Retrofit Decision-Making considering Seismic Benefits and Environmental Impacts
In recent years, there has been a large drive towards a more resilient and environmentally friendly built environment. This is evident within the Italian context through recent government initiatives offering tax deductions of up to 110% of the costs for those who upgrade the seismic and environmental classifications of their buildings. With many different facets to consider in the construction process, designers, clients and decision-makers often face different trade-offs in the solutions they choose to implement to obtain the desired outcome. Different lines of research are being developed at the ROSE Centre in this regard.
First is the development and extension of methodologies to consider multiple criteria which can quantitatively indicate which retrofitting strategy best addresses the stated needs for a particular scenario. This intends to leave decision-makers with a solution that can, for example, be financially competitive, architecturally appealing, quick to implement and have a minimal environmental impact. These are studied within the context of seismic retrofit of existing buildings where various structural systems are examined and tested for different criteria. Data needed to allow such frameworks to function are being collected and aggregated with existing studies to ensure that these methodologies sufficiently match the Italian construction context. In tandem with these developments from a structural engineering perspective, the environmental impact of these approaches is also being evaluated. Appropriate treatment of environmental aspects using state of the art methodologies is being adapted via data collection, analysis and case study applications to show how it may be used and integrated within multi-criteria decision-making methods.
In terms of seismic performance, non-structural elements play a crucial role in the accumulation of economic losses, expected interruption and potential fatalities in structures. Further studies to better characterise the behaviour of non-structural elements are crucial to understanding how their impacts on performance may be mitigated. Also, methods with which to adequately estimate the expected demands on these non-structural elements in various structural contexts are needed.
Several lines of research at the ROSE Centre focus on addressing these issues. Ongoing research is focused on developing standardised methodologies to quantify performance factors, classify their risk and also developing fragility curves to estimate the probability of different damage states. Design methods to appropriately size protective systems for these elements are being studied for various typologies also. Methods to estimate the seismic demands on these elements via floor response spectra are being developed for a variety of structural systems, with care taken to ensure that consistent methodologies predicting the displacement and acceleration demands on the non-structural elements can be formulated. Finally, a comprehensive database for non-structural elements comprising experimental, numerical and field observations is currently being developed.
See more: https://sites.google.com/iusspavia.it/nonstructural/
Seismic Design, Assessment and Risk Classification Methodologies
When the level of damage, economic loss, fatality and overall disruption caused by seismic events over past years is considered, it is clear that the seismic resilience of existing and future buildings needs to be improved. This comes through the development of methodologies and guidelines that are both feasible to implement but also in line with what society expects in terms of performance during earthquakes. These aspects are being comprehensively considered at the ROSE Centre with the overall aim of providing methodologies that can address the needs and expectations of society.
In particular, novel design approaches for structures are being developed and tested that can effectively ensure that: 1) expected levels of collapse risk safety are met, and 2) defined thresholds of expected monetary losses are not exceeded, which are both fundamental requirements that current buildings codes do not effectively address.
Furthermore, the seismic assessment of existing structures, utilising refined and appropriately calibrated numerical models, is being examined in detail on both an individual building and regional scale to provide decision-makers with improved tools to mitigate the devastating impacts of future earthquakes. Among these developments is the recent proposal of a methodology to ensure proper conversion of internationally available economic loss data to the European context to give more accurate loss predictions. These approaches are intended to be in line with recent guidelines aiming to quantify and classify seismic risk via the so-called Sismabonus scheme introduced by the Italian government, where further refinements and extensions are envisioned through this ongoing research.
Revision of Seismic Input
When examining the definition of seismic input in building codes for the design and assessment of infrastructures, many of the assumptions made during their conception several decades ago have been recently reviewed and critiqued. This relates to a fundamental rethinking of the pertinent features of such seismic input and the factors affecting their formulation when brought to a design and assessment context within building codes.
As such, a redefinition of seismic spectra is being carried out at the ROSE Centre. It studies the impact of local soil amplification effects in a general overhaul of existing practices shown to be obsolete when considering the empirical evidence accumulated over the years. Numerical analysis is being utilised out to complement and verify the empirical results observed with the ever-increasing database of recordings and observations from past events. These ongoing developments aim to bring about changes in the parameters and approaches used for the definition of the seismic input in seismic building standards.
Probabilistic Models for Seismic Risk
While the development of tools for designing and assessing both new and existing structures plays a key role in mitigating seismic risk, so too do the underlying methodologies and approaches used to quantify performance. These methods aim to describe seismic performance, during both single and multiple earthquake events, in a manner that minimises uncertainty, mitigates bias and leads to accurate probabilistic descriptions of the risks faced.
One area of research currently under development at the ROSE Centre is the development of ground-motion models for the inelastic displacement of structures. Furthermore, the effects of ground motion duration and potential bias introduced by existing methods currently adopted are under examination. Some of the outputs of this research are more accurate fragility models and the development of state-dependent fragility functions for structures accounting for foreshock and aftershocks. These account for the existing damage induced in a structure and lead to more accurate predictions of damage due to further shaking. This general research thrust aims to foster more accurate risk quantification and provide a basis with which to refine existing risk models. These, for example, can be used within risk management and reinsurance industries when assessing regional portfolios of structures and infrastructures.
Bridge infrastructures and their interconnectivity play a key role in society. The performance of bridges to seismic action in addition to their increased vulnerability due to ageing and deterioration are of paramount importance. Italy, in particular, has seen numerous cases of bridges being rendered unsafe due to extensive damage or having collapsed completely, causing the loss of life and the interruption of key infrastructure network nodes. Numerous efforts are being made at the ROSE Centre along this line of research. In particular, detailed numerical analysis and forensic investigation is being conducted to investigate potential causes behind recent bridge collapses observed across the country. Simplified methodologies are being examined to aid in the decision-making process that leads to bridges being deemed unsafe in post-earthquake recovery, or in the shrewd allocation of limited resources to improve overall bridge network resilience. Several aspects to complement this broad scope are being addressed, with tools to simply analyse such structures being developed. These incorporate actual data representative of the Italian context for the estimation of repair costs due to damage in addition to the potential indirect losses due to network disruption. Advanced and simplified methods are being explored for the development of fragility functions that more accurately describe the damage. Methods to retrofit and improve their performance, both individually and globally, are currently under development also.