基于PPP-BOTDA技术的PBL剪力键群应变测试研究

STRAIN MEASUREMENT ON PBL SHEAR CONNECTOR GROUP BASED ON PPP-BOTDA DISTRIBUTED FIBER OPTIC SENSING TECHNIQUES

为研究混合结构PBL剪力键群各剪力键的剪力传递,在开孔板界面摩擦效应测试中引入了光纤传感测试技术。阐述了PPP-BOTDA(Pulse-Pre Pump Brillouin Optical Time Domain Analysis)技术的测量原理,根据多中间层的剪滞理论,建立了基体-光纤间的应变传递模型,推导了表贴式光纤的应变传递公式,基于4个四排PBL剪力键群试件的静载破坏试验,实现了对PBL剪力键开孔钢板及混凝土应变的空间分布式测量,并对分布式传感光纤的应变传递进行了敏感性分析。测试结果及分析表明:在仪器的空间分辨率一定时,传感光纤的粘贴宽度、光纤护套的厚度对应变传递影响显著,粘结层胶体的剪切模量对应变传递影响不甚明显;对比剪力键试验中应变片与分布式光纤的应变数据,试验采用的两种光纤均具有良好的应变测量精度,试验结果与理论敏感性分析较为一致;基于PPP-BOTDA的分布式光纤测试方法,克服了传统应变片测试中的不足,在既定的光纤铺设工艺下,适用于结构的大应变、高精度、分布式测量。

In order to investigate the shear transfer mechanism among shear connectors of PBL groups, fiber optic sensing techniques are introduced into the strain measurement of perforated plates on the interface friction effect. Measurement principles of pulse-preppump Brillouin optical time domain analysis(PPP-BOTDA) techniques are presented, then a strain transfer model for matrix-fiber structures is built according to the shear lag theory of multiple middle-layers and strain transfer formulas for the surface-attached fibers are deduced. Based on the static loading tests of four four-row PBL shear connector group specimens, spatially distributed strain measurement for the perforated plate and surrounding concrete is achieved, and parameter sensitivity analysis on the strain transfer of distributed fiber optic sensors is conducted. The measurement results and analysis show that the pasted width and the coat thickness of optical fibers have significant effect on the strain transfer ratio, but the shear modulus of the adhesive layer has no obvious effect on the strain transfer in case of invariant spatial resolution of the instrument. Comparing the strain data from strain gauges and optical fibers, it is evident that both types of optical fibers have preferable measurement accuracy, and the test results are consistent with the sensitivity analysis in theory. The measurement method for distributed fiber optic sensors on the basis of PPP-BOTDA techniques solves the problems of traditional strain measurement using resistance strain gauges, and can be used for distributed large-strain and high-accuracy measuring for bridge structures by means of the setup method of the optical fibers.