纤维格栅增强ECC加固火灾后钢筋混凝土柱受力性能的研究

Reinforced concrete (RC) column is one of the important load-carrying members of structures, and the high temperature effect of fire will reduce its mechanical properties. However, the researches on strengthening of fire-damaged RC columns are not sufficient. .This project intends to combine fiber reinforced polymer (FRP) grid and engineered cementitious composites (ECC) to form composite strengthening system, i.e. FRP grid strengthened ECC, to strengthen fire-damaged RC columns. This strengthening technique takes full advantage of high tensile strength of FRP grid and tensile strain hardening property of ECC, and thus significantly increases the bearing capacity and deformability of the strengthened columns. This project aims to conduct comprehensive experimental research, numerical simulation and theoretical analysis. Firstly, the residual mechanical properties of concrete and steel after fire, and the mechanical properties of composite strengthening layer will be studied; Secondly, researches on the interfacial fracture properties of ECC and fire-damaged concrete will be further conducted; Thirdly, the influence of strengthening parameters on the axial compressive performance of strengthened columns and the behavior of strengthened columns under horizontal cyclic load, along with the corresponding mechanisms, will also be investigated..In this project, the mechanical mechanism of fire-damaged RC columns strengthened with FRP grid reinforced ECC will be revealed, and further the theoretical model and simplified formula for the calculation of load-carrying capacity of strengthened columns will be established. The results of the project will provide theoretical basis and technical supports for the strengthening design of the fire-damaged RC columns.

钢筋混凝土柱是结构的重要承重构件之一，火灾的高温作用会降低其力学性能，而目前国内外对火灾后钢筋混凝土柱加固的研究较少。.本项目拟采用纤维格栅和超高韧性水泥基复合材料（ECC）组成复合加固体系—纤维格栅增强ECC，加固火灾后的钢筋混凝土柱，充分发挥纤维格栅抗拉强度高和ECC拉伸应变硬化的优势，极大提高加固柱承载能力和变形能力。本项目旨在通过试验、数值模拟和理论分析相结合的方法，（1）以研究火灾后混凝土、钢筋的残余力学性能和复合加固层的力学性能为基础，（2）探究ECC与火灾后混凝土界面的断裂性能，（3）进一步研究纤维格栅增强ECC加固火灾后钢筋混凝土柱的轴压性能和低周反复荷载作用下的受力性能随加固参数变化的规律及内在影响机制。.本项目拟揭示纤维格栅增强ECC加固火灾后钢筋混凝土柱的受力机理，建立加固柱承载力计算理论模型和简化公式，为火灾后钢筋混凝土柱的加固提供理论依据和技术支持。

现阶段建筑火灾频繁易发，火灾产生的高温作用会降低结构的力学性能。高延性水泥基复合材料ECC具有优越裂缝分散能力和应变硬化特性，在火灾后结构加固中有良好应用前景。在本项目资助下，主要的研究内容和结论如下：（1）研究了受火时间、加固层厚度、纤维格栅层数和加固层是否直接受压等因素对纤维格栅增强ECC加固火灾后RC柱力学性能的影响，发现加固层约束作用明显，可显著提高加固柱承载性能，直接受压时还发挥抗压作用，承载力最高；加固层抑制了裂缝快速发展，提高加固柱变形能力；建立了加固柱的有限元分析模型并提出加固柱承载力计算公式。（2）研究了加固层材料、加固箍筋配筋率和剪跨比等因素对加固梁抗剪性能的影响，ECC加固显著提高了加固梁的抗剪承载力和变形能力，剪切延性系数大幅提高，加固箍筋配筋率较高时会改变破坏模式；采用DIC法测试了梁剪跨区的应变场，发现ECC加固梁剪跨区应变分布均匀；根据桁架-拱模型，建立了加固梁抗剪承载力计算模型。（3）通过对35个Z型试件开展剪切试验，研究了ECC与高温后混凝土黏结面的剪切性能，发现当温度高于400 ℃时，其剪切强度随温度的升高而降低；粗糙度在3.5 mm时，试件剪切强度最高；混凝土试块水中冷却，黏结面用水泥浆或粉煤灰浆处理，均会降低试件抗剪强度，提出预测试件黏结面剪切强度的数学模型。（4）采用双材料楔入劈拉试件研究了高延性水泥基复合材料ECC与高温后混凝土的界面断裂性能。考虑混凝土经历的最高温度和界面粗糙度对界面破坏模式、断裂韧度和断裂能的影响。结果表明：在400 ℃时，双材料试件的破坏模式由完全界面破坏转为混合破坏，此时试件的断裂韧度和断裂能数值最高，当混凝土经历的最高温度超过400℃时，试件的断裂韧度和断裂能随温度升高而降低；适当的粗糙度处理对界面断裂性能的提高是非常有利的，本文中双材料试件在界面粗糙度为3 mm时取得最大断裂韧度值和最大断裂能值。