Questions tagged [bridges]
72 questions
21
votes
4 answers
What makes suspension bridges unsuitable for railways?
I recall reading in an old issue of Model Railroader an article about railroad bridges. In it, the author mentioned that you shouldn't have a model suspension bridge for a railroad track on your layout because no such arrangement would be…
Dave Coffman
- 313
- 3
- 13
20
votes
2 answers
Why are earthfills fully covered in concrete where they join bridges?
Here's how a typical earthfill carrying a roadway joins a typical bridge
Parts of the earthfill slopes are greenish - that's grass - and parts are whitish - that's concrete.
The earthfill slope is fully covered in concrete where it joins the bridge…
sharptooth
- 2,099
- 15
- 27
20
votes
3 answers
Does a roadway bridge experience more load when vehicles are parked or when they are moving?
Bridges are designed for the loads that come from the vehicles that are expected to cross them. This includes the weight the vehicle and any dynamic loads that may be introduced from movement of the vehicle. Dynamic loads may be from "bouncing" or…
hazzey
- 10,682
- 9
- 42
- 93
16
votes
5 answers
Why is this bridge thickest above the support pillars instead of the mid-span where the bending stress is highest?
Why is a bridge designed like this?
The depth of the section at pillars is more than the depth at middle.
If I model this as a simply supported beam having load at mid span then the bending moment will be maximized at the middle and the area is…
MechaTrex
- 335
- 2
- 7
15
votes
4 answers
How should the public raise questions about unsafe structures in the United States?
In a program on NPR that I was listening to, there was a bit about a bridge that from the description sounded to a layman as unsound and is still in use. The program described it as an old wooden railway (and I'm aware that has its own set of…
user348
14
votes
4 answers
Derivation for bridge natural frequency estimate in Eurocodes
The Eurocodes gives the following equation for estimating a "simply supported bridge subject to bending only"*:
$$n_0 = \frac{17.75}{\sqrt{\delta_0}}$$
Where
$n_0$ is the natural frequency in hertz
$\delta_0$ is the deflection at mid-span under…
thomasmichaelwallace
- 944
- 2
- 10
- 25
14
votes
3 answers
Are pontoon bridges being considered to extend bridge span?
Pontoon bridges differ from traditional bridges in that they are supported not by structures anchored to the floor of the body being spanned but by floating pontoons that are connected by a more rigid structure that supports a roadway. They're often…
HDE 226868
- 2,495
- 16
- 34
13
votes
1 answer
Additional jacking force to overcome stiction/dry friction
It is common to lift bridges to replace bearings, etc.
In an ideal world the lifting capacity required of the jacks would be the self-weight of the bridge divided by the number of jacks (+ allowances for wind/snow, etc.).
From my (limited)…
thomasmichaelwallace
- 944
- 2
- 10
- 25
12
votes
3 answers
How can large bridges be made resistant to earthquakes?
How can large bridges, with spans on the order of 1 km, be made resistant to earthquakes?
I'm no expert on quakes, but there are at least two kinds of shaking: lateral and vertical. The vertical shaking in particular really worries me. I don't know…
DrZ214
- 495
- 1
- 4
- 15
12
votes
2 answers
Why was a coil chosen over a straight for this overbridge?
I saw this meme on Facebook showing a coiled railway overbridge and an alternative plan. I replied that straightening that overbridge will force it to start at the other side of the road, and you need to build a u-turn and there is a valuable…
Jesvin Jose
- 325
- 3
- 7
11
votes
2 answers
How accurately are moveable span bridges balanced?
Movable span bridges (bascule and lift) typically employ a counterweight to help reduce the amount of energy and size of motor required to move the span. Due to variations in the the construction of the bridge and counterweight, the theoretical…
hazzey
- 10,682
- 9
- 42
- 93
11
votes
3 answers
Why would a bearing plate that further concentrates load onto small surface be used?
Here's a photo of a bearing plate where a bridge reinforced concrete beam meets the earthfill
The bridge span is about 20 meters long and consists of two reinforced concrete beams each resting on two bearing plates like the one shown - one plate…
sharptooth
- 2,099
- 15
- 27
10
votes
1 answer
Detailing Fixed Cotton Duck Bridge Bearings
I'm looking for a justification for the use of cotton duck bearing pads without a sole plate. I'm specifically considering their use with precast I-girders.
Say I have a two span bridge, simply supported for dead load, with expansion bearings at the…
CableStay
- 2,790
- 1
- 13
- 29
10
votes
3 answers
Can the structural integrity of bridges be measured in real-time for safety?
As a follow up to this question, I wonder if structural integrity monitoring information can be provided real-time and to a sufficient degree that safety decisions can realistically be made from the information.
To put things in context, in the USA…
Mahendra Gunawardena
- 7,153
- 5
- 25
- 65
10
votes
1 answer
Determining the difference between US Bailey Bridge, UK Bailey Bridge, Mabey Compact 100 and Acrow 300
Background
The Bailey Bridge panel bridge system has been around since WWII. It has been credited as being one of the top 3 technological advancements that allowed the allies to win the war. After the war, the surplus of Bailey Bridge parts were…
Forward Ed
- 1,137
- 9
- 23