The MODERATE project studies the hot topic of Performance-Based Multi-Hazard Design (PB-MH-D) of structures, with specific focus on the steel frame structural typology.
First: an advanced and comprehensive procedure for the PB-MH-D of steel frames will be developed by taking into account three kind of hazards: earthquake, wind and blast. This is necessary to develop exhaustive applications to consider two specific issues related to the PB-MH-D: i) the consideration of hazard-chain scenarios (e.g. blast following earthquakes) and; ii) the consideration of concurrent independent hazards determining conflicting design strategies (wind- VS earthquake-driven design).
Second: a number of case studies will be developed (frames of different heights).
Third: an optimal risk-targeted design procedure will be devised for a MH design context.
Structural performances related to Ultimate Limit States, Serviceability Limit States and Structural Robustness against Progressive Collapse will be considered in the devised design procedure.
The results of the MODERATE project will cover the literature gap regarding the two i) and ii) above-mentioned issues for steel frames used as structural system in mid- to high- rise buildings and will provide structural design/optimization guidelines in a true multi-hazard view.
Due to the complexity and the broadness of the topic, the initial research unit will be composed by five members in total (two full professors, one associate, one assistant plus one PhD), such a research team is strategically assembled to cover the main needed expertise: wind- earthquake- and blast- engineering, structural robustness assessment, reliability analysis, non-linear numerical modeling, structural optimization techniques. The request of an additional post-doctoral employment is strategic for the development of the large number of numerical models that will be necessary to take into account the different multi-hazard interactions listed above.
1. Innovatività della ricerca
The MODERATE research innovation concerns the definition of a general framework for the coherent performance-based design of structures in MH context (PB-MH-D) considering both natural (wind and earthquake) and man-made hazards (blast) and taking into account three different limit states for structural performances evaluation: ULS, SLS and Robustness LS.
This is a masterpiece that is still missed in the literature and that currently prevents the reaching of true optimal design solution in the real environment. What we usually call "global optimal design" should be better defined as a "local optimal" solution (which is optimal for a single hazard but is not optimal, globally, for the complex MH environment in which our structure is built). The adoption of single-hazard optimal design strategies also limits our decisional space as designers by not allowing the consideration of the solutions that comes from the "optimal compromise" between performances reached under actions of different nature.
The MODERATE project will provide a valuable contribution in covering this literature gap.
Innovative products of the MODERATE project will be in detail:
- definition of an original SAC-FEMA style procedure for the performance-based wind engineering (PBWE)
- definition of a novel risk-targeted design optimization procedure for steel frames under the simultaneous actions of wind and earthquake
- definition of innovative numerical analysis procedures for the structural robustness assessment of steel frames under the chained action of earthquake and blast
2. Potenzialità di realizzare un avanzamento delle conoscenze rispetto allo stato dell'arte
Specific advancements of knowledge with respect to the state of the art will be provided about two specific MH effects of the structural design configuration:
- conflicting effects of concurrent independent hazards for ULSs and SLSs
- effects of the Hazard Chain interactions on the design configurations for the robustness LS
By focusing on the above effects, newly insights regarding the best design compromises for steel frame buildings considering some aspects that are currently ignored in the state of art design procedures for this kind of structures. Wind and Earthquake for example, drive the design in opposite directions regarding the global stiffness of mid-rise steel frames (15 to 30 floors): the stiffer is the building, the less it is sensitive to winds and the more is sensitive to earthquakes. In this view, the MH optimal design algorithm that will be defined in MODERATE, will allow for the ¿global¿ structural design optimum, representing the best compromise between these opposite design indications. On the other side, current robustness analysis procedures aim to identify the location in the frame which is critical for the global structural progressive collapse under a certain local damage (e.g. column removal due to the blast destruction). What the Designer identifies as the critical damage location is expected to change if hazard-chain scenarios are considered.
Potential long-run effects of the findings of the MODERATE project will regard the state of practice in structural design: the change of viewpoint from single- to multi-hazard design will impact on all the current conventionally reached risk levels for single hazard. In this sense, it is expected that Standards will be re-written in a multi-hazard view, with appropriate re-calibration of current partial safety factor, design occurrences for hazard intensity and load cases to be considered in the design.