Behavior of High-Strength Lightweight Concrete Slabs under Punching Loads

The use of high-strength lightweight aggregate (HSLW) concrete is increasing faster than the development of appropriate design recom-mendations. Punching shear failure at an interior column can read-ily initiate a progressive collapse in a flat plate structure. In the pres-ent study, six slabs were tested under central loads. Four slabs were constructed of high-strength lightweight concrete of compressive strength higher than 70 MPa, with steel ratios ranging from 0.5 to 2.0%. The two reference specimens were constructed with normal-strength concrete and lightweight aggregates and had steel rein-forcement ratios of 1 and 0.5%. The results included the ultimate loads, deflections, modes of failure, crack patterns, ductilities, con-crete strains, and steel strains. The test results were compared with other test data on high-strength and normal-strength normalweight concrete slabs and code predictions for slab strength. Normally, a reduction factor of 0.85 is recommended for lightweight aggregates by the ACI code. A similar reduction of 0.80 is suggested by the BS 8110 code. These reduction factors are conservative when applied to high-strength concrete. A reduction factor of 0.95 is more appropri-ate for high-strength lightweight concrete, and of 0.85 for normal-strength lightweight. The results revealed that the change of rein-forcement has a more serious effect on the general behavior of high-strength lightweight concrete slabs compared with normal-strength and high-strength concrete slabs.