Composite Steel and Concrete Construction- General observations. Material properties

The engineer's art in designing and calculating a mixed structural element lies in knowing how to make one part of the concrete element work with another part of the steel element, by associating these two materials at their interface by means of connectors working essentially in shear. Thanks to the effect of the connection, it is then possible to appreciably increase the rigidity and strength of the element, for example in its bending behavior if the element is a metal I-beam connected on its upper flange to a concrete slab. In some cases, the steel-concrete connection may only have to withstand low shear forces, and may be ensured by simple adhesion and friction, without the need for connectors. This is the case, for example, of a composite column with a type I or H steel section encased in concrete, or with a hollow section section filled with concrete, the column being loaded essentially by the normal force. The mixed operation of the column gives it greater resistance to buckling.

In France, while the concept of "double girder" composite bridges in the field of engineering structures led to a remarkable boom in road bridges in the 1980s, and later in rail bridges, the building sector has not seen the development of many composite structures, with this type of construction appearing more often than not in the form of composite floors or columns within a predominantly steel-framed structure. There are several possible explanations for this situation, not least the attitude of French concrete and steel construction companies, who remain deeply attached to the habit of specific, traditional designs, in contrast to what has happened over the last few decades with other European countries such as Scandinavia, Germany, England, Poland, Hungary, etc., where companies routinely work with both concrete and steel. On the other hand, to the credit of French project owners, there was a total absence of official regulations in the field of mixed construction until 2005, when the French standard NF EN 1994-1-1 (translated from Eurocode 4) was published, supplemented only in 2007 by a National Annex. It could be argued that, from 1994 to 2005, there was indeed a transitional period with the experimental ENV 1994-1-1 standard, but as this was subject to revision and therefore implicitly of weak status, it did little to encourage project owners to refer to it in a public or private contractual framework. In fact, during the ENV period, numerous international exchanges on technical points and additional research work financed by the European Committee for Standardization (CEN) led to the definitive version of EN 2005, covering a wider field of application than that of ENV, enabling a building to be designed and calculated entirely in mixed design. Some construction products for mixed-use buildings cannot...