| 摘要: | 本研究主要在探討隅撐抗彎構架應用於石化廠房耐震行為,而廠房結構一般為開放式結構(Open Frame),其主要目的在支撐設備支及管線等,因此結構系統佈置為配合廠房維修及操作機能,於鋼柱強軸方向以傳統式抗彎構架(SMRF)為主,而鋼柱弱軸方向則以倒V或X型同心斜撐構架(CBF)為主。柱強軸方向之抗彎構架(SMRF),具有良好韌性,但其側向勁度較柔軟,致彈性側位移過大,且受限於規範對結構物容許側位移量或層間相對位移不得超過二百分之一的結構物或層間高度,因此設計者欲符合規範限制只好加大樑柱桿件尺寸,因而得到較高成本的結構。 因此吾人尋求將高韌性抗彎構架(SMRF)加設隅撐(Knee Bracing),簡稱隅撐抗彎構架 (Knee Bracing Moment Resistance Frame),並以KBRF縮寫來表示之。分別透過相對側向勁度、強度、韌性及經濟性等方面分析,再配合工程實例進行分析設計,藉以比較隅撐抗彎構架相對於抗彎構架之耐震行為及經濟性。 首先針對相對側向勁度分析結果,發現隅撐抗彎構架可藉著調整隅撐距柱中心線距離eb,來提高構架勁度,且為考慮整體構架實用性及安全性,建議隅撐斜率以1:1及eb構架寬度)為宜, 並可提高側向勁度1.3~1.8倍。 其次關於構架韌性及強度分析初步結論,當隅撐位置介於 時,隅撐抗彎構架強度優於抗彎構架,其隅撐抗彎構架與抗彎構架為之初始降伏強度比為1.25~1.75,極限強度比為1.2~1.65倍。至於韌性方面,當 時, 隅撐抗彎構架稍小於抗彎構架,但 時,則隅撐抗彎構架優於抗彎構架,唯建議當構架樓層高度與寬度比 及 配置時,建議外柱與樑塑性彎矩強度比 需大於1.5,俾利若構架進入線性行為時,塑性鉸逐步發生於每一樓層的樑與隅撐交點之樑上,減少發生於樓層柱與隅撐交點之柱上,引致破壞機構過早產生而減低其韌性值。 在經濟性分析方面,採用實例構架狀況進行評估,其結果隅撐抗彎構架比抗彎構架可節省鋼料9%~11%,視構架規模而定。 綜合上述,只要正確佈置隅撐於抗彎構架上及注意柱樑塑性彎矩強度比值,則隅撐抗彎構架之耐震能力優於抗彎構架,且其塑性鉸產生的位置可遠離樑端,避免樑柱抗彎接頭因塑性轉角能力不足而導致接頭脆性破壞,為隅撐應用於抗彎構架之重要效益。 This paper is focused to apply the knee bracing combined with special moment resistance frame on petrochemical-oil plants. The structures of petrochemical plants are usually open frame structures supporting equipment and piping. For operation and maintenance reasons, Special Moment Resisting Frames (SMRF) are utilized in the direction parallel to column web and Special Concentrically Braced Frames (SCBF) with inverted-V-type or X-type braces are utilized in another direction. But, the lateral drifts of SMRF are often too large to meet the 1/200 story drift limit. So the designers have to enlarge the member size of columns and beams to reduce the lateral displacement of the rigid frames. Consequently the cost for structural construction will be high. To avoid the above-mentioned disadvantage of SMRF, we investigated a rigid frame system with knee braces. This system is called Knee Bracing Moment Resisting Frame and abbreviated as KBRF. Through this research, we analyzed the following items of SMRF and KBRF. 1. Lateral stiffness of frame 2. Ductility of structural system 3. Strength of structural system 4. Cost savings 5. A really engineering sample By comparing the results of the five items, we will know KBRF is ductile and economical structure for petrochemical-oil plants, and the design criteria will be provided simultaneously. By analyzing the lateral stiffness of KBRF, we found that the lateral stiffness would be raised by adjusting the distance from the intersection of beam and knee brace to column center (eb). For safety and operation reasons, a 1:1 slope and (w=span) of knee braces are recommended. According to the analysis result, the lateral stiffness of KBRF is about 1.3~1.8 times SMRF. For ductility and strength of structural system, we also have some conclusion below. 1. When knee brace is located with , initial strength of KBRF will be raised about 1.25~1.75 times SMRF. And ultimate strength of KBRF will be raised about 1.20~1.65 times SMRF 2. When knee brace is located with , ductility of KBRF is slightly less than SMRF. When knee brace is located with , ductility of KBRF is larger than SMRF. However, when the floor height (h1) to span width (w) ratio of frame is more than 1.0 ( ) and , the exterior column-beam moment ratio should be more than 1.5 in order to prevent the early formation of plastic hinge in exterior column. As a result, most plastic hinge of KBRF will be formed on beam of the intersection of beam and knee brace. About the costs of both systems, by really engineering example, we found that the total steel weight of KBRF is 9%~11% less than the weight of SMRF. So we can say that the KBRF is more economical than SMRF. In a word, we can design a ductile KBRF to sustain seismic load by properly locating the knee braces and adjusting the exterior column-beam moment ratio. On the other hand, most plastic hinges of KBRF are far away from beam-to-column joints. Therefore the moment connection failure as Northridge earthquake in the United States can be avoided. This is one of the important results of this research. |
