Design method of lap splice in reinforced concrete structure

目前的兴趣是在抗震结构中使用大钢筋进行加固，以减少拥挤并保持它们之间的清晰间隔。虽然已经进行了大量的试验和分析工作来研究规模对钢筋混凝土的抗剪强度和抗弯强度的影响，但相对较少关注规模对钢筋粘结强度的影响，包括规模对拉伸搭接接头强度的影响。本文通过拉拔试验和搭接试验，研究了钢筋尺寸、肋形和横向配筋对钢筋与混凝土粘结强度的影响。试件参数为三种钢筋直径、两种肋形、保护层厚度、有无箍筋。试验结果表明：1）保护层厚度最小的拉拔试件具有最大的尺度效应; 2）保护层混凝土或箍筋的约束作用越大，尺度效应越小; 3）尺度效应的产生是由于变形钢筋周围的脆性劈裂，而不是由于肋前混凝土的局部压碎。并结合断裂力学理论进行了有限元分析。根据实验和分析结果，提出了搭接接头的设计方程。方程产生大规模的拼接与小覆盖和短拼接长度的脆性行为的预期效果。另一方面，对于具有较低肋高和许多箍筋的钢筋，方程产生较小的尺度效应，其中预期具有延性行为。所提出的方程与已有的实验结果一致。

There is a current interest in using large bars for reinforcing in seismically resistant structures to both reduce congestion and maintain clear spacing between them. While a larger amount of experimental and analytical works have been carried out to study the effects of scale on the shear strength and flexural strength of reinforced concrete, relatively less attention has been devoted to the effects of scale on the bond strength of reinforcement including the effects of scale on tension lap splice strength. This issue has become important for the seismic resistant design of lap splices because the use of small diameter bars leads to congestion and splitting bond failure under strong earthquake loadings.This work is to investigate the effects of scale, rib-shape and lateral reinforcement on bond strength between deformed bar and concrete using pullout and lap splice tests. The specimen parameters are three kinds of bar diameter, two kinds of rib shape, cover thickness, and with/without stirrups. From experimental results, the following conclusions are obtained: 1) pullout specimens with smallest cover thickness showed the largest scale-effect; 2) larger confinement by either cover concrete or stirrups resulted in smaller scale-effect; and 3) scale-effect is attributable to brittle splitting crack around deformed bars and not to local crushing of concrete in front of ribs. Finite element analyzes are also conducted considering the fracture mechanics theory. Based on the experimental and analytical results, design equations are proposed for lap splice. The equations yield large scale-effect for splice with small cover and short splice length where brittle behavior is expected. On the other hand, the equations yield small scale-effect for bars with lower rib height and many stirrups where ductile behavior is expected. The proposed equations agree with the existing experimental results.