Composite steel beams using precast concrete hollow core floor slabs
The main aim of this thesis is to develop an insight into the behaviour of composite floors that utilise steel beams acting in combination with precast concrete hollow core floor slabs and to produce design recommendations for use by industry for this type of construction. Full scale bending tests of proprietary precast prestressed concrete hollow core unit floor slabs attached through 19mm diameter headed shear studs to steel Universal Beams (UB) have been carried out to determine the increased strength and stiffness when composite action is considered. The results show the bending strength of the composite beam to be twice that of the bare steel beam, and its flexural stiffness to be more than trebled. In addition to the beam tests, isolated push-off tests and horizontal eccentric compression tests were used to study the horizontal interface shear resistance of the headed studs and the strength of the slab, respectively. Maximum resistances were compared with the predictions of the Eurcode EC4, and a reduction formula for the precast effect derived. In addition to the experimental investigations, finite element (FE) studies were also conducted using the FE package ABAQUS to extend the scope of the experimental work. Results show a 2-dimensional plane stress analysis to be sufficiently accurate, providing the correct material input data obtained from isolated push-off and compression tests are used. The FE model for the composite beam was designed and validated using the full scale beam tests. A parametric study, involving 45 analyses, was carried out to cover the full range of UB sizes and floor depths used in practice. From the finite element work, design charts are formulated which may be used to simplify the design rules. Given the results of this work, a full interaction composite beam design may be carried out using the proposed design equations. The results show that precast slabs may be used compositely with steel UB's in order to increase both flexural strength and stiffness at virtually no extra cost, except for the headed shear studs. The failure mode is ductile, and may be controlled by the correct use of small quantities of transverse reinforcement and insitu infill concrete.