Conference abstracts

2007 International Experts Seminar on Stainless Steel in Structures

This Seminar was a gathering of researchers investigating the behavior of stainless steels applied to structures. The document listed below are the papers presented at the seminar and are available to purchase from the Science Direct website. This collection of papers represents the latest research on stainless steels used in structures.

Strength enhancements induced during cold forming of stainless steel sections
by Rachel Cruise

The material properties of stainless steel are sensitive to plastic deformation which causes an increase in yield strength by a process termed cold working. The different strain paths experienced around cold-formed cross sections during manufacture create unique material strength distributions for sections from different forming routes and also influence residual stress patterns. The research program presented herein has examined experimentally the material and residual stress distributions found in two types of cold-formed sections–cold-rolled box sections and press-braked angles. Predictive tools to harness the observed strength enhancements have been proposed and incorporated into models. Subsequent comparisons have shown that these strength enhancements, in particular those observed for cold-rolled box sections, should be employed in structural design to avoid considerable underestimation of member resistance.

Tests of concrete-filled stainless steel tubular T-joints
by Ben Young

This paper describes a test program on a wide range of concrete-filled cold-formed stainless steel tubular T-joints fabricated from square hollow section (SHS) and rectangular hollow section (RHS) brace and chord members. A total of 27 tests was performed. The chord member of the test specimen was filled with concrete along its full length. Both high strength stainless steel (duplex and high strength austenitic) and normal strength stainless steel (AISI 304) specimens filled with nominal concrete cylinder strength of 30 MPa were tested. The axial compression force was applied to the top end of the brace member, which was welded to the center of the chord member. Local buckling failure of brace member was the main failure mode observed during the tests. Hence, the axial compression force was then applied by means of a steel bearing plate to avoid failure of brace member. The failure modes of chord face failure and chord side wall failure as well as crushing of the concrete infill were observed. All the tests were performed by supporting the chord member of the specimen along its entire length to apply the pure concentrated force without any bending moment. The test results were also compared with design rules for carbon steel tubular structures, which is the only existing design guideline for concrete-filled tubular joints. It is shown that the design strengths predicted by the current design rules are quite conservative for the test specimens. It is also recommended that the contribution of stainless steel tubes should be included in the design rules since it has significant effects on the ultimate bearing capacity of concrete-filled stainless steel tubular T-joints.

Structural design of stainless steel concrete filled columns
by Dennis Lam

This paper presents the behaviour and design of axially loaded concrete filled stainless steel circular and square hollow sections. The experimental investigation was conducted using different concrete cube strengths varied from 30 to 100 MPa. The column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with existing design methods for composite carbon steel sections—Eurocode 4 and ACI. It was found that existing design guidance for carbon steel may generally be safely applied to concrete filled stainless steel tubes, though it tends to be over-conservative. A continuous strength method is proposed and it is found to provide the most accurate and consistent prediction of the axial capacity of the composite concrete filled stainless steel hollow sections due largely to the more precise assessment of the contribution of the stainless steel tube to the composite resistance.

Lateral–torsional buckling of stainless steel I-beams in case of fire
by Paulo Vila Real

This work presents a numerical study of the behaviour of stainless steel I-beams subjected to lateral–torsional buckling in case of fire and compares the obtained results with the beam design curves of Eurocode 3. New formulae for lateral–torsional buckling, that approximate better the real behaviour of stainless steel structural elements in case of fire are proposed. These new formulae were based on numerical simulations using the program SAFIR, which was modified to take into account the material properties of the stainless steel.

Experimental and numerical investigation of high strength stainless steel structures
by Ben Young

The paper summarises research on high strength stainless steel tubular structures conducted at the University of Hong Kong, and the Hong Kong University of Science and Technology. Square and rectangular hollow sections were investigated. The test specimens were cold-rolled from high strength austenitic and duplex stainless steel sheets. The material properties of the test specimens were determined by tensile coupon tests at normal room and elevated temperatures. The initial geometric imperfection and residual stress of the specimens were measured. The experimental and numerical investigation focused on the design and behaviour of cold-formed high strength stainless steel structural members. The results were compared with design strengths calculated using the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures.

A design model for stainless steel box columns in fire
by Bjorn Uppfeldt

A study of stainless steel cold-rolled box columns at elevated temperatures is presented, which is a part of an on-going RFCS project ‘‘Stainless Steel in Fire’’, 2004–2007. Experimental results of six, class 4, stub columns at elevated temperature, tested by Ala-Outinen [Members with Class 4 cross sections in fire: Work package 3, ECSC project stainless steel in fire. Contract no. RFS-CR-04048, Espoo, Finland; 2005], were used to evaluate the finite element (FE) model. The FE analysis obtained using the commercially available software, ABAQUS, shows that the critical temperature was closely predicted. Further, a parametric study was performed using the same numerical model. This was a basis to check the quality of prediction of a newly proposed improvement for design rules of class 4 cross-sections in fire according to EN 1993-1-4 [Eurocode 3 - Design of steel structures — Part 1-4: General rules — Supplementary rules for stainless steels, CEN; 2006] and EN 1993-1-2 [Eurocode 3: Design of steel structures — Part 1.2: General rules — Structural fire design, CEN; 2005].

Interaction of bending and axial compression of stainless steel members
by Richard Greiner

The paper deals with the buckling behaviour of stainless steel members with the main focus on developing design formulae for use in the latest version of the European Standard EN 1993-1-4: Eurocode 3 – Design of steel structures – Part 1–4: General rules—Supplementary rules for stainless steel. Brussels; 2005. It is based on numerical simulations of single span members of various section type, which are subjected to axial compression and bending. Both flexural buckling and lateral–torsional buckling are dealt with so that the buckling behaviour of both I-sections and hollow sections can be covered. On the basis of these numerical results interaction factors have been derived in context with the design model for member design in Eurocode 3-1-1. For statistical evaluation the test results available from other authors have been used. The outcome of this investigation has been incorporated in the present EN 1993-1-4 as a recommendation in restricted form.

Structural uses of stainless steel — buildings and civil engineering
by Graham Gedge

Stainless steels have not traditionally been widely used as structural materials in building and civil engineering. Where the steels have been used for this purpose there has been some other imperative driving the design, usually corrosion resistance or architectural requirements rather than the inherent structural properties of the steel. The primary reason for this low use in structural applications is usually the perceived and actual cost of stainless steel as a material. Developments over the last 10 years, both in available materials and attitudes to durability, are now offering a new opportunity for stainless steels to be considered as primary structural materials.

Analysis of the behaviour of stainless steel bolted connections
by Hamid Bouchair

This study is focused on two types of bolted connections that are common in steel structures. They concern cover plate connections and T-stubs, where the bolts are loaded in shear or in tension. The Eurocode 3 requirements for stainless steel connection design are essentially the same as for carbon steel. The study considers the case of austenitic stainless steel for which the conventional elastic limit is relatively low compared to the ultimate strength. In bearing, criteria on deformation limits have to be considered for cover plate connections. In T-stubs, strain hardening of stainless steel exhibits a continuous increase of the applied load and can influence the failure mode. A finite element model is developed and validated for the two types of connections. A more extensive parametric study should be carried out to develop a better understanding of the behaviour of stainless steel connections.

A method to predict pitting corrosion of stainless steels in evaporative conditions
by Pekka Pohjanne

Stainless steels are used in architecture and building because of their good corrosion resistance and visual appearance. Despite all precautions localised corrosion has caused unexpected material failures in environments which should be harmless. These failures are associated to surface contamination with corrosive salt solutions that are formed when splash water concentrates due to evaporation. This paper reports on studies carried out to investigate the localised corrosion risk of stainless steels in concentrated salt solutions. A quantitative corrosion risk prediction approach based on the experimental corrosion studies and quantitative pitting corrosion models developed for evaluation of pitting corrosion risk are presented.

Shear resistance in stainless steel plate girders with transverse and longitudinal stiffening
by Imma Estrada

This paper summarizes and presents main results of the investigation conducted in the Department of Construction Engineering of the UPC dealing with shear behaviour of stainless steel plate girders. Initial shear buckling stress together with ultimate shear capacity of these structural elements have been evaluated with special attention paid to the effect of including stiffeners, both transverse and longitudinal. The studies conducted, both numerical and experimental tests, have permitted the development of new and simple design expressions to determine more accurately the initial shear buckling stress in stainless steel web panels and the ultimate capacity of plate girders considering the presence of a rigid or non-rigid end post.

Discrete and continuous treatment of local buckling in stainless steel elements
by Marios Theofanous

Cross-section classification is an important concept in the design of metallic structures, as it addresses the susceptibility of a cross-section to local buckling and defines its appropriate design resistance. For structural stainless steel, test data on cross-section capacity have previously been relatively scarce. Existing design guidance has been developed based on the limited experimental results and conservative assumptions, generally leading to unduly strict slenderness limits. In recent years, available test data for stainless steel cross-sections have increased significantly, enabling these slenderness limits to be re-assessed. In this paper all available stainless steel test data have been collected and additional moment–rotation curves have been presented. The study covers both cold-formed and welded plated elements as well as CHS. Following analysis of the test results, new slenderness limits for all loading conditions have been proposed and statistically validated. In addition to re-assessment of the current slenderness limits, a new approach to the treatment of local buckling in structural elements – the Continuous Strength Method – has been outlined. The Continuous Strength Method (CSM) is based on a continuous relationship between cross-section slenderness and deformation capacity and is applied in conjunction with accurate material modelling. The method enables more rational and precise prediction of local buckling than can be achieved with the traditional cross-section classification approach, thus allowing better utilization of material and more economic design.

The direct strength method for stainless steel compression members
by Kim Rasmussen

The paper presents a complete set of direct strength equations for stainless steel members and sections in compression. The direct strength equations are based on recent research on the local, distortional and member bucking of stainless steel compression members, including the interaction of local and member buckling. The paper summarises the underlying research and presents the direct strength equations in a consistent format using a notation similar to that used in the North American Specification and the Australian Standard for (carbon) steel structures. Direct strength equations are proposed for local, distortional and combined local and member buckling, which fit within the framework of the Australian, North-American and European standards for stainless steel.

Stainless steel in construction: A review of research, applications, challenges and opportunities
by Imma Estrada

Stainless steel has unique properties which can be taken advantage of in a wide variety of applications in the construction industry. This paper reviews how research activities over the last 20 years have impacted the use of stainless steel in construction. Significant technological advances in materials processing have led to the development of duplex stainless steels with excellent mechanical properties; important progress has also been made in the improvement of surface finishes for architectural applications Structural research programmes across the world have laid the ground for the development of national and international specifications, codes and standards spanning both the design, fabrication and erection processes. Recommendations are made on research activities aimed at overcoming obstacles to the wider use of stainless steel in construction. New opportunities for stainless steel arising from the shift towards sustainable development are reviewed, including its use in nuclear containment structures, thin-walled cladding and composite floor systems.

Assessment of stainless steel reinforcement for concrete structures rehabilitation
by Jose Perez

The aim of this study was to revise the factors influencing the service life of galvanic coupling between carbon steel and stainless steel reinforcements in simulated concrete pore solution, simulating the condition of a damaged structure repaired with stainless steel reinforcing bars. Numerous investigations have reported that austenitic stainless steel rebar, compared to carbon steel, when embedded in concrete, offer superior corrosion resistance in aggressive environments, especially chloride contaminated concrete. In concrete, contact with other metals should be avoided because of the risk of galvanic corrosion. When passive, both carbon steel and stainless steel have comparable corrosion potentials and the coupling of the two materials is of little effect on the corrosion behaviour of either material. Galvanic current values measured between carbon and stainless steel are negligible.

Residual stresses in cold-rolled stainless steel hollow sections
by Michal Jandera

Stainless steel exhibits a pronounced response to cold-work and heat input. As a result, the behaviour of structural stainless steel sections, as influenced by strength, ductility and residual stress presence, is sensitive to the precise means by which the sections are produced. This paper explores the presence and influence of residual stresses in cold-rolled stainless steel box sections using experimental and numerical techniques. In previous studies, residual stress magnitudes have been inferred from surface strain measurements and an assumed through-thickness stress distribution. In the present study, through thickness residual stresses in cold-rolled stainless steel box sections have been measured directly by means of X-ray diffraction and their effect on structural behaviour has been carefully assessed through detailed non-linear numerical modelling. Geometric imperfections, flat and corner material properties and the average compressive response of stainless steel box sections were also examined experimentally and the results have been fully reported. From the X-ray diffraction measurements, it was concluded that the influence of through-thickness (bending) residual stresses in cold-rolled stainless steel box sections could be effectively represented by a rectangular stress block distribution. The developed ABAQUS numerical models included features such as non-linear material stress–strain characteristics, initial geometric imperfections, residual stresses (membrane and bending) and enhanced strength corner properties. The residual stresses, together with the corresponding plastic strains, were included in the FE models by means of the SIGINI and HARDINI Fortran subroutines. Of the two residual stress components, the bending residual stresses were found to be larger in magnitude and of greater (often positive) influence on the structural behaviour of thin-walled cold-formed stainless steel sections.