Structural evaluation and testing of damaged reinforced concrete bent caps

Abstract

The structural assessment of aged and existing reinforced concrete infrastructure represents a major challenge faced by the structural engineering community. The growing inventory of degrading civil infrastructure throughout the world advocates addressing a number of real-world needs: evaluating the implications of now-deficient design details comprising existing structures, assessing causes of visual distress observed in reinforced concrete infrastructure and its impact on structural performance, and verifying the feasibility of structural retrofit strategies to maintain adequate levels of safety and extend service life.

This thesis presents findings obtained from an experimental research program involving the field-extraction and subsequent laboratory testing of two reinforced concrete bent caps removed from a pair of 60-year old bridges. The bridges forming the subject of this investigation were scheduled for replacement as a result of several structural performance-related issues, including extensive shear cracking observed in the bent caps comprising both bridges. Bent cap cracking damage was documented prior to removal from the field and was used as a means of benchmarking in-service load levels. The bent caps were subsequently tested in the laboratory in a manner that simulated service dead loads and extreme lane loading scenarios.

The first bent cap was tested as-built, while the second bent cap was retrofitted using a carbon fiber-reinforced polymer wrap to investigate the suitability of such retrofits for enhancing the shear resisting performance of damaged reinforced concrete bent caps. Results from the testing of the first shear-damaged bent cap showed that, while the cap had developed severe diagonal cracking under service and was constructed with very light shear reinforcement levels that would not satisfy modern design standards, it possessed significant post-cracking shear strength. The second, retrofitted bent cap achieved meaningful shear resistance enhancements when compared to the non-retrofitted bent cap, and was ultimately governed by the flexural failure modes. In summary, both reinforced concrete bent caps possessed significant residual post-cracking shear strengths despite having developed large-widths shear cracks while in service and having been constructed with only light shear reinforcement volumes and shear reinforcement placement details that do not conform with modern design provisions.