Ambient Vibration Tests and Modal Response Analysis of Guayaquil Metropolitan Cathedral in Guayaquil, Ecuador

Abstract

This paper describes a series of ambient vibration tests and modal analysis conducted on Guayaquil Metropolitan Cathedral, located in Guayaquil, Ecuador. The Guayaquil Cathedral is composed of the reinforced concrete frames and masonry infills, constructed in mid 1920s. Modal response analysis was performed to identify the dynamic properties of the structure, including predominant natural frequencies and the corresponding mode shapes to support seismic assessment and upgrading of the Cathedral. The testing program consisted of several setups on different locations of the structure including the roof of the main building, towers, and the dome. Two series of sensors were used to carry out the vibration measurements: (1) Tromino® velocity/acceleration wireless sensors; and (2) Polytec® Laser Vibrometers. The sensors were placed on predetermined locations according to the test plan; The wireless sensors were located on top of the roof, along the height of the towers, and top of the dome whereas the Laser Vibrometers were reflected to the Diaphragms to study the flexibility and also to determine the modal frequencies of the Diaphragms. The computer program ARTeMIS version 4, was used to perform the system identification of the structure. The software allows to develop a 3D model of the structure and test points; the resulting mode shapes are displayed using this geometry. Two different techniques were used for modal identification: the Enhanced Frequency Domain Decomposition (EFDD) and the Stochastic Subspace Identification (SSI). These two modal identification techniques were used to cross-validate the results. The joint analysis of the signals measured in various strategic points of the structure made it possible to identify the modal configurations and the corresponding natural frequencies. As the results of this study, the vibration modes of the main building, towers and dome in translational and torsional directions, as well as the motions of the diaphragms were discussed. Also, the natural frequencies and corresponding dynamic mode shapes were presented.