Periodic Reporting for period 1 - CoDe-S (Codes for Design of Sustainable Structures)
Período documentado: 2021-04-01 hasta 2023-03-31
The international research community is in demand to find solutions that provide the foundation for our sustainable development. Here, the built environment is of obvious importance as it not only facilitates societal activity but also has a major share on the worldwide turnover of economic and environmental resources. To date the built environment is developed and maintained by broadly following structural design standards, which did evolve continuously over time and contain safety concepts that support daily structural engineering decision making based on simple calculus. The major objective that has been followed in their development, was the provision of sufficient safety, and the observed relative low failure rates do proof success in this regard. However, as conceived, structural design codes, and in particular the underlying structural safety concepts and rules, do not allow for the optimal allocation of the limited economic and environmental resources into the structural performance.
The project CoDe-S has investigated potential improvements of this situation. Risk- and reliability based methodologies have been deployed and their overall saving potential with respect to the status quo – i.e. a conventional design based on the semi-probabilistic safety format set out in the Eurocodes - quantified. The project has demonstrated the economic and environmental benefits of using such approaches as a basis for the calibration of the standardized decision rules. In addition, efforts have been dedicated to material flow analysis within the framework of an intradisciplinary research between structural engineering and industrial ecology, with the aim to assess the environmental benefits (material savings and reduction of GHG emissions) of code calibration in a societal context.
The project CoDe-S has investigated potential improvements of this situation. Risk- and reliability based methodologies have been deployed and their overall saving potential with respect to the status quo – i.e. a conventional design based on the semi-probabilistic safety format set out in the Eurocodes - quantified. The project has demonstrated the economic and environmental benefits of using such approaches as a basis for the calibration of the standardized decision rules. In addition, efforts have been dedicated to material flow analysis within the framework of an intradisciplinary research between structural engineering and industrial ecology, with the aim to assess the environmental benefits (material savings and reduction of GHG emissions) of code calibration in a societal context.
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(se abrirá en una nueva ventana)). 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(se abrirá en una nueva ventana)). 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).
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(se abrirá en una nueva ventana)). 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(se abrirá en una nueva ventana)). 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).
The conducted research implies several advancements beyond the state of the art:
- The establishment of a objective function for risk-based design and calibration grounded on environmental objectives, such as the reduction of material consumption and GHG emissions.
- The quantification of the economic and environmental impact of suboptimal design decisions based on the current partial factor rules in the Eurocodes.
- The reliability-based calibration of a consistent set of load PF for the Eurocodes, which leads to more efficient design decisions in terms of a better trade-off between the structural reliability level and the resources invested.
- The risk-based calibration of load PF illustrated for different practical case-studies and the quantification of the corresponding benefits.
- The development of a scientific, versatile tool for consistent risk- or reliability-based code calibration.
- The material flow analysis-based estimation of the environmental benefits of a code calibration on a societal level.
The described developments provide a discussion basis for the design of structure-specific policies in view of a more sustainable development of our built environment. In particular, they constitute valuable input to standardization committees and procedures, where the foundations for improvements of current structural design practices are being established.
- The establishment of a objective function for risk-based design and calibration grounded on environmental objectives, such as the reduction of material consumption and GHG emissions.
- The quantification of the economic and environmental impact of suboptimal design decisions based on the current partial factor rules in the Eurocodes.
- The reliability-based calibration of a consistent set of load PF for the Eurocodes, which leads to more efficient design decisions in terms of a better trade-off between the structural reliability level and the resources invested.
- The risk-based calibration of load PF illustrated for different practical case-studies and the quantification of the corresponding benefits.
- The development of a scientific, versatile tool for consistent risk- or reliability-based code calibration.
- The material flow analysis-based estimation of the environmental benefits of a code calibration on a societal level.
The described developments provide a discussion basis for the design of structure-specific policies in view of a more sustainable development of our built environment. In particular, they constitute valuable input to standardization committees and procedures, where the foundations for improvements of current structural design practices are being established.