Experiments On Web Cracking Of RC Girders Under Indirect Static Loading

With the increase of the web depth, web diagonal cracking of a RC beam may occur under the serviceability limit state, especially in the area where a girder and a beam intersect. For example, the girders in a composite structure, in which the lower parts are RC frames and the upper parts, are masonry flats. As such kind of beam is usually with a large section, web diagonal cracking is a problem need to be dealt with.On the basis of reviewing the related research on web cracking in large RC beams both in China and abroad, this paper focuses on mechanism of web cracking of girders in the lower RC frame in the composite structure. Qualitative experiments were carried out for this purpose.In an effort to investigate the development mechanism of cracking, and the effect of longitudinal distributed side-face reinforcement on web cracking of the girder, the research was conducted as follows:1. Four continuous beam specimens were designed and fabricated under the requirements of China Code for Design of Concrete Structures, GBJ10-89, and GB 50010-2002. Tests were conducted by imposing indirect loading.2. Reinforcement strains were analyzed with the cracks developing.3. Effect of longitudinal distributed reinforcement on controlling the beam web cracking was evaluated.4. Shear equations of Chinese and American codes were used to predict the shear capacity of large continuous RC beams under indirect loading.The results indicate that: the longitudinal distributed reinforcement has favorable effect on controlling of web cracking. Increasing the amount or the ratio of longitudinal distributed reinforcement reduces the width and spacing of cracks in the web. In the area with additional transverse reinforcement, the longitudinal distributed reinforcement and the transverse reinforcement intersect as reinforcement webs, which can confine the web cracking quite well. The provisions to determine the longitudinal distributed reinforcement in current Code for design of concrete structures GB 50010-2002 may be inadequate both in amount and in spacing. For beams, which have different requirements on cracking control under the serviceability state, further research should be taken to decide the amount and arrangement of the longitudinal distributed reinforcement quantitatively.Comparison of the shear equations of different codes indicates that there are many factors that affect the shear capability of the large continuous RC beam with different shear span-depth ratio under indirect loading, and further studies are imperative.