Angel C. Aparicio

Testing of externally prestressed concrete beams

This paper presents the results of a test program on externally prestressed concrete beams. Five monolithic and three segmental beams were tested in bending and in combined bending and shear. The most significant results are presented such as carrying capacity, prestressing steel stress increase at ultimate, shear behavior of open joints. Conclusions on ultimate load capacity of externally prestressed beams and influence of the tendon length on this capacity are obtained. These tests have been used to validate a numerical finite element model already presented.

Preliminary static analysis of suspension bridges

Dimensionless charts, useful for the the understanding of the static behaviour of single-span suspension bridges, are generated in this paper by applying numerical methods to the equations of the deflection theory. Charts include displacements and bending moments under concentrated loading and maximum displacements and bending moments under distributed loading. Based on these charts, explicit formulae useful for design are given. Extension to the analysis of three span suspension bridges is performed. The accuracy of this extension is checked by analysing 19 existing and hypothetical suspension bridges.

Computer aided design of prestressed concrete highway bridges

Abstract The paper presents a computer aided design system for prestressed concrete highway bridges which, starting from few geometrical data, provides the complete geometry, prestressing steel, reinforcing steel, amount of materials and cost of all the bridge elements: deck, bearings, piers, abutments and foundations. Different configurations are devised, from short and medium to long-span bridges, accounting for different deck super-structures and erection methods. All the results are displayed on the computer screen and can be printed. The system provides also DXF files containing the general layout, cross-sections and prestressing arrangement of box girder bridges. This system allows, in a short time, an accurate design and an economical estimation of a particular bridge, taking into account the most important technical requirements. It is a useful decision-making tool for both design and administration engineers.

Structural behaviour and design criteria of under-deck cable-stayed bridges and combined cable-stayed bridges. Part 2: Multispan bridges.

This paper deals with the application of under-deck cable-staying systems and combined cable-staying systems to prestressed concrete road bridges with multiple spans of medium length. Schemes using under-deck cable-staying systems are not suitable for continuous bridges, as they are not efficient under traffic live load and only allow for the compensation of permanent load. However, combined cable-staying systems are very efficient for continuous bridges and enable the design of very slender decks (1/100th of span) where the amount of materials used is halved in comparison with conventional schemes without stay cables. In this paper, the substantial advantages provided by combined cable-staying systems for continuous bridges (such as high structural efficiency, varied construction possibilities, both economic and aesthetical benefits, and landscape integration) are set out. Finally, design criteria are included.

FLEXURAL STRENGTH OF EXTERNALLY PRESTRESSED CONCRETE BRIDGES

The authors conducted a study on the behavior up to failure of 74 externally prestressed concrete bridges using a nonlinear finite element model. Results of the study are presented. The aim of the study was to derive accurate values of the stress increase of tendons beyond the effective prestress. A code proposal is derived from the results and is compared with existing current codes.

Shear Behavior of Unbonded Post-Tensioned Segmental Beams with Dry Joints

The response of segmental concrete beams with external prestressing under shear is studied. Beams have been tested to evaluate their shear response and load-carrying capacity at various levels of prestressing. The combined flexure and shear structural response has been carefully inspected to obtain design guidelines concerning reinforcement details for the structures. Tests were conducted on both conventional and steel fiber-reinforced concrete elements (SFRC) to also evaluate the possible benefits of SFRC. Conclusions include that the addition of fiber to concrete does not seem to increase the load-carrying capacity of the beams, and that the shear failure of the beams is spatial, not flexure.

Rain-wind-induced cable vibrations in the Alamillo cable-stayed bridge (Sevilla, Spain). Assessment and remedial action

Rain combined with wind action provoking vibration has been observed in the longest stays of the Alamillo cable-stayed bridge in Sevilla (Spain). The maximum displacements observed are in the order of magnitude of 0.5 m and have caused discomfort problems to the pedestrian circulation across the bridge. The paper shows the analytical and experimental studies carried out to analyse the possible solutions and also the steps developed to stop the vibration phenomenon. In 2004, a dynamic test in the cables was envisaged to measure the actual damping in the cables. It became clear that damping in the cables was very low and the solution required the installation of dampers. The damping devices had to be in accordance with the relevant aesthetic constraints of the structure. The installation of the damping devices took place during 2007. After the installation of the damping devices, a new dynamic test was carried out in February of 2008 to check if the level of damping introduced by the dampers was appropriate. During the tests performed in 2004, the natural frequencies of vibration were also obtained at the same time than damping. The comparison between the two sets of natural frequencies (1992 and 2004) allow to extract important conclusions about the correct performance and condition state of the bridge as well as the evolution of forces in the cables after 12 years of construction due to creep in the tower.

New Structural Joint by Rebar Looping Applied to Segmental Bridge Construction: Fatigue Strength Tests

The objective of this research has been to design, develop, and evaluate experimentally a modified type of construction joint of limited length between concrete slab segments. The design concept is based on an anchorage hook of reduced development length stiffened by transverse reinforcement bars. The purpose of this paper is to investigate the mechanical behavior of the joint in terms of stiffness and strength for an application that requires high durability, which often leads to serviceability problems such as cracking and water leakage at transverse joints. This can regularly appear in bridges. Additionally, bridge decks are structures that are subjected to repeated loading such as traffic loads, making it necessary to evaluate the behavior of joints under fatigue load. Therefore, studies focusing on the strength, stiffness, and serviceability of the joints must be carried out. This paper investigates experimentally the fatigue behavior and strength of loop joints with regard to the loop bar diameter, loop joint width, and applied load ranges. These results were compared with the behavior of RC slabs without joints. A total of eight slabs were fabricated for fatigue loading tests, and the failures of the different specimens (with loop joints and without) were obtained. From the test results, the mechanical behavior of the slabs with loop joints was confirmed to be similar to that of the slabs without joints. The experimental loop joint design was found to perform correctly under fatigue loads.

Structural behaviour of segmental concrete continuous bridges with unbonded prestressing and dry joints

This work presents a finite-element method (FEM) analysis of the behaviour of continuous segmental concrete bridges with external prestressing and dry joints, focusing on the response under combined shear and flexure, at the service limit state (SLS) and at the ultimate limit state (ULS). A previously validated FEM model has been applied to simulate the structural behaviour of continuous bridges until failure. A geometrically non-linear analysis has been performed, where the particular behaviour of the dry joints, the concrete plasticity and the slipping of the prestressing tendons at the deviators have been considered. Results of the analysis have been compared with the available data of the modelling of simply supported bridges, and the different behaviour introduced by the support redundancy has been pointed out. Analysis proves that the SLS can govern the design of the prestressing force, whereas in simply supported bridges, it is the ULS that always governs the design. Concrete and steel remain essentially linear under ultimate loads, which implies that there is an extra safety factor against failure. Before failure, when support and mid-span joints are opened, moment redistribution has occurred and an arch springing from the bearings is formed within the concrete, which equilibrates the external loads.

Computer-Based Bridge Management System for Permit Vehicle Routing

The traffic of special overloaded trucks (special permits) over bridges may create structural problems at the time of crossing and also during the service life of the bridge. Therefore, the owner agency responsible for a bridge network should carefully look at the maximum loads acting on the bridges and the problems they may cause according to their actual condition. This article presents work conducted by the authors concerning the possibility of passage permission of overload permits in the main highway network of Spain. Most of the bridges are quite new and very well documented, but some older undocumented bridges are also present. The work is summarized in a bridge management system (BMS) installed on a PC. The computational model performs the structural analysis of the bridges crossed by a defined special vehicle in a quick and automatic way and compares the results with the maximum allowable actions over the bridge, the result being authorization or not of the passage. The computational models are developed for most common bridge types in the network and are of limited value for very complex structures. The BMS is now in use in the complete trunk road system in Spain. The software developed has shown its usefulness in assisting bridge engineers in the decisionmaking process of permit passage.