32
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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 ...
- 13.1k
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 ...
- 6,874
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 ...
- 5,751
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 ...
- 13.1k
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 ...
- 13.1k
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 ...
- 10.7k
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,...
- 1,000
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 ...
- 8,109
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. (...
- 10.7k
6
votes
Why design a cable stayed bridge with pylons inclined towards the obstacle being spanned?
Why build pylons which are inclined away from the obstacle being spanned?
As well as being aesthetically interesting, this can also be structurally efficient. Personally I love the many bridges by ...
- 3,135
6
votes
Why would a column expand before accepting load through a narrow thunk?
The column top holds some narrow thunk and that thunk holds the driveway floor.
I think we have some nomenclature that needs to be cleared up here.
What I believe you're calling a "thunk" is ...
- 3,587
6
votes
Accepted
How and WHY does the tension in an arch dam or bridge change as the degree of curvature and radius of curvature change?
The presence of tension in an arch is not really dependent on the curvature but on how well the arch matches a catenary shape.
Robert Hooke famously stated:
As hangs a flexible cable so, inverted, ...
- 2,631
5
votes
Accepted
Most efficient way to build a toothpick bridge
As you are spanning 10 feet and the length of the toothpicks is small in comparison you have quite a lot of options in terms of the design of the structure you use. In fact one approach would be to ...
- 15.2k
5
votes
How can large bridges be made resistant to earthquakes?
Actually very long bridges (and super-tall buildings) often have less issues with earthquakes than their smaller brethren. This is due to them generally being much more flexible and therefore having ...
- 318
5
votes
Accepted
Derivation of the AASHTO formula of interior girder moment
The live load distribution formulas in the AASHTO LRFD Bridge Design Specifications cannot be derived. As I understand it, they are based on calibration to extensive finite element modeling.
This is ...
- 2,760
5
votes
Why are expansion joints on prestressed concrete box girder bridges sometimes not located directly above the bridge piers?
Because the extension of the longer span past the column into a cantilever allows it to enjoy the benefit of the cantilever part's positive moment effect on the reduction of the midspan negative ...
- 22.1k
4
votes
Why design a cable stayed bridge with pylons inclined towards the obstacle being spanned?
As AndyT says - it seems it's aesthetics in most cases.
Given the above as the answer, the following is essentially comment, but seemed worth posting as it gives a lot of detail of what goes into a ...
- 3,854
4
votes
Why is this box girder made of lattice on one side only?
I can see a few reasons why three of the sides would be solid and one side open. They are listed in roughly order of decreasing importance.
Because of how the tower legs (columns) slope, the laced (...
- 10.7k
4
votes
Accepted
What is the preferred composition for modern concrete bridges?
In structural situations, portland cement concrete is what is used.
The properties of asphalt change with temperature and it never really "sets". It is a viscous liquid that cannot support long-term ...
- 10.7k
4
votes
Light frame at tunnels and bridges
Such measures do exist, but they don't always prevent careless drivers from ignoring the measures and crashing into low bridges.
One bridge that I know of has been hit at least 100 times and has been ...
- 9,642
4
votes
Accepted
What is the deepest bridge pier in the world?
It's not a bridge, but if you wish to consider the depth of marine structures generally, a good example is the Troll A platform in the North Sea. From Wikipedia:
"The Troll A platform has an overall ...
- 652
4
votes
Accepted
Bridge terminology - railing-like parapet
I do a lot of bridge inspections in Ontario, Canada following OSIM (Ontario Structural Inspection Manual). Based on your photo, I would hazard to guess this is an older style barrier system. I would ...
- 1,201
3
votes
When should anti-bursting reinforcement be used?
BS5400 has been superseded and withdrawn, so you probably shouldn't be using it.
That said, when I last used it, I did provide bursting reinforcement for bearing plinths.
In general, just because ...
- 3,135
3
votes
Why design a cable stayed bridge with pylons inclined towards the obstacle being spanned?
I believe there is a sensible engineering reason no one has pointed out yet. In the picture in the original question the central span appears to be slightly longer than twice length of each outer ...
- 133
3
votes
Strand layout in prestressed concrete girders: is a partially filled bottom row acceptable/advisable?
@hazzey has answered your main question quite effectively, so I'll just add two comments.
While I agree that partially filling rows is perfectly fine, I would just like to add that it may be better ...
- 13.1k
3
votes
Strand layout in prestressed concrete girders: is a partially filled bottom row acceptable/advisable?
Strands in Upper Rows Versus Debonded Strands
You have the right idea that placing strands in upper rows is better than debonding strands. Debonded strands are more time consuming (e.g. cost more) ...
- 10.7k
3
votes
Is there a specific name for diagonally braced truss members like those on the Queensboro Bridge?
There are a variety of names for these, but they all have a similar theme:
Laced strut/tie
Lattice or Batten bracing
Lattice truss
Lattice Girder
I'm sure you get the idea. These were popular in ...
- 2,631
3
votes
Accepted
Did this artist take some licence with the Royal Albert Bridge - or has its appearance changed?
Probably artistic interpretation. #i see the differences you are alluding to but they don't look like things you could reasonably alter in a structure.
The artist's rendering looks like an ...
- 15.2k
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