A framework for the calibration of the decision rules applied in everyday structural engineering design practice has been defined. A generic function which adecuately represents the structural limit states to be accounted for, and which is consistent with the semi-probabilistic partial factor method (PFM) set out in the Eurocodes, was formulated. The framework distinguishes between a reliability and risk-based calibration of partial factors (PF). The latter accounts for both economic and environmental objectives (material use and embodied GHG emissions). Societal preferences for investments into human safety are considered based on the marginal life saving cost principle.
The objective function represents a portfolio of design situations, that is complex enough to test flexibility and generality, but sufficiently simple to perform test runs in feasible time horizons. For the reliability based approach, such a portfolio consists of altogether 810 design situations. For the risk-based approach a reduced portfolio has been adopted, consisting of a representative set of structural floor systems involving different construction materials and loading conditions. The adopted probabilistic modelling assumptions are supported by the CEN/TC 250/SC 10 Ad-Hoc Group on the Reliability Background in the Eurocodes (AHG).
The defined framework has been implemented in a tool based on the scientific programming language Python (
https://www.co-de-s.com(s’ouvre dans une nouvelle fenêtre)). The tool enables a calibration of the load PF based on user-specific choice of the type of objective function, the corresponding target, the design situations and a specification of the PF that are object of the calibration.
The developed tool has been used to perform a consistent reliability-based calibration of the load PF for design of structural members in building structures. The results show that the variability of the reliability index can be substantially reduced when the degree of complexity of the safety format is slightly enhanced with respect to the current formulation by considering different PF for variable loads. Thereby, the percentage of design situations, which do not comply with the Eurocode reliability requirement is significantly reduced, and so is the number of situations where this requirement is largely exceeded. In general, the environmental saving potential of the calibration depends largely on the ratio between variable and total loads. Case studies involving different structural floor systems point to average material and GHG emission savings of the order of 5% with respect to the current status quo. The case studies also show that the reliability-based calibrated solution is still at a considerable distance (approximately 10-25%) from the optimum obtained in explicit risk-based design. A risk-based calibration of load PF can reduce this distance to less than 10%, depending on the objective (economic or environmental) and on the variety of design situations covered by the the calibration procedure.
In order to estimate the impact of a code-calibration on a societal level, the near future stocks and flows of structural materials and their associated emissions embodied in residential buildings in Germany have been evaluated. The study includes a scenario analysis under combination of different emission mitigation measures, among them a general downsizing of structural material quantities, which simulates the benefit of the structural design code calibration. The results show that such measures could contribute with about 4% to 8% to the German average target mitigation rate required for achieving emission neutrality in 2045. Future efforts could extend the system boundaries to non-residential buildings and public infrastructure as well as to other countries.
The project results have been disseminated in journal publications and international conferences (
https://www.co-de-s.com(s’ouvre dans une nouvelle fenêtre)). In addition, they have been presented to professional working groups of standardization bodies (CEN) and renowned engineering associations (fib, JCSS). Moreover, communication to broader audiences took place at different workshops, e.g. at the Joint Committee on the GLOBE Consensus, or at the Centre for Green Shift in the Built Environment (GREEN 50, NTNU).
