·在组合梁的分析中，需要考虑施工条件对组合梁受力 状态的影响.当跨度小于7m时，每跨内可设1-2个临时 支撑；当跨度大于7m时，一般要求不少于2个支撑点。 当施工中钢梁下无临时支撑时，应按两阶段受力构件 进行设计和验算。 ·施工阶段，组合梁的自重及其上部施工荷载由钢梁单 独承受，应按照<<钢结构设计规范>>中的相关规定 计算钢梁的应力、挠度和稳定性等。 ·当混凝土强度达到设计要求以后，续加的永久荷载和 活荷载由组合截面承受，由此引起的挠度和应力分别 进行计算，并与第一阶段的挠度和应力相叠加。 ·当混凝土强度达到设计要求后，除续加的永久荷载和 可变荷载之外，还要考虑由撤除临时支撑引起的组合 梁内力和变形
• 在组合梁的分析中，需要考虑施工条件对组合梁受力 状态的影响. 当跨度小于7m时,每跨内可设1-2个临时 支撑;当跨度大于7m时，一般要求不少于2个支撑点。 当施工中钢梁下无临时支撑时，应按两阶段受力构件 进行设计和验算。 • 施工阶段，组合梁的自重及其上部施工荷载由钢梁单 独承受，应按照<<钢结构设计规范>>中的相关规定 计算钢梁的应力、挠度和稳定性等。 • 当混凝土强度达到设计要求以后,续加的永久荷载和 活荷载由组合截面承受，由此引起的挠度和应力分别 进行计算，并与第一阶段的挠度和应力相叠加。 • 当混凝土强度达到设计要求后，除续加的永久荷载和 可变荷载之外，还要考虑由撤除临时支撑引起的组合 梁内力和变形
The construction procedures can affect the structural behavior of the composite beam. In the case of the unshored construction,the steel section has to be checked for all the possible loading condition arising during construction. In the case of shored constructions,the overall load, including self weight,is resisted by the composite member
• The construction procedures can affect the structural behavior of the composite beam. • In the case of the unshored construction, the steel section has to be checked for all the possible loading condition arising during construction. • In the case of shored constructions, the overall load, including self weight, is resisted by the composite member
4.4 Effective width of concrete slab (混凝土有效翼缘宽度) Mean bending stress ·A typical composite in concrete flange construction consists of a slab connected to a series of parallel steel members, and the concrete flange width may not be fully (a)Effect of shear lag effective in resisting compression due to Deformed ‘shear lag’(剪力滞) shape Midspan Effect of shear lag (b)Effect of shear lag
4.4 Effective width of concrete slab （混凝土有效翼缘宽度） • A typical composite construction consists of a slab connected to a series of parallel steel members, and the concrete flange width may not be fully effective in resisting compression due to ‘shear lag’（剪力滞） Effect of shear lag
theorefical design approximation be.1 b1 be.2 s b2 Effective width of concrete slab
• Effective width of concrete slab
Effective width is adopted as a simplification of the shear lag problem.The effective width(有效翼缘宽度)b.is defined as 'that width of slab which acted on by the actual maximum stress would cause the same static effect as the variable stress which exists in fact'. point load b udl B/L 2,dx=2b.max 0.8 0.3 be 0.6 B 0.2-0.6 04 Research shows that 0.2 0.408 the ratio b/B depends 0.6 1.0 not only the relative Support Midspan Support dimensions of the system,but also on the type of loading, the support conditions and the cross section considered
• Effective width is adopted as a simplification of the shear lag problem. The effective width（有效翼缘宽度）be is defined as ‘that width of slab which acted on by the actual maximum stress would cause the same static effect as the variable stress which exists in fact’. b x dx be 0 2 2 max dimensions of the system, but also on the type of loading, the support conditions and the cross section considered. Research shows that the ratio be /B depends not only the relative