دانلود رایگان مقاله اثر مفاصل ساخت و ساز در استحکام کششی بتن

ABSTRACT

The purpose of this study is to experimentally correlate the compressive strength (f 0 c) of concrete to the splitting tensile strength (T) for plain concrete in the existence of a construction joint, and formulate an empirical equation relating T to f 0 c. Both the American Concrete Institute code (ACI 318-08 (ACI Committee 318, 2008)) and the American Society for Testing and Materials (ASTM (ASTM Standard C496, 2002; ASTM Standard C192/C192M, 2002; ASTM Standard C39/C39M, 2005; ASTM Standard C617, 2002)) provide the testing methods and standards, as well as the applicable theoretical and experimental formulas for the correlation between T to f 0 c for concrete specimens, which are monolithic, indicating that the specimens lack any construction joints. Providing a useful reduction factor in the splitting tensile strength of concrete due the existence of a construction joint is essential. It is a well known fact that construction joints are used in every concrete structure, which indicates that engineers would definitely benefit from an equation that could relate the splitting tensile strength of concrete in function of its compressive strength. The results suggest that the reduction in the splitting tensile strength in the presence of a construction joint is not as much as most engineers tend to believe. Due to that belief, most engineers tend to overdesign for steel reinforcement at those joints to compensate for this reduction. The objective of the study is to better the understanding of the effects of a construction joint on the splitting tensile strength. Thus provide an empirical equation to assist engineers in their design calculations, therefore reducing the amount of steel reinforcement at the construction joints. Thus also leading to cost saving on projects.

5. Conclusions

Construction joints (CJ) are used to facilitate construction works in the construction execution process. All concrete structures contain construction joints. CJ would definitely affect the splitting tensile strength (T) of concrete. The purpose of this study is to understand the effect of a CJ onT with respect to the compressive strength (f 0 c). ACI introduces an equation for T relating it to f 0 c which only assumes monolithic structures. Experiments were conducted following ASTM testing methods and standards, which lead to the demonstration of the real effect of a CJ on the splitting tensile strength and coming up with a new equation relating the splitting tensile strength T with a construction joint to the compressive strength (f 0 c). Thus, based on the conducted experimental, the following conclusions could be drawn: As the strength of concrete increases so does its corresponding tensile splitting strength, regardless if it is containing a construction joint or not. Having a construction joint reduces the splitting tensile strength of a monolithic specimen by approximately 55%. Relating T for construction joints to f 0 c is expressed as TCJ ¼ 0:25pf 0 c vs. for monolithic construction expressed as T ¼ pf 0 c=1:80. It is recommended, that when designing the steel reinforcement, the increase in the amount of steel placed in the presence of construction joints should compensate for the 55% reduction of the splitting tensile strength. Thus in order to compensate for this weakness in the strength of concrete, the amount of steel should be doubled.