At present, the popularity of timber as a structural material is booming. However, the current knowledge on disproportionate collapse prevention and extreme loading of timber buildings is scarce. To prevent disproportionate and progressive collapse, catenary action is an important mechanism, where the axial capacity of bending members is activated. Because of the brittle behavior of timber in the relevant failure modes, it can only achieve catenary action via strengthening. In this paper, analytical expressions are derived for the elastic, plastic, and catenary capacity of laterally loaded wood and timber beams with a tension-side strip reinforcement. A load-path dependent M-N interaction diagram with damage accumulation explains the ultimate catenary capacity and the transition between the bending- and catenary-dominated load-carrying mode. The analytical expressions are validated and discussed based on tests on beech clearwood specimens reinforced with carbon fibers in a polyurethane matrix. Furthermore, a case study on glued laminated timber beams is presented to demonstrate the potential of reinforcing timber beams subjected to extreme loading.