| 摘要: | 本研究是以反覆載重實驗方式，探討不同跨距之高拉力鋼筋混凝土梁(New RC梁)塑鉸外移設計。主要參考紐西蘭規範NZS 3101之塑鉸外移設計方法，經實驗方式驗證是否適用於New RC梁，討論其耐震行為差異。
塑鉸外移方法藉由置入超額鋼筋於梁端，由梁柱接頭內延伸至梁端外一倍梁深(h_b)，以T頭錨定，提升原斷面彎矩強度之40%，轉移塑性鉸位置為一倍梁深(450mm)。使用SD690螺紋節#8與#10為梁主筋、SD790竹節#3與#4為梁箍筋、f_c^′=60MPa高強度混凝土，製作四支矩形斷面為300mm×450 mm之懸臂梁試體:無塑鉸外移之2.4m梁HR-Y0-L、塑鉸外移450mm之2.4m梁HR-Y450-L、無塑鉸外移之1.9m梁HR-Y0-S、塑鉸外移450mm之1.9m梁HR-Y450-S。
研究結果顯示，四支梁試體均符合ACI 374.2-13之良好耐震性能規定，試體強度於DR=6%後才開始衰退。其中，塑鉸外移試體因梁端配置較多主筋，試驗最大荷重提升了20%，並成功使塑鉸位置由梁端轉移至梁區，避免柱面之破壞。有塑性鉸轉移設計之New RC梁其塑鉸區長度較原型梁為長，且剪力裂縫較原型梁大，呈集中X型斜裂縫，且發現在最終DR=6%時，T頭錨定端有垂直剪力滑移之現象，故建議梁端超額鋼筋改配置為彎起筋型式作改善，應可抑制垂直剪力滑移現象發生。由於有塑鉸外移試體之量測剪力較原型梁為高，為求保守設計剪力，建議以1.15M_n/l_(n,R) 求設計剪力，其中M_n為原型斷面標稱降伏彎矩強度，l_(n,R)為塑鉸外移點以後之梁長。
;The thesis discusses how to design the plastic hinge relocation of New RC beams. The method of hinge relocation referred basically in according with New Zealand Standard (NZS 3101 2006). The study performed the cyclic load testing on the New RC cantilever beams to verify the validation of the plastic hinge relocation design specified in NZS 3101. Meanwhile, this verification is also to check the application to the New RC beams.
To relocate the plastic hinge a distance away from column face toward the beam middle span, an extra beam bar setting at the beam end will be used. That is, the extra steel bars anchored in both beam and into beam-column joint with t-head bars. The extra t-headed bars extended a length normally equal to beam depth (h_b) from column face. The extra flexural strength according to the detailing of the section is increased up to 40%. Then, the plastic hinge can move away a distance of beam depth (450mm). Totally four 350 mm wide x 450 mm deep New RC are tested, in which two are 2.4 meters and the other two are 1.9 meters long. The longitudinal bars are arranged with three SD690 #8 in the top section and three SD690 #10 in the bottom. Three extra t-headed bars (3-SD690 #8) are placed at the top lower and bottom upper layers, respectfully. The transverse bars are arranged with SD790 #3 and SD790 #4. The concrete compressive strength is about 60 MPa. One beam with 2.4 meter long is control specimen RC beam, called as HR-Y0-L. The other with 2.4 meter long, having plastic hinge relocation of 450 mm away from beam end, is called as HR-Y450-L. The other two beams with 1.9 meters long are control specimen (HR-Y0-S) and hinge relocation specimen (HR-Y450-S).
Test results indicated that all the specimens (HR-Y0-L, HR-Y450-L, HR-Y0-S, and HR-Y450-S) satisfied the minimum seismic performance required by ACI 374.2r-13. The load degradation of all specimens happened at the drift ratio of 6%. Because HR-Y450-L and HR-Y450-S arranged more bars (40% increase in flexure) at the column face, it was observed this two specimens increased 20% in shear strength. Thus the design of the hinge relocation can force the plastic hinge exert in the desired region and prevent the joint failure from occurring. However, plastic hinge length (l_p) and and diagonal shear cracks in plastic hinge relocation beams are longer than control beams. The shear crack pattern at the hinge region presented non-smear x-shape and sliding shear like in the plastic hinge zone when the specimens were loaded until drift ratio reached 6%. So, the bent-up extra bars instead of t-headed bars may be used to prevent the non-smear diagonal shear cracks develop. It is also recommended for New RC beams a more conservative design shear of 1.15M_n/l_(n,R) shall be considered to obtain a higher shear demand, where M_n is nominal flexure strength of prototype beams, and l_(n,R) is a beam structural length accounting from new relocated hinge zone. |
