This study investigated the concrete-to-concrete friction behavior under dynamic cyclic loading at different loading rates, vertical loads, and surface roughness. The present work answers essential questions about the dynamic behavior of concrete-to-concrete friction since most of the available literature deals with static or quasi-static loading conditions. To this end, an experimental program was devised by casting 96 concrete blocks. A total of 48 dynamic push–pull tests were performed on each pair of blocks (mobile top block and fixed bottom block). Test variables included three types of surface roughness, four different loading rates, and two normal stresses. Performance measures included the static and dynamic friction forces coefficients of static and kinetic friction in addition to effective stiffness and effective damping. Moreover, the test results showed that the static and kinetic friction coefficients, effective stiffness, and effective damping decrease with increasing loading rates. Moreover, increasing the normal stress increases the friction force, thus increasing the effective stiffness and reducing the effective damping surface for all surface roughness types. The effects of test variables on the hysteresis behavior were also investigated.

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The main objective of this paper was to study the concrete-to-concrete shear friction behavior under cyclic loading and different test rates. Eight dynamic push-pull tests were performed on concrete specimens with as-cast surface roughness type applying four different test rates. The test results include the hysteresis loops of the friction force-displacement relations. It is concluded that the dynamic coefficient of friction decreased with the increased test rate. This reduction in the dynamic coefficient of friction should be considered in the design of structural elements under cyclic or dynamic loading.

The strength reduction factors (ϕ) adopted by ACI-440.1R-15 standard code for the flexure design of Fiber Reinforced Polymers Reinforced Concrete (FRP-RC) beams are calibrated in this study. The code calibration process aims to achieve a particular target reliability index (βT) for the selected FRP-RC rectangular beams. An extensive experimental database is collected and used in the calibration process of the resistance factors. It was found that the calibrated ϕ led to a more economical and less conservative design while satisfying the safety requirements imposed by the design code. To meet the βT, a recommended value of ϕ, is found to be 0.70 for cast-in-situ beams failing in compression and 0.65 for tension-controlled cast-in-situ beams. Thus, the proposed values are slightly greater than comparable factors adopted by the ACI code of 0.65 for compressioncontrolled and 0.55 for tension-controlled cast-in-situ beams.