In this thesis it is investigated how common connection-elements in steel-construction can be manufactured by means of Wire Arc Additive Manufacturing (WAAM). The idea was to replace the manual and time-consuming assembly process, which is still common today, by a fully-automated manufacturing-step through additively manufacturing the connection elements directly onto the steel beams. The basics and particularities of WAAM are explained and described. To enable WAAM-compatible design, theorems as science-based statements are formulated. With the 8-step optimization process presented in this work, the structures of the connection-elements are determined. This ensures that the material is statically optimally utilized while a fast and error-free manufacturing process is guaranteed. Numerical topology-optimization and numerical ultimate-load analysis are used in the optimization process. For practical demonstration, three connection elements (beam hook, load-introduction stiffener, clamping element) are optimized. In a following chapter, suitable manufacturing strategies for these connection elements are outlined. The manufacturing process with the WAAM is described. The ultimate load-capacity of the connection elements is determined via destructive tests. In an evaluation chapter, the outcomes of these tests are compared with the numerical ultimate load-capacities.