Behavior of bond between reinforcement and concrete under fire

火灾下钢筋与混凝土之间的粘结行为

• 批准号: 317099919
• 负责人: Dr.-Ing. Josipa Bosnjak
• 金额: --
• 依托单位: MPA Stuttgart, Otto-Graf-Institut (FMPA)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/317099919?language=en
• 关键词: Behavior; bond; between; reinforcement; concrete

Understanding the bond behavior under fire is essential for both design and assessment of reinforced concrete structures. One of the challenges in case of reinstatement is the assessment of the residual capacity of the existing members. Currently, there are no clear guidelines on the evaluation of the residual bond capacity after exposure to fire. The simplified guidelines given by codes are insufficient for a realistic estimation of the residual bond capacity. In order to realistically model the bond behavior, it is necessary to differentiate between the possible failure modes (pure bond failure and/or concrete splitting failure), which is recognized by the fib Model Code 2010 for the bond at room temperature. This code recommends an analytical bond stress-slip relationship for pull-out failure or splitting failure based on different parameters such as concrete cover, concrete strength, rebar diameter etc. Even though a lot of research work on bond behavior under elevated temperatures has been performed so far, an appropriate model for the bond behavior under heating (real fire scenarios) and realistic boundary conditions (unconfined specimens) is still missing. The majority of the existing literature data on the bond behavior at high temperatures was obtained for steady state conditions and by preventing concrete splitting. Furthermore, the majority of the experiments were performed at relatively low heating rates. These data lack the information about the effect of thermally induced stresses and consequent concrete damage developed in real fire scenarios on bond behavior. Increased concrete damage can contribute to concrete splitting before the theoretical bond strength is achieved, resulting in a possible overestimation of the theoretically obtained residual bond capacity. The main objectives of the present research project are to investigate the bond behavior and to develop a practical model for the estimation of residual bond capacity after exposure to standard fire considering realistic boundary conditions. The proposed research work includes an experimental campaign augmented by numerical simulations. The investigations are to be performed using beam-end test specimens exposed to standard fire curve (ISO 834). The following parameters will be investigated: heating duration, heating type (one- or three-sided exposure), thickness of the concrete cover, transverse reinforcement and reinforcement diameter. The two heating types, one- and three- sided heating, represent the realistic fire exposure in slab and beam elements, respectively. Experimental results will be further extended by numerical simulations. The results of the experimental and numerical work will be used to propose a practical model for the estimation of residual bond capacity after exposure to standard fire. The model will be developed as an extension of the existing bond model (fib Model Code 2010).

了解火灾下钢筋混凝土结构的粘结性能对于钢筋混凝土结构的设计和评估都是至关重要的。恢复工作的挑战之一是评估现有成员的剩余能力。目前，对于暴露于火灾后的剩余粘结能力的评估没有明确的指导方针。规范给出的简化准则不足以对残余粘结能力进行现实的估计。为了真实地模拟粘结行为，有必要区分可能的失效模式（纯粘结失效和/或混凝土劈裂失效），这是由2010年fib模型代码在室温下的粘结识别的。该规范建议基于不同的参数，如混凝土保护层、混凝土强度、钢筋直径等，对拉拔破坏或劈裂破坏的粘结应力-滑移关系进行分析。尽管迄今为止已经对高温下的粘结性能进行了大量的研究工作，在加热（真实的火灾场景）和现实边界条件（无约束试样）下的粘结行为的适当模型仍然缺失。现有的大多数文献数据的粘结性能在高温下获得的稳定状态条件下，并通过防止混凝土分裂。此外，大多数实验是在相对较低的加热速率下进行的。这些数据缺乏有关热应力和随后的混凝土损坏的影响，在真实的火灾场景对债券行为的信息。在达到理论粘结强度之前，混凝土损伤的增加可能导致混凝土开裂，从而可能高估理论上获得的残余粘结能力。本研究项目的主要目标是调查债券的行为，并制定一个实用的模型，估计暴露于标准火灾后，考虑现实的边界条件下的剩余债券的能力。拟议的研究工作包括一个实验活动，增加了数值模拟。使用暴露于标准防火曲线（ISO 834）的梁端试样进行调查。将研究以下参数：加热持续时间、加热类型（单面或三面暴露）、混凝土保护层厚度、横向钢筋和钢筋直径。两种加热类型，单面和三面加热，分别代表板和梁单元中的真实火灾暴露。实验结果将通过数值模拟得到进一步扩展。实验和数值计算工作的结果将被用来提出一个实用的模型暴露于标准火灾后的剩余粘结能力的估计。该模型将作为现有债券模型（fib模型代码2010）的扩展开发。