Prestressed concrete (PC) hollowcore slabs are increasingly used in building applications due to numerous advantages they offer over traditional forms of slab construction. Structural fire safety is one of the primary considerations in building design and hence, building codes specify fire resistance requirements for these hollowcore slabs. PC hollowcore slabs, under fire conditions, are susceptible to failure through shear failure modes, in addition to flexural failure mode, due to presence of hollow cores. Moreover, these slabs are not provided with any additional shear reinforcement due to unique fabrication process aimed at achieving cost-effective construction. However, there is limited data and understanding in literature on the mechanism of shear failure in PC hollowcore slabs under realistic loading and fire conditions. To overcome some of these knowledge gaps, a comprehensive study was undertaken to develop an understanding on the fire performance of PC hollowcore slabs under fire conditions. A three dimensional finite element based numerical model was developed for tracing performance of prestressed concrete hollowcore slabs under fire conditions. The model developed in ANSYS software, accounts for temperature induced degradation of properties of concrete and prestressing strands, cracking in concrete, material and geometrical nonlinearities, realistic fire, loading, and restraint conditions, as well as different failure limit states. For validating the numerical model, fire resistance tests were carried out on six PC hollowcore slabs under standard and realistic fire scenarios. The test variables included type of aggregate in concrete, load level, fire exposure and restraint conditions at the supports, and data generated from fire tests showed that these parameters have significant influence on the fire performance of PC hollowcore slabs. Data obtained from these fire tests, as well as that reported in literature, were utilized to validate the above numerical model by comparing cross-sectional temperatures, mid-span deflection, axial restraint force, concrete cracking patterns and failure times.The validated model was applied to carry out parametric studies to quantify the effect of various factors on the fire response of PC hollowcore slabs. Data from parametric studies show that slab depth, load level, loading pattern, axial restraint, level of prestressing and fire severity have significant influence on the fire response of PC hollowcore slabs. Results obtained from numerical study indicate that failure in hollowcore slabs under fire conditions can occur through shear limit state prior to reaching flexural limit state under loads inducing high shear force.Results generated from the experimental and parametric studies are utilized to develop a rational design approach for evaluating fire resistance of PC hollowcore slabs. The proposed approach comprises of evaluating cross-sectional temperatures in the critical sections of the slab, and then determining moment and shear capacities at any given duration of the fire exposure by utilizing an approach similar to that at room temperature but incorporated with temperature dependent strength properties of concrete and prestressing steel. For predicting sectional temperatures in fire exposed hollowcore slabs, a simplified approach is developed by utilizing data obtained from parametric studies. Fire resistance of a PC hollowcore slab is determined as the time when external bending moment or shear force exceeds moment or shear capacity at the critical sections. The validity of the proposed approach is established by comparing resulting fire resistance predictions with those obtained from detailed finite element analysis and fire tests. This approach can be utilized for estimation of fire resistance of PC hollowcore slabs, and thus suited for incorporation in design codes and standards.
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