結構平面配置變化對建築結構體建材用量及碳排放量之影響

Effects of Structural Layout Variation on Material Usage and Carbon Emission of RC Building Structures

一般認為，建築平立面規則時，結構用量較為經濟，因此台灣現行減碳評估指標亦不鼓勵平立面幾何形狀 之變化，為因應建築設計者對空間及造型變化之需求，本研究挑選四種結構平面配置變化因子，包括：梁線不 連續、梁線斜交、梁線轉折，以及出挑，設定以RC 低層公共建築為原型之分析模型實際進行結構設計，探討 各種因子對結構體建材用量及碳排量的影響，以提供建築設計者於初步設計階段採行經濟設計及節能減碳決策 之參考依據。分析結果顯示，梁線不連續對結構體建材用量影響最為顯著，單位樓地板面積碳排量隨梁線不連 續程度上升而增加；梁線斜交及梁線轉折之影響在本文探討範圍內均不顯著，僅因梁跨距不等導致應力分布不 均，造成建材用量及碳排量稍微提高，但與原始模型之差異量皆不超過3%；平面出挑時，總建材用量與碳排 量雖然增加，但因出挑亦增加樓地板面積，換算為單位面積建材用量及碳排量反較原始模型來得經濟。本研究 結果顯示只要能維持良好的構件連續性，即使平面幾何形狀非矩形、有若干凹凸、構架非正交，並不會顯著提 升結構體碳排量，設計者亦可善用適度出挑或外周柱退縮來形構立面造型變化，兼顧結構經濟性與設計自由度。

Irregular structural layout due to the change of plan and elevation shape is usually considered a negative factor to the material usage of the structure. Therefore, the current green building evaluation manual in Taiwan also discourages the design of irregular building shapes. This research was aimed to investigate the actual effect of varying structural layout on the material usage and carbon emission. Computer structural models were established for hypothetical low-rise RC buildings. Experimental models were developed with four types of variation, including: discontinuous beams, oblique beams, deviate beams, and cantilever. Structural member sections of the models were designed in accordance with the present structural design procedure in Taiwan. Concrete and steel usage and the corresponding CO2 emission were then calculated. The results showed that when there were incomplete frames due to discontinuous beams in the structural layout, the material usage and CO2 emission significantly increased. Oblique beams and deviate beams did not obviously affect the structural behavior and the material usage. A reduction of CO2 emission per unit floor area was found in the models with cantilevers because the increase in material usage was not proportional to the increase in floor area. These results suggested that the continuity of structural members is a more essential factor than the geometric regularity of structural layout for the design of economic structures. The smart use of cantilevers might be an efficient strategy to reduce the carbon emission and achieve the design variety simultaneously.