الفهرس 
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Abstract
Lattice steel transmission towers (LSTTs) are essential components of overhead transmission lines that play an important role in supporting the electrical power grids. This thesis presents different failure types observed during full-scale experimental performance testing on three LSTTs. The tests were performed in accordance with the requirements of the current version of IEC 60652:2002-06 “Loading test on overhead line towers”. The fullscale tests were performed at CELPI towers testing station – Bucharest – Romania. The three LSTTs were designed to carry 33 kV double circuits’ overhead transmission lines, the loading conditions and design complied with the relevant requirements of the technical specification of ASCE-10. The structural design was performed using the software of power line system (PLS-TOWER) and validated by a model performed with analytical software ANSYS Workbench 2019 R3 whereas the detailed design and drawings were performed using TEKLA STRUCTURE structural engineering software. Observed failures were studied and reasons are investigated. As a result, modifications for each tower were performed to enhance the performance to sustain loads and decrease the overall deflection. Also in this thesis, towers bolted joints connections are studied experimentally at laboratory and calculated mathematically according to EC3 for the purpose of studying behavior and failure modes of the lapsplice/ single leg bolted joints of such three LSTTs. Lap-splice bolted connections are used for long primary (leg) members, single-leg bolted connections usually used to connect bracing and redundant members with a single bolt or multi bolt arrangements. 17 lap-splice bolted joints, and 8 single-leg bolted connections with real-scale dimensions as used in real three iv LSTTs, are experimentally tested under compression, with the bolts being under shear. The joints relationships by means of the axial load versus joint deformation under shear forces on bolts are measured and evaluated, where the bolted joints are found to show pre-slippage, slippage, bearing and plastic stages. The axial stiffness of the joints is then obtained from these load– displacement curves. from the mechanical point of view, stress distribution and forces acting on the bolts depend on the stiffness of both the bolts and the connecting steel elements. Accordingly, an exact theoretical analysis for design purpose is practically not possible. Instead, the bearing design of bolted shear joints can be performed by means of consistent empirical formulae available in design guides or codes under different loadings but not for shear. Therefore, stiffness and shear strength of the current joints are compared with component-based method CBM, as presented in EN 1993- 1- 8 (2005). In this method, the structural steel joint under shear loading is treated as a multi-spring model composed of in-series springs, which enables obtaining its force-displacement relationship. A validation scheme is considered based on previous experimental works of shear bolted connections available in the literatures performed by Ungkurapinan et al (2003), Y. Zhan et al (2015). Comparisons based on this simple formula (including the connected plates in tension, bolt in shear and plate in bearing) show a good agreement with the experimental results and it is valid for analysis for both of initial stiffness and strength. Additionally, the strength obtained by CBM is shown to conform to the experimental failure modes. Based on the results, the laboratory v experimental compression tests as well as CBM estimations of bolted joints connections are useful tools to evaluate behavior of the two types of joints. Finally at the end of this thesis, it is suggested to be taken into consideration during the overall elastic design of the towers by using a well calibrated finite element modeling instead of using expensive full-scale loading prototype testing method in accordance with IEC 60652 (2002). Proposed to use a model created by Ansys workbench 2019 R3 for the purpose of global FE simulation using beam elements for angle members and using joints connections data related to the studied towers from the laboratory tests/ CBM calculations is almost a real behavior as investigated in full scale prototyping testing. This hybrid simulation considering real joints axial stiffness with a plastic value suggested to be 1/3 of the obtained joint elastic stiffness values is suitable and accurate to model LSTTs tested in testing station with full scale manner. By using this procedure, it is applicable to implement data received from joints laboratory connection tests/CBM calculations into FE global analysis to obtain real behavior of lattice steel transmission towers. The results are a low-cost methodology to simulate/validate lattice steel transmission towers under testing.