鋼管鷹架之承載力及頻率量測研究

A Study on the Capacity and Frequency Measurement of Steel Scaffolds

模板工程之倒塌通常會造成嚴重的生命財產損失，因此有必要對此臨時性支撐系統之結構特性加以探討。本文將針對國內常使用的簡易式門型鋼管鷹架，分別探討其承載力和加載時頻率變化特性。於鷹架承載力方面，探討鷹架在多架間組搭形式下，其承載能力與一架間單元組之關係；以及受非均勻載重情形下，鷹架承載力的變化情形。試驗結果發現：1.無論鷹架承受均勻或非均勻載重時，由於同一層數的鷹架支撐，其單組鷹架所能提供的最大承載能力皆相近。因此，造成該區域的鷹架先行挫屈，進而導致整體鷹架支撐能力下降。2.多架間鷹架的交叉拉桿僅能提高面外方向之勁度，對於面內方向之勁度幫助不大。3.我們可以用“組單元”的概念來估算多架間鷹架的最大承載能力。鋼管架加載時，理論上其本身自然頻率將會變小，本文利用全尺寸鷹架組合單元試驗，來探討其水平振動頻率變化情形，以及是否可作為支撐系統倒塌之監測指標。試驗結果發現，頻率變化未如理論分析般的明顯，因而目前在工地實用上仍有困難。然而全尺寸鷹架試驗所得之承載力，仍可作為設計之用。

The collapse of formwork often causes losses of life and property. Hence there is a need to understand the behavior of such temporary supporting frames. This study is mainly concerned with the capacity and frequency characteristics of simple steel scaffolds, which are widely used in Taiwan. Both uniform and nonuniform load patterns are considered. As for loading capacity, the relation between the capacity of multi-bay scaffolds and that of a unit set of single-bay scaffolds is investigated. The following observations can be drawn from the experimental work. Firstly, whether the loading is uniform or not, the capacity of the most critical unit set is almost constant for scaffolds of the same story. Also, collapse usually initiates from buckling of this critical set. Secondly, the cross tie-bars enhance mainly the out-of-plane stiffness; they contribute very little to the in-plane stiffness. Thirdly, the concept of unit set can be used to estimate the capacity of multi-bay scaffolds. With regard to frequency characteristics, the natural frequencies of scaffolds during the application of loading are measured. Theoretically, the frequencies will decrease as the loading is increased because of the degradation of their stiffnesses. Full scale tests are carried out to study the changes in frequency which can be adopted as a precaution indicator for avoiding scaffold collapse. It is found that the changes in frequency are not significant. Therefore, using the change in frequency as a precaution indicator is infeasible at this moment. However, the loading capacities obtained from the full scale tests can still be used in designing steel scaffold systems.