UHPC模壳-RC叠合盖梁受力性能试验

由于整体预制RC盖梁对起重和运输设备要求高，而分段预制盖梁的拼接缝容易发生渗水且在节段分界面上纵筋不能连续传力，因此提出一种在UHPC模壳内部现浇混凝土的半预制叠合盖梁。开展带剪力键和不带剪力键的2个UHPC模壳-RC叠合盖梁和1个现浇RC盖梁对比试件的静力试验，并通过有限元模型分析了结合面黏结程度对叠合盖梁受力性能和破坏模式的影响规律。研究结果表明：UHPC模壳-RC叠合盖梁的破坏模式与现浇RC盖梁一致，均为剪压破坏；不带剪力键的叠合盖梁开裂荷载和极限承载力分别比现浇RC盖梁提高了42.1%和13.8%，同时可以有效降低裂缝宽度的扩展，但叠合盖梁存在界面脱开，核心混凝土拱起和UHPC模壳竖向开裂等现象；剪力键可以增大交界面黏结程度，有效减小最大裂缝宽度和交界面裂缝宽度的扩展速度，其交界面开裂荷载和极限承载力比不带剪力键的叠合盖梁提高50.0%和12.1%；理想界面黏结状态下，UHPC模壳可以达到极限压应变，材料性能得到充分发挥，说明UHPC模壳可以完全参与整体受力，但极限承载力仅比带剪力键叠合盖梁提高8.8%。以上结果说明，带剪力键的UHPC模壳-RC叠合盖梁具有良好的截面黏结强度和整体受力性能，可以推荐实际工程使用。

Experimental Study on Mechanical Performance of UHPC Formwork-RC Composite Cap Beam

To address the excessive requirements of lifting and transportation equipment for integral reinforced concrete (RC) precast cap beams, as well as water seepage at the joints and a discontinuous force transmission of longitudinal reinforcement at the interface for a segmental precast cap beam, a semi-precast composite cap beam with cast-in-place RC in an ultra-high-performance concrete (UHPC) formwork shell was proposed. Static tests were performed on UHPC shell-RC (URC) composite cap beams with and without shear keys and on an RC cap beam, and the influence of the degree of bonding of the inter-surface on the mechanical properties and failure modes of the URC composite cap beams were also analyzed using a finite element model. The results show that, just as for the cast-in-place RC cap beam, the URC composite cap beam was subjected to shearing compression failure, but interface separation, core concrete arch and vertical cracking of the UHPC shell were observed in the URC composite cap beams. However, the cracking load and ultimate bearing capacity of the URC composite cap beam without shear keys were 42.1% and 13.8% larger, respectively, than those of the cast-in-place RC cap beam. A shear key used in an URC composite cap beam can increase the bonding degree of the interface, and also lead to a decrease in the propagation speed of the maximum crack and crack width at the interface. The interface cracking load and ultimate load capacity of the URC composite cap beam with shear keys are 50.0% and 12.1% larger, respectively, than those of the URC composite cap without shear keys. Under the ideal interface bonding state, the UHPC formwork can achieve ultimate compressive strain, indicating that the material properties can be fully utilized and the UHPC formwork can fully participate in the overall stress. However, the ultimate load capacity is only 8.8% higher than that of the URC composite cap with shear keys. All these results indicate that the UHPC formwork-RC composite cap with shear keys has good section bonding strength and overall mechanical performance, and can be recommended for practical purposes.