# Tag Info

24

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 piles. Steep Slopes The soil that is used to create the earthen fills will only stand up naturally to a certain steepness. By placing a layer (~4in) of ...

21

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, especially when compared to lanes of highway traffic. This means that long spans require very strong support structures, which in the case of suspension bridges ...

20

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 changes in angle. and the sliding joint between the upper hinge plate and the flat plate on the bottom of the beam allows changes in length. If the connections were ...

17

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 to account for the vertical curve in the road so the max grade would be quite a bit higher. The max grade allowed for non-local roads in the US is about 8% (...

16

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 - stretching force). In practice these come with more problems of their own. They drift on water surface and as result, rise and fall with water waves. The larger the ...

13

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 code TMH7: It is generally accepted and can readily be shown that except in the very small span range, the worst loading condition occurs under congested (...

13

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 the River Tees, designed by Samuel Brown. (Illustration by William Miller, from The North Eastern Railway by William Tomlinson, 1915.) Intended to carry trains ...

11

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 said "maintenance", because this might be a different entity than the owner due to agreements. Due to the number of complaints that the public agencies receive, it ...

11

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 bridge in Japan is currently the longest span bridge in the world and is in a severe seismic zone. It is designed to withstand a magnitude 8.5 earthquake. In ...

10

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 harmonic motion: $$n_0 = \frac{1}{2 \pi} \sqrt{ \frac{ k } { m } }$$ Where $n_0$ is the natural frequency, $k$ is the ratio between restorative force and ...

10

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 applied to its adjacent section. However, when you think a bit more deeply, it becomes apparent that each section is pulling its adjacent section and that section ...

10

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 structures (including buildings). That being said, some of these concepts are location-agnostic and others may apply to the US as well. Firstly, as mentioned by ...

10

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 substantially higher), but most ordinary structures don't use such high strength concrete. This bridge seems relatively weathered, so the concrete is probably at most \$...

9

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 items. His comments: It really depends on the specific situation. For mild steel bolts in good condition which have not been too excessively deformed, and where ...

8

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 "The bridge destined to host light rail is the Homer M. Hadley Memorial Bridge, one of the longest floating bridges in the world, which currently carries the ...

8

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 floating bridge in the world.". It carries 4 lanes of traffic on SR 520. Having lived in the area and used the bridge, I can recall a few times that bridge has ...

8

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, they have to hold the ends of the rope up but they don't have to pull much, end to end. The straighter the rope is, the more they will have to pull. If you ...

7

"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 6000 kilometers. That's far more than your dimensions. Hence, you can ignore the electro-magnetic aspects and treat this as an electro-static problem. Arcing ...

7

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, the fourth is the cables, the fifth would be the substructure and the sixth is the foundation. A failure of any one of these systems (with the exception of ...

7

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 situations where concrete is not feasible. These situations could be: Very long span lengths. Skewed spans. Shallow structure depths. In these situations, steel ...

6

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 previously available, but the need wasn't as apparent to the public. Sensors Accelerometers Strain Gauges Displacement Transducers Level Sensing Stations (Tilt ...

6

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 Massachusetts it's the Department of Transportation, often known as "Mass DOT". Nowadays state governments have web sites, so it should not be hard to at least find a ...

6

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 rain/ocean, humidity, avg. temperature, the acidity of rain, so on so forth. The principle behind protective coatings may differ in terms of layers, but ...

6

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 carry heavy rail traffic, and also to resist large accumulations of ice. The trains run in a deck below the road trafic. As the article in wikipedia lacks a ...

6

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 Officials) manuals such as those below: AASHTO LRFD Movable Highway Bridge Design Specifications AASHTO Maintenance Manual for Roadways and Bridges The general ...

6

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. (strut and tie). Rigid links are ok. Just make sure that you are capturing the various induced moments. I usually have rigid links from the bearing locations to the ...

6

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 Calatrava using this concept, in particular the Puente del Alamillo. The pylon is actually fully in compression under dead load: the cable stress and the self-...

6

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 actually a bearing plate. This is a little steel platform that transfers the load from the bridge to the column. (source) The expanded portion at the top of the ...

6

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, stand the touching pieces of an arch. So a catenary arch will have only compression stresses (since a flexible cable can only have tension stresses). Notice ...

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