Strength Evaluation by Load Testing: Recommendations for Test Load Magnitude and Acceptance Criteria

Load testing concrete structures in the United States, which began in the 1890s, acted to proof test newly constructed concrete structures and systems. By demonstrating safe load carrying capacities of various reinforcing systems then being developed in the United States and Europe, it also furthered the development of reinforced concrete. Since 1971, the current strength evaluation test load is 0.85 (1.4D + 1.7L), with D defined as total dead load and L as total live load. Load factors for design were revised in 2002 in American Concrete Institute (ACI) 318 "Building Code Requirements for Structural Concrete". The authors summarize ACI committee work, which will soon be available in report form, to update recommendations for load testing as a way to verify the safety of existing concrete structures, as well as debate on proposed load testing practice changes. Questions include whether a rational test load to establish safety can be defined; the appropriateness of using a lower test load for determinate elements, regardless of whether all suspect structural elements are load tested; whether in addition to traditional 24-hour monotonic load tests, cyclic load testing should be used; inclusion of crack widths in both full test and service load level acceptance criteria; and whether adequate preparation has been done to define new maximum deflection criteria. The authors provide background on both historical and current practices in load testing concrete structures in the United States.