# Base Isolation Compared to Capacity Design for Long Corner Periods and Pulse-Type Seismic Records
###### Abstract  
Southern Romania is a geographic region with alluvial deposits. This soil type leads to rather long corner periods and provides as a particularity of the response spectrum an enlarged plateau. These conditions produce large displacement demands. Moreover, pulse-type ground acceleration records make this seismic area more unique. Research on the seismic behaviour of structures built under such unusual conditions is limited and Romanian engineers are not confident to apply alternative solutions such as base isolation. Although capacity design is still the regular design method applied in Romania, modern base isolation solutions may overcome the large displacement demand expectation produced by seismic events and fulfil immediate occupancy requirements. This study presents the seismic performance of an existing hospital from Bucharest, for which two seismic design solutions were applied: (i) classical approach based on capacity design and (ii) base isolation. Both approaches are compared in terms of drift, acceleration and base shear values. Static as well as non-linear dynamic analysis methods were applied.  
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Footnote †: journal: Medical Sciences  
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of near-fault ground motions to the seismic response of the ground [4, 5]. The authors have chosen an existing hospital building in Bucharest (corner period Tc = 1.6 s, of irregular plan and elevation, for which construction drawings were available (see Section 2). Advantages and the structural impact of base isolation are outlined.  
Base isolation of buildings is considered worldwide a suitable alternative to the classical design approach based on the capacity method [6, 7, 8]. Due to decoupling of the super-structure from the foundation ground, the earthquake input for the isolated building was reduced dramatically. In this way not only structural elements, but especially the building content (non-structural elements, equipment, furniture) are protected from damage. Currently, an increasing number of people choose base isolation for the seismic protection of their homes. For example, in 2017 in Japan, approximately 4300 commercial and multi-family residential buildings, and more than 5600 single family homes were provided with base isolation systems [7].  
Hospital buildings especially, should remain operational after important seismic events, in order to shelter and help injured people [9]. Immediate occupancy requirements can be fulfilled through an elastic seismic response. Two possible seismic design solutions are compared: (1) a stiffening approach--expecting high response acceleration and damage [10, 11, 12, 13] and (2) base isolation [14, 15, 16].  
Despite the advantages that base isolation offers (reduced damage expectation, functionality after important seismic events), its efficiency is still questionable in high corner period regions, which request high displacement demands [1, 17]. Therefore, the authors conducted a study on an existing hospital building from Bucharest, the capital city of Romania (which is a high corner period region, Tc = 1.6 s [18, 19, 20, 21, 22].  
Two design approaches, a classical stiffening solution and a base isolation design were analytically compared. Modal analysis (for design) and static as well as non-linear dynamic analysis (for checking the structural behaviour) were performed [23, 24, 25]. Ambient vibration measurements helped estimating the building's modal periods [26]. Further experimental investigations, for example for the validation of analytical results, were not possible, especially due to the large dimensions of the analysed structure.  
Due to their special characteristics (reduced sliding path due to double curvature and enlarged damping by properties of sliding surface) Curved Surface Sliders were chosen for the base isolation solution [9, 27, 28]. Other slider types (like High Damping Rubber Bearings or Lead-Plug Rubber Bearings) were not investigated due especially to their larger sizes, which significantly increases the cost of the base isolation solution.