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Headed bar lap splices : effects of clear cover and splice length on splice capacity / by Jerod James Rudolf.

by Rudolf, Jerod James.

Reinforced concrete -- Testing

Reinforcing bars -- Testing

Strains and stresses

Anchorage (Structural engineering)

121 leaves : ill. ; 29 cm.

Thesis advisor: Dr. Richard De Vries.

Committee members: Dr. Douglas Stahl, Christopher Raebel.

Introduction -- Materials -- Variables, controls, and measured values -- Construction, setup, and testing -- Test results -- Limit states and effects of variables on splice capacity -- Equation development and comparisons -- Conclusions and recommendations.

Research has been performed on headed bar anchorage over the last three decades, and provisions for headed bar anchorage development were included in the ACI 318-05 code. In the most recent decade, research began on the use of headed bar lap splices in reinforced concrete masonry; however, little-to-no research has been performed investigating the use of headed bar lap splices in concrete sections. For this reason, the following project was established to investigate the possibility of reducing lap splice lengths by using headed bars. To narrow the scope of the research, the bond length along the bars was eliminated in order to isolate the effect that only the bar heads have on the splice capacity.

Twelve concrete specimens with #7 headed bar lap splices, representing splices with three clear cover values and three splice lengths, were cast and tested until no additional load could be sustained. Based on the test results, three theoretical limit states were investigated: side face blowout in two directions and the formation of a compression strut between the bar heads. The test results were compared to two equations from previous research for side face blowout, and theoretically derived equations, based on previous research and code recommendations, for all three limit states in an attempt to predict the splice capacities and determine the controlling limit states of the tested specimens.

Due to the small number of specimens tested, the main conclusions from this research are only relevant for use as a starting point for future research and may not match conclusions from more extensive testing. In general, lap splice capacity increases by increasing clear cover, and splice capacity doesn't necessarily increase by increasing lap length. The only clearly visible limit state observed during testing was a face blowout failure for the two shallowest clear cover specimens and the two longest lap splice specimens. The derived equations and equations from previous research did not provide any solid evidence towards a clear relationship between clear cover and a controlling limit state, and splice length and a controlling limit state.

With respect to real-world design, that headed bar lap splices with clear covers of 1.50 inches or less cannot develop the yield strength of the bar, relying only on the bar heads. It was determined, however, that an 8-inch lap splice can fully develop the yield capacity of a #7 bar with clear cover greater than or equal to 3 inches. Based on the findings of this research, the use of headed bar lap splices can result in a significant reduction in steel compared to standard ACI 318-05 lap splices used in engineering practice today.

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