selected types of the bacteria genus Bacillus , along with a calcium-based nutrient known as calcium lactate, and nitrogen and phosphorus, are added to the ingredients of the concrete when it is being mixed. These self-healing agents can lie dormant within the concrete for up to 200 years.
However, when a concrete structure is damaged and water starts to seep through the cracks that appear in the concrete, the spores of the bacteria germinate on contact with the water and nutrients. Having been activated, the bacteria start to feed on the calcium lactate.
As the bacteria feeds oxygen is consumed and the soluble calcium lactate is converted to insoluble limestone. The limestone solidifies on the cracked surface, thereby sealing it up. It mimics the process by which bone fractures in
the human body are naturally healed by osteoblast cells that mineralise to re-form the bone. The consumption of oxygen during the bacterial conversion of calcium lactate to limestone has an additional advantage. Oxygen is an essential element in the process of corrosion of steel and when the bacterial activity has consumed it all it increases the durability of steel reinforced concrete constructions.
The bioconcrete healing itself (Image Courtesy of Delft University)
The two self-healing agent parts (the bacterial spores and the calcium lactate-based nutrients) are introduced to the concrete within separate expanded clay pellets 2-4 mm wide, which ensure that the agents will not be activated during the cement-mixing process. Only when cracks open up the pellets and incoming water brings the calcium lactate into contact with the bacteria do these become activated. Testing has shown that when water seeps into the concrete, the bacteria germinate and multiply quickly. They convert the nutrients into limestone within seven days in the laboratory.
Outside, in lower temperatures, the process takes several weeks.
FINDING THE RIGHT BACTERIA
The starting point of the research was to find bacteria capable of surviving in an extreme alkaline environment.
Cement and water have a pH value of up to 13 when mixed together, usually a hostile environment for life:
most organisms die in an environment with a pH value of 10 or above.
The search concentrated on microbes that thrive in alkaline environments which can be found in natural environments, such as alkali lakes in Russia, carbonate-rich soils in desert areas of Spain and soda lakes in Egypt. Samples of endolithic bacteria (bacteria that can live inside stones) were collected along with bacteria found in sediments in the lakes. Strains of the bacteria genus Bacillus were found to thrive in this high-alkaline environment. Back at Delft University the bacteria from the samples were grown in a flask of water that would then be used as the part of the water mix for the concrete.
Different types of bacteria were incorporated into a small block of concrete. Each concrete block would be left for two months to set hard. Then the block would be pulverised and the remains tested to see whether the bacteria had survived.
It was found that the only group of bacteria that were able to survive were the ones that produced spores comparable to plant seeds. Such spores have extremely thick cell walls that enable them to remain intact for up to 200 years while waiting for a better environment to germinate.
They would become activated when the concrete starts to crack, food is available, and water seeps into the structure.
This process lowers the pH of the highly alkaline concrete to values in the range (pH 10 to 11.5) where the bacterial spores become activated.
Finding a suitable food source for the bacteria that could survive in the concrete took a long time and many different nutrients were tried until it was discovered that calcium lactate was a carbon source that provides biomass.
If it starts to dissolve during the mixing process, calcium lactate does not interfere with the setting time of the concrete.
