Experimental Study And Design Method Of Rebar Development Length Under Impact Loading

Reinforced concrete is the most common building materials used in impact resistant infrastructure due to its ability to absorb energy produced by collisions.The detailing of reinforcing bar within concrete elements is the key to achieving increased structural integrity and ductility.Thus,it is important to attain high-quality bond of reinforcing bar to concrete in structural elements through the effective development length of reinforcing bar.However,the existing design methods of rebar development length are based on static loading.The current experimental research program combined with nonlinear numerical simulation was conducted to investigate rebar development length under impact loading,the main work are as follows:Firstly,based on nonlinear numerical analysis of reinforced concrete beams subjected to impact loading,an energy conservation based impact resistance design method was introduced.A calculation model of mid-span deflection of reinforced concrete beams subjected to impact loading was proposed by considering strain rate effect of material and confinement effect of stirrup.Secondly,drop-weight impact tests of 16 RC beams with longitudinal rebar partially bonded at beam end and 24 RC beams with longitudinal rebar lap spliced at mid-span were carried out.The effects of longitudinal rebar diameter,development length,anchorage mode and position on dynamic bonding properties of RC beams under different impact heights and impact weight were investigated.The impact force history,mid-span deflection history,longitudinal rebar strain history,crack distribution and typical failure mode were obtained.Finally,the applicability of energy conservation based impact resistance design method was verified by the test results.Further,the dynamic increase factor considering the strain rate effect of concrete tensile strength under impact loading and dynamic yield strength of rebar was proposed and verified.Moreover,Considering the effect of impact damage on bond strength,the equation for rebar development length in existing design codes was modified,thus the development length of rebar under impact loading can be reasonable predicted.