Studies of the nonlinear response of stainless steel structures

Current design guidance on stainless steel structures is largely based on assumed analogies with carbon steel, thereby neglecting stainless steels* actual material behaviour in favour of simplicity. However, its high initial cost warrants the development of improved design guidance which is rational, safe, efficient and in accordance with the actual nonlinear material behaviour. Within the current research project, all reported test data on stainless steel cross- sections (beams and stub columns) have been gathered and utilized to update current European design guidance and to propose alternative novel design methods which account for actual material behaviour and allow for more efficient material use. Existing design methods which allow for the effect of element interaction on cross- section capacity of carbon steel plated sections have been adapted to stainless steel and a modification to the continuous strength method has been proposed, which leads to a significant decrease in the scatter of the predictions. Moreover, the possibility of expanding the scope of the current codified provisions of Eurocode 3: Part 1-4 to new material grades and cross-sections has been investigated through experimental and numerical studies. A series of tests and finite element (FE) analyses on stainless steel Oval Hollow Section (OHS) members was carried out to investigate the structural behaviour of these sections. Similarly, experimental and numerical studies on a new grade of stainless steel with a low nickel content, termed lean duplex stainless steel (EN 1.4162) were also conducted and its applicability for structural applications was verified. Finally, a series of tests on continuous stainless steel beams has been undertaken to investigate the effect of moment redistribution on the capacity of indeterminate stainless steel structures and assess the applicability of nonlinear structural analysis procedures, equivalent to the plastic design of carbon steel structures, to indeterminate stainless steel structures. It was found that plastic design can be safely applied to stainless steel structures and an extension to the continuous strength method has been proposed.Open Acces

Plastic design of stainless steel continuous beams

In this paper an experimental study on eight simply-supported and four two-span continuous beams employing austenitic and duplex stainless steel rectangular hollow sections (RHS) is reported. In parallel with the tests, finite element models were developed. Upon validation against the experimental results, parametric studies were conducted to expand the available structural performance data over a range of cross-section slendernesses, structural systems and load configurations likely to occur in practice. The obtained experimental and numerical results along with collated test data were used to assess the accuracy of EN 1993-1-4 design provisions and to explore the possibility of plastic design for stainless steel indeterminate structures, simultaneously accounting for the effect of strain-hardening at cross-sectional level and moment redistribution exhibited by structures employing stocky cross-sections

Experimental behavior and design of reinforced concrete exterior beam-column joints strengthened with embedded bars

Shear-deficient reinforced concrete (RC) beam-column joints (BCJs) represent one of the main factors behind the seismic damage suffered by existing concrete infrastructure, as well as the associated loss of life. This study presents a novel technique for strengthening shear-deficient RC BCJs. The technique involves embedding carbon fiber reinforced polymer (CFRP) or steel bars into epoxy-filled holes drilled within the joint core. Six exterior RC BCJs were constructed and tested under displacement-controlled cyclic loading. Five specimens, of which four were strengthened with embedded bars, were designed with shear-deficient joints according to the pre-1980s building codes. The remaining specimen was adequately designed according to ACI 352R-02. The test parameters are the type (steel or CFRP) and number (4 or 8 bars) of embedded bars. The unstrengthened control specimen experienced joint shear failure in the form of cross-diagonal cracks. The strengthened specimens, namely those strengthened with embedded steel bars, exhibited less brittle failure where damage occurred in the beam region at the early stages of loading, suggesting the outset of a beam hinge mechanism. Additionally, the strengthened specimens exhibited enhancements in joint shear strength, ductility, dissipated energy and stiffness of 6-21%, 6-93%, 10-54% and 2-35%, respectively, compared to the control specimen. This paper also presents a mechanics-based design model for RC BCJs strengthened with embedded bars. The proposed model covers all possible failure modes including yielding of the existing steel reinforcement, concrete crushing and debonding of the embedded bars. The accuracy of the proposed model was checked against the test results. The model gave good predictions with an average predicted-to-experimental ratio of 1.05 and a standard deviation of 0.04. Keywords: Analysis; Beam-column joints; Design; Embedded bars; Fiber reinforced polymer; Reinforced Concrete; Shear strengtheningDirectorate General of Higher Education, Ministry of Research and Higher Education of Indonesi

Design of stainless steel cross-sections with outstand elements under stress gradients

This is an accepted manuscript of an article published by Elsevier in Journal of Constructional Steel Research on 09/01/2021, available online: https://doi.org/10.1016/j.jcsr.2020.106491 The accepted version of the publication may differ from the final published version.A significant amount of research has been reported on stainless steel tubular sections, while studies on I- and C-sections remain relatively limited. This paper presents a comprehensive numerical study on the response of stainless steel I- and C-sections subjected to minor axis bending, with outstand flanges subjected to stress gradients. Numerical models are developed and validated against reported test data on austenitic stainless steel sections under minor axis bending. Subsequently, parametric studies using standardised material properties on austenitic, duplex and ferritic stainless steel grades, covering a wide variety of cross-section slendernesses, are carried out to expand the structural performance data. The results are used to assess the applicability of the Eurocode slenderness limits, revealing that the Class limit 3 for outstand flanges under stress gradient is overly conservative. Moreover, Eurocode underestimates the predicted bending strengths, whereas the level of accuracy and consistency improves for stocky sections, when the Continuous Strength Method is used. Aiming to address the lack of accuracy and consistency in the design predictions of slender sections, particular focus is placed on their performance. It is demonstrated that outstand elements under stress gradients exhibit significant inelastic behaviour after the compression flanges have locally buckled. Inelastic buckling behaviour is not considered in current design guidance, thus resulting in overly conservative and fundamentally incorrect strength predictions. An alternative design method based on the plastic effective width concept is proposed for slender stainless steel I- and C-sections in minor axis bending, which leads to more favourable and less scattered strength predictions.Accepted versio

Testing, numerical simulation and design of prestressed high strength steel arched trusses

The structural behaviour of prestressed high strength steel arched trusses is studied in this paper through experimentation and numerical modelling. Four 11 m span prestressed arched trusses fabricated from S460 hot finished square hollow section members were loaded vertically to failure. Three of the tested trusses were prestressed to different levels by means of a 7-wire strand cable housed within the bottom chord, while the fourth truss contained no cable and served as a control specimen. Each truss was loaded at five points coinciding with joint locations along its span, and the recorded load-deformation responses at each loading point are presented. Inclusion and prestressing of the cable was shown to delay yielding of the bottom chord and enhance the load carrying capacity of the trusses, which ultimately failed by either in-plane or out-of-plane buckling of the top chord. For the tested trusses, around 40% increases in structural resistance were achieved through the addition of the cable, though the self-weight was increased by only approximately 3%. In parallel with the experimental programme, a finite element model was developed and validated against the test results. Upon successful replication of the experimentally observed structural response of the trusses, parametric studies were conducted to investigate the effect of key parameters such as prestress level, material grade and the top chord cross-section on the overall structural response. Based on both the experimental and numerical results, design recommendations in the form of simple design checks to be performed for such systems are provided

Aluminium SHS and RHS subjected to biaxial bending: Experimental testing, modelling and design recommendations

This is an accepted manuscript of an article published by Elsevier in Engineering Structures on 06/11/2020, available online: https://doi.org/10.1016/j.engstruct.2020.111468 The accepted version of the publication may differ from the final published version.Traditionally, experimental research on structural members has focused on the isolated fundamental cases of pure compression/tension, major axis bending or minor axis bending, whilst beam columns under compression and uniaxial bending have also been tested. Biaxial bending has received less experimental attention and it has always been assumed that tests on the idealised cases of major axis bending and minor axis bending can be used together with numerical predictions of biaxial bending to determine suitable interaction curves. This investigation reports an experimental study on aluminium flexural members with variable angles between the plane of bending and the major axis of the cross-section. Cross-sections with various thicknesses and hence plate slenderness values are considered. The experimental results are used to validate a numerical model that allows a large number of cross-sectional dimensions and loading cases to be examined. Following parametric studies and generation of numerical data, the design provisions for biaxial bending specified in EN 1999-1-1 are compared against the predictions provided by the Continuous Strength Method (CSM) and a new proposed method. The comparison shows that EN 1999-1-1 provides overly conservative results with biaxial bending resistances underestimated by approximately 17%. Both the CSM and the proposed method are observed to significantly improve predictions by reducing, on average, underestimations down to 3% and 1%, respectively, and consequently enabling a better usage of the material and ultimately a more economic and sustainable design.Accepted versio