薄壁方钢管混凝土柱劲化设计及轴压性能探讨

对于薄壁方形钢管混凝土柱,有效且经济地提高柱的承载力、刚度和延性,增强其抵抗局部屈曲的能力是目前的一项重要研究课题。据此,进行8个薄壁方形钢管混凝土轴压试件的研究,比较普通薄壁钢管混凝土柱与劲化薄壁钢管混凝土柱的轴压极限承载力、延性性能、局部屈曲模态及相应耗钢量,研究表明:劲化设置在增加较少用钢量的情况下,使钢管壁对核心混凝土的约束作用相对于普通钢管混凝土柱和单纯加设约束拉杆的钢管混凝土柱更趋均匀,提高了整体约束效应,混凝土强度得以提高,本构关系明显改善。从而增加了钢管混凝土柱的轴压承载力和延性,改变了钢管的局部屈曲变形状态,其实用效益与经济效益极其可观,具有良好推广价值。     

Cyclic behavior of laterally loaded concrete piles embedded into cohesive soil

Modern seismic design codes stipulate that the response analysis should be conducted by considering the complete structural system including superstructure, foundation, and ground. However, for the development of seismic response analysis method for a complete structural system, it is first imperative to clarify the behavior of the soil and piles during earthquakes. In this study, full‐scale monotonic and reversed cyclic lateral loading tests were carried out on concrete piles embedded into the ground. The test piles were hollow, precast, prestressed concrete piles with an outer diameter of 300 mm and a thickness of 60 mm. The test piles were 26 m long. Three‐dimensional (3D) finite element analysis was then performed to study the behavior of the experimental specimens analytically. The study revealed that the lateral load‐carrying capacity of the piles degrades when subjected to cyclic loading compared with monotonic loading. The effect of the use of an interface element between the soil and pile surface in the analysis was also investigated. With proper consideration of the constitutive models of soil and pile, an interface element between the pile surface and the soil, and the degradation of soil stiffness under cyclic loading, a 3D analysis was found to simulate well the actual behavior of pile and soil. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental investigation on seismic behavior of single piles in sandy soil

This paper describes a quasi-static test program featuring lateral cyclic loading on single piles in sandy soil. The tests were conducted on 18 aluminum model piles with different cross sections and lateral load eccentricity ratios, e/d, (e is the lateral load eccentricity and d is the diameter of pile) of 0, 4 and 8, embedded in sand with a relative density of 30% and 70%. The experimental results include lateral load-displacement hysteresis loops, skeleton curves and energy dissipation curves. Lateral capacity, ductility and energy dissipation capacity of single piles under seismic load were evaluated in detail. The lateral capacities and the energy dissipation capacity of piles in dense sand were much higher than in loose sand. When embedded in loose sand, the maximum lateral load and the maximum lateral displacement of piles increased as e/d increased. On the contrary, when embedded in dense sand, the maximum lateral load of piles decreased as e/d increased. Piles with a higher load eccentricity ratio experienced higher energy dissipation capacity than piles with e/d of 0 in both dense and loose sand. At a given level of displacement, piles with circular cross sections provided the best energy dissipation capacity in both loose and dense sand.     

Investigation of a cyclic laterally loaded model pile group

In certain regions of the world, designing deep foundations to withstand seismic loading is a reality. Seismic loading of structures and foundations reaches its most critical state as a cyclic lateral force. The response of soils and foundations to repetitive lateral forces is highly complex, relegating most design methods to be based upon overly conservative rules-of-thumb. The primary objective of this research was to analyze the mechanics of seismic loading on pile groups in clay soils. To achieve this a model testing facility was constructed to house a fully instrumented 1×5 model pile group that was subjected to cyclic lateral loading. An empirically based method for pile group design is suggested based upon the results generated from model pile group testing.     

变厚度钢板内芯防屈曲支撑试验研究

提出了一种变厚度钢板内芯防屈曲支撑（VTBRB）。设计了2个足尺变厚度钢板内芯防屈曲支撑试件,其中:1个试件在变厚度内芯端部设置加劲肋;另1个试件采用无肋式变厚度内芯。通过拟静力试验分析了2种内芯构造形式对变厚度钢板内芯防屈曲支撑的滞回性能、失效模式、受压承载力调整系数和累计塑性变形等的影响。研究表明:2个变厚度钢板内芯防屈曲支撑均表现较好的抗震耗能特性,其受压承载力调整系数均满足相关规范的限值要求。设置加劲肋可以减少变厚度内芯端部无粘结材料的磨损,并可以有效提高变厚度内芯防屈曲支撑的低周疲劳性能。     

半刚接框架-斜加劲钢板剪力墙低周反复荷载试验研究

对一榀单跨两层半刚接框架-斜加劲钢板剪力墙结构进行了低周反复荷载试验,分析结构破坏模式和耗能机理,得到了承载力、延性、刚度、耗能能力等指标.结果表明:该种结构具有良好的延性和耗能性能,安全储备高;半刚框架和墙板协同工作良好;斜加劲肋的设置缓解了钢板沿拉力带方向的面外变形,提高了墙体的弹性屈曲倚载及初始刚度,减轻了滞回曲...     

Nonlinear analysis for dynamic lateral pile response

An analysis of pile lateral response to transient dynamic loading and to harmonic loading is presented allowing for nonlinear soil behavior, discontinuity conditions at the pile-soil interface and energy dissipation through different types of damping. Furthermore, the effect of neighbouring piles is taken into account for piles in a group. The validity of the approach was examined and a reasonable agreement with field tests and more rigorous solutions was found. Equivalent linear stiffness and damping parameters of single piles and interaction factors for approximate nonlinear analysis are presented.     

应用OpenSees模拟钢管混凝土不等跨框架抗震性能

基于一榀方钢管混凝土柱-H型钢梁不等跨平面框架的抗震性能试验,应用OpenSees有限元软件,模拟了低周反复荷载作用下框架的荷载-位移曲线,并对其抗震性能影响参数进行分析。研究结果表明:OpenSees中塑性铰纤维单元模拟栓焊连接的H型钢梁具有合理性。混凝土强度对框架的抗震性能影响较小,提高钢材强度可以有效提升框架结构的承载力和延性,其中Q345具有较高的性价比。柱截面宽厚比越小,框架承载力越高。轴压比增大会对框架抗震性能产生不利影响,工程中应避免出现高轴压比。在钢管混凝土不等跨框架结构设计中,钢梁跨度要综合考虑梁截面抗弯能力和梁柱线刚度比,其变梁异型中节点宜选择合适的梁高比。     

用机械阻抗法确定作业井架地锚桩的极限承载力

由于油田井下作业井架为一两腿落地的空间钢架结构,需要用绷绳作支撑,所以用于固定油田井下作业井架绷绳的地锚桩,其抗拔极限承载力的研究与确定对保证井下作业安全至关重要。本文用机械阻抗法对井下作业系统中地锚桩的极限抗拔载荷进行了测试与研究。采用瞬态激励法,用变时基技术分别测试了4种规格尺寸的油管桩和一种规格尺寸的水泥桩在瞬态激励下的速度信号,进行变时基传函分析得出动刚度,确定了极限承载力。结果分析表明,在大庆油田粘性土使用条件下,水泥桩的极限抗拔拉力很大,完全可以满足井下作业需要;不同尺寸油管桩的极限抗拔拉力差异较大,井下作业时应使用2．5m以上长度的油管桩。     

K型加强节点承载力及滞回性能分析

K型相贯节点区域容易出现主管管壁的局部屈曲与撕裂,可以采用主管与内套管之间夹层灌混凝土的方法进行加强。采用有限元软件ANSYS,对加强前后节点的静力极限承载力和滞回性能进行分析。结果表明:在主管与内套管之间夹层灌混凝土可有效改善节点的破坏模式,减小节点附近的应力集中问题,同时增强节点的刚度与承载力;无加强节点滞回曲线较为丰满,承载力下降相对平缓,但和加强节点比较,承载力相差明显;减小内套管的尺寸在一定程度上可以提高节点的极限承载力。     

海洋工程中桩基抗拔承载力研究

抗拔承载力是桩基设计的重要组成部分,随着海上风电场的建设,海洋工程中出现了越来越多需要提供足够抗拔力的抗拔桩。现有规范中桩基抗拔承载力的计算来源于对抗压承载力的修正,理论研究成果也仅限于半经验法及极限平衡算法,因此与实测数据存在较大差异。系统阐述现有的桩基抗拔承载力计算方法,并结合实际工程计算桩基的抗拔承载力,对比各种计算方法的结果发现:黏土中API规范法计算的桩基上拔承载力更接近实测值;Meyerhof和Das算法适合计算长径较小的桩;Chattopadhyay和Shanker算法适用于砂土中抗拔桩的计算;现有抗拔承载力计算方法忽略了黏土中的黏附力和负孔隙水压力,导致计算结果与实测值偏差较大。     

Experimental investigation on seismic behavior of single piles in sandy soil

This paper describes a quasi-static test program featuring lateral cyclic loading on single piles in sandy soil. The tests were conducted on 18 aluminum model piles with different cross sections and lateral load eccentricity ratios, e/d, (e is the lateral load eccentricity and d is the diameter of pile) of 0, 4 and 8, embedded in sand with a relative density of 30% and 70%. The experimental results include lateral load-displacement hysteresis loops, skeleton curves and energy dissipation curves. Lateral cap...     

Stiffened steel box columns. Part 2: Ductility evaluation

The purpose of this study is to evaluate the ultimate strength and ductility capacity of stiffened steel box columns failed by local and overall interaction instability under a constant compressive axial force and cyclic lateral loading. In a companion paper, a finite element formulation accounting for both geometrical and material non‐linearity was developed to obtain cyclic hysteretic behaviour of such columns. In this paper, the effect of loading patterns on the cyclic inelastic behaviour is first studied; then, a parametric study is carried out to investigate the effects of flange plate width–thickness ratio parameter, column slenderness ratio parameter, stiffener's equivalent slenderness ratio parameter, magnitude of axial load, and material type of stiffeners on the strength and ductility of the columns. Last but not least, empirical formulae of both the ultimate strength and ductility capacities are proposed for stiffened steel box columns, and the limit values of various parameters for the required ductility demand are also discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

沿深度强度增加软土中吸力锚循环承载力模型试验

采用分层底部真空预压技术,在模型试验箱内制备强度沿深度增加的模型试验土层;进而利用自行开发的电动伺服加载装置,在荷载控制方式下,针对水平破坏模式,进行两种直径的吸力锚在最佳系泊点受倾斜方向静荷载与循环荷载共同作用下的承载力模型试验。试验结果表明,循环荷载作用过程中锚的循环变形没有明显增加,导致锚破坏的是循环累积变形。强度沿深度增加软土和均一强度软土中吸力锚循环承载力的相对变化规律一致,当循环破坏次数为100时,循环承载力是静承载力的90%左右;当循环破坏次数增加至2 000时,循环承载力减小至静承载力的70%左右。锚径的变化只影响循环承载力的大小,不影响其相对变化。强度沿深度增加土层中的吸力锚,其循环荷载下竖向阻力弱化程度大于水平阻力弱化程度,这与均一强度土层中吸力锚受循环荷载作用时的性态一致。     

Evaluation of plastic energy dissipation capacity of steel beams suffering ductile fracture under various loading histories

The energy dissipation capacity of a structure is a very important index that indicates the structural performance in energy‐based seismic design. This index depends greatly on the structural components that form the whole system. Owing to the wide use of the strong‐column weak‐beam strength hierarchy where steel beams dissipate the majority of earthquake input energy to the structures, it is necessary to evaluate the energy dissipation capacity of the beams. Under cyclic loadings such as seismic effects, the damage of the beams accumulates. Therefore, loading history is known to be the most pivotal factor influencing the deformation capacity and energy dissipation capacity of the beams. Seismic loadings with significantly different characteristics are applied to structural beams during different types of earthquakes and there is no unique appropriate loading protocol that can represent all types of seismic loadings. This paper focuses on the effects of various loading histories on the deformation capacity and energy dissipation capacity of the beams. Cyclic loading tests of steel beams were performed. In addition, some experimental results from published tests were also collected to form a database. This database was used to evaluate the energy dissipation capacity of steel beams suffering from ductile fracture under various loading histories. Copyright © 2011 John Wiley & Sons, Ltd.     

深水高桩嵌岩桥墩抗撞能力分析

以2007年6月15日广东九江大桥船撞倒塌事故中被撞深水高桩嵌岩桥墩为研究对象,采用更新拉格朗日列式考虑结构几何非线性,Hognestad模型和Mander模型分别模拟无约束和受约束混凝土,理想弹塑性模型模拟钢筋作用;考虑桩基和周围介质的非线性作用,采用P-Y、T-Z和Q-Z弹簧模拟计算了单个高桩桥墩的抗撞能力,揭示了桩顶与承台结合处截面为深水高桩桥墩的薄弱环节。在此基础上,分析了桩基直径、河床冲刷与淤积程度、桩基倾斜角度、桩身配筋率、水下砂土内摩擦角对深水高桩桥墩抗撞能力的影响。     

钢管混凝土柱-钢筋混凝土环扁梁节点性能试验研究

本文进行了钢管混凝土柱-钢筋混凝土环扁梁节点的静载和低周反复荷载试验,分析了节点的破坏形态、承载能力、延性、耗能能力等性能。本次试验结果显示,钢管混凝土核心区未发生屈服破坏情况,塑性铰产生于扁梁和环扁梁交界处(静载)和环扁梁上(低周反复荷载),环扁梁与钢管混凝土柱间未发生明显滑移现象;试验节点连接可靠,具有较好的承载力、延性以及耗能能力,能够满足延性抗震设计要求。     

Nonlinear lateral interaction in pile dynamics

A model for pile lateral response to transient dynamic loading and to harmonic loading is presented allowing for nonlinear soil behaviour, discontinuity conditions at the pile-soil interface and energy dissipation through different types of damping. The approach is used to establish equivalent linear stiffness and damping parameters of single piles as well as dynamic interaction factors for approximate nonlinear analysis of pile groups. The applicability of these parameters to the pile-group analysis was examined, and a reasonable agreement with the direct analysis was found. The superposition technique may be used to analyze the response of small pile groups. Also, the dynamic stiffness of pile groups is greatly affected by both the nonlinear behavior of the soil and the slippage and gapping between the pile and soil. For a basic range of soil and pile parameters, equivalent linear stiffness and damping parameters of single piles and interaction factors for approximate nonlinear analysis are provided.     

Factors affecting shear modulus degradation of cement treated clay

Cement stabilization is often used to improve the bearing capacity and compressibility of soft clays. The present paper aims to investigate the shear modulus degradation of cement treated clay during cyclic loading. A series of cyclic triaxial test was conducted on artificially cement treated marine clay to study the factors affecting the shear modulus degradation. The parameters considered for the study are cement content (2.5–7.5%), curing days (7–28), cyclic shear strain amplitude (0.3–1%), number of loading cycles (1–100) and loading frequency (0.1–0.5 Hz). As in the case of natural clays, cement treated clays exhibit stiffness degradation which depends on mix ratio, curing days and loading conditions. The results show that the shear modulus degradation decreases with increase in the shear strain amplitude, cement content and curing days. It is also noted that irrespective of the mix ratio and curing conditions, the degradation decreases with increase in loading frequency. An empirical relationship is proposed to predict the shear modulus degradation based on Idriss׳s degradation model. The performance of the proposed empirical model is validated with the present experimental results.     

Low cyclic fatigue and hysteretic behavior of U‐shaped steel dampers for seismically isolated buildings under dynamic cyclic loadings

Energy dissipation devices are necessary for base‐isolated buildings to control the deformation in the isolation system and to dissipate the earthquake‐induced energy. U‐shaped steel dampers (also known as U‐dampers) dissipate energy through plastic deformation of specially designed U‐shaped steel elements. This type of device can be installed at several locations in the isolation system. U‐dampers have been widely used in Japan for different types of isolated structures, such as hospitals, plants and residential buildings, since the 1995 Kobe Earthquake. Previous research has used static tests to estimate the performance of U‐dampers. However, the ultimate plastic deformation capacities and hysteretic behaviors of full‐scale U‐dampers under dynamic excitations still remain unclear. In addition, it is unclear whether the initial temperature has an effect on the hysteretic behavior and plastic deformation capacity of U‐dampers. In this paper, two series of dynamic loading tests of U‐dampers were conducted to evaluate the issues described earlier. The major findings of the study are (i) the loading speed has little effect on the plastic deformation capacity of U‐dampers; (ii) method to evaluate the ultimate plastic deformation capacities of U‐shaped steel dampers of different sizes is established using a Manson–Coffin relation‐based equation that is based on the peak‐to‐peak horizontal shear angle γ_t, which is defined as the lateral deformation amplitude (peak‐to‐peak amplitude) divided by the height of the dampers; (iii) the loading rate and the initial temperature have a minimal effect on the hysteretic behavior of the U‐dampers; and (iv) a bilinear model is proposed to simulate the force‐deformation relationships of the U‐dampers. Copyright © 2014 John Wiley & Sons, Ltd.