后浇整体式预制混凝土梁-板子结构抗连续倒塌机理研究

为研究后浇整体式预制混凝土(PC)结构的抗连续倒塌性能，设计并制作了两个2跨1/3缩尺后浇整体式PC梁-板子结构模型。试验中采用堆加均布荷载与Pushdown结合的加载方式研究其在边柱失效下的抗力曲线与破坏模式。试验结果表明：后浇整体式PC结构中预制板的整体性较好，开裂主要集中在预制板与梁交界处；在加载过程中PC子结构可有效发展二级抗力机制提供附加抗力；预制板沿短跨布置的子结构抗倒塌性能优于沿长跨布置子结构。随后通过有限元软件LSDYNA进行精细化有限元建模，研究PC子结构去柱后荷载重分配机理和新旧混凝土界面黏结强度对其抗倒塌性能的影响规律。有限元分析表明：预制板结合后浇叠合层可以保证楼板体系的整体性从而提升荷载重分布能力，塑性铰出现在梁端而不是柱端；沿短跨布置预制板与后浇叠合层在加载过程中的平均抗力贡献占比高达54%；新旧混凝土界面黏结强度对结构整体性有一定影响；但是当界面黏结强度降低不超过50%时，对结构的抗力影响不大。

Load resisting mechanisms of assembled monolithic precast concrete beam-slab substructures to resist progressive collapse

To study the performance of precast concrete (PC) frames with monolithic joints to resist progressive collapse, two one-third scaled two-bay PC beam-slab substructures were fabricated in the laboratory. The failure modes and load resisting mechanism of the PC substructures were investigated by using the method combining equivalent uniform distributed weights and the Pushdown approach. The test results indicate that the integrity of the PC substructure slab is good. Cracks occur at the interface between the PC slabs and the PC beams. Secondary load resisting mechanisms are able to be developed in the PC substructures to resist progressive collapse. The substructure with the PC slabs placed along the short spans performes better than that with the PC slabs along the long spans. To investigate the load redistribution mechanism and the effects of interface strength between the PC concrete and cast-in-situ concrete on progressive collapse resistance, physics-based finite element models were developed using the software LSDYNA. The finite element analysis shows that the PC slabs together with the cast-in-situ topping layer can increase the integrity of the PC substructure significantly, so that the plastic hinges are formed at the beam ends instead of at the column ends. The average load resisting contribution of the PC slabs together with the topping layer along the short span is about 54% during the loading process. Moreover, the interface strength between the new and old concretes has certain influence on the structural integrity. However, it has little effect on the load resisting capacity as long as the loss of strength of interface does not exceed 50%.