Abstract
The unbalance moments at the edge connections of flat plate structures induced by lateral forces (i.e. an earthquake) may not always act in parallel directions of the building axes. Most research studied the unbalanced moments in one direction, a few of them in biaxial directions, and none of them in incline directions. This paper presents the results of a nonlinear finite element analysis on punching shear capacity at edge column-slab connections subjected to three directions of the unbalanced moments namely perpendicular, incline 45°, and parallel to the slab free edge in combination with the shear force. A 3-D numerical analysis of ten isolated edge column-plate connections was conducted by applying an appropriate element size, mesh, and calibrated material parameters of the concrete damage plasticity (CDP) model in ABAQUS. the connections were subjected to ten variations of the moment to shear (M/V) ratios. The results show that the punching shear capacity decreases exponentially for the unbalanced moment acting perpendicular and parallel to the slab free edge, and linearly for unbalanced moment incline 45° as the increase in M/V ratio. The M-V interaction at the edge connections depends on the unbalanced moment directions which are slightly different from the ACI 318 code.
Highlights
A flat plate reinforced concrete structure is one of the structural systems having slabs directly supported by columns without beams
The analysis results show that for M/V ratio (e) < 0.4, the punching shear capacity of the connections decreases as the unbalanced moment directions changes from the perpendicular, incline 45°, and parallel to the slab free edge
For the eccentricity (e) of 0.5 and 0.6, the maximum loads can be resisted by the connections with the direction of unbalanced moment incline 45° to the free edge and the minimum loads occurred in the connection with unbalanced moment parallel to the slab free edge
Summary
A flat plate reinforced concrete structure is one of the structural systems having slabs directly supported by columns without beams. The simplifications associated with both the structural form and the technology required in their construction, are accompanied by some difficulties in analysis and design in ensuring safety and serviceability. The main drawback of this system is the punching shear phenomenon in the slab around columns which may cause catastrophic failure. The risk of punching shear failure may increase with the presence of an unbalanced moment that is transferred from the slab to the column. Different spans length, and any lateral load (i.e. earthquake or wind) can result in an unbalanced moment. In high-risk seismic areas, a flat plate structure is recommended only for low-rise buildings, the system in high-rise buildings requires adding a special lateral force resisting system such as a shear wall or special frames [1]
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