Effect of Impact Load on Splice Length of Reinforcing Bars

Hyeon-Jong Hwang,Fan Yang,Jang-Woon Baek,Li Zang,Gao Ma

doi:10.1186/s40069-020-00414-z

Abstract

Impact loading damage of reinforced concrete (RC) members deteriorates bond strength of reinforcing bars. To understand the effect of strain rate on the bond strength of reinforcing bars in RC beams under impact load, drop hammer test was performed on twenty-four simply supported RC beams with lap spliced bars at the mid-span. The test parameters were reinforcing bar diameter, splice length, drop height, and hammer mass. The dynamic responses including the impact load history, mid-span deflection history, crack distribution, and strain history of reinforcing bar were evaluated. Although the designed bar development length was 31–69% of the requirement of current design codes under static load, the tensile strength of bar splices was greater than the dynamic yield strength when subjected to large impact energy under impact load. On the basis of the test results, existing design equations for the bar development length under static load were modified to consider the impact loading effect on the bond strength. Factors related to the strain rate effect of materials, impact damage, and impact energy loss were proposed. The prediction of the proposed method agreed well with the tensile strength of bar splices under impact load.

Highlights

In reinforced concrete (RC) structures, impact damage is a critical issue: piers of bridge collided by ships or other vehicles, retaining walls damaged by heavy rocks, and high-rise buildings attacked by aircraft
Twenty-four RC beam specimens using D18 and D25 bars with the bar splice lengths of 300 mm and 400 mm were tested under seven different drop heights and three different hammer masses
A modification method was proposed to predict the tensile strength of bar splices under impact load, and it was compared with the test results

Summary

Introduction

In reinforced concrete (RC) structures, impact damage is a critical issue: piers of bridge collided by ships or other vehicles, retaining walls damaged by heavy rocks, and high-rise buildings attacked by aircraft. Impact damage on the development length of reinforcing bars may deteriorate the structural integrity significantly. Current design codes specify the bar development length based on test results under static load. To consider the strain rate effect due to impact load on the bar development length, available studies and test results are extremely limited. The impact resistance of RC structures depends on the material properties of concrete and reinforcing bars. The load transfer from reinforcing bars to adjacent concrete becomes essential for the structural integrity and ductile response. Understanding the bond between concrete and reinforcement in RC structures under impact load is of great importance. Hansen and Liepins (1962) performed pull-out tests of reinforcing bars under impact load, and The existing studies reported that the bond strength increases as strain rates increase (Shah and Hansen 1963, Rezansoff et al 1975). Hansen and Liepins (1962) performed pull-out tests of reinforcing bars under impact load, and

Methods

Results

Conclusion