An experimental investigation on the bearing failure load of glass fibre/epoxy laminates

This paper deals with an experimental investigation on the bearing failure load of glass fibre/epoxy (GFRP) laminates. The effects of fibre-to-load inclination angle and laminate stacking sequence on the bearing load capacity have been determined experimentally on two different type of laminates: unidirectional and bi-directional (cross-ply). Significant reductions in bearing failure load when fibre inclination angle increases are highlighted. Bearing design formulas are also proposed based on the results of the experiments.     

Development of a tool for the structural design of the vertical load‐bearing capacity of unreinforced masonry

Before the introduction of EC 6, simple codes permitted masonry to be designed manually. The simplified procedure according to EN 1996‐3 still allows manual design, but its application is restricted. Therefore, a more laborious design according to EN 1996‐1‐1 is often required. This article presents a newly developed software tool, which facilitates the structural design of the vertical load‐bearing capacity of unreinforced masonry according to EN 1996‐1‐1. The tool is intuitive to use and has been developed based on experience from working in the field. The tool assists the planner in making decisions during the masonry design process. This article describes and explains the implemented, theoretical assumptions as well as the software tool N_Rd‐Pro‐Tool itself. This software tool facilitates simple, clear und transparent structural design of the vertical load bearing capacity of unreinforced masonry.     

On the notch effect in load bearing capacity,apparent fracture toughness and fracture mechanisms of polymer PMMA,aluminium alloy Al7075-T651 and structural steels S275JR and S355J2

This paper presents an analysis of the notch effect in the load bearing capacity, the apparent fracture toughness and the fracture mechanisms of four different materials: polymer PMMA, aluminium alloy Al7075-T651, and structural steels S275JR and S355J2 within their corresponding ductile-to-brittle transition zone.Concerning the load bearing capacity and the apparent fracture toughness, a clear notch effect has been observed. In the case of the apparent fracture toughness, this has been adequately predicted here through the Theory of Critical Distances.As for fracture mechanisms, it is shown how these progressively change with the notch radius, from basically brittle ones in cracked conditions, to non-linear mechanisms observed for higher notch radii. This evolution has been observed in the four analysed materials and, in all cases, has justified the corresponding consequences of the notch effect on both the load bearing capacity and the apparent fracture toughness.     

分舱板对海上风机混凝土筒型基础承载模式的影响

出于拖航稳性、施工下沉、精细调平及结构强度的原因,混凝土筒型基础筒内须设置分舱板。一般设计时不考虑分舱板对承载力的作用,实际上分舱板的存在对于筒型基础的承载模式和承载能力本身是有一定的影响。通过数值模型定量对比带分舱板和无分舱板两种混凝土筒型基础的承载特性,得到分舱板对承载模式的影响。结果显示带分舱板的基础与无分舱板的基础承载模式基本相似,当荷载较小时分舱板对承载力的作用不明显,因此基础设计时可以不考虑分舱板的作用,但随着荷载的增加,分舱板对承载力的提高作用逐渐显现,当达到极限承载时,基础竖向承载力提高6.9%,水平承载力提高18.3%,弯矩承载力提高16.5%,在极端条件下,带分舱板的混凝土筒型基础将具有更大的安全储备。     

Interaction of interface delamination and plasticity in tensile steel members reinforced by CFRP plates

This paper presents experimental and numerical results related to double shear lap tests performed on steel specimens reinforced using CFRP plates. These tests have been simulated taking into account the elastic–plastic behavior of the steel and the delamination between steel and CFRP by means of a cohesive approach. The results obtained are discussed in terms of: (i) maximum load bearing capacity, (ii) minimum bond length in order to exploit the maximum load bearing capacity, (iii) brittle to ductile transition of the interface failure (iv) combination of interface delamination and plastic deformation of the steel. Design formulas for the definition of the minimum bond length and the load bearing capacity of the joint are validated.     

波形钢板剪力墙及组合墙抗剪承载力研究

为研究波形钢板剪力墙及其组合墙在水平荷载作用下的破坏形态、受力性能以及抗剪承载力计算方法,设计了4个波形钢板剪力墙及其组合墙试件,进行了低周往复加载试验,并采用ABAQUS有限元软件对24个波形钢板剪力墙及其组合墙模型进行了模拟分析。研究结果表明:波形钢板剪力墙具有较好的变形能力,波形钢板能有效抑制混凝土裂缝的发展,并与混凝土具有很好的界面粘结力,水平波形钢板剪力墙较易在约束边缘构件底部形成塑性铰;波形钢板剪力墙及其组合墙具有较好的承载能力、延性和耗能能力,且承载力下降缓慢; ABAQUS有限元软件能较好地模拟试验,模拟结果与试验结果吻合较好,有限元计算结果表明:承载力随波形钢板的厚度和波角的增加有少量增加,此外,波形钢板-混凝土组合剪力墙承载力随剪跨比的增加而降低,竖向波形钢板剪力墙的抗侧承载力性能与水平波形钢板剪力墙的基本相同;该文提出的波形钢板剪力墙及其组合墙抗剪承载力计算公式,计算值与试验值吻合良好,可为设计和工程实际参考; H型钢柱对波形钢板-混凝土组合剪力墙的抗剪承载力贡献最小,竖向波形钢板对组合墙剪力分担率大于水平波形钢板的,竖向波形钢板更有利于提升组合墙的承载性能。     

建筑结构构件基于性能的抗爆设计方法

在我国,基于性能的设计方法已运用于工程结构抗震设计,但尚没有运用在结构抗爆设计。该文将基于性能的设计方法引入结构抗爆领域,提出了基于性能的结构抗爆设计方法,明确了基于性能的抗爆设计中的关键问题,给出了设计思路与步骤。在此基础上,以RC柱为研究对象,以轴心受压承载力损失为性能水平参数,划分了3个等级性能水平;根据典型的爆炸场景,确定爆炸的不同烈度等级,计算出RC柱承受的荷载;针对不同类别的建筑,确定两个水准的抗爆性能目标;结合现有RC柱承载力损失的研究成果,分析不同爆炸烈度下的RC柱的承载力损失,提出RC柱基于承载力损失的性能设计方法;基于确定的性能目标和设计方法,提出RC柱基于性能的抗爆设计步骤;最后,给出了RC柱基于性能的抗爆设计的算例。     

Test on pultruded GFRP I-section under web crippling

This paper presents the details of experimental and numerical research study on web crippling property of pultruded GFRP I-section under concentrated web crippling loadings. A total of 12 pultruded GFRP I-section with different loading conditions and bearing lengths was tested. The experimental scheme, failure modes and load–displacement curves were also presented. The investigation was focused on the effects of different loading condition and bearing length on web crippling ultimate capacity and ductility of pultruded GFRP I-section. The failure mode comprised longitudinal bending main crack, bending wrinkling cracks and shear cracks. Specimens with interior bearing load had slightly higher ultimate strength and greater deformation capacity than those of specimens with end bearing load. The ultimate strengths usually decreased with the increase of the bearing length except IG condition. Finite element models were developed to numerically simulate the tests performed in the experimental investigations by using commercial ABAQUS software. Based on the results of the parametric study, a number of design formulas proposed in this paper can be successfully employed as a design rule for predicting web crippling ultimate capacity of pultruded GFRP I-section under four loading and boundary conditions by using single parameter analysis.     

Experimentelle und analytische Untersuchung des out‐of‐plane‐Verhaltens von unbewehrten Mauerwerkswänden unter Erdbebenbelastung

Experimental and analytical investigation of the seismic out‐of‐plane behavior of unreinforced masonry walls In addition to the vertical and horizontal load‐bearing in‐plane, masonry must also withstand out‐of‐plane loads that occur in earthquake scenarios. The out‐of‐plane behavior of unreinforced masonry walls depends on a variety of parameters and is very complex due to the strong non‐linearity. Current design methods in German codes and various international codes have not been explicitly developed for out‐of‐plane behavior and contain considerable conservatism. In the present work, shaking‐table experiments with heat‐insulating masonry walls have been conducted to investigate the out‐of‐plane behavior of vertical spanning unreinforced masonry walls. As shown in previous numerical investigations, important parameters are neglected in existing design and analysis models and the out‐of‐plane capacity is underestimated significantly. In the conducted experiments the results of these numerical investigations are verified. Furthermore, the development of an analytical design model to determine the force‐displacement relationship and the out‐of‐plane load‐bearing capacity considering all significant parameters is presented.     

Influence of process induced defects on the failure of composite T-joint specimens

An experimental investigation of the failure load of T-joint structures has been undertaken, with a focus on the influence of process induced defects within the deltoid area. Static pull-off tension tests have been conducted for a comparative assessment. An extensive literature review on the subject to place is also presented. The role of the deltoid area in stabilizing the primary load bearing plies and minimising the volume fraction reduction in the off-axis plies is critical to maximise the failure load and minimise the performance variability of the T-joint structures. A deltoid area reduction of 25%, with no change in the external geometry, yielded a similar mechanical performance to the nominal baseline specimen but with increased variability. However, a reduction of 50% in the deltoid area yielded a strength reduction of 33%. The findings of this study suggest that the reduction in the deltoid area can be tolerated within certain limits.     

Influence of material spatial variability on required safety factors for masonry walls in compression

Since masonry is one of the oldest and most traditional construction types, corresponding safety concepts are usually based on experience instead of being calibrated by structural reliability methods. For this reason, reliability analyses of masonry structures are needed to check if safety factors should be adjusted. Masonry is a non‐homogenous material. Because of that, it is very important to consider the spatial variability of material properties when assessing the reliability of masonry walls. Therefore, it is useful to know if and to what extent spatial variability increases or decreases the reliability of masonry walls and the required safety factors. The influence of spatial variability depends on the length of a wall due to the capability of load redistribution. Also, it is affected by the governing failure mode, which depends on the slenderness of the wall, and can be local compression or stability failure. This paper demonstrates the effect of spatial variability on the load‐bearing capacity of masonry walls in terms of mean value, scatter and design value. For this purpose, walls of varying length and slenderness were analysed with and without the consideration of spatial variability by performing Monte Carlo simulations. Based upon that, safety factors were determined which are required to meet the target reliability defined by EN 1990.     

基于振动测试参数的井架钢结构极限承载力预测

提出了基于振动测试参数预测井架钢结构极限承载力的两种新方法。第一种方法是针对井架钢结构的结构形式和受力特征,将其简化为简支梁,由载荷与振动频率之间的关系,推导出振动频率直接确定极限承载力的简易表达式。该方法简单易行,不需要建立系统的模型。第二种方法是应用一阶搜索优化算法修正动力有限元模型,然后进行线性屈曲、几何非线性和双重非线性分析从而确定井架钢结构的极限承载力,这种方法计算复杂些,但提高了预测准确度。最后利用近似平稳随机激励,对某型号井架钢结构进行了振动参数测试,分别应用这两种方法对极限承载力进行了预测。结果表明这两种基于动力参数的预测值相差不大,均能真实预测井架钢结构的极限承载性能,为复杂承载钢结构的极限承载力预测和安全评估开辟了新途径。     

DX旋挖挤扩灌注桩不同承力盘数性能对比研究

通过数值模拟计算,对DX单桩的沉降和承载力特性进行了研究,分析了在相同的桩长、桩径等条件下直孔桩、两个承力盘DX桩和三个承力盘DX桩的性能差异。沉降方面,在桩顶荷载增加相同的情况下,两个承力盘DX桩对桩顶沉降的控制明显强于普通直孔桩的控制效果,三个承力盘DX桩则进一步优越于两个承力盘DX桩。承载力方面,两个承力盘DX单桩的抗压承载力大约为直孔桩的1.5倍,而三个承力盘DX桩又进一步优越,大约为两个承力盘DX桩的1.2倍。     

Tragfähigkeitstafeln für unbewehrtes Mauerwerk nach DIN EN 1996‐3/NA:2019‐12

Load‐bearing capacity tables for unreinforced masonry according to DIN EN 1996‐3/NA:2019‐12 Practical design aids are important tools in the day‐to‐day business of structural design. The design of primarily vertically loaded masonry walls in usual building construction can be carried out with the help of so‐called load‐bearing capacity tables. A table value is read off exclusively as a function of the geometric conditions, which – multiplied by the masonry compressive strength – results in the load‐bearing capacity of the wall for cold design and in case of fire. By comparing the acting and resisting force, the verification of structural design can be provided in a simple and yet economical form. The bearing capacity tables based on the simplified calculation methods according to DIN EN 1996‐3/NA:2019‐12 [1], [2] and DIN EN 1996‐1‐2/NA:2013‐06 [3], [4] are presented in this paper. Compared to the previous edition of Part 3 of Eurocode 6, the extended scope of application is taken into account, as well as the normative changes to the construction method with partially supported slabs.     

Testing of anchorages in concrete under dynamic tensile loading

The tensile dynamic behaviour of anchors in concrete has been experimentally investigated by employing Hopkinson bar techniques. Dynamic pull-out tests with two anchor size diameters have been performed, concrete cone breakout failure has been predominantly induced, and full force-displacement curves have been obtained. The test results show that properly post-installed anchors can achieve the same load bearing capacity as the cast-in-place ones. It has also been verified that the three different types of anchors tested (with chemical adhesive, undercut, and headed studs) can develop comparable failure loads under similar embedment depths. Test results have demonstrated that force-displacement diagrams for dynamic loading tend in general to lie well above the corresponding static ones, i.e. additional ductility is available. Comparisons with predictions from design formulae have been conducted.     

The Specific Load Capacity of Radial-Flux Radial Magnetic Bearings

This paper addresses the specific load capacity of radial-flux radial magnetic bearings and provides some insight into what values are achievable and how these values depend on various parameters such as air-gap thickness, allowable temperature rise in the coils, certain heat-transfer coefficients, and certain de-rating factors associated with the distribution of the bearing load in time and space. We define the specific load capacity of a radial magnetic bearing as the ratio of the largest sustainable root-mean-square radial force to the total self-weight of all parts necessary for the electromagnetic function of the bearing. We show that it is possible to push the limit of the specific load capacity of naturally cooled bearings up to around 35:1 with present-day materials, for a wide range of practical bearing sizes. This figure is still very small compared with the capacity of mechanical bearings.     

海上风电大尺度顶承式筒型基础承载力特性有限元分析

与现有的海上风电传统筒型基础相比,新型筒型基础——大尺度筒顶承载式筒型基础凭借其特有的宽浅式筒顶承载模式和更大的承载能力已经越来越受到关注。所以,合理地建立此类新型筒基基础的极限承载力和地基的破坏包络面,分析其承载特性,对于该基础结构设计和实际应用过程中的安全性和稳定性研究起着重要的作用。通过大型有限元软件ABAQUS,利用位移加载控制方法﹑Swipe试验加载方式和荷载-位移联合控制搜索方式,对5MW海上风机大尺度筒型基础的两种典型形式进行承载力特性弹塑性分析和对比,得出在单方向荷载单独作用下,弧线型筒型基础的极限承载力比直线型高出6%~8%,在荷载组合作用下,弧线型筒基比直线型有更广泛的三维破坏包络面,即弧线型筒基在各个方向上的极限破坏值,都要比直线型的要大,表现出更好的承载性能;同时对两种大尺度筒型基础的破坏模式进行分析。研究结果为进一步的基础结构选型和优化设计提供参考依据。     

Reliability strength design through inverse distributions-exponential and Weibull cases

This paper illustrates the inverse reliability design techniques for exponential and Weibull stress-strength models. Expressions for factor of safety, mean strength and its variability have been derived for a given range of target reliability and external load conditions. In the case of exponential models a global solution has been found out whereas in the case of the Weibull model only some specific cases have been considered. The difficulty in obtaining a global solution in the Weibull model has been discussed with possible methods to attain it.     

黏土中负压桶形基础下沉与承载特性试验及有限元分析研究

负压桶形基础是一种适宜于软土地基上的新型港口水工建筑物,在深海区域静水压力有助于桶形基础压入至海床内预定深度而完成安装,而在水深较浅的滩海则可能出现负压不足、土塞等作用影响桶形基础下沉,导致承载力不能满足设计要求等问题。此外对于桶形基础竖向承载力的计算没有现成的规范可参考,桶裙、顶板的荷载承担特性,桶土相互作用等问题也鲜有研究。因此,通过室内模型试验研究黏土中不同负压下桶形基础的下沉特性和竖向承载能力,分析下沉负压与土塞的关系,提出软黏土中桶形基础下沉就位的工程措施。并通过试验结果验证的有限元计算模型,研究竖向荷载作用下桶形基础竖向承载特性,得出适用于桶形基础竖向承载力的计算方法,为桶形基础竖向承载力的设计与计算提供依据。     

Micro Air Bearing for a Microturbine

The dynamic characteristics of air bearings for microsystems are investigated. Micro air bearings investigated in this paper include journal and thrust air bearings. The dynamic thrust air bearing employs spiral groove configuration, and the dynamic journal air bearing is formed by a plain circular trench with a short journal length of L, a diameter of D, and a narrow radial clearance of C. The optimum values of the bearing system are explored and presented in terms of maximum load carrying capacity. Stability analysis shows that motion stability and load capacity impose contradictive requirements on the groove pattern of the thrust bearing. Shock tolerance analysis shows that the shock tolerance of the air bearing system increases with the bearing number, rotational speed, bearing aspect ratio of L/D, and initial equilibrium eccentricity ratio epsiv₀. A prototype of the turbine device has been realized using the recommended bearing configurations. The primary tests of the prototypes demonstrate that a stable operation of 15 000 rpm has been achieved.