يك مدل تحليلي يكتا براي تيرهاي پيوند كوتاه، مياني و بلند در قابهاي مهاربندي شده ي واگرا

هدف از انجام اين پژوهش بسط و گسترش مدل تحليلي يكتا براي پيش بيني رفتار الاستيك و غيرالاستيك تيرهاي پيوند مي­باشد، به نحوي كه براي انواع مختلف تير پيوند شامل تير پيوند كوتاه، متوسط و بلند قابل استفاده باشد. هنگامي كه قابهاي مهاربندي شده­ي واگرا تحت اثر زلزله­هاي شديد قرار مي­گيرند، تيرهاي پيوند از خود رفتار غيرالاستيك نشان مي­دهند، درحاليكه تيرهاي خارج از ناحيه­ي تير پيوند، ستون­ها و مهاربندها به نحوي طراحي شده­اند كه در محدوده­ي الاستيك باقي بمانند. براي انجام تحليل­هاي غيرخطي مناسب بر روي قابهاي مهاربندي شده­ي واگرا، نياز به مدلي تحليلي مي­باشد كه بتواند با دقت زيادي رفتار غيرالاستيك تيرهاي پيوند را پيش بيني كند. طبق اطلاع نويسندگان، در حال حاضر تنها براي تيرهاي پيوند كوتاه مدل تحليلي ارائه شده است. در اين پژوهش يك مدل تحليلي ارائه شده است كه مي­تواند با دقيت بسيار زيادي مقادير بيشينه و همچنين مقادير مياني نيروها و تغيير شكلهاي تيرهاي پيوند كوتاه، متوسط و بلند را پيش بيني كند. پارامترهاي مدل بر اساس نتايج چندين آزمايش صورت گرفته بر روي تيرهاي پيوند و قابهاي مهاربندي شده­ي واگرا كاليبره شده­اند. مقايسه نتايج به دست آمده از مدل­سازي عددي با منحني­هاي هيسترسيس آزمايشها نشان دهنده­ي دقت بسيار بالاي مدل تحليلي ارائه شده مي­باشد. استفاده از مدل پيشنهادي جهت انجام تحليل­هاي غيرالاستيك بر روي قابهاي مهاربندي شده­ي واگرا توصيه مي­شود.

The purpose of this study is to develop the previous proposed analytical model by the first and second authors for short links, so it can be used for all kinds of links including short, intermediate, and long links. Eccentrically braced frames (EBF) offer high lateral stiffness because of their braced configuration while also providing high ductility and energy dissipation. They are widely used as a lateral-force resisting system for multi-story buildings located in seismic areas. The key components of the EBF system include columns, collector beams, braces and active links. The link is defined by a horizontal eccentricity between the intersection points of the two brace centerlines with the beam centerline (or between the intersection points of the brace and column centerlines with the beam centerline for links adjacent to columns). The active links are designed to provide ductility and energy dissipation through yielding under design basis earthquakes, while all other structural members are designed to be stronger than the links and stay in elastic range. The link length is often normalized with respect to the ratio between the plastic moment capacity and the plastic shear capacity of the link section. This normalized link length is called the length ratio. Links with a length ratio less than 1.6, called short or shear links, yield primarily in shear and can be designed for 0.08 radian inelastic rotation. Links with length ratio greater than 2.6, called long links, form flexural hinges at either end and can be designed for 0.02 radian inelastic rotation. Links with length ratios between 1.6 and 2.6, called intermediate links, experience a combination of flexural and shear yielding and can be designed for inelastic rotations between 0.02 and 0.08 radian depending on the length ratio. Sufficient analytical model which can accurately predict the inelastic performance of the links is needed to perform reliable nonlinear analyses of EBFs. Analytical models that are used to study the inelastic seismic response of the EBFs usually reflect the anticipated behavior of the different frame elements. Links are modeled as inelastic elements with concentrated end flexural and shear hinges. Beams outside of the link, braces, and columns are typically modeled as elastic beam-column elements, because no inelastic behavior is anticipated in design. It is said in the literature that available analytical models for short links generally predict very well the maximum shear forces and deformations from experiments on short links, but may underestimate the intermediary values. In this study it is shown that available analytical models do not predict very well the maximum shear forces and deformations too. To the authors’ knowledge, currently there are only suitable analytical models for short links. In this study an analytical model which can accurately predict both maximum and intermediary values of forces and deformations for short, intermediate, and long links, is proposed. The parameters of model are established based on test results from several experiments on links and EBFs. Comparison of available test results with the hysteresis curves obtained using the proposed analytical model established the accuracy of the model. The proposed model is recommended to be used to perform inelastic analyses of EBFs.