Effective Flange Width Based on Equivalence of Slab Crack Width at Hogging Moment Region of Composite Frame Beam

Steel-concrete composite structures have advantages in terms of strong bearing capacity and full utilisation of performance, and thus, composite frame beams are widely used in building construction. However, in the design and use of existing composite frame beams, the composite effect of a slab and steel beam cannot be completely taken into account. In this study, the effective flange width method is utilised to calculate the contribution of the slab reinforcement to the section moment of inertia to check the beam-end crack width via simulations using the general finite-element software MSC.MARC 2020. A parameter sensitivity analysis of the reinforcement tensile stress is conducted to determine critical influential geometric parameters for the side-column and centre-column hogging moment regions. Finally, design formulae for calculating the effective flange widths of the side- and centre-column hogging moment regions are proposed. In the formula for the side-column hogging moment region, the half column width (R) and steel-beam height (hs) are critical variables, whereas, in the formula for the centre-column hogging moment region, the steel-beam height (hs), slab width (bc), and half clear-span length (l) are critical variables. Both formulas are verified via a multiparameter simulation, which enables more accurate crack-checking calculations for the hogging moment region in the serviceability limit state. This study provides an important reference for fine finite-element simulations of serviceability limit states and shows the factors affecting the effective flange width that differ from those in the ultimate limit state.