17 votes

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

There are a few reasons. I'm firstly going to assume you're talking about replacing a bunch of small rebars by a single reasonably-sized one: i.e. instead of $15\phi8$ (7.54 cm2), using $1\phi32$ (8....
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  • 13k
10 votes

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

The main purpose of rebar is to improve the tensile strength of concrete and in practice most of these loads come from bending rather than pure tension. When a beam in subject to bending forces the ...
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10 votes

Can steel be replaced with aluminum alloy in reinforced concrete?

A very important property of steel used in reinforced concrete is that it has similar coefficient of thermal expansion as concrete: Concrete: $14.5 \cdot 10^{-6} \frac{m}{m\,K}$ Steel: $12.0 \cdot ...
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  • 1,835
10 votes
Accepted

In a reinforced concrete detail drawing what does 'reinforcement to be GK 60' mean?

Check this book out; it seems to be talking about that particular grade of steel used for reinforcement. The choice of main bonded reinforcement is based on its high tensile strength and interaction ...
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  • 402
9 votes
Accepted

Relative strength of wire mesh vs rebar for reinforcing a concrete slab

This is going to depend a great deal on what you want to achieve with the reinforcement. I'm not aware of any ultimate strength increase for using welded wire mesh allowed by Eurocode 2 or ACI318. I ...
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  • 2,631
7 votes
Accepted

How do units of mm^2/mm represent the reinforcing steel area in a slab?

Your second bar description is what you need to compare it to: #8 @ 12" O.C. A #8 bar is 0.79 in2. This gives us $\frac{0.79in^2}{12in}$ or in2 over in. This is the similar to your mm2/mm. (...
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  • 10.6k
7 votes

Can steel be replaced with aluminum alloy in reinforced concrete?

In short: you can't use aluminium to reinforce concrete. You shouldn't even embed uncoated aluminium in concrete. Quoting Corrosion of Non Ferrous Metals in Contact with Concrete, "Aluminium suffers ...
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  • 407
7 votes
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What's the name and purpose of this specific shape of hollows in a reinforced concrete slab?

It looks like a typical precast concrete "hollow-core" or "voided" slab. A quick Google image search reveals the variety of void shapes employed by manufacturers. The image on the left (from ...
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  • 2,770
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 ...
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  • 3,587
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 ...
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  • 3,145
6 votes

Material Properties: Does bending reduce iron rebar's strength?

It depends what you mean by bearing capacity. Plastic deformation increases yield strength at the expense of ductility. Also possibly toughness and fatigue durability if strained too much. Metals ...
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  • 3,971
5 votes

Which one is preferable? Multiple layers of reinforcements or one layer of reinforcement?

On average, it's best to limit the number of layers of rebar. There are a few reasons for this. Firstly, the more layers you have, the more complex the construction of the beam becomes. The first ...
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  • 13k
4 votes

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

Reliability of Data Are you able to repeat the test to confirm the 7ksi break? Did you have a second 28 day cylinder or 7 day breaks which were also higher than typical? How sure are you that the ...
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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 ...
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4 votes
Accepted

Telehandler wall collision forces

In a situation like this you will need to resort to energy methods. Depending on how complicated you wanted to get you could do a dynamic calculation also. I would recommend looking at the guidance ...
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  • 2,631
4 votes

do prestressing tendons located in the compression zone contribute to compression reinforcement?

The short answer would be "yes", but there is a lot of things to be aware: First of all, you should check that the building code you are following allows you to do so. You should check adherence ...
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  • 407
4 votes
Accepted

What is the splice length for two reinforcement bars in tension of different diameter?

The use of the smaller diameter is theoretically correct. What is a splice? It is when tension force in a rebar is transferred to the concrete via adhesion and then to another rebar. Since concrete ...
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  • 13k
4 votes
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Is continuous beam design deemed "unsafe" by any code of practice/design practice for reinforced concrete building structures?

You question starts with (emphasis mine): Given that continuous beam predicts less deflection This is not correct. A continuous beam does not predict less deflection, a continuous beam results in ...
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  • 3,145
4 votes
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Reinforcing beam and slab with correct steel bar structure

Model 1 is always better, but may need some modifications Whenever you have two reinforced concrete elements, you always need to facilitate the transfer of internal stresses between them. This is ...
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  • 13k
4 votes

Why is this structurally sound?

What you see is temporary support, only till the time the floors attain their design strength. Then all these will be removed. The rate of progress of the project must be faster than the time ...
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  • 21k
4 votes

Impact of having flexible electrical hose buried into the reinforced concrete slab

You haven't specified any material parameters, so for calculation purposes, I am going to assume a reinforcement yield strength of 500MPa and a cylinder compression strength for both concrete and ...
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  • 1,278
3 votes

What are safe locations for openings in reinforced concrete beams?

This is the sort of thing that is best defined by each country's structural codes. I'm from Brazil, so I'm going to use the NBR 6118, our concrete code. That being said, the general gist behind all of ...
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  • 13k
3 votes
Accepted

Basic Hook development length using CSA A23.3 provisions

I'd agree, you cannot fit a horizontally oriented 5" 90° bar bend in an 8" thick wall if you want your rebar curtain to be located at the center-line of the wall. However, there is no reason that the ...
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3 votes
Accepted

Design behind typical keyed construction joints in concrete walls

Typically one does not consider the key when checking a slab - footing interface. This is based on ACI318 Section 15.8.1.4, which discusses the transfer of lateral forces to footings and directs the ...
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3 votes

How monolitic is concrete when falsework is being crafted for parts of future structure only?

In a continuous structure such as a beam or a column (under the expected loads for such elements), the structure is effectively indistinguishable from a truly monolithic one. This has to do with how ...
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  • 13k
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 ...
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3 votes

Does screed increase the slab tension capacity?

No, a screed does not increase a slab's capacity in any practical way. It is considered non-structural.
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  • 3,145
3 votes
Accepted

Are the design load values in this floor determination table (span chart) inclusive or exclusive of the given floor weight (inherent dead load)?

The load values in the table is described as the design load with no further qualifiers and that will generally mean the total load including all dead load and live load as well as safety factors. It ...
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  • 1,278
3 votes
Accepted

Why is there a row of circular holes in this concrete beam?

I've not seen them before but I think that they are surely penetrations to run wiring. They on top for reasons including close to the lid where wiring would be normally attached between the beams in ...
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  • 358
3 votes

What is this circular metal object embedded in spalled concrete?

It looks like a prestressed cable anchor.
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