Research On Cast-in-situ Reinforced Concrete Slabs Of Frame Structures By Considering Influence Of Varying Column Section

Cast-in-situ Reinforced concrete slab cracks have been attracting the attention of researchers at home and abroad, and they have great influence on the durability and applicability of structures. Nowadays, due to the lack of land, high-rise buildings and super high-rise buildings are constructed more extensively. With the increase of the total number of floors, column cross sections of lower floors are relatively large, beam cross sections basically remain unchanged, which makes the corresponding slabs become special-shaped plates. However, designers still use traditional design methods, i.e., one-way slab or two-way slab, and corresponding detailing measures, ignoring special mechanical behaviors of special-shaped plates, especially their particularity of stress distribution, which leads to cracks. With this in mind, mechanical behaviors of slabs under vertical load action and temperature effect are studied by considering varying column section. The study is based on theory analysis and numerical simulations using ANSYS Program and is in terms of principle tensile stress, deflection, bending moment, yield line and cracks. The motivation of the study is to offer some reference to reinforcement design and detail measures of floor slabs in structures of large cross-section column. The main contents and achievements are as follows:①The variation rules of tensile stress and shear stress of slabs under vertical loads are studied with varying column section. The results reveal that: top tensile stress around column corner and top shear stress along slab-column interface increase with the increase of column section; auxiliary reinforcement is required at those regions when design slabs of large column sections.②The variation rules of deflection and bending moment of slabs under vertical loads are studied with varying column section, resulting zero-moment lines of slabs of different column sections. The results reveal that: slab bending moment around column corner increases and zero-moment line shrinks considerably, with the increase of column section; length of negative-moment bar designed after the two-way slab method does not cover the negative moment zone, and therefore it is expected to be extended when designing slabs of large column sections.③The variation rule of moment-yield line of slabs under vertical loads is studied with varying column section, resulting moment-yield lines of slabs of different column sections. The results reveal that: moment-yield line varies considerably, with the increase of column section and therefore plastic solutions based two-slab method is unfavorable.④ The variation rule of tensile stress of slabs under even temperature action is studied with varying column section, and is compared with respect to that under vertical loads. The results reveal that: top tensile stress around column corner increases with the increase of column section; top tensile stress around column corner is extremely higher than that at slab center if the corresponding columns are fat; top tensile stress around inner and outer column corner is not ignorable with respect to that caused by vertical loads and even temperature action is expected to considered when designing slabs of large column sections.⑤The variation rule of slabs’ cracks under vertical loads and even temperature action are studied with different reinforcement schemes, and available scheme is proposed. The results reveal that: diagonal crack via column corner and crack along slab-column interface are two typical cracks of slabs of large column section; different reinforcement schemes induces different crack controlling effect; by contrast, an integrative scheme including orthogonal bars, adding plate is efficient to reduce slab cracks.