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PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Analysis of the Traffic Induced Vibrations on a 19th Century Heritage Chapel using Finite Element Modelling
P. Tamvakou, M.M. Paredes and R.C. Barros
Department of Civil Engineering, Faculty of Engineering, University of Porto, Portugal
P. Tamvakou, M.M. Paredes, R.C. Barros, "Analysis of the Traffic Induced Vibrations on a 19th Century Heritage Chapel using Finite Element Modelling", in , (Editors), "Proceedings of the Tenth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 140, 2010. doi:10.4203/ccp.93.140
Keywords: traffic vibrations of heritage chapel, masonry historic constructions, finite element modeling, ANSYS, serviceability limit conditions, peak sway ratio, peak accelerations.
To study the consequences of traffic vibrations on a patrimony chapel, a finite element model of the chapel and adjoining soil and road was developed using commercial software ANSYS . The dynamic loads corresponding to vehicles moving along the road were simulated and the corresponding maximum displacements accelerations and stresses of some chapel key points were obtained.
The dimensions of the heritage chapel are 4.91 m wide, 9.2 m long, 7.15 m high. To include the effect of the adjacent manor-house, a small wall attached to the eastern side of the chapel in line with the façade of the chapel southern front wall (9,82 m long), and a large wall attached to the eastern side of the chapel alongside its length (20 m long) were considered. The complex finite element model of the chapel-house-soil-road was meshed with 20-node brick elements.
The first three modes of vibration had the natural frequencies: f1=16.23 Hz, f2=22.19 Hz and f3=24.85 Hz; they matched (with some accuracy) the values obtained by system identification using four seismographs at four implantation points of the chapel and detecting the motion characteristics induced by ambient vibrations .
As the hypothetical vehicle moves along the road, its weight is always between two road nodes. Some nodes were selected on the walls of the chapel, for which the displacements and the accelerations were explicitly calculated. When the vehicle is near the chapel wall, the displacements begin to increase up to the point that the wall reaches its maximum displacement. Some nonlinear graphs of normal and shear stresses variations were determined for the operating weight of a large hydraulic excavator on tracks as heavy circulating vehicle.
Although the chapel structure might look safe for ultimate limit conditions, that apparently do not reach critical stress values, the chapel behaviour indicates indexes and conditions which imply reduction or loss of serviceability. The peak sway ratios for this chapel under heavy traffic reached values only characteristic of much slender structures like masonry bell towers . Also, the calculated peak transient horizontal accelerations for several nodes on the west wall, far exceeded the peak recommended value of 42 mm/s2 defined in BS 6472  for adverse human exposure to vibration in buildings.
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