Alessandro Vittorio Bergami

Proposal and application of the Incremental Modal Pushover Analysis (IMPA)

Existing reinforced concrete frame buildings designed for vertical load only could suffer severe damage during earthquakes. In recent years, many research activities have been paid to develop reliable and practical analysis procedure to identify the safety level of existing structures. The Incremental Dynamic Analysis (IDA) is considered to be one of the most accurate methods to estimate seismic demand and capacity of structures. But it requires the execution of many nonlinear response history analyses (NL_RHA) in order to describe the entire range of structural response. The research discussed in this paper deals with proposal of an efficient Incremental Modal Pushover Analysis (IMPA) to obtain capacity curves by replacing the NL_RHA of the IDA procedure by Modal Pushover Analysis (MPA). In this work, the basic idea of IMPA is presented and the step-by-step computational procedure is then summarized. This new procedure, accounting the higher modes effects, does not need the execution of complex NL-RHA, but only simpler nonlinear static analysis. Then, the new procedure is applied to an existing irregular building. The capacity curves obtained by different procedures (standard pushover analysis, IMPA and IDA) are presented and discussed.

Proposal of a Modal Pushover Based Incremental Analysis

Existing reinforced concrete frame buildings designed for vertical load only could suffer severe damage during earthquakes. In recent years, many research activities have been paid to develop reliable and practical analysis procedure to identify the safety level of existing structures. The research discussed in this paper deals with proposal of an efficient incremental procedure to estimate seismic capacity of irregular structures performing few pushover analysis (one for every relevant modal shape) and applying a series of Modal Pushover Analysis (MPA). This approach, similar to the Incremental Dynamic Analysis (IDA), replaces the Nonlinear Response History Analyses (NL_RHA) by simple pushover analyses. In this work, this idea, named IMPA (Incremental Modal Pushover Analysis), is proposed for a 3D complex building and this application is described and discussed.

A DESIGN PROCEDURE FOR SEISMIC RETROFITTING OF REINFORCED CONCRETE FRAME AND CONCENTRIC BRACED STEEL BUILDINGS WITH DISSIPATIVE BRACINGS

Abstract. The research presented in this paper deals with the seismic retrofitting of existing frame structures by means of passive energy dissipation. An iterative displacement-based procedure, based on capacity spectrum is described and some applications are discussed. The general proce-dure has also been discussed referring to the case of existing steel concentric braced frame struc-tures (CBF). The procedure can be used with any typology of dissipative device and for different performance targets. In this work the procedure has been applied, with both traditional pushover (load profile proportional to first mode) and multimodal pushover, to an existing r.c. frame build-ing. In the application presented the buckling restrained braces have been used in order to prevent damages to both the structure and non structural elements. The use of multimodal pushover proves to be more effective than pushover based on single mode in case of medium rise r.c. frame building (higher than 30 metres) but, once this building is retrofitted, and therefore regularized, with a brac-ing system, the difference between using monomodal or multimodal pushover becomes not signifi-cant.

Design of dissipative braces for an existing strategic building with a pushover based procedure

The research presented in this paper deals with the seismic protection of existing frame structures by means of passive energy dissipation. An iterative displacement-based procedure, based on capacity spectrum, to design dissipative bracings for seismic retrofitting of frame structures is described and some applications are discussed. The procedure can be used with any typology of dissipative device and for different performance targets. In this work the procedure has been applied, with both traditional pushover (load profile proportional to first mode) and multimodal pushover, to an existing r.c. frame building. In the application presented the buckling restrained braces have been used in order to prevent damages to both the structure and non structural elements. The use of multimodal pushover proves to be more effective than pushover based on single mode in case of medium rise r.c. frame building (higher than 30 metres) but, once this building is retrofitted, and therefore regularized, with a bracing system, the difference between using monomodal or multimodal pushover becomes not significant.

Cyclic Behaviors of Steel Braces in Concentrically Braced Frames

In this paper, a new model named as “brace01” for steel brace is presented on the basis of experimental data on different types of steel struts. This model shows a peasant capability in the structural analysis of Concentrically Braced Frames. A brace is idealized as a pin-ended member with a plastic hinge located at its midspan. This expression of the model is proposed by combining the mechanical properties and the phenomenological characters. The model for steel brace is implemented in an effective way in OpenSees. The calibration of the material model is done by comparing the numerical curves generated by the numerical model with the experimental curves of pin-ended steel braces. The new model is proved applicable to practical Concentrically Braced Frame.