膨脹錨栓於混凝土版內之力學行為研究

Abstract

本研究試驗主要在探討不同尺寸之內牙敲擊式膨脹錨栓於混凝土版上錨定後，分別單施拉拔力、單施剪力或施加組合式應力時之力學行為與破壞機制。包含荷重與變位的關係、最終極限破壞值與破壞模式。試驗中並探討在錨定邊距影響下，單施拉拔力、單施剪力或施加組合式應力的最終極限破壞值折減情況與最終破壞模式。 膨脹錨栓單施拉拔力時所造成之混凝土破壞角錐與水平面大致呈30°角，進行試驗結果回歸分析時，可以30°圓錐破壞面有效投影面積為應力影響區，則可得此類型膨脹錨栓於淺埋時之容許拉拔力建議公式為 P ＝ 0.479×f'c1/2×Ac（kgf），而單拉安全邊距可設定約為2倍之錨定深度，理想間距可設定約為4倍之錨定深度。 膨脹錨栓單施剪力時，當錨定邊距大於或等於1.5倍錨定深度時，破壞模式皆為錨栓螺桿剪斷，所以膨脹錨栓之容許剪力直接與膨脹錨栓外接螺桿的性質有關，其值為V1＝0.577×fy（kgf），而當錨定邊距小於1.5倍錨定深度時，破壞模式轉混凝土側向崩離，其容許剪力建議由V2 ＝ 0.355×f'c1/2×Ac（kgf）計算之。 當膨脹錨栓承受組合式應力在有邊距效應影響下，先施剪力對後施拉拔力所造成之折減會比先施拉拔力對後施剪力所造成之折減來得大，其破壞模式亦都趨向於受剪破壞的模式。牙徑為5/16"的膨脹錨栓在承受組合式應力之安全邊距可設定為1.5倍錨定深度，而牙徑為1/2"和3/8"的膨脹錨栓安全邊距可設定為2.0倍錨定深度。

The test of the research attempts mainly to investigate the dynamic behavior and failure mechanism after anchorage of the Drop-In Type Expansion Anchors of different sizes in concrete slabs, to be separately applied with pullout force solely, shear force solely, or compound stress. It shall include load and position deviation, final limit failure value and failure mode. In the test, it is also studied, under the influence of anchorage span,the final limit failure value attenuation situation and final failure mode of being applied with pullout force solely, shear force solely, or compound stress. The concrete failure cone to concrete caused to expansion anchors while being applied with pullout force solely and level surface generally shows a 30°angle. While conducting test result regression analysis, the effective projection area of a 30°cone failure surface can be considered as the stress influence area, then the recommendation formula of tolerance pullout force of this type of expansion bolt in shallow embedding is P = 0.479×f'c1/2×Ac(kgf), while single pull safe edge span can be set to be about 2 times of anchorage depth, and ideal anchorage span can be set to be about 4 times of the anchorage depth. As an expansion anchor is applied solely with shear force, as the anchorage edge span is larger than or equals to 1.5 times of anchorage depth, the failure mode shall be anchor bolt shank cut off, therefore, the tolerable shear of expansion anchor is directly related to the externally connected bolt shank nature of an expansion anchor, with the value as V1= 0.577×fy (kgf）, while anchorage edge span is less than 1.5 times of anchorage depth, the failure mode turns to concrete side to collapse, with the tolerable shear recommended to be calculated by V2 = 0.355×f'c1/2×Ac(kgf). As the expansion anchor undertakes compound stress to be under influence of edge span, the attenuation of shear applied first to pullout force applied later shall be larger than the attenuation of pullout force applied first to shear applied later ; its failure mode also tends to the failure mode under shear. The safe edge span of an anchorage bolt with tooth diameter at 5/16" in undertaking compound stress can be set to be 1.5 times of anchorage depth, while the safe edge span of anchorage bolts with tooth diameters at 1/2" and 3/8" can be set to be 2 times of anchorage depth.