Site Measurements and Analysis of Three Real Tall Buildings Tested in Laboratory before Construction

Xilin Lu
Professor, State Key Laboratory of Disaster Reduction in Civil Engineering
Tongji University, China

Abstract: In this work, three real tall buildings were instrumented and studied. Model tests of the three buildings were all implemented on shaking table in laboratory before construction. A recently developed fast Bayesian FFT method is utilized to perform analysis. In addition to the most probable values, the associated posterior uncertainty is also obtained, providing an estimation tool to assess the accuracy of the identified modal parameters.

The first structure is the Palms Together Dagoba at Famen Temple, which is a 12-storey steel-reinforced concrete high-rise building. It has an irregular configuration with the first two and the top two floors connected while the remaining floors are separated. The ambient vibration tests were performed one month after the Wenchuan earthquake of 8.0 magnitude struck about 500 km away. In the full-scale field tests and the shaking table tests, five modes had been focused including the first two translational modes along both the X and Y directions and the first torsional mode. The damping ratios were all about several percent, indicating good energy dissipation capability. The second structure is Shanghai World Financial Center, which is a super high-rise building of 492 m and 101-storey with active tuned mass damper installed. Both free and ambient vibration tests were performed. For the first three modes, the identified natural frequencies were at 0.155, 0.158, and 0.486 Hz. The identified results from shaking table tests were consistent with field tests with the maximum difference of 15% occurred at Mode 3. The third one is Shanghai Tower, which is a Mega frame – tube - outrigger structure with a height of 632m. Ambient vibration test was used to collect structural response. Eight modes below 1 Hz were investigated, including three translational modes in X direction, three translational modes in Y direction and two torsional modes, where the damping ratios of almost all the modes were less than 1%.

This study shows again that the vibration test and modal identification could provide the dynamic property of a building in a reliable manner. The comparison between the results of field and shaking table tests could assist to verify the design and accuracy of the shaking table model, which provides a reference for the reliability of the estimation of seismic performance taking use of the same model and shaking table tests. Challenges do exist simultaneously, for instance, the prediction of damping ratios using the shaking table model. It is still a difficulty to find the relationship of damping ratio between the real structure and the one tested in the shaking table test, however, the comparison results are helpful to improve the future design and testing of shaking table model.

Bio: Professor Xilin LU, received his Ph. D. in December 1984, and now works at State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University. He currently has the following academic and professional positions: Chief Editor of “The structural Design of Tall and Special Buildings”; Vice President of Earthquake Resistance and Disaster Reduction Committee, China Architectural Society; Editorial Board Members: Journal of “Soil Dynamics and Earthquake Engineering”, Journal of “Smart Materials and Systems”, Journal of “Earthquake Engineering”; Editorial Board Member, Journal of Asia architecture and Building Engineering; Member and fellow, International Association for Bridge and Structural Engineering. His research interests are Structural Engineering and Earthquake Engineering.