1. Feb 22, 2009

prettys073

question is:- a reinforced concrete beam is to be 700mm deep. the minimum width of beam is to be used and 20mm size aggregate has been specified. three 25mm diameter bars have been calculated for tension reinforcement and three 16mm diameter bars have been calculated for compression reinforcement. shear reinforcement will consist of 100mm diameter stirrups. The level of exposure requires 40mm cover to the reinforcement. sketch the beam cross-section, detailing the reinforcement if the beam is simply supported at its ends.

2. Feb 22, 2009

mathmate

The answer to the question depends on where you practise, since the codes in force will differ. For example, for the United States, you would be using the ACI (American Concrete Institute) code for structural concrete.

The question does not appear to require calculation of the strength of the cross-section. So the only variables left to be determined are:
1. cover between reinformcement and the formwork for 20mm aggregates, noting that the stirrups are on the outside of the main reinforcement.
2. mimimum distance betweent the tension reinforcement (at bottom).
3. same for compression reinforcement (top). However, since 3-16mm bars would have more clearance than 3-25mm bars, item 2 above would govern.
4. From the cover and minimum (clear) distance, calculate the minimum width of the beam, round to the nearest cm for practical purposes.

Now draw the cross section of the beam, placing the reinforcing bars in place, according to the code in force at your location.

Note that for a 700 mm deep beam for the calculated width, certain codes require minimum reinforcement for the given section. Supply additional reinforcement if required.

It is not possible to detail the reinforcement (i.e. give the lengths, and the bending schedule) for the beam since the length of the beam is not known.

3. Feb 23, 2009