基于光纤传感技术的混凝土支撑轴力监测及数据分析

支撑轴力作为地铁深基坑施工监测的主要监测项目,是考察基坑自身安全状况的重要指标。针对目前混凝土支撑轴力监测值与实际情况差异较大的问题,分析造成混凝土支撑轴力监测值偏大的原因。利用光纤传感技术,在混凝土支撑纵向主筋肋槽上胶粘封装光纤光栅传感器(FBG),通过监测钢筋的应变推算出支撑梁的内力。在现有计算公式的基础上提出考虑混凝土收缩、徐变、应力应变关系非线性影响的轴力修正公式,对监测数据进行修正。以某市地铁深基坑为例,验证了光纤传感轴力监测技术及轴力修正公式的有效性。结果显示,FBG与钢筋计轴力曲线变化趋势一致,FBG考虑了温度补偿,监测值较钢筋计更加稳定;对轴力监测值进行修正,修正后的轴力值约为修正前的1/3,结果更加符合实际。

Monitoring and data analysis of axial force of concrete support based on optical fi ber sensing technology

As the main monitoring system of subway deep foundation pit construction,the supporting axial force is an important index to investigate the safety condition of the foundation pit itself.In view of the big difference between the current monitoring value of concrete support axial force and the actual situation,this paper analyzes the reasons for the large monitoring value of concrete support axial force.The Fiber Bragg Grating(FBG)sensor is glued on the longitudinal main rib groove of the concrete support by using the optical fiber sensing technology.The internal force of the support beam is calculated by monitoring the strain of the reinforcement.Based on the existing calculation formula,the axial force correction formula considering the nonlinear influence of concrete shrinkage,creep,stress-strain relationship is proposed to correct the monitoring data.Taking the deep foundation pit of a metro as an example,the validity of the optical fi ber sensing axial force monitoring technology and the axial force correction formula is verifi ed.The results show that the change trend of the axial force curve of FBG and the reinforcement meter is identical.The FBG takes temperature compensation into account,the monitoring value is more stable than the reinforcement meter,the revised axial force monitoring value is about 1/3 of the revised axial force value,the results are more practical and truer.