Chapter 16 Effects of Seismic Retrofit on the Dynamic Properties of a 4-Storey Parking Garage Ilaria Capraro and Carlos E. Ventura Abstract This paper presents the results of an Ambient Vibration Test (AVT) conducted in March 2015 on the Health Sciences Parkade at the University of British Columbia in Vancouver, Canada. A similar test was conducted in March 2014 before the Parkade was subjected to different interventions for seismic retrofit purpose between July and October 2014. Natural frequencies, modal damping and mode shapes were identified with the Frequency Domain Decomposition (FDD), the Enhanced Frequency Domain Decomposition (EFDD) and the Stochastic Subspace Identification (SSI) techniques. Results showed good agreement between the different methods and confirmed the ones obtained from the 2014 data analysis. Six modes were identified up to a frequency of 8.4 Hz, showing a slight increase of the frequency values with respect to the 2014 results, with a maximum of about 10% for the fundamental mode. In addition to the previous test, it was also possible to identify the site period, which corresponded to a frequency of 0.64 Hz. The effects of the retrofit on the values of natural frequencies are further discussed in the paper. Keywords Ambient vibration test • Modal analysis • Seismic retrofit • Operational conditions • Site period 16.1 Introduction This paper presents the results of an Ambient Vibration Test on the Health Science Parkade at the University of British Columbia in Vancouver, Canada. The test was conducted during the spring 2015 after the Parkade was subjected to significant interventions for seismic upgrade. The purpose of the test was to compare the results and to understand how and in what extent such interventions affected the natural properties of the structure. The Health Sciences Parkade can be considered as a combination of two 4-storey reinforced concrete buildings which are interconnected by sets of three ramps each level. The principal lateral force resisting systems is composed by internal shear walls which work jointly with a reinforced concrete moment frame. The north building has also a basement to which is allocated extra parking space. At basement level, external shear walls and additional internal walls are present, providing additional stiffness to the structure at that level. A picture of the Health Science Parkade is given in Fig. 16.1. 16.2 Seismic Upgrade The Health Sciences Parkade was built in 1979. After the first Ambient Vibration Test, the Parkade was subjected to different structural interventions during the summer of 2015. These interventions aimed to improve the structural performance of the Parkade to seismic loads. The works of seismic upgrade affected several locations of the Parkade, which was kept operational during the interventions. The principal shear walls have been reinforced at each end with additional reinforced concrete columns and the application of fibre reinforced polymer (FRP) composites. Some details of these interventions are shown in Figs. 16.2 and 16.3. Moreover, new foundation at the ground floor have been constructed with the installation of anchor bolts and mini-piles. Similar technique involving FRP composites was applied to strengthen some of the slabs at the upper floors. The external perimeter of the basement has been walled up with a new reinforced concrete shear wall on I. Capraro ( ) • C.E. Ventura Department of Civil Engineering, The University of British Columbia, 6250 Applied Science Lane, Vancouver, BC, V6T 1Z4, Canada e-mail: icapraro@civil.ubc.ca © The Society for Experimental Mechanics, Inc. 2017 J. Caicedo, S. Pakzad (eds.), Dynamics of Civil Structures, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-54777-0_16 121
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