Structural assessment of existing concrete buildings

Abstract

An approach to the general issue of existing concrete structures safety analysis is presented, referring to the most relevant uncertainties in the process of structural assessment and the various ways of characterizing them. The structural reliability and reliability index concepts and a procedure to measure them probabilistically are presented, as well as the basic problem of structural reliability and a semi‐probabilistic approach to safety compliance. The importance of characterizing the strength properties of structural materials is discussed, and the main related aspects are pointed out. Methods prescribed in some standards and recommendations are presented, emphasizing those suitable for safety analysis of existing structures. The importance of a priori data, the sources normally used in data acquisition and of the inspection and tests planning stages is stressed. The number of tests (sample dimension) needed to infer and statistically validate results is discussed. The importance of characterizing probabilistically actions and effects is stressed. The code criteria for their quantification are presented and the types of probabilistic distribution and variability inherent to each action type are briefly described. Some methods for their quantification in existing structures are pointed out. Special importance is given to the quantification of variable actions, owing to the high associated uncertainties, especially seismic action, in the process of structural safety assessment. Ways of reducing their nominal values or the respective safety factors, depending on the degree of uncertainty involved, namely due to the reduction of the existing structure's expected service life, are pointed out. The probabilistic methodologies developed for structures safety analysis, based on the reliability classical techniques, namely the second moment methods, of First and second order, and those based on the numerical simulation (Monte Carlo) techniques, are discussed, emphasizing the difficulty in its application to case studies of the assessment of existing structures. Copyright © 2003 John Wiley & Sons, Ltd.

Método para avaliação da segurança de edificios durante a recuperação estrutural dos pilares

“…An expressive reduction of that parameter can be obtained by measurements of the structure (ALLEN, 1991). In this case, according to Laranja & Brito (2003), δ G,eval could be reduced to 5%. The factor to permanents actions (α G,eval ) can be Evaluation method for safety conditions of buildings during the structural repair of columns taken according to the calibration values for design codes (ACHE, 2003).…”

“…The evaluation should incorporate all the information obtained in the inspections, including the performance of the structure. Alike other researchers, load effects were compared for the sake of safety, such as (bending moments and compression loads) that were more probable to occur in the columns of the first level starting from the foundations, usually in the garage of residential buildings, with the effective resistances of their cross sections at the moment of the intervention, through an ultimate limit state equation (LARANJA & BRITO, 2003). In order to obtain the evaluation load effects, an adjusted structural modeling was used which was calculated by the program.…”

“…This fact induced the author to introduce different levels of safety for existing structures, through adjustment done with the individual contribution of the factors given in Table 2. Such a procedure demands common sense on behalf of the structural engineers responsible for the evaluation (Laranja & Brito, 2003), as well as involving a subjective criteria as inspection quality and probability of personal risks. However, the method allows determination of the reliability index in the evaluation (β eval ) starting from the β of design, applying some reduction terms that vary from one structure to another, according to equation 13:…”

“…The concrete strength given in tests is frequently represented by normal distribution (e.g. FUSCO, 1976;MELCHERS, 1999;LARANJA & BRITO, 2003). The partial factor in terms of a semiprobabilistic method can be defined by equation 16, valid for the normal distribution (TANNER, 1995).…”

Using Ultrasound for In-Service Assessment of Rendered Walls

“…14 The indirect method leads to less satisfactory results, 11 as does its in-situ use. 17 The variability of the ultrasound technique when used on rendering has been studied in several in-service buildings. The average velocity can be given by the slope of the linear regression that best fits the readings obtained.…”