Flexural behaviour of lightweight aggregate concrete columns

The flexural performance of lightweight concrete (LWC) columns was evaluated and limitations of ACI 318-19 in predicting the flexural crack (M-cr) and maximum (M-n) moments, as well as the minimum amount of transverse reinforcing bar (A(sh(ACI))), were examined. Six LWC columns with different amounts of transverse reinforcing bar (A(sh)), compressive strengths of concrete (f(c)') and concrete types were prepared and tested under constant axial and cyclic lateral loads. The test results show that ACI 318-19 agrees well with the M-cr of tested columns, considering the lower tensile stress of LWC columns by introducing modification factors (lambda) (all-lightweight concrete, lambda = 0.75; sand-lightweight concrete, lambda = 0.85) for the fracture modulus of concrete (f(r)). In addition, ACI 318-19 underestimates M-n, irrespective of A(sh), f(c)' and concrete type. The ductility of LWC columns increased with the increase in volumetric transverse reinforcing bar index (omega(vh)). The increasing rate was lower than that of normal-weight concrete (NWC) columns. The displacement ductility ratio (mu(Delta)), work damage indicator (W-80) and equivalent damping coefficient (xi(80)) of a column with 1.0A(sh(ACI)) were, on average, 30, 36 and 18% lower in LWC than NWC columns. Consequently, double the A(sh(ACI)) was required to retain a flexural ductility equivalent to that of a NWC specimen.