Design Response Spectrum Research Articles

Fully Nonstationary Spatially Variable Ground Motion Simulations Based on a Time-Varying Power Spectrum Model

By analyzing the evolutionary spectrum method for multivariate nonstationary stochastic processes, a simulation method for fully nonstationary spatially variable ground motion is proposed based on the Kameda time-varying power spectrum model. This method can properly simulate nonstationary spatially variable ground motion based on a target response spectrum. Two numerical examples, in which the Kameda time-varying power spectra are calculated for different conditions, are presented to demonstrate the capabilities of the proposed method. In the first example, the nonstationary spatially variable ground motion that satisfies the time-frequency characteristics and response characteristics of the original ground motion is simulated by identifying the parameters of the given time-varying power spectrum. In the second example, the ground motion that satisfies the design response spectra is simulated by defining the parameters of the time-varying power spectrum directly. The results demonstrate that the method can effectively simulate nonstationary spatially variable ground motion, which implies that the proposed method can be used in engineering applications.

CALIBRATION OF 1-D NUMERICAL CODES SOFTWARE FOR SITE RESPONSE ANALYSES

Ground response analyses are used to predict surface ground motions for development of design response spectra, to evaluate dynamic stresses and strains for evaluation of earthquake hazards, and to determine the earthquake induced forces that can lead to instability of earth-retaining structures. The effects of local soil on ground motion are commonly evaluated by performing numerical analyses either in frequency or time domains.In order to evaluate the differences between frequency and time domain analysis, several analyses were conducted for homogenous stiff soil deposit with respective codes which are SHAKE and D-MOD2000. Linear and non linear analyses have been conducted. The non linear analyses with D-MOD2000 code have been carried out by using different frequencies in the Rayleigh damping formulation, i.e. fundamental and predominant frequency. For linear, PGA 0.1g is used in the analysis while for non linear PGA is scaled into three different value of 0.1, 0.3, and 0.5g.The results for both linear and non linear approach are similar. For the non linear analyses, it is shown that the curves derived using predominant frequency perform better than those using fundamental frequency. Main differences are for non linear approach where the differences between two codes are higher for higher input motion. As the calibration using predominant frequency between the two codes perform good, the respective codes are applied to evaluate soil response in Sant’ Agostino and San Carlo, in terms of PGA, due to May 20th 2012 Emilia Earthquake. There are 139 accelerometric station recorded strong motion. In this analysis, we consider one record which is in Mirandola station, the closest recording station where the Magnitude in epicentral area was 5.9 and 5.8 in Mirandola station. The recorded surface motion in Mirandola is transferred to the bedrock in 112 m depth and used as input motion for the two evaluated sites, San Carlo village and nearby municipality Sant’Agostino on 17 km distance from Mirandola station. The preliminary data presented here shows the PGA recorded in the bedrock of Mirandola station is 0.75g, while in Sant’Agostino and San Carlo is 0.92g and 0.81g.

Application of Simulated Annealing Particle Swarm Optimization in Response Spectrum Fitting of Simulated Earthquake Wave

In order to get a simulated earthquake wave whose response spectrum fitted well to the smooth design response spectrum, a model was established by making the standard error between the response spectrum of simulated earthquake wave and the design response spectrum as the minimal optimization objective. Simulated annealing particle swarm optimization algorithm, which was an improvement algorithm of particle swarm optimization, was used to solve the model. This spectrum fitting method was compared with the conventional spectrum fitting method, which adjusted Fourier amplitude spectrum in frequency domain. The results show that the method of response spectrum fitting by applying simulated annealing particle swarm optimization algorithm has a good convergence. And the response spectrum of simulated earthquake wave generated by simulated annealing particle swarm optimization algorithm agrees better with the design response spectrum than that by conventional spectrum fitting method.

Application of Simulated Annealing Particle Swarm Optimization in Response Spectrum Fitting of Simulated Earthquake Wave

In order to get a simulated earthquake wave whose response spectrum fitted well to the smooth design response spectrum, a model was established by making the standard error between the response spectrum of simulated earthquake wave and the design response spectrum as the minimal optimization objective. Simulated annealing particle swarm optimization algorithm, which was an improvement algorithm of particle swarm optimization, was used to solve the model. This spectrum fitting method was compared with the conventional spectrum fitting method, which adjusted Fourier amplitude spectrum in frequency domain. The results show that the method of response spectrum fitting by applying simulated annealing particle swarm optimization algorithm has a good convergence. And the response spectrum of simulated earthquake wave generated by simulated annealing particle swarm optimization algorithm agrees better with the design response spectrum than that by conventional spectrum fitting method.

Modeling of spatially correlated, site-reflected, and nonstationary ground motions compatible with response spectrum

Seismic risk analysis and mitigation of spatially extended structures require the synthesis of spatially varying ground motions in the response history analysis of these structures. These synthetic motions are usually desired to be spatially correlated, site reflected, nonstationary, and compatible with target design response spectra. In this paper, a method is presented for simulating spatially varying ground motions considering the nonstationarity, local site effects, and compatibility of response spectra. The scheme for generating spatially varying and response spectra compatible ground motions is first established for spatial locations on the ground surface with varying site conditions. The design response spectrum is introduced as the “power” spectrum at the base rock. The site amplification approach is then derived based on the deterministic wave propagation theory, by assuming that the base rock motions consist of out-of-plane SH wave or in-plane combined P and SV waves propagating into the site with assumed incident angles, from which tri-directional spatial ground motions can be generated. The phase difference spectrum is employed to model ground motions exhibiting nonstationarity in both frequency and time domains with different site conditions. The proposed scheme is demonstrated with numerical examples.

Characteristics of near-source ground motions from the 2012 Varzaghan–Ahar double earthquakes, Northwest of Iran

Wavelet-based analyses were used in this study to interpret the near-source ground-motion characteristics of records obtained during the 2012 Varzaghan–Ahar double earthquakes in the East-Azerbaijan province of Iran. For this purpose, the large pulse of ground motions was extracted by applying continuous wavelet transforms, and then, the residual motions were achieved by subtraction of extracted pulse from the original motions. Analysis of ground motions illustrated that the records obtained at Varzaghan station could be classified as pulse-like motions with pulse index around 0.9. As well, the acceleration response spectra for horizontal directions were compared with the design response spectrum of Iranian seismic design code (Standard No. 2800). The comparisons showed a relatively large amplification in spectral values due to near-source pulse effects.

Site Response Evaluation of Agartala City Using Geophysical and Geotechnical Data

In this paper, the study addressed how the local geology and soil condition influences on incoming ground motion. Subsurface Geotechnical (SPT) and geophysical (MASW) data in 27 locations at Agartala city have been obtained and used to estimate the surface level response. The vulnerable seismic source (Sylhet fault) has been identified based on deterministic seismic hazard analysis (DSHA). The stochastic point source seismological model has been used to generate synthetic ground motion at 27 locations where MASW tests were conducted. The site response analyses have been performed using SHAKE2000.The results are presented in the form of contour maps in terms of PGA, amplification factor (AF) and spectral accelerations of periods (0.20sec, 1.0sec). The highest amplifications (2 to 3) were observed in the intermediate periods between 0.20 to 1.0sec ranges. However, the mean response spectrum has also been developed for both the rock and ground surface that has mean PGA 0.285g at rock and 0.35g at the surface. Further, the IS code and NEHRP provisions were compared with the mean surface level response spectrum. The IS code provision overestimates the mean response spectrum for all the periods except the periods from 0.26-0.42 sec. Based on the present study, the average shear wave velocity (Vs30=236±52 m/s) of Agartala actually falls a site class-D category (180 m/s <Vs30<360 m/s) as per NEHRP provisions and the design response spectrum has been developed. The developed site specific design response spectrum and other results would be very useful for city planners/designers and the Govt. for earthquake resistant design, city planning, also to identify vulnerable locations, structures suitability identification and also better disaster mitigation planning of the city area.

FRACTAL CHARACTERISTICS OF PHASE SPECTRUM OF EARTHQUAKE MOTION

The purpose of this research is to make clear the phase spectrum characteristic of earthquake motion. After the introduction of past researches we introduce the concept of fractional Brownian process (FBP). A simple method is proposed to determine the Hurst index and the variance of a given process characterized by the FBP. We find that the phase characteristic of earthquake motion can be expressed by this process which is a non-stationery function of the circular frequency with a constant correlation coefficient. Using several observed earthquake motion we demonstrate this fact and show the efficiency of newly founded result to simulate realistic earthquake motion phase and also compare simulated earthquake motions with those of observed ones. We also simulate design response spectrum compatible earthquake motions by simulating the earthquake motion phase using the identified Hurst index and variance of the given earthquake motion. We investigate the effect of hypocenter distance on the variance and Hurst index of earthquake motion phase, as well as on the mean gradient of earthquake motion phase with respect to the circular frequency.

Modified complex mode superposition design response spectrum method and parameters optimization for linear seismic base-isolation structures

Earthquake response calculation, parametric analysis and seismic parameter optimization of base-isolated structures are some critical issues for seismic design of base-isolated structures. To calculate the earthquake responses for such non-symmetric and non-classical damping linear systems and to implement the earthquake resistant design codes, a modified complex mode superposition design response spectrum method is put forward. Furthermore, to do parameter optimization for base-isolation structures, a graphical approach is proposed by analyzing the relationship between the base shear ratio of a seismic base-isolation floor to non-seismic base-isolation one and frequency ratio-damping ratio, as well as the relationship between the seismic base-isolation floor displacement and frequency ratio-damping ratio. In addition, the influences of mode number and site classification on the seismic base-isolation structure and corresponding optimum parameters are investigated. It is demonstrated that the modified complex mode superposition design response spectrum method is more precise and more convenient to engineering applications for utilizing the damping reduction factors and the design response spectrum, and the proposed graphical approach for parameter optimization of seismic base-isolation structures is compendious and feasible.

The engineering merit of the "Effective Period" of bilinear isolation systems

This paper examines whether the "effective period" of bilinear isolation systems, as defined invariably in most current design codes, expresses in reality the period of vibration that appears in the horizontal axis of the design response spectrum. Starting with the free vibration response, the study proceeds with a comprehensive parametric analysis of the forced vibration response of a wide collection of bilinear isolation systems subjected to pulse and seismic excitations. The study employs Fourier and Wavelet analysis together with a powerful time domain identification method for linear systems known as the Prediction Error Method. When the response history of the bilinear system exhibits a coherent oscillatory trace with a narrow frequency band as in the case of free vibration or forced vibration response from most pulselike excitations, the paper shows that the "effective period" = <TEX>$T_{eff}$</TEX> of the bilinear isolation system is a dependable estimate of its vibration period; nevertheless, the period associated with the second slope of the bilinear system = <TEX>$T_2$</TEX> is an even better approximation regardless the value of the dimensionless strength,<TEX>$Q/(K_2u_y)=1/{\alpha}-1$</TEX>, of the system. As the frequency content of the excitation widens and the intensity of the acceleration response history fluctuates more randomly, the paper reveals that the computed vibration period of the systems exhibits appreciably scattering from the computed mean value. This suggests that for several earthquake excitations the mild nonlinearities of the bilinear isolation system dominate the response and the expectation of the design codes to identify a "linear" vibration period has a marginal engineering merit.

Seismic microzonation for the northeast Texcoco lake area, Mexico

The Texcoco Lake area is currently undergoing a rapid urbanization. This has required designing and building strategic infrastructure. However, this zone has been poorly explored, and thus, a building code design response spectrum is not available. This paper presents the exploration and laboratory works, as well as the analytical studies conducted for obtaining a design response spectrum for the northeast Texcoco Lake area. From geotechnical information gathered previously for other projects in the studied zone, and applying the ordinary kriging technique, the necessary dynamic soil parameters for site response analysis were determined. A total of 2501 virtual soil profiles were generated. The seismic environment was characterized throughout a uniform hazard spectrum obtained in a nearby rock outcrop. Probabilistic site response analyses were performed using the uniform hazard spectrum computed in rock as input motion for all 2501 virtual profiles. Finally, a design response spectrum for the studied area was proposed.

Study on the Dynamic Behavior of Semi-Rigid Frames

The dynamic behavior of semi-rigid concrete filled steel tube frames is different from that of their rigid counterparts. ANSYS was employed to model ten-story concrete filled steel tube frames with three different connection types（ rigid, semi-rigid and flexible）. Natural period, inter-story drifts and total drifts of the frames subjected to design response spectra excitation were analyzed. Time-history analyses when the frames subjected to two different earthquakes were studied. It seems that connection flexibility noticeably increases the natural periods of the lower modes, however, its effect on higher modes is negligible. The use of rigid frames may not be the best option in seismic region. The seismic design suggestions of the frames were proposed.

Comparative Study of Codes for Seismic Design of Structures

Abstract This paper presents a comparative evaluation among some international, European and American, seismic design standards. The study considers the criteria for the analysis of conventional (residential and commercial) buildings. The study is focused on some critical topics: definition of the recurrence periods for establishing the seismic input; definition of the seismic zonation and shape of the design response spectra; consideration of local soil conditions; definition of the seismic force-resisting systems and respective response modification coefficients; definition of the allowable procedures for the seismic analysis. A model for a standard reinforced concrete building (“Model Building”) has been developed to permit the comparison among codes. This building has been modelled with two different computer programs, SAP2000 and SOFiSTiK and subjected to seismic input according to the several seismic codes. The obtained results compared are leading to some important conclusions.

Application of the performance-goal based approach for establishing the SSE site specific response spectrum for new nuclear power plants in South Africa

Nuclear installation license holders in South Africa have become increasingly interested in the performance-goal based approach defined in the American Society of Civil Engineering Standard ASCE/SEI 43-05 for establishing the safe shutdown earthquake (SSE) site specific design response spectrum (SSRS) for new nuclear power plants. This approach has been adopted by the U.S. Nuclear Regulatory Commission (NRC) and has now been followed at more than 20 sites in that country. Quantitative performance goals are required when establishing seismic design basis parameters using the performance-goal based approach. However, the quantitative performance goals recommended in ASCE/SEI 43-05 were established based on country-specific operating experience and seismic probabilistic risk assessment (SPRA) applications conducted for existing plants designed and operated to meet specific safety criteria, set by a specific regulatory body. Whilst ASCE/SEI 43-05 provides enough flexibility for the selection of other user-specified quantitative performance goals, there is no guidance on how quantitative performance goals should be established in the absence of extensive operational experience accompanied by data derived from rigorous SPRA applications. This paper presents two practical approaches that can be used to provide a technical basis and to demonstrate the derivation of quantitative values of target performance goals when no data related to past and present operational experience exist to justify technical specifications.

Comparative study of codes for the seismic design of structures

A general evaluation of some points of the South American seismic codes is presented herein, comparing them among themselves and with the American Standard ASCE/SEI 7/10 and with the European Standard Eurocode 8. The study is focused in design criteria for buildings. The Western border of South America is one of the most seismically active regions of the World. It corresponds to the confluence of the South American and Nazca plates. This region corresponds roughly to the vicinity of the Andes Mountains. This seismicity diminishes in the direction of the comparatively seismically quieter Eastern South American areas. The South American countries located in its Western Border possess standards for seismic design since some decades ago, being the Brazilian Standard for seismic design only recently published. This study is focused in some critical topics: definition of the recurrence periods for establishing the seismic input; definition of the seismic zonation and design ground motion values; definition of the shape of the design response spectra; consideration of soil amplification, soil liquefaction and soil-structure interaction; classification of the structures in different importance levels; definition of the seismic force-resisting systems and respective response modification coefficients; consideration of structural irregularities and definition of the allowable procedures for the seismic analyses. A simple building structure is analyzed considering the criteria of the several standards and obtained results are compared.

Edificios de concreto reforzado siguiendo la NSR-10 vs sismo de Quetame registrado en Bogotá D.C.

Se presenta el análisis no lineal dinámico en tres direcciones de 6 edificios de concreto reforzado de 5, 12 y 20 pisos, diseñados con la NSR-10 yla zonificación de respuesta sísmica de Bogotá del año 2010. Estos 6 edificios, con planta típica idéntica, fueron sometidos a 78 señales sísmicas del sismo de Quetame (año 2008) registradas por 26 estaciones de la red de acelerógrafos de Bogotá (RAB). Para el diseño de los edificios se utilizaron los espectros de respuesta de aceleración absoluta para las zonas: «Piedemonte-B» y «Lacustre-500» de la microzonificación sísmica de Bogotá. Posteriormente, se calcularon las rótulas plásticas para cada elemento estructural de los 6 edificios, y en el caso de las columnas, también sus diagramas de interacción. Luego, las edificaciones tridimensionales fueron sometidas simultáneamente a los registros contra el tiempo norte-sur, este-oeste y vertical. Para cada edificio sometido a las señales de cada estación, se obtuvieron las demandas de deriva, los desplazamientosde la cubierta, el cortante en la base y los niveles de daño según estimadores internacionalmente aceptados. Finalmente, se generaron mapas de demandas de deriva y aceleración por edificio en la ciudad de Bogotá D.C. Los resultados sugieren que los edificios diseñados con la amenaza sísmica dela nueva microzonificación de Bogotá y con las estipulaciones de la NSR-10, presentarán daños excesivos asociados a estados límites como son los de «seguridadde vidas» para un sismo de baja magnitud como fue el de Quetame, que equivalió a solo una fracción de aquel que corresponde al comportamiento real bajo el escenario de diseño.

Application of Differential Evolution Algorithm for Calibrating Design Seismic Response Spectra

Differential evolution (DE) algorithm is a heuristic approach that has a great ability to solve complex optimization and converges faster and with more certainty than many other acclaimed global optimization methods. In this paper, DE algorithm is applied to calibrate design seismic response spectra, the basic idea is that design response spectra and calculated response spectra are defined as objective function of characteristic parameters, the first turning point, the second turning point (characteristic period), the platform height and the attenuation index, of design response spectra, and the characteristic parameters are obtained by minimizing the objective function. Three pieces of the calculated response spectra for one real are calibrated as an application example. The obtained results demonstrate the effectiveness and efficiency of the proposed method.

October 23, 2011 Turkey/Van–Ercis earthquake: structural damages in the residential buildings

On October 23, 2011, a magnitude of Mw 7.2 earthquake struck the Van province in eastern Turkey which caused approximately 600 life loss and 4,000 injured people. Although the recorded peak ground accelerations were relatively low (0.15–0.2 g) compared with that of other recent destructive Turkish earthquakes and the code-based design response spectrum, a large number of reinforced concrete buildings with 4–6 stories and non-engineered masonry buildings were either heavily damaged or collapsed in the region. Based on the post-earthquake technical inspections, the goal of this paper is to introduce major reasons for structural damages in the disaster area and to discuss these failures along with the approaches given in the design code which is renewed after August 17, 1999 Marmara Earthquake. Some remarkable lessons learned from earthquake-induced failures and damages specific to building construction techniques are presented in this paper.

Acceptable Seismic-Induced Risks per U.S. Department of Energy Standards at Nuclear Facilities

This paper investigates the potential impacts of the transition to the U.S. Department of Energy (DOE) Order 420.1B requirements and the criteria promulgated by the new DOE-STD-1189 on the current practice for seismic design of structures, systems, and components (SSCs). Addressed in the review is the modification of the prescribed methodology provided in ANSI/ANS-2.6-2004 by the new DOE standard. The new ANSI/ANS standards provide criteria and guidance in selecting the seismic design category (SDC) and the limit state (LS) for the SSCs that are important to safety. An unmitigated consequence analysis considering the uncertainties in estimating failure and the safety consequences of the failure may be performed to determine the SDC and the LS, which then are used to establish the level of peak ground acceleration and design response spectra. The new DOE-STD-1189 modifies the prescribed methodology provided in ANSI/ANS-2.6-2004 for calculation of unmitigated radiological dose consequence. Unmitigated consequence analysis is a procedure that has been used by the DOE for the purpose of incorporating safety in the design and operation of its nuclear facilities and is also used in 10 CFR 70, the U.S. Nuclear Regulatory Commission regulation applicable to fuel cycle facilities, and the associated Standard Review Plan (NUREG-1520). This paper identifies the iterative DOE double-pronged approach to seismic design, and a simplified example demonstrates the unmitigated seismic hazard consequence analysis.

Development of probabilistic seismic site coefficients of Korea

It is current practice to use seismic site coefficients that are derived deterministically with ground motion parameter(s) from probabilistically derived seismic hazard maps. Even though there is an inherent incompatibility between two approaches, they are linked to develop the design response spectrum. This paper applied a novel probabilistic seismic hazard analysis procedure that integrates the seismic site effects and developed probabilistic site coefficients that are compatible with seismic hazard maps of Korea. The analysis method accounted for the uncertainties and randomness of the ground properties by randomly selecting the site profiles and dynamic curves from the measured database. The calculated coefficients were compared to those recommended in the Korean seismic design guideline and another set of site coefficients developed in Korea. The comparisons indicate that the site coefficients recommended in the current design guideline are not suitable for soil profiles of Korea. Further comparison with another set of site coefficients demonstrate the differences between the probabilistically and deterministically derived values.