No. R894, April, 2009
Pham, CH and Hancock, GJ
Experimental Investigation of High Strength Cold-Formed C-Section in Combined Bending and Shear
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Abstract
In roof systems, high strength steel profiled sheeting fastened to high strength steel cold-formed purlins of lipped C or Z-section are commonly used throughout the world. The design of such systems is performed according to the provisions of the limit states Australia/New Zealand Standard AS/NZS 4600:2005 (Standards Australia 2006) in Australia and the North American Specification (NAS) for the Design of Cold-Formed Steel Structural Members (AISI 2007) in the USA. In both Standards, which include the newly developed Direct Strength Method of design (DSM), the method presented [Chapter 7 of AS/NZS 4600:2005, Appendix 1 of (AISI 2007)] is limited to pure compression and pure bending. The situations of pure shear and combined bending and shear as occurs in a continuous purlin system are not considered.
In order to extend the DSM to purlin systems, three different test series on high strength cold-formed C-section purlins have been performed at the University of Sydney. The test series include predominantly shear, combined bending and shear and bending only test series. Two different section depths and three different thicknesses of lipped channel section were tested in this study. Farther, tests with and without torsion/distortion restraint straps screwed on the top flanges adjacent to the loading points were also considered. This report summarizes the test results and formulae developed from the Effective Width Method (EWM) and Direct Strength Method of Design (DSM). Proposals for design are included in this report. Comparisons with AS 4100:1998 (Standards Australia 1998) are also included to take account of tension field action.
Keywords
Cold-formed; High strength steel; Direct strength method; Effective width method; Combined Bending and Shear; Shear Test; Tension Field Action.
No. R895, June, 2009
Chandrangsu, T and Rasmussen, KJR
Investigation of Geometric Imperfections of Support Scaffold Systems
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Abstract
The report describes the findings from various site measurements of geometric imperfections on support scaffold systems, also known as falsework in industry. The measurements consist of out-of-straightness of the standards (uprights), out-of-plumb of the frame and loading eccentricity between the timber bearer and the U-head. A special-made tool instrumented with a dial gauge was used to measure the out-of-siraightness of standards at the mid-height of each lift. A theodolite was employed to measure the angle difference between top and bottom of the frame in order to compute storey out-of-plumb, and a vernier calliper was used to measure the loading eccentricity at the top. The measurements were taken from different support scaffold construction sites before ihe pouring of concrete, representing actual initial imperfections and loading eccentricity encountered in practice.
Keywords
Geometric imperfections. Out-of-straightness, Out-of-plumb, Loading eccentricity, Support scaffold systems. Falsework
No. R896, June, 2009
Chandrangsu, T and Rasmussen, KJR
Structural Modelling of Support Scaffold Systems
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Abstract
In this report, accurate three-dimensional advanced analysis models are developed to capture the behaviour of support scaffold systems, as observed in full-scale subassembly tests consisting of three-by-three bay scaffold systems with combinations of various lift heights, number of lifts and jack extensions. The paper proposes methods for modelling spigot joints, semi-rigid upright-to-beam connections and base plate eccentricities. Material nonlinearity is taken into account in the models based on the Ramberg-Osgood expression fitted to available experimental data. Actual initial geometric imperfections including member out-ofstraightness and storey out-of-plumb are also incorporated in the models. The ultimate loads from the nonlinear analyses were calibrated against failure loads and load-deflection responses obtained from full-scale subassembly tests. The numerical results show very good agreement with tests, indicating that it is possible to accurately predict the behaviour and strength of highly complex support scaffold systems using material and geometric nonlinear analysis. The report is a milestone in the ongoing development of a design methodology for support scaffold systems based on advanced analysis currently undertaken at the University of Sydney.
Keywords
Advanced analysis, Formwork subassemblies, Support scaffold systems, Steel scaffolds, Falsework, Subassembly tests, Structural models, Calibrations
No. R897, May, 2009
Hegarty, DG
Comparison of Structural Design actions Part 4: Earthquake Actions in Australia AS1170.4 – 1993 & 2007
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Abstract
This report investigates the differences between the old AS1170.4:1993 code and the new AS1170.4:2007 code and has examined the implications to building frame structural systems. The principles of seismic design and the advances in the field that lead to development of the new AS1170.4:2007 code [7] have been presented.
A detailed comparison of the differences between the Layout, Notation, Factors and Calculation of the Design Base shear has been examined. The magnitude of the design base shear applied for all structural system types and for all sub-soil classes has been carried out. Graphs showing the percentage of seismic weight applied to structural systems for all the sub-soil classes have been included in Appendix A. To highlight the revisions and implications of the new AS1170.4:2007 code, analysis of a typical concrete building frame structural system with reinforced concrete shear walls has been carried out. A comparison of the calculation methods and the errors and discrepancies of analysis procedures has been carried out and presented.
Keywords
Seismic Response Spectrum, Elastic, Dynamic, Natural Period, Earthquake Base Shear, Structural Systems, Reinforced Concrete
No. R898, June, 2009
Trahair, NS
Lateral-Distortional Buckling of Monorails
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Abstract
This paper is concerned with the elastic lateral-distortional (LD) buckling of single span steel monorail I-beams and its influence on their design strengths. The distortion of a slender web reduces the elastic buckling resistance of an intermediate length beam below its flexural-torsional (FT) resistance.
A finite element computer program was used to study the elastic LD buckling of single span beams. The LD to FT buckling moment ratios were generally higher for simply supported beams with bottom flange central concentrated loads than for uniform bending, and lower for shear centre concentrated loads. For beams with bottom flange loading and unrestrained bottom flanges, there were very significant reductions in these ratios, but they increased when rigid web stiffeners or top flange torsional restraints were provided at the supports. For beams with bottom flange loading and unrestrained bottom flanges, the reductions in the elastic buckling resistance were greater for beams with stocky flanges than for slender flanges.
Approximations were found for estimating the reduced resistances which were generally of high accuracy or conservative, and for estimating the increased resistances caused by elastic and rigid top flange end torsional restraints.
A method of designing steel beams against LD buckling was proposed and its use demonstrated by a worked example.
Keywords
Beams, bending, buckling, design, distortion, elasticity, member resistance, monorails, steel, torsion.
No. R899, October, 2009
Gilbert, BP and Rasmussen, KJR
Experimental test on steel storage rack components
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Abstract
Steel storage racks are commonly used worldwide to store goods on pallets and represent complex and challenging freestanding structures to design. In the current competitive market, storage racks have to be able to carry heavy loads while being designed as lightly and economically as possible. Often unbraced, their stability may depend solely on the pallet beam to column connector and on the base plate connection to the floor characteristics (Baldassino and Bemuzzi (2000)). Moreover, to allow bracings and pallet beam connections, the web and flanges of the upright section are perforated at regular intervals along the length affecting the axial and bending resistance of the section (Hancock (1998)). The main international racking specifications recognise the importance of accurately determining the properties of individual components of storage racks and require testing for this purpose. This report presents experimental results from tests performed on individual components, namely coupon tests, stubcolumn tests, pallet beam to column connection tests, base plate floor connection rotational and uplift tests, upright frame shear tests and four point bending tests of uprights. Clarification of the guidance provided by the European Standard HN 15512 (2009) for the base plate to floor connection test is presented as is an alternative test set-up to the upright frame shear test described in HN 15512 (2009), allowing accurate determination of the in-plane global stiffness of an upright frame.
Keywords
Steel storage racks, individual component tests. Base plate tests, Upright frame shear tests.
No. R900, October, 2009
Gilbert, BP and Rasmussen, KJR
Stillness tests, failure tests and load transfer in steel drive-in storage racks
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Abstract
Steel storage racks, made of cold-fomied steel, are used extensively in industry for storing goods. Two main racking systems prevail, referred to as “selective” and “drive-in” racks. International racking design codes mainly deal with selective racks, while limited design guidelines are available for drive-in racks. Drive-in racks require minimal floor space by storing pallets one after the other with no space between them. The forklift truck drives into the rack to store the pallets on the first-in, last-out principle. To allow forklift truck passage, drive-in racks can only be braced at the back (spine bracing) and at the top (plan bracing) in the down-aisle direction resulting in a complex slender structure with poorly understood 3D behaviour and increased risk of collapse. As yet, tests on drive-in rack systems to accurately capture the 3D rack behaviour are not available in the literature. This paper presents the experimental results from full-scale tests conducted on a complete drive-in rack system. Experimental investigations of the load transfer and relative stiffness under various horizontal loading conditions are presented. Experiments have been performed on racks with and without pallet loads. The mechanisms involved during failure when the rack is subjected to a forklift truck impact are also presented through experimental testing.
Keywords
Steel storage racks. Drive-in racks, 3D behaviour. Load transfer. Full-scale tests. Pallet drop through.
No. R901, October, 2009
Gilbert, BP and Rasmussen, KJR
Finite Element modelling of steel drive-in rack structures
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Abstract
Steel storage racks, principally made from cold-formed steel profiles, are freestanding structures and designed to carrying heavy loads. Yet the amount of material used in their fabrication is minimised in structural design and racking companies often rely on 3-Dimensional second-order Finite Element Analysis to design storage racks as economically as possible. The FEA often includes non-linear material and/or connection stiffness. As storage racks are complex and slender structures, whose behaviour is influenced by the base plate to floor connection and by the pallet beam to upright connection (Baldassino and Bemuzzi (2000)), building accurate FG models is challenging. This report presents a Finite Element model of an unloaded and loaded drive-in rack structure. Contrary to the main type of racking system, referred to as ”selective rack”, where racks are one pallet deep and separated by aisles allowing each pallet to be always accessible, “drive-in” racks are typically 3 to 7 pallets deep and store pallets one after the other, with no space between them, on the “first-in last-out” principle. By optimising floor allocation, drive-in racks are often an attractive alternative to selective racks. The reported FE model is built using the commercial software Abaqus (2005) and numerical results are found to accurately reproduce experimental static test results performed on a full-scale drive-in rack (Ciilbert and Rasmussen (2009b)). The FE model is used to study the influence of the uplift of base plates on the global behaviour of the rack. Results show that the uplift of the base plate may significantly influence the overall displacement of the rack, and needs to be considered in design. Finally, the influence of pallets on the bending moment distribution in the uprights is analysed and reported herein.
Keywords
Steel storage racks, drive-in racks, FE modelling, base plate uplift.
No. R902, October, 2009
Gilbert, BP and Rasmussen, KJRDetermination of accidental forklift truck impact forces on drive-in steel rack structuresFull Report in PDF
Abstract:
The report addresses the problem of determining the accidental forklift truck impact forces on steel storage racks. Based on first principles of mechanics, simple models of a loaded forklift truck and a drive-in racking structure are presented. Model masses, as well as stiffness and damping coefficients are calibrated against experimental results obtained from tests of a forklift truck and a drive-in racking structure. Comparisons between experimental results and solutions obtained from the simple mechanical models show that the simple models accurately reproduce the static and dynamic behaviours of their associated structures. Based on the drive-in rack impact test results presented in a companion research report (Ciilbert et al. (2009)) and the simple mechanical models for drive-in racks, actual impact forces are calculated and presented. Finally, using the impact test results and the simple mechanical models, the actual motion of the forklift) truck body is calculated. This motion, being a common characteristic to all drive-in racking impacts, allows impact forces to be obtained for various pallet loads, impact elevations and rack characteristics. Thus, the report concludes with a general method for calculating forces generated under forklift truck impact.
Keywords
Steel storage rack, drive-in rack, impact force.
No. R903, October, 2009
Gilbert, BP; Rasmussen, KJR and Zhang, H
Impact tests, parametric impact studies and design impact forces on drive-in steel storage racks
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Abstract
Extensively used in the industry to store goods, storage racks are frequently subjected to accidental impact forces from operating forklift trucks. There is currently little understanding of the nature of these impact forces, leading to occasional catastrophic failures because of inadequate structural design. International racking design codes deal with impact but use an arbitrary value of impact force with no scientific justification. This report focuses on an impact-sensitive type of storage rack, called “drive-in racks”. Contrary to classical “selective racks”, where pallets are stored on beams and where each single pallet is always accessible; “drive-in racks” allow the forklift truck to drive into the rack to store pallets on rail beams, one after each other, on the first-in, last-out principle. This type of design leads to slender uprights in the down-aisle direction, only restrained at the base and at the top. When subjected to an impact force, the bowing of the upright triggers progressive failure by allowing the pallets to drop through. This report presents experimental test results from impact tests on a complete full-size drive-in rack structure. Six series of twenty tests each, representing three pallet loads and two rack loading configurations have been conducted by striking the drive-in rack by a forklift truck. Parametric impact studies using finite element analysis are also presented. Factors affecting the sensitivity of drive-in racking structures to impact are investigated and conclusions are drawn about the parameters most significantly influencing the progressive collapse of this type of rack under impact. Based on a reliability analysis, realistic design impact forces formulas are proposed.
Keywords
Steel storage rack, drive-in rack, impact force, impact sensitivity
No. R904, October, 2009
Pham, CH and Hancock, GJ
Numerical Simulation of High Strength Cold-Formed Purlins in Combined Bending and Shear
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Abstract
The report provides numerical non-linear simulation, based on the finite element method (FEM) using the software package ABAQUS/Standard, of high strength C-section cold-formed steel purlins in shear and combined bending and shear. The simulations are compared with and calibrated against tests performed at the University of Sydney on a variety of section sizes and thicknesses. Studies of the effects of boundary condition, geometric imperfection, and element type as well as mesh size are included. Geometric imperfections are often taken as a scaled multiple of the eigenvalue modes. Selection of eigenmodes and their scaling is given in the report. The accurate results of the numerical simulations show that the finite element analysis can be used to predict the ultimate loads of thin walled members including the post-buckling behavior of thin-walled sections in shear and combined bending and shear. It is demonstrated that the finite element analysis can therefore be used to design and optimize thin-walled sections of high strength steel.
Keywords
Cold-formed; High strength steel; Direct strength method; Effective width method; Combined Bending and Shear; Shear Test; Finite element method.
No. R905, October, 2009
Chandrangsu, T and Rasmussen, KJR
Review of Past Research on Scaffold Systems
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Abstract
This article presents an overview Of scaffold research and current practice in the design Of scaffold systems. It covers brief description Of scaffold systems including types Of joints and materials currently used. Also, types Of analysis, loads, initial geometric imperfections, and modelling Of complex joints are described. The prediction Of the ultimate load Of scaffold systems derived from simplified equations and their failure modes are shown. In addition, the article explains the design of scaffold systems based on British and Australian standards as well as how effective lengths and bracings commonly apply. The recommendations are provided for modelling, analysis and design Of scaffold systems.
Keywords
Scaffold systems, Falsework, Structural analysis, Ultimate load, Design, Standards
No. R906, October, 2009
Trahair, NS
Distortional Buckling of Overhanging Monorails
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Abstract
This paper is concerned with the elastic lateral-distortional (LD) buckling of overhanging steel monorail I-beams and its influence on their design strengths. Distortion of a slender web reduces the elastic buckling resistance of an intermediate length beam below its flexural-torsional (FT) resistance.
A finite element computer program was used to study the elastic LD buckling of overhanging monorails with bottom flange loads at the free ends. The ratio MLD / MFT of the elastic LD to FT buckling moments decreased significantly as the flange width-thickness ratio bf /tf decreased, but varied only slightly with the web depth-thickness ratio bw/tw. The value of MLD varied almost linearly with the ratio of the supported span to the overhang length, and the effect of top flange torsional restraint at the exterior support on MLD was similar to that on MFT. Distortion effects were very small when there was no torsional restraint, but increased significantly with the torsional restraint stiffness. The full plastic moment was often reached before MLD, especially for low values of bf /tf and high values of the torsion parameter K.
Conservative approximations were developed for predicting the elastic LD buckling moments for ranges of sections, slendernesses, span ratios, and torsional restraint stiffnesses.
A method of designing overhanging steel monorails against LD buckling was proposed and its use demonstrated by a worked example.
Keywords
Beams, bending, buckling, design, distortion, elasticity, member resistance, monorails, overhanging, steel, torsion.
No. R907, December, 2009
Pham, CH and Hancock, GJ
Experimental Investigation of High Strength Cold-Formed SupaCee Sections in Combined Bending and Shear
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Abstract
High strength steel cold-formed purlins of lipped C or Z-sections are commonly used throughout the world, one of which is the SupaCeeE section (Lysaght, 2003). They contain additional return lips and web stiffeners which enhance the bending and shear capacity of the sections. These sections are widely used in Australia as purlins in roof and wall systems. Design methods for these sections are normally specified in the Australian/New Zealand Standard for Cold-Formed Steel Structures AS/NZS 4600:2005 (Standards Australia 2005) or the North American Specification for Cold-Formed Steel Structural Members (AISI 2007). In both Standards, which include the newly developed Direct Strength Method of design (DSM), the method presented [Chapter 7 of 4600:2005 (Standards Australia 2006), Appendix I of (AISI 2007)] is developed for beams and columns, including the reliability of the method. Both the Effective Width Method (EWM) and the Direct Strength Method (DSM) can be used for the design of C-sections although no formal rules for shear and combined bending and shear exist for the DSM in either standard/specification.
This report presents three different test series on SupaCee sections performed at the University of Sydney for the extension to the DSM for shear, and combined bending and shear. The test series include predominantly shear, combined bending and shear, and bending only test series. Two different section depths and three different thicknesses of lipped channel section were tested and are described in this report. Tests with and without torsion/distortion restraint straps screwed on the top flanges adjacent to the loading points were also considered. The test data were used to compare with the existing EWM without tension field action. The report also proposes new DSM formulae based on the North American Specification in DSM Format in shear without tension field action and a proposal in DSM Format including tension field action. Both test results and formulae developed from the EWM and DSM are summarized.
Keywords
Cold-formed; SupaCee sections; High strength steel; Direct strength method; Effective width method; Combined Bending and Shear; Shear Test; Tension Field Action.