鋼骨鋼筋混凝土柱圍束箍筋量之試驗與耐震設計

Abstract

本研究進行20支包覆型鋼骨鋼筋混凝土(Steel Reinforced Concrete, SRC)短柱試體之軸向抗壓試驗，並依據力學原理探討耐震設計時SRC柱中所需之圍束箍筋用量。由於SRC柱中有鋼骨存在，鋼骨的翼板可以對SRC柱內之混凝土發揮圍束功能，因此本研究乃針對SRC柱內「鋼骨翼板寬度」的變化作為主要參數，來探討鋼骨翼板對混凝土圍束效應之影響。試驗結果顯示，鋼骨翼板寬度愈寬確實能夠對SRC柱核心混凝土提供愈好的圍束作用，因此對於鋼骨翼板較寬之SRC柱，將可以適當的減少其圍束箍筋用量。另一方面，試驗結果亦顯示，由於SRC柱中的鋼骨能分擔一部份的柱軸力，使得SRC柱中混凝土所需要承擔之軸力相對的降低，故柱中所需之箍筋用量亦得以減少。基於上述發現，本研究嘗試提出一套SRC柱圍束箍筋量之耐震設計新方法，該法的主要特色是能夠同時考量「鋼骨用量」及「鋼骨翼板寬度」對SRC柱中混凝土圍束效應的雙重影響，使得設計時SRC柱中所需之圍束箍筋量能合理的放寬，此一新設計法除了具有經濟效益之外，亦有助於簡化SRC柱箍筋施工的複雜度。

The objective of this study is to investigate both analytically and experimentally on the seismic requirement of hoop reinforcements of steel reinforced concrete (SRC) columns. The experimental work emphasizes the parameter of “flange width” which is considered to provide effective concrete confinement. Two analytical models called “triangle” and “rectangle” model are considered for SRC columns with imbedded H shape and cross-H shape steel section to consider the contribution of concrete confinement provided by the steel flanges. The test results of 20 stub SRC columns are compared with the results of hoop reinforcements designed according to the ACI-318 code (2002), AISC-Seismic Provisions (2002) and the two new design approaches adopted in this study. Based on the test results and analytical study, a new method is proposed to evaluate the hoop reinforcement required for the seismic design of SRC columns. The new proposed design method shows that the amount of hoop reinforcement required for SRC columns can be reasonably reduced if the contribution of the concrete confinement provided by the steel flanges and the amount of steel used in the SRC column are properly considered.