Design of composite beams for buildings Regular T-beams with solid web

In mixed steel-concrete construction of buildings, the beam is the basic element to be mastered by calculation, the most classic configuration being that of the T-beam with a slab above and connected to a steel section. This is the purpose of the present article, which focuses essentially on the calculation aspect, the configuration and manufacturing aspects of beams having been dealt with in the article [C 2 560] .

A priori, one might think that the classical elastic theory of the Resistance of Materials, generalized to the case of heterogeneous sections, would suffice to answer the purpose of the article. In reality, this is not the case, due to the many phenomena that come into play when dimensioning a beam, such as the construction phase, possible underpinning of the beam, the effect of creep and cracking of the concrete on deformations and the redistribution of internal forces, the effect of slip at the connection level, especially if this is only partial, etc.

Contrary to the approach used for composite beams in engineering structures, which are very often supported by elastic calculations, for composite beams in buildings it is very much in the interest to use plastic calculations of the sections, or even the beams themselves, whenever possible, even if this means choosing sufficiently compact metal sections or modifying certain reinforcement percentages appropriately. Not only is the plastic calculation simpler in general, making it possible to neglect some of the phenomena to be taken into account in the elastic calculation. But it also provides a better understanding of the ultimate limit states of beams, giving the design a uniform level of safety. Of course, the serviceability limit states of building beams remain within the scope of elastic design. It is with this in mind that the developments that follow place a major emphasis on plastic calculations.

Among the various ultimate limit states of building beams, we must not neglect to include that of the steel-concrete connection, the dimensioning of which can be handled simply, also by plastic calculation, provided that ductile connectors are used, the precise definition of which is given later in the article. In general, welded-head studs in solid or composite slabs are such connectors, unlike stops and angles in solid slabs, which are non-ductile connectors, requiring elastic-type connection dimensioning. Moreover, the use of ductile connectors is a prerequisite for benefiting,...