29
votes
Accepted
Why is this bridge thickest above the support pillars instead of the mid-span where the bending stress is highest?
If I model this as a simply supported beam having load at mid span [...]
I suspect that this is where your analysis went awry.
First off, you should always model bridges with distributed loads, not a ...
- 13k
24
votes
Why are earthfills fully covered in concrete where they join bridges?
This is called Slope Paving. (In the US at least.)
It is done for two reasons at bridge abutments. These reasons are related:
Steeper slopes are possible.
Protection from undermining abutments and ...
- 10.6k
23
votes
Accepted
What makes suspension bridges unsuitable for railways?
There are a few main reasons why suspension bridges aren't used for railroads.
The main reason is that suspension bridges are typically used where very long spans are needed. Trains are very heavy, ...
- 10.6k
22
votes
Accepted
Why would a bearing plate that further concentrates load onto small surface be used?
Because bridges and other structures are not static objects. They must be allowed to flex under varying loads and also accommodate changes in length from thermal expansion. The hinge pin allows ...
- 6,749
18
votes
Accepted
Why was a coil chosen over a straight for this overbridge?
source google maps
The distance between the intersection and the rail is 100m, The road would need to rise about 10m to clear the track. This would mean a average grade of 10%. However you also need ...
- 5,666
16
votes
Accepted
Are pontoon bridges being considered to extend bridge span?
Theoretically pontoon bridges with rope anchors keeping them to the bottom would work against wind and flow, overcoming the problem jhabbot mentioned in his answer (same as train length limit - ...
- 6,123
13
votes
Accepted
Does a roadway bridge experience more load when vehicles are parked or when they are moving?
Parked vehicles vs moving vehicles
Closely spaced parked (or slow moving) vehicles are definitely more onerous, as stated on page 89, Appendix 2.A, Clause 2.A.1 of the South African bridge design ...
- 3,145
13
votes
What makes suspension bridges unsuitable for railways?
Possibly the reputation of railway suspension bridges was fatally damaged by the poor performance of the very first one?
In 1830, the Stockton and Darlington Railway built a suspension bridge over ...
- 446
12
votes
Accepted
How should the public raise questions about unsafe structures in the United States?
I can understand your concern. This is going to be difficult for two reasons:
Finding out the agency that is responsible for the maintenance may be next to impossible for a layperson. Note that I ...
- 10.6k
12
votes
Accepted
How can large bridges be made resistant to earthquakes?
You can never make something earthquake proof, but there are many things that can be done to resist earthquakes.
There are long-span bridges built in earthquake zones. For example, the Akashi Kaikyo ...
- 2,631
11
votes
Why are concrete bridges more prevalent than steel bridges in the United States?
I live in Brazil, so the relevance of my answer to your US experience is somewhat questionable. This is exacerbated by the fact that Brazil is almost 100% concrete, with very few steel or wooden ...
- 13k
10
votes
Accepted
Derivation for bridge natural frequency estimate in Eurocodes
If we simplify the whole bridge into 2D thin beam with a constant section size, no internal damping and subject only to small vertical deflections, then the natural frequency is determined by simple ...
10
votes
Are pontoon bridges being considered to extend bridge span?
The problem with long span pontoon bridges is not obvious at first. You would think that each section is perfectly capable of withstanding the relatively small amount of force from wind or currents ...
- 5,930
10
votes
Why would a bearing plate that further concentrates load onto small surface be used?
The reason is pretty simple. Steel is significantly stronger than concrete.
Nowadays we have high-performance concretes with $f_c > 100~\text{MPa}$ (and ultra-high-performance, which is ...
- 13k
9
votes
Accepted
Can nuts safely be removed from bolts where the threads have been intentionally damaged?
I asked a friend who is a highly competent EE by day - but who restores super sized steam engines by night and collects olde heavy metal engines etc and has much experience with old large corroded ...
- 3,824
8
votes
What makes suspension bridges unsuitable for railways?
Light rail, and a floating rather than a suspension bridge, however I suspect many of the issues are the same:
http://bulletin.pbworld.com/volumes/2014_04/taking_light_rail_over_floating_bridge.aspx
"...
- 488
8
votes
Are pontoon bridges being considered to extend bridge span?
Yes, and they have been used successfully in some major applications. One of the example in your list is Evergreen Point Floating Bridge "Its 2,310 meters (7,580 ft) floating section is the longest ...
- 1,062
8
votes
Why are concrete bridges more prevalent than steel bridges in the United States?
Initial Cost
When span lengths allow, concrete spans are cheaper than steel spans. This is partially because of material costs and partial because of labor (fabrication) costs.
There are a few ...
- 10.6k
8
votes
How does the parabolic curve help in the integrity of a suspension bridge?
The next time you see some kids playing jump rope, go out and ask them to hold the rope perfectly straight. If two kids hold the two ends of the rope with it dangling until it is almost on the ground,...
- 905
7
votes
Accepted
Building a steel footbridge over a railway line and its catenary
"standard EM interaction range" depends a lot on frequency, or its inverse which is wavelength. Your 25 kV catenary probably is 50 Hz or 60 Hz, same as your national grid. That means the wavelength is ...
- 391
7
votes
Accepted
Can the structural integrity of bridges be measured in real-time for safety?
There are many different sensors that can be placed on a bridge to help monitor its condition. After the I-35 bridge collapse, this area has seen a lot of publicity. Most of these sensors were ...
- 10.6k
7
votes
Accepted
How do protective coatings affect the lifetime of bridges?
If you are really considering catastrophic failure, what you are asking actually has several parts. The first is the coatings aspect, the second is the metal structure, the third is the connections, ...
- 652
7
votes
Why is this bridge thickest above the support pillars instead of the mid-span where the bending stress is highest?
Since this bridge is crossing over a waterway, besides aesthetics, the arch-shaped bridge provides several advantages:
Less restrictive over the height of marine traffic due to more headroom in the ...
- 7,481
6
votes
Can the structural integrity of bridges be measured in real-time for safety?
Real-time monitoring can be done and has already been done. The technology is there and as pointed out by hazzey, is a matter of cost versus the risk involved.
As a practising Engineer, I am/was ...
6
votes
How do protective coatings affect the lifetime of bridges?
The goal of using protective coating/paint is to reduce corrosion of the metal framework. The degree of corrosion varies from the top to sea level and depends on several parameters such as salinity of ...
- 61
6
votes
How should the public raise questions about unsafe structures in the United States?
Here in the US, I would contact the state department that manages roadways. Those are referred to as the "highway department", "department of public works", and various other names. Here in ...
- 11.2k
6
votes
What makes suspension bridges unsuitable for railways?
If you look at the Øresund Bridge they state that the bridge was designed with heavy rail traffic in mind:
A girder and cable-stayed design was chosen to provide the specific rigidity necessary to ...
- 161
6
votes
Accepted
How accurately are moveable span bridges balanced?
This paper from the Heavy Movable Structures group goes into detail about how roadway movable spans are balanced. It references AASHTO (American Association of State Highway and Transportation ...
- 10.6k
6
votes
Accepted
Simple Finite Element Modeling of Wall Piers
I'll go through your questions one by one:
A simple model like you have shown is fine to get model loads. Once you get those loads, you can then use a more specific technique to design the pier. (...
- 10.6k
Only top scored, non community-wiki answers of a minimum length are eligible