| Generally electric transmission towers have two types which is angle member tower (AM tower) and circle hollow section member tower (CHS tower). There are differences of joints between the two kinds of towers. For AM towers, the joints are set up by gusset plates connected with single angle members, called single angle-gusset plate connection, so the gusset plate is the key part of the joint. The gusset plates connected with single angle members are loaded under eccentricity condition. However, current design methods for statically loaded gusset plates are achieved by analyzing the concentrically loaded gusset plates connected with double angle members. In short, there is no method to rationally predict the ultimate strength of single angle-gusset plate connections. For CHS towers, the joints have two types including CHS joints, in which members are connected by welding directly, and gusset plate to CHS joints. For the time being, the fruits of the study on behavior of CHS joints are plentiful. However, there is little technical information regarding the behavior of gusset plate to CHS joints. The Chinese steel structure codes (GB50017-2003) even can't conduct the design of these joints.In this study, a systematic research was conduced to investigate the behavior of joints of transmission towers. The followings were accomplished:①Four full-scale tests were conducted to investigate the behavior of single angle -gusset plates connections in compression and in tension. The failure modes were observed and the procedure of the experiment was presented. The results are treated as the basis of the follow-up FEA analyses. From the test, the buckling failure mode and lateral-torsional deformation of gusset plates in compression were observed. And the tension and block shear failure modes of guest plates in eccentric tension were examined which were in agreement with those in axial tension.②FE model validation studies of AM tower joints were conducted. Two kinds of models were set up based on the solid element and shell element respectively. Geometric nonlinear, material nonlinear and iterate way were considered to investigate the behavior of joints. Comprised by two models analytical and test results, the applicability of the model based on the shell element was verified for parametric analyses.③A parametric study was conduced to investigate the behavior of AM tower joints. Thirty test specimen parametric FE models and a series of K-joints parametric FE models were investigated for compressive behavior. Thick of gusset plate, unbraced length and eccentricity were considered to study the ultimate strength of gusset plates. Besides, effects of proportion of loads on vertical web members and length spliced into bending line were investigated. In the study on behavior in tension, shape of gusset plate, distance between bolt holes and eccentricity were considered as key parameters.④A formula for predicting the ultimate strength of single angle-gusset plates in compression was proposed. Besides effect of eccentricity on the ultimate strength, c′, length spliced into bending line, was suggested to consider the effect of boundary restrict conditions. Based on the analytical results, its applicability was verified. By statistics analyses, it was found that the methods based on gusset plates loaded concentrically in tension are suited to single angle-gusset plates.⑤Based on the FE model of CHS tower joints developed appropriately, a parametric study was conducted to investigate the ultimate strength of gusset plate to CHS K-joints and KK-joints. For K-joints, effects of geometry and chord load on the ultimate strength were considered. For KK-joints, effects of inclination of gusset plates and proportion of loads on diagonal web members were investigated additionally. The key parameters greatly affected on the ultimate strength of CHS tower joints are as follows, ratio of plate length to chord diameter h/D, ratio of chord diameter to chord thick D/t0, eccentricity between chord axis and web member axis e and axial stress ratio in chord. Inclination of chord axis and web member axisθand inclination of gusset platesβhave little effect on the ultimate strength of joints. Axial stress ratio in chord and proportion of loads on diagonal web members have a complex effect on the ultimate strength of KK-joints.⑥Design methods of predicting the ultimate strength of gusset plate to CHS K-joints and KK-joints were proposed, and its applicability was verified. Moreover, Based on the analytical results, it was found that the current design methods were conservative for ignoring the restriction of web member. |
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