The strength of existing concrete buildings and structures can be evaluated analytically and supplemented where necessary with load testing. The recommendations in this report indicate when such an evaluation may be needed, establish criteria for selecting the evaluation method, and indicate the data and background information necessary for an evaluation. Methods of determining material properties used in the analytical and load test investigations are described in detail. Analytical investigations should follow the principles of strength design. Working stress analysis can supplement the analytical investigations by relating the actual state of stress in structural components to the observed conditions.