2001 Research Reports No R805-R811

Abstract
This report presents the laboratory test results on fillet and flare-bevel welded truss connections in 5 50× 50× 2. DuraGal® angle sections. The arc welded connections between the DuraGal® sections and 10-mm hot-rolled steel plates were fabricated using the gas metal arc welding (GMAW) process. It was found that failures of the fillet and the flare-bevel welds occurred in both the weld metal and the DuraGal® angle section. The ultimate test loads of the connection specimens were compared with their predicted failure loads and their nominal capacities computed using the equations specified in the cold-formed steel standard AS/NZS 4600:1996 and the steel structures code AS 4100-1998, respectively. It is concluded through a reliability analysis that Clauses 5.2.3.2(a) and 5.2.6.2(3) of AS/NZS 4600 may be used to design fillet and flare-bevel welded connections in 2.5-mm DuraGal® angle sections, respectively. The use of Clause 9.7.3.10 of AS 4100 to compute the nominal capacities of the fillet and the flare-bevel welded connections in 2.5-mm DuraGal® angle sections fabricated in the present work was found to be conservative.

Keywords
Angle section, cold-formed steel, design standards, fillet welds, flare-bevel welds, load and resistance factor design, sheet metal, welded connections

Abstract
This paper investigates the reliability of the existing design equations specified in AS/NZS 4600:1996 for flare-bevel and flare-vee welded connections in cold-reduced high-strength G450 sheet steels. The existing design equations are adapted from the AWS D1.3 Structural Welding Code, which is based on the testing results on flare-bevel welded connections only in mainly mild sheet steels. In the present work, flare-bevel and flare-vee welded connections in 1.5-mm and 3.0-mm sheet steels were fabricated using different GMAW procedures and tested to failure. All the transverse flare-bevel welded connections failed in the HAZs of the parent material. The longitudinal flare-bevel and flare-vee welded connections in 1.5-mm sheet steel also failed in the HAZs of the parent material, while those in 3.0-mm sheet steel failed in the weld metal. Nevertheless, it was found that the existing design rules may be applied conservatively to transverse and longitudinal flare-bevel welded connections in G450 sheet steels provided the weld quality is comparable to that produced in-house. On the other hand, it was found that the existing equations overestimate the capacity of flare-vee welded connections in G450 sheet steels. Ideally, flare-bevel and flare-vee welded connections in 3.0-mm G450 sheet steel are design in accordance with AS 4100. A survey of arc welded connections produced by industry fabricators suggested that the quality of in-house welded connections is unlikely to be matched in practice.

Keywords
Cold-formed steel, design standards, flare-bevel welds, flare-vee welds, load and resistance factor design, sheet metal, welded connections

Abstract
The bearing behaviour of footings on layered soils has received significant attention from researchers, but most of the reported studies are limited to footings resting on the surface of the soil and are based on the assumption of small deformations. In this paper, large deformation analyses, simulating the penetration of strip and circular footings into two-layered clays, are described. The upper layer was assumed to be stronger than the lower layer. The importance of large deformation analysis for this problem is illustrated by comparing the small and large deformation predictions. The bearing behaviour is discussed and the undrained bearing capacity factors are given for various cases involving different layer thicknesses and different ratios of the undrained shear strengths of the two clay layers. The development of the plastic zones and the effect of soil self-weight on the bearing capacity are also discussed in the report.

Keywords
Large deformation, penetration, strip footing, circular footing, layered clays, bearing capacity

Abstract
The performance of three-dimensional hexahedral elements has been compared in this study. The standard quadratic 20-noded hexahedral element has shown robust performance in many applications, however, it has a high number of nodes, which necessitates relatively large computational time. The standard linear 8-noded hexahedral element has the least number of nodes in elements of this geometric type, but it is unable to model adequately a state of pure bending. The 8-noded element can be modified by including non-conforming displacements to improve its efficiency. The modified hexahedral element has been adopted in finite element analyses and its excellent performance in terms of accuracy and time efficiency is described.

Keywords
Non-conforming elements, 3-D finite element analysis

Abstract
Steel angle sections are commonly used as beams to support distributed loads which cause biaxial bending and torsion. However, the recommendations of many design codes are unnecessarily conservative when applied to the bending of angle section beams, or are of limited application, or fail to consider some effects which are thought to be important.

In this paper, consideration is given to the first-order elastic analysis of the biaxial bending of angle section beams including the effects of elastic restraints, and proposals are developed for the section moment capacities of angle sections under biaxial bending which approximate the effects of full plasticity in compact sections, first yield in semi-compact sections, and local buckling in slender sections. Proposals are developed for the bearing, shear, and uniform torsion capacities of angle section beams in a companion paper.

The proposals in this and the companion paper can be used to design steel angle section beams which are laterally restrained so that lateral buckling or second-order effects are unimportant.

Keywords
Angles, beams, bending, design, local buckling, moments, plasticity, section capacity, steel, yielding.

Abstract
Steel angle sections are commonly used as beams to support distributed loads which cause biaxial bending and torsion. However, many design codes do not have any design rules for torsion, while some recommendations are unnecessarily conservative, or are of limited application, or fail to consider some effects which are thought to be important. In this paper, proposals are developed for the section capacities of angle sections under bearing, shear, and uniform torsion.

In a companion paper, consideration is given to the first-order elastic analysis of the biaxial bending of angle section beams, including the effects of restraints, and proposals are developed for the section moment capacities of angle sections under biaxial bending.

The proposals in this and the companion paper can be used to design steel angle section beams which are laterally restrained so that lateral buckling or second-order effects are unimportant.

Keywords
Angles, beams, bearing, buckling, design, plasticity, section capacity, shear, steel, torsion, yielding.

Abstract
The report develops an expression for the stress-strain curves for stainless steel alloys which is valid over the full strain range. The expression is useful for the design and numerical modelling of stainless steel members and elements which reach stresses beyond the 0.2% proof stress in their ultimate limit state. In this stress range, current stress-strain curves based on the Ramberg-Osgood expression become seriously inaccurate principally because they are extrapolations of curve fits to stresses lower than the 0.2% proof stress. The extrapolation becomes particularly inaccurate for alloys with pronounced strain hardening.

The report also develops expressions for determining the ultimate tensile strength (σu) and strain (εu) for given values of the Ramberg-Osgood parameters (E0,σ0.2,n). The expressions are compared with a wide range of experimental data and shown to be reasonably accurate for all structural classes of stainless steel alloys. Based on the expressions for (σu) and (εu), it is possible to construct the entire stressstrain curve from the Ramberg-Osgood parameters (E0,σ0.2,n).

Keywords
Stainless steel, stress-strain curves, Ramberg-Osgood curve, tests.