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首页> 外文期刊>Case Studies in Construction Materials >Effect of premature loading on punching resistance of reinforced concrete flat slabs
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Effect of premature loading on punching resistance of reinforced concrete flat slabs

机译：早产载荷对钢筋混凝土平板冲击性的影响

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Premature loading of reinforced concrete flat slabs in multi storey buildings during construction may occur after shuttering removal and loading slabs earlier than usual to meet project time targets. Some case studies showed failure of flat slabs, which were prematurely loaded during the construction process before it reaches its full characteristic strength (at 28 days), which was used in structural design. This research aims to address this problem through experimental testing and design application according to current building codes. Eight specimens with dimensions of 1100 * 1100?mm and a total thickness of 120?mm were experimentally tested to study the effect of concrete age and actual compressive strength at loading on the punching shear capacity of reinforced concrete slabs. All specimens were supported by a square column with dimensions of 150?×?150?mm and loaded at the four corners with a span of 1050?mm. Accelerating admixture was used in three studied specimens to achieve higher concrete compressive strength at early ages compared to their companions of normal concrete without these admixtures. It was found that increasing concrete compressive strength of slab from 25N/mm2to 35Nlmm2(40 % increase) for normal concrete, without early admixture, improved punching shear capacity by 26 %, while increasing it to 45N/mm2(80 % increase) improved punching shear capacity by 49 % when the specimens were loaded 7 days after casting. In addition, using an accelerating admixture increased early concrete compressive strength, which improved punching shear capacity of reinforced concrete slab over that without accelerating admixture by 31 % and 29 % after 7 days and 14 days, respectively. According to inclusion of reinforcement ratio, BS8110 - 97 and Eurocode-2004 (EC2) design codes showed the most accurate prediction of punching shear capacity at 28 days, while ACI-2014 and ECP 203-2018 seemed conservative as their equations do not take steel ratio into consideration. At early ages, BS8110 - 97 and Eurocode-2004 (EC2) design equations did not provide accurate prediction of punching shear capacity while ACI and ECP provided reliable equations. It is recommended to use the actual compressive strength of concrete at early age (7 days for example) for calculating punching shear resistance of flat slabs prior to shuttering removal to prevent any premature loading.
机译：在比平时更早地拆卸和装载平板后，施工期间，在施工期间的钢筋混凝土平板的过早负载可能会发生，以满足项目时间目标。某些案例研究显示出扁平板的失效，在施工过程中过早地装载，然后在其达到其结构设计中使用的全部特征强度（28天）。本研究旨在通过根据当前建筑码的实验测试和设计应用来解决这个问题。实验测试了八个尺寸，尺寸为1100×1100Ωmm和120毫米的总厚度，研究了混凝土时代和实际抗压强度在加载钢筋混凝土板的冲压剪切容量中的影响。所有标本由方形柱支撑，尺寸为150Ω×150Ω·mm，并在跨度为1050Ωmm的四个角落。加速混合物用于三个研究的标本中，以在未经这些混合物的正常混凝土的同伴中获得更高的抗压强度。结果发现，对于正常混凝土，将平板的混凝土压缩强度从25N / mm2增加到正常混凝土，没有早期混合物，改善冲压剪切容量为26％，同时将其增加到45n / mm2（增加80％）改善冲孔当铸造后7天装样本时，剪切容量为49％。此外，使用加速混合物提高早期混凝土抗压强度，这改善了钢筋混凝土板的冲压剪切容量，而不会在7天和14天后加速31％和29％的加速。根据纳入率，BS8110 - 97和EUROCODE-2004（EC2）设计代码显示出在28天时最精确的冲压剪切容量预测，而ACI-2014和ECP 203-2018似乎保守，因为它们的方程不拿钢铁比率考虑。在早期，BS8110 - 97和Eurocode-2004（EC2）设计方程没有提供冲压剪切容量的精确预测，而ACI和ECP提供可靠的方程。建议在早期（例如，7天）使用混凝土的实际压缩强度，用于在快门去除之前计算平板的冲压剪切电阻，以防止任何过早负载。

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