Nondestructive Assessment of Axial Load–Deflection Behavior of Drilled Shafts for a Suspension Bridge

FEDERICO PINTO; CARLOS GERBAUDO; CARLOS A. PRATO

JOURNAL OF INFRAESTRUCTURE SYSTEMS (ASCE)

ASCE-AMER SOC CIVIL ENGINEERS

Lugar: Reston, Virginia; Año: 2012 vol. 18 p. 47 - 55

1076-0342

The new Río Cuarto Bridge, currently under construction in the Province of Córdoba, Argentina, consists of a 110-m long, cable-stayed main span with prestressed concrete deck, steel pylons, and two 50-m long side spans founded on groups of drilled shafts. The construction method, structural configuration of the superstructure, and post tensioning sequence of the cables required a detailed characterization of the axial load behavior of the drilled shafts, both for the temporary support shafts and the foundation piers. Small strain and working load level predictions were made during design, based on conventional site investigation information, as well as additional in-situ geophysical testing. A series of nondestructive evaluations, coupled with nonlinear extrapolations calibrated to represent the measured small strain range were carried out in lieu of conventional verification of design predictions by means of more cumbersome large strain testing. The testing program consisted on monitoring accelerations generated at the top of the shaft due to a small amplitude dynamic load measured by means of a dynamic force transducer. A nonlinear numerical model was then calibrated so as to reproduce the initial stiffness measured during the small strain testing program in order to extrapolate the load deflection curve into the service load range, and thus define load deflection curves of the shafts at each pier location up to service load levels. In order to obtain an experimental validation of the approach at the site, a conventional static load test, carried up to the service load level was performed on a main pier shaft. Results showed a reasonable agreement between the nondestructive evaluation with nonlinear extrapolation, large strain measurements, and design predictions for the main pier shafts, whereas some differences were observed between the design predictions and small strain measurements at other locations, mainly due to as-built conditions unforeseen in the original design. Thus, the nondestructive testing program was not only instrumental in the verification of the as-built behavior of the shafts, but also allowed the development of load deflection curves for the drilled shafts that accurately represented the behavior up to the service load level.