رفتار لرزه ای سازه های فولادی مهاربندی شده متحد المرکز تنش واحد
Abstract
1- Introduction
2- Description of the steel structures under study
3- Structural modelling and seismic motions used
4- Results from seismic analyses
5- Conclusions and future needs
References
Abstract
This paper summarizes the estimated results from three-dimensional non-linear time-history seismic analysis of tension-only concentrically braced steel structures. The braces of these type of steel structures are properly detailed in order to sustain only tension and no compression. In particular, a cheap and easy to fabricate brace detailing allows the brace to slide when in compression and to develop a resisting force when in tension. A comparison between steel structures designed with the proposed tension-only braces and with buckling-restrained braces is performed on the basis of commonly used seismic response and demand indices. It is shown that tension-only and buckling-restrained braced structures may exhibit similar behavior. Nevertheless, column overstress in compression is larger for the tension-only braced structures. Preliminary conclusions regarding the use of the proposed tension-only braces as a seismic force-resisting system for steel structures are drawn.
Introduction
Concentrically braced frames (CBFs) constitute a popular seismic force-resisting system for steel structures. They are typically separated in ordinary concentrically braced frames (OCBFs) and special concentrically braced frames (SCBFs). Seismic codes distinguish these two types of CBFs by enforcing appropriate design and detailing requirements, even though OCBFs generally are not recommended for areas of high seismicity [1,2]. Useful overviews on the seismic behaviour of CBFs and of SCBFs taking into account the properties and the configurations of the braces can be found in literature, e.g., [1–4] and references therein. Buckling-restrained braced frames (BRBFs) are a special type of CBFs where braces are appropriately detailed against global buckling and strength loss [1,2,4,5]. A BRBF is usually more flexible than a SCBF and its design is governed by code-specified drift limits [1]. BRBFs tend to concentrate damage in specific storeys producing large permanent drifts [1,4,5] as well as to induce substantial deformational demands at beam-column joints, e.g., [6]. Alternative types of braces that can be used in a CBF and seem to exhibit a stable hysteretic behaviour is the three-segment brace recently proposed by Seker et al. [7] and the superelastic shape memory alloy (SMA) brace proposed by McCormick et al. [8]. A comparative study on the seismic performance of CBFs with SMA braces and BRBFs, has been also performed [9]. To avoid common brace buckling problems, CBFs with tension-only braces (employing steel rods) have been proposed [10–12] but their use seems to be restricted only in seismic retrofitting of existing structures [13–15]. On the other hand, application of tension-only braces in SCBFs is prohibited [2,3], whereas in [1], tension-only bracing type behaviour due to purely elastic buckling of the braces is mentioned but without any further recommendation. The use of tension-only braces (using spiral strand ropes or cables) in a seesaw configuration [16–18] seems to be a promising seismic force-resisting system but further research is demanded before its codification.