Xavier Romão

An empirical power comparison of univariate goodness-of-fit tests for normality

A comprehensive power comparison study of existing tests for normality is proposed. Given the importance of this subject and the widespread development of normality tests, comprehensive descriptions and power comparisons of such tests are of considerable interest. Since recent comparison studies do not include several interesting and more recently developed tests, a further comparison of normality tests is considered to be of foremost interest. The study addresses the performance of 33 normality tests, for various sample sizes, considering several significance levels and for a number of symmetric, asymmetric and modified normal distributions. General recommendations for normality testing resulting from the study are defined according to the nature of the non-normality.

Evaluation of the EC8-3 confidence factors for the characterization of concrete strength in existing structures

A probabilistic framework is defined to evaluate the values of the Confidence Factors (CFs) proposed in Eurocode 8 Part 3 (EC8-3) for the characterization of material properties. This evaluation is presented for the concrete compressive strength but its validity for other material properties can also be inferred from the results obtained. The number of material tests and the existence of prior knowledge are the essential aspects for the CF quantification. The probabilistic framework proposed in the first part of the study does not consider the existence of prior knowledge and is based on the concept of confidence intervals. In the second part of the study, the effects of prior knowledge are considered using a Bayesian framework. The combination of testing data obtained from different types of tests is also addressed as an extension of the referred Bayesian approach. Results indicate that the EC8-3 proposed CFs for KL1 and KL2 are adequate, but for KL3 it is suggested that a larger value should be used.

Assessment of the Statistical Distributions of Structural Demand Under Earthquake Loading

Many existing probabilistic seismic safety assessment studies assume that structural demand conditional to a seismic intensity follows a lognormal distribution. Based on the analysis of five reinforced concrete structures subjected to real earthquake records scaled to several intensities, an in-depth analysis of this assumption is performed using adequate statistical methods. The considered demand parameters are the chord rotation, curvature, shear force, and inter-story drift. The results found indicate that the lognormal distribution is suitable for the probabilistic modeling of the considered demand parameters. In addition, the normal distribution was also found suitable for the shear force demand.

Statistical Characterization of Structural Demand under Earthquake Loading. Part 1: Robust Estimation of the Central Value of the Data

This article is the first of two companion articles addressing the statistical characterization of seismic demand. Performance-based earthquake engineering methodologies often require the characterization of central value estimates of structural demand. Since outliers can occur in the data, central value estimates should be determined by robust estimation methods. The performance of 50 robust central value estimators is evaluated, for different sample sizes, using the chord rotation, curvature, shear force, and inter-story drift demands obtained after analyzing five reinforced concrete structures under real earthquake records scaled to several intensities. Based on the results, seven estimators are proposed for different sample sizes.

Statistical Characterization of Structural Demand under Earthquake Loading. Part 2: Robust Estimation of the Dispersion of the Data

Performance-based earthquake engineering methodologies often require a probabilistic model of structural demand. Since observations masking the probability distribution of the majority of the data are frequently found, robust estimation methods are proposed to estimate the probabilistic model parameters (i.e., central value and dispersion). The performance of thirty-three robust dispersion estimators is evaluated, for different sample sizes, using the chord rotation, curvature, shear force, and inter-story drift demands obtained after analyzing five reinforced concrete structures under real earthquake records scaled to several intensities. Based on the results, combinations involving dispersion and central value (defined in a companion article) estimators are proposed.

Probabilistic Performance Analysis of Existing Buildings under Earthquake Loading

A probabilistic methodology is proposed for the seismic performance analysis of existing buildings using global metrics to determine if the behavior conforms to a given limit state. The referred performance metrics are the mean annual frequency of the limit state, the corresponding expected loss associated to the repair of the building, and the corresponding number and type of mechanisms that occur. The consideration of these assessment parameters to control building performance widens the scope of the limit state definitions proposed in current codes. Therefore, current limit state descriptions were updated to establish adequate risk- and cost-related limit state definitions using the Eurocode 8 Part 3 proposals as a basis for discussion. The description of the proposed procedure is detailed and addresses its applicability for different limit states and its ability to include the uncertainty in the limit state capacities. An application involving the performance analysis of a reinforced concrete structure for several limit states is also presented and discussed.

Manipulating the alpha level cannot cure significance testing

We argue that making accept/reject decisions on scientific hypotheses, including a recent call for changing the canonical alpha level from p = 0.05 to p = 0.005, is deleterious for the finding of new discoveries and the progress of science. Given that blanket and variable alpha levels both are problematic, it is sensible to dispense with significance testing altogether. There are alternatives that address study design and sample size much more directly than significance testing does; but none of the statistical tools should be taken as the new magic method giving clear-cut mechanical answers. Inference should not be based on single studies at all, but on cumulative evidence from multiple independent studies. When evaluating the strength of the evidence, we should consider, for example, auxiliary assumptions, the strength of the experimental design, and implications for applications. To boil all this down to a binary decision based on a p-value threshold of 0.05, 0.01, 0.005, or anything else, is not acceptable.

Critical orientation of earthquake loading for building performance assessment using lateral force analysis

The orientation of the seismic action is known to have a non-negligible effect on the seismic behaviour of buildings. However, modern earthquake-related standards only partially cover the effect of this factor and results of practical utility on this topic are still limited. To address this issue, a methodology enabling the determination of the critical angle of seismic incidence in the context of Lateral Force Analysis is proposed. The analytical methodology determines the critical angle of seismic incidence for the storey displacements and the interstorey drifts of buildings that conform with standard-based provisions for linear static analysis. The applicability of the methodology is illustrated for three buildings comprising different typologies in plan and in elevation. The accuracy of the analytical results obtained is validated by performing a parametric lateral force analysis of the buildings for different orientations of the bidirectional seismic action.

Robust Calibration of Macro-Models for the In-Plane Behavior of Masonry Infilled RC Frames

Masonry-infilled reinforced concrete (RC) frames are a widely adopted building system. Although usually disregarded in design, masonry infills are known to affect the behavior of structures under e...

A framework to assess quality and uncertainty in disaster loss data

There is a growing interest in the systematic and consistent collection of disaster loss data for different applications. Therefore, the collected data must follow a set of technical requirements to guarantee its usefulness. One of those requirements is the availability of a measure of the uncertainty in the collected data to express its quality for a given purpose. Many of the existing disaster loss databases do not provide such uncertainty/quality measures due to the lack of a simple and consistent approach to express uncertainty. After reviewing existing literature on the subject, a framework to express the uncertainty in disaster loss data is proposed. This framework builds on an existing uncertainty classification that was updated and combined with an existing method for data characterization. The proposed approach is able to establish a global score that reflects the overall uncertainty in a certain loss indicator and provides a measure of its quality.