之字型配置挫屈束制支撐於鋼筋混凝土構架之接頭耐震試驗與分析研究

Abstract

挫屈束制支撐(Buckling-Restrained Brace, BRB) 為一廣泛應用的制震消能構件，其受拉及受壓時皆能發展至降伏強度而不發生挫屈，擁有飽滿且穩定的受力變形遲滯迴圈。近年來許多研究及試驗已證明BRB 能提供結構良好的勁度、強度與韌性，已廣泛的被應用在鋼結構建築中，但將BRB 應用於新建鋼筋混凝土(RC)構架的技術與研究仍不多，主要原因為BRB 的端部接合部位為鋼材，鋼材與RC 構架的連接介面處設計與施工較複雜且困難。 本研究針對採之字型配置挫屈束制支撐於新建RC 構架中的BRB 與梁柱節點接合介面進行探討，依據現行耐震設計規範提出一棟新建含挫屈束制支撐之十二層RC 結構設計例，擷取位於十樓的BRB 與RC 構架梁柱接頭處進行接頭處的細部設計，包含BRB 接合設計、U 型接頭鐵件設計、短深型托架設計，並依照設計製作梁柱接頭子結構試體，探討其施工性並進行反覆載重試驗以瞭解此BRB 與梁柱節點的受力變形反應。此外，本研究以PISA3D 建立十二層BRB_RCF 設計例的結構分析模型，將分析所得反應對試體進行子結構實驗，藉由試驗結果探討本研究所提設計方法之有效性。 試驗結果顯示，接頭處U 型鐵件與短深型托架在試驗過程中並無發生明顯損壞，可傳遞BRB 接合板與RC 構架間的力量，並證實所提U 型鐵件接頭形式、施工與設計方法可行，在設計載重下並不會發生非預期的破壞。為了更進一步探討此種採之字型配置BRB 之RC 構架的受震行為，本研究使用240 組地震加速度歷時對此十二層結構之PISA3D 模型進行非線性動力歷時分析。分析結果顯示，各地震下BRB 抗側力比例約為20%。分析結果顯示此十二層BRB_RCF 之高模態反應並不顯著，接頭處水平拉力可使用0.7 倍的BRB 可能發展之最大拉力強度的水平合力設計即可。最後本研究提出採之字型配置BRB 於RC 構架的設計流程與方法。

A Buckling-restrained brace (BRB) can develop full yield strength under large tensile and compressive strain reversals through its restraining member by preventing its steel core from undergoing flexural buckling failure. Thus, a BRB can effectively absorb seismic input energy. In recent years, a number of researches have confirmed BRBs can enhance the lateral stiffness, strength and ductility of building structures. Buckling restrained braces (BRBs) have been widely used as energy dissipation members for seismic resistant steel buildings. However, researches on applying BRBs in RC buildings are somewhat limited. The main reason could be that the BRB and RC are two different construction material, issues in the interface between the BRB and RC frame do not seem completely resolved yet. In this study, a beam-to-column joint sub-assemblage in the buckling-restrained K-braced RC frame is tested using cyclically increasing loads and displacements. This study first proposes a twelve-story RC example building with BRBs arranged in a zigzag manner. In order to study the seismic performance of the interface joint, this study select a joint in the tenth-floor and design its gusset plate, U-shape steel cast-in anchor and RC corbels following the provisions in the model steel and RC building codes. The performance of the joint connection details is evaluate through imposing cyclically increasing displacements and loads computed from using a PISA3D analytical model. The test results show that no evident failure of the U-shape steel cast-in anchor or RC corbels is observed. Tests confirm that the use of the proposed U-shape steel cast-in anchor as the interface for the BRB and RC frame can be successfully implemented into real RC frames. Test results show that the proposed BRB-to-RC connection details performed very well in the K-braced RC frame system. This study demonstrates that the proposed design and construction method are effective. In order to further study the seismic performance of the 12-story K-braced RC frame using BRBs, nonlinear response history analyses are conducted using a total of 240 (SLE, DBE and MCE) earthquakes ground motion records. Analysis results indicate that the ratios of maximum total BRB shear to base shear are about 23% (SLE), 21% (DBE) and 20% (MCE). The maximum inter-story drift ratios (IDRs) under the MCE and DBE earthquakes are 2.1% and 1.7%, respectively. Analysis results also suggest that the high mode effect is not very significant. It is found that the peak demand of the horizontal tension force on the steel cast-in anchor can be estimated by considering only 70% of the sum of the two horizontal force components computed from the two BRBs‘ maximum possible tension strengths. This study proposes the construction and design procedures of the joint in the K-braced RC frame using BRBs.