Dynamic Response of Existing Steel Frames With Masonry Infills Under Multiple Earthquakes

Abstract

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 nonseismically 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 HITFRAMES. 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.

Preliminary Numerical Analysis of the Seismic Response of Steel Frames With Masonry Infills Retrofitted by Buckling Restrained Braces

“…For this purpose, the elastic and modal properties of the bare frame OpenSees model are validated by comparing the results of the lab characterisation tests (i.e., material testing, snapback test) [13] with the numerical model. The validated numerical model of the bare frame is then subjected to the storey displacement history observed during the PsD testing in a displacement-controlled manner, with the resulting storey shear values (Vn) recorded.…”

“…This damage is consistent with damage reported in previous earthquakes (e.g., [4][5][6]). Although masonry infills can significantly contribute to the overall strength and stiffness of a steel MRF [7][8][9], their structural properties easily degrade with strong or long ground motions (GMs), as well as with cumulative demands, such as foreshock-mainshock-aftershock sequences, as in the case of the 2016 Central Italy Earthquake [10][11][12][13].…”

A simplified homogeneous approach for non-linear analysis of masonry infill panels under in-plane loads

“…While these models accurately predicted the response of masonry infills [ 16 ], they were originally developed based on the behavior of RC frames. Therefore, their reliability when applied to steel frames cannot be assured due to the greater flexibility of steel frames and the intricate detailing at connections, which may impact the interactions between the infill walls and the steel frame [ 17 ]. The need for a comprehensive method to consider both steel and RC frames and predict the nonlinear behavior and failure mechanism of solid and perforated masonry infill panels is evident.…”

“…Interestingly, this approach still incorporates contact surfaces at the interface between the masonry panel and the surrounding structure [ 28 ]. Sarno et al [ 17 ] discuss the numerical modeling of masonry infill walls in existing steel frames. They mentioned the use of macro-modeling approaches that consider the masonry infill as a homogeneous isotropic material.…”