4.3 Construction methods(施工方法) ·组合梁的工作性能与施工方法有关 Propped construction to support the steel beam until the concrete hardened,(propped at quarter-span points and mid-span);Props are usually left in place until the concrete slab has developed three-quarters of its design strength. .'unpropped construction'casting of concrete without props;Initially,the steel beam alone resists its own weight,and that of the formwork. wet concrete,and placement loads4.3 Construction methods （施工方法） • 组合梁的工作性能与施工方法有关 • ‘Propped construction ’ to support the steel beam until the concrete hardened, (propped at quarter-span points and mid-span); Props are usually left in place until the concrete slab has developed three-quarters of its design strength. • ‘unpropped construction’ casting of concrete without props; Initially, the steel beam alone resists its own weight, and that of the formwork, wet concrete, and placement loads