Behavior of High-Strength Lightweight Aggregate Concrete Slabs under Column Load and Unbalanced Moment


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Title: Behavior of High-Strength Lightweight Aggregate Concrete Slabs under Column Load and Unbalanced Moment

Author(s): H. Marzouk, Moustafa Osman, and Sherief Helmy

Publication: Structural Journal

Volume: 97

Issue: 6

Appears on pages(s): 860-866

Keywords: high-strength concrete; lightweight aggregate; moment; normalweight aggregate; punching shear; slab

Date: 11/1/2000

One of the advantages of the use of flat slabs made with high-strength lightweight concrete is the resulting reduction in the weight of a structure, which offers substantial cost savings. However, punching-shear failure of concrete in the column periphery and the crushing of concrete before steel yield are not desirable modes of failure and should be avoided in slab design. To investigate these issues, seven slab-column connections were tested using high-strength lightweight (HSLW) concrete slabs. Two reference slabs were also tested; the first using normal-strength normalweight (NSNW) concrete, and the second using normal-strength lightweight (NSLW) concrete. Ultimate shear strength, deflection, ductility, joint rotation between column and slab, mode of failure, radius of punching, concrete strain, and steel strain were investigated. The variables of the test program were the flexural reinforcement ratio, concrete strength, aggregate type, and moment-load ratio. Deflection and ultimate central load increased as the applied moment decreased. 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 secondary 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, while the value of the energy absorption decreased as the tensile steel ratio increased. In general, HSLW concrete slabs were almost equal to normal-strength concrete slabs made with normalweight aggregate in terms of shear strength, flexural strength, and general performance. NSLW concrete slabs were the lowest in shear strength, flexural strength, and general performance, compared with NSNW and HSLW slabs.