Damage-based design earthquake load inputs for inelastic structures (original) (raw)

Damage-based design earthquake loads for single-degree-of-freedom Inelastic structures

Journal of Structural Engineering, 2011

This paper develops a new framework for modeling design earthquake loads for inelastic structures. Limited information on strong ground motions is assumed to be available only at the given site. The design earthquake acceleration is expressed as a Fourier series, with unknown amplitude and phase angle, modulated by an envelope function. The design ground acceleration is estimated by solving an inverse dynamic problem, using nonlinear programming techniques, so that the structure performance is minimized. At the same time, the design earthquake is constrained to the available information on past recorded ground motions. New measures of the structure performance based on energy concepts and damage indexes are introduced in this paper. Specifically, the structural performance is quantified in terms of Park and Ang damage indexes. Damage indexes imply that the structure is damaged by a combination of repeated stress reversals and high-stress excursions. Furthermore, the use of damage indexes provides a measure on the structure damage level, and making a decision on necessary repair possible. The material stress-strain relationship is modeled as either bilinear or elastic-plastic. The formulation is demonstrated by deriving the design earthquake loads for inelastic frame structures at a firm soil site. The damage spectra for the site are also established, to provide upper bounds of damage under possible future earthquakes.

Critical earthquake load inputs for multi-degree-of-freedom inelastic structures

Journal of Sound and Vibration, 2009

The problem of modeling earthquake ground motions as design inputs for multi-degree-of-freedom 10 inelastic structures is studied. The earthquake acceleration is expressed as a Fourier series 11 modulated by an envelope function. The coefficients of the series representation are calculated such 12 that the structure inelastic deformation is maximized subjected to predefined constraints. These 13 constraints are taken to reflect known characteristics of recorded earthquakes such as upper bounds 14 on the energy and peak values of the ground acceleration, velocity and displacement, and upper and 15 lower limits on the Fourier spectra of the ground acceleration. The material stress-strain behavior is 16 modeled using bilinear and elastic-plastic relations. The resulting nonlinear optimization problem is 17 solved by using the sequential quadratic optimization method. Issues related to various forms of 18 energy dissipated by the inelastic structure are explored. The study also examines the effect of 19

Inelastic response spectra for an integrated displacement and energy-based seismic design (DEBD) of structures

Frontiers in Built Environment, 2023

The severe socioeconomic impact of recent earthquakes has further highlighted the crucial need for a paradigm shift in performance-based design criteria and objectives towards a low-damage design philosophy, in order to reduce losses in terms of human lives, repair/reconstruction costs, and recovery time (deaths, dollars and downtime). Currently, displacement-based parameters are typically adopted to design/assess the seismic performance of the structures, by limiting the maximum displacement or the maximum interstorey drift ratio (IDR) reached by the structure under different earthquake intensities. However and arguably, displacement-based quantities are characterized by inherent weaknesses, since, for instance, they are not cumulated parameters, thus not able to capture directly the effects of multiple cycles, deterioration and damage cumulation. Therefore, in the last decades, energy-based approaches were investigated and developed in order to establish alternative engineering demand parameters for the assessment of post-event damage through a dynamic energy balance. Towards the main goal of developing an integrated Displacement and Energy-Based Design/assessment procedure (DEBD) for actual use in practice, this research work proposes an innovative approach based on the use of inelastic spectra correlating the energy components with the corresponding maximum displacement response parameters of the structure. In practical terms, the proposal is to further integrate and develop the well-known Direct Displacement-Based Design, by directly adopting the hysteretic energy as an additional design parameter. The energy inelastic spectra are developed through an extensive parametric analysis of Single-Degree-of-Freedom (SDoF) systems, with different nonlinear hysteretic models. In such an approach, the maximum seismic energy demand imparted to a structure can be directly predicted and controlled, whilst distinguishing the various components of the energy balance, including the hysteretic one. The effects of near-field and far-field earthquakes are also investigated. Results show that in the first case the seismic demand is concentrated in the peak of a few large cycles that absorb the demand energy induced by the high component in peak ground velocity in the second case the higher equivalent number of plastic cycles tends to become critical for structures with inadequate structural details and prone to suffer by cumulative cycles and overall plastic fatigue mechanisms.

L Seismic Performance Assesment Based on Damage of Structures – Part 1 : Theory Udc 699

2011

The paper presents methodology for safety assessment and design of earthquake resistant structures based on application of damage spectra. The damage spectrum can be used for seismic evaluation of vulnerability of structures with given properties and can provide information of damage potential of the recorded ground motions. Damage spectrum represents a variation of a damage index versus structural period for a single-degree-of-freedom system subjected to an earthquake ground motion. The improved damage index, based on plastic deformation and hysteretic energy dissipation, is applied. It depends on maximal plastic deformation, ductility capacity and function including cumulative damage effects. This function, besides the parameter including influence of deterioration, depends on the history of cyclic deformations and on both cyclic and accumulative ductility.

Seismic performance assessment based on damage of structures, Part 1: Theory

Facta universitatis - series: Architecture and Civil Engineering, 2011

Evaluation of the inelastic demand of structures subjected to multiple ground motions

2007

In the current seismic design format, the key issue in establishing realistic seismicÂ loads is the behavior factor. It accounts for all the dissipative mechanisms that aÂ structural system may develop under a strong ground motion, however not clearlyÂ enough stated yet. It corresponds to the performance level associated to theÂ ultimate limit state (i.e. life safety), related to a 100 years mean return interval ofÂ earthquake ground motion with a prescribed peak acceleration of ground. The paper investigates the effect of repeated Vrancea strong ground motions on theÂ behavior factors and the related parameters that accounts for cyclic structuralÂ deterioration due to inelastic response. A large number of integrated analyses,Â nonlinear response analyses and energy balance-based analyses were carried outÂ and estimates were made on the behavior factors for inelastic SDOF systemsÂ controlled by flexure with stiffness degradation. The correlation between behavior factors and damage l...

Damage spectrum and its applications to performance-based earthquake engineering

Improved damage spectra are proposed to quantify the damage potential of recorded earthquake ground motion. The damage spectra are based on a combination of normalized hysteretic energy and deformation ductility of a series of inelastic single-degree-offreedom systems. The damage spectra proposed will be zero if the structure remains elastic, i.e., no significant damage is expected, and will be unity if there is a potential of collapse. By varying a coefficient in their formulations, improved damage spectra can be reduced to commonly used normalized hysteretic energy or displacement ductility spectra. The damage spectra are computed for hundreds of horizontal ground motions recorded during the Landers and Northridge earthquakes. Source-to-site attenuation of the damage spectra in the Northridge earthquake is examined. Calibration of the damage spectra for an instrumented building damaged during the Northridge earthquake is also carried out. The improved damage spectra are promising for assessment of the performance-based seismic vulnerability of existing structures. For example, following an earthquake, near real-time contour maps of damage spectral ordinates at selected periods provide useful information on the spatial distribution of the damage potential of recorded ground motion for specific types of structures. The concept of damage spectra is also promising for carrying out performance-based design of new structures.

Effects of multiple earthquakes on inelastic structural response

The basic approach for seismic design of structures utilizes a single loading scenario and a single performance criterion; usually life-safety. In recent years, social and economic considerations have necessitated that more than one performance criterion is used, and also more than one level of earthquake intensity. This multiple load-and-limit state seismic design is the current best practice. There are a few locations around the world that warrant an alternative approach. These locations are affected by more than one earthquake within a relatively short period of time due to their special seismo-tectonic setting. Few existing studies simply assume that the first earthquake will impose the maximum damage. An opportunity has presented itself to study the effect of multiple strong earthquakes on structures as a consequence to the exceptionally rich set of records obtained from the earthquake sequence of Tohoku (Japan), starting on March 2011. In this technical note, five stations are selected to represent a set of sites subjected to multiple earthquakes of varying magnitudes and source-to-site distances. From the tens of records captured at these five sites, three are selected for each site to represent scenarios of leading and trailing strong-ground motion. A leading set is where the first earthquake has the largest peak ground acceleration (PGA) in the sequence of three, while a trailing set has the second or third records as its highest PGA signal. A short list of earthquake response parameters is selected, and the records are treated in two different manners. Inelastic constant ductility spectra for acceleration response are examined, alongside force reduction factor spectra. The final part of the technical note is a reinforced concrete (RC) frame analysis subjected to the same set of ground motions used for the response spectra. The inelastic response and force reduction factor spectra, alongside the inelastic response of the RC frame, not only confirm that multiple earthquakes deserve extensive and urgent studies, but also give indications of the levels of lack of conservatism in the safety of conventionally-designed structures when subjected to multiple earthquakes.

Modeling Critical Ground-Motion Sequences for Inelastic Structures

Advances in Structural Engineering, 2010

The specification of earthquake loads as inputs to engineering structures is a crucial task in earthquake engineering. There are cases, however, where the site under consideration has limited or scarce seismic data, making this process a difficult task. Meanwhile, structural engineers are often concerned with the worst-case scenario that can happen to the structure during its service-life under possible future earthquakes. Repeated ground-motion sequences occurring after short intervals of time, resulting from mainshock-aftershock earthquakes, have been observed in many parts of the world. Such ground motion is capable of creating severe damage in the structure due to accumulation of inelastic deformations from multiple sequences before any structural repair is possible. This paper models ground motions of multiple sequences that produce the maximum damage in the structure. The ground acceleration is represented as Fourier series, with unknown amplitudes and phase angles, modulated by envelope functions. The unknown parameters are optimized to produce the maximum damage in the structure while the ground motion is constrained to the available seismic data at the site. The resulting inverse nonlinear dynamic problem is tackled using optimization techniques, nonlinear time-history analysis and damage indices. Numerical illustrations on modeling critical earthquake sequences for inelastic frame structures are provided. It is shown that critical repeated acceleration sequences produce larger structural damage compared to single critical earthquakes.

Inelastic Displacement Ratios for Displacement-Based Earthquake Resistant Design

Proceedings of the 12th World Conference on …, 2000

A summary of results of a comprehensive statistical study of inelastic displacement ratios is presented. An inelastic displacement ratio is defined as the ratio of the maximum lateral inelastic displacement demand of a structure to the maximum lateral elastic displacement demand. ...

Damage-based design earthquake load inputs for inelastic structures (original) (raw)

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