Behavior of high-strength lightweight concrete slabs under punching loads

The use of high-strength lightweight aggregate (HSLW) concrete is increasin g faster than the development of appropriate design recommendations. Punchi ng shear failure at an interior column can readily initiate a progressive c ollapse in a flat plate structure. In the present study, six slabs were tes ted under central loads. Four slabs were constructed of high-strength light weight concrete of compressive strength higher than 70 MPa, with steel rati os ranging from 0.5 to 2.0%. The two reference specimens were constructed w ith normal-strength concrete and lightweight aggregates and had steel reinf orcement ratios of 1 and 0.5%. The results included the ultimate loads, def lections, modes of failure, crack patterns, ductilities, concrete strains, and steel strains. The test results were compared with other test data on h igh-strength and normal-strength normalweight concrete slabs and code predi ctions for slab strength. Normally, a reduction factor of 0.85 is recommend ed for lightweight aggregates qv the ACI code A similar reduction of 0.80 i s suggested by the BS 8110 code. These reduction factors are conservative w hen applied to high-strength concrete. A reduction factor of 0.95 is more a ppropriate for high-strength lightweight concrete, and of 0.85 for normal-s trength lightweight. The results revealed that the change of reinforcement has a more serious effect on the general behavior of high-strength lightwei ght concrete slabs compared with normal-strength and high-strength concrete slabs.