Bond Slip and Strength of Lapped Bar Splices


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Title: Bond Slip and Strength of Lapped Bar Splices

Author(s): M. Betzle

Publication: Special Publication

Volume: 55


Appears on pages(s): 493-514

Keywords: beams (supports); bond (concrete to reinforcement); bond stress; lap connections; loads (forces); reinforced concrete; rein-forcing steels; splicing; strength

Date: 8/1/1978

Lapped splices play an important role in the con-struction of reinforced concrete structures. The tensile force at a reinforced bar end is transferred over the concrete to the beginning of the next bar by means of tbe bond action alone. Investigations on the capacity of lapped splices were carried out at the Institute for Structural Engineering, University of Technology, Munich. This research was initiated by Professor Kupfer. The purpose of these tests was to gain more knowledge regarding the stress in the surrounding concrete and to ascertain the force distribution along the spliced bars. The first part of the research program comprised of slab tests with full splicing of reinforced bars with large diame- ters. For the judgement of the capacity of a reinforcing bar the most important criterion is the bond behaviour of the concrete and steel along the lapping length. By means of a new method specially developed for this research it was possible to measure the slip of the spliced bars in comparison to the concrete within short distances along the bar with scarcely any bond disturbance. In connection with the steel strain, measured by bonded wire strain gauges, it was possible to ascertain the bond strain-slip relations (C-A) for different sections of the lapping length. Parallel to these tests, investigations on photoelastic models were carried out. These tests in conjunction with a special technique allowed the spacial course of stress in the vicinity of the reinforced bar to be studied. With the aid of the bond laws derived from reinforced concrete tests and the knowledge gained from the photoelastic tests the splices were calculated on the basis of the finite element method and compared with the results obtained from tests.