Reliability assessment of the superstructure of precast prestressed bridges

Abstract

Given that all buildings are designed for a certain "lifespan", there comes a time when the question must be asked whether they are still safe and serviceable? The need to ask this question arises from the fact that over time, each object is exposed to external influences and suffers certain geometric and material degradations, mechanical damage, increased intensity of moving load (weight and frequency of vehicles), and also the production and control of materials was then at a lower level. The answer to this question can only be revealed through their research and reliability assessment, and the final answer can be: demolition and reconstruction, repairing and / or strengthening, no interventions required. Reliability is the probability that a system (construction) will perform the functions for which it is designed during a certain time interval ("lifespan") under specific operating conditions. In order to determine the reliability index of the structure (βsystem), the reliability indices at the level of the structural element (βi) should be determined first, and then through their connection (depending on the structural system and the limit states) the reliability of structure is determined. Due to the lack of means and conditions to examine the necessary geometric, material and other data for an old bridge, a reliability assessment was performed on a relatively new bridge, i.e. reinforced concrete pre-stressed girder overpass on the highway section Miladinovci - Stip. For that purpose, the project of the same was used, as well as all available reports on the embedded materials that are of particular use for modeling the real model. Reliability is examined in terms of ultimate limit state (flexural moments) using FORM (First Order Reliability Method) and MonteCarlo simulation technique. At the end of the paper, a comparative analysis is performed between the results of the two methods with the recommended minimum values in EN1990 [1] for a 1 year reference period.