Slender Members Research Articles

European alternatives to design perforated thin-walled cold-formed beam–columns for steel storage systems

Summary Rack systems to store goods and products are one of the most important applications for thin-walled cold-formed steel members. Adjustable pallet racks are used widely worldwide and are characterized by regular systems of perforations along the uprights (i.e. vertical members) to connect easily pallet beams and diagonal members forming the skeleton frame. Design rules are based on the well-established approaches for the more traditional solid members, suitably extended to account for the presence of regular perforations via component tests accurately described in rack specifications. This paper focuses on the performance of isolated uprights under axial load and gradient moment. In particular, three European alternatives to design beam–column rack members have been discussed and applied: the first and the second are traditionally used for thin-walled cold-formed steel members while the latter, the so-called general method of Eurocode 3 part 1-1, allows to take directly into account the key features associated with upright response. The geometry of the cross-sections and of their perforation system, the member slenderness and the load condition has been assumed as parameters of this study. Research outcomes demonstrate that the predicted performances can result significantly different, reflecting directly on the weight and the cost of the whole storage system. Furthermore, numerical analyses and design calculations show that standard codes need urgent revisions, leading in few cases to design beam–columns from the unsafe side.

Vibration Problems of an Example of Temporary Steel Grandstand under Human-Induced Excitation / Problemy Drgań Przykładowej Tymczasowej Trybuny Stalowej Poddanej Oddziaływaniom Dynamicznym Wywołanym Przez Ludzi

Lighter and slender structural members of a typical grandstand leads to a significant reduction in the frequencies, that is why such structures are more easily induced to vibrations. The aim of the present paper is to show the results of the experimental tests and the numerical analyses focused on the behaviour of a part of a typical temporary steel grandstand under dynamic loads. The peak values of accelerations of a steel scaffolding grandstand under human-induced excitation have been determined and compared with the limit values concerning the perception of vibrations by people. The results of the study indicate that the human-induced excitation may induce structural vibrations which substantially exceed the allowable limits.

Buckling analysis of partially protected cold-formed steel channel-section columns at elevated temperatures

This paper presents a numerical investigation on the buckling behaviour of plasterboard protected CFS channel-section columns subjected to axial loading when exposed to fire on its one side. The work involves temperature-dependent pre-buckling stress analysis and buckling analysis. Two non-uniform temperature distributions with linear and nonlinear temperatures along the web and constant temperatures in flanges and lips have been included in this paper. Bernoulli beam theory has been used in the pre-buckling stress analysis with considering the effects of temperature on strain and mechanical properties. The buckling analysis is performed using combined finite strip analysis and classical Fourier series solutions, in which the mechanical properties are considered to be temperature dependent. The results show that the temperature distributions have a significant influence on both the pre-buckling stress distribution and slenderness of CFS column members. It is also found that the thermal bowing effect improves the buckling performance of intermediate CFS members, but deteriorates that of long CFS members. This paper gives a better understanding of the effect of non-uniform temperatures on the buckling behaviour of CFS columns, and further extends the potential application of the finite strip method to the buckling analysis of CFS members at elevated temperatures.

RESISTANCE AND DURABILITY ANALYSIS OF STEEL SUPPORTING STRUCTURE ON THE BELL TOWER OF ST. TRINITY CHURCH IN KROSNO

The paper describes the analysis of steel structure, supporting three bells in the belfry of St. Trinity Church in Krosno. The structure is dated from 1928 and has a form of riveted space truss, with slender members. The total mass of all bells, coming from the 17th century, is nearly equal to 4200 kilograms, so the dynamic forces coming from bells swinging are quite large. The paper describes specific problems associated with assessing the resistance of old steel structure, treated as a relic. The analysis covered technical condition assessment of the structure, evaluation of actions and environmental influences, mechanical parameters prediction of steel and rivets by non-destructive methods and also static and dynamic analysis of the structure. According to many years of exploitation, the fatigue verifications were also performed using the classification method.

Noncompact and slender circular CFT members: Experimental database, analysis, and design

The AISC 360-10 Specification categorizes circular concrete filled steel tube (CFT) members as compact, noncompact or slender depending on the slenderness ratio (diameter-to-thickness D/t ratio) of the steel tube walls. International design codes typically focus on the design of compact circular CFT members with relatively small slenderness (D/t) ratios, and the behavior and design of noncompact and slender circular CFT members is not addressed directly. This paper presents the basis of the current AISC Specification (AISC 360-10) for the design of noncompact and slender circular CFT members under axial compression, flexure, and combined axial and flexural loading. An experimental database of tests conducted on noncompact and slender circular CFT members is compiled, and used to establish the conservatism of the design equations in the AISC Specification. Detailed 3D finite element method (FEM) models are developed for circular CFT members, and benchmarked using the database of experimental results. The benchmarked models are used to conduct parametric studies to address gaps in the experimental database, and further verify the conservatism of the design equations. The AISC 360-10 Specification is recommended for the design of noncompact and slender circular CFT members. Additionally, the numerical models developed and benchmarked for circular CFT members are recommended for future investigations.

Crash analysis and evaluation of cable median barriers on sloped medians using an efficient finite element model

Perpetual high traffic volumes on U.S. highways have raised more public concern than ever about transportation safety. Over the years, various traffic barrier systems, including cable median barriers (CMBs), have been developed to reduce the number and severity of vehicle crashes. Despite their general effectiveness, there remains room for improvement, especially when CMBs are installed on unlevelled terrains such as sloped medians. The destructive nature of crashes imposes significant challenges to barrier design using full-scale physical testing; numerical simulations thus become a viable means to support crash analysis, performance evaluation, and barrier designs. In this study, validated vehicle and CMB models were used to perform full-scale simulations of vehicle-CMB impacts. Several CMB designs, including the currently used one, were evaluated under vehicular impacts at different velocities and angles. To address the challenge of modeling slender members such as cables and hook-bolts in contact analyses, an efficient beam-element contact model was employed in the analysis. Different design options of cable height and spacing under various impact velocities and angles were investigated in this study.

Experimental Investigation of Response of Vertical Slender Cylinder under Breaking Wave Impact

Coastal and offshore structures consist of slender cylindrical member as the fundamental component. Structural damages and failures are catastrophic due to wave impact, it is necessary to understand the influence of breaking wave impact on the structural members. Since the standard codal provisions of breaking wave impact on structural members is scarce, it is essential to understand the physics of the interaction of breaking waves on structural members. In the present study, an experimental investigation has been carried out to measure the response of the slender vertical cylinder under breaking waves due to constant amplitude spectrum. Pressure and Acceleration measurements were made under the incidence of breaking waves of different intensities varying from Plunging to Spilling. The maximum acceleration observed under severe plunging is higher under constant amplitude spectrum while under constant steepness spectrum, the acceleration is maximum only for moderate plunging even though the pressure is maximum for severe plunging event.

Response of Slender Vertical Cylinder under Breaking Waves

Coastal and offshore structures consist of slender cylindrical member as the fundamental component.Breaking wave loads are significantly important now a days due to calamities and disasters occurring in ocean environment. Structural damages and failures are catastrophic due to wave impact and it is necessary to understand the influence of breaking wave impact on the structural members. The standard codal provisions of breaking wave impact on structural members is scarce, it is essential to understand the physics of the interaction of breaking waves on structural members. In the present study, an experimental investigation has been carried out to measure the response of the slender vertical cylinder under breaking waves due to constant amplitude spectrum. The structural response of the vertical cylinder under constant amplitude spectrum was found from the measured acceleration. The deflection of the vertical cylinder due to breaking wave impact from acceleration measurements were found out by using omega arithmetic method. The acceleration and deflection are found to be maximum for both severe and moderate plunging events. The maximum deflection observed for severe plunging event is nearly 0.1m for the present study.

A Study on the Development of Force Limiting Devices of Cross-Section Cutting Types

This paper describes the development of force limiting device(FLD). The FLD could induce compressive yield before occurring elastic buckling for slender member under compressive load. Therefore, it might prevent reduction of load carrying capacity by elastic buckling and the structures with the devices would behave stable. A new type of FLD reduced cross area is proposed in this study different to existing studies like as out of plane type, slit type and folded plate type. The parameters of specimens are depth, width and number of cutting. The structural capacity and characteristics of proposed types were verified by experiment and FEM analysis. The FLD of cutting type is efficient in compressive member.

서브스페이스 반복계산법을 이용한 선형좌굴해석용 컴퓨터프로그램의 개발

There are many accidents in the construction of a structure owing to the collapse of concrete formwork. It is usually occurred in many cases because of the buckling of slender column members in system support. So, recently, it is considered more important that the buckling analysis results must be checked in the design of system support. Therefore, in this study, methods for the computer program development based on linearized buckling analysis algorithm using subspace iteration method are investigated first, then some algorithms available in case of a computer program development are studied on the basis of investigated methods. On the basis of studied algorithms, a computer program sNs is developed and the results by this program is compared with the results by theory and structural analysis programs - SAP2000, MIDAS - for the verification of their accuracy.

Performance assessment of steel plate shear walls under accidental blast loads

Previous research on properly-designed steel plate shear wall systems has proven that it has a high level of lateral shear strength and stiffness and large ductility. These properties, along with ample redundancy, robustness, and superior energy dissipation capacity under severe cyclic loading, have made the system a viable lateral force resisting system for seismically-active regions. Although similar properties are desirable for protective structures, their application in this regard has been largely neglected. The potential application of some form of the steel plate shear wall as a protective system in industrial plants possibly subjected to accidental explosions is studied by means of iso-response curves. To capture all important aspects in blast response, a comprehensive numerical model is developed. The constitutive model for the steel material includes mixed-hardening, strain-rate effects, and damage initiation and evolution. The pressure–impulse diagrams for both in-plane and out-of-plane blast orientations, along with the corresponding weight–standoff distance diagrams, are produced with the aid of the numerical model. Different response criteria and wall sizes are considered. A method is proposed to produce dimensionless iso-response curves to broaden their applicability. The results show that despite the inherent slenderness of the steel members, the wall system has the potential to be an effective system for use in a protective structure for industrial plants, especially for the in-plane blast load condition.

Short-term probability distribution of the extreme values of offshore structural response by an efficient time simulation technique

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. Wave loading on slender members of bottom-supported jacket structures is frequently calculated by Morison's equation. Due to nonlinearity of the drag component of Morison wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian; therefore, simple techniques for derivation of their extreme response probability distributions are not available. To this end, the conventional time simulation technique (CTS) is frequently used for predicting the probability distribution of the extreme values of response. However, this technique suffers from excessive sampling variability and hence a large number of simulated response extreme values (hundreds of simulated response records) are required to reduce the sampling variability to acceptable levels. In this paper, a more efficient version of the time simulation technique (ETS) is introduced to derive the probability distribution of response extreme values from a much smaller sample of simulated extreme values. The ETS procedure is found to be many times more efficient than the CTS method.

Extreme structural response values from various methods of simulating wave kinematics

In offshore engineering, the main forces that are loaded onto ocean structures come from wind-generated random waves. The prediction of wave forces that are applied onto slender cylindrical members is usually based on the Morison's equation, in which the wave force at any section of a member is expressed directly in terms of wave kinematics. It is essential to be able to estimate sensible kinematics at all levels of a structure to determine accurate prediction of wave forces and corresponding responses of these structures in a random wave field. Linear random wave theory (LRWT) is the simplest and most often used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record. However, water particle kinematics calculated from LRWT grossly overpredicts the kinematics above the mean water level (MWL). Methods have been introduced to overcome this problem of high kinematics above the MWL, which consists of using linear wave theory (such as Wheeler, vertical stretching, effective node elevation and effective water depth methods) to provide a more realistic representation of near-surface wave kinematics. This is promising as there is some evidence that the water particle kinematics from the Wheeler method are underestimated and that those from the vertical stretching method are somewhat exaggerated. In this paper, the comparisons of the probability distributions of extreme values from different methods of simulation wave kinematics are investigated by using conventional time simulation procedure.

An Analytical Investigation of the Trapeze Effect Acting on a Thin Flexible Ribbon

This paper systematically explores the extensional–torsional coupling due to the trapeze effect acting on a thin flexible ribbon subjected to combined tension and torsion. Kinematic relationships as well as expressions for the restoring torque associated with this effect are analytically derived. Additionally, the locus of points about which the cross sections of a twisted ribbon under tension rotate is derived. These points, called torsional centers, are found to be coincident with the centroids of the axial stress field at each station along the ribbon. More generally, it is shown that when a flexible slender member is in tension, combined transverse forces must act at the centroid of the axial stress field to produce pure bending and no twist. As a result, the elastic axis (EA) of the member shifts from the locus of shear centers to the locus of centroids of the axial stress field. A numerical model is developed to investigate the effect of the position of the EA on the prediction of steady-state deformations and natural frequencies of a rotating ribbon with tip mass. By assuming the EA to be the locus of the shear centers, the tip twist is overpredicted by a factor of 2 for small twist angles, and up to 2.5 for large twist deformations. In addition, assuming the EA to be the locus of shear centers results in an error of up to 60% in the predicted natural frequencies at large twist angles.

연직파이프쿨링 공법에 의한 매스콘크리트 온도균열 제어

In case of the slender mass concrete like attached wall, retaining wall and bridge tower, the low heat cement and the control joint are mainly used for thermal cracking control. However, even if these cracking control methods are considered, it is impossible to control thermal cracks perfectly, because the external restraint is largely in these mass concrete. Because these cracks occurring in slender mass concrete members almost penetrate concrete member, the special cracking control is demanded in these mass concretes. The vertical pipe cooling method improving existing pipe cooling method was developed for the active thermal cracking control of slender mass concrete, and applied at the field attached wall. In results, the maximum temperature dropped more than by vertical pipe cooling method, and the cracks decreased about more than 50%.

Experimental Investigations of Acceleration on Slender Cylindrical Member under Breaking Waves

Many of the coastal and offshore structures consist of slender cylindrical member as the fundamental component. Since the structural damages and failures are catastrophic under wave impact, it is essential to understand the influence of breaking wave impact on the structural members. Past literature dictates that the magnitude of impact pressures is of the order of ten times more than the non breaking wave induced pressure. The standard codal provisions for the structural design of those members under breaking wave impact are scarce. In the present study, an experimental investigation has been carried out to measure the response of the slender vertical cylinder under breaking waves. Acceleration measurements were made under the incidence of breaking waves of different intensities varying from Plunging to Spilling. Deflections are found out from the measured acceleration. The maximum acceleration observed under severe plunging event is 0.5 times that of moderate plunging event, the deflection induced by the moderate plunging is two order higher than that of severe plunging. Acceleration is maximum not only above still water level (SWL) but also lies in the impact zone. Hence moderate plunging events with higher impulse and larger pressure rise time is crucial in the design of offshore and coastal structural member under breaking wave impact load.

Assessment of the ACI-DAfStb Database of Shear Tests on Slender Reinforced Concrete Beams without Stirrups for Investigations on the Shear Capacity Scatter

The shear transfer mechanism of RC slender members without stirrups still presents very high uncertainties and the question has generated many controversies and debates since the beginning of the l ...

Full-scale measurement of wind pressure on the surface of an oscillating circular cylinders

Under wind excitation, many slender structural members with circular cross sections have exhibited large-amplitude vibrations. The nature of some problematic vibrations remains to be fully understood. To investigate the excitation mechanisms that can cause the vibrations, an experimental campaign was conducted to measure simultaneously the wind pressure on the surface of a circular cylinder in the atmospheric boundary layer and the acceleration of this cylinder. The pressure and acceleration measurements were used to investigate the interaction between the cylinder and the turbulent wind in subcritical and critical Reynolds number ranges. The study revealed several effects of turbulence in wind in the atmospheric boundary layer on the critical transition, including the promotion of early critical transition, the attenuation of the single separation bubble, and the early cessation of the coherent vortex shedding. A coherent fluctuating axial flow component in the wake of circular cylinders yawed to the flow, which has been previously observed in wind tunnel tests in smooth flow and postulated to be critical for the onset of dry cylinder vibration at high reduced velocity, was not observed in the present experiment.

VIV response of a flexible cylinder with varied coverage by buoyancy elements and helical strakes

Many significant engineering challenges have emerged as the petroleum industry has moved their field development and production activities into increasingly deeper water depths. The design of deepwater marine risers presents the combined challenges to minimize top tensioning requirements, mitigate any flow-induced vibrations, and if possible to increase the expected fatigue life of these slender structural members. As part of the design process to achieve these goals external buoyancy modules and strakes have been employed. To gain insight into the complex multi-mode response behavior a recent experimental study was performed and the analysis of selected data sets is presented. In the experiments a horizontal cylinder with a length to diameter ratio of 263 was fitted with a variety of strake and buoyancy element configurations. The models were towed at uniform speeds ranging from 0.4 to 2.0 m/s and fiber optic strain gages were used to measure both in-line and cross-flow strain response. The resulting time series information was processed utilizing the method of time domain decomposition formulated for strain data input and the introduction of modal assurance criterion to resolve the modal strain information that included frequency, mode shape, and critical damping ratio information. The pre-tensioned cylinder without appendages was used as a base case and the results were basically consistent with expectations. In the case of 0.8 m/s low-tension test, multiple closely spaced non-overlapping peaks were observed in both in-line and cross-flow directions and were identified as being of the same mode with mode shapes distorted away from purely sinusoidal behavior. The test data for the 100% coverage by helical stakes demonstrated the effectiveness of that suppression device over the range of current velocities investigated. The most interesting case was that of a staggered combination of helical strakes and buoyancy element whose total for each type of coverage was equal. This effective asymmetric VIV suppression approach is presented and discussed in detail.

Noncompact and slender rectangular CFT members: Experimental database, analysis, and design

Rectangular concrete-filled steel tube (CFT) members are categorized as compact, noncompact or slender depending on the slenderness ratio (width-to-thickness b/t ratio) of the steel tube walls. International design codes typically focus on the design of compact CFT members with relatively small slenderness (b/t) ratios. The behavior and design of noncompact or slender CFT members is not addressed directly. This paper presents the basis of the current AISC Specification (AISC 360-10) for the design of noncompact or slender rectangular CFT members under axial compression, flexure, and combined axial and flexural loading. The experimental database of tests conducted on noncompact and slender CFT members is reviewed. Design equations are developed based on the experimental results and observations. Detailed 3D finite element method (FEM) models are developed for noncompact and slender CFT members, and benchmarked using experimental results. The benchmarked models are used to address gaps in the experimental database, and further verify the conservatism of the design equations.