One-way shear strength design of flat-plate voided slabs

Abstract

Current design standards do not include design provisions to handle the reduced shear capacity of voided flat-plates, and the current design practice considers its shear capacity as a percentage of the solid slab. The study presents an investigation of the one-way shear capacity of flat-plate voided slabs. The investigation is carried out using a compiled evaluation experimental database and an experimental program. A capacity reduction factor for flat-plate voided slabs, λvoid, is proposed and is a function of void height to the slab height (hvoid/h) ratio. The proposed factor is calibrated to the ACI 318-19 shear model. The proposed factor allows for section optimization based on shear capacity, where the height of the void former can be selected based on the shear load subjected to and the required shear strength. This is not possible using the current practice of the manufacturers, where they use either a constant capacity reduction factor or a factor that is slightly affected by the hvoid/h ratio. The model is applicable for voided slabs with a void former clear spacing of 0.10–0.16 of its diameter, or higher. Incorporating the reduction factor, λvoid, resulted in an average experimental-to-predicted (Vexp/Vpred) of 1.67 and COV of 16 %. By comparing the average Vexp/Vpred and COV of voided slabs to solid slabs, the strength reduction factor (ϕ) of 0.75 for shear will still be applicable.