Formation mechanism of multi-plastic regions in concrete flexural members with graded GFRP bars
传统钢筋混凝土受弯构件在一个荷载峰值处往往仅产生一个塑性铰，这造成了一个严重的问题，即塑性铰区域的性能得到了充分的发挥，而塑性铰以外的区域没有进入塑性状态，抗震性能很少得到利用，表现为局部发生了严重的破坏，其它区域基本完好。这个问题浪费了材料的性能，严重限制和削弱了构件的抗震能力。本文提出在一个荷载峰值处构建多个塑性区的理念，其实质是沿着构件长度方向形成抗震功能梯度。本文的创新性和亮点体现在如下几个方面：1. 提出了一种多塑性区混凝土受弯构件的构建方案，并进行了试验验证。2. 证实了多塑性区优良的抗震力学效果。3. 揭示了多塑性区形成的机制：1) 受弯构件抗弯承载能力梯级分布和外力弯矩梯度分布相适配是多塑性区形成的决定条件；2) 各塑性区的塑性发展程度和构件的破坏模式具有可调控性；3) 线弹性的GFRP筋是多塑性区形成和调控的关键。本文的理念和核心内容还未见于报道，具有显著的创新性和重要的应用价值。 多塑性区形成机制(曲率单位：10-4mm-1，弯矩单位：kN·m)Abstract: In order to enhance the seismic capacity of concrete flexural members, a graded reinforcement scheme with the glass fiber reinforced plastic (GFRP) bars and the steel bars was developed to make a graded distribution of bearing capacity that matches the external force distribution, and then multiple-plastic regions were formed. Five concrete flexural members with different graded reinforcement parameters were designed, and the comparison parameters included the height of the grades, the type of bars, the reinforcement ratios and the construction methods. Through the pushover experiment, the formation and mechanical effects of multi-plastic regions were studied, and the formation mechanism of multi-plastic regions was analyzed in details. The results show that the reasonable graded reinforcement scheme can form multi-plastic regions in the concrete flexural member. The number and development degree of plastic regions significantly affect the seismic behaviours of members. The formation condition of the multi-plastic regions is that the external moment is between the sectional yield moment and ultimate moment in several grades. The development level of each plastic region can be effectively controlled by adjusting the length and reinforcement of the grades, and the failure position and failure mode of the member can be designed. A great increment provided by GFRP bars with line elasticity properties on the bending bearing capacity after yielding is a key factor for the formation and regulation of multi-plastic regions.
表 1 各试件梯级配筋详细参数
Table 1. Parameters of each specimen's graded reinforcement
Specimen Grade Length of each
Details of reinforcement Reinforcement ratio Steel bars GFRP bars A 1 0-700 4$ \phi $16 Steel bars +4$ \phi $14 GFRP bars 1.29% 0.99% 2 700-2700 4$ \phi $16 Steel bars 1.29% - B 1 0-1000 4$ \phi $16 Steel bars +4$ \phi $14 GFRP bars 1.29% 0.99% 2 1000-2700 4$ \phi $16 Steel bars 1.29% - C 1 0-500 4$ \phi $16 Steel bars +10$ \phi $10 GFRP bars 1.29% 1.26% 2 500-760 4$ \phi $16 Steel bars +6$ \phi $10 GFRP bars 1.29% 0.75% 3 760-2700 4$ \phi $16 Steel bars 1.29% - D 1 0-650 4$ \phi $14 GFRP bars +10$ \phi $10 GFRP bars - 2.24% 2 650-1400 4$ \phi $14 GFRP bars +6$ \phi $10 GFRP bars - 1.74% 3 1400-2700 4$ \phi $14 GFRP bars - 0.99%