钢-UHPC华夫板组合梁负弯矩区抗弯性能试验

为研究钢-UHPC华夫板组合梁负弯矩区抗弯性能，考虑华夫板板肋高度比、纵筋配筋率以及采用抗拔不抗剪栓钉连接件对钢-UHPC华夫板组合梁的破坏模式、裂缝发展规律及承载能力的影响，采用跨中单点加载方式完成了4根钢-UHPC华夫板组合梁试件在负弯矩作用下的静力加载试验。基于简化塑性理论，并考虑将UHPC受拉区的拉应力分布等效为均匀应力分布，提出了负弯矩区钢-UHPC华夫板组合梁的极限抗弯承载力计算方法。研究结果表明：负弯矩作用下，4根钢-UHPC华夫板组合梁试件的破坏形态均为典型的弯曲破坏；极限状态下，华夫板内纵向受拉钢筋屈服，钢梁上翼缘受拉屈服，钢梁下翼缘受压发生局部屈曲，华夫板跨中主裂缝贯通，其余裂缝呈现密集分布且纤细的特点。保证华夫板总高度90 mm不变，板肋高度比由1∶1减小为1∶2会加剧华夫板的裂缝开展，使试件的开裂荷载和初始刚度略有降低，但承载能力基本不变。华夫板配筋率增大1.05%，试件的承载力与刚度分别提高18.4%与7.7%，并且有助于约束华夫板的裂缝宽度。采用抗拔不抗剪栓钉连接件可在一定程度上抑制试件在正常使用阶段时的裂缝开展，但会导致试件承载力、刚度和延性下降，下降幅度分别为6.9%、9.6%和19.7%。根据所提出的钢-UHPC华夫板组合梁负弯矩区极限抗弯承载力的理论计算公式所得的计算值略低于试验值，且相对误差在10%以内。

Experimental Study on the Flexural Behavior of Steel-UHPC Composite Beams with Waffle Slab in Negative Moment Regions

To investigate the flexural behavior of steel-ultra-high performance concrete (UHPC) composite beams with waffle slab in negative moment regions, this study considered the influence of the slab to rib height ratio, reinforcement ratio, and adopting uplift-restricted and slip-permitted connections on the failure mode, crack development, and flexural capacity of the steel composite beams. A static loading test was conducted on four composite beam specimens subjected to a negative moment, by single-point loading at the mid-span. Based on the simplified plastic theory and the fact that the tensile stress distribution of the UHPC tensile zone is equivalent to a uniform stress distribution, a method is proposed to calculate the ultimate flexural capacity of steel-UHPC composite beams in negative moment regions. The results show that under the action of a negative moment, the failure mode of steel-UHPC composite beams with waffle slab presents typical bending failure characteristics. In the ultimate state, the longitudinal reinforcements in the waffle slab and the top flange of the steel beam yield under tension, and the bottom flange of the steel beam locally buckles under compression. The mid-span of the waffle slab passes through by the main crack, and the remaining thin cracks are intensely distributed. When the total height of the waffle slab is 90 mm and the slab to rib height ratio is reduced from 1:1 to 1:2, crack development is more severe in the waffle slab, and the cracking load and initial stiffness of the specimen slightly reduce, but the bearing capacity hardly reduces. By increasing the reinforcement ratio of the waffle slab by 1.05%, the ultimate load and stiffness of the specimen increase by 7.7% and 18.4%, respectively, and the main crack width of the waffle slab is better controlled. Adopting uplift-restricted and slip-permitted connections inhibits the development of main cracks in the serviceability states to a certain extent, but the ultimate load, stiffness, and ductility of the specimen reduce by 6.9%, 9.6%, and 19.7%, respectively. Finally, theoretical models were developed to calculate the ultimate flexural capacity of steel-UHPC composite beams with waffle slab under negative moments. According to the theoretical calculation method proposed in this study, the calculated value is slightly less than the experimental value, and the relative error is within 10%.