| Summary: |
In the last decade the concern about the safety of bridges has been increasing, as a result of some serious accidents and because of the great level of deterioration of a significant number of bridges. In this context, powerful tools for structural safety assessment (SSA) are needed and adequate retrofitting techniques must be available. A reflection of this, is the recent proposal of Prof. Kappas (Greece) to set up a new EAEE Task group named "TG11: Seismic Design, Assessment, and Retrofit of Bridges' in which the members of this project are involved.
The first objective of this project is to improve existing methodologies for SSA with different levels of complexity, allowing including the effect of retrofitting procedures for the piers.
The high level methodology for structural modeling will include non-linear dynamic material behavior analysis, that shall be considered using detailed models (based on a concrete damage model) and a simple model using bar elements with plastic hinges. Structural safety will be assessed in a probabilistic way by evaluating the failure probability according to statistical characterization of the action and of relevant structural strength parameters.
This methodology will be used in order to establish the applicability of the pushover analysis procedures for bridges proposed in EC8. For the cases not within the field of application of the EC8, improved methods for pushover analysis will be pursued. Numerical test will also be carried out to assess the validity of the proposed methods by comparing the results with those obtained by nonlinear analysis.
A simple assessment methodology will also be developed in order to estimate the distribution of heavy damage that is expected due to seismic action, a very helpful tool ehen a rapid assessment of a large set of bridges is needed.
Concerning the second objective, a set of piers will be experimentally analyzed under cyclic loads in order to calibrate the numerical models. After havi  |
Summary
In the last decade the concern about the safety of bridges has been increasing, as a result of some serious accidents and because of the great level of deterioration of a significant number of bridges. In this context, powerful tools for structural safety assessment (SSA) are needed and adequate retrofitting techniques must be available. A reflection of this, is the recent proposal of Prof. Kappas (Greece) to set up a new EAEE Task group named "TG11: Seismic Design, Assessment, and Retrofit of Bridges' in which the members of this project are involved.
The first objective of this project is to improve existing methodologies for SSA with different levels of complexity, allowing including the effect of retrofitting procedures for the piers.
The high level methodology for structural modeling will include non-linear dynamic material behavior analysis, that shall be considered using detailed models (based on a concrete damage model) and a simple model using bar elements with plastic hinges. Structural safety will be assessed in a probabilistic way by evaluating the failure probability according to statistical characterization of the action and of relevant structural strength parameters.
This methodology will be used in order to establish the applicability of the pushover analysis procedures for bridges proposed in EC8. For the cases not within the field of application of the EC8, improved methods for pushover analysis will be pursued. Numerical test will also be carried out to assess the validity of the proposed methods by comparing the results with those obtained by nonlinear analysis.
A simple assessment methodology will also be developed in order to estimate the distribution of heavy damage that is expected due to seismic action, a very helpful tool ehen a rapid assessment of a large set of bridges is needed.
Concerning the second objective, a set of piers will be experimentally analyzed under cyclic loads in order to calibrate the numerical models. After having suffered some damage, piers will be retrofitted and tested again in order to allow investigating the performance of the adopted retrofitting technique.
The third objective aims at evaluating the impact of the NA of the EC8, in which a significant increment for the seismic intensity is introduced in the north region of Portugal. Moreover, in this region it was not necessary to consider the seismic action for the structural design before 1985 (when the present Portuguese codes were published), thus implying that the most part of the bridges are not prepared to stand with the revised seismic action. In addition, a large number of Portuguese bridges are near the end of their structural period of life and some may even be in danger if the necessary repairs are not carried out. The collapse of an important bridge (with several casualties) and a viaduct in the last five years, have confirmed this general concern about bridge safety which has forced the national authorities to undertake a general campaign of bridge Inspection.
Therefore, the main purpose within this objective is to assess the actual safety of the bridges built in the north of Portugal and to identify the most adequate retrofitting technique to adopt for those that can not stand with the new seismic intensity.
Within the scope of a cooperation agreement established with the Roadway Portuguese Institute (IEP), a set of Portuguese bridges will be used as an application of the SSA methodologies developed. Bridges will be selected in order to be representative of different and common types, as far as structural type and level of irregularity are concerned. The simpler methodology will be applied in order to identify the most vulnerable types of bridges. Those with an unsatisfactory safety will be analyzed in detail with the mentioned methodologies, and the results will be compared. Concerning the unsafe bridges different retrofitting strategies will be analyzed in order to identify the most suitable.
Finally, the fourth objective consists on calibrating some of the rules included in the EC8-2, namely the new seismic intensity impact, the pushover analysis methodology and t
Additionally, Portugal is preparing its National Annex (NA) for the application of the Eurocode 8 (EC8), where substantial changes are introduced for the seismic zones, namely, a significant increment of the seismic intensity at the northern Portugal, implying a severe reduction at the safety of the structures.
Moreover, having in mind that before the present Portuguese codes were enforced it was not necessary to consider the seismic action for the structural design in that region, it becomes quite apparent how deep can be the changes on seismic effects foreseen for bridges. Therefore, an enormous task will be prompted to the Portuguese authorities in order to assess the actual safety of the structures, some of them built without any seismic provision. |