Experimental Study On Axial Compression Behavior Of Confined Lightweight Aggregate Concrete Under Concentric Loading

Lightweight aggregate concrete（LWAC）has the advantages of light weight and high strength,excellent good heat preservation,heat insulation and low cost,while it exhibits higher brittleness compared with the normal weight concrete（NWC）.The compressive strength and ductility of LWAC can be improved by the composite confinement of stirrups for the reason that LWAC columns using common stirrups could not meet aseismic demands.However,there is few investigations on confined LWAC,and the specimens with low concrete strength and simple tie configuration.Therefore,it’s necessary to carry out the research on stress-strain response of confined LWAC under uniaxial compression.This paper has carried out experimental research and theoretical analysis on the axial compression behavior of confined LWAC under concentric loading.The main contents are showed below:（1）According to an experimental study of 12 LWAC columns with cube compressive strength of 50MPa confined by reinforcement under concentric loading with the transverse reinforcement ratio and tie configuration as main variables,the failure process and failure mode were studied,and the axial compressive stress-strain curve was measured,the effect of the transverse reinforcement ratio and tie configuration on confined were reported,and the relationship between the actual strain of steel and the axial strain of the confined concrete was analyzed.Results show that the columns with closely spaced and reasonable selection of tie configuration may lead to a higher lateral restraint force and larger confined area of core concrete.And the stirrup may not yield for the columns with larger spaced and unreasonable selection of tie configuration when confined LWAC reaches peak strength.（2）Based on the characteristics of lightweight aggregate concrete confined by reinforcement,choosing effective confined stress as the main calculation parameter,the confinement effectiveness coefficient of rectangular section was corrected,and the calculation method of the stress in the transverse reinforcement at the peak strength was given.The formulas for peak strength and peak strain were suggested by assembling a database of 119test results of confined LWAC columns,then the axial compression bearing capacity of the specimens was calculated,and the calculated results were compared with the current code provisions.（3）The formulas forε₅₀0 andε₈₅ were derived from a regression analysis using the data collected.Based on typical constitutive models,combined with boundary conditions and characteristic point coordinates,a stress-strain constitutive model,applicable to the confined lightweight aggregate concrete was proposed,and the calculation method for model parameters was given.The research on the basic mechanical properties of confined LWAC columns is of great significance for proposing the stress-strain curves for confined LWAC under uniaxial compression and further study of the performance of the confined LWAC,and it helps to promote the application of LWAC in engineering practice.