State of Bond along Lap Splices

Abstract

Design requirements for development length of lap-spliced reinforcing bars in concrete refer to the associated rules for anchorage, practically treating the two problems as one. This was based on the empirical observation that development capacity of reinforcement obtained from both lap-splice and anchorage tests converge to the same experimental values. Nevertheless, from a theoretical viewpoint the similarity between the states of stress of these two problems is not well addressed. In order to trace the underlying relationship between these two bond conditions, the field equations governing lap-splice behavior are established and solved from first principles using simplified constitutive relationships for steel and bond between reinforcement and concrete; the state of stress thus estimated is subsequently compared with the state of stress that occurs along an anchorage of the same length. Because lap splices occur in the clear span of members in the presence of flexural moment, an essential point in the solution of the differential equations of bond is the onset of crack stabilization in the splice region. Both longitudinal and transverse concrete cover cracking is considered in solving for the associated bond stress distribution, whereas debonding that initiates at the lap ends and spreads inward to cross inner flexural cracks is reproduced in the solution. Model verification is based on comparisons with indicatively selected published data from elastic lap-splice tests. The main conclusion derived from the model is the confirmation of the empirical rule embedded in the Code Design procedures, namely that bond in lap-splice regions behaves exactly the same as in the anchorage.