Deep wall with a moderate slenderness

Let's now analyse a more slender partition beam than the one studied previously, with a span twice as long as before. The two loads act at a quarter and three-quarters of the span relative to the supports.

Strut-and-tie models with direct support

The structural behaviour changes compared to the previous cases: the distance between the load and the support is now considerable, and the strut is too inclined for direct support, as the behaviour of compressed struts with a resultant direction close to that of the tension member is problematic. Indeed, if the beam has only flexural reinforcement, without stirrups, a flexural crack can propagate in the compressed zone and cause a brittle failure of the beam due to shear forces.

Strut-and-tie model

If we want to avoid a failure due to shear forces, it is necessary to introduce stirrups. To better understand the behaviour of reinforced concrete, it is important to remember that the capacity of concrete to withstand tensile forces is quite low. Consequently, under low loads, reinforced concrete behaves like a homogeneous elastic material; once the tensile forces exceed the concrete's resistance, cracks begin to form. From this point on, the reinforcement starts to play an important role, which is to take on the tensile forces. We can conclude that:

• Reinforcement is activated after the concrete has cracked

• A redistribution of internal forces occurs after the cracking of concrete

• After cracking, reinforced concrete structures behave in accordance with the manner in which the reinforcement has been provided

• To obtain a better behaviour under the service state, it is recommended to lay reinforcement according to the directions in which tension forces act in the elastic phase