| With the comprehensive development of ultra-high voltage (UHV) engineering projects in China, traditional strength of steel can not meet the demands of UHV Transmission Tower because of the great height, span and load. Therefore, it is necessary to widely use Q460 equal angle steel. The deficiency of studies on related theories and tests leads to the lack of sufficient basis for its use.On the other hand, conventional designs are usually carried out under the assumption that connections joining members are either ideally pinned or fully rigid while the connections are actually semirigid, which would bring about unsafe factors to the transmission towers.Based on the literature review of previous researches and designs, focusing on Q460 equal angle steel's mechanical behavior under different circumstances, the influence of joint stiffness on loading capacity of transmission towers'members, the following researches have been carried out in this dissertation.①The inverse calculation segment length method and computer program made with Fortran95 language were employed to calculate 63 different Q460 equal angle steel's column curves. Stability coefficient table which can be directly used for designing was obtained, and simplified formula was presented.②Axial Compression test of 15 Q460L125×10 equal angle steel specimens with five slenderness ratios was carried out. ANSYS was adopted to analyze. A comparison was made between test results and related standards. The rationality of current standards was evaluated and design suggestions were proposed.③9 Q460L140×12 equal angle steel specimens with three slenderness ratios were tested when connected by one leg with bolts. ANSYS was adopted to analyze. Based on the test results and the study on those of related researches, design suggestions and methods were put forward. The results calculated by suggested methods and those by related standards were compared to prove the rationality of the former.④Axial Compression test of 18 Q460L125×8 equal angle steel specimens with 6 slenderness ratios and the ANSYS analysis were carried out. The influence of local buckling caused by too large width-thickness ratio on the bearing capacity of axially loaded compression members of Q460 equal angle steel was analyzed and related design methods and formula were proposed. The results calculated by suggested methods and those by related standards were compared to prove the rationality of the former.⑤By Timoshenko's elastic stability theory, diagonal members in UHV Transmission Tower were replaced by elastically supported members, considering supporting stiffness of intermediate nodes, length factor's calculating method of Transmission Tower's diagonal members and its simple formula were worked out. The formula can be directly applied in designing.⑥Through the application of the semistiffness theory and classical four-moment equation in wider scope, on the condition of taking into account the influence of joint rotation stiffness, the effective length factor's calculating method was derived for transmission tower's diagonal members. Numerical methods were used to calculate the effective length table of the transmission tower's diagonal members as well as simplified formula. Quantitative assessment was conducted regarding the influence of the main and diagonal member's linear stiffness ratio and the ratio of diagonal member and joint rotation stiffness on diagonal members'effective length value.
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