Seismic design procedures for concentrically braced frames

2010

Engineering Structures

136

101

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...

Section: Hysteretic Responsementioning

confidence: 99%

mentioning

confidence: 99%

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

Nip

Gardner

2010

Engineering Structures

136

101

“…Indeed, design approaches in seismic codes typically aim to concentrate inelastic deformation in the bracing members while ensuring elastic behaviour in other parts of the structure by means of the application of capacity design principles and failure mode control [10].…”

Section: Concentrically-braced Frames (Cbf)mentioning

confidence: 99%

Rigid‐plastic models for the seismic design and assessment of steel framed structures

Mariotti

Earthq Engng Struct Dyn

Bento

2009

Self Cite

This paper demonstrates the applicability of response history analysis based on rigidplastic models for the seismic assessment and design of steel buildings. The rigid-plastic force-deformation relationship as applied in steel moment-resisting frames is re-examined and new rigid-plastic models are developed for concentrically braced frames and dual structural systems consisting of moment-resisting frames coupled with braced systems. This paper demonstrates that such rigid-plastic models are able to predict global seismic demands with reasonable accuracy. It is also shown that, the direct relationship that exists between peak displacement and the plastic capacity of rigid-plastic oscillators can be used to define the level of seismic demand for a given performance target.

“…Although seismic codes of practice, such as Eurocode 8 [5] and AISC [6] consider the main behavioural aspects of bracing members, they differ on the quantification of important design parameters and limiting criteria [7]. While these discrepancies may not be significant in conventional static design, which is largely based on conservative estimates of stiffness and capacity, appropriate implementation of the capacity design procedures adopted in seismic codes requires that the main response parameters be adequately quantified.…”

Section: -[4[)mentioning

confidence: 99%

Behaviour of tubular steel members under cyclic axial loading

Goggins

Broderick

Journal of Constructional Steel Research

et al. 2006

This paper examines the cyclic performance of axially-loaded tubular members used as bracing elements to provide lateral seismic resistance in steel framed structures. An experimental study into the response of members with square and rectangular hollow sections, made from cold-formed steel, is described. Three cross-sectional geometries were employed to represent a range of local and overall slenderness. Fifteen specimens, with normalised slendernesses between 0.4 and 3.2, were tested under cyclic axial displacements of increasing amplitude. In addition, twenty-one short specimens were tested under displacement-controlled monotonic tension loading, focusing primarily on the relationship between the tensile resistance of the material and that of the cross-section.Based on the results obtained in both sets of tests, and with due consideration of existing design provisions, the paper assesses the influence of section and member properties on the structural parameters that are most important for seismic design. These include the tensile capacity, initial and post-buckling compressive resistance, ductility capacity, energy dissipation, and mid-length lateral deformations of bracing members.