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Computer-Assisted Analysis and Design of Steel Beams based on AISC-ASD
|關鍵字:||ASD;鋼樑容許應力;Lateral-Torsional Bucklling;Flange Local Buckling;Web Local Buckling;Metal Structures;Compactness;AISC;Fortran;電腦化分析;板樑;局部挫屈;柔細肢材;結實性;規範;鋼樑容許彎矩||出版社:||土木工程學系||摘要:||
AISC-ASD(1989)對於鋼樑受純彎矩下所能承受之最大容許應力主要依據Lateral-Torsional Buckling(LTB)、Flange Local Buckling (FLB)和Web Local Buckling(WLB)等三種破壞模式來決定，其中LTB破壞和鋼樑肢材之無側撐長度Lb有關，而FLB和WLB則和鋼樑斷面之結實情形(Compactness)有關。不同於ASD規範中將LTB、FLB和WLB破壞之各計算公式與使用條件列在一起討論且加以簡化其使用條件後，散列於各章節中，本研究中將LTB、FLB和WLB破壞之公式與使用條件分開討論，旨在整理出一有系統之計算公式並釐清三種破壞的發生時機和計算公式之使用條件與限制。
In the current ASD Specification of AISC, the allowable bending stress (Fb) of steel beam is obtained based on three buckling modes which include Lateral-Torsional Buckling (LTB), Flange Local Buckling (FLB), and Web Local Buckling (WLB). The Fb for LTB mode is evaluated in terms of unbraced length (Lb). The Fb for FLB and WLB modes is, however, based upon the compactness of section. The ASD Specification presents its Fb formulas in Chapter F of the Specification, sections F1 through F3. When one goes through the sections F1 to F3 of the Specification, it can be concluded that the Specification is not clear enough for the user to apply its formulas when the section consists of noncompact or slender element especially when the bucklings include the modes of FLB and WLB.
In this study, the Fb formulas for LTB, FLB, and WLB are summarized and carefully reviewed with flow charts and related formulas, respectively. When the calculation of Fb involving the section reduction factor Q is really a long and tedious process, it is not an efficient way to obtain the value of Fb through this long process in routine design. This study provides an easy and fast approach, which is a computer way, to solve the problem. Both hand and computer calculations are presented in each selected example and the results are also compared. It was found that the computed values do match with the tabulated ones in the AISC-ASD design manual of 1989.
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