Numerical Modeling of RC Bridges for Seismic Risk Analysis

Numerical Modeling of RC Bridges for Seismic Risk Analysis

Pedro Silva Delgado (Instituto Politécnico de Viana do Castelo, Portugal), António Arêde (Faculdade de Engenharia, Universidade do Porto, Portugal, Portugal), Nelson Vila Pouca (Faculdade de Engenharia, Universidade do Porto, Portugal, Portugal) and Aníbal Costa (RISCO, Universidade de Aveiro, Portugal)
DOI: 10.4018/978-1-4666-8823-0.ch015
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The main purpose of this chapter is to present numerical methodologies with different complexities in order to simulate the seismic response of bridges and then use the results for the safety assessment with one probabilistic approach. The numerical simulations are carried out using three different methodologies: (i) plastic hinge model, (ii) fiber model and (iii) damage model. Seismic response of bridges is based on a simplified plane model, with easy practical application and involving reduced calculation efforts while maintaining adequate accuracy. The evaluation of seismic vulnerability is carried out through the failure probability quantification involving a non-linear transformation of the seismic action in its structural effects. The applicability of the proposed methodologies is then illustrated in the seismic analysis of two reinforced concrete bridges, involving a series of experimental tests and numerical analysis, providing an excellent set of results for comparison and global calibration.
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It is during the occurrence of earthquakes that deficiencies, which cause a bad behavior of structures, has been highlighted and that can be drawn lessons with regard to design aspects that allow to provide it with a good seismic behavior.

Reports of seismic effects on reinforced concrete bridges, especially those built according to the codes of practice of the seventies, show that a lot of them behave poorly and have an inadequate safety assessment. Some efforts, therefore, must be made to accurately define bridge assessment and hence evaluate the need for reliable solutions to improve safety levels and behavior during seismic activity in the future.

In recent earthquakes it has been demonstrated that bridges and viaducts are structures that suffer extensive damage. Even in “moderate magnitude” earthquakes, the consequences in these structures have been very important, on many occasions causing their partial destruction or even total collapse, with correspondingly heavy costs. When compared, these consequences have been greater than those observed in current structures. Some examples of these earthquakes in the United States are the Loma Prieta (Soberón et al., 1999; Priestley et al., 1996) and the Northridge (Oliveira et al., 1995), in Japan the Kobe earthquake (Legeron, 2000) and in China the Sichuan earthquake (ISSN, 2008), with a magnitude of 7.9 on the Richter scale and more than seventy thousand deaths.

The evaluation of seismic vulnerability of bridges, considering their nonlinear behavior (a necessary consideration when a realistic analysis of the seismic response is intended), involves enormous computing resources and corresponding calculation efforts. On the other hand, the development of research studies in this field has enabled a better understanding of their behavior, and the availability of numerical and experimental results allows the possibility of the calibration of simplified procedures.

However very high refined models could be adopted, involving a 3D space modeling and the spread of the plasticity along the member length as well as across the section area, in this work a substantially more simplified model (without losing accuracy) is also explored. This simplicity is evidenced by a much lower number of parameters involved and an enormous lesser computing time – about 50 times less when compared with a more refined model. Therefore, the adoption of such simplified model shows the great advantage, from the practical usage point of view, when a large number of analysis is needed, as is the case of vulnerability analysis.

Key Terms in this Chapter

Hollow Bridges Piers: Columns of large bridges which is not solid section and therefore with flange and web walls.

Seismic Analysis: Calculation of the structure response subjected to earthquakes.

Shear Effects: Effects of lateral load (such as seismic load) acting on a structure and more significant on short and hollow piers.

Plastic Hinge Model: Structural model with non-linear behavior concentrated at the extremities of the elements.

Safety Assessment: Evaluation of the structural safety by a deterministic or probabilistic methodology.

Damage Model: Structural model that is supported on refined finite element meshes, with high complexity and detail levels in the material constitutive laws.

Structural Modeling: The creation of analytical models to simulate the structures behavior.

Fiber Model: Structural model with non-linear behavior distributed along the elements and cross sections.

Non-Linear Behavior: When the structural materials lose the capacity of elastic behavior.

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