A Henriques

Probabilistic models for mechanical properties of concrete, reinforcing steel and pre-stressing steel

This paper presents probabilistic models for mechanical properties of pre-cast and cast-on-site concrete as well as of reinforcing and pre-stressing steel. An extended review of models available in the literature is made and new probabilistic models are developed based on a significant amount of data collected by the authors. New probabilistic models are proposed for concrete ultimate strength (separately for precast and cast-in-place concretes), for yield and ultimate strength of reinforcing steel and for proportionality limit and ultimate strength of pre-stressing steel. The new models account for a recent improvement of production and are more appropriate for the probabilistic assessment of modern concrete structures then the models available in the literature.

Safety format for the design of concrete frames

A contribution to the definition of a novel safety format for the design of concrete structures based on non‐linear methods of analysis is the main purpose of this work. A brief discussion of design formats proposed by codes of practice is introduced. Probabilistic analyses of current concrete frames are performed and the corresponding results are used as a basis to derive simplified and coherent practical rules. The analyses have been carried out taking into account the non‐linear material behaviour and the variability of the structural parameters by simulation of probabilistic density functions. A simple procedure is proposed to evaluate the structural safety of concrete frame structures. Mean values are recommended to characterise the material properties to be used in the analysis and a global safety factor is defined to evaluate the structural design resistance.

Reliability analysis of steel connection components based on FEM

Abstract An analytical description of the behaviour of a connection has to cover all sources of deformabilities, local yielding, local instabilities, etc. Due to the multitude of influencing parameters, a macroscopic inspection of a complex connection — by subdividing it into components — has proved to be most appropriate. This is the approach recently proposed by the Eurocode 3. One of the basic components is the equivalent T-stub, which adequately models several parts of a connection: column flange in bending, end plate in bending and flange cleat in bending. Reliability techniques combined with non-linear analysis of structures have been applied to interpret the effects of parameter variability on the T-stub behaviour. Simplified safety rules are derived from this probabilistic high-level approach.

Probabilistic assessment of the train running safety on a short-span high-speed railway bridge

In this work the running safety of high-speed trains on a short-span bridge is assessed. A probabilistic approach that combines Monte Carlo simulation with the extreme value theory is used and the existence of track irregularities is taken into account along with the variability of parameters related to the bridge, the track and the train. As case study, a 12 m span filler beam bridge was selected as the train–bridge interaction effects are most significant for short spans. The running safety is assessed for the case of loss of contact between the wheel and the rail, taking into consideration only the vertical wheel–rail interaction and assuming that no lateral forces act on the train. This research enables the characterisation of the wheel unloading coefficient, the identification of the critical wheel and also the definition of the maximum allowable speed for trains to run safely on the bridge.

Probability-Based Assessment of Existing Concrete Bridges ― Stochastic Resistance Models and Applications

This paper presents newly established probabilistic models of ultimate shear and bending resistance of typical reinforced concrete (RC) and prestressed concrete (PC) bridge cross-sections. These new models were developed using advanced analysis methods and the most recent data regarding variability in mechanical properties of material and cross-section geometry. The models also take into account the uncertainty related to the inaccuracy of the analysis method used to evaluate member resistance. In the second part of the paper, some of the developed models are applied to the probability-based assessment of an existing PC highway bridge that fails the traditional load capacity assessment performed using a standard partial safety factor method. The presented calculations clearly show the benefits of using the probabilistic methods in the assessment of existing bridges and demonstrate how straightforward the reliability analysis can become when the presented models are used.

Assessment of traffic load events and structural effects on road bridges based on strain measurements

AbstractSeveral technical and scientific publications have been made available focussing on Bridge Weight-in-Motion (BWIM) concerning railway bridges. On the contrary, BWIM analysis on road bridges are more scarce and therefore, this work intends to provide a contribution by presenting the BWIM analysis performed on two major road bridges in Portugal – Leziria Bridge and Pinhao Bridge. These bridges are equipped with electric and optical strain gauges, acquisition systems with features that allow high sampling rates. Based on the collected data and focussing on the bridges’ lifetime, a probabilistic approach to quantify extreme traffic loads was implemented using extreme distribution functions. The bridges’ behaviour to these extreme traffic loads is numerically evaluated and a comparison with the alarm levels established by the bridge designers is performed. Although the bridges safety is not compromised, it was concluded that the representativeness of the observation period is a critical issue and the ...

Robustness assessment—A new perspective to achieve a performance indicator

Robustness has been recognized as interesting research topic due to several collapses that have been occurring over last years. Indeed, this subject is related with global failure or collapse. However, its definition is not consensual since several definitions have been proposed in the literature. This short-paper aims to present a framework for assessing bridge’s robustness as a probabilistic performance indicator. In this study, a non-linear model of a clamped beam with two point loads using DIANA software was developed to validate the framework presented. By means of a probabilistic approach, the load carrying capacity and structural safety were evaluated. In this regard, special focus is placed on an adaptive Monte Carlo simulation procedure to achieve a proper meta-model.

SAFETY ASSESSMENT OF A SMALL SPAN HIGH-SPEED RAILWAY BRIDGE USING AN EFFICIENT PROBABILISTIC METHODOLOGY

The behaviour of small span railway bridges is known to be particularly difficult to predict due to the complexity of the coupled train-track-bridge system, as well as for being particularly sensitive to resonant phenomena. The objective of this paper is to present an efficient methodology to evaluate the safety of small span bridges in high-speed railway lines, bearing in mind the real variability of the parameters that influence the dynamic response of the train-track-bridge coupled system. This requires the development of adequate numerical models for the bridge, the track and the train subsystems, as well as the definition of the distributions and variability of all the variables related to the structure, the train, the track and also the wheel-rail contact. Track irregularities are also accounted for in the dynamic analysis. Canelas railway bridge, located in the North of Portugal, was selected as case study. The bridge has six simply supported spans of 12 m each, leading to a total length of 72 m. The deck is a composite structure with two half concrete slab decks with nine embedded rolled steel profiles HEB 500, each supporting one rail track. In order to assess the safety of the bridge two simulation methods were used: the Monte Carlo method and the Latin Hypercube method. Furthermore, both simulation methods are combined with two different approaches to enhance efficiency. One based on the extreme value theory that uses the Generalized Pareto Distribution to model the tail of the distribution. The other uses an approximation procedure based on the evaluation of the failure probabilities at moderate levels to estimate the target probability of failure by extrapolation. The track stability safety due to the deck vibrations level is used as the safety criterion to validate the proposed methodology. The results are extremely promising and indicate the feasibility of this methodology due to the very reasonable computational costs that are required.

Reliability Assessment of Eurocode 7 Spread Foundations Design Methodology

This paper is a contribution for the application of Eurocode 7 design methodology and analysis of related features in geotechnical engineering, such as uncertainty, risk and reliability. The design methodology of Eurocode 7 is applied to a strip foundation resting on a relatively homogeneous c-φ soil, and the different design approaches are compared to deterministic and semi-probabilistic solutions. A reliability assessment is performed for different conditions, particularly selecting different characteristic values and coefficients of variation of soil properties. Several uncorrelated and correlated random variables are considered, and probabilistic solutions are achieved and compared with a target reliability index. For this purpose, reliability techniques such as the first-order reliability method (FORM) and the Monte Carlo simulation (MCS) are applied and compared to other methodologies. Based on the obtained results, the Eurocode 7 design methodology is discussed, and the indispensable engineering judgment is outlined.

Probabilistic Shear and Bending Resistance Models for Assessment of Reinforced and Prestressed Concrete Bridges

Newly established probabilistic models of ultimate shear and bending resistance of a typical reinforced and prestressed concrete bridge section are presented in this paper. The models that are presented in the paper have been developed using recently collected data regarding variability of mechanical properties of concrete, reinforcing and prestressing steel, and also a variability of the section dimensions. The uncertainty of the mathematical models, used for the calculation of the sectional response, has also been taken into account. The proposed models have been developed for use in the load capacity evaluation of existing bridges by means of probabilistic methods. However, they can also be used for the calibration of the partial safety factor in the existing design or assessment codes.