Cyclic behavior of lightweight engineered cementitious composite beam-column joints

This study investigated the behavior of exterior beam-column joints made of engineered cementitious composites (ECC) with varying densities (i.e., ranging from 1740 to 2080 kg/m3) under reversed cyclic loading. In total, six ECC joints were cast using different mixtures detailed as: (a) two normal weight ECC (NWECC) mixtures developed with silica sand (SS) as a filler and either polyvinyl alcohol (PVA) fibers or polypropylene (PP) fibers; (b) two lightweight ECC (LWECC) mixtures developed with lightweight slate sand (SL) as a filler and either PVA fibers or PP fibers; (c) one LWECC mixture developed with PVA fibers and the filler consisting of a combination of SL and powder rubber (PR) in a ratio of 70%:30% (by volume); and (d) one LWECC mixture developed with PVA fibers and the filler consisting of a combination of SL and crumb rubber (CR) in a ratio of 70%:30% (by volume). An additional joint made of conventional lightweight concrete (LWC) with a density of 1850 kg/m3, was tested for comparison. The steel reinforcement details were kept the same on all specimens conforming to the typical design of strong column-weak beam concept. The hysteretic behavior, capacity, stiffness, cracking behavior, ductility, and energy dissipation capacity of all tested joints were assessed. The results indicated that utilizing SL alone helped to successfully develop lightweight joints with a mixture density of less than 1850 kg/m3 and strength-to-weight ratios comparable to those of NWECC. However, these joints exhibited lower ductility and energy dissipation capacity compared to NWECC joints. Using PR or CR with SL appeared to be a more efficient alternative over using SL alone, in constructing LWECC joints with lighter self-weight, higher ductility, and higher energy dissipation capacity. Notably, all LWECC joints demonstrated superior structural performance compared to the LWC joint, even though they were lighter, thus indicating promising potentials of LWECCs for lightweight structures. The results also revealed that in all tested specimens, the PVA fibers exhibited better performance over those with the PP fibers.