Simon Petrovčič

Effects of Horizontal and Vertical Mass-Asymmetric Distributions on the Seismic Response of a High-Rack Steel Structure

The paper examines the seismic response of an existing externally braced steel frame high-rack structure and analyses the effects of mass eccentricities that can be realistically achieved by asymmetric positioning of the stored payload. Apart from the symmetric, three different extreme payload distributions with varying occupancy levels have been considered, with the payload mass concentrated: (i) at the topmost part of the structure, (ii) at the upper corner of the structure and (iii) at the outermost edge of the structure. The seismic performance has been analysed by using unidirectional non-linear dynamic analyses as well as by non-linear static analyses, with the structures response observed in the cross-aisle direction in which it is possible to account for the effects of torsional twist. The results showed that most unfavourable payload eccentricities might increase the seismic risk leading to local instability of the rack columns. From a seismic point of view, a fully occupied structure does not present the most critical condition. It is obtained at an intermediate occupancy level, which allows more space to produce horizontal and/or vertical eccentricities. Very small occupancy levels in turn produce smaller induced seismic forces and might therefore not be of critical concern. The paper concludes that the payload distribution concentrated symmetrically at the topmost part is the most critical for the central part of the rack structure and that concentrating the payload eccentrically at the outermost edge is the most critical for the flexible side of the structure, while shifting the payload to one of the upper corners is generally not of critical concern.

Seismic Rehabilitation of Masonry Heritage Structures with Base-Isolation and FRP Laminates – A Case Study Comparison

The cultural and historical significance of architectural heritage buildings demands intrinsic considerations regarding appropriate conservation measures that need to be undertaken in order to restore or maintain their historical values. In this paper two contemporary seismic strengthening measures with varying degrees of invasiveness and strengthening efficiency are employed in a case study numerical simulation on a typical neo-renaissance masonry heritage building. The use of fibre reinforced polymer composites and the implementation of base-isolation was considered in the study in order to achieve the desired, code-based seismic protection levels. Non-linear static analyses with incremental increases in levels of seismic intensities were conducted on mathematical models of the fixed-base, FRP-strengthened and base-isolated variants of the structure. The comparison of results based on static pushover analyses for various ranges of seismic intensity was presented, while each strengthening measure was assessed in terms of its efficiency.

Seismic Retrofitting of Historic Masonry Structures with the Use of Base Isolation—Modeling and Analysis Aspects

ABSTRACT The seismic retrofitting measures which are appropriate for buildings belonging to the architectural heritage are limited, since the extent to which such buildings are allowed to be altered is severely limited. In the paper the possibilities which exist for the implementation of base isolation in the case of the seismic upgrade of unreinforced masonry (URM) structures belonging to the valuable architectural heritage have been investigated. A new methodology for the modeling of URM buildings, based on an equivalent frame model with plastic hinges, was used for this purpose. A case study involving a typical neo‐renaissance masonry building is presented, in which base isolation is implemented, and a comparison is made with the response of the building in its original state. A refined approach for the selection of proper isolation devices is proposed which is based on the nonlinear static (pushover) analysis of such buildings and on the desired level of seismic protection, with reference to the code-based damage limit states. Additionally, the incremental nonlinear dynamic analyses were also applied in order to estimate what increases in seismic safety could be achieved if the employed base isolation system was used in the case of different seismic intensities.