S08.123受压概述性能.ppt

⑶ Bearing load Mu is related to the axial load N; ● When N is small，Mu will increasing with the improve of N（CB段）； ● When N is small，Mu is decreasing with the increase of N （AB段）； 8.2 偏心受压构件的承载力计算 ⑷ Bearing load Mu reach to maximum at point B (Nb，Mb) ，it’s a balanced failure point； ●In CB（N≤Nb）is tension failure， ● In AB（N Nb）is compression failure； 一、破坏特征 偏心受压构件的破坏形态与偏心距e0和纵向钢筋配筋率有关 1、受拉破坏 tensile failure 8.2 偏心受压构件的承载力计算 M较大，N较小 偏心距e0较大 As配筋合适 1、 Tensile failure 8.2 偏心受压构件的承载力计算 ◆ Cracks will first appear in the tension zone ,the stress of As will improve quickly with increase of load and will yield first. ◆ Then, the crack will be wider and the neutral axis depth will be reduced. ◆Finally the bar As in the compression zone will yield and the concrete is crushed. ◆ There be visible warning of failure and have large deflection ,it likes the beam with suitable reinforcement. Its bearing capacity depends on the steel in the tension zone. ◆ Condition is that the eccentricity e0 is large and the longitudinal bar ratio is suitable. 1、受拉破坏 8.2 偏心受压构件的承载力计算 ◆ 截面受拉侧混凝土较早出现裂缝，As的应力随荷载增加发展较快，首先达到屈服。 ◆ 此后，裂缝迅速开展，受压区高度减小 ◆ 最后受压侧钢筋As 受压屈服，压区混凝土压碎而达到破坏。 ◆ 这种破坏具有明显预兆，变形能力较大，破坏特征与配有受压钢筋的适筋梁相似，承载力主要取决于受拉侧钢筋。 ◆ 形成这种破坏的条件是：偏心距e0较大，且受拉侧纵向钢筋配筋率合适，通常称为大偏心受压。 2、Compressive failure There are two conditions for a compression failure ： ⑴Relative eccentricity e0/h0 is small. 8.2 偏心受压构件的承载力计算 ⑵ Although relative eccentricity e0/h0 is large, the amount of tension reinforcing bar is big. As太多 2、受压破坏 产生受压破坏的条件有两种情况： ⑴当相对偏心距e0/h0较小 8.2 偏心受压构件的承载力计算 ⑵或虽然相对偏心距e0/h0较大，但受拉侧纵向钢筋配置较多时 As太多 8.2 偏心受压构件的承载力计算 ◆The stress of the concrete and steel in the compression zone is very large. ◆ The stress of steel in the tension zone is small. ◆ When the relative eccentricity e0/h0 is small，the steel in the tension zone will under compressive. 2、Compressive failure ⑴When relative eccentricity e0/h0 is small ⑵Although relative eccentricity e0/h0 is large that the amount of tension reinforcing bar is