反复压力作用下橡胶的承载力—变形特性的试验研究

对3种不同刚度的橡胶试件进行了反复抗压加载试验,考察了在竖向反复压力作用下橡胶的承载力—变形特性.试验结果表明,当竖向荷载较小时,橡胶试件的荷载—变形呈线性变化;随着竖向荷载不断增大,荷载—变形出现非线性特性.当经历多次反复加载—卸载试验后,橡胶的荷载—变形曲线趋于稳定.当荷载卸至零时,橡胶的竖向压缩变形及横向膨胀变形不能完全恢复至零,存在一定的残余变形;而且,刚度越大,残余变形越大.多次反复压缩加载的压力较大时,橡胶试件的非线性刚度比初次加载时略有增大,但是,对整体力学性能影响较小,即橡胶具有较好的反复压缩力学性能.     

Finite element simulation of pile behaviour under thermo-mechanical loading in integral abutment bridges

To study the behaviour of piles in integral abutment bridges, under seasonal and daily thermal loading, a three-dimensional, nonlinear finite element model was constructed for a bridge. The model was parametrically run for five different bridge lengths that varied from 122 to 549 m. A sinusoidal model was used to represent the daily and seasonal temperature variations. The results showed that maximum lateral displacement of the piles occurs during the winter when the thermal contraction and the dead and live loads on the bridge produce displacements in the same direction. Maximum stress occurred in the pile furthest from the centre of the bridge and was found to be in the flange of the pile immediately below the concrete abutment. Plastic deformation was observed in all of the piles for all bridge lengths. The lateral displacement and maximum plastic deformation in piles increased as the length of the bridge increased. A linear relationship was found between the length of the bridge and the lateral displacements for both seasonal and daily temperature variations.     

注浆抗压桩破坏性静载试验分析

结合某工程桩端注浆抗压桩破坏性静载试验,通过桩身埋设钢筋应力计对各土层的平均极限侧阻值进行了分析,得到在竖向极限承载力作用下,单位侧阻的极限值比工程地质报告提供的侧阻极限值提高了2%~29%,下部土层比上部土层侧阻值增加多数要高等结论。     

桩靴在静载荷作用下的沉降预测

为了研究桩靴在静载荷作用下的沉降,基于圆孔扩张理论,推导出桩靴在荷载作用下的桩端阻力表达式.将桩端阻力作为桩靴受压状态下的荷载传递函数,结合桩侧摩阻力函数,采用分段位移迭代算法进行计算,预测出桩靴在受压状态下的荷载—沉降曲线.开展砂土中的桩靴静载模型试验,将模型试验结果与理论结果进行对比验证.结果表明:推导的理论公式计...     

FRP-混凝土-钢双壁空心管短柱轴心抗压试验研究

为研究FRP-混凝土-钢双壁空心管短柱的轴压性能,完成了3个圆钢管短柱和10个双壁空心管短柱试件的轴心抗压试验。结果表明:双壁空心管短柱内层钢管受到管内混凝土的径向压力,屈曲被延迟;管内混凝土受到外层FRP管和内层钢管的共同约束;试件具有良好的延性。在轴压力作用下,圆钢管短柱的破坏形态与其径厚比有关。双壁空心管短柱在轴压作用下有3种破坏形态:FRP管的纤维拉断,FRP管的纤维拉断和钢管压屈,整体压屈。破坏形态主要与钢管径厚比、空心率、FRP管的约束程度有关。通过分析本文和国内外相关试验结果,提出了双壁空心管内混凝土受压应力-应变关系模型的3种类型及模型参数的计算公式。模型考虑空心率、内层钢管径厚比、外层FRP管约束程度、FRP层合结构和加载方式的影响,与试验结果符合较好。     

Numerical modelling of the axial compressive behaviour of short concrete-filled elliptical steel columns

This paper investigates the axial compressive behaviour of short concrete-filled elliptical steel columns using the ABAQUS/Standard solver, and a new confined concrete stress-stain model for the concrete-filled elliptical steel hollow section is proposed. The accuracy of the simulation and the concrete stress-strain model was verified experimentally. The stub columns tested consist of 150 × 75 elliptical hollow sections (EHSs) with three different wall thicknesses (4 mm, 5 mm and 6.3 mm) and concrete grades C30, C60 and C100. The compressive behaviour, which includes the ultimate load capacity, load versus end-shortening relationship and failure modes, were obtained from the numerical models and compared against the experimental results, and good agreements were obtained. This indicated that the proposed model could be used to predict the compressive characteristics of short concrete-filled elliptical steel columns.     

Hysteretic behaviour of tubular joints under cyclic loading

This paper examines the cyclic performance of CHS joints used in steel tubular structures. Quasi-static experimental study into the response of eight T-joint specimens is described. Four of them are subjected to cyclic axial load, and the other four are subjected to cyclic in-plane bending. The general test arrangement, specimen details, and most relevant results (failure modes and load-relative deformation hysteretical curves) are presented. Some indexes to assess the seismic performance of tubular joints, including strength, ductility and energy dissipation, are synthetically analyzed and compared. Test results show that failure modes of axially loaded joints mainly contain weld cracking in tension and chord plastification in compression. But for joints under cyclic in-plane bending, both punching shear and chord plastification become regular failure modes accompanied by ductile fracture of the welds. Hysteretic curves take on a plump form in general. Ultimate strengths of joints are also compared with equation values for monotonic loading from various design codes. Results indicate the strength at a certain deformation limit can be regarded as the ultimate strength of a T-joint under cyclic loading and existing codes can be used to check it. It is also found that there is a significant distinction in the energy dissipation mechanism for tubular joints under different loading conditions. Finite element analyses are performed by taking into account weld geometry to facilitate the interpretation of the test results. It is identified that high tensile stress triaxiality can be one primary cause of weld cracking which happened under low cyclic load level.     

Centrifuge modelling of the behaviour of pile groups under vertical eccentric load

Annular shaped pile groups are a very common foundation layout for onshore wind turbines and other slender structures. In this study, their performance under vertical loads of moderate to high eccentricity, including moment rotation response and bearing capacity, was investigated by centrifuge testing on small scale physical models embedded in kaolin clay. To identify experimentally the capacity of the examined pile groups under different load paths, the model foundations were loaded monotonically until a clear collapse mechanism was achieved. The testing procedure and the proposed interpretation methodology can be easily adapted to load paths or pile layouts other than those considered in the current study. The experimental data can be adopted as a useful benchmark for mathematical models aimed at predicting the response of pile groups to complex load paths. The results of this testing program can also be used to assess the degree of conservatism of current methods adopted by industry for the design of piled foundations subjected to eccentric loads.     

模型边界对大型哑铃型承台群桩基础承载变形特性的影响

利用三维弹塑性有限元,考虑群桩基础周围外侧土体竖向变形影响范围和桩端土体压缩层厚度的因素,研究分析其对大型哑铃型承台群桩基础承载变形特性的影响,从而研究大型超深群桩基础边界问题以及离心模型试验边界对其承载变形特性的影响。研究表明:群桩基础边界大小由群桩基础变形特性控制,成桥阶段时大型哑铃型承台群桩基础周围外侧土体竖向变形影响范围和桩端土体压缩层影响深度,分别为一倍承台宽度和一倍桩长;设计的离心模型试验边界对群桩基础桩身受力大小与分布影响不大,而对承台沉降和桩端土体整体压缩变形比等变形特性影响较大。     

桩端后注浆桩抗压静载试验对比分析

通过对杭州某工程2根注浆桩与2根非注浆桩进行的静载试验,分析了注浆桩与非注浆桩承载力及沉降的不同。试验结果表明,注浆桩单桩承载力比非注浆桩增加至少20%,桩端后注浆对钻孔灌注提高承载力效果显著,根据单桩沉降计算理论分析,桩端后注浆由于显著的提高了桩端土层的弹性模量,因此,对减少灌注桩沉降量将产生显著的效果。     

Inelastic behaviour of composite members under combined bending and axial loading

This paper presents an account of the results of a series of tests on partially-encased composite steel/concrete beam-columns. The experimental inelastic behaviour of members is examined under idealised conditions representing extreme lateral loading in combination with co-existing axial gravity loads. Members with three different cross-sectional sizes, utilising Grade S460 steel, were employed in the tests. The specimens were tested under major- or minor-axis bending in conjunction with a constant level of axial loading. The experimental arrangement and test rig constructed for this purpose are described together with the material properties and details of the specimens. The main experimental results from tests carried out on ten composite models are presented and discussed. In addition to providing essential data for validating future analytical and design studies, the experimental results and observations enable a direct assessment of several important factors. Particular emphasis is placed on key parameters related to yield and ultimate capacity as well as on ductility and residual strength considerations.     

柱锤冲扩夯实混凝土桩桩身填料工程特性试验研究

为了研究夯实混凝土作为柱锤冲扩桩新型桩身填料的工程特性,首先通过室内击实试验获得了夯实混凝土材料的最佳配合比参数,然后采用最佳配合比参数进行无侧限抗压强度试验,研究了夯实混凝土的工程特性.并与普通浇筑混凝土的强度特性进行了比较.研究结果表明:通过击实成型的夯实混凝土密实性很好,并具有快硬、早强的特点.在水泥用昔较小的情况下即可获得较好的强度特性.在标准养护、水中及饱和土中养护时,强度均能得到较充分的发展,因此可在各种地基处理环境下应用.     

浅谈静压法沉桩在桩基础中的应用

阐述了静压法沉桩的适用范围,就如何判断静压法的沉桩阻力作了探讨,提出了静压法沉桩施工的注意事项,对常见质量事故产生的原因进行了分析,同时提出了相应的处理措施,指出静压法沉桩具有无噪声、无振动、无冲击力等优点,值得推广使用。     

某铁路CFG桩复合地基试桩静荷载试验与分析

通过对龙厦铁路某里程段CFG桩复合地基试桩静荷载试验,确定了该里程段的复合地基承载力特征值,对试验过程和结果进行了分析,试验结果显示,该CFG桩单桩复合地基承载力满足设计要求,为施工过程提供了科学依据和数据参考。     

软土地区静压预制桩的压桩力探讨

针对软土地区静压预制桩施工中出现的问题,结合工程实例进行了分析,探讨研究了压桩力与单桩竖向极限承载力标准值的关系,以及桩型、桩周土与持力层的影响,提出了适宜于软土地区的压桩力和压桩系数,以供软土地区静压预制桩设计施工参考。     

基于BP神经网络的静压桩承载力时间效应预测

基于珠海软土地区3根PHC管桩隔时复压试验数据,采用BP神经网络建立了静压桩承载力时间效应的BP神经网络模型来预测静压桩的长期承载力。在建模过程中将桩长、桩截面积、土体摩擦角、土体变形模量、渗透系数、最终压桩力及休止期等与静压桩承载力密切相关的7个参数引入到输入层,用Visual Basic语言编制了以最终压桩力和休止期为主要输入因素的计算程序,程序可以对比显示计算和实测曲线。在样本训练和学习过程中,任意选取2根桩的试验数据来预测第3根桩的长期承载力。通过对施工现场工程桩的试算,预测结果与实测值较为吻合,表明提出的BP神经网络模型用于预测静压桩长期承载力是切实可行的。     

锚杆静压桩在桩基础补强中的研究分析

通过对某学院实训楼工程的桩基础质量事故进行分析,并经过方案比选,确定锚杆静压桩的加固补强方案,通过对锚杆静压桩的设计、施工工艺及注意事项进行逐条分析,从而达到实现基础加固补强的效果。     

静压预应力管桩施工质量控制

介绍了静压预应力管桩施工的质量控制措施，对静压预应力管桩施工有一定的参考作用。     

Hysteretic behaviour of square tubular T-joints with chord reinforcement under axial cyclic loading

The stiffness of hollow section tubular joints is weak in the chord radial direction, and thus failure frequently occurs at the weld toe in the form of brittle fracture caused by crack propagation due to cyclic loading. To avoid such brittle failure, the chord at the intersection can be reinforced by increasing the chord thickness. With the chord reinforced, the failure position can be transferred to the chord intersection, and hence the cracking along the weld toe is prevented. To verify the efficiency of the proposed reinforcing method, both experimental test and finite element analysis are carried out on reinforced and un-reinforced square tubular T-joints subjected to quasi-static cyclic loads. The hysteretic curves, ductility ratio, energy dissipation and failure mode of the two full-scale specimens are studied experimentally, and it is found that the hysteretic curves of both specimens are plump, which show the T-joints can absorb much energy when they are subjected to seismic action. However, the enclosed area of the hysteretic curves of the reinforced T-joint is larger than that of the un-reinforced specimen because the chord reinforcement can prevent the fracture failure as well as improving the bearing capacity. The failure performance of the reinforced and un-reinforced specimens also show that a T-joint with chord reinforcement is more advantageous in resisting seismic action. Finally, the effect of the reinforced chord length and thickness on the hysteretic behaviour of square tubular T-joints is also investigated from a parametric study.     

预制桩静压施工工艺与控制重点

根据静压桩的沉桩机理,探讨了静压桩的施工工艺与控制重点,并对工程中常见质量问题及处理方法进行了分析,通过对静压桩施工工序的严格控制,使其满足了施工要求。