Response of pierced fixed corrugated steel roofing systems subjected to wind loads

The low-cycle fatigue response of corrugated metal roof cladding to fluctuating wind loads was studied by subjecting cladding specimens to a series of static, cyclic and simulated “real” cyclonic wind loads using a Pressure Loading Actuator (PLA), and measuring fastener response using a x–y–z load cell. The overall performance of cladding including crack initiation, propagation and patterns, and cycles to failure was found to be similar to previous tests that used line-loads to simulate wind pressure. The reaction at a fastener to spatially varying pressures was assessed by analysing the influence coefficients, to show that it is predominantly influenced by local loads acting along the screwed crest. In addition, the response of roofing specimens subjected to fluctuating cyclonic wind pressures replicated failures observed in the field. The fastener response varied with the load level and the response spectrum followed the wind load spectrum up to 5 Hz even with deformation and cracking of the cladding showing that these higher frequency wind “load cycles” were transferred into the supporting structure via the fastener.     

Plastic collapse analysis of CFRP strengthened and rehabilitated degraded steel welded RHS beams subjected to combined bending and bearing

Innovative techniques using the lightweight, high strength and corrosion resistance of carbon fibres reinforced polymers (CFRP) composites have been proposed in a recent paper by the author. The present paper presents plastic mechanism analyses of CFRP strengthened and rehabilitated rectangular hollow sections (RHS) under quasi-static large deformation 3-point bending. The strengthening series was for un-degraded RHS beams from the manufacturer reinforced using externally wrapped CFRP sheets. The rehabilitation series was for artificially degraded RHS beams repaired using externally wrapped sheets or bonded plates. The main parameters examined in this paper were the section type, section and member slenderness and the type and number of the CFRP sheets. Three different phases of plastic deformation were observed during the test, namely, denting, denting and bending, and structural collapse. Two methods were used to model the large plastic deformation measured during plastic collapse of the composite RHS beams, namely, equilibrium and energy methods of analysis. It was found that the predicted collapse curves using the equilibrium approach were in good agreement with the measured curves for the bare and composite specimens examined in the strengthening and rehabilitation series, particularly for the latter series. This may be caused by a number of factors such as the specimens in the rehabilitations series were comparatively longer and had larger bearing width. The energy theory was found to have deficiencies represented in the simplified linear polygon shape adopted for the mechanism geometry, and adopting the plastic 1/2-wave length used for I-sections, as well as the use of a simplified formulae to describe the relationship between the local denting displacement and global bending rotation angle for the three phases of deformation observed during the test.     

Structural sensitivity of circular sewer liners to geometrical imperfections

The impact of geometrical defects of liners on their structural performance has been examined in this article. The major common imperfections, such as gap, ovality and wavy imperfections, have been taken into consideration. In the first step, the influence of separate imperfections is presented. Then, the combination of coinciding defects is examined. The formula for weighted influence of individual defects has been found, based on a wide range of FEM calculations and statistical interpretation. All the examinations performed led to improving the general formula for critical groundwater pressure.     

Non-linear analysis of perforated steel plates subjected to localised symmetrical load

Although the literature contains a number of studies which have been developed to describe the non-linear behaviour of ordinary plates, few works are available on perforated plates, and studies on non-linear behaviour of perforated plates under localised symmetrical load are not studied in depth. The aim of this paper is to provide some insights into the elasto-plastic behaviour of plate girder web panels with circular holes under localised symmetrical load.Numerical analyses of square and rectangular perforated plates with centred and eccentric holes were developed. Results provide new insights into post-critical mechanisms in perforated plates subjected to localised loads when the length of the symmetrical compressive load, hole diameter and steel yield limit vary. An increase in the critical slenderness of the plate (a value at which transition from elastic to plastic collapse occurs) and a corresponding reduction in the elastic critical load occur when the dimensions of the hole increase. A further increase in the critical slenderness occurs when the length of the localised load is reduced. High-performance steel may be subject to buckling with a lower possibility of post-critical mechanisms: a reduction in critical slenderness occurs when the steel grade increases. Lastly, numerical analyses of slender and thick perforated plates were developed and their results compared.     

Performance of an unprotected steel structure subjected to repeated fire at a firefighter training facility

An evaluation of a single story unprotected steel structure exposed to repeated fire during the training of fire fighters is described. Temperatures are monitored on the structure using resistance temperature detectors connected to a data acquisition system. Temperatures of up to 384 °C are measured in the steel of the structures, which are below levels likely to cause much degradation in stiffness or strength. Uniform heating of the columns was shown to result in minimal stresses in the structure as the columns were relatively free to deform axially. Differential temperatures, however, where one side of the member is heated by a greater amount than the opposite side of the member, resulted in stresses calculated using an elastic analysis, up to 16 times greater than the yield strength and can thus explain large permanent curvatures observed in the columns. Coupon tests on steel samples from the columns exposed to repeated fire showed some hardening of the steel, possibility attributed to the plastic deformations in the columns, although the ultimate strain in the material was not greatly affected. Based on the monitoring and analysis, no aspects of the structure are considered to present an immediate hazard to the safety of the users. However, without improved cooling, plastic deformation of some members is expected.     

Prediction to nonlinear behavior of steel frames subjected to fire

A new approach is presented for analysis of nonlinear behavior of steel frames subjected to fire. The material and geometrical nonlinearity as well as the non-uniform profile of temperature across section of frame members are taken into account. Thermal forces induced by temperature variation are also considered. The elasto-plastic stiffness equation of elements is established by using the generalized Clough model. The analysis of strutures subjected to fire is converted to analysis of structures subjected to unbalanced forces induced by temperature increment. Then a procedure to calculate the nonlinear response and ultimate load of steel frames exposed to fire is proposed.

For verifying the validity of the approach proposed, tests on two large-scale models of single-story two-bay steel frames are conducted in gas furnace to simulate fire. The temperature elevation and deformation response of the models due to fire are measured. Good agreements between the results measured and calculated are demonstrated on the behavior of the models exposed to fire.     

Experimental behavior of steel beam-columns subjected to fire-induced thermal gradients

Fire tests were performed to investigate the mechanics and capacity of steel beam-columns that develop a thermal gradient through their depth when exposed to fire. Wide-flanged specimens were loaded axially and tested vertically in a furnace recently commissioned at Michigan State University. The placement of insulation simulated a realistic three-sided heating scenario such as that experienced by a column on the perimeter of a building frame. Specimens were tested with several combinations of load level, fire scenario, and direction of the thermal gradient (which dictates the direction of bending). The different combinations of tested parameters had a significant influence on the fire response of these columns, which all failed by full section yielding due to a combination of axial load (P) and moment (M). These columns developed bending moments in response to through-depth thermal gradients as well as a moment reversal due to a shift in the section’s center of stiffness. The plastic resistance to combinations of axial load and moment was also affected by the thermal gradients such that the critical section, located in the hottest region along the column length, was where moment was the smallest (not the largest, as would be intuitively expected). The experiments and computer models showed good agreement with the predicted demands (i.e. bending moment reversal) and capacity (i.e. changes in the plastic P-M capacity).     

Performance of CFST column to steel beam joints subjected to simulated fire including the cooling phase

This paper presents the experimental results of three concrete filled steel tube (CFST) column to steel beam joints with reinforced concrete (RC) slabs under combined loading and fire including the heating and cooling phases. The test parameters include heating time and thickness of the fire protection material. Temperatures and deformations of the joint specimens during the heating, cooling and post-fire phases were measured. A finite element analysis (FEA) model to simulate the action of a CFST column to steel beam joint under combined loading and fire is developed. The FEM model was verified by the experimental results. The FEA model is then used to analyse the temperature distribution in the heating and cooling phases. The moment versus relative rotation angle between the CFST column and the beam under combined loading and fire including the heating and cooling phases is also discussed.     

Analysis of accelerated failure times of rehabilitation liners subjected to a constant or variable pressure

Pipe rehabilitation liners are often installed in host pipes that lie below the water table. As such, they are subjected to external hydrostatic pressure. The external pressure leads to early deformation in the liners, which could ultimately lead to its failing or buckling before its expected service lifetime is achieved. Experiments involving long term buckling behavior of liners are typically accelerated lifetime testing procedures. In an accelerated testing procedure involving type I censoring a liner is often subjected to a constant external hydrostatic pressure and observed until it fails or for a certain time, t whichever occurs first. Liners that do not fail at time t are deemed censored observations. While a constant pressure is convenient to use in experimental situations, in reality pressure fluctuates under soil conditions over time depending on the water table. It is, therefore, desirable to study and compare accelerated life testing models under variable and constant pressure. Statistical analysis of data on accelerated time till buckling is based on the maximum likelihood procedure for censored or uncensored observations. It is known that maximum likelihood estimates of model parameters are asymptotically (for very large samples) unbiased and normally distributed. In practice, however, it is important to determine the applicability of these asymptotic assumptions for relatively small samples with censored observations under constant and variable pressure.In this study, the accelerated Weibull model for time till buckling under constant pressure is extended to variable pressure and the applicability of the model is investigated by simulation for different sample sizes and different levels of censoring. Data were generated through computer simulation and estimates of parameters were obtained using the maximum likelihood and Newton–Raphson methods. Results on the statistical properties (concerning distribution and bias) of model parameter estimates were used to make inference about the applicability of the accelerated life testing procedure for relatively small censored samples encountered in practice. Expressions from the model are given for computing the probability of survival until a given time or the survival time for a given probability of survival.     

Mechanical analysis of circular liners with particular reference to composite supports. For example, liners consisting of shotcrete and steel sets

This paper describes a methodology for the mechanical analysis of composite supports, such as liners consisting of shotcrete and steel sets. The methodology presented here is based on an established technique of structural analysis commonly referred to as the ‘equivalent section’ approach. This technique consists in treating the composite section of a straight beam as a homogenized section of equivalent mechanical properties. The equations presented in this paper have been derived from application of the theory of elastic shells (or curved beams) and therefore are more appropriate for the analysis of circular tunnel liners. The proposed methodology for the design of liners is based on the construction of capacity diagrams, another established technique of structural analysis and concrete design that can be conveniently extended to the analysis of composite sections for tunnel liners. When applying the theory of elastic shells to derive the equations that conform to the proposed methodology, the problem of determining the mechanical response of semi-circular arches treated with the theory of thin and thick formulations has been re-visited. Observations of practical interest arising from the comparison of results obtained with both approaches are discussed.     

Combining EPS geofoam with geocell to reduce buried pipe loads and trench surface rutting

This paper reports full scale experiments, under simulated heavy traffic, of geocell and EPS (expanded polystyrene) geofoam block inclusions to mitigate the pressure on, and deformation of, shallow buried, high density polyethylene (HDPE) flexible pipes while limiting surface settlement of the backfilled trench. Geocell of two pocket sizes and EPS of different widths and thickness are used. Soil surface settlement, pipe deformation and transferred pressure onto the pipe are evaluated under repeated loading. The results show that using EPS may sometimes lead to larger surface settlements but can alleviate pressure onto the pipe and, consequentially, result in lower pipe deformations. This benefit is enhanced by the use of geocell reinforcement, which not only significantly opposes any EPS-induced increase in soil surface settlement, but further reduces the pressure on the pipe and its deformation to within allowable limits. For example, by using EPS geofoam with width 0.3 times, and thickness 1.5 times, pipe diameter simultaneously with geocell reinforcement with a pocket size 110 × 110 mm² soil surface settlement, pipe deformation and transferred pressure around a shallow pipe were respectively, 0.60, 0.52 and 0.46 times those obtained in the fully unreinforced buried pipe system. This would represent a desirable and allowable arrangement.     

Dynamic buckling of anchored steel tanks subjected to horizontal earthquake excitation

We investigate dynamic buckling of aboveground steel tanks with conical roofs and anchored to the foundation, subjected to horizontal components of real earthquake records. The study attempts to estimate the critical horizontal peak ground acceleration (Critical PGA), which induces elastic buckling at the top of the cylindrical shell, for the impulsive hydrodynamic response of the tank-liquid system. Finite elements models of three cone roof tanks with height to diameter ratios (H/D) of 0.40, 0.63 and 0.95 and with a liquid level of 90% of the height of the cylinder were used in this study. The tank models were subjected to accelerograms recorded during the 1986 El Salvador and 1966 Parkfield earthquakes, and dynamic buckling computations (including material and geometric non-linearity) were carried out using the finite element package ABAQUS. For the El Salvador accelerogram, the critical PGA for buckling at the top of the cylindrical shell decreased with the H/D ratio of the tank, while similar critical PGAs regardless of the H/D ratio were obtained for the tanks subjected to the Parkfield accelerogram. The elastic buckling at the top occurred as a critical state for the medium height and tallest models regardless of the accelerogram considered, because plasticity was reached for a PGA larger than the critical PGA. For the shortest model (H/D=0.40), depending on the accelerogram considered, plasticity was reached at the shell before buckling at the top of the shell.     

Non-linear thermoelastic analysis of steel arch members subjected to fire

This paper addresses the non-linear thermoelastic behaviour of steel arches acted on by a sustained uniformly distributed load, when subjected to elevated temperatures as caused by fire. The steel arch is restrained at its two ends by elastic translational springs in both the horizontal and vertical directions, as well as by counterpart elastic rotational springs, which simulate a generic semi-rigid connection, or restraint by other members in a frame, or when the arch acts as a large-span roofing element supported and restrained by columns. The study is restricted to the thermoelastic structural response of the steel material and therefore the high-temperature effects of catenary action and yielding are not considered; however the important effect of the second order term in the strain–displacement relationship is included. In order to model structural response of an elastically supported steel arch under thermal loading, an alternative geometric formulation is needed since the tangential and radial deflections and rotations as well as the axial compressive force in the member are substantial at the early stage of the fire. The formulation presented in this paper takes into account the degradation of the stiffness of the steel arch prior to yielding at elevated temperatures and it is argued that there are many situations for which analyses of a real fire situation in the thermoelastic range are valid. It is shown that the proposed model agrees well with independent solutions obtained using finite element analyses. The proposed model has significant potential for use in the analysis of restrained steel arches subjected to uniformly distributed load at elevated temperatures, such as large-span roofs and can provide a foundation for codified procedures in design.     

复合荷载作用下钢梁弯扭屈曲临界弯矩研究

基于由完备的复合荷载作用下钢梁弯扭屈曲总势能方程推导的平衡微分方程,采用Galerkin法推导了考虑横向荷载作用点高度和横截面不对称参数的复合荷载作用下钢梁弯扭屈曲临界弯矩的计算式,建立了等效弯矩系数的计算理论。依据等效弯矩系数的计算理论确定了7种常见工况的等效弯矩系数理论计算式并给出了6种特殊工况的Cb实用计算式,从Cb计算式的计算精度、适用范围和形式三个方面对国内外文献的Cb计算式进行对比,验证了等效弯矩系数理论的正确性并提出了Cb计算式的选用准则,最后通过2个数值算例验证了复合荷载作用下钢梁临界弯矩Mcr计算式的正确性和Cb计算式选用准则的合理性。结果表明：考虑了横向荷载作用点高度和横截面不对称参数的复合荷载作用下钢梁弯扭屈曲临界弯矩的计算式形式简单、物理意义明确且便于计算;Cb实用计算式的适用范围广且精度高;等效弯矩系数的选用准则合理、有效。     

锤击荷载作用下大直径钢管群桩的动力特性分析

上海某机械厂有一大直径钢管桩,用于所生产柴油打桩锤出厂前的试用。目前试桩已不满足新生产大吨位柴油打桩锤的试打要求,因此拟增加8根短桩与试桩组成群桩。由于锤击荷载作用下长短组合群桩中荷载的分配及沉降的研究较少,为得到合理的群桩加固型式,采用有限元方法研究锤击荷载作用下群桩的动力承载特性。首先建立单桩有限元模型,分析竖向静荷载作用下钢管桩的沉降,并将模拟结果与现场静荷载试验结果进行对比,验证有限元模型的准确性,再分析锤击荷载作用下单桩的动力响应;其次建立锤击荷载作用下的长短组合群桩有限元模型,分析承台质量、承台埋深、辅桩桩长对群桩桩顶荷载分布及沉降的影响。结果表明锤击荷载作用过程中,角桩、边桩桩顶最大压应力较大,主桩桩顶最大压应力较小;承台埋深越浅,群桩桩顶应力越大,沉降反而越小;承台质量、辅桩桩长对群桩动力特性影响不大。     

Model of local buckling in steel hollow structural elements subjected to biaxial bending

This paper presents a general formulation for the analysis of steel hollow structural beams subjected to biaxial bending. The model has been developed within the framework of lumped damage mechanics. In this approach, the models are based on methods of continuum damage mechanics and the concept of plastic hinge. The model was implemented in a commercial finite element program. In order to calibrate the model, a set of experimental tests were carried out in the Structural Mechanics Laboratory at the Lisandro Alvarado University. The model was evaluated by the numerical simulation of these tests finding a good agreement between the experimental tests and the numerical simulations.     

Effect of substructures upon failure behavior of steel reticulated domes subjected to the severe earthquake

This paper presents the study on the influence of substructures on the failure behavior of steel reticulated domes subjected to the severe earthquake. The full-range dynamic response analysis method is applied to investigate the failure characteristics of single-layer steel reticulated domes with substructures subjected to the severe earthquake. The natural vibration properties are studied. Two typical failure modes of steel reticulated domes with substructures are illustrated according to the stiffness of substructures. Failure criterion is proposed to estimate the ultimate load strength for single-layer steel reticulated domes. It is observed that the substructure has great influence on the failure characteristics and the ultimate load strength of steel reticulated domes subjected to the severe earthquake. It is necessary to take substructure into consideration in analysis and design stage.     

Experimental investigation on the behavior of corrugated steel shear wall subjected to the different angle of trapezoidal plate

Studies on corrugated steel shear walls (CSSWs) generally indicate noticeable increase of energy absorption, as well as increasing shear buckling capacity of corrugated plates being more likely rather than the flat plates. In this paper, the effect of variation in the angle of trapezoidal plate on the behavior of CSSWs has extensively been investigated. Three specimens of CSSW with 1 story and single bay in half scale are tested under cyclic load. The observations of experiment do indicate that stress concentration has been increased in the corner of subpanels, by increasing of the corrugation angle. Development of the tensile field and wall yield and damage depends on the geometry of the plate. By increasing the corrugation angle, the stiffness and energy dissipation decrease; in addition, large loss of strength takes place. Comparing the numerical and experimental results indicates that for a closer look at behavior of trapezoidal CSSWs, fracture mechanics, fatigue, and damping of materials should be considered by numerical analysis.     

八边形中空双钢管混凝土短柱力学性能的非线性分析

基于八边形中空双钢管混凝土轴压短柱的试验结果,选择了合适的材料本构关系模型与界面处理,采用实体有限元分析方法对此类构件进行了非线性分析。之后,对模拟结果作了详细分析,结果表明,由有限元模型分析得出的荷载-应变关系曲线、内外钢管的破坏形态以及极限承载力与试验结果能较好的吻合。在此基础上,利用该模型在几何尺寸与材料强度等方面进行了扩展,并作了相应的解释。最后,提出了此类构件承载力的计算公式,与试验结果能较好的吻合。