Keywords: pushover, static non-linear analysis, performance based design, dynamic analysis.

In the design of structures under seismic actions several methodologies can be used to describe the structural seismic response. The recent role of performance based design led to the development and use of methods based on non-linear analysis, namely the so-called pushover analysis. This analysis is a particularly realistic methodology to evaluate the seismic performance of a structural system since the time dependence of the structural behaviour, namely through material and/or geometric non-linearity, is included in the methodology.

The pushover analysis is a simplified methodology to obtain the structural response to seismic actions through a non-linear static analysis. This analysis evaluates the performance of the structures through control of its displacements (at local and global levels), still giving information about the ductility and the resistant strength capacity. Several analysis methods have been proposed like the N2-method [1] that is actually included in the Eurocode 8 [2].

The implementation of this methodology in this regulation manifests the relevance of this analysis in the structural design. Therefore, the present study was developed to compile some information about this new dynamic structural analysis and design concept. In this context, the main objective of this work consists on the presentation of the above-mentioned method with some numerical applications to steel [3] and reinforced concrete (RC) structures [4,5].

The steel structures (3, 6 and 10 floors) were modelled using the commercial FEM package MIDAS/Civil, and for each structure three structural resisting solutions (one solution without bracing and two bracing solutions) were considered: (i) the structure is built without any bracing element; (ii) the building presents glass facades and a bracing system composed by diagonals in X-braces; (iii) the building presents glass facades and the bracing system, by architectural or by strength reasons, is constituted by K-braces. Based on this study it was verified that the bracing system increase the overall inelastic performance compared with the frames without these bracing systems as can be verified in this study. As expected lower top displacement are obtained with the corresponding decrease in the inelastic range.

The pushover analysis can be an easy and efficient technique to study the response of RC buildings under seismic actions. In this case, the sequence of component cracking, yielding and failure, as well as the deformation pattern and shear evolution in the structure, can be traced as the lateral loads or displacements are increased. To complete the study several RC frames with and without masonry infill panels were analyzed based on some numerical models proposed in commercial software.

The study that was carried out was based in the concept of equivalent tie and several configurations of a regular RC frame were analyzed. It is intended to simulate several asymmetries in order to compute the structural performance of each configuration and compare the resistant capacity evolution during the pushover procedure. The nonlinear static Pushover analyses used and compared three software packages.

In these analyses it was verified that this pushover methodology allows evaluating the performance of structures through control of their displacements (at local and global levels), still giving additional information about the ductility and the resistant capacity.

[1]

P. Fajfar, M. Fischinger, "N2 – A Method for Non-Linear Seismic Analysis of Regular Buildings", Proceedings of the 9th World Conference in Earthquake Engineering, Tokyo, Kyoto, Japan, 5, 111-116, 1988.

[2]

Eurocode 8, "Design of structures for earthquake resistance; Part 1: General Rules, Seismic Actions and Rules for Buildings", CEN, Brussels, 2003.

[3]

M.B. Cesar, R.C. Barros, "Seismic Performance of Metallic Braced Frames by Pushover Analyses", in M. Papadrakakis, N.D. Lagaros, M. Fragiadakis, (Editors), Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2009), Rhodes, Greece, 22–24 June 2009.

[4]

V.G. Pereira, R.C. Barros, M.B. Cesar, "A Parametric Study of a R/C Frame Based on Pushover Analysis", in J.F. Silva Gomes, S.A. Meguid, (Editors), 3rd International Conference on Integrity, Reliability & Failure (IRF 2009), Porto, Portugal, 20-24 July 2009.

[5]

V.G. Pereira, R.C. Barros, M.B. Cesar, "Pushover Analyses of a R/C Frame by distinct Software", 12th International Conference on the Enhancement and Promotion of Computational Methods in Engineering and Science (EPMESC XII), Hong-Kong and Macao, 30 Nov–3 Dec 2009. doi:10.1063/1.3452153

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