Web Bearing Capacity of Cold-Formed Ferritic Stainless Steel Unlipped Channels with Web perforations under the End-Two-Flange (ETF) Loading

Laboratory and numerical evaluations on the web bearing capacity of unlipped cold-formed ferritic stainless steel channels are described in this paper. The channels considered have circular perforations in the web and are loaded under the end-two-flange (ETF) load case. A total of 387 results comprising 27 laboratory and 360 numerical results are presented. A nonlinear quasi-static finite element (FE) model was developed for the numerical investigation. An extensive parametric study is described to determine web bearing capacity reduction factors for different sizes of circular web perforations and cross-section dimensions; the circular web perforations are either centred or offset to the load and reaction plates. It is noted that no cold-formed stainless steel standard provides capacity reduction factors for any end-two-flange load case. The capacity reduction factor equations are first compared to reduction factors previously recommended for lipped cold-formed stainless steel channels. It is found that these existing equations are unreliable and unconservative for unlipped channels by as much as 11%. From both laboratory and finite element results, web bearing capacity design equations are proposed for both sections, with and without web perforations

Development of a Novel Pinned Connection for Cold-Formed Steel Trusses

Cold-formed steel trusses are a popular form of construction for light-weight buildings, particularly portal frame structures, for which spans up to 25m are increasingly common. In these long span trusses, providing high strength connections with sufficient elastic stiffness is a current limitation to developing cost-effective solutions. A novel pin-jointed truss connection named the Howick Rivet Connector (HRC) has been tested, firstly in a T-joint arrangement, then in a truss assemblage to determine its reliable strength and stiffness. Results showed that the HRC performs similarly to a bolted connection in terms of failure modes observed and loads reached. Additionally, the process of installing the HRC creates a bearing fit, eliminating slip due to tolerances. The elastic stiffness and proportionality limit of trusses with HRCs installed was shown to be appreciably greater than similarly dimensioned conventional screwed systems. Finite element (FE) models of both T-joints and trusses tested showed good agreement with experimental results, particularly in the transition from elastic to inelastic behaviour. The peak loads predicted from the FE models were however not accurately determined. To better predict this, it is recommended that the HRC forming and installation process be modelled to capture geometric irregularities and inelastic distributions which were idealised

Web Crippling Behavior of Cold-Formed Ferritic Stainless Steel Unlipped Channels under Interior-One-Flange And End-One-Flange Loadings

The web crippling strength of cold-formed ferritic stainless steel unlipped channels subject to interior-one-flange and end-one-flange loading is considered in this paper. A total of 144 results are presented, comprising 36 laboratory and 108 numerical results. These results cover the cases of both flanges restrained and unrestrained to the load and reaction plates. Unlike other work in the literature, the numerical analysis in this paper uses nonlinear quasi-static finite element analysis with an implicit integration scheme, which has advantages over static and quasi-static with an explicit integration scheme analyses, particularly for post buckling predictions of unlipped channels subject to web crippling. The laboratory and numerical investigations show current stainless steel design guidance to be too conservative. In terms of design standards, while no cold-formed stainless steel standard distinguishes between flanges restrained and unrestrained to the load and reaction plates, with each standard providing only one equation to cover both restrained and unrestrained, the web crippling strengths for the flanges unrestrained case were found to be higher than those predicted from SEI/ASCE-8 by as much as 24%. Also, the web crippling strengths for the flanges restrained case are shown to be higher than those predicted from equations found in the literature by as much as 48%. New web crippling design equations are proposed; the proposed equations are shown to be reliable when compared against laboratory and numerical results

Critical Design Criteria for Standard, Truncated, and Parallel Chords Cold-Formed Steel Trusses

The design of cold-formed steel trusses can be a very complicated and long repetitive process involving up to 28 load combinations added to serviceability checks depending on the design standards being used. This process is particularly tedious if a near optimal solution is required. Additionally, the risk of introducing human errors is usually quite high as it is a process often done by hand. FRAMECAD Structure is a niche software solution born from the desire to provide a complete solution for constructing with cold-formed steel by a company selling roll-forming machines. FRAMECAD Structure specialises on automating the calculations and design of cold-formed steel framed panels, trusses and joists with minimal user input. However, computational-oriented software applications are often not optimised for performance, hence the inefficiency in obtaining a design solution, i.e. the proposed solution is either not optimal or takes a considerable time to compute. To provide guidelines on the design of cold-formed trusses, this research uses FRAMECAD Structure to study which design parameters are critical and what impact they have on optimising the design outcome

Direct Strength Method for Ultimate Strength of Bolted Moment-Connections between Cold-Formed Steel Channel Members

Experimental tests have previously shown that the strength of bolted moment-connections between cold-formed steel members, where the connections are formed through an array of bolts in the web, is dependent on the length of the bolt-group. This reduced strength has been observed in tests on portal frame joints as well as over-lapped purlin joints. For a short bolt-group length, in the order of the depth of the section, this paper shows that a reasonable lower bound to this reduced strength can be predicted by using the Direct Strength Method (DSM), modified to include the effect of the bimoment at the connection. The upper bound would be the full in-plane major axis moment-capacity of the section, which can be achieved with a long bolt-group length and can also be predicted using the conventional DSM

Low Fatigue Response of Crest-Fixed Cold-Formed Steel Drape Curved Roof Claddings

Cold-formed steel roof claddings are subjected to significant suction/uplift pressures during high wind events. In New Zealand, the strong prevailing winds makes this a common occurrence. Suction pressures are generated by the turbulence of the wind flow around the building which can vary both spatially and temporally. The weakest link in the roofing system is the connection between roof sheeting and screw fasteners, which if fails, can lead to progressive collapse of the whole roofing assembly. Fluctuating high wind suction pressures can result in either static or fatigue pull-through failure of the roof sheeting at its screw fastener connections. Current literature has covered the static and fatigue wind uplift performance of crest-fixed corrugated and trapezoidal roof claddings. However, no research has been undertaken to understand the wind uplift performance of the typical crest-fixed cold-formed steel drape curved roof claddings used in New Zealand. This issue is addressed herein. In total, 35 large scale experimental tests are presented for crest-fixed drape curved steel roof claddings subjected to static and cyclic wind suction/uplift loads applied using a Pressure Loading Actuator. The material properties of claddings were determined using tensile coupon tests while the initial geometric imperfections of claddings were measured using a laser scanner. The critical fastener reactions were determined using a three axis load cell. Crack initiation, propagation of cracks, crack patterns and the number of load cycles to failure are discussed for such claddings under different load levels. Tests showed that the drape curved roof claddings are also subjected to localised dimpling and pull-through failures at their screw connections under static and cyclic wind uplift loads with the occurrence of low cycle fatigue failures under cyclic loading

Design of cold-formed stainless steel lipped channel sections with web openings subjected to web crippling under end-one-flange loading condition

This article presents a numerical investigation on the web crippling strength of cold-formed stainless steel lipped channel sections with circular web openings under end-one-flange loading condition. In order to take into account the influence of the circular web openings, a parametric study involving 1992 finite element analyses was performed, covering duplex EN1.4462, austenitic EN1.4404 and ferritic EN1.4003 stainless steel grades; from the results of the parametric study, strength reduction factor equations are proposed. The web crippling strengths predicted by the reduction factor equations are first compared to the strengths calculated using the equations recently proposed for cold-formed carbon steel lipped channel sections. It is demonstrated that the strength reduction factor equations proposed for cold-formed carbon steel are unconservative for the stainless steel grades by up to 7%. Unified strength reduction factor equations are then proposed that can be applied to all three stainless steel grades

Web Crippling Strength of Cold-Formed Duplex Stainless Steel Lipped-Channel Sections with Web Openings Subjected to Interior-One-Flange Loading

Cold-formed stainless steel sections are becoming more widely used in the residential and commercial sectors due to their high corrosion resistance and high strength-to-weight ratio. However, their susceptibility to web crippling at points of concentrated loading is well-known to be an important design issue. In addition, web openings are also become popular, as they improve ease of installation of services. This paper presents the results of an investigation into the effect of web crippling on cold-formed duplex stainless steel lipped channel-sections, having such openings, under the interior-one-flange (IOF) loading condition. 742 non-linear elasto-plastic finite element analyses are undertaken, with web openings located either centred beneath the bearing plate or offset to bearing plate. The effect of the size of the web opening, length of bearing plate and location of the web opening is considered. Strength reduction factor equations are proposed, that can be used to take into account such openings in design

The influence of strategy on lexical access in aphasia

The activation of words in semantic memory occurs through automatic or controlled processes. Semantic priming experiments have revealed that these processes may be influenced by word relatedness and word expectancy. In a primed lexical decision task, automatic and controlled processing in ten individuals with mild to moderate aphasia were investigated through manipulation of stimulus relatedness, stimulus expectancy and stimulus onset asynchrony (SOA). The group with aphasia was significantly influenced by expectancy at the short and long SOAs. The overall results of this study suggest that lexical-semantic activation in individuals with mild to moderate aphasia is influenced by strategic processing