Innovative Procedures to Assess Seismic Behaviour of Existing Structures by Means of Non Linear Static Analysis: Polar Spectrum and Capacity Domains

Luigi Petti,Ivana Marino

doi:10.3390/buildings2030271

Abstract

In the last few years, the need to evaluate the seismic performances of buildings on sustaining strong motion has encouraged the development of simplified non-linear static analyses. Several procedures are available today to assess the behavior of plane-frame systems or plan-regular framed buildings suitable for engineering purposes. Less accurate procedures are instead available for irregular structures. This study introduces new tools to assess the seismic performance of irregular structures by using capacity domains and polar spectra. In particular, the capacity domains, plotted in terms of base shear and node control displacements and obtained by means of static non-linear analyses, lead to the evaluation of the direction of least seismic capacity of the investigated structure. The polar spectrum, instead, leads to taking into account the directivity and site effects of seismic events. In particular, the polar spectrum represents the spectral seismic response evaluated for different in-plan directions.

Highlights

As known, the standard analysis for traditional seismic design is Linear Dynamic Procedure (LDP)with assigned response spectrum (Response Spectrum Analysis)
In the field of seismic engineering, an existing open issue is the need to define a feasible procedure to evaluate the seismic performance of irregular structures
New tools, devised in order to assess the non-linear behaviour of an irregular building and the spectral seismic demand in the plan, have been presented

Summary

Introduction

The standard analysis for traditional seismic design is Linear Dynamic Procedure (LDP). Non-linear static procedures can lead to unsuitable results when applied to irregular structures because of the difficulties in taking into account dynamic lateral-torsional effects and higher mode effects As it is known, an asymmetric distribution of mass and stiffness, or of strength in plan, leads to high ductility demand for the elements near the soft or weak edge [1–3]. This tool is based on the spatial spectral surface obtained by the spectral seismic response evaluated for different in-plan directions and the in-plan projection is defined “Polar Spectrum” Both polar spectrum and capacity domains allow researchers to investigate the non-linear seismic capacities of irregular structures. The goal of the presented results is to investigate the seismic behavior of irregular structures by considering the least seismic-resistant directions of the investigated structure and the spatial features of the seismic event

Description of the Benchmark Structures

The Concept of Capacity Domains

The Concept of Polar Spectrum

Critical Alignment

Conclusions