Code Calibration of the Eurocodes

This article addresses the process to optimally select safety factors and characteristic values for the Eurocodes. Five amendments to the present codes are proposed: (1) The load factors are fixed, γG = γQ, by making the characteristic load of the variable load changeable, it simplifies the codes and lessens the calculation work. (2) Currently, the characteristic load of the variable load is the same for all variable loads. It creates excess safety and material waste for the variable loads with low variation. This deficiency can be avoided by applying the same amendment as above. (3) Various materials fit with different accuracy in the reliability model. This article explains two options to reduce this difficulty. (4) A method to avoid rounding errors in the safety factors is explained. (5) The current safety factors are usually set by minimizing the reliability indexes regarding the target when the obtained codes include considerable safe and unsafe design cases with the variability ratio (high reliability/low) of about 1.4. The proposed three code models match the target β50 = 3.2 with high accuracy, no unsafe design cases and insignificant safe design cases with the variability ratio 1.07, 1.03 and 1.04.

Seismic reliability of axially loaded vertical piles

The reliability of single vertical pile foundations subjected to seismic loads is assessed and compared with the minimum acceptable reliability level for static load conditions mandated by the Canadian codes. The analysis is executed for a site with a mean shear-wave velocity of the top 30 m of the ground equal to 250 m/s subjected to the ground motion hazard of five Canadian cities. Using both a full probabilistic analysis and simplified probabilistic model, the results seem to indicate that the current design practice is unable to achieve the reliability target of the codes. The shortfall is particularly significant when the limiting pile settlement is relatively small. The calculated reliability level of small limiting settlements is impacted by the geotechnical variability, whereas the seismic hazard variability affects large pile limiting settlements. Finally, the simplified probabilistic model produces the same results as the full probabilistic model for large pile settlement and is a convenient tool to execute code calibration.

Live Load Factors for Military Traffic in Bridge Evaluation

Military vehicles are sometimes required to transit bridges owned and operated by civilian bridge authorities. Using available data regarding the gross vehicle weight and associated axle loads of military traffic, live load factors, calibrated to the Canadian Highway Bridge Design Code, are proposed for bridge design and evaluation. This paper recommends live load factors for three categories military vehicles: (1) Wheeled-Transport vehicles; (2) Wheeled-Fighting vehicles; and (3) Tracked-Fighting vehicles. The values are derived for interior girders of a simply supported slab-on-girder bridges subjected to a single lane of traffic loading and are believed to be generally applicable for other structural elements and bridge types. Inherent differences between fighting vehicles, which are heavily armoured, and transport vehicles, which although armoured have high payloads, suggest that highway bridges should be evaluated separately for military fighting vehicles and military transport vehicles using distinct live load factors. Keywords: Bridge Evaluation, Code Calibration, Military Vehicles.

Calibration of Load and Resistance Factors for the Design of Cable Members in Cable-supported Bridges Using Optimization of Strength

<p>This proceeding presents the calibration process of load and resistance factors for the design of cable members under a gravitational loads-governed limit state adopting optimization scheme. In reliability-based bridge design code, although the cable members show various behavior depending on the structural types of bridges, a proper reliability level should be satisfied by the load and resistance factors. A cable is a nonlinear component, thus tension of it also shows nonlinear characteristics. In this study, the limit state function is linearized, and the tension of each load component is normalized by total nominal tension. With the purpose of performing code calibration independent of structural types of bridges, the normalized tensions are parameterized by three load ratios. The target reliability indices of cable members are determined considering results of reliability analyses of existing cable-supported bridges in South Korea, and a target strength, which satisfies the target reliability indices exactly, is evaluated. Optimization problem to minimize an error between the target strength and nominal strength, which is calculated by the load and resistance factors, is defined, and optimal values of the factors are calibrated. Reliability analyses for the strength calculated from the optimal factors are performed and it is verified that the factors can lead to the design with a uniform reliability level.</p>

The Uranie platform: an open-source software for optimisation, meta-modelling and uncertainty analysis

The high-performance computing resources and the constant improvement of both numerical simulation accuracy and the experimental measurements with which they are confronted bring a new compulsory step to strengthen the credence given to the simulation results: uncertainty quantification. This can have different meanings, according to the requested goals (rank uncertainty sources, reduce them, estimate precisely a critical threshold or an optimal working point), and it could request mathematical methods with greater or lesser complexity. This paper introduces the Uranie platform, an open-source framework developed at the Alternative Energies and Atomic Energy Commission (CEA), in the nuclear energy division, in order to deal with uncertainty propagation, surrogate models, optimisation issues, code calibration, etc. This platform benefits from both its dependencies and from personal developments, to offer an efficient data handling model, a C++ and Python interface, advanced graphi graphical tools, several parallelisation solutions, etc. These methods can then be applied to many kinds of code (considered as black boxes by Uranie) so to many fields of physics as well. In this paper, the example of thermal exchange between a plate-sheet and a fluid is introduced to show how Uranie can be used to perform a large range of analysis.

Impact of Hydrological Modellers’ Decisions and Attitude on the Performance of a Calibrated Conceptual Catchment Model: Results from a ‘Modelling Contest’

In this study, 17 hydrologists with different experience in hydrological modelling applied the same conceptual catchment model (HBV) to a Greek catchment, using identical data and model code. Calibration was performed manually. Subsequently, the modellers were asked for their experience, their calibration strategy, and whether they enjoyed the exercise. The exercise revealed that there is considerable modellers’ uncertainty even among the experienced modellers. It seemed to be equally important whether the modellers followed a good calibration strategy, and whether they enjoyed modelling. The exercise confirmed previous studies about the benefit of model ensembles: Different combinations of the simulation results (median, mean) outperformed the individual model simulations, while filtering the simulations even improved the quality of the model ensembles. Modellers’ experience, decisions, and attitude, therefore, have an impact on the hydrological model application and should be considered as part of hydrological modelling uncertainty.