The document specifies a method of determining the shear strength for in-plane forces of joints between prefabricated components made of autoclaved aerated concrete (AAC) or lightweight aggregate concrete with open structure (LAC). The shear strength for in-plane forces of longitudinal joints between two adjacent prefabricated AAC- or LAC-components or sections there of is determined by applying an in-plane shear forces parallel with or with an angle ? to the joint. The test can be carried out with or without lateral restrains preventing dislacements in transverse direction. The load is increased continouosly or in steps until failure. The load-displacement diagram and the rupture load are determined. The shear strength is determined from the rupture load