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Analysis of the torsional effects induced by the seismic action in plan asymmetric structures

Keywords: plan asymmetric structures, maximum rotational response, seismic excitation, corner magnification factors
Fig. 1. Plan asymmetric structure (Silvestri).
Fig. 2. Predictive capabilities of the ALPHA parameter (Silvestri).
Fig.3 Maximum corner displacement magnification vs centre mass displacement of the equivalent noteccentric system centre mass displacement (Silvestri)

Structures characterized by non coincident centre of mass and centre of stiffness (eccentric structures) when subjected to dynamic excitation, develop a coupled lateral-torsional response that may increase the local peak dynamic response. This behaviour has been investigated by many researchers since the late 1970s. Nevertheless a number of issues still remain unresolved in the areas of inelastic response and development of simplified, yet physically-based design procedures. In particular, in order to effectively apply the Performance-Based Design approach to seismic design, there is a growing need for code oriented methodologies aimed at predicting deformation parameter.

Starting from the governing equations of motion of linear elastic eccentric systems, a key system parameter which controls the maximum rotational response of such systems under free and forced vibration, is identified. This parameter, called ALPHA, is defined as the mass radius of gyration of the structure multiplied by the ratio of the maximum rotational to the maximum longitudinal displacement response developed by a one-story eccentric system in free vibration. A number of numerical, experimental (through shaking table tests of linear elastic and inelastic systems) and field data (from historically recorded structural responses) analyses have shown that the parameter ALPHA is capable of providing a tight upper bound for the maximum rotational response developed by the eccentric systems starting from the knowledge of the maximum longitudinal response of the “equivalent” non eccentric system.

Total number of publications: 35.

Main publications

Palermo, M., Silvestri, S., Gasparini, G., & Trombetti, T. (2016). Maximum Corner Displacement Amplifications for Inelastic One- Storey In-Plan Asymmetric Systems Under Seismic Excitation. In Seismic Behaviour and Design of Irregular and Complex Civil Structures II (pp. 243-254). Springer International Publishing.

Palermo, M., Silvestri, S., Gasparini, G., and Trombetti, T. (2013). Physically-based prediction of the maximum corner displacement magnification of one-storey eccentric systems. Bulletin of Earthquake Engineering, 11(5), 1467-1491.

Trombetti T., Silvestri S., Gasparini G., Palermo M. (2013), “Physically Based Prediction of the Maximum Corner Displacement of One-Storey Eccentric Systems”, Chapter 10, in O. Lavan, M. De Stefano (Eds.), Seismic Behaviour and Design of Irregular and Complex Civil Structures. Series: Geotechnical, Geological and Earthquake Engineering, Vol. 24, 2013, XIV, 374 p. 206 illus., 91 illus. in color. ISBN: 978-94-007-5376-1 (print), 978-94-007-5377-8 (ebook).

Trombetti T., Palermo M., Silvestri S., Gasparini G. (2012). Period Shifting Effect on the Corner Displacement Magnification of One-Storey Asymmetric Systems. Proceedings of the 15th World Conference on Earthquake Engineering.

Silvestri S., Gasparini G., Trombetti T., “Maximum seismic rotational response of multi-storey structures”, Proc. SEMC 2010, Cape Town, South Africa, September 6-8, 2010.

Gasparini G., Silvestri S., Orci C., Trombetti T., “A synthetic formulation for evaluating the maximum displacement of the corner points in eccentric structures due to the seismic effects” Paper n. 212b, Proceedings of 5th International Structural Engineering and Construction Conference – ISEC5 – Las Vegas, Nevada, USA, September 21-27, 2009.

Gasparini G., Silvestri S., Trombetti T., “A simple code-like formula for estimating the torsional effects on structures subjected to earthquake ground motion excitation”, Paper 05-01-0269. Proceedings of the 14th World Conference on Earthquake Engineering (14WCEE), Beijing, China, 12-17 October 2008.

Silvestri S., Trombetti T., Gasparini G., “An upper bound and an estimation for the maximum non-linear rotational response of one-storey asymmetric buildings”, Proc. of the 5EWICS, Catania, Italy, 16-17 September 2008. Pg 51-62.

Silvestri S., Trombetti T., Gasparini G., “Closedform solutions for corrective eccentricity, sensitivity to accidental eccentricity and increase in peak local displacements”, Proc. of the 5EWICS, Catania, Italy, 16-17 September 2008. Pg 63-77.

Trombetti T., Silvestri S., Gasparini G., Pintucchi B., De Stefano M., “Numerical verification of the effectiveness of the “ALPHA” method for the estimation of the maximum rotational response of eccentric systems”, Journal of Earthquake Engineering, Vol. 12, No. 2 (2008), pp 249-280.

Gasparini G., Silvestri S., Trombetti T., “A synthetic parameter capable of capturing the torsional behaviour of one-storey asymmetric structures”, Paper n. 1282, Proceedings of the 100th Anniversary Earthquake Conference, EERI’s Eight U.S. National Conference on Earthquake Engineering, 8NCEE, 18-22 April 2006.

Trombetti T.; Conte J.P. (2005). New Insight Into and Simplified Approach to Analysis of Laterally- Torsionally Coupled One-Story Systems. Journal of Sound and Vibration.

Gasparini G., Silvestri S., Trombetti T., Pintucchi B., De Stefano M., “A genetic approach for the optimal insertion of viscous dampers into torsionally coupled structures”, Proceedings of the 4EWICS, Thessaloniki (Greece), 2005.

Gasparini G., Trombetti T., Silvestri S., Ceccoli C., “Predictive capabilities of the alpha method: shaking table tests and field data verification”, Proceedings of the “13th World Conference on Earthquake Engineering”, 13WCEE, Vancouver, B.C., Canada, 1-6 August 2004, Paper No. 472.

Research projects

Research project RELUIS Line 2: “Evaluation and reduction of vulnerabilità of existing RC buildings.” (Executive Project 2005-2008); National Coordinators: Prof. E. Cosenza and Prof. G. Monti; Chief-Responsible for the Bologna Research Unit: Prof. A. Benedetti.