Cyclic loading of high-strength lightweight concrete slabs

Ductility often governs the design of structures in seismic zones, while monotonic punching shear strength governs the design of flat-plate structures in nonseismic zones. Because the ductility of concrete increases as strength increases, high-strength lightweight concrete (HSLW) located in low to moderate seismic zones can be used to enhance ductility, energy dissipation, and seismic energy. Six interior slab-column connections were tested under simulated earthquake-type conditions. Loading was investigated to examine the effect of using HSLW concrete. Of the six specimens studied, two slabs were made of 70 MPa concrete, two slabs were made of 35 MPa normal-strength lightweight (NSLW) concrete, and two were made of 35 MPa normal-strength normal aggregates (NSNW) concrete. The steel reinforcement ratios were 0.5 and 1% for the three types of concrete. Under seismic loading, HSLW concrete slabs showed a better performance in general than the other two types of concrete. Specimens made of NSLW and NSNW concrete failed at a drift lower than that of HSLW. A higher displacement after initial failure was sustained by HSLW as compared with the other types of concrete. The results indicated that HSLW concrete had a higher ductility compared with NSLW and NSNW concrete. The load capacity degradation of HSLW concrete indicated superior energy dissipation compared with NSNW concrete. The ACI code recommendations for semilightweight concrete should be examined further to reflect the high strength and ductility behavior of HSLW concrete. A reduction factor of 0.90 is more appropriate for HSLW concrete than the current 0.85 recommended for lightweight concrete.