Application of bi-directional static loading test to deep foundations

Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.

Static load test and load transfer mechanism study of squeezed branch and plate pile in collapsible loess foundation

As a special geological phenomenon, the character of collapsible loess foundation is collapsible when penetrated by water. This character leads to the soil losing load bearing capacity largely and may lead to foundation failure. Pile is a popular foundation used in collapsible loess. The squeezed branch and plate pile is a new type of pile developed in recent years and has not be used in a project before. In this paper three squeezed branch and plate piles are tested in collapsible loess after immersion processing. The results may be used for reference in similar construction project, and to provide theoretical references for de- signing of the squeezed branch and plate piles in engineering practice.

Effects of Microstructure on Quasi⁃Static Transverse Loading Behavior of 3D Circular Braided Composite Tubes

The effects of microstructure on quasi-static transverse loading behavior of 3D circular braided composite tubes were studied. Transverse loading tests were conducted. Transverse load-deflection curves were obtained to analyze the effects of braiding parameters including the braiding angle, the wall thickness, and the diameter on the transverse loading of 3D circular braided composite tubes. Breaking loads, moduli and strengths had also been used to describe the transverse loading behaviors. The failure morphologies were shown to reveal damage mechanisms. From the results, the increase in braiding angle, wall thickness and diameter increases the ability of anti-deformation and breaking load of braided tubes. The breaking load of specimen with a braiding angle of 45° is about 1.68 times that of specimen with a braiding angle of 15°. The breaking load of specimen with 4 layers of yarns is about 2.15 times that of specimen with 2 layers of yarns. The breaking load of the tube with a diameter of 25.5 mm is about 2.39 times that of the tube with a diameter of 20.5 mm.

Bearing capacity and mechanical behavior of CFG pile composite foundation

CFG pile (i.e., pile constructed by granular materials of cement, fly-ash and gravel) composite foundation is applied in subsoil treatment widely and successfully. In order to have a further study of this kind of subsoil treatment technology, the influencing factors and calculation methods of the vertical bearing capacity of single CFG pile and the CFG pile composite foundation were discussed respectively. And based on the obtained solutions, effects by the cushion and measurements to reduce negative friction area were analyzed. Moreover, the developing law of settlement and bearing capacity eigenvalue controlled by the material strength with the increase of load were given for the CFG composite foundation. The in-situ static load test was tested for CFG pile. The results of test show that the maximum test load or half of the ultimate load is used from all the points of test, the average bearing capacity eigenvalue of single pile is 390 kN, and slightly greater than the design value of bearing capacity. The bearing capacity eigenvalues of composite foundation for 3 piles are greater than 300 kPa, and the mechanical properties of CFG pile composite foundation are almost identical in the case of the same load and cushion thickness. The pile-soil stress ratio and the load-sharing ratio can be adjusted through setting up cushion thickness.

Experiments of Multi-element Composite Foundation with Steel Pipe Pile and Gravel Pile

A set of serf-developed apparatus for foundation physical model were utilized to conduct model tests of the multi-element composite foundation with a steel pipe pile and several gravel piles. Some load-bearing characteristics of the multi-element Composite foundation, including the curves of foundation settlement, stresses of piles, pile-soil stress ratio, and load-sharing ratio of piles and soil, were obtained to study its working performances in silty sand soil. The experimental results revealed that the multi-element composite foundation with steel pipe pile and gravel pile contributed more than the gravel pile composite foundation in improving the bearing capacity of the silty fine sand.

Comparison Structure Forms Between Isogrid and Orthogrid of C/E Composite Trellis Wound Structure Based on Calculation of Load-Carrying

This paper calculated load-carrying of isogrid and orthogrid of carbon-epoxy composite trellis wound structure(C/E CTWS) using non-linear finite element method.Based on the analysis,test cases were designed and tests of axial compression were carried.Analysis result and test result fit well.In order to be used in the project,this kind of structure cut-out repairing was calculated.The method presented in this paper has been proved and can be used to solve complicated engineering problems.According to calculations and experimental results combined with application,a principle of choosing wound structure is obtained and principle could be applied to engineering.

部分充填式窄幅钢箱-UHPC组合梁抗剪试验研究

目的为研究部分充填式窄幅钢箱-UHPC组合梁的抗剪性能,方法对4根倒置组合梁试件通过三点加载方式进行了静载试验,通过研究其负弯矩作用下的破坏形态及变形特征,得到了组合梁的荷载-挠度曲线、应变分布、荷载-滑移曲线、最终破坏形态等。结果试验研究结果表明:UHPC翼板显著提升了组合梁的变形能力和极限承载力;相较于试件SUCB-3(NC翼板),试件SUCB-1(1/2UHPC翼板和SUCB-4(全UHPC翼板))的承载力分别提高了18.2%和27.3%,变形能力则分别增强了38.02%和41.2%;钢纤维的添加能有效地抑制翼板裂缝的开展,钢纤维掺量从0提高到2%,试件的最大裂缝宽度从1.06 mm降低到0.92 mm,变形能力增强了23.61%,承载力则提高了4%。结论提出了考虑钢箱、UHPC翼板和充填混凝土贡献的组合梁抗剪承载力计算公式。

窄幅钢箱-UHPC组合梁负弯矩下抗弯性能试验研究

为改善钢-混凝土组合梁负弯矩下的受力性能,提出一种新型窄幅钢箱-超高性能混凝土(UHPC)组合梁。通过6根试验梁的反向静力加载试验,得到试验梁受力全过程跨中荷载-挠度、荷载-应变、荷载-最大裂缝宽度关系曲线、裂缝发生发展及破坏形态等,基于简化塑性理论推导出了组合梁极限抗弯承载力计算公式。结果表明:窄幅钢箱-UHPC组合梁在负弯矩下具有良好的受力性能;提高配筋率、钢纤维掺量和UHPC相对板厚都可在一定程度上改善组合梁延性,提高其极限抗弯承载力;翼板配筋率对承载力影响较大,配筋率由1%增加至2%时,其极限抗弯承载力提高了15%;钢纤维掺量和UHPC相对板厚对初始开裂荷载影响较大,钢纤维掺量从1%增加到2%时,初始开裂荷载提高32%,UHPC相对板厚由0增加到0.5时,初始开裂荷载提高56%;增加钢纤维掺量和UHPC相对板厚可有效控制裂缝宽度,减少结构主裂缝数量,改善组合梁耐久性;组合梁极限抗弯承载力计算公式计算值与试验值吻合较好,表明塑性理论适用于窄幅钢箱-UHPC组合梁的承载力计算。

岩溶区PST管桩复合地基的工程应用

经对某场地高层建筑地基素填土厚度大、下伏基岩岩溶发育、以多层串珠状溶洞为主的地层条件研究,提出一种PST管桩刚性复合地基。采用试验和监测等方法来指导复合地基处理设计与施工,根据场地试桩数据来验证设计的合理性。施工完成后,采用静载荷试验对复合地基进行质量验收检测,并连续进行沉降监测。结果表明:岩溶区PST管桩复合地基是一种处理高层建筑地基很可行的方法,处理后可以满足高层建筑物对地基强度、变形及稳定性的要求。

火灾后正六边形孔蜂窝组合梁受力性能研究

火灾后蜂窝组合梁受力性能研究可为建筑结构受火后的加固修复提供重要依据。文章通过两个火灾后正六边形孔蜂窝组合梁的静力加载试验,分析了不同开孔率的正六边形孔蜂窝组合梁的破坏形态和承载性能。结果表明:火灾后正六边形孔蜂窝组合梁在正弯矩作用下会发生弯曲破坏,临近梁端的第3个孔压缩变形较为严重且两侧钢梁腹板局部屈曲,两加载点之间板顶混凝土破坏严重,钢梁上部板面出现纵向贯通裂缝;开孔率是影响火灾后正六边形孔蜂窝组合梁极限承载力的重要因素,相较于开孔率为70%的蜂窝组合梁,开孔率为60%的蜂窝组合梁的极限承载力和延性分别提高了20%和35%;所提出的正六边形孔蜂窝组合梁受火后剩余承载力计算方法具有较好的精度。

重载码头堆场CFG桩网复合地基离心模型试验研究

CFG桩网复合地基广泛应用于处理软土地基。采用土工离心模型试验研究某码头堆场超大荷载下CFG桩网复合地基的变形和桩土应力特性,试验模拟了地基、CFG桩、树根桩、加筋垫层、防尘网和轨道梁基础、矿石堆载等,分析了超大荷载作用下复合地基表面变形、桩顶轴力、桩间土压力、桩土应力比的变化规律。试验结果表明,复合地基的沉降速率在稳定控制标准之内,沉降量满足堆场使用要求,防尘网基础和轨道梁基础水平位移和沉降均很小,桩土应力比为25.2~43.8,CFG桩网复合地基在350 kPa荷载作用下是稳定安全的,达到了预期加固效果。

大直径嵌岩灌注桩竖向承载特性试验研究

为了探讨泥岩地基大直径灌注桩竖向承载性能,依托青岛某机场桩基工程,对嵌入泥岩的9根大直径灌注桩进行了竖向抗压静载试验和桩身应力监测,分析大直径嵌岩灌注桩的竖向抗压性能,明确大直径灌注桩的荷载传递规律。结果表明,试桩桩身完整性较好,桩身质量可靠;试桩荷载沉降(Q-s)曲线均为缓变型,加载初期存在明显的压密段,桩顶沉降量为10.31 mm,最低回弹率大于50%;最大荷载作用下,各试桩的竖向抗压极限承载力特征值均不小于6480 kN,试桩竖向抗压承载能力仍有较大潜力;试桩均表现出端承摩擦桩的特性,轴力自桩顶到桩端逐渐衰减,桩侧摩阻力峰值发生在中风化泥岩段,桩端阻力占桩顶荷载的10.55%~34.48%。

钢企口连接的预制叠合主次梁节点受力性能试验研究

为研究采用钢企口连接的预制叠合主次梁节点受力性能,设计了一个钢企口连接的预制叠合主次梁节点试件和一个整浇主次梁节点试件,进行静力加载试验,考察两试件的破坏模式、承载力、变形能力、荷载-悬臂端挠度关系、钢筋应变和钢企口栓钉应变等。研究结果表明:钢企口连接的预制叠合次梁的裂缝主要集中在主次梁交界面、次梁固端至钢企口范围内和次梁底部,表现为次梁固端弯曲破坏;钢企口连接的预制叠合次梁的开裂荷载和屈服荷载可基本等同整浇次梁,正截面受弯承载力比整浇次梁提高约100%;梁端荷载小于80kN时,钢企口近端栓钉受压、远端栓钉受拉,梁端荷载大于80kN时,钢企口各栓钉应力突增;钢企口连接的预制叠合次梁的正截面受弯承载力实测值与《混凝土结构设计规范》(GB 50010—2010)(2015年版)计算值的比值为109,可按规范计算值预测其正截面受弯承载力;拉-压杆模型计算得出钢企口连接的预制叠合次梁的破坏模式为拉杆破坏(受弯破坏)。

复合地基沉降量计算的平均切线模量法

地基的沉降量计算一直是地基基础工程中的重点问题,在地基基础设计过程中地基沉降量是重要的建筑变形控制参数,在满足地基承载力要求的前提下,只要将地基的沉降控制在允许变形的范围内,就能达到更好的经济效益,因此地基沉降量的准确计算对地基基础工程至关重要。地基沉降量的计算不仅与地基土层的物理力学性质、强度参数、变形指标有关,还与基础的尺寸有关,本文在原位载荷试验p-s曲线符合双曲线的基本假定条件下,采用切线模量法反算地基土层的切线模量和强度指标黏聚力,得到地基土层的变形和强度指标参数后,再用平均切线模量法计算实际基础的p-s曲线,进而确定实际基础的地基沉降量。文中通过CFG桩复合地基原位载荷试验及地基沉降量计算案例对切线模量法计算地基沉降量进行了优化,并与现行规范中地基沉降量计算方法进行了比较说明,验证了该计算方法的合理性。

FRP-钢组合板本构模型研究

为探讨FRP-钢组合板的抗拉性能,文中根据复合材料混合理论,提出FRP-钢组合板应力-应变本构模型。考虑FRP与钢板不同材料用量的影响,制作4组8个FRP-钢组合板试件,进行单轴拉伸试验。通过试验得到破坏模式、荷载-位移曲线,结果表明组合板均发生FRP拉断破坏。最后推出组合板的应力-应变关系,与理论模型进行对比,二者吻合较好,表明文中提出的理论模型能较准确描述拉伸作用下组合板的本构模型,为FRP-钢组合板的设计和应用提供依据。

循环荷载下粉煤灰复合地基竖向承载特性模型试验研究

为研究粉煤灰单桩复合地基竖向循环承载特性,开展在循环荷载作用下的室内模型试验。通过监测桩身及土体变化情况,分别从桩顶累计沉降、土压力、桩身内力等方面进行分析。试验结果表明:循环桩顶累计沉降前期呈现快速增长,而循环荷载比临界值为0.6,将后期沉降变化划分为稳定型和增长型两种趋势;桩侧土压力主要影响桩身上半部分土体,并沿竖向和径向均出现衰减现象,且竖向衰减更为明显;对桩端阻力强化系数Z和桩侧阻力弱化系数D分别进行拟合,可得到对实际工程中不同循环周期下桩端、桩侧阻力强弱变化情况分析,具有参考依据的函数方程;循环荷载下的桩端/桩侧荷载分担比呈现动态变化,循环周期的增加,将会存在桩端所占承载比例超越桩侧所占比例的占比反超点,循环幅值越大,出现反超点所需的循环次数也越少。

运载火箭静力试验加载装置结构拓扑优化设计

针对运载火箭结构静力试验中工装部件多、重量大的情况,开展轻量化设计,提出一种加载装置精细拓扑优化方法。基于变密度法,构造了以柔顺度最小为目标函数、以体积比为约束条件的拓扑优化模型,通过分段选取材料密度值,实现了结构精细拓朴。根据优化结果确定主承力结构及可减重部分,采用最小二乘法对结构不规则边界进行曲面拟合以提高其工艺性。最终承载1 500 t轴压的加载装置单个减重19.7%,结构应力和变形减小且分布更为均匀。本研究对于飞行器结构力学试验高承载部件的设计具有参考意义和实用价值。

变电站配电楼新型装配式基础承载性能试验

为改进现有变电站配电楼基础的性能,提出了一种新式的装配式基础方案,并进行了新型基础的足尺试验,研究其在偏心受压作用下的力学性能。试验结果表明,在设计荷载作用下,仅连接部位有少量钢筋屈服,在基础变阶处产生少量裂缝,倍设计荷载时,部分钢筋屈服并在靠近荷载中心变阶处出现竖向裂缝,此阶段整体未出现明显破损现象,从而体现出其良好的承载力特性;在设计荷载作用下,基础的沉降量满足设计要求,显示出较好的变形性能;在2倍设计荷载时,连接各个组合构件的后浇带未出现明显的破坏。基于本次试验可知,该装配式基础具有良好的承载能力、变形特性,以及具备不错整体性,能够满足基础设计研究。基础底部连接部位是整个装配式基础的薄弱部位,在实际工程设计中,应适当加强构造配筋。

预制钢板组合梁静载力学试验研究

为了解预制钢板组合梁结构的基本受力性能,以长益高速扩容工程30 m跨的预制钢板组合梁为工程背景,开展多级静载力学试验,通过实测数据和理论计算值的对比分析,评价结构在标准设计荷载作用的承载能力。结果表明:在设计荷载作用下的跨中挠度实测值为16.15 mm,应变实测值为190×10^(-6),实测值均小于理论值,结构实际工作状况比理论状况要好;π形组合梁的各测点挠度和应变的校验系数均小于2.0,相对残余变形均小于0.2,在设计荷载作用下结构处于弹性工作状态,结构具有良好的强度与刚度,满足设计要求,可作为桥梁上部主体结构使用。结论可为同类型桥梁的推广使用提供参考。

公路桥梁桩基础静载试验检测案例分析

文中以某公路桥梁工程为例,在明确施工现场的土层类型及关键参数后,进行千斤顶、锚桩横梁反力装置等设施的配置,设计单桩静载试验方案,从沉降、桩身轴力、桩侧摩阻力等多个方面综合分析被测桩基础的承载特性。结果表明,该桩基础的承载力达标,得出的静载试验检测数据对管控桩基础施工质量具有重要意义。