Afonso Serra Neves

Numerical Evaluation of the Long-Term Behavior of Precast Continuous Bridge Decks

Continuous bridge decks constructed with precast girders undergo significant stress changes caused by the concrete delayed deformations because of creep and shrinkage. These effects must be taken into account in the design of new structures. The validation of the analysis procedures should ideally be carried out through the comparison between the calculations and the results observed in real structures. However, experimental results of the construction and long-term behavior of these structures are scarce. The construction of a major bridge in Portugal has provided the opportunity to monitor one such structure. This paper presents the monitoring campaign and the analysis strategy that was developed to assess the long-term variation of strains and stresses in precast continuous bridges. The numerical analysis was validated by comparison with the results observed in the real bridge. The consequences of carrying out simplified analyses based on limited information about the concrete properties and the construction sequence are also evaluated.

Long-term monitoring and assessment of a precast continuous viaduct

Precast girders have recently been widely employed in the construction of bridges and viaducts. The new bridge over the Tagus River in Portugal, the Lezíria Bridge, comprehends a 9160 m long south approach viaduct, which was built with precast girders made continuous in situ. Given the relevance of this construction, a long-term monitoring system was implemented and measurements were taken since the start of the construction. The observed parameters were concrete strains and temperatures, deck rotations, joint displacements, accelerations and also environment temperature and relative humidity. The work presents the precast structure, the monitoring system and the appraisal of a statistical procedure for the long-term assessment of the structural behaviour. This procedure is based on prediction models, which establish the normal correlation patterns between environmental and material parameters (such as concrete temperature and shrinkage strains), and the observed structural response in terms of strains, rotations and movements of expansion joints. The calculation of the normal correlation pattern comprehends the minimisation of a square error. By applying the prediction model to the structural response measured in the south approach viaduct of the Lezíria Bridge, it was found that this methodology is a feasible tool for real-time damage detection of bridges.

Push-Off Tests in the Study of Cyclic Behavior of Interfaces between Concretes Cast at Different Times

AbstractThe knowledge about the cyclic behavior and effects of fatigue on interfaces between concrete cast at different times, subjected to shear stress, is still very limited. This aspect is particularly relevant in structures subjected to important cyclic loads, such as railway bridges. In this context, first, a brief state of the art on the monotonic and cyclic behavior of interfaces between concretes cast at different times is presented. Then, the test campaign, which was aimed at obtaining experimental support for modeling the behavior of such interfaces, subjected to a high number of load cycles, is described, and the corresponding results are discussed and analyzed in terms of slip and crack opening, stress variations in the monotonic tests, failure mode, and number of resisting load cycles. It was further observed that the number of resisting load cycles increases as the maximum load level decreases. On the basis of this evidence, an experimental S-N curve was set for this type of interface.

New Methodology for Calculation of Required Prestressing Levels in Continuous Precast Bridge Decks

The calculation of minimum required prestressing levels in prestressed bridge deck girders is usually governed by serviceability requirements in terms of allowable stress levels. In the case of continuous structures, different quantities of prestressing steels have to be quantified for different critical locations and, owing to the structure hyperstaticity, the prestressing force required for a given critical cross section depends on the quantities of prestressing steels adopted in the remainder of the structure. This paper presents a feasible methodology for quantification of the minimum required prestress forces for different critical cross sections, avoiding the use of iterative procedures. A methodology for taking into account the variability of the structure response, owing to the uncertainty associated with the quantification of creep, shrinkage, and construction timings is also presented. Monte Carlo simulations, based on the Latin Hypercube sampling method, are used in the calculation of the statistical distribution of the long-term structure response. Two case studies are presented to show the relevance of the aforementioned variability and its consequences in terms of minimum required prestressing levels.