Project Overview

The extension of the use of Nonlinear Static Procedures (NSP) to the case of irregular structures has so far been the object of only restricted scrutiny, which effectively ends up by limiting significantly the employment of NSPs to assess actual existing structures, the majority of which tend to be non-regular. In addition, such few studies have typically concentrated on the application and verification of a single NSP approach, thus not providing useful elements of comparison between the different methodologies available.

An important contribution to an increase in the effective application of these procedures to 3D irregular structures can perhaps be obtained by intensifying the exchange of research results, ideas and experiences. A national research project on this topic, constituted thus a step in this direction.

For the considered nonlinear static procedures to 3D irregular structures, the scientific issues open to research in this project are summarised in the paragraphs given below. Within this framework, and departing from the available knowledge, different specific objectives have been identified and set out as the prerequisites for development of adequate nonlinear static procedures to non-regular structure:

1. Scrutinizing in detail each of the selected procedures with a view to establish their “optimum configuration”;
2. Development of parametric comparison of the approaches chosen for irregular buildings and bridges, with the purpose of emphasizing relative advantages and disadvantages and, eventually, coming up with suggestions for possible preferred choices;
3. Studying the influence of modelling issues on nonlinear static and dynamic analysis of 3D irregular structures
4. Performance verification of the generalised pushover curve for 3D irregular structures
5. Development of a new version of the Adaptive Capacity Spectrum Method (ACSM) for the seismic assessment/design of irregular 3D buildings\n6. Intensifying the exchange of research results, ideas and experiences on the topic by means of an international Workshop and through a information portal of the project.

According to previous results it is expected that ACSM apparently managed to follow slightly better the change of response characteristics of the structures with the increase of seismic intensity. The Adaptive Capacity Spectrum Method essentially consists in using a displacement-based adaptive pushover analysis (which accounts for higher modes and stiffness degradation) to then derive an equally adaptive SDOF capacity curve which is in turn intersected with the acceleration-displacement response spectrum of the design earthquake. It is noted that the equivalent SDOF capacity curve is calculated step-by-step using the actual deformed pattern of the MDOF at any given instant, and hence is not based on the modification of the MDOF capacity curve with reference to the displacement of a specific physical location. In this manner, the need to define a somewhat arbitrary reference node is avoided. An over-damped elastic response spectrum is employed to define the seismic demand. The spectrum is scaled using the equivalent viscous damping and spectrum scaling equations. The computation of seismic forces makes use of the Modified Modal Superposition (MMS), whereby higher modes elastic forces are combined, through SRSS, with the pushover analysis derived forces at the performance point (intersection between demand spectrum and capacity curve).

To fulfil the abovementioned specific objectives a comprehensive approach needs to be established, forming the basis of the overall strategy for this project and, accordingly, of this present work plan, detailed presented in the tasks section. Thus, the key intended impacts of this project and main expected contributions to the topics in question are related to the study of non-linear static procedures for the seismic design and assessment of 3D irregular structures, focusing on the development of next-generation related procedures and guidelines.