Reliability analysis of structural stainless steel design provisions

Since the establishment of the Eurocode design provisions for structural stainless steel, a considerable amount of both statistical material data and experimental results on structural elements has been generated. In light of this, the current partial resistance factors recommended in EN 1993-1-4 for the design of stainless steel elements are re-evaluated. First, following an analysis of material data from key stainless steel producers, representative values of the over-strength and the coefficient of variation (COV) of the material yield strength and ultimate tensile strength were established. For yield strength, over-strength values and COVs of 1.3 and 0.060 for austenitic, 1.1 and 0.030 for duplex and 1.2 and 0.045 for ferritic stainless steels were determined. For the ultimate tensile strength, an over-strength value of 1.1 was found to be suitable for all stainless steel grades, and COV values of 0.035 for the austenitic and duplex grades and 0.05 for the ferritic grade were proposed. For the variability of the geometric properties, a COV value of 0.05 was recommended. Analysis of available experimental results based on the First Order Reliability Method (FORM), set out in EN 1990 Annex D, and utilising the derived statistical material parameters, revealed that the current recommended partial resistance factors in EN 1993-1-4 (γM0 = γM1 = 1.1 and γM2 = 1.25) cannot generally be reduced, and in some cases, modified design resistance equations are required, if the current safety factors are to be maintained

Elevated temperature material properties of stainless steel reinforcing bar

Corrosion of carbon steel reinforcing bar can lead to deterioration of concrete structures, especially in regions where road salt is heavily used or in areas close to sea water. Although stainless steel reinforcing bar costs more than carbon steel, its selective use for high risk elements is cost-effective when the whole life costs of the structure are taken into account. Considerations for specifying stainless steel reinforcing bars and a review of applications are presented herein. Attention is then given to the elevated temperature properties of stainless steel reinforcing bars, which are needed for structural fire design, but have been unexplored to date. A programme of isothermal and anisothermal tensile tests on four types of stainless steel reinforcing bar is described: 1.4307 (304L), 1.4311 (304LN), 1.4162 (LDX 2101®) and 1.4362 (2304). Bars of diameter 12 mm and 16 mm were studied, plain round and ribbed. Reduction factors were calculated for the key strength, stiffness and ductility properties and compared to equivalent factors for stainless steel plate and strip, as well as those for carbon steel reinforcement. The test results demonstrate that the reduction factors for 0.2% proof strength, strength at 2% strain and ultimate strength derived for stainless steel plate and strip can also be applied to stainless steel reinforcing bar. Revised reduction factors for ultimate strain and fracture strain at elevated temperatures have been proposed. The ability of two-stage Ramberg-Osgood expressions to capture accurately the stress-strain response of stainless steel reinforcement at both room temperature and elevated temperatures is also demonstrated

The use of stainless steel in structures

The past 15 years have seen the introduction or major revision of structural stainless steel design codes throughout the world, and at the same time, interest in the use of stainless steel in construction has been accelerating. Historically the high initial material cost of stainless steel has limited its use primarily to specialist and prestige applications. However, the emergence of design codes, a better awareness of the additional benefits of stainless steel and a transition towards sustainability are bringing more widespread use into conventional structures. Although a number of similarities between stainless steel and ordinary carbon steel exist, there is sufficient diversity in their physical properties to require separate treatment in structural design. In addition to the straightforward differences in basic material properties (such as Young's modulus and yield strength), further fundamental differences exist, such as the nature of the stress–strain curve and the material's response to cold-work and elevated temperatures; these have implications at ultimate, serviceability and fire limit states. This paper describes the use of stainless steel as a structural material, discusses current structural design provisions, reviews recent research activities and highlights the important findings and developments

Structural glass beams with embedded GFRP, CFRP or steel reinforcement rods: comparative experimental, analytical and numerical investigations

The use of hybrid and composite solutions for structural applications represents a common approach for the development of safe design principles. Consolidated examples exist for concrete, steel and masonry structures. As a general rule, materials are combined so as to obtain an enhanced redundancy, strength and/or (lateral) stiffness for these systems. In this paper, structural laminated glass (LG) beams including reinforcement rods are investigated, and special attention is spent on the effect of embedded rod features, consisting of GFRP, CFRP or stainless steel reinforcement tendons. The examined embedded solution, as shown, can offer a certain benefit to the bending performance of traditional LG beams, including positive effects on stiffness, resistance and redundancy. The intrinsic properties of rods can otherwise largely affect the overall observations. To this aim, unpublished experimental tests are first briefly summarised for a set of 1\u202fm span LG beams. Support for the preliminary discussion of the examined design concept is also derived from simple analytical calculations. Finite-Element (FE) numerical simulations are then presented, reporting on major expected behaviours due to variations in the geometrical/mechanical features of the rods, with respect to the experiments. A key role in the FE models is given by the reliable description of mechanical properties and interactions between the structural components. Comparative results are hence discussed for the post-fracture assessment of beam specimens. As shown, even a limited presence of reinforcing rods ( 48100-to-400 the explored range for the ratio of glass-to-rods cross-sectional area) can provide ductility and redundancy to the LG beams. Maximum benefits (+30% residual resistance) are given by ductile steel rods, while positive effects can also be achieved with GFRP and CFRP tendon rods

Strength enhancements in cold-formed structural sections — Part II: 2 Predictive models

Cold-formed structural sections are manufactured at ambient temperature and hence undergo plastic deformations, which result in an increase in yield stress and a reduction in ductility. This paper begins with a comparative study of existing models to predict this strength increase. Modifications to the existing models are then made, and an improved model is presented and statistically verified. Tensile coupon data from existing testing programs have been gathered to supplement those generated in the companion paper and used to assess the predictive models. A series of structural section types, both cold-rolled and press-braked, and a range of structural materials, including various grades of stainless steel and carbon steel, have been considered. The proposed model is shown to offer improved mean predictions of measured strength enhancements over existing approaches, is simple to use in structural calculations and is applicable to any metallic structural sections. It is envisaged that the proposed model will be incorporated in future revisions of Eurocode 3