箍筋约束轻骨料混凝土轴心受压应力-应变曲线研究

Axial compressive stress-strain relationship of confined lightweight aggregate concrete with stirrups

为研究轻骨料混凝土轴心受压应力-应变曲线,考虑箍筋约束效率的影响,以有效侧向约束应力与非约束轻骨料混凝土强度之比为参数,建立了适用于轻骨料混凝土的峰值应力、峰值应变和下降段代表点计算模型,给出了轴心受压应力-应变曲线峰值点时箍筋实际应力计算方法;根据箍筋约束轻骨料混凝土应力-应变曲线的特点,基于箍筋强度和混凝土强度,通过试验数据拟合给出了曲线下降段特征点的计算模型;完成12个不同配箍形式和配箍率的箍筋约束轻骨料混凝土试件轴心受压试验研究,对比分析了建议计算模型和典型模型。研究结果表明:对于轻骨料混凝土,约束混凝土应力达到峰值时箍筋未屈服;建议的箍筋应变计算模型可较好地用于峰值点时箍筋实际应力的计算,基于所给出的轻骨料混凝土的峰值应力、峰值应变、下降段代表点及箍筋实际应力计算方法得出的建议模型能够较好地表达箍筋约束轻骨料混凝土轴压应力-应变全曲线趋势。

Theoretical models adapted to LWAC( lightweight aggregate concrete) were proposed by considering the efficiency of stirrups confinement and the ratio of lateral confined stress to unconfined LWAC strength,which can be used to calculate the stress and strain corresponding to ultimate stage,and predict the characteristic points in descending branch. Stress of transverse reinforcement corresponding to ultimate stage was proposed. According to the characteristics of stress-strain curves of confined LWAC,a fitted model for characteristic points of descending branch was regressed based on strength of stirrups and concrete. 12 LWAC columns with various types of transverse reinforcements and transverse reinforcement ratios were tested under uniaxial compression. The results were compared with those obtained from the proposed model and typical models. The results show that stirrups do not yield when the ultimate strength of confined concrete is reached. It is proved that the proposed model can be used for calculating the practical stress of stirrups corresponding to peak point. The proposed model obtained by peak stress,peak strain,characteristic points of descending branch of constitutive curves and calculation for actual stress of stirrups performs well in presenting stress-strain relation of confined LWAC.