EFFECT OF REINFORCED-CONCRETE BETWEEN THE FLANGES OF THE STEEL PROFILE OF PARTIALLY ENCASED COMPOSITE BEAMS

During the last 20 years composite structures have been built in incre asing numbers. Composite steel concrete constructions are able to take full advantage of the respective properties and performance of both m aterials and lead to building with the following advantages: easy pref abrication, building time reduction, extremely reduced cross-sections, flexibility, fire resistance. ... However in the last version of the Eurocode 4 (pr ENV1994-1-1/April 1992)sectional sign 4.1.2(2)) it is n ot allowed to take into account reinforced concrete between the flange s of the steel beams with concrete-encased steel webs for the load bea ring capacity and for the deflection calculation. The reinforcing bars and the concrete may be assumed to contribute only to resistance to l ocal buckling or lateral-torsional buckling. From this point of view t his version of the Eurocode 4 is too conservative. Indeed 13 tests, pe rformed in 1991 and 1992 in the University of Bochum (Institut fu kons truktiven Ingenieurbau), have indicated the importance of the reinforc ing bars and the concrete between the flanges for the calculation of t he ultimate bending moment, the ultimate shear force and the deflectio n. From these tests were deduced methods taking into account the incre ase in the bearing capacity and in ridigity due to the reinforced conc rete. This research has already provoked changes in the Eurocode 4 and will be an important data source for writing the annex of EC4 dealing with partially encased composite beams.