Evaluation and control of cracking for bending reinforced one-way concrete voided slab with plastic hollow inserts

Abstract

Analysis of experimental tests data of bending one-way reinforced concrete slabs from various articles of science revealed that voided slabs with a grid of hollow plastic inserts inside have smaller mechanical and physical parameters compare to continuous cross section slabs (solid slab). Negative influence to reinforced concrete slab is impacted by hollow plastic inserts, which makes grid of voids in the middle of the cross-sectional area of reinforced concrete slab. Formed grid of voids reduces slab’s stiffness, which influences slab’s param-eters of serviceability, like deflection and cracking. Primary investigation of data, established during experiments, illustrates that cracks occur faster in the tensile surface of voided slab under bending com-pared to bending solid slab. It means that the crack bending moment force for voided slab is smaller than solid slab and the reduction can variate in the range of 14 --- 40 %. Reduce of resistance to cracking can be controlled by changing a lot of factors: shape of plastic hollow in-sert, plastic insert height, steps between plastic inserts, usage of pre-stressed reinforcement, diameter of reinforcement bar, slabs effective depth, bottom cover thickness of concrete, effective cross-section of concrete area about reinforcement and etc. Mentioned parameters are used to evaluate crack width and step of cracking, but existing ana-lytical calculation methods for cracking evaluation of voided slab with plastic inserts are not so exact and results of cracking evalua-tion in this paper are higher than results of analysed experiments. Therefore, analytical calculations according to experi-mental bending tests of voided reinforced concrete slabs with plastic hollow inserts to find and propose corrections for evaluation of cracking for reinforced concrete voided slabs with plastic hollow in-serts.