The optimized-section precast slab (OPS) is a half precast concrete (PC) slab that highlights structural aesthetics while reducing the quantity of materials by means of an efficient cross-sectional configuration considering the distribution of a bending moment. However, since a tapered cross section where the locations of the top and bottom flanges change is formed at the end of the member, stress concentration occurs near the tapered cross section because of the shear force and thus the surrounding region of the tapered cross section may become unintentionally vulnerable. Therefore, in this study, experimental and numerical research was carried out to examine the shear behaviour characteristics and performance of the OPS with a tapered cross section. Shear tests were conducted on a total of eight OPS specimens, with the inclination angle of the tapered cross section, the presence of topping concrete and the amount of shear reinforcement as the main test variables and a reasonable shear-design method for the OPS members was proposed by means of a detailed analysis based on design code and finite-element analysis.

In current design codes, crack control design criterion for prestressed concrete (PSC) members is stricter than conventional reinforced concrete (RC) members. In particular, it is stipulated that the net tensile stress of prestressing strands should be controlled under 250 MPa in the serviceability design of PSC members belonging to the Class C category section that is expected to be cracked due to flexure under service load conditions as defined in ACI318 code. Thus, the cracked section analysis is essentially required to estimate the tensile stress of the prestressing strands under the service loads, which requires very complex iterative calculations, thereby causing many difficulties in the applications of the Class C PSC members in practice. Thus, this study proposed a simple method to estimate the net tensile stress of the prestressing strands (Df ps ) under the service load conditions, and also provided a summary table to be used for checking whether the net tensile stress (Df ps ) exceeds the stress limit (250 or 350 MPa) with respect to the magnitude of effective prestress (f se ).

The dual potential capacity model was developed in the authors’ previous studies to estimate the shear strengths of reinforced concrete members, in which the shear crack concentration factor was adopted as the key concept of the proposed approach. In this study, a shear test program was carefully prepared and conducted on five reinforced concrete beam specimens to investigate the crack development, propagation, and merging behavior of critical shear cracks. To this end, concrete cover thickness, diameter of reinforcement, presence of skin reinforcement, and shear reinforcement ratio were taken as the main test variables. From the experiments, the crack merging and concentration phenomena were clearly observed, and the crack concentration factors were estimated from the measured flexural and shear crack widths and spacings. The crack concentration factors were compared to those estimated by the dual potential capacity model, and the shear strengths of the test specimens were also compared with those estimated by the dual potential capacity model and other models in detail.

This study investigates the time-dependent mechanical properties of concrete deteriorated by the alkali-silica reaction (ASR). Previous analytical and experimental studies have indicated the positive impact of ASR gel in the cracks against mechanical damage in concrete. To study the effects of ASR gel on cracked concrete, groups of cylinder specimens with different expansion levels were prepared and tested at different material ages. The compression test results showed that the deteriorated elastic modulus of the specimens could be recovered over time. Mechanical property data from the other ASR studies were collected and assessed to observe similar trends across the literature. It was observed that the recovery of the elastic modulus also occurred in previously reported experiments. The recovery of the elastic modulus is assumed to be due to the time-dependent chemical and physical properties of ASR gel, which fills the cracks. Moreover, the data indicated that parameters other than material age and expansion could be attributed to the time-dependent mechanical properties of concrete affected by ASR.

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