Modelling of the Uplift of Buildings to Install Base Isolation Systems

The present paper assesses the uplift of existing buildings where base isolation systems are installed as a retrofitting measure. Two reinforced concrete (RC) foundation mats are generally created at the base of the existing structure to uplift the sample building, either in RC or masonry. Hydraulic jacks are located close to the columns in the RC buildings and along the bearing walls in masonry structures. Such jacks are controlled automatically through an ad-hoc algorithm aimed at minimising the overstress of the superstructure and preventing significant differential settlements. The overstress and differential settlements are limited by uplifting, with an iterative procedure, the RC foundation mat that is rigidly connected to the superstructure. Modelling of the uplift of the foundation mat and the superstructure is a challenging task. Two case studies are investigated in the present work: a typical RC multi-storey residential framed building and a traditional masonry structure. Refined yet versatile finite element (FE) models of the sample structures have been implemented and are used to determine the stress/strain distributions within the superstructure. The FE models were calibrated on the basis of in-situ measurements for both RC and masonry structures. The calibrated numerical models were then utilized to perform parametric analyses. Extreme working conditions for the hydraulic jacks are considered; the effects of the worst displacement scenarios for the jacks during uplift is also presented for masonry buildings. This paper illustrates, with a companion paper, the preliminary results of a comprehensive ongoing research activity within the framework an European funded three-year project aimed at optimizing the uplifting technology and its modelling