Concrete structures. Contribution to the safety assessment of existing structures

Abstract

ResumoThe safety evaluation of an existing concrete structure differs from the design of new structures. The partial safety factors for actions and resistances adopted in the design phase consider uncertainties and inaccuracies related to the building processes of structures, variability of materials strength and numerical approximations of the calculation and design processes. However, when analyzing a finished structure, a large number of unknown factors during the design stage are already defined and can be measured, which justifies a change in the increasing factors of the actions or reduction factors of resistances. Therefore, it is understood that safety assessment in existing structures is more complex than introducing security when designing a new structure, because it requires inspection, testing, analysis and careful diagnose. Strong knowledge and security concepts in structural engineering are needed, as well as knowledge about the materials of construction employed, in order to identify, control and properly consider the variability of actions and resistances in the structure. With the intention of discussing this topic considered complex and diffuse, this paper presents an introduction to the safety of concrete structures, a synthesis of the recommended procedures by Brazilian standards and another codes, associated with the topic, as well a realistic example of the safety assessment of an existing structure.Keywords: structures safety, existing concrete structures safety, concrete structures evaluation.A avaliação da segurança de uma estrutura de concreto existente difere daquela adotada no projeto de estruturas novas. Os coeficientes de ponderação das solicitações e das resistências, adotados na fase de projeto, levam em conta incertezas e imprecisões relacionadas com os processos de construção das estruturas, variabilidade da resistência dos materiais, além das aproximações numéricas dos processos de cálculo e dimensionamento. Entretanto, quando se analisa uma estrutura acabada, um grande número de fatores desconhecidos durante a etapa de projeto já se encontram definidos e podem ser mensurados, o que justifica uma redução nos coeficientes de majoração das ações ou de minoração das resistências. Diante disso, entende-se que analisar a segurança de uma estrutura acabada é muito mais complexo que introduzir a segurança no projeto de uma estrutura nova, pois requer inspeção preliminar, ensaios, análises e vistoria criteriosa. São necessários sólidos conhecimentos e conceitos de segurança em engenharia estrutural e também conhecimentos sobre os materiais de construção empregados, de forma a identificar, controlar e considerar corretamente a variabilidade das ações e das resistências na estrutura. Com a intenção de discutir este tema considerado complexo e difuso, apresenta-se neste artigo uma introdução à segurança das estruturas de concreto, uma síntese da revisão bibliográfica dos procedimentos recomendados por normas nacionais e normas internacionais associadas ao tema, bem como um exempl...

Análisis de concretos con no conformidades: efectos de larga duración

“…In determining admissible compressive stress, σcd, coefficients γc and β are used -design values based on characteristic values defined from probabilistic considerations for each limit state. γc coefficient represents differences between concrete from standard specimen and concrete from structural element as well uncertainties related to actions (Couto et al, 2015), while β is derived from the product of partial coefficients, i.e., by the multiplication of benefic effects of compressive strength evolution over time (β1) by harmful effects of long lasting load (β2) (Silva Filho; Helene, 2011).…”

“…This can point out problems that put in doubt the structural design, possible repairs or total and/or partial condemnation of some elements. Within this context, many studies and research has been made to understand non-conformity of structural concrete, addressing aspects of safety, confiability and risk analysis (Kausay;Simon, 2007;Pereira, 2008;Taerwe, 2011;Helene, 2011;Santiago, 2011;Santiago;Beck, 2011;Taerwe, 2014;Larrossa et al, 2014;Magalhães, 2014;Rao et al, 2014;Couto et al, 2015;Magalhães et al, 2015). In Brazil, the subject led the creation of a group of studies of the Brazilian Association of Structural Engineering and Consulting (ABECE), which resulted in the recommendation ABECE 001: Case studies in non-conformity of concrete.…”

Strength reduction method for a factor of safety determination of damaged concrete structures

“…The fib Model Code considers two approaches possible for assessing the structural safety of concrete structures (Couto et al., 2015): the Probabilistic Method and the Partial Safety Factor Method. In addition, the fib Model Code presents two partial safety factor methods for existing concrete structures as possibilities to determine FoS (Caspeele et al., 2013; Lara et al., 2021): the Design Value Method (DVM) and the Adjusted Partial Factor Method (APFM).…”

Influence of the molding process and different surface regularization methods on the compressive strength of concrete specimens

“…The compressive strength test is applied to evaluate the concrete elements load capacity and it is one of the most important proprieties for the structural performance of a building (Helene, 2011;Neville & Brooks, 2013;Thandavamoorthy, 2015). If the results show that the concrete in use did not reach the design characteristics, then it can compromise the stability of the structure and its users (Couto, Carvalho, Cintra, & Helene, 2015). It is important to assure the quality of building materials, so the facility to run the compressive strength test and its low cost make it the most usedformaterial quality control (Moreno, Solís-Carcaño, Varela-Rivera, & López, 2016).…”