Experimental Study on Shear Strength of Prestressed PC-CIP Composite Beams

Abstract

Recently, demands of precast (PC) composite method combined prestressed PC concrete and cast-in place(CIP) concrete increase in modular architectures. Because there is not obvious design code for shear strength of composite beam, in spite of increasing demands, engineers lead to being in difficulty to estimate shear strength of composite beams. Current design code (KCI 2012, ACI 318-11) suggests that properties of the individual elements or the most critical values shall be used in design if the specified strength, unit weight, or other properties of the various elements are different. Based on current code, 34 of prestressed composite specimens were tested and investigated consideration for shear design of composite beam. Test variables were section type, prestressing force (fse/fpu), shear span-to-depth ratio (a/d), and shear reinforcement ratio (ρvfy). In the result of tests, there were three failure modes: shear compression failure, horizontal shear failure, and web shear failure. Shear strength occurred shear compression failure was 2.4 times higher than that occurred horizontal shear failure and web shear failure. Also, shear strength increased as prestressed area and prestressing force increased and shear span-to-depth ratio decreased. Especially, in the case of specimens having a/d=3.0 and 62 percent~65 percent of effective prestressing force, shear strength did not increase though shear reinforcement ratio increased. Comparison between experimental values in this study and predicted values with current design code (KCI 2012, ACI 318-11), Eurocode2, empirical equation of Sozen et al., and theoretical equation of Bažant et al. was investigated. Consequently, shear strength with simplified method and detailed method of ACI 318 were in safety side and detailed method was rather conservative than simplified method. Thus it is reasonable to estimate shear strength of composite beams using current design code (ACI 318-11) which reflects properties of the individual elements. In addition, shear database (UTPCSDB) analysis which the number of specimens is 159 was performed included data in this study. As a results according to experimental variables, there was 2.3 percent of non-safety side in the case of upper 40 percent effective prestressing force in the case of simplified method (ACI 318-11) but all specimens were in safety side in case of detailed method.