Analysis of Structural Capacity and Stiffness of Drilled Shafts with Construction Defects and Repairs-Paper

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The paper presents a fiber-element analysis method for evaluating the flexural strength and stiffness of drilled shafts containing construction defects. The method, implemented in OpenSees, divides a shaft cross-section into fibers with independently defined nonlinear material behavior. This allows defective concrete to be represented by its actual estimated shape and location, including as a void. The model accounts for confined and unconfined concrete, reinforcing steel, and their nonlinear stress-strain responses.<br /><br />The method was verified by comparing moment-curvature results for a reinforced-concrete section with results from two established analysis programs. The programs showed close agreement in flexural rigidity, cracking moment, post-yield stiffness, and ultimate strength.<br /><br />A case study examined shafts with defective cover concrete remaining in narrow “shadow” zones behind reinforcing bars after hydro-jetting and grout repair. Analysis under the project’s factored axial load found that the defects reduced peak moment capacity by about 5 percent. The repaired section’s factored capacity, including the remaining defects, was 12,320 kip-feet—above the 12,041 kip-foot demand, though below the 13,230 kip-foot capacity of the defect-free design.<br /><br />The authors conclude that explicitly analyzing defects can provide a rational basis for accepting shafts or selecting repairs, rather than automatically repairing or replacing them. The approach can incorporate integrity-testing findings, assess different defect geometries and materials, and potentially reduce construction costs and delays.

Keywords

fiber-element analysis

drilled shafts

construction defects

flexural strength

flexural stiffness

OpenSees

moment-curvature analysis

reinforced concrete

concrete voids

grout repair