DEC_CI http://hdl.handle.net/10362/1747 2013-05-23T23:37:57Z 2013-05-23T23:37:57Z Cavaco, Eduardo S. Neves, Luis A. C. Casas, Joan R. http://hdl.handle.net/10362/6892 2012-01-25T12:09:11Z 2011-01-01T00:00:00Z

Title: A reliability-based measure of robustness for concrete structures subjected to corrosion Authors: Cavaco, Eduardo S.; Neves, Luis A. C.; Casas, Joan R. Abstract: This work is a contribution to the definition and assessment of structural robustness. Special emphasis is given to reliability of reinforced concrete structures under corrosion of longitudinal reinforcement. On this communication several authors’ proposals in order to define and measure structural robustness are analyzed and discussed. The probabilistic based robustness index is defined, considering the reliability index decreasing for all possible damage levels. Damage is considered as the corrosion level of the longitudinal reinforcement in terms of rebar weight loss. Damage produces changes in both cross sectional area of rebar and bond strength. The proposed methodology is illustrated by means of an application example. In order to consider the impact of reinforcement corrosion on failure probability growth, an advanced methodology based on the strong discontinuities approach and an isotropic continuum damage model for concrete is adopted. The methodology consist on a two-step analysis: on the first step an analysis of the cross section is performed in order to capture phenomena such as expansion of the reinforcement due to the corrosion products accumulation and damage and cracking in the reinforcement surrounding concrete; on the second step a 2D deteriorated structural model is built with the results obtained on the first step of the analysis. The referred methodology combined with a Monte Carlo simulation is then used to compute the failure probability and the reliability index of the structure for different corrosion levels. Finally, structural robustness is assessed using the proposed probabilistic index.

2011-01-01T00:00:00Z Cavaco, Eduardo S. Neves, Luis A. C. Gonçalves, Rui C. Casas, Joan R. http://hdl.handle.net/10362/6891 2012-01-25T12:03:02Z 2011-01-01T00:00:00Z

Title: Robustness analysis of deteriorating reinforced concrete slabs Authors: Cavaco, Eduardo S.; Neves, Luis A. C.; Gonçalves, Rui C.; Casas, Joan R. Abstract: Corrosion of reinforcement bars in concrete structures is the most significant deterioration mechanism in these structures. Corrosion is extremely difficult to predict and, consequently, can be regarded as an unpredictable event. Following this, robustness assessment methods can be employed to define the susceptibility of a structure to corrosion. In this work, robustness is measured in terms of the remaining safety of a deteriorated structure. The proposed methodology is illustrated by means of a reinforced concrete (RC) slab subjected to dead and live loads. The performance of the corroded slab is evaluated using non-linear analysis. The reliability index is adopted to assess the safety of the deteriorated structure. To compute the reliability index a strategy combining the First Order Reliability Method (FORM) and the Response Surface Method (RSM) is used.

2011-01-01T00:00:00Z Cavaco, Eduardo S. Casas, Joan R. Neves, Luis A. C. Huespe, Alfredo H. http://hdl.handle.net/10362/6804 2012-01-19T09:38:11Z 2012-01-19T00:00:00Z

Title: A framework for robustness assessment in the context of corroded RC structures Authors: Cavaco, Eduardo S.; Casas, Joan R.; Neves, Luis A. C.; Huespe, Alfredo H. Abstract: Structural robustness is an emergent concept related to the structural response to damage. At the present time, robustness is not well defined and much controversy still remains around this subject. Even if robustness has seen growing interest as a consequence of catastrophic consequences due to extreme events, the fact is that the concept can also be very useful when considered on more probable exposure scenarios such as deterioration, among others. This paper intends to be a contribution to the definition of structural robustness, especially in the analysis of reinforced concrete structures subjected to corrosion. To achieve this, first of all, several proposed robustness definitions and indicators and misunderstood concepts will be analyzed and compared. From this point and regarding a concept that could be applied to most type of structures and dam-age scenarios, a robustness definition is proposed. To illustrate the proposed concept, an example of corroded reinforced concrete structures will be analyzed using nonlinear analysis numerical methods based on a contin-uum strong discontinuities approach and isotropic damage models for concrete. Finally the robustness of the presented example will be assessed.

2012-01-19T00:00:00Z Dimitrovová, Zuzana Rodrigues, Helder C http://hdl.handle.net/10362/4347 2012-01-01T01:01:17Z 2009-01-01T00:00:00Z

Title: Design of New Materials for Passive Vibration Control Authors: Dimitrovová, Zuzana; Rodrigues, Helder C Abstract: The aim of this contribution is to extend the techniques of composite materials design to non-linear material behaviour and apply it for design of new materials for passive vibration control. As a first step a computational tool allowing determination of macroscopic optimized one-dimensional isolator behaviour was developed. Voigt, Maxwell, standard and more complex material models can be implemented. Objective function considers minimization of the initial reaction and/or displacement peak as well as minimization of the steady-state amplitude of reaction and/or displacement. The complex stiffness approach is used to formulate the governing equations in an efficient way. Material stiffness parameters are assumed as non-linear functions of the displacement. The numerical solution is performed in the complex space. The steady-state solution in the complex space is obtained by an iterative process based on the shooting method which imposes the conditions of periodicity with respect to the known value of the period. Extension of the shooting method to the complex space is presented and verified. Non-linear behaviour of material parameters is then optimized by generic probabilistic meta-algorithm, simulated annealing. Dependence of the global optimum on several combinations of leading parameters of the simulated annealing procedure, like neighbourhood definition and annealing schedule, is also studied and analyzed. Procedure is programmed in MATLAB environment.

2009-01-01T00:00:00Z