Dynamic response of existing steel frames with masonry infills under multiple earthquakes

Existing steel moment-resisting frames in several seismic regions worldwide are often characterised by high vulnerability to earthquakes due to insufficient local and/or global ductility. Therefore, it is of paramount importance to assess their response under strong motions and provide cost-effective retrofitting remedies. However, the current code-based assessment framework utilized in Europe for assessing existing structures is inadequate and requires improvement, especially to account for the contribution of masonry infills as they significantly influence the seismic response of steel buildings. To this end, the H2020-INFRAIA-SERA project HITFRAMES (i.e., Hybrid Testing of an Existing Steel Frame with Infills under Multiple Earthquakes) aims at experimental evaluation of a case study building representative of non-seismically designed European steel frames. This paper presents the dynamic response analyses of the case study building and serves as a theoretical prediction of the experimental results for HTTFRAMES. The case study building is analysed as a bare, an infilled and a retrofitted frame with buckling restrained braces (BRBs), respectively. It is subjected to the natural seismic sequence recorded during the 2016-2017 Central Italy earthquakes. The modal properties of the case study building are determined first, followed by the investigation of its non-linear dynamic response. The dynamic tests are performed with the earthquake records scaled to different intensity levels to simulate the structural performance under different limit states according to Eurocode 8-Part 3. The impact of masonry infills and BRB-retrofit is also investigated by comparing the response of models with different configurations. It can be concluded that appropriately-designed BRBs are effective in protecting steel frames from experiencing critical damage during earthquakes and reducing significantly the transient and residual drift

Seismic Damage Accumulation of Highway Bridges in Earthquake Prone Regions

Civil infrastructures, such as highway bridges, located in seismically active regions are often subjected to multiple earthquakes, such as multiple main shocks along their service life or main shock-aftershock sequences. Repeated seismic events result in reduced structural capacity and may lead to bridge collapse causing disruption in normal functioning of transportation networks. This study proposes a framework to predict damage accumulation in structures under multiple shock scenarios after developing damage index prediction models and accounting for the probabilistic nature of the hazard. The versatility of the proposed framework is demonstrated on a case study highway bridge located in California for two distinct hazard scenarios: a) multiple main shocks along the service life, and b) multiple aftershock earthquake occurrences following a single main shock. Results reveal that in both cases there is a significant increase in damage index exceedance probabilities due to repeated shocks within the time window of interest

Analysis in seismic provisions for buildings: past, present and future

The analysis of structures is a fundamental part of seismic design and assessment. It began more than a 100 years ago, when static analysis with lateral loads of about 10% of the weight of the structure was adopted in seismic regulations. For a long time seismic loads of this size remained in the majority of seismic codes worldwide. In the course of time, more advanced analysis procedures were implemented, taking into account the dynamics and nonlinear response of structures. In the future methods with explicit probabilistic considerations may be adopted as an option. In this paper, the development of seismic provisions as related to analysis is summarized, the present state is discussed, and possible further developments are envisaged