Evaluation and Load Testing of Posttensioned Concrete Structure Exhibiting Distress

Abstract

This article discusses the evaluation of a posttensioned concrete structure exhibiting cracking using nondestructive evaluation, laboratory testing of concrete samples, and subsequent in situ load testing. During a field survey, it was identified that the posttensioned beams exhibited visually apparent deflections. An engineering evaluation was initiated to identify the cause of this type of cracking in the posttensioned structural system. Following a field survey and document review, an analysis was initiated for the estimation of potential posttension losses and analytical expected deflections for the purposes of comparing it to measured deflections in the field. After the analytical phase, an in situ, nondestructive evaluation phase and a subsequent material testing phase were initiated. The in situ evaluation of the structure involved nondestructive testing of concrete slabs and beams using ground-penetrating radar (GPR) to locate tendons. Cores were removed, and compressive strength testing and petrographic analysis of the cores were performed in the laboratory. Based on the review of the findings of the engineering analysis, nondestructive evaluation, and laboratory testing, the concrete beams and slabs were load-tested in accordance with ACI 318, Chapter 20. The load test served to verify that the structure could safely sustain the service load requirements of the building code. This paper should be of value to consulting engineers engaged in condition assessment of posttensioned structures exhibiting distress, in terms of the test methods used and the methodology used in developing various aspects of the load-testing program.