MODIFICATION OF THE BUILDING DYNAMIC RESPONSE DUE TO STRUCTURAL DAMAGING DURING STRONG EARTHQUAKEs (original) (raw)

Inelastic Behavior of Buildings Under Repeated Vrancea Earthquakes

2007

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

Damage assessment by stiffness identification for a full- scale three-story steel moment resisting frame building subjected to a sequence of earthquake excitations

This research experimentally investigates a practical hysteresis loop analysis method for damage assessment through stiffness identification using a full scale three-story steel moment resistant frame structure subjected to a sequence of 6 shake table tests with different magnitudes of 3D excitations. The effective elastic stiffness, k e , is calculated based on the analysis of the experimentally measured and reconstructed hysteresis loops. Structural degradation is then evaluated by tracking changes in identified stiffness over time and across different earthquake events. Finally, the fundamental frequency of the building is calculated using the identified stiffness to compare with the experimental frequency from experimental transfer functions. Results show average differences between the final stiffness of one event and the initial stiffness of the following event are less than 5% in both horizontal directions, indicating a good continuity and accuracy of the identification over events. The average difference between the experimental and calculated fundamental frequency are less than 0.1 Hz in both directions over all events. The overall results clearly delineate the capability of the method to accurately and consistently quantify and localize structural damage that may not be detected by external visual detection over several earthquake events of different magnitude, indicating its ability to be used in long term monitoring.

Improvement of Seismic Performance of Seven Story Steel Building with Hysteretic Steel Dampers Under Severe Seismic Excitation

The uses of supplementary hysteretic steel dampers have been recognized as effective and inexpensive techniques to reduce seismic responses of structural systems induced by a major earthquake. During a large earthquake event, these dampers will absorb the earthquake input energy to the structure through hysteretic behavior of its elements, where the main members are designed to remain elastic and/or within low inelastic deformation. The purpose of this paper is to study the effectiveness of the hysteretic dampers improving the structural performance of a steel building subjected to a major earthquake excitation. To do this, seven story's steel building with and without hysteretic steel dampers are investigated using non-linier dynamic time history analysis under a set of selected ground motion records. The ground motions are matched to the response spectrum design of the National Indonesian Standard of seismic hazard map. In this study, hysteretic steel dampers are applied with various stiffness ratio values in the steel bracing of the Chevron types configurations. To quantify the structure's performance, a damage indicator derived from the energy damage model is introduced and evaluated. Finally, the seismic performance of the building with and without hysteretic steel dampers are discussed and compared.

The Effect of Structural Degradation on the Seismic Behavior of Structures

The aim of this paper is to illustrate the change in dynamic behavior of structures associated with system degradation. The acceptance of plastic hinges occurrence in a building according to the seismic design standards is not a safe method for slow earthquakes, as Vrancea intermediate earthquakes, when can result important building damages or even collapse. The paper presents new solutions to increase reliability and safety of a new or an existing building at seismic actions. It consists in controlling, limiting and damping the seismic movements using the mechanical devices SERB.

Earthquake Disaster Control - Damping and Structural Behavior

According to recent literature on earthquake ground motion and induced waves subject of study for building damage assessment, strong ground motion is subject to the study of movement in near fault and far fault locations as well as integrated to the variability of ground consistency, where natural period variability resides. Ground motion can have large periods as well as short periods dependant on distance from the fault and the impact of elastic deformations in ground soil. This behavior can be attributed to the soil composition and its geological behavior towards ground motion. This is represented by amplitudes which defer from structural amplitudes. Even though a structural behavior can be different from ground motion's natural period oscillation, foundations are calculated in the approximate measure of that period after loss or damping. If both the building and the ground coincide in their movement during an earthquake, the structure will behave in accordance to calculation. Nonetheless, if a structure is calculated for short period and high amplitude ground motion and the actual ground motion takes an opposite direction with long period osccilations and low amplitudes then the structure's flexibility for deformation is tested and its when vibration damage can occur.

Instability of buildings during seismic response

Engineering Structures, 1998

The issue of gravity induced instability during response to severe seismic excitation is examined. It is contended that while static instability is fully determined by the existence of at least one negative eigenvalue in the second-order tangent stiffness, this condition is necessary, but not sufficient for instability during dynamic response. It is noted that the likelihood of collapse is strongly dependent on the shape of the mechanism that controls during the critical displacement cycle and that this shape can be reasonably identified using a pushover analysis with an appropriately selected lateral load distribution. A characterization of the instability limit state based on reduction of a multistorey building to an equivalent SDOF system is presented.

Distribution of Drift, Hysteretic Energy and Damage in Reinforced Concrete Buildings with Uniform Strength Ratio

14 th World Conference on …, 2008

Assessment of the behavior of structures during recent earthquakes indicates that much damage has happened to the buildings including those designed according to the engineering principles. The preliminary design of most of buildings is based on equivalent static and spectral dynamic forces specified by the governing seismic codes. The height-wise distribution of these horizontal forces seems to be based implicitly on the elastic vibration modes. Studies have shown that most structures subjected to strong ground motions fall into an inelastic state. Thus it is necessary to study the inelastic behavior of structures undergoing such earthquakes. The aim of this study is to investigate the effect of the two above-mentioned lateral loading patterns on height-wise distribution of drift, hysteretic energy and damage subjected to severe earthquakes by considering four reinforced concrete buildings. The results indicate that in strong ground motions, none of the lateral loading patterns will lead to uniform distribution of drift, hysteretic energy and damage, and an intense concentration of the values of these parameters can be observed in one or two stories especially in equivalent static method. This will consequently hinder the serviceability of the maximum capacity of structures.

Hysteretic Energy Demand in SDOF Structures Subjected to an Earthquake Excitation: Analytical and Empirical Results

Süleyman Demirel Üniversitesi Fen Bilimleri Enstitüsü Dergisi, 2018

In energy-based seismic design approach, earthquake ground motion is considered as an energy input to structures. The earthquake input energy is the total of energy components such as kinetic energy, damping energy, elastic strain energy and hysteretic energy, which contributes the most to structural damage. In literature, there are many empirical formulas based on the hysteretic model, damping ratio and ductility in order to estimate hysteretic energy, whereas they do not directly consider the ground motion characteristics. This paper uses nonlinear time history (NLTH) analysis for energy calculations and presents the distribution of earthquake input energy and hysteretic energy of single-degree-offreedom (SDOF) systems over the ground motion duration. Seven real earthquakes recorded on the same soil profile and three different bilinear SDOF systems having constant ductility ratio and different natural periods are selected to perform NLTH analyses. As results of nonlinear dynamic analyses, input and hysteretic energies per unit masses are graphically obtained. The hysteretic energy to input energy ratio (EH/EI) is investigated, as well as the ratio of other energy components to energy input. EH/EI ratios of NLTH analysis are compared to the results of empirical approximations related EH/EI ratio and a reasonable agreement is observed. The average of EH/EI ratio is found to be between 0.468 and 0.488 meaning nearly half of the earthquake energy input is dissipated through the hysteretic behavior.