Design method of lap splice in reinforced concrete structure

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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.