Material tests of 316L austenitic stainless-clad steel at elevated temperatures

[EN] Mechanical properties of stainless-clad (SC) steel plates at elevated temperatures are key parameters for fire resistant design and numerical simulation analysis of SC steel structures. Compared with pure stainless steel and pure ordinary steel, SC steel not only combines advantages of the two component metals, but may also balance the performance and cost; however, it behaves quite differently in terms of material properties. In order to quantify this performance, tension coupon tests at room as well as elevated temperatures are conducted on the SC steel plate. Based on the test results, failure modes of the tension coupons are analysed, and full-range stress-strain curves are obtained; material properties are accordingly determined and described herein, and analyses are performed on several properties including yield strength, ultimate tensile stress, elastic modulus and elongation after fracture. It is found that with an increase of the temperature, both the elastic modulus and strengths are reduced remarkably. For determining these material properties quantitatively and developing robust constitutive models of the SC steel at elevated temperatures, more test data are needed, and the incorporation of the effects of the clad ratio on the material properties at both room and elevated temperatures is also necessary. The present research outcomes may provide valuable reference for fire design and calculations of the SC steel.This work was financially supported by the National Natural Science Foundation of China (Nos. 51608300, 51778329), which are gratefully acknowledged.Bai, R.; Ban, H.; Chung, K.; Bai, Y. (2018). Material tests of 316L austenitic stainless-clad steel at elevated temperatures. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 851-855. https://doi.org/10.4995/ASCCS2018.2018.7011OCS85185

Research progress on material properties of clad steel

[EN] Clad steel possesses benefits of the both component metals in terms of mechanical performance, corrosion resistance, sustainability and lower full lifecycle cost, etc. As a result, it has been more and more widely used in the petroleum, chemical, marine, shipbuilding and metallurgical industries, including stainless-clad steel and titanium clad steel. Such clad steel has also great potential for application in building and bridge structures. For better understanding material properties of such clad steel, a review of research progress available in the literature is conducted herein, as well as recent research undertaken by the authors’ group at Tsinghua University. It can be found that very limited research reported in the literature mainly concerns static material properties of the clad steel, and primary relations between clad ratio and strength are suggested. The authors carried out material tests on both titanium and stainless-clad steel plates, with different clad ratios being incorporated. For the stainless-clad steel tests, both material and butt welded connections are tested, and various elevated temperatures are considered. In addition, tension coupon tests under cyclic loadings are also briefly introduced herein. Primary constitutive relations developed by the authors are reviewed in this paper. All the research findings and proposed formulae may provide an essential basis for future structural analysis, and may promote its application in structural engineering.This work was financially supported by the National Natural Science Foundation of China (Nos. 51778329, 51608300), which are gratefully acknowledged.Ban, H.; Bai, R.; Chung, K.; Zhu, J.; Bai, Y. (2018). Research progress on material properties of clad steel. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 653-658. https://doi.org/10.4995/ASCCS2018.2018.7010OCS65365

Strength of multi-span composite beams subjected to combined flexure and torsion

An improved understanding of the performance of composite beams subjected to combined flexure and torsion is essential for practical design as such loading states are very common in bridges for the main girder and in buildings for edge beams.Multi-span steel–concrete composite beams consisting of two steel joists and one concrete slab are concerned herein, on which an experimental study and finite element (FE) modelling analyses are presented. Eight reduced scale beams under combined flexure and torsion to varying degrees are tested, with both full and partial shear connection being incorporated. Either flexure-dominated or torsion-dominated failure modes are observed in each test depending on the ratio between the bending and torsional moments applied externally. Load-deformation responses, ultimate strengths as well as flexure–torsion interaction of all specimens are also reported and discussed. Based on the experimental outcomes, a three-dimensional FE model is developed and further validated against the test results, and an extensive range of parametric analyses are undertaken by using the FE model. It is indicated that in addition to well-known parameters relating to the concrete slab and stirrups, the torsional strength of multi-span composite beams is also sensitive to the degree of shear connection, spacing of the joists and span-to-depth ratio. Contributions of the steel joist and its constraint on the slab towards the torsional strength are increased. With respect to their flexure–torsion interaction relation, no increase in the torsional strength is observed within the presence of combined flexure, and vice versa. The interaction is insensitive generally to various parameters considered herein and the test results exhibit consistent phenomenon. Design guidance and new equations for predicting the torsional strength and the flexure–torsion interaction relation are proposed based on the test and FE analysis results as well as a comprehensive review of existing approaches in the literature

Non-linear analysis of multi-span composite beams under combined flexure and torsion

Multi-span steel-concrete composite beams fabricated from two steel joists and one concrete slab are widely utilised in bridges and highway interchanges, and are commonly subjected to combined actions of flexure and torsion. However, few national standards involve such loading combinations for the design of composite beams, and little research reported in the literature concerns the multi-span composite beams. With the aim of understanding the strength characteristics of such members subjected to combined flexure and torsion, a three-dimensional finite element (FE) model is introduced herein, and is calibrated against experimental results in terms of the loading capacities, the ultimate strength in torsion as well as the load-deformation response. A large number of parametric analyses are subsequently presented by using the FE model, and the effects of various parameters relating to the degree of shear connection, material strengths, stirrups and geometries are elucidated. Based on the non-linear analysis results, the degree of shear interaction, the spacing of the joists and the span-to-depth ratio are found to be influential in the ultimate strength in pure torsion of multi-span composite beams, in addition to the well-known parameters relating to the plain concrete and stirrups. Regarding the flexure-torsion interaction relation, the torsional and bending strengths are decreased within the presence of combine flexure and torsion, respectively. Furthermore, the interaction is generally consistent with varying parameters being incorporated. In accordance with a review of previous methodologies reported in the literature and the non-linear analysis results, practical design guidance and equations are developed for evaluating the torsional strength and the flexure-torsion interaction relation

Tensile Behavior of Titanium-Clad Bimetallic Steel Butt-Welded Joints

Because of the promising corrosion resistance and load-bearing capacity, titanium-clad (TC) bimetallic steel has gained increasing attention in ocean/coastal civil and structural engineering. Due to the double-layer nature of TC bimetallic steel, the characteristics of the structural member’s geometry and weld details are considerably different from that of conventional steel members. Even though previous studies have conducted systematical clarifications on parent material of TC bimetallic steels, the mechanical behaviors of weld joints are still vague. This paper firstly describes the manufacture features of TC bimetallic steel welded joints and welded members. Subsequently, the type II and type III butt-welded joints provided by GB/T 13149-2009 are selected to study the corresponding tensile mechanical behavior. Two butt-welded TC bimetallic steel plates were fabricated from hot-rolled bonding TA2 + Q355B TC bimetallic steel and welding wire of ER55-Ni1 and ERTA2ELI. Eight tensile coupons were then extracted from the two welded plates and loaded to failure monotonically. The failure mechanism, stress–strain curves and key mechanical properties are studied and compared with that of parent material. It is found that both types of welded joints possess two fracture points. The first one refers to the fracture of weld joint between the clad layer and titanium cover plate, whilst the second one is the eventual fracture of substrate metal. When the first fracture point is reached, the stress–strain relation exhibits a sharp drop in stress value. Thereafter, a strain-hardening behavior can still be observed prior to the ultimate strength point. The first fracture-induced stress drop of type II joint is less than that of type III joint, whilst the strain-hardening amount of type II joint is more outstanding than that of type III joint. The fracture elongations of type II joint and type III joint are respectively 37% and 57% that of the parent material, whilst the proportions between the ultimate strengths of welded joints and parent material are, respectively, 90% and 93%. In general, the two types of TC bimetallic steel weld joints investigated herein exhibit favorable load-bearing capacity but unfavorable ductility and deformability. Based upon the experimental results, the structural design methodology of welded TC bimetallic steel structure is discussed. The investigations conducted in this paper can provide reference for development of structural design theory of welded TC bimetallic steel structure

Flexural strength and rotation capacity of welded I-section steel beams with longitudinally profiled flanges

Application of longitudinally profiled (LP) steel plate in the flange of flexural members may provide a good solution to optimize their mechanical performance and to improve the efficiency of steel use, whilst existing design codes provide no design guidance or prediction methodology for such advanced beams in terms of flexural behaviour. To clarify their flexural strength and rotation capacity, tests on two full-scale welded I-section steel beams with longitudinally profiled flanges (LPB members) are carried out herein, as well as two traditional beams with uniform cross-section for comparison. All the specimens exhibit sufficient flexural strength and rotation capacity for seismic plastic design, and specifically, the LPB members possess even better performance in case of identical steel usage. Parametric analyses of 250 beams incorporating a wide range of flange slenderness and steel grades, are conducted by employing the validated nonlinear FE model to investigate the effects of rate of thickness change for the LP flanges. The results show that the effect is limited on the flexural strength but significant on rotation capacity. The existing design provisions for beams with uniform cross-section give generally conservative design results for the flexural strength of the LPB members, but limiting values of flange slenderness needs to be reduced. The research outcomes may provide an important basis for promoting the application of LP plates in flexural members.</p

Time-dependent behaviour of composite beams with blind bolts under sustained loads

The use of blind bolts in steel–concrete composite beams is beneficial for promoting sustainable design and for retrofitting existing steel structures. This paper presents an experimental study as well as finite element (FE) modelling analyses for the time-dependent behaviour of composite beams with blind bolts subjected to sustained loads. Four full-scale simply supported beams utilising different types of bolts and studs were tested under long-term static loads. The mid-span deflections were monitored for a period of over 260 days. Short term push-out tests were also carried out on the connectors used in the composite beams, and their slip deformation was recorded for determining the initial stiffness. The experimental results were modelled by using a three-dimensional FEmodel, inwhich the creep of the concretewas simulated through defining a viscoelastic response and the shrinkage of concrete was incorporated by means of notional thermal expansion. The FE model was validated against the experimental results reported herein and other independent results of composite beams using conventional welded studs reported elsewhere, and it was subsequently applied to carry out parametric studies. An extensive body of parameters was considered to clarify their effects on the time-dependent behaviour of composite beams with blind bolts, including the mechanical properties and configuration details of shear connectors, the concrete strength, the loading conditions, the span-to-depth ratio and the reinforcement ratio. It was demonstrated that the time-dependent behaviour was sensitive to the stiffness and the bolt-to-hole clearance of connectors, and some other parameters also possessed effects with different degrees. The research findings implied that using blind bolts in composite beams was beneficial to the time-dependent response due to their relatively lower deflections resulting from the creep and shrinkage of the concrete over time. The outcome may provide an important basis and guidance for designing such composite beams when considering their long-term response with time effects

Flexural strength and rotation capacity of welded I-section steel beams with longitudinally profiled flanges

Application of longitudinally profiled (LP) steel plate in the flange of flexural members may provide a good solution to optimize their mechanical performance and to improve the efficiency of steel use, whilst existing design codes provide no design guidance or prediction methodology for such advanced beams in terms of flexural behaviour. To clarify their flexural strength and rotation capacity, tests on two full-scale welded I-section steel beams with longitudinally profiled flanges (LPB members) are carried out herein, as well as two traditional beams with uniform cross-section for comparison. All the specimens exhibit sufficient flexural strength and rotation capacity for seismic plastic design, and specifically, the LPB members possess even better performance in case of identical steel usage. Parametric analyses of 250 beams incorporating a wide range of flange slenderness and steel grades, are conducted by employing the validated nonlinear FE model to investigate the effects of rate of thickness change for the LP flanges. The results show that the effect is limited on the flexural strength but significant on rotation capacity. The existing design provisions for beams with uniform cross-section give generally conservative design results for the flexural strength of the LPB members, but limiting values of flange slenderness needs to be reduced. The research outcomes may provide an important basis for promoting the application of LP plates in flexural members.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite Structure