Element-based stiffness reduction coefficient of steel–concrete composite beams with interface slip

The interface slip between steel beam and concrete slab increases the maximum deflection of steel–concrete composite frame beams. In this paper, Newmark’s model (NM) for steel–concrete composite beams is used to simulate the response of composite beams considering interface slip. Then finite element models of composite beams are established to verify the theoretical models. The interfacial behaviors between the concrete slab and the steel beam are modeled with a shear spring model. An element-based stiffness reduction coefficient is defined by comparing directly the deflection of the NM with that of the conventional Euler–Bernoulli model. Parametric analyses based on numerical solutions of the theoretical models are carried out to study the key factors affecting the stiffness reduction coefficient of composite beams. Simplified design formulas for calculating the element-based stiffness reduction coefficient are proposed. Comparisons between the results of the simplified formulas and the test results indicate the accuracy of the proposed formulas.