Influence of vertical steel reinforcement on the behaviour of edge restrained reinforced concrete walls
Influence of vertical steel reinforcement on the behaviour of edge restrained reinforced concrete walls
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竖向钢筋对边缘约束钢筋混凝土墙性能的影响
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
M. Shehzad
中科院分区：
文献类型：
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作者：
M. Shehzad
新浇混凝土由于热和收缩机制而经历体积变化，这些机制可以在内部和外部受到限制。外部施加的约束可以是端部、边缘或两者的组合。由于体积变化的限制，特别是在早期老化期间，通常会导致开裂，从而引起拉伸应力。这些是“贯穿”裂缝，并且在液体保持结构、核安全壳室、隧道和地下室中特别令人关注，其中除了在美学上令人不愉快之外，这种裂缝还可能导致水泄漏、有害化学品的进入/排放以及钢筋的腐蚀。这就要求对裂缝的机理和约束形成所涉及的因素有一个清晰的认识，以便在设计和施工阶段采取适当的缓解措施。
目前可用的指南是基于端部约束的情况下，并已从实验和分析研究轴向加强棱柱。在墙和板中，纵向和横向都有钢筋，现有指南中没有分析和纳入横向钢筋对开裂的影响。对以往研究的批判性回顾表明，受到边缘约束的构件的开裂行为与受到端部约束的构件的开裂行为有很大不同。因此，需要进行实验研究，以确定主要影响因素的影响，如垂直钢销和构件的几何形状实现。
本研究探讨了边缘约束构件中施加应变的约束，特别是，实验说明了约束（墙）和约束（底板）构件之间的竖向钢筋对约束发展机制的影响。调查建造了真实的规模的钢筋混凝土墙钢筋混凝土基础上，也说明了为什么以前的研究，主要是利用钢构件来限制施加的应变，是不合适的边缘约束的理解，因为它们不能反映墙和基础之间的热传递。试验中还改变了试验壁的厚度，以确定两个构件的相对几何形状对约束程度的影响。结果表明，约束显着增加的存在下，垂直钢筋。他们还表明，由于钢筋，约束随时间增加，而在没有钢筋的情况下则会减少。此外，为了确定横向钢筋的重要性，对钢筋混凝土板进行了试验。试验结果表明，当横向钢筋存在时，试件的开裂荷载降低了25 ~ 30%，而裂缝宽度和裂缝数量增加。
由于缺乏时间和资源，在实验研究中，有限元分析已被用来研究的行为的墙壁受到端部和边缘约束的组合。通过参数分析，研究了复合约束对裂纹数量、尺寸和宽度的影响。通过对不同高宽比墙体的研究，发现了低高宽比墙体的端部约束在较高部位占主导地位，并通过有限元分析指出了正确考虑约束底板的真实的时间边界条件的重要性。
Freshly cast concrete undergoes volume changes due to thermal and shrinkage mechanisms which can be restrained both internally and externally. Externally applied restraint can be either end, edge or a combination of the two. Tensile stresses are induced as a consequence of restraint of volume changes which often result in cracking particularly during early age. These are ‘through’ cracks and are of particular concern in liquid retaining structures, nuclear containment chambers, tunnels and basements where besides being aesthetically unpleasant, such cracks can also result in water leakage, ingress / discharge of harmful chemicals and corrosion of steel reinforcement. This calls for development of a clear understanding of the mechanism of cracking and the factors involved in restraint formation so that appropriate mitigation measures at the design and construction stage can be taken.
Currently available guidance is based on the end restraint cases and has been evolved from experimental and analytical investigations on axially reinforced prisms. In walls and slabs, reinforcement is present in both longitudinal and transverse directions and the influence of transverse reinforcement on cracking has not been analysed and incorporated in existing guidance. Critical review of previous research revealed that cracking behaviour of members subjected to edge restraint is very different from those under end restraint. Therefore, the need to undertake experimental investigation for determining the influence of major influencing factors like vertical steel dowels and members geometry was realized.
This research investigates the restraint of imposed strains in edge restrained members and in particular, experimentally illustrates the influence of vertical steel reinforcement between the restrained (wall) and the restraining (base slab) members on the mechanism of restraint development. The investigation constructed real scale reinforced concrete walls onto reinforced concrete bases and also illustrated why previous studies, which have mostly utilized steel members to restrain the imposed strain, are inappropriate for gaining an understanding of edge restraint as they fail to reflect the heat transfer between the wall and the base. Thickness of the tested walls was also varied in the tests to ascertain the influence of relative geometries of the two members on degree of restraint. Results revealed that the restraint significantly increased in the presence of vertical steel reinforcement. They also showed that restraint increases with time due to the steel reinforcement and decreases in its absence. Moreover, in order to ascertain the significance of the transverse reinforcement, tests on reinforced concrete panels were performed. The panels were subjected to direct tension and the results indicate that when transverse reinforcement was present, the cracking load for the tested specimens decreased by 25 – 30 %, whereas the crack widths and number of cracks increased.
Due to paucity of time and the resources involved in experimental investigation, finite element analysis has been utilized to study the behaviour of walls subjected to combination of end and edge restraint. Parametric study was carried out to investigate the influence of combined restraint on the number and size of cracks and crack widths. By investigating walls of different aspect ratios, the domination of end restraint in higher parts of the walls having lower aspect ratios was found. Through finite element analysis the significance of correctly incorporating the real time boundary conditions of the restraining base slab was also identified.