Questions tagged [civil-engineering]

Questions that fall into the problem domain of civil engineering or one of its sub-disciplines. Questions about buildings or other structures could usually use the "structural-engineering" tag also.

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22
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2answers
6k views

What is the purpose of these “steps” in rivers?

I have seen a number of structures within rivers, which resemble steps, and which allow the water to cascade down them instead of flowing naturally down the course of the river. Example 1: River ...
20
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4answers
6k views

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 ...
20
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1answer
2k views

Why does the Channel Tunnel enter the ground around 10 km from the coast?

I know that digging tunnels is always much more costly than building ways or train above ground. Why doesn't the Channel Tunnel start around the coastline? Why does it have an around 10 km long ...
20
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2answers
2k views

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 ...
20
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3answers
5k views

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 ...
18
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3answers
14k views

How does a traffic light sense the proximity of vehicles?

Some traffic lights don't operate periodically but instead detect when a car is close by and then turns green. I have heard that they use a magnetic sensor embedded in the road to sense cars as they ...
18
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1answer
4k views

Why are truss bridges the way they are?

Just by taking a train ride across my home city I can see truss bridges like the one in above picture everywhere. There are numerous variations, but the most common design seems to be this. But why ...
18
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1answer
428 views

Is there a method to determine the runoff for arid areas in developing countries?

Note: this question was totally rephrased and expanded on, addressing the comments and questions posed to the first version. The de-facto standard source for runoff calculations in South Africa is ...
17
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5answers
2k views

How are passive houses made in very hot regions (like Saudi Arabia)?

I think, here is the main problem the difference between the internal and the external temperature. For example, in Saudi Arabia, in 50 C, a passive house needed probably much sophisticated planning ...
17
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3answers
7k views

What is the most efficient means of warming a building with a high ceiling?

Consider a large auditorium, a church, or some other very large, essentially one roomed building with a high ceiling. Suppose that the building has many entrances which enable cold air in/hot air out ...
17
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1answer
4k views

How many train passes can railway tracks endure?

I know that the rubber on car and truck tires wear, and the road concrete wears out. I wondered: While steel is hard and elastic, it still causes friction (interaction between molecules) and ...
17
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1answer
2k views

How to design a house to be cooled passively? [duplicate]

I live in Louisiana these days, in an area that is known for its numerous antebellum plantation homes (circa early 1800s). While touring one of these homes it was clear that almost everything about ...
15
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2answers
417 views

What is this large steel structure used in excavation?

I keep seeing these large rectangular structures on job sites they put in the ground. I'm guessing something for strengthening the surface structures?
14
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3answers
675 views

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 ...
14
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4answers
1k views

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 ...
14
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6answers
3k views

Why does column buckling occur when the load is parallel to the column?

I'm studying Euler's work on structural engineering from a book out of curiosity and it is mentioned that he developed a mathematical theory describing the buckling of columns under a parallel load (...
13
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3answers
16k views

What is a Spiral Curve, and How is it Different from a Normal Curve?

I've heard the term spiral curve used to describe a section of highway that is more aesthetically pleasing to the driver's eye. However, I believe I've driven on enough road to say that I can't ...
13
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1answer
375 views

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 ...
12
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4answers
4k views

How thick is it reasonable for the walls of a steel gas pipeline to be?

The TurkStream project site claims the gas pipeline will use pipes made from 39 millimeters of high-quality carbon manganese steel with additional plastic coatings on both sides. Yes, they claim 39 ...
12
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2answers
1k views

Why are three way bridges rare?

It's true that most bridges are "two directional." But three way bridges are pretty rare, globally. I can understand why there wouldn't be many for rivers, but if bridges are designed based on the ...
12
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2answers
1k views

Why do earth cuts sometimes have steps on their walls

A neat image from Wikipedia: There're clearly visible steps on the cut wall. This makes the cut wider at the top and so requires more work so those steps have some serious reason behind them. What's ...
12
votes
1answer
6k views

At what point does an I-beam becomes a H-beam?

According to BS5950, a beam section can be classified as plastic, semi-compact, compact or slender. For the same section area, a H-beam can take axial compression (without buckling) better than an I-...
12
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2answers
477 views

Foiling vortex traps around buildings

I have had three houses with right angles in the layout, and in each one that configuration causes vortices to form that suck in leaves, snow, and any debris blowing by and keep it in the nook of the ...
11
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5answers
5k views

Why are some public benches made with arm rests that waste so much space?

While watching a YouTube video today, I noticed this public/park bench somewhere in the USA: It looks strange to me the way the arm rests on each side are so far into the bench, wasting a rather ...
11
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3answers
4k views

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 ...
11
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7answers
16k views

Why do we use multiple reinforcing bars instead of one bar with a big diameter in reinforced concrete?

Why do we use multiple reinforcing bars instead of one with a big diameter in reinforced concrete? Does increasing the number of reinforcing bars means that the reinforced concrete will have a higher ...
11
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2answers
594 views

Why do air entrainment admixtures improve the freeze-thaw resistance of concrete?

It is stated on here that: Air-entraining admixtures cause small stable bubbles of air to form uniformly through a concrete mix. The bubbles are mostly below 1 mm diameter with a high proportion ...
11
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2answers
5k views

Why are tremors of an earthquake felt more on upper floors?

Why are tremors of an earthquake felt most on the upper floors of a building in comparison to lower floors? Does this have something to do with a third class lever?
11
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3answers
562 views

How different is using styrofoam rather than empty cans when pouring concrete?

In the recent 6.4 earthquake that hit Taiwan, it was seen in a newswire photograph of rubble that metal cans were embedded in the concrete. The quote from an official regarding this practice: For ...
11
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2answers
235 views

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 ...
11
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1answer
202 views

Has a specific type of alternative intersection been shown to reduce congestion & accidents?

Localities in the US have different road layout and setups. For example the Michigan Left, Jersey Left/Jug Handle, vs a standard 4 way stop with left turns at the intersection. Have any of them come ...
11
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3answers
4k views

Should I reject a concrete mix design for having too high of a compressive strength?

I usually design precast concrete members for the common concrete strength of f'c=4,000 psi at 28 days. Occasionally, a mix design will be submitted that has a very high strength. In one case, the mix ...
11
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1answer
1k views

How to determine the lateral earth pressure in a double-walled cofferdam?

The design of a retaining wall commonly involves determining the lateral earth pressure using either Rankine theory or Coulomb theory. Both theories involve mobilising the shear resistance of a ...
11
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4answers
17k views

What is the difference between “Crushed Stone” and “Crushed Gravel” aggregate?

Crushing Question While reading a material specification for crushed aggregate, the text mentions both "crushed stone" and "crushed gravel" are acceptable. These materials sound ...
10
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3answers
6k views

Why is it unwise to choose cylindrical horizontal beam

I heard that it is unwise to choose cylindrical horizontal beam. My question is why?
10
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4answers
21k views

Why does the stress-strain curve decrease?

This is a stress-strain diagram I have noticed that the curve decreases between points C & D and between E & F. Why does that happen? I expected the curve to always increase since the ...
10
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2answers
694 views

Why don't we just build a giant wind turbine?

The power generated by a wind turbine is given by: $$\mathrm{Power} = \frac{1}{2}C\rho AV^3$$ Where: $\rho = \text{Air density}$ $C = \text{Coefficient of performance}$ $A = \text{Frontal area}$ $V ...
10
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3answers
2k views

How does one go about building an underground structure without concrete?

I was reading an article that was linked on another site I frequent on "India's forgotten stepwells", which are basically elaborate wells with stairs to go down to the water level, sometimes 10 m or ...
10
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2answers
11k views

How is the design life of a reinforced concrete structure calculated?

The specifications for large structural projects typically call for the structure to have a specific design life. This can be 50 years, 100 years, etc. Accommodating the design life for steel can be ...
10
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5answers
2k views

Low cost, moderately accurate water depth measurement

tl;dr: After an extended conversation with an old-timer, I realized a few things: The single most valuable measurement for the majority of people will be water-depth-in-well. The second most valuable ...
10
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2answers
1k views

Soil swelling and mass/volume relationships

Given moisture content, Specific gravity of solids, initial volume, and weight. I'm asked to compute the moist unit weight, dry unit weight, and degree of saturation of this compacted soil. This is ...
10
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1answer
268 views

Developing a stochastic differential equation model for concrete fibers

I am working on modeling concrete fibers (metallic fibers) as a mathematical model. My work is for my thesis. I am a PhD student of numerical analysis, but I am working on a real tunnel project. I ...
9
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7answers
4k views

Why do we pave roads instead of making them from removable parts?

If roads were made of removable parts, we'd probably have fiber cable internet everywhere by now I'd say. It'd be so much easier to install e.g. new electricity and water infrastructure and to ...
9
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4answers
10k views

How does pressure change with depth in earth?

I've learned in school that pressure in water changes like $$p(h) = \rho g h$$ where $h$ is depth in meters, $\rho$ is density (e.g. 1000 $\frac{\text{kg}}{\text{m}^3}$ for water) and $g$ is ...
9
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5answers
765 views

How can I measure the thickness of a sedimentation layer in a closed tank?

Biogas slurry often contains sand and grit and organic matter that eventually sediments. Clearing thetank from sedimentation is expensive (plant downtime, additional equipment) and dangerous. So it ...
9
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3answers
1k views

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 ...
9
votes
1answer
644 views

Differences between 2D hydrological modelling programs eg. HECRAS 5.0 (2D), TUFLOW, MIKE Flood

Just wondering what the difference is between 2D flood modelling programs. I am primarily considering whether HECRAS 5.0 (2D - currently in Beta) would be an acceptable alternative for simple 2D flood ...
8
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3answers
628 views

Determining the properties of members of historic structures

From time to time I am tasked with additions or alterations to old buildings or structures. I would need to establish the "as built" structure and from that analysis see how the amended/new structure ...
8
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2answers
2k views

As built vs as recorded

When an infrastructure project is complete, the professional team has to prepare drawings representing the infrastructure, as it was completed in the end. All on-site changes and deviations from ...
8
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2answers
2k views

What is the practical limit on the number of storeys in residential buildings built with monolithic reinforced concrete?

I have recently bought a flat in a 25-storey building. I wonder what is the practical limit for the number of storeys in a mass-produced residential buildings built from monolithic reinforced concrete?...

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