柱下素混凝土独立扩展基础破坏性状试验研究

The Experimental Researches of Plain Concrete Single Footing under Column with Failure Characteristics

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摘要试验表明,柱下无筋扩展基础由两种破坏形式控制:其一为沿柱根部基础垂直截面抗弯承载力的要求和基础底部中心区域混凝土抗拉强度满足横向拉应力要求;其二为沿柱根与地面成45°角的基础斜向剪切承载力要求。随着荷载的增加,柱下混凝土的抗拉强度首先达到极限值而发生开裂,在柱下基底部首先出现"十"字形裂缝,然后裂缝逐渐以柱下基底部位为中心向基础的四周扩展,并由基础底部向上部延展,进而基础完全破坏。根据试验结果,对地基规范(GB50007)提出以下修订建议:素混凝土基础挑出边的宽高比除符合规范表8.2.1的要求外,尚应进行墙边缘的受弯承载力以及距墙边缘h_o处的受剪承载力验算;基础的强度和厚度应满足柱荷载在扩散时沿斜截面产生的主拉应力的水平分量的拉应力要求。 Tests show that the unreinforced expanded foundation under a column is controlled by two types of failure:one is the requirement for the bending capacity of the vertical section along the column root foundation and the tensile strength of the concrete in the center of the bottom of the foundation meets the requirement for lateral tensile stress;The other one is the requirement for the oblique shear bearing capacity of the foundation at a 45°angle from the column root to the ground.With the increase of the loads,the tensile strength of the concrete under the column first reaches the limit value and occurs cracks.At the bottom of the foundation under the column,a"+"-shaped crack first appears,and then the crack which is centered on the bottom of the foundation under the column gradually expands to the four sides of the foundation,these cracks extend from the bottom of the foundation to the upper part,and then the foundation is completely destroyed.According to the test results,the following amendments are proposed for the foundation code(GB50007):the width-to-height ratio of the extracted side of the plain concrete foundation in addition to meeting the requirements of Table 8.2.1 of the code,the bending capacity of the edge of the wall and the shear bearing capacity at the distance h_o from the edge of the wall should be checked calculation;The strength and thickness of the foundation should meet the requirements often sile stress,which is the horizontal component of the main tensile stress,which is generated during the column load spreads along the oblique section.

作者宫剑飞李昊侯光瑜薛慧立康景文 Gong Jian-fei;Li Hao;Hou Guang-yu;Xue Hui-li;Kang Jing-wen(China Academy of Building Research,Beijing 100013,China;State Key Laboratory of Building Safety and Environment,Beijing 100013,China;Disaster Prevention Research Center,Ministry of Housing and Urban-Rural Development,Beijing 100013,China;Beijing Jiao Tong University,Beijing 100044,China;Beijing Institute of Architectural Design(Group)Co.,Ltd;China Southwest Geotechnical Investigation Design Institute Co.,Ltd)