Near-field earthquakes and their implications on seismic design codes

Ph.D. - Doctoral Progra

A Probability Based Seismic Loss Model Concerning The Common Concrete Buildings İn Turkey

Kapsam Bu çalışmada Türkiye'deki betonarme yapıların karakteristik özellikleri ve bu binaları temsil eden modeller ile deprem davranışı incelenecektir. Ayrıca yer hareketi seçme ve bu hareketlere ait genliklerin ölçeklendirilmesine (ground-motion scaling) dair yöntemler ele alınacak, yapısal davranımdaki saçılımın (dispersiyon) azaltılmasını hedefleyen bir yöntem geliştirilecektir b. Yöntem Türkiye'deki betonarme yapı stoğunu temsil eden veritabanları incelenecek ve elde edilen sonuçlar ışığında 3 boyutlu analitik modeller tasarlanacaktır. Daha sonra gerçek yer hareketi kayıtlarını seçme ve ölçeklendirme hususu incelenecek, geliştirilecek yöntem ile yer hareketi değişkenliğine bağlı yapısal davranımdaki belirsizlik azaltılmaya çalışılacaktır. Bu yöntem öncelikle tek serbestlik dereceli sistemler ile analiz edilecek, böylece yapısal özelliklere bağlı karmaşık faktörler sonuçlara etki etmeyecektir. Çalışmanın son kısmında ise daha önce elde edilen 3 boyutlu modellerden yapı davranışını temsil eden çerçeveler seçilecek, çok serbestlik dereceli bu sistemlerin doğrusal olmayan zaman tanım alanı analizleri gerçekleştirilecektir. c. Beklenen Sonuç Bu çalışmada yer hareketi genliklerinin ölçeklendirilmesi için kullanılabilecek bir yöntem önerilmesi hedeflenmektedir. Önerilecek metot yer hareketi değişkenliğine bağlı saçılımı düşürürken, deprem olayının jeofiziksel temellerini de muhafaza etmeyi amaçlayacaktır. Ayrıca Türkiye'deki betonarme yapı stoklarının istatistiksel sonuçları elde edilecek, bunları temsil eden 3 boyutlu analitik modellerin ölçeklendirilmiş gerçek yer hareketi kayıtları ile analizleri yapılacaktır. Böylece Türkiye'deki binaları deprem davranışı ve yer hareketi değişkenliğinin bu davranışa etkisi incelenmiş olacaktır

Assessment of Point-Source Stochastic Simulations Using Recently Derived Ground-Motion Prediction Equations

The simplicity of the point-source stochastic simulation method makes it one of the most appealing tools for the quantification of ground motions for seismic hazard related studies. In this article, we scrutinize the limitations of this technique in terms of fundamental geophysical model parameters. To achieve this objective, we use the estimations of recent Next Generation Attenuation (NGA) and European empirical ground-motion models that are based on global strong-motion databases. The generated synthetics account for the local nonlinear soil effects through 1D site-response analysis. Thus, apart from our major objective, we also derive a probability-based soil-profile model that considers the random variation of shear-wave slowness as a function of depth. We discuss the critical variations of dynamic material properties, such as shear modulus and material damping, during the site-response analysis. We generate a total of 6000 synthetic records with a magnitude range of 5: 0 <= M-w <= 7: 5 and source-to-site distances (d) less than 100 km. The site class of the synthetics is defined by the average shear-wave velocity of the upper 30 m soil profile (V-S30), with V-S30 values ranging between 180 m/sec and 1500 m/sec. Our analysis indicates that synthetics that are generated using R-hyp (hypocentral distance) as the reference distance metric may fail to describe compatible variations of ground-motion demands with respect to global ground-motion prediction equations (GMPEs), particularly for small-magnitude and short-distance recordings. The performance of synthetics for these latter cases can be improved if one uses R-rup (shortest distance from the fault rupture). Our inspections on the frequency-domain behavior of synthetics reveal that they can be reliably used in spectral calculations for periods up to 20 sec. Within the context of this article, we also present a simple baseline correction method to obtain reliable ground displacements from the synthetics that are subjected to site-response analysis

Direct use of PGV for estimating peak nonlinear oscillator displacements

A predictive model is presented for estimating the peak inelastic oscillator displacements (S-d,S-ie) from peak ground velocity (PGV). The proposed model accounts for the variation of S-d,S-ie for bilinear hysteretic behavior under constant ductility (mu) and normalized lateral strength ratio (R) associated with postyield stiffness ratios of alpha = 0 and 5%. The regression coefficients are based on a ground-motion database that contains dense-to-stiff soil site recordings at distances of up to 30 km from the causative fault. The moment magnitude (M) range of the database is 5.2 <= M <= 7.6 and the ground motions do not exhibit pulse-dominant signals. Confined to the limitations imposed by the ground-motion database, the model can estimate S-d,S-ie by employing the PGV predictions obtained from the attenuation relationships (ground-motion prediction equations). In this way, the influence of important seismological parameters can be incorporated to the variation of S-d,S-ie in a fairly rationale manner. This feature of the predictive model advocates its implementation in the probabilistic seismic hazard analysis that employs scalar ground-motion intensity indices. Various case studies are presented to show the consistent estimations of S-d,S-ie by the proposed model. The error propagation in the S-d,S-ie estimations is also discussed when the proposed model is associated with attenuation relationships. Copyright (C) 2008 John Wiley & Sons, Ltd

Near-fault ground motions: Demand and structural capacity requirements

The improvement of structural capacity against large displacement demand of near-fault ground motions has been the subject of research for the last decade. Parallel to the developments in performance-based seismic design (PBSD) this issue has attracted researcher interest further, as assessment of structural displacement capacity has become one of the main concerns for the procedures employed in this new design concept. This Chapter focuses on the near-fault ground motion demand and corresponding structural capacity requirements. We have used soil site, near-fault records from various M > 6.5 events including the 1999 Turkey and Taiwan earthquakes. The spectral quantities were computed through an attenuation relationship that is based on these near-fault ground motion records. We employ these spectral quantities to calculate the distance and magnitude dependent inter-story drift demand limits for frame-type structures. We compare our findings with the Uniform Building Code provisions and other attenuation relationships used in defining the NEHRP spectrum shapes

Assessment of improved nonlinear static procedures in FEMA-440

Nonlinear static procedures (NSPs) presented in the FEMA-440 document are evaluated for nondegrading three- to nine-story reinforced concrete moment-resisting frame systems. Evaluations are based on peak single-degree-of-freedom displacement, peak roof, and interstory drifts estimations. A total of 78 soil site records and 24 buildings with fundamental periods varying between 0.3 s-1.3 s are used in 2,832 linear and nonlinear response-history analyses to derive the descriptive statistics. The moment magnitude of the ground motions varies between 5.7 and 7.6. All records are within 23 km of the causative fault representing near-fault ground motions with and without pulse signals. The statistics presented suggest that lateral loading patterns used in pushover analysis to idealize the building systems play a role in the accuracy of NSPs investigated. Both procedures yield fairly good deformation demand estimations on the median. Displacement coefficient method (DCM) tends to overestimate the global deformation demands with respect to the capacity spectrum method (CSM). The conservative deformation demand estimations of DCM are correlated with the normalized lateral strength ratio, R. The CSM tends to overestimate the deformation demands for the increasing displacement ductility, mu

Nonlinear drift demands on moment-resisting stiff frames

Drift demands for stiff moment-resisting frames are investigated. A total of 8 regular frame models with 3- to 9-stories are subjected to 40 soil site records. The moment. magnitude and source-to-site distance of the ground motion data set varies between 5.7 <= M <= 7.6 and 2.5 km <= d <= 23 km, respectively. The ground motion data set is divided into 2 equal bins to represent different seismic hazard levels. The frames conforrn to the seismic code provisions for the median design spectra of the ground motion bins and they are classified as stiff frames according to their fundamental periods. Nonlinear response history analyses are conducted to present the height-wise variation of maximum lateral displacement profiles and story drift demands for the frame models considered. The accuracy in estimating the maximum roof and interstory drifts is investigated through simplified procedures that use the first-mode approach. The statistics presented show that the maximum interstory drift is strongly correlated with the building configuration and ground-motion features. Use of first-mode approach associated with building elastic dynamic properties generally yields conservative maximum roof drift estimations. A novel approach is also evaluated that can reveal preliminary information about the nonlinear maximum interstory drift if the concern is not the exact location of this deformation demand

A New Procedure for Selecting and Ranking Ground-Motion Prediction Equations (GMPEs): The Euclidean Distance-Based Ranking (EDR) Method

We introduce a procedure for selecting and ranking of ground-motion prediction equations (GMPEs) that can be useful for regional or site-specific probabilistic seismic hazard assessment (PSHA). The methodology is called Euclidean distance-based ranking (EDR) as it modifies the Euclidean distance (DE) concept for ranking of GMPEs under a given set of observed data. DE is similar to the residual analysis concept; its modified form, as discussed in this paper, can efficiently serve for ranking the candidate GMPEs. The proposed procedure separately considers ground-motion uncertainty (i.e., aleatory variability addressed by the standard deviation) and the bias between the observed data and median estimations of candidate GMPEs (i.e., model bias). Indices computed from the consideration of aleatory variability and model bias or their combination can rank GMPEs to design GMPE logic trees that can serve for site-specific or regional PSHA studies. We discussed these features through a case study and ranked a suite of GMPEs under a specific ground-motion database. The case study indicated that separate consideration of ground-motion uncertainty (aleatory variability) and model bias or their combination can change the ranking of GMPEs, which also showed that the ground-motion models having simpler functional forms generally rank at the top of the list. We believe that the proposed method can be a useful tool to improve the decision-making process while identifying the most proper GMPEs according to the specific objectives of PSHA

Scaling and Selection of Ground Motion Records for Nonlinear Response History Analysis of Structures

Accurate estimation of structural response for a given target hazard level requires a suitable set of ground-motion records that represents a pre-defined scenario event. With the aim of assessing the seismic performance of structural systems, this study presents a ground motion selection and scaling methodology. Given a relatively larger ground-motion database, the method uses the differences between individual records and corresponding estimations of a ground-motion prediction equation in order to determine the optimum subset of recordings. This way, the procedure provides a group of modified records whose median elastic spectral ordinate matches with the target intensity level without excessively manipulating the inherent aleatory variability in the selected recordings. Considering the sensitivity of overall structural response to the nonlinear behavior, the procedure approximately estimates the median and dispersion of inelastic structural response. The case study suggests that, the methodology can be a useful tool for building performance assessment studies