嵌岩桩基础抗震性能试验研究
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摘要
基桩按照桩端持力层是否嵌入基岩通常分为嵌岩桩和非嵌岩桩。在地震作用下,上述两种不同约束条件下的桩基础的工作反应性状差异有多大目前尚不明确。为比较地震动作用下该两类基桩的响应,得到其破坏模式以及对于上部结构的影响,开展了大型室内振动台模型试验,分别在大型模型箱内布置带承台的嵌岩或非嵌岩群桩以及自由单桩,采用三条基岩场地地震波进行加载。结果表明:对于嵌岩的带承台群桩基础,在桩顶和桩端——两个嵌固端均会形成较为明显的应力集中现象,桩身内力呈"两头大,中间小"的分布规律,而非嵌岩桩由于只在桩顶形成一定的约束效应,桩端完全自由,因而桩身内力呈现桩顶附近大,而沿桩身自上至下呈内力逐渐减小的规律。在同一地震作用工况下,相比桩顶自由的单桩,桩顶嵌固的基桩桩身应变幅值较大,说明桩顶和桩端的约束作用以及上部结构惯性力对桩身的内力影响显著;通过比较不同地震波下桩身的应变响应规律,表明桩身的动力响应与所输入地震动的频谱特性有关。
The piles were divided into socketed and unsocketed piles. Under the action of the earthquake,the differences of response the two kinds of pile were not clear up to now. In order to compare the responses of the two types of pile to get different failure modes and the influences on the superstructure under the action of the earthquake,the large scale indoor shaking table model test was carried out. The socketed group piles,unsocketed group piles and the free single pile were arranged in the large model box. Three bedrock site seismic waves were adopted and inputted individually. The results showed that: for the socketed pile with pile cap,the fix of pile top and ends would resulted in obvious stress concentration phenomenon,pile body internal force was larger at both the ends but smaller in the middle. However,the unsocketed pile only formed a certain constraint effect on the top of the pile,so the internal force of the pile was larger near the top of the pile,while the internal force gradually decreased along the pile shaft from top to bottom. In the same seismic action conditions,compared with the single pile with free ends,the strain amplitude of socketed pile was more obvious,the impact of the restraint effect of the pile and the inertia force from the superstructure on pile internal force was more significant. By comparing the strain response of the pile under different inputted seismic waves,it showed that the dynamic response of the pile internal force was related to the ground motion frequency spectrum characteristics.
The piles were divided into socketed and unsocketed piles. Under the action of the earthquake,the differences of response the two kinds of pile were not clear up to now. In order to compare the responses of the two types of pile to get different failure modes and the influences on the superstructure under the action of the earthquake,the large scale indoor shaking table model test was carried out. The socketed group piles,unsocketed group piles and the free single pile were arranged in the large model box. Three bedrock site seismic waves were adopted and inputted individually. The results showed that: for the socketed pile with pile cap,the fix of pile top and ends would resulted in obvious stress concentration phenomenon,pile body internal force was larger at both the ends but smaller in the middle. However,the unsocketed pile only formed a certain constraint effect on the top of the pile,so the internal force of the pile was larger near the top of the pile,while the internal force gradually decreased along the pile shaft from top to bottom. In the same seismic action conditions,compared with the single pile with free ends,the strain amplitude of socketed pile was more obvious,the impact of the restraint effect of the pile and the inertia force from the superstructure on pile internal force was more significant. By comparing the strain response of the pile under different inputted seismic waves,it showed that the dynamic response of the pile internal force was related to the ground motion frequency spectrum characteristics.
引文
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[14] MIZUNO H. Pile Damage During Earthquakes in Japan(1923-1983)[C]//Proceedings of the Dynamic Response of Pile Foundations.USA,VA,Reston:ASCE,1987.
[2]刘金砺,高文生,邱明兵.建筑桩基技术规范应用手册[M].北京:中国建筑工业出版社,2010.
[3]陈国兴.岩土地震工程学[M].北京:科学出版社,2007.
[4]黄雨,舒翔,叶为民,等.桩基础抗震研究的现状[J].工业建筑,2002,32(7):50-53.
[5]刘惠珊.桩基震害及原因分析:日本阪神大地震的启示[J].工程抗震,1999(3):37-43.
[6]闫明礼,张东刚.CFG桩复合地基技术与工程实践[M].北京:中国水利水电出版社,2006.
[7]史佩栋.桩基工程手册[M].北京:人民交通出版社,2008.
[8]刘惠珊.桩基抗震设计探讨:日本阪神大地震的启示[J].工程抗震,2000(3):27-33.
[9]刘惠珊,乔太平.可液化土中桩基设计计算方法的探讨[J].工业建筑,1983,19(4):19-24.
[10]中华人民共和国城乡建设部.建筑桩基技术规范:JGJ 94—2008[S].北京:中国建筑工业出版社,2008.
[11]中华人民共和国城乡建设部.建筑抗震设计规范:GB 50011—2010[S].北京:中国建筑工业出版社,2010.
[12] ROSS G A,SEED H B,MIGLIACCIO R. Bridge Foundations in the Alaska Earthquake[J]. Journal of Soil Mechanics&Foundations Divsion,ASCE,1969,110(6):757-772.
[13] NISHIZAWA T,TAJIRI S,KAWAMURA S. Excavation and Response Analysis of a Damaged RC Pile by Liquefaction[C]//Proceedings of the 8th World Conference of Earthquake Engineering. 1984.
[14] MIZUNO H. Pile Damage During Earthquakes in Japan(1923-1983)[C]//Proceedings of the Dynamic Response of Pile Foundations.USA,VA,Reston:ASCE,1987.
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