Behavior of high-strength lightweight aggregate concrete slabs under column load and unbalanced moment

One of the advantages of the use of flat slabs made with high-strength ligh tweight concrete is the resulting reduction in the weight of a structure, w hich offers substantial cost savings. However, punching-shear failure of co ncrete in the column periphery and the crushing of concrete before steel yi eld are not desirable modes of failure and should be avoided in slab design . To investigate these issues, seven slab-column connections were tested us ing high-strength lightweight (HSLW) concrete slabs. Two reference slabs we re also tested; the first using normal-strength normalweight (NSNW) concret e, and the second using normal-strength lightweight (NSLW) concrete. Ultimate shear strength, deflection, ductility, joint rotation between colu mn and slab, mode of failure, radius of punching, concrete strain, and stee l strain were investigated. The variables of the rest program were the flex ural reinforcement ratio, concrete strength, aggregate type, and moment-loa d ratio. Deflection and ultimate central load increased as the applied moment decrea sed. The deflection of HSLW slabs under moment decreased by between 20 and 60%, compared with similar slabs tested under a central load and no moment. The ductility of HSLW slabs decreased as the applied moment increased. A s econdary bond-splitting failure with a complete separation between concrete and reinforcement at high moment is unique for lightweight aggregate slabs . The slab stiffness degradation decreased as the moment level increased, w hile the value of the energy absorption decreased as the tensile steel rati o increased. In general, HSLW concrete slabs were almost equal to normal-strength concre te slabs made with normalweight aggregate in terms of shear strength, flexu ral strength, and general performance. NSLW concrete slabs were the lowest in shear strength, flexural strength, and general performance, compared wit h NSNW and HSLW slabs.