Marcelo A. Ceballos

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.

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

Numerical evaluation of integrals involving the product of two Bessel functions and a rational fraction arising in some elastodynamic problems

Abstract This paper presents numerical techniques for evaluating integrals of the form ∫ 0 ∞ J β ( k ρ ) J γ ( k R ) k α ( k − s ) d k . These integrals arise during the application of the Hankel transform to pass the displacements of a layered soil profile from the wave number domain to the spatial domain in three-dimensional problems of elastodynamics. The objective here is to obtain solutions with an adequate accuracy from the engineering point of view to the integrals that arise in a first order formulation of a wave propagation model widely used for layered soils.

Evaluación de vibraciones de cuerpo entero según normativas vigentes

We present the computer implementation of different standards for the evaluation of human exposure to whole-body vibration. The resulting computer tool enables assessment and quantitative analysis of vibration records in accordance with current standards ISO 2631-1:1997, VDI 2057 Part 1 2002, and BS 6841:1987. The objective is to provide a user-friendly computer system, as a complement to a basic vibrometer, which provides a quick and effective quantification of vibration effects using appropriate descriptors. The numerical implementation of a Matlab code is described, including the conversion of analog filters to digital in the time domain. The development of the computer tool presented here was motivated by the lack of flexibility found in commercial equipment; although commercial vibrometers satisfy basic requirements, they are limited to specific processing and restrict the possibility of a thorough study or research. The performance and potentiality of the computer tool, which has been conveniently validated, are illustrated through examples of practical interest.

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.