Drone LiDAR or Photogrammetry?

Drone LiDAR vs Photogrammetry

With the recent development in the drone surveying space, there has been a lot of myths and misconceptions around UAV LiDAR and photogrammetry. In fact, these two technologies have as many differences as similarities. It is therefore essential to understand that they offer significantly different products, generate different deliverables and require different capture conditions but most importantly they should be used for different use cases.

There are no doubts that compared to traditional land surveying methods both technologies offer results much faster and with a much higher data density (both techniques measure all visible objects with no interpolation). However, the selection of the best technology for your project depends on the use case, environmental conditions, delivery terms, and budget among other factors. This post aims to provide a detailed overview of the strengths and limitations of LiDAR and photogrammetry to help you choose the right solution for your project.

HOW DO BOTH TECHNOLOGIES WORK?

Let’s start from the beginning and have a closer look into the science behind the two technologies.

LiDAR that stands for Light Detection and Ranging is a technology that is based on laser beams. It shoots outs laser and measures the time it takes for the light to return. It is so called active sensor as it emits its energy source rather than detects energy emitted from objects on the ground.

Photogrammetry on the other side is a passive technology, based on images that are transformed from 2D into 3D cartometric models. It uses the same principle that human eyes or 3D videos do, to establish a depth perception, allowing the user to view and measure objects in three dimensions. The limitation of photogrammetry is that it can only generate points based on what the camera sensor can detect illuminated by ambient light.

In a nutshell, LiDAR uses lasers to make measurements, while photogrammetry is based on captured images, that can be processed and combined to enable measurements.

OUTPUTS OF LIDAR AND PHOTOGRAMMETRY SURVEYS

The main product of LiDAR survey is a 3D point cloud. The density of the point cloud depends on the sensor characteristics (scan frequency and repetition rate), as well the flight parameters. Assuming that the scanner is pulsing and oscillating at a fixed rate, the point cloud density depends on the flight altitude and speed of the aircraft.

Various use cases might require different point cloud parameters, e.g., for power line modeling you might want dense point cloud with over 100 points per square meter, while for creating Digital Terrain Model of a rural area 10 pts/m2 cloud be good enough.

It is also important to understand that LiDAR sensor is only sampling positions without RGB, creating a monochrome dataset which can be challenging to interpret. To make it more meaningful, the data is often visualized using false-color based on reflectivity or elevation.

Example of point cloud before and after adding a color attribute. Courtesy of TerraSolid

It is possible to overlay color on the LiDAR data in post-processing based on images or other data sources however this adds some complexity to the process. The color can also be added based on classification (classifying each point to a particular type/group of objects, e.g., trees, buildings, cars, ground, electric wires).

Photogrammetry, on the other hand, can generate full-color 3D and 2D models (in the various light spectrum) of the terrain that is easier to visualize and interpret than LiDAR. The main outputs of photogrammetric surveys are raw images, ortophotomaps, Digital Surface Models and 3D points clouds created from stitching and processing hundreds or thousands of images. The outputs are very visual with a pixel size (or Ground Sampling Distance) even below 1cm.

Aerotriangulated images and generated 3D point cloud. Screen from Pix4D software.

With that in mind, photogrammetry seems to be the technology of choice for use cases where visual assessment is required (e.g., construction inspections, asset management, agriculture). LiDAR, on the other hand, has certain characteristics that make it important for particular use cases.

Laser beams as an active sensor technology can penetrate vegetation. LiDAR is able to get through gaps in the canopy and reach the terrain and objects below, so it can be useful for generating Digital Terrain Models.

LiDAR is also particularly useful for modeling narrow objects such as power lines or telecom towers as photogrammetry might not recognize narrow and poorly visible objects. Besides, LiDAR can work in poor lighting conditions and even at night. Photogrammetry points clouds are more visual (each pixel has RGB), but often with generalized details, so it might be appropriate for objects where a lower level of geometric detail is acceptable but visual interpretation is essential.

ACCURACY

Let’s start with defining what the accuracy is. In surveying, accuracy always has two dimensions: relative and absolute. Relative accuracy is the measurement of how objects are positioned relative to each other. Absolute accuracy refers to the difference between the location of the objects and their true position on the Earth (this is why any survey can have a high relative but low absolute accuracy).

LiDAR is one of the most accurate surveying technologies. This is particularly the case for terrestrial lasers where the sensor is positioned on the ground, and its exact location is measured using geodetic methods. Such a setup allows achieving sub-centimeter level accuracies.

Achieving a high level of accuracy with aerial LiDAR is however much more difficult as the sensor is on the move. This is why the airborne LiDAR sensor is always coupled with IMU (inertial motion unit) and GNSS receiver, which provide information about the position, rotation, and motion of the scanning platform. All of these data are combined on the fly and allow achieving high relative accuracy (1-3cm) out of the box. Achieving high absolute accuracies requires adding 1-2 Ground Control Points (GCPs) and several checkpoints for verification purposes. In some cases when additional GNSS positioning accuracy is needed, one can use advanced RTK/PPK UAV positioning systems.

Photogrammetry also allows achieving 1-3 cm level accuracies however it requires significant experience to select appropriate hardware, flight parameters and process the data appropriately. Achieving high absolute accuracies requires using RTK/PPK technology and additional GCPs or can be based purely on a large number of GCPs. Nonetheless, using $500 DJI Phantom-class drone with several GCPs, you can easily achieve 5-10cm absolute accuracy for smaller survey areas, which might be good enough for most of the use cases.

DATA ACQUISITION, PROCESSING, AND EFFICIENCY

There are also significant differences in the acquisition speed between the two. In photogrammetry one of the critical parameters required to process the data accurately is image overlap that should be at the level of 60-90% (front and side) depending on the terrain structure and hardware applied. The typical LiDAR survey requires only 20-30% overlap between flight lines, which makes the data acquisition operations much faster.

Additionally, for high absolute accuracy photogrammetry requires more Ground Control Points to achieve LiDAR level accuracy. Measuring GCPs typically require traditional land surveying methods which mean additional time and cost.

Moreover, LiDAR data processing is very fast. Raw data require just a few minutes of calibration (5-30min) to generate the final product. In photogrammetry, data processing is the most time-consuming part of the overall process. In addition, it requires powerful computers that can handle operations on gigabytes of images. The processing takes on average between 5 to 10 times longer than the data acquisition in the field.

On the other hand, for many use cases such as power line inspections, LiDAR point clouds require additional classification which might be very labor intensive and often needs expensive software (e.g., TerraScan).

COST

When we look at the overall cost of LiDAR and photogrammetry surveys, there are multiple cost items to be considered. First of all the hardware. UAV LiDAR sensor sets (scanner, IMU, and GNSS) cost between $50.000-$300.000, but for most use cases the high-end devices are preferable. When you invest so much in a sensor, you don’t want to crash it accidentally. With that in mind, most users spend additional $25.000-$50.000 for the appropriate UAV platform. It all adds up to $350.000 for a single surveying set which is equivalent to 5x Telsa Model S. Quite pricey.

For photogrammetry, all you need is a camera-equipped drone, and these tend to be much cheaper. In the $2.000-$5.000 range, you can find a wide selection of professional multirotor devices such as DJI Inspire. For the price level of $5.000-$20.000 you can buy RTK/PPK enabled sets such us DJI Matrice 600 or fixed-wing devices Sensfly eBee and PrecisionHawk Lancaster.

Another cost item is a processing software. In case of LiDAR, it is typically added for free by a sensor manufacturer. However, post-processing, e.g. point cloud classification might require using 3rd party software, such as TerraScan that cost $20.000-$30.000 for a single license. Photogrammetry software prices are closer to the level of $200 a month per license.

Obviously, another important factor that influences the cost of the service is labor and time. Here, LiDAR has a significant advantage over photogrammetry, as it not only requires significantly less time to process the data but also to lay and mark GCPs. Overall depending on the use case business model it is not given that

Overall, depending on the use case and business model photogrammetry services are typically cheaper than LiDAR simply because the investment in the hardware has to be amortized. However, in some cases, the efficiency gains that come with LiDAR can compensate for the sensor cost.

CONCLUSIONS

When comparing LiDAR and photogrammetry, it is a key to understand that both technologies have their applications as well as limitations, and in the majority of use cases they are complementary. None of these technologies is better than the other and none of them will cover all the use cases.

LiDAR should be certainly used when for surveying narrow structures such as power lines or telecom towers and for mapping areas below tree canopy. Photogrammetry will be the best option for projects that require visual data, e.g., construction inspections, asset management, agriculture. For many projects, both technologies can bring valuable data (e.g., mines or earthworks) and the choice of method depends on a particular use case as well as time, budget, and capturing conditions among other.

LiDAR and photogrammetry are both powerful technologies if you use them the right way. It is clear that with decreasing prices of hardware and software it will become more and more available. Both technologies are still in its early days when it comes to UAV applications and in the following years, we will undoubtedly witness further disruptions (especially when it comes to hardware prices, and machine learning software automation). Stay tunes. We will keep you posted.

How Accurate is LiDAR?

LiDAR is an acronym for Light Detection and Ranging. It is an active remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light. It is similar to RADAR but instead of using radio signals, it uses laser pulses. LiDAR depends on Infrared, ultraviolet and visible rays to map out and image objects. By illuminating the target using a laser beam, a 3D point cloud of the target and its surrounding can be generated. Three types of information can be obtained using LiDAR:

• Range to target (Topographic LiDAR)

• Chemical Properties of target (Differential Absorption LIDAR)

• Velocity of Target (Doppler LiDAR)

History of LiDAR

The initial attempts were made in the early 1930s to measure the air density profiles in the atmosphere by determining the scattering intensity from the searchlight beams. LiDAR was first created in 1960 shortly after the invention of the laser. The very first initial attempts at LiDAR were made by combining the laser-focused imaging with the ability to calculate distances by measuring the time for a signal to return using appropriate sensors and data acquisition electronics. The first LiDAR application came in meteorology where the National Centre for Atmospheric Research used it to measure clouds.

LiDAR’s accuracy and usefulness was made available to the public first in 1971 during the Apollo 15 Mission. During this mission, astronauts used a laser altimeter map to obtain the correct topographical representation of the moon. The first commercial airborne LiDAR system was developed in 1995.

Accuracy of LiDAR

The accuracy of LiDAR technology is no longer in doubt. LiDAR applications varies in a number of fields across all industries in the world. The most common application of LIDAR is in the field of forestry and agriculture and most recently in the field of autonomous cars. In considering driverless cars, for instance, the accuracy of LiDAR is guaranteed in the sense that manufacturers of these cars trust the technology to maintain order and avoid any incidences on the road. Autonomous cars depend on the laser pulses to measure the distance between the vehicle and any proximate vehicle. The laser pulses are transmitted at the speed of light towards an object and the time taken for the laser pulses to hit the target is recorded. The laser pulses are consequently reflected back to the transmitter and the time taken for the reflected pulse to hit the transmitter is also recorded.

This cycle is repeated over a number of times and the distance between the vehicle and the object can then be calculated. As the distance between the vehicle and the object reduces, the vehicle’s onboard diagnostics are able to decide whether or not to apply the brakes.

A better understanding of the accuracy of LiDAR is perhaps best described on the speed guns often used by cops. The speed guns employ the use of LiDAR technology to determine accurately the speed of approaching vehicles. Previously, radar was used to acquire these speeds but the accuracy of the system was always in doubt. Radar shoots out a short, high-intensity burst of high-frequency radio waves in a cone-shaped pattern. Officers who have been through the painfully technical 40-hour Doppler radar training course know it will detect a variety of objects within that cone pattern, such as the closest target, the fastest moving target or the largest target. Officers are trained to differentiate and properly match targets down range to the radar readings they receive. Under most conditions, skilled users get good results with radar, and it is found to be most effective for open stretches of roadway. But for more congested areas, locking radar on a specific target is more difficult.

Experts opine that Laser systems are more accurate when it comes to providing traffic and speed analysis as compared to other systems including radar. A laser can point at a specific vehicle in a group while radar cannot. A laser beam is a mere 18 inches wide at 500 feet compared to a radar beam’s width of some 150 feet.

Source: http://lidarradar.com

Collaboration is key: How BIM helps a project from concept to operations

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Collaboration is key: How BIM helps a project from concept to operations

Talking about collaboration and delivering a truly collaborative project through the use of BIM are two very different things. Ryan Simmonds of voestalpine Metsec Framing discusses the keys to success

At voestalpine Metsec, we recognise the fact that BIM is more than just a 3D modelling tool for design. BIM, at its core – and done correctly – is an integrated management system that allows 3D design, together with onsite construction and information, that enables handover to operationally manage the client’s facility. Metsec was the first company to achieve BIM Kitemark for design and construction and also for BIM objects.

Within BIM sits key elements for success. Coordination with other team members, or those working on a project, is crucial to ensure nothing is missed, as well as making sure there are no unnecessary duplications. Cooperation is another important area, and one where teams can often fall down through a lack of communication or sharing of vital information.

Together, cooperation and coordination help to contribute to true collaboration, with all parties working together to achieve a single goal and BIM has proved to be an essential tool to allow this approach.

Benefits of collaboration in construction projects

Collaboration is a method that the construction industry has historically struggled to adopt, but one that has been consistently demonstrated to greatly benefit the industry as a whole.

Collaborating on a project from the initial stages brings numerous benefits, including reducing time delays and the need for contingency funds. The appointed design team, contractors, manufacturers and installers all working collaboratively means designs, issues, priorities and construction methods are all agreed upon in the initial stages and fully understood by all parties.

While the theory of collaboration can seem abstract, it is a very real requirement for successful projects. If co-dependent elements of a project are executed in silos with no communication or coordination, projects can hit stumbling blocks.

For example, if the installer of the framing solution on a project has not communicated with the main contractor as to when they are required onsite, the project can either be delayed as the installer is not ready, or alternatively they’ll turn up onsite but not be able to gain access and begin the installation, resulting in wasted days and money.

Similarly, if the framing manufacturer and installer have not cooperated and communicated, the project could be delivered before it’s required, taking up valuable space onsite, or be delayed – again resulting in lost days.

BIM as a collaborative method

However, collaboration needs to go deeper and this is where Building Information Modelling (BIM) is vital. A structured, measured and comprehensive approach to team working, BIM has a fixed set of processes and procedures to guide users and participants how best to employ collaborative methods. Design coordination is an in-depth and involved process and BIM’s regular data exchanges ensure that the whole team is working on the same, and most up-to-date, model.

The notion of BIM is the process of designing, constructing or operating a building, infrastructure or landscape asset using electronic information. In practice, this means that a project can be designed and built using datasets and images digitally, even before the first spade goes in the ground.

Detecting conflict at early stages means they are addressed and resolved promptly and still during the planning stages. Without BIM, issues are often only picked up at major project milestones and at this point they can be difficult and expensive to rectify.

The objective of BIM is to satisfy the three components of a successful project, namely time, cost and quality, by managing the project using an efficient, collaborative and reliable method of work.

Sharing a 3D model with all parties communicates the planned end result in a clear, concise and fully comprehensible way – helping the full project team to understand the requirements and see what they are working towards. The information held within the model can be extracted from within in the form of Cobie files, which is also essential. Within these, if done to Level 2 standard, the manufacturer will host the correct file extensions and product parameters to allow asset management in future years.

However, another crucial element of BIM is the promotion, and adoption, of collaborative working. The digital designs, including product parameters, are shared with all parties to outline the work planned and give everyone the opportunity to fully understand what is proposed and all the requirements, including specifications such as fire and acoustic data. The BIM Execution Plan (BEP) is a critical document as it underpins project integration and is a written plan to bring together all of the tasks, processes and related information.

The BEP should be agreed at the outset and defines what BIM means for the project. It outlines the standards being adopted, outputs required, when these should be supplied and in what format, plus any supporting documentation.

As a working document, the BEP is regularly reviewed and evolves throughout the project, ensuring design teams, suppliers, manufacturers and all other stakeholders have all the relevant information, promoting collaboration between all parties.

The BIM Implementation Plan (BIP) is the blueprint for integrating BIM into an organisation’s working practices. This should align to the objectives and aspirations of the organisation, its business partners, its skill base, levels of investment and the nature and scale of projects that it wishes to undertake now and in the future.

Hosting both of these documents in a centrally coordinated Common Data Environment (CDE) means they can be updated, accessed or extracted at any time throughout the project. Adding all other BIM documents, including the 3D drawings, gives all of those involved in the overall project full visibility and input, promoting a collaborative approach throughout.

Conclusion

Talking about collaboration and delivering a fully collaborative project through the use of BIM are two very different things, and will have very different outcomes when it comes to a construction project.

While there have been moves to adopt a more collaborative approach, using BIM ensures that all stakeholders are consulted at all stages throughout the project and that the most up-to-date documents are hosted in one central location, reducing errors in file versions or timing plans.

In addition, the use of BIM means that a design and build is fixed from a certain, agreed point onwards, removing the need for additional contingency budget or project delays due to unplanned changes caused by a lack of communication, coordination, cooperation or collaboration.

Source: www.pbctoday.co.uk

PRESENTATION ON DESIGN OF HILL ROAD ALIGNMENT

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PRESENTATION ON DESIGN OF HILL ROAD ALIGNMENT

Hill Road Definition
Design Issues in Hill Roads
Special Consideration in Hill Road Design
Route Selection
Engineering Data for Design
Geometric Design Standards

1. Hill Road Definition

A hill road may be defined as the one which passes through a terrain with a cross slope of 25% or more. There may be sections along hill roads with the cross slope less than 25%, especially when the road follows a river route. Even then these sections are also referred to as hill roads. Hence, to establish a hill road overall terrain must be taken into account.

The hilly regions generally have extremes of climatic conditions, difficult and hazardous terrains, topography and vast high altitude areas. The region is sparsely populated and basic infrastructural facilities available in plain terrain are absent. Hence, a strong stable and feasible road must be present in hilly areas for overall development of other sectors as well.

IRC:SP:73-2015 and IRC:SP:84-2014 have merged the Mountainous and Steep Terrain having Cross Slope more than 25%.

2. Design Issues in Hill Roads

Design and Construction of Hill roads are more complex than in plain terrain due to factors summarized below:

Highly broken relief with vastly differing elevations and steep slopes, deep gorges etc. which increases road length.
The geological condition varies from place to place.
Variation in hydro-geological conditions.
Variation in the climatic condition such as the change in temperature due to altitude difference, pressure variation, precipitation increases at greater height etc.
High-speed runoff due to the presence of steep cross slopes.
Filling may overload the weak soil underneath which may trigger new slides.
Need of design of hairpin bends to attain heights.
Need to save Commercial and Residential establishments close to the road.
Need to save the ecology of the hills.

3. Special Consideration in Hill Road Design

a – Alignment of Hill Roads

The designer should attempt to choose a short, easy, economical and safe comforting route.

b – General considerations

When designing hill roads the route is located along valleys, hill sides and if required over mountain passes.
Due to complex topography, the length of the route is more.
In locating the alignment special consideration should be made in respect to the variations in:

Temperature
Rainfall
Atmospheric pressure and winds
Geological conditions
Resettlement and Rehabilitation considerations
Environment Considerations

c – Temperature

Air temperature in the hills is lower than in the valley. The temperature drop being approximately 0.5° per 100 m of rising.
On slopes facing south and southwest snow disappears rapidly and rain water evaporates quickly while on slopes facing north and northeast rain water or snow may remain for the longer time.
Unequal warming of slopes, sharp temperature variations and erosion by water are the causes of slope failure facing south and southwest.

d – Rainfall

Rainfall generally increases with increase in height from sea level.
The maximum rainfall is in the zone of intensive cloud formation at 1500-2500 m above sea level. Generally, the increase of rainfall for every 100 m of elevation averages 40 to 60 mm.
In summer very heavy storms/cloud burst may occur in the hills and about 15 to 25% of the annual rainfall may occur in a single rainfall. The effects of these types of rainfall are serious and should be considered in design.

e – Atmospheric pressure and winds

Atmospheric pressure decreases with increase in elevation.
At high altitudes, the wind velocities may reach up to 25-30 m/s and depth of frost penetration is also 1.5 to 2 m.
Intensive weathering of rocks because of sharp temperature variations.

f – Geological conditions

The inclination of folds may vary from horizontal to vertical stratification of rock. These folds often have faults. Limestone or sandstone folds may be interleaved with layers of clay which when wetted may cause fracturing along their surface. This may result in shear or slip fold.
The degree of stability of hill slopes depends on types of rock, degree of strata inclination or dip, occurrence of clay seams, the hardness of the rocks and presence of ground water.
When locating the route an engineer must study the details of geological conditions of that area and follow stable hill slopes where no ground water, landslides, and unstable folds occur.

g – Resettlement and Rehabilitation

Due to limited availability of flat areas and connectivity issues, most of the residential and commercial activity happens very close to the road leading to large scale R&R and becomes a challenge in alignment design.

h – Environment

Hills are ecologically sensitive areas relatively untouched by human activity. The alignment design must attempt to minimize tree cutting and large scale earth filling/cutting to minimize damage.

4. Route Selection

Hill road alignment may follow alignment at Valley bottom or on a ridge depending on the feasibility of the road. The first is called River route and the second is called Ridge route.

a – River route

Most frequent case of hill alignment as there is a great advantage of running a road at a gentle gradient.
Runs through lesser horizontal curvature.
Requirements for the construction of bridges over tributaries.
Construction of special retaining structures and protection walls on hill side for safe guarding the road against avalanches in high altitude areas.
Benefit of low construction cost and operation cost.

b – Ridge route

Characterized by the very steep gradient.
Large number of sharp curves occurs on the road with hair pin bends.
Extensive earthwork is required.
The requirement for the construction of special structures.
High construction and operation cost.

5. Engineering Data for Design

The design data includes:

The terrain classification all along the alignment – to be established through topographic data/ Contours of the area using Satellite Imagery.

All features like river course, streams, cross-drainage structures (for existing alignment), flooding areas, high flood levels, landslide areas, snow/avalanche prone areas etc.

River Morphology and Regime data.

Chainage wise inventory of the side slope material type i.e. soil with classification and properties, rock type and its structural geology of the area.

Hydrological data for all stream and river crossings.

Available material and resources that can be used in the road construction.

Geometric standards.

6 – Geometric Design Standards

a – Hill Road Capacity

Type of Road	Design Service Volume in PCU per day
	As per IRC:SP:48-1998 and IRC:52- 2001		As per IRC:SP:73-2015 & IRC:SP:84-2014
	For Low Curvature (0-200 degrees per km)	For High Curvature (above 0-200 degrees per km)	Level of Service ‘B’	Level of Service ‘C’
Single lane	1,600	1,400	–	–
Intermediate lane	5,200	4,500	–	–
Two Lane	7,000	5,000	9,000	–
Four Lane	–	–	20,000	30,000

b – Design Speed:

The design speed for various categories of hill roads are given below:

Road Classification	As per IRC:SP:48-1998 and IRC:52- 2001				As per IRC:SP:73-2015 & IRC:SP:84-2014
	Mountainous Terrain		Steep Terrain		Mountainous and Steep Terrain
	Ruling	Minimum	Ruling	Minimum	Ruling	Minimum
National and State Highways	50	40	40	30	60	40
Major District Roads	40	30	30	20	–	–
Other District Roads	30	25	25	20	–	–
Village Roads	25	20	25	20	–	–

c – Sight Distance:

Visibility is an important requirement for safety on roads.

It is necessary that sight distance of sufficient length is available to permit drivers enough time and distance to stop their vehicles to avoid accidents.

Design Speed (Km/h)	As per IRC:SP:48-1998 and IRC:52- 2001		As per IRC:SP:73-2015 & IRC:SP:84-2014
	Mountainous and Steep Terrain
	Stopping Sight Distance (m)	Intermediate Sight Distance (m)	Safe Stopping Sight Distance (m)	Desirable Minimum Sight Distance (m)
20	20	40	–	–
25	25	50	–	–
30	30	60	–	–
35	40	80	–	–
40	45	90	45	90
50	60	120	60	120
60	–	–	90	180

d – Minimum Radius of Horizontal curves

Classification	As per IRC:SP:48-1998 and IRC:52- 2001								As per IRC:SP:73-2015 & IRC:SP:84-2014
	Mountainous terrain				Steep terrain				Mountainous and Steep
	Area not affected by snow		Snow Bound Areas		Area not affected by snow		Snow Bound Areas		Mountainous and Steep
	Ruling Minimum	Absolute Minimum	Ruling Minimum	Absolute Minimum	Ruling Minimum	Absolute Minimum	Ruling Minimum	Absolute Minimum	Desirable Minimum Radius	Absolute Minimum Radius
National Highway and State Highways	80	50	90	60	50	30	60	33	150	75
Major District Roads	50	30	60	33	30	14	33	15	–	–
Other District Roads	30	20	33	23	20	14	23	15	–	–
Village Roads	20	14	23	15	20	14	23	15	–	–

e – Typical Cross-sections – 2 lane carriageway (as per IRC:SP:73-2015)

f – As per IRC:SP:48-1998 and IRC:52- 2001

Road Classification	Carriageway Width (m)	Shoulder Width (m)
National and State Highways
i) Single lane	3.75	2 x 1.25
ii) Double Lane	7.00	2 x 0.9
Major District Roads and Other District Roads	3.75	2 x 0.5
Village Roads	3.00	2 x 0.5

i –Typical Cross-sections – 4 Lane Carriageway Widening Towards Valley Side (as per IRC:SP:84-2014)

j –Typical Cross-sections – 4 Lane Carriageway Widening Towards Hill Side (as per IRC:SP:84-2014)

TOP 4 MAJOR CHALLENGES WITH FINITE ELEMENT ANALYSIS

The Finite Element Analysis is an amazing process in which the simulation of any physical object is done by leveraging the mathematical technique known as Finite Element Method (FEM). This technique improves the product manufacturing to a greater precision.

By using the extensive finite element analysis services, optimization of product design is possible by redesigning and eliminating the flaws present in the previous prototype. All in all, this is an unskippable technique used by every industry to ensure best product quality. But this perfect technique also possesses some of the major challenges on which engineers are working.

HERE ARE TOP 4 MAJOR CHALLENGES WITH FINITE ELEMENT ANALYSIS:

Stress Concentration Challenge:

The FEA is not that accurate when it comes to stress concentration testing. In stress concentration, there is a greater stress on the material of a very small area. These occur because of the frequent changes in equipment geometry. The stress in such areas may be greater than the yield strength of the material. However, this is not ideal when it comes to perfectly implementing the 3d mechanical drawing.

Time Consuming:

This process of analyzing physical object takes too many parameters for giving the results and improvements. Finite element analysis is a complex process and requires higher time for compilation as compared with other similar methods. When comparing FEA with FEM (Finite Element Method), it is slightly slower than FEM. The complexity of this process goes up even more when it is running with other practices like 3d scanning services.

FEA Needs Higher Configuration System :

This may be an issue if you want to do finite element analysis on a normal configuration system. As this process takes numerous inputs for generating different results, it demands a higher configuration system which can run multiple finite element analysis queries easily without any interruption. This may be a challenge for many who are trying to use this technique on lower configuration systems as compared to running normal AutoCAD drafting services.

The Final Results May Varies In FEA:

This is the challenge which bothers the engineers the most. The final result after processing may vary due to various factors. The factors such as material property, the stress and fatigue property of the material and many similar factors alter the final result of the test as compared to similar other techniques. If you are also looking for efficient FEA or cad outsourcing company, you must reach to us.

Source : www.zcads.com.au

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

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 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?

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?

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).

The Length is larger than Double the Width (Long/Short > 2)
100% of the Loads Travel in the Short Direction only.
Only the 2 Supports on this Short Direction will carry the slab and 100% of its the loads.
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.
We will study and design based on one direction only.
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).

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

The Length is smaller than Double the Width (Long/Short <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.
All support (2 pairs in each direction) will carry the slab, but each pair will receive different percentage of the loads.
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)
We will study and design each direction separately (different loads, different bending moments, different reinforcement)
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)