# Tag Info

## Hot answers tagged reinforced-concrete

17

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 $1\phi32$ (8.04 cm2). One reason is to improve ease of constructibility. Reinforced concrete beams also have transversal reinforcement, and it's very common to place rebars ...

10

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 greatest stress are at the edges and faces of the beam so just having one big bar running down the centre wouldn't do very much as this part of the structure ...

10

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: $12.0 \cdot 10^{-6} \frac{m}{m\,K}$ Compare this with: Aluminum: $22.2 \cdot 10^{-6} \frac{m}{m\,K}$ So a likely result of putting aluminum inside a concrete beam would ...

10

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 between it and concrete, resulting in higher bond length and an improved degree of crack control. A considerable experimental work has been carried out by ...

9

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 had a quick look and couldn't find anything. I'm also sceptical that welded wire mesh is mandated for all slabs in Germany. However, it is common in Germany. I ...

7

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. (Obviously the units are not interchangeable!) This method of describing reinforcing is useful if you don't care about the actual size of rebar used. It could be #8 ...

7

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 attack when embedded in concrete". Corrosion of aluminium embedded in concrete causes total destruction of aluminium bars, therefore it's dangerous and ...

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

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

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 virtually always exhibit increased yield strength when strained plastically below their strain recovery temperatures. The phenomenon is referred to as strain ...

6

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 Oldcastle Precast, incidentally) nicely shows the variation of void shape with increasing slab thickness. As noted in the other answers, we care about the concrete ...

5

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 layer of rebar is easy to place: it simply rests on the stirrups and is held in place with some tie wire. All other layers, however, require the placement of ...

4

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 cylinder was formed properly and followed ASTM? Application Specific Requirements Does the specifications from the design engineer call for a max and min ksi or ...

4

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 design and how there are issues that are not apparent to "outsiders" but which can be important. eg in this example the span is very slightly curved resulting ...

4

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 in Eurocode 1991-1-7 (Accidental Actions). In particular look at Annex C which describes dynamic design for impact. This essentially involves equating the ...

4

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 between steel and concrete. Since the ratio between strength and lateral surface is a lot higher for tendons than for passive reinforcing steel, adherence ...

4

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 is very weak against tension, large lap lengths are required such that the stress at any point in the concrete is not excessive. However, once the splice is over,...

4

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 less deflection (than a pair of simply supported beams). Similarly to this question, you seem confused between how a structure behaves in real life and how it ...

4

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 done by "mixing" their reinforcement. For instance, model 2 will have no steel between the slab steel and the beam steel. This means that the connection between ...

4

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 required for the concrete to be strong enough. As far as using rebars, just looking at the spans and proportion of cantilevered area's it seems they are using some of ...

4

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 mortar of 25MPa. As I am basically just guessing these values, you will have to adjust the conclusion accordingly, if I haven't been so lucky as to guess correctly. ...

3

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 the codes tends to be pretty similar. Doing a free translation, this is what is described in the Brazilian code: 13.2.5.1 Openings that cross a beam along its ...

3

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 bent bars will not fit if you orient the bend vertically. The bars can be placed such that the 5" 90° bar bend is oriented vertically.

3

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 reader to Section 11.6. 11.6 which says this, 11.6.3 A crack shall be assumed to occur along the shear plane considered. Therefore, you do not consider the ...

3

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 the elements are poured, with joints perpendicular (or at least not parallel) to the load direction. Columns are poured so that the joints are horizontal, while ...

3

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 cable-supported span. This implies a greater load from each half of the central span than from each outer cable-supported span. Furthermore, the cables from ...

3

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

3

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 would usually be problematic to specify the capacity exclusive of the inherent dead load because multiple load safety factors need to be checked, that is both ...

3

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 a place of lower bending stress, near the compression zone, not in the tension zone were reinforcing would be located or concentrated I suppose that they could ...

3

It looks like a prestressed cable anchor.

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