Carlos A. Prato

Dynamic Bending Stresses near the Ends of Parallel-Bundle Stay Cables

Dynamic bending stresses in stay cables may have a significant influence on their fatigue life, especially when they are not provided with sufficiently stiff lateral supports at a certain distance from the sockets. This work is concerned with the analysis of dynamic bending stresses near the ends of parallel wire cables of the following characteristics: a) Poly Ethylene (PE) sheath pipe grouted with cement mortar along the cable length except for short segments at the ends where the grout material is a bituminous epoxy, and b) the cables do not have guides or lateral supports near the sockets. It is shown that the maximum dynamic stresses due to global and local bending of the wires are always higher than what it would be if there were no discontinuities of the mortar cement grout at the cable ends. It is shown that the increase of bending stresses is caused by localised deformations that take place at the free length of the cable near the sockets.

Design of Energy Absorbing Structures For Barge Collision Protection of Bridge Piers

The design of bridge structures against barge collision generally relies on the assumption that flexible protection systems absorb the kinetic energy of the vessels by means of elastoplastic deformation. For large tows, however, protection systems become massive structures with considerable stiffness and yield loads that may become larger than that of the barge bow. Furthermore, when the stiffness of the impacted structure increases, the lashings that join together the tow may brake during the collision process; leading to a different energy absorption scenario.

Case Studies of Failure, Damage Assessment, and Repair of Multispan Bridges in Argentina

The paper is concencemed with the evaluation, strengthening and follow-up of two case studies of multispan prestressed concrete bridges in Argentina. The two case studies, and the ensueing repair works, were prompted by different circurnstances: one of them, by the catastrophic collapse of one of twelve identical 60 m span arches -tied by the presetressed concrete deckafter passage of a regular passenger bus, and the other one, consisting of fourteen simply supported spans of cast-in-place prestressed concrete girders, by systematic and excessive deformations and cracking of the longitudinal girders. Although both cases were built more than 30 years ago used for prestressing a postensioning system (Hoyer) no longer applied in Argentina, and were located in the same geographic region with similar mild environmental conditions (temperate weather, with rains concentrated on the summer months), the difference between their respective structural configurations led to very different critical limit states. The tied arch collapsed without warning just after a bus had passed over the bridge; the collapsed span was the last of the twelve spans the bus had passed. At the time of collapse no signs of damage or of abnormal structural behavior had been noticed. The experimental and modelling forensic study revealed that failure of the prestressed concrete tie beams near the arch abutments incorporated to the structure of the deck was the cause of collapse. The failure mechanism involved only partial redistribution of forces from the broken high stregnth steel tendons of the tie beams to the reinforced concrete deck slab before the onset of collapse. The tendon failure was found to have been caused by corrosion associated with the spilling of a water on the initial section of the tie beam by a drainage pipe of the water runoff of the bridge deck. Design of the external prestressing needed to restore the safety requirements of the eleven identical spans that remained in service was immediately undertaken, implemented and controlled by a follow up process of the prestressing force of the new external tendons. On the other hand, the simply supported beams reached a service limit state of excessive vertical deflections and cracking, that led to bridge owner to restrict the circulation over the bridge to a maximum of one truck in one of the two traffic lanes. The i Professor, National University of Crrdoba, Los Homillos 1596, 5014 Crrdoba, Argentina; phone 0351464-4320; fax 0351-433-4144; cprato@mafcor.fis.uncor.edu

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

The new Rio Cuarto Bridge, currently under construction in the Province of Cordoba, Argentina, consists of a 110-m long, cable-stayed main span with a 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, on the basis of conventional site investigation information and 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 as a result of 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 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. 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, primarily as a result of as-built conditions unforeseen in the original design. Thus, the nondestructive testing program was instrumental in the verification of the as-built behavior of the shafts and allowed the development of load-deflection curves for the drilled shafts that accurately represented the behavior up to the service load level.

Dynamic and Static Tests of Bridges and Viaducts of the Rosario-Victoria Highway Link Project

The paper presents the main objectives and results of a series of static and dynamic load tests performed on the bridges and viaducts of the Rosario-Victoria highway connection across the Parana River in Argentina that was completed and opened to traffic in May of 2003. The work reported in the paper was carried out by the authors as independent consultants to the link operator. A brief summary of the structural components of the project illustrates the type and scale of the project: a 350 m central span cable-stayed bridge, access viaducts on both sides of the main span, and a series of Gerber type bridges over secondary arms of the Parana river with a total length of approximately 12.5 km. The main bridge and access viaducts were designed by Leonhardt Andra and Partners Gmb of Stuttgart, and the bridges over the secondary water courses by INCO Consultants of Milan. The contractor and operator of the link is Puentes del Litoral S.A., a consortium of construction companies working under a BOT contract agreement with the Federal Government of Argentina. The paper addresses the objectives and main features of the specifications for the tests within the terms of reference of the bid documents for construction and operation of the project. These documents required that load tests be performed before opening it to traffic, although they left the details and scope of the tests to be proposed by the contractor for approval by the supervisory board set forth by the Argentine Federal Government for control of public services provided by private operators. The test specifications are discussed, from definition of loading schemes and instrumentation, to acceptance criteria and test results. Beyond the obvious advantage of the purpose of the tests as a means to define a “zero or reference state” of the structures before opening them to the full traffic load, the paper focuses on the use of the test results to comply with a contractual requirement by the terms of reference that the bridge operator develop before commissioning, a “deterioration model” of all the major structures of the project describing the parameters and variables to assess their performance during the 25 year period of concession. This particular requirement was a direct consequence of recent experience with similar projects where such requirements had not been included in the tender documents.

Road bridge across the Uruguay River

The Santo Tome-Sao Borja road bridge between Argentina and Brazil over the Uruguay river has two vehicle lanes and two pedestrian walkways. It was opened to traffic in January 1998 after 16 months of construction and consists of 33 simply supported spans of 42.50 m.