Design of Rivet Fastened Rectangular Hollow Flange Channel Beams Subject to Local Buckling

The innovative, rivet fastened Rectangular Hollow Flange Channel Beam (RHFCB) is a new type of cold-formed steel section, proposed as an extension to the widely researched hollow flange beams. The hollow flange beams have garnered much interest in the past due to the sections having capacities more typically associated with hot-rolled steel sections. Various researches have been carried out to investigate the behavior of continuously welded hollow flange beams but little is known on the behavior of RHFCBs. The structural behaviour of the RHFCB is unique compared to other conventional cold-formed steel sections and its moment capacity reduces with rivet spacing. The current cold-formed steel design standards do not provide a calculation method to include the effects of intermittent fastening. In this research an extensive parametric study was conducted using validated finite element models to investigate the section moment capacity of RHFCBs. This paper presents the findings from the parametric study and proposes new design equations for the section moment capacity of RHFCBs in the Direct Strength Method format. The parametric study considers various slenderness regions, section dimensions and rivet spacing. In the new design equations, a reduction factor parameter is included to calculate the section moment capacity of RHFCBs at any rivet spacing up to 200 mm

New Web Crippling Design Rules for Cold-Formed Steel Beams

Lipped channel beams (LCBs) and SupaCee sections are commonly used as floor joists and bearers in the construction industry. SupaCee section is one of the cold-formed steel members, which is increasingly used in the building construction sector. It is characterized by unique ribbed web and curved lip elements, and is claimed to be more economical with extra strength than the traditional channel sections. These thin-walled LCBs and SupaCee sections are subjected to specific local and global failures, one of them being web crippling. Several experimental and numerical studies have been conducted in the past to study the web crippling behaviour and capacities of different cold-formed steel sections under different concentrated load cases. However, due to the nature of the web crippling phenomenon and many factors influencing the web crippling capacities, capacity predictions given by most of the cold-formed steel design standards are either unconservative or conservative. Hence both experimental and finite element studies were conducted to assess the web crippling behaviour and strengths of LCBs and SupaCee sections under ETF, ITF, EOF and IOF load cases. New equations were proposed to determine the web crippling capacities of LCBs and SupaCee sections based on the results from experiments and finite element analyses. Suitable DSM based web crippling design equations were also developed

Endotoxin leads to rapid subcellular re-localization of hepatic RXRα: A novel mechanism for reduced hepatic gene expression in inflammation

BACKGROUND: Lipopolysaccharide (LPS) treatment of animals down-regulates the expression of hepatic genes involved in a broad variety of physiological processes, collectively known as the negative hepatic acute phase response (APR). Retinoid X receptor α (RXRα), the most highly expressed RXR isoform in liver, plays a central role in regulating bile acid, cholesterol, fatty acid, steroid and xenobiotic metabolism and homeostasis. Many of the genes regulated by RXRα are repressed during the negative hepatic APR, although the underlying mechanism is not known. We hypothesized that inflammation-induced alteration of the subcellular location of RXRα was a common mechanism underlying the negative hepatic APR. RESULTS: Nuclear RXRα protein levels were significantly reduced (~50%) within 1–2 hours after low-dose LPS treatment and remained so for at least 16 hours. RXRα was never detected in cytosolic extracts from saline-treated mice, yet was rapidly and profoundly detectable in the cytosol from 1 hour, to at least 4 hours, after LPS administration. These effects were specific, since the subcellular localization of the RXRα partner, the retinoic acid receptor (RARα), was unaffected by LPS. A potential cell-signaling modulator of RXRα activity, c-Jun-N-terminal kinase (JNK) was maximally activated at 1–2 hours, coincident with maximal levels of cytoplasmic RXRα. RNA levels of RXRα were unchanged, while expression of 6 sentinel hepatic genes regulated by RXRα were all markedly repressed after LPS treatment. This is likely due to reduced nuclear binding activities of regulatory RXRα-containing heterodimer pairs. CONCLUSION: The subcellular localization of native RXRα rapidly changes in response to LPS administration, correlating with induction of cell signaling pathways. This provides a novel and broad-ranging molecular mechanism for the suppression of RXRα-regulated genes in inflammation

Effect of Corner Strength Enhancement on Shear Behaviour of Stainless Steel Lipped Channel Sections

During the cold-forming process of manufacturing, stainless steel sheets undergo plastic deformations, in particularly around corner regions of press braked sections. These plastic deformations lead to significant changes in material properties of stainless steel compared to its flat sheet properties. Consequently, yield strength and ultimate strength increments can be envisaged and this process is termed as cold working. Stainless steel exhibits significant level of strain hardening under plastic deformations. This is the main reason for these strength enhancements. In the structural design process of stainless steel sections, these strength increments are required to be considered to harness the benefits arising from it. Therefore, previous research proposed predictive models for these strength enhancements. In this context, the effect of corner strength enhancement on press-braked stainless steel lipped channel sections under shear was examined in this paper. 120 finite element models were developed. Different corner radii and section thicknesses were taken into account. Results highlighted that the effect of cold working on the shear capacity of stainless steel lipped channel sections is more significant in compact sections compared to slender sections where up to 9% increment was observed. Further analysis was conducted using 40 finite element models to highlight the inelastic reserve capacity available in compact stainless steel lipped channel sections in shear. From the results, it was concluded that when web slenderness is less than 0.25 more than 40% shear capacity increment can be achieved due to strain-hardening of stainless steel

Shear Behaviour of Cold-Formed Stainless Steel Lipped Channels with Reduced Support Restraints

Lipped channel beams are commonly used in buildings for load-bearing components such as floor joists and roof purlins. The typical practice is to use one-sided web side plates (WSPs) to attach beams from their webs to the supports at the connections, through bolts. In such realistic conditions, it is not practical to use WSPs over the full height of the webs, thus only a part of the web height is restrained at the supports. This controls the mobilising of diagonal tension field in the web and also provides less restraint to the lateral movement of the web. Therefore, realistic support conditions affect the shear capacity due to the lack of restraint of the web at the supports. On the other hand, the current shear design rules are based on ideal support conditions which do not represent the true scenario. Therefore, it is critical to investigate the effect of reduced support restraints on the shear capacity since it has been given less attention in the literature. This paper presents the effect of reduced support restraints on the shear capacity of stainless steel lipped channel beams. Finite element models were developed to study the effect with regard to various influential parameters. From the finite element results, it was found that the shorter the WSP—the higher the shear capacity reduction, where about 50% shear capacity reduction was observed for 60% reduction in WSP height. Furthermore, it was concluded that compact sections exhibit more significant capacity reduction than slender sections when reducing the WSP height. Therefore, a reduction factor was introduced to the current direct strength method shear design rules considering the effect of reduced support restraints on the shear capacity

Web crippling behaviour and design of cold-formed steel sections

Cold-formed steel sections are used in many different shapes based on their applications. Recently, a new C-section known as SupaCee was introduced in Australia with higher flexural capacities compared to traditional channel sections. However, all cold-formed steel sections are vulnerable to web crippling failures due to their higher plate slenderness. Australian/New Zealand (AS/NZS 4600) and North American (AISI S100) Standards use a unified web crippling design equation with four coefficients while Eurocode 3 Part 1.3 uses different design equations to predict the web crippling capacities of cold-formed steel sections. The web crippling coefficients were developed based on the experimental studies undertaken since the 1940s. These experimental studies utilised different test set-ups and specimens lengths and hence the accuracy of predictions using these coefficients may be inadequate. No coefficients are available for unlipped channel sections with fastened supports and high strength SupaCee sections while the same coefficients are used for lipped channels with fastened and unfastened supports. To address these shortcomings, the web crippling behaviour of unlipped and lipped channel and SupaCee sections was experimentally investigated based on recently developed AISI S909 web crippling test guidelines. Finite element analyses were then performed to extend the range of cold-formed steel sections. Using the web crippling capacity results from both experiments and finite element analyses, new equations were proposed to determine the web crippling capacities of lipped and unlipped channel and SupaCee sections. Suitable direct strength method based web crippling design equations were also developed. This paper presents the important details of several detailed web crippling studies undertaken recently including a suite of web crippling design equations that can be adopted in relevant cold-formed steel standards.</p