Cyclic testing and numerical modelling of carbon steel and stainless steel tubular bracing members

Abstract

Satisfactory behaviour of structures under severe seismic loading is usually largely dependent on the ability of key components to undergo significant inelastic deformations. In the case of concentrically braced frames, the critical elements are the diagonal bracing members which are expected to experience repeated cycles involving yielding in tension and member buckling in compression. The performance of bracing members depends on various factors, including local slenderness, global slenderness, material yield strength, section shape and end restraint [1]. Due to the difficulty in modelling the non-linearity and cyclic plasticity accurately, numerous experimental studies have been carried out to study the cyclic inelastic behaviour of bracing members.The interest of researchers in the early days was primarily in the load-displacement hysteretic response of the braces. Models were proposed to predict residual elongation at zero load, loss of compressive strength, the area under the hysteresis loops which represents the amount of energy dissipation, and other key characteristics of the hysteresis loops [2][3][4][5]. It was generally concluded [4,5] that global slenderness was the most important parameter influencing the hysteretic behaviour of braces. Slender members lost compressive resistance more rapidly than stocky members, resulting in fewer inelastic response cycles and lower amount of energy dissipation.More recently, attention has shifted to examination of the factors influencing the fracture life of bracing members. Through experimental testing, both global and local slenderness were found to be important factors in determining fracture life. Tang and Goel [6] proposed one of the first empirical equations for predicting the fracture life of bracing members, which suggests that fracture life is proportional to both the aspect ratio of the cross-section and the global member slenderness but inversely proportional to the square of the local slenderness. However, the validity of this prediction method is limited to bracing members in inverted V braced frames. Further developments [7][8][9] in the prediction of fracture life of brace members have utilised this basic proposed equation and generalised the applicability to bracing members in other concentrically braced frame configurations.A more general relationship was established following a comprehensive survey of the experimental cyclic behaviour of steel bracing members conducted by Tremblay [7], in which buckling resistance, post-buckling resistance in compression, tensile resistance, fracture life and a number of other properties from about 50 members were assessed. Shaback and Brown [8] carried out tests on square hollow section bracing members and calibrated a more sophisticated expression of fracture life, defined as Revised Manuscript Click here to view linked References 2 the weighted sum of normalised compressive and tensile deformation, in terms of global slenderness, local slenderness, aspect ratio of the cross-section and material yield strengt...

Description of stress–strain curves for stainless steel alloys

“…Bock et al [39] conducted a detailed study of the prediction of  u for ferritic stainless steel, and proposed a revised expression, described by Eq. (17). As shown in Figure 14 and Table 10, Eq.…”

“…Based on the described analyses, the proposed predictive expressions and the recommended modifications to made to Annex C of EN1993-1-4 are summarised as follows: for austenitic, duplex and lean duplex (11) for ferritic grades (17) Additionally, the revised values for the first strain hardening parameter n, presented in Table 7, are recommended for inclusion in EN1993-1-4. The numeric values of Young's modulus for stainless steel proposed by Afshan et al [6] are also recommended herein.…”

Cyclic response of hollow and concrete-filled circular hollow section braces

“…Displacement ductility, ì˜is defined in this study as the ratio of maximum axial displacement to yield displacement, similar to the definition used by Nip et al (2010). Table 7 summarises the total number of cycles to fracture and displacement ductility for each of the specimens.…”

“…Nip et al, 2010), comparing the response of hot-rolled carbon steel, cold-formed carbon steel and stainless steel members. The cold-formed steel response was largely governed by the variation in residual stress between the corner and flat regions, and hot-rolled tubes displayed a superior performance overall.…”

“…Specimens were subjected to the cyclic loading protocol outlined by ECCS (1986), facilitating a direct comparison with the results of Nip et al (2010) and Broderick et al (2005). This loading sequence does not represent a real earthquake but was developed as a standardised procedure to establish the response of individual elements, substructures or entire structures under cyclic loading, since the behaviour of steel can deviate from the idealised elastoplastic response after repeated loading cycles.…”