Welded joints and screw connections are found in almost every structure, building, or mechanical device. These connections are carefully dimensioned to meet the requirements of the joined parts so that the screws are tightened against separation between parts and welds dimensioned against failure. This thesis work focuses on welded load-carrying lattice structure modules that are stacked and connected via screw connections. Typical applications of such structures include cranes, wind turbine towers, and radio towers. Computations of these module towers have typically been done using elementary beam theory equations which in today’s more modern world do not meet the requirements.

When building new simulation software for one of such towers, equations and limits need to be known which this work aims to contribute to. The scope of the project includes answering whether the lattice module tower can be modeled taller using simplified methods, what the relation between separation inducing moment on the tower and the screw connection’s clamping forces is, how the welds strength are affected by the forces in the screws as well as how the possibilities of a reduction in screw size look.

To analyze a taller tower in a Finite element analysis using Ansys Mechanical and include as much of the modules’ structural properties as possible, entire modules were simplified from solid elements to a shell element- and a beam element representation in Ansys Spaceclaim. Two shell element modules were stacked and meshed with a fine mesh to gather information on separation in their intersections. Beam element modules requiring far fewer elements were used as lever arms for the applied bending moment and to compose a higher tower. A sub-model of the most exposed welded joint and surrounding materials including an adjacent screw was made of the full tower model. The fillet weld was modeled with Eurocode (1993-1-8:2005) criteria in mind to be used as a strength evaluation method. Lastly, screws in the tall tower simulation were reduced in diameter to observe the effects of such a change.

Lastly, the answers to the questions setup for this work is given by the results and discussion, where the baseline of the model simplifications is that similarities in structural behavior between solid-, shell-, and beam element representations of the lattice module were intended to be as high as possible. The results and conclusions are made only based on the towers bending load cases in the x-direction because of the simplifications required to create the beam element module weakened the model in its z-direction more than what was considered negligible. The directional method for fillet weld evaluation in Eurocode yielded the maximum permitted pre-tensioning force for the screw connections between the lattice modules against failure in nearby welds. A linear equation for the applied moment to get separation between modules and the pre-tensioning force appliedin its screw connections was produced. The workload in the screws during bending load cases causing separation was observed to always vary between −6% and +5% from its pre-tensioning force, regardless of value. The results of the reduction in the screw diameter indicate that it is possible and has less variation in workload around its pre-tensioning value.