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Background and limitations-Engineering judgment based on rational, scientific principles is critical in the strength evaluation of concrete structures. Such judgment of a qualified licensed design professional is needed for proper application of relevant code provisions to the case being studied. An assessment of structural safety can be achieved with the information and data from field investigations, scientific computations based on sound principles, as well as subjective engineering judgment from the licensed design professional. This is particularly true for structures deteriorated from prolonged exposure to the environment or damaged in an extreme event, such as a fire, earthquake, or explosion.

Similarly, there are no generally recognized criteria for evaluating serviceability of an existing concrete structure. Such evaluation requires engineering judgment based on scientific principles, and close consultation with the owner regarding the intended use of the structure and expected level of performance.

ACI 562 discusses potential conclusions resulting from a strength evaluation; however, the determination of one or more of the following conclusions regarding the integrity of a concrete structure is possible from a strength evaluation:

a) The structure or structural element has an adequate margin of safety according to the provisions of the applicable building code.

b) The strength determined by evaluation is less than that required for factored loads but greater than required for service loads (load factors equal to or greater than 1.0 for all load cases). In this case, the structure or structural element is not adequate. In some cases, restricted use of the structure that limits the applied loads in recognition of the computed strength may be permitted.

c) The design strength of the structure is less than required for service loads under the applicable building code. In such cases, the owner should be notified and consideration given to the installation of shoring, severe restriction of use, or evacuation of the structure until remedial work can be done.