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Showing posts with label Bridge. Show all posts
Showing posts with label Bridge. Show all posts
Friday, October 15, 2010
World’s longest tunnel “Gotthard Base Tunnel” : Hot Topic
Civil Engineering Award for Delhi Metro
The Delhi Metro Rail Corporation(DMRC) has won the Outstanding Civil Engineering Project Award for the year 2010 specially for completing various infrastructural projects in record time, an official said today. The award will be given by the international Asian Civil Engineering Coordinating
Council(ACECC). The council works for the promotion and advancement of the science and practice of civil engineering and related professions for sustainable development in the Asian region.
The award is given to agencies involved in infrastructural projects that have made exemplary contribution to the progress of civil engineering works.
The project taken up by the agency should contribute to the nation where the project is located and they should have impacted on or spread through other Asian nations or ACECC member economies.
Work on a 125-km stretch of the Delhi Metro is in progress in Phase II and will be completed before the Oct 3-14 Commonwealth Games. Large sections of this have already been opened for the public.
Council(ACECC). The council works for the promotion and advancement of the science and practice of civil engineering and related professions for sustainable development in the Asian region.
The award is given to agencies involved in infrastructural projects that have made exemplary contribution to the progress of civil engineering works.
The project taken up by the agency should contribute to the nation where the project is located and they should have impacted on or spread through other Asian nations or ACECC member economies.
Work on a 125-km stretch of the Delhi Metro is in progress in Phase II and will be completed before the Oct 3-14 Commonwealth Games. Large sections of this have already been opened for the public.
Thursday, October 14, 2010
Hoover dam bridge finally completed: Hot News
The 1,900ft engineering wonder perched 890ft above the Colorado River is expected to slash travel time along the main route between Las Vegas, Nevada, and Phoenix, Arizona, as motorists will no longer have to make their way across the dam's winding two-lane road at a snail's pace.
Tuesday, October 12, 2010
What is Underwater Antiwash Concrete?
PDF version here
Although underwater concreting has been in use for a long time, development of the technique has mainly proceeded in the areas of concrete placing method and improvements to the construction machinery. The prepacked concrete method, tremie method, concrete pump method, and others are now the representative underwater concreting methods. With all these concreting methods, the essential aim of technological development has been to improve how the concrete is placed and to minimize contact between the water and mortar so as to prevent the concrete from segregating under water.
Although underwater concreting has been in use for a long time, development of the technique has mainly proceeded in the areas of concrete placing method and improvements to the construction machinery. The prepacked concrete method, tremie method, concrete pump method, and others are now the representative underwater concreting methods. With all these concreting methods, the essential aim of technological development has been to improve how the concrete is placed and to minimize contact between the water and mortar so as to prevent the concrete from segregating under water.
On the other hand, antiwashout underwater concrete is quite different in concept from the methods mentioned above; the developmenta1aim in this case was improved performance of the fresh concrete. That is, the viscosity of the concrete was increased and its resistance to segregation under the washing action of water was enhanced by mixing an antiwashout admixture with the concrete. The effect of this is not only to greatly improve the reliability of Concrete placed underwater, but it also has remarkable effects on environmental preservation in the construction area. In addition, the earlier tremie and concrete pump placing methods can be adopted for construction.
The specific advantages of antiwashout underwater concrete include the following:
- Compared with ordinary concrete, antiwashout underwater concrete is highly resistant to the washing action of water, and rarely separates even when dropped under water
- Its yield value is small and viscosity high, so the concrete components never segregate and it displays high fluidity.
- As a result of the high fluidity, filling property and self-leveling ability are improved.
- Almost no bleeding occurs.
These qualities are taken full advantage of in work which would be difficult to handle using conventional underwater concrete. This includes work where high reliability is required, work in flowing water, work where water turbidity is restricted due to environmental considerations, and work where construction stretches over a considerable area and good flatness is necessary. On the other hand, however, handling is more difficult than with ordinary concrete, and in order to produce concrete of the required quality and a structure of the required performance, careful consideration of mix proportion, mixing, transport, and placing, etc. is necessary when antiwashout underwater concrete is used.
In particular, when producing the underwater antiwash concrete it is necessary to mix it for longer than ordinary concrete in a mixer large enough to uniformly disperse the antiwashout admixture. Also, when using concrete pumps for placement, it is necessary to design a pumping plan with care as regards pumping equipment, pumping distance, etc., because the pumping resistance is increased by the higher viscosity.
Monday, October 11, 2010
The Era of Flexible Concrete?
PDF version here
Looks like the brittle concrete has been tamed at last!
A team of researchers at the University of Michigan has developed a concrete material that bends like rubber, cracks very little, heals itself with no manual intervention, and is almost as good as new concrete upon recovery, with its stiffness and strength intact.
The research team led by Professor Victor C. Li more here , Professor of Civil and Environmental Engineering
at the University of Michigan, has achieved this by designing the new material with tiny crack widths. This ensures that any damage caused due to overloading and subsequent tensile strain manifests itself as small cracks that are autogenously healed.
Here’s how the self-healing mechanism works. The extra dry cement that is exposed on the surface of the crack reacts with water and carbon dioxide to form calcium carbonate, a strong and resilient compound that brings back the material to its original state. But this works only if the crack width is tiny, a factor that is taken care of by the nature of the material itself. The new material is an improvement over the bendable engineering cement composite (ECC) that Li and his team have been developing for the past decade and a half. The research team discovered that the brittleness of concrete could be altered by limiting the crack width to 150 microns, preferably 50 microns to enable full healing. The average crack width in the ECC was found to be 60 microns, half the width of human hair.
While traditional concrete is brittle and rigid, prone to failure and breakage under strain, the flexible ECC is held together with reinforcing fibers. So while traditional concrete fractures under a tensile strain of 0.1%, experiments revealed that the ECC is able to withstand a tensile strain of up to 5%. That makes it an astounding 500 times more durable than concrete.
The flexible ECC has several obvious advantages over traditional concrete as a construction material.
However, the one crucial factor that could put a wrench in the works is that the self-healing process is almost entirely dependent on the availability of water. Under laboratory conditions, ECC was found to require about one to five cycles of wetting and drying in order to self-heal. Extrapolating this finding to large structures such as bridges, it can be concluded that the ability for the material to self-heal is likely to be seasonal in nature. This leads one to question whether the new material would be suitable for commercial use in dry arid lands, and under all climatic conditions. And, would the alternate freeze-thaw cycles during our cold winters, complicated by use of de-icing salts, affect ECC’s material properties? These are some of the questions that should be addressed.
All said and done, should ECC prove to be a success in terms of industrial and commercial use, we are likely to see safer, smarter and more durable structures being erected.
Looks like the brittle concrete has been tamed at last!
A team of researchers at the University of Michigan has developed a concrete material that bends like rubber, cracks very little, heals itself with no manual intervention, and is almost as good as new concrete upon recovery, with its stiffness and strength intact.
The research team led by Professor Victor C. Li more here , Professor of Civil and Environmental Engineering
at the University of Michigan, has achieved this by designing the new material with tiny crack widths. This ensures that any damage caused due to overloading and subsequent tensile strain manifests itself as small cracks that are autogenously healed.
Here’s how the self-healing mechanism works. The extra dry cement that is exposed on the surface of the crack reacts with water and carbon dioxide to form calcium carbonate, a strong and resilient compound that brings back the material to its original state. But this works only if the crack width is tiny, a factor that is taken care of by the nature of the material itself. The new material is an improvement over the bendable engineering cement composite (ECC) that Li and his team have been developing for the past decade and a half. The research team discovered that the brittleness of concrete could be altered by limiting the crack width to 150 microns, preferably 50 microns to enable full healing. The average crack width in the ECC was found to be 60 microns, half the width of human hair.
While traditional concrete is brittle and rigid, prone to failure and breakage under strain, the flexible ECC is held together with reinforcing fibers. So while traditional concrete fractures under a tensile strain of 0.1%, experiments revealed that the ECC is able to withstand a tensile strain of up to 5%. That makes it an astounding 500 times more durable than concrete.
The flexible ECC has several obvious advantages over traditional concrete as a construction material.
Stronger Structures
Presently, concrete structures are reinforced with steel reinforcement (aka “rebar”) to minimize concrete cracking, as well as provide tensile strength for bending moments for structural beams and columns. While ECC cannot replace rebar for structural tensile strength, it can reduce the need for rebar to limit concrete cracking. In addition, ECC has the added benefit of self-healing these cracks, thereby reducing the risk of water and de-icing salts penetrating into the structure, causing corrosion of reinforcement steel that might be present.
Presently, concrete structures are reinforced with steel reinforcement (aka “rebar”) to minimize concrete cracking, as well as provide tensile strength for bending moments for structural beams and columns. While ECC cannot replace rebar for structural tensile strength, it can reduce the need for rebar to limit concrete cracking. In addition, ECC has the added benefit of self-healing these cracks, thereby reducing the risk of water and de-icing salts penetrating into the structure, causing corrosion of reinforcement steel that might be present.
Decreased Costs
While ECC is three times as expensive as traditional concrete, these costs are outweighed in the long run since the structure would not require extensive repair and maintenance. Li claims that ECC could help do away with repair and rebuilding processes for about an additional five to ten years. It could also eliminate the need to monitor seismic stresses on structures.
While ECC is three times as expensive as traditional concrete, these costs are outweighed in the long run since the structure would not require extensive repair and maintenance. Li claims that ECC could help do away with repair and rebuilding processes for about an additional five to ten years. It could also eliminate the need to monitor seismic stresses on structures.
Reduced Environmental Impacts
Use of the ECC is also expected to reduce the energy and carbon footprints of infrastructure, thereby reducing the detrimental effects of construction on the natural environment.
Use of the ECC is also expected to reduce the energy and carbon footprints of infrastructure, thereby reducing the detrimental effects of construction on the natural environment.
Quieter Structures
In 2006, a bridge over Interstate 94 in Michigan was built with a similar self-healing concrete, which was reinforced with toothed metal slats that allowed concrete to expand and contract without bending. However, this structure turned out to be a noisy affair as vehicles rattled over the metal slats. In contrast, ECC is a silent material.
The research certainly bodes well for the construction industry. In addition to the obvious applications in buildings and infrastructure, self-healing concrete could also very well be the solution to potholes and cracks on roads and bridges, and leaky walls. Flexible ECC is also being considered for use in irrigation channels in Montana.In 2006, a bridge over Interstate 94 in Michigan was built with a similar self-healing concrete, which was reinforced with toothed metal slats that allowed concrete to expand and contract without bending. However, this structure turned out to be a noisy affair as vehicles rattled over the metal slats. In contrast, ECC is a silent material.
However, the one crucial factor that could put a wrench in the works is that the self-healing process is almost entirely dependent on the availability of water. Under laboratory conditions, ECC was found to require about one to five cycles of wetting and drying in order to self-heal. Extrapolating this finding to large structures such as bridges, it can be concluded that the ability for the material to self-heal is likely to be seasonal in nature. This leads one to question whether the new material would be suitable for commercial use in dry arid lands, and under all climatic conditions. And, would the alternate freeze-thaw cycles during our cold winters, complicated by use of de-icing salts, affect ECC’s material properties? These are some of the questions that should be addressed.
All said and done, should ECC prove to be a success in terms of industrial and commercial use, we are likely to see safer, smarter and more durable structures being erected.
Sunday, October 10, 2010
Friday, October 1, 2010
Reinforced concrete Design philosophy and concepts
Reinforced concrete Design philosophy and concepts
The design of a structure may be regarded as the process of selecting proper materials and proportioned elements of the structure, according to the art, engineering science and technology. In order to fulfill its purpose, the structure must meet its conditions of safety, serviceability, economy and functionality.
| Serviceability: No excessive deflection, no excessive deformation and no cracking or vibrations No excessive reinforcement. Must be able to perform the function, it is built for. |
Strength design method
It is based on the ultimate strength of the structural members assuming a failure condition, whether due to the crushing of concrete or due to the yield of reinforced steel bars. Although there is additional strength in the bar after yielding (due to Strain Hardening), this additional strength in the bar is not considered in the analysis or design of the reinforced concrete members. In the strength design method, actual loads or working loads are multiplied by load factor to obtain the ultimate design loads. The load factor represents a high percentage of factor for safety required in the design. The ACI code emphasizes this method of design.
Working stress design
This design concept is based on elastic theory, assuming a straight line stress distribution along the depth of the concrete. The actual loads or working loads acting on the structure are estimated and members are proportioned on the basis of certain allowable stresses in concrete and steel. The allowable stresses are fractions of the crushing strength of concrete (fc') and the yield strength (fy). Because of the differences in realism and reliability over the past several decades, the strength design method has displaced the older stress design method.
Limit state design
It is a further step in the strength design method. It indicates the state of the member in which it ceases to meet the service requirements, such as, loosing its ability to withstand external loads or local damage. According to limit state design, reinforced concrete members have to be analyzed with regard to three limit states:
- Load carrying capacity (involves safety, stability and durability)
- Deformation (deflection, vibrations, and impact)
- The formation of cracks
The aim of this analysis is to ensure that no limiting sate will appear in the structural member during its service life.
what is Reinforced Concrete ?
Concrete is a stone like substance obtained by permitting a carefully proportioned mixture of cement, sand and gravel or other aggregate and water to harden in forms of the shape and of dimensions of the desired structure.
Reinforced cement concrete:
Since concrete is a brittle material and is strong in compression. It is weak in tension, so steel is used inside concrete for strengthening and reinforcing the tensile strength of concrete. The steel must have appropriate deformations to provide strong bonds and interlocking of both materials. When completely surrounded by the hardened concrete mass it forms an integral part of the two materials, known as "Reinforced Concrete".
Advantages and disadvantages of reinforced concrete
Reinforced Concrete is a structural material, is widely used in many types of structures. It is competitive with steel if economically designed and executed.
Advantages of reinforced concrete
|
Disadvantages of reinforced concrete
- It needs mixing, casting and curing, all of which affect the final strength of concrete.
- The cost of the forms used to cast concrete is relatively high.
- It has low compressive strength as compared to steel (the ratio is about 1:10 depending on material) which leads to large sections in columns/beams of multistory buildings Cracks develop in concrete due to shrinkage and the application of live loads
Conference 2010-on Engineering Design Technology
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Produced By: CE News, Structural Engineering & Design
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1. Earn up to 2 FREE Professional Development Hours
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4. Find, and network with, your peers using the chat feature.
5. All from the convenience of your office or home computer - no travel or expenses necessary!
Fore more info go for "technology" website
1. Earn up to 2 FREE Professional Development Hours
2. Attend up to 3 live webcasts throughout the eConference.
3. Visit virtual booths and pick up product information, and white papers and have a live Q&A with booth representatives.
4. Find, and network with, your peers using the chat feature.
5. All from the convenience of your office or home computer - no travel or expenses necessary!
Fore more info go for "technology" website
How to repair the cracked concrete structures yourself
Crack injection repair to concrete structures
Scope of work:
Injection of dead cracks with low viscosity 2 components epoxy resin in order to repair the concrete structures.
Injection of dead cracks with low viscosity 2 components epoxy resin in order to repair the concrete structures.
PREPARATION FOR INJECTION WORK
- 14mm holes must be drilled along the crack path between 200 – 300 mm centres. The holes must be deep enough to receive the ‘metal pipe sleeves’ (approx. 20mm)
- Insert Sika ‘metal pipe sleeves’ into all the holes and epoxy into position using Sikadur 731
- Clean the concrete surface adjacent to the crack with a wire brush or sandpaper.
- Wipe down the concrete with a clean rag to remove any dust and loosely adhering particles.
- The cleaned surface is then sealed using Sikadur 731 applied by a spatula or trowel.
CRACK INJECTION
- Following the curing of the Sikadur 731 (minimum of 12 hours at 30oC) the epoxy injection can commence.
- Starting from one side or the lowest point of the crack a Sika ‘nipple’ is screwed into the first pipe sleeve and Sikadur 752 injected into the crack until the epoxy is seen to ooze from the adjacent pipe sleeve, this pipe sleeve is then sealed with a nipple, continue to inject the current port until refusal (epoxy resin can not be injected more) and then start the injection of the adjacent port and so on. This procedure is continued in the sequence indicated until all have been completed.
- Beginning at the first nipple filled, the nipple is removed and checked for incomplete filling. If any of the pipe sleeves are found to be incompletely filled, the injection of Sikadur 752 must recommence from the previous pipe sleeve to the one found incomplete until full and the nipple replaced. This checking process is continued (without interruption) along the crack until all have been checked.
- After a curing time of 12 hours the sleeve and nipples are trimmed off with an angle grinder or other suitable equipment.
Thursday, September 30, 2010
what are B and D regions?
B-Regions are parts of a structure in which Bernoulli's hypothesis of straight-line strain profiles applies. D-Regions, on the other hand, are parts of a structure with a complex variation in strain. D-Regions include portions near abrupt changes in geometry (geometrical discontinuities) or concentrated forces (statical discontinuities). Based on St. Venant's principle, the extent of a D-Region spans about one section depth of the region on either side of the discontinuity. 
Figure 1 and Figure 2 show examples of the division between B-Regions and D-Regions in building and bridge structures, respectively. In the figures, the unshaded area with a notation B indicates B-Region, and the shaded area with a notation D is used to indicate D-Region. The notations h1, h2, h3, ... are used to denote the depth of structural members. The notations b1 and b2 denote the flange width of structural members.
Figure 1 Example of D-Regions in a Common Building Structure
(Click here to view a larger image)
(Click here to view a larger image)
Figure 2 Example of D-Regions in a Common Bridge Structure
(Click here to view a larger image)
(Click here to view a larger image)
Most design practices for B-Regions are based on a model for behavior. As examples, design for flexure is based on conventional beam theory while the design for shear is based on the well-known parallel chord truss analogy. By contrast, the most familiar types of D-Regions, such as deep beams, corbels, beam-column joints, and pile caps, are currently still designed by empirical approaches or by using common detailing practices. For most other types of D-Regions, code provisions provide little guidance to designers. The Strut-and-Tie Method (STM) is emerging as a code-worthy methodology for the design of all types of D-Regions in structural concrete.
It is worth noting that although the STM is equally applicable to both B- and D-Region problems, it is not practical to apply the method to B-Region problems. The conventional beam theory for flexure and parallel chord truss analogy for shear are recommended for those designs.
What is LRFD?
Limit state design (LSD) refers to a design method used in structural engineering. The method is in fact a modernization and rationalization of engineering knowledge which was well established prior to the adoption of LSD.[citation needed] Beyond the concept of a limit state, LSD simply entails the application of statistics to determine the level of safety required by or during the design process for LRFD from Bridge Design, please read this book about Design of Highway Bridges: An LRFD Approach
Criteria
Limit state design requires the structure to satisfy two principal criteria: the ultimate limit state (ULS) and the serviceability limit state (SLS).[1] A limit state is a set of performance criteria (e.g. vibration levels, deflection, strength, stability, buckling, twisting, collapse) that must be met when the structure is subject to loads.
Example Treatment of LSD in Codes
The following is the treatment of LSD found in the National Building Code of Canada:
NBCC 1995 Format
φR > αDD + ψ γ {αLL + αQQ + αTT}
where φ = Resistance Factor
ψ = Load Combination Factor
γ = Importance Factor
αD = Dead Load Factor
αL = Live Load Factor
αQ = Earthquake Load Factor
αT = Thermal Effect (Temperature) Load Factor
Any design process involves a number of assumptions. The loads to which a structure will be subjected must be estimated, sizes of members to check must be chosen and design criteria must be selected. All engineering design criteria have a common goal: that of ensuring a safe structure and ensuring the functionality of the structure.
The State of the Art
Limit state design has replaced the older concept of permissible stress design in most forms of civil engineering. Notable exceptions are geotechnical engineering and transportation engineering. Even so, new codes are currently being developed for both geotechnical and transportation engineering which are LSD based. As a result, most modern buildings are designed in accordance with a code which is based on limit state theory. For example, in the UK, Steel structures are designed in accordance with BS 5950, and reinforced concrete structures to BS 8110, both of which are codes based on limit state theory. Australia, Canada, China, France, Indonesia, and New Zealand (among many others) utilise limit state theory in the development of their design codes. In the purest sense, it is now considered inappropriate to discuss safety factors when working with LSD, as there are concerns that this may lead to confusion.
Limit State Design in the United States
The United States has been particularly slow to adopt Limit State(s) design (known as Load and Resistance Factor Design in the US), and as a result it is more thoroughly adopted outside the United States. Inside the U.S. there has been significant resistance to this technique, so much so that the American Institute of Steel Construction (AISC) is now issuing a combined manual of steel construction (the 2005 manual) that contains two methods of design side by side (newly named ASD - Allowable Strength Design, not to be confused with ASD - Allowable Stress Design last updated in 1989), and LRFD - load and resistance factor design).[citation needed] In terms of the US steel code, research and progress has been reserved to LRFD code, with the exception of addenda regarding safety concerns. Even so, many American engineers continue to prefer the former ASD code. The difficulty may lie in the high regionalization of US Engineering practice, coupled with the high number of governing bodies, codes and states which each regulate the engineering profession individually.
Criteria
Limit state design requires the structure to satisfy two principal criteria: the ultimate limit state (ULS) and the serviceability limit state (SLS).[1] A limit state is a set of performance criteria (e.g. vibration levels, deflection, strength, stability, buckling, twisting, collapse) that must be met when the structure is subject to loads.
Example Treatment of LSD in Codes
The following is the treatment of LSD found in the National Building Code of Canada:
NBCC 1995 Format
φR > αDD + ψ γ {αLL + αQQ + αTT}
where φ = Resistance Factor
ψ = Load Combination Factor
γ = Importance Factor
αD = Dead Load Factor
αL = Live Load Factor
αQ = Earthquake Load Factor
αT = Thermal Effect (Temperature) Load Factor
Any design process involves a number of assumptions. The loads to which a structure will be subjected must be estimated, sizes of members to check must be chosen and design criteria must be selected. All engineering design criteria have a common goal: that of ensuring a safe structure and ensuring the functionality of the structure.
The State of the Art
Limit state design has replaced the older concept of permissible stress design in most forms of civil engineering. Notable exceptions are geotechnical engineering and transportation engineering. Even so, new codes are currently being developed for both geotechnical and transportation engineering which are LSD based. As a result, most modern buildings are designed in accordance with a code which is based on limit state theory. For example, in the UK, Steel structures are designed in accordance with BS 5950, and reinforced concrete structures to BS 8110, both of which are codes based on limit state theory. Australia, Canada, China, France, Indonesia, and New Zealand (among many others) utilise limit state theory in the development of their design codes. In the purest sense, it is now considered inappropriate to discuss safety factors when working with LSD, as there are concerns that this may lead to confusion.
Limit State Design in the United States
The United States has been particularly slow to adopt Limit State(s) design (known as Load and Resistance Factor Design in the US), and as a result it is more thoroughly adopted outside the United States. Inside the U.S. there has been significant resistance to this technique, so much so that the American Institute of Steel Construction (AISC) is now issuing a combined manual of steel construction (the 2005 manual) that contains two methods of design side by side (newly named ASD - Allowable Strength Design, not to be confused with ASD - Allowable Stress Design last updated in 1989), and LRFD - load and resistance factor design).[citation needed] In terms of the US steel code, research and progress has been reserved to LRFD code, with the exception of addenda regarding safety concerns. Even so, many American engineers continue to prefer the former ASD code. The difficulty may lie in the high regionalization of US Engineering practice, coupled with the high number of governing bodies, codes and states which each regulate the engineering profession individually.
Segmental bridge
As its name implies, a segmental bridge is a bridge built in short sections (called segments), i.e., one piece at a time, as opposed to traditional methods that build a bridge in very large sections. The bridge is made of concrete that is either cast-in-place (constructed fully in its final location) or precast concrete (built at another location and then transported to their final location for placement in the full structure).
These bridges are very economical for long spans (over 100 meters), especially when access to the construction site is restricted. They are also chosen for their aesthetic appeal.
History
The first segmental concrete bridge, built in 1950, was cast-in-place across the Lahn River in Balduinstein, Germany.[citation needed]
The first precast segmental concrete bridge, built in 1962, crossed the Seine River in France.[1]
Construction
The sequence of construction is similar to traditional concrete bridge building, i.e., build the support towers (columns), build the temporary falsework, build the deck, perform finish work. The principal differences are as follows:
1. The support towers may be built segmentally. Often this is accomplished using "slip-form" construction, where the falsework moves (slips) upward following sequential concrete "pours." The falsework uses the newly constructed concrete as the basis for moving upward.
2. After the towers are built, a superstructure is built a top the towers. This superstructure serves as the "launching" point for building the deck. (The deck is often built in both directions away from the tower, simultaneously.)
3. The deck is now constructed sequentially, beginning at the tower, one section at a time.
* In cast-in-place bridges, the falsework is connected to the previously installed concrete and allowed to cantilever freely. Next, the permanent reinforcing steel and supports are installed. Finally, the concrete is placed and cured, freeing the falsework to be moved.
* In pre-cast bridges, the concrete segment is constructed on the ground, and then transported and hoisted into place. As the new segment is suspended in place by the crane, workers install steel reinforcing that attaches the new segment to preceding segments. Each segment of the bridge designed to accept connections from both preceding and succeeding segments.
4. The process in step 3 is repeated until the span is completed.
These bridges are very economical for long spans (over 100 meters), especially when access to the construction site is restricted. They are also chosen for their aesthetic appeal.
History
The first segmental concrete bridge, built in 1950, was cast-in-place across the Lahn River in Balduinstein, Germany.[citation needed]
The first precast segmental concrete bridge, built in 1962, crossed the Seine River in France.[1]
Construction
The sequence of construction is similar to traditional concrete bridge building, i.e., build the support towers (columns), build the temporary falsework, build the deck, perform finish work. The principal differences are as follows:
1. The support towers may be built segmentally. Often this is accomplished using "slip-form" construction, where the falsework moves (slips) upward following sequential concrete "pours." The falsework uses the newly constructed concrete as the basis for moving upward.
2. After the towers are built, a superstructure is built a top the towers. This superstructure serves as the "launching" point for building the deck. (The deck is often built in both directions away from the tower, simultaneously.)
3. The deck is now constructed sequentially, beginning at the tower, one section at a time.
* In cast-in-place bridges, the falsework is connected to the previously installed concrete and allowed to cantilever freely. Next, the permanent reinforcing steel and supports are installed. Finally, the concrete is placed and cured, freeing the falsework to be moved.
* In pre-cast bridges, the concrete segment is constructed on the ground, and then transported and hoisted into place. As the new segment is suspended in place by the crane, workers install steel reinforcing that attaches the new segment to preceding segments. Each segment of the bridge designed to accept connections from both preceding and succeeding segments.
4. The process in step 3 is repeated until the span is completed.
Universities & Research Institutions in Bridge Engineering
Universities & Research Institutions
- Center for Advanced Technology for Large Structural Systems (ATLSS)
- Center for Infrastruture and Transportation Studies (CITS)
- Center for Innovative Bridge Engineering at the University of Deleware
- Center for Transportation Research (CTR)
- Constructed Facilities Center
- Curtin University of Technology — School of Civil Engineering
- Infrastructure Technology Institute (ITI) — Bridge Clearinghouse
- Institute for Structural Engineering (IBK)
- National Bridge Research Organization (NaBRO)
- National Information Service for Earthquake Engineering (NISEE)
- Northern California Earthquake Data Center (NCEDC)
- Southern California Earthquake Center (SCEC)
- Structural Dynamics and Control / Earthquake Engineering Laboratory (SDC/EEL)
- Swedish Institute of Steel Construction (SBI) - Steel Bridges of the World
- Texas Transportation Institute (TTI)
- Transportation Research Center (TRC)
- Turner-Fairbank Highway Research Center (TFHRC)
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