This paper examines the ice cover effects on the seismic response of concrete gravity dam-reservoir-foundation interaction systems subjected to a horizontal earthquake ground motion. ANSYS program is used for finite element modeling and analyzing the ice-dam-reservoir-foundation interaction system. The ice-dam-reservoir interaction system is considered by using the Lagrangian (displacementbased) fluid and solid-quadrilateral-isoparametric finite elements. The Sariyar concrete gravity dam in Turkey is selected as a numerical application. The east-west component of Erzincan earthquake, which occurred on 13 March 1992 in Erzincan, Turkey, is selected for the earthquake analysis of the dam. Dynamic analyses of the dam-reservoir-foundation interaction system are performed with and without ice cover separately. Parametric studies are done to show the effects of the variation of the length, thickness, elasticity modulus and density of the ice-cover on the seismic response of the dam. It is observed that the variations of the length, thickness, and elasticity modulus of the ice-cover influence the displacements and stresses of the coupled system considerably. Also, the variation of the density of the ice-cover cannot produce important effects on the seismic response of the dam.
Post-tensioned balanced cantilever reinforced concrete (RC) bridges allow the economic spanning of wide spans using fewer columns than in more traditional bridges. More and more post-tensioned balanced cantilever bridges are constructed every year all round the world. The aim of this study was to investigate numerically the effects of near-fault vertical ground motions (VGMs) on the seismic behaviour of segmentally constructed, balanced cantilever RC bridges. Two long bridges constructed in Artvin, Turkey – the three-span Budan Bridge and the two-span Sengan Bridge – were selected for the application. Three-dimensional finite-element models (FEMs) of the bridges were created to obtain their dynamic characteristics such as natural frequencies and mode shapes numerically. The frequencies calculated from the FEMs of the bridges were then verified using experimental frequencies measured from ambient vibration tests. Acceleration records of near-fault earthquakes (1992 Erzincan (M = 6·69), 1999 Kocaeli (M = 7·51), 1999 Düzce (M = 7·14) and 1989 Loma Prieta (M = 6·93)) were selected for the seismic analyses. The seismic behaviours of the verified FEMs of the bridges with two and three spans were determined by considering horizontal, vertical and combined horizontal and vertical components of the earthquakes. It was found that near-fault VGM significantly affects the seismic response of segmentally constructed, balanced cantilever bridges.
This paper discusses the application of system identification of a highway bridge using finite-element method and ambient-vibration testing. The posttensioned Gülburnu Highway Bridge located on the Giresun-Espiye state highway was selected as a case study. A finite-element model of the bridge was developed using SAP2000 software, and dynamic characteristics were obtained analytically. During the test, sources of ambient excitations were provided by the traffic effects over the bridge. Ambient-vibration tests were applied to the bridge to identify dynamic characteristics. The selection of measurement time, frequency span, and effective mode number was considered from similar studies in the literature. Two output-only system identification methods, enhanced frequency domain decomposition and stochastic subspace identification, were used to estimate the dynamic characteristics of the bridge experimentally. The accuracy and efficiency of both methods were investigated and compared with finite-element results. Results suggest that ambient-vibration measurements are sufficient to identify structural modes with a low range of natural frequencies. In addition, the dynamic characteristics obtained from the finite-element model of the bridge have a good correlation with experimental frequencies and mode shapes.
Cable-stayed bridges have been constructed with different type of towers (pylons) in the World, namely H-shaped, A-shaped, inverted Y-shaped, single column, diamond-shaped. More than half of the cable-stayed bridges utilised the towers with inclined legs. The dynamic response of inclined tower legs can be extremely complicated during earthquakes. Real earthquakes provide an excellent opportunity to gain insight into the performance of the towers. The present paper focuses on the real dynamic responses of inverted Y-shaped towers in long span cable-stayed bridges by using monitoring data recorded during moderate earthquakes. Nissibi cable-stayed bridge with two inverted Y-shaped towers constructed in Adıyaman, Turkey is selected for the application. Samsat (Adıyaman) earthquake with magnitude 5.5 (Mw) occurred near the bridge site. The dynamic responses of the bridge towers during the earthquake have been recorded using 3 D accelerometers. Vertical and horizontal spatial variations of the acceleration responses recorded during the earthquake at the foundation, deck and top levels of the two towers in longitudinal, transverse and vertical directions are evaluated and compared with each other. Significantly acceleration amplifications along the height of the towers and arrival time delays between the tower foundations are observed on the selected cable-stayed bridge.
Using experimental methods, this study presents the estimation of the dynamic and static (secant) elasticity modules of a prototype arch dam. These experimental methods are ambient vibration tests, uniaxial compression tests, and ultrasonic velocity tests. Implementation of the methods on a prototypical arch dam–reservoir–foundation model of the dam, constructed under laboratory conditions, allows estimation of the elasticity modules. Random impact loads excite the arch dam during ambient vibration testing, which creates response signals for measurement. Commercially available software transfers the signals, and processing those signals allows estimation of the experimental natural frequencies of the arch dam. Analysis of a three-dimensional (3D) finite element model (FEM) of the arch dam determines natural frequencies. The estimation of the elasticity modules of the arch dam arises from a comparison of the experimental and analytical frequencies. The uniaxial compression tests use several specimens of the fresh and hardened concrete of the prototype model, and those tests provide the compressive strengths and stress-strain relationships. The ultrasonic velocity tests apply several velocity measurements to the arch dam and foundation, resulting in estimation of the elasticity modulus from empirical equations related to concrete mix design, compressive strength, and velocity values. This study discusses the difficulties of the determination of the elasticity modulus and suggests that ambient vibration testing and the finite element method are useful for overcoming these difficulties.
Seismic response of concrete-faced rockfill (CFR) dams subjected to asynchronous base excitation is determined by considering dam–reservoir interaction. The equations of motion of the coupled system are obtained using the Lagrangian approach, and the surface sloshing motion is included in the finite element formulation. Torul dam constructed in the city, Gumushane, Turkey, is selected as a numerical example, and its material properties are considered in the analysis. The dam–reservoir interaction system is modelled using the Lagrangian (displacement-based) fluid and solid-quadrilateral-isoparametric finite elements. The east–west component of Erzincan earthquake, which occurred on 13 March 1992, recorded near the region of the dam is used as a ground motion. Propagation velocities of the seismic wave are chosen as 1000 m/s, 3000 m/s, and infinite. Stresses are calculated for empty and full reservoir cases and compared with each other.Key words: concrete-faced rockfill dam, Lagrangian approach, dam–reservoir interaction, finite element method, earthquake.
Bu calismada, Malatya-Elazig karayolu uzerinde bulunan Komurhan Koprusu’nun analitik ve deneysel olarak elde edilen dinamik karakteristiklerinin karsilastirilmasi ve koprunun mevcut durumunu yansitan gercek sonlu eleman modelinin olusturulmasi amaclanmistir. Koprunun sonlu eleman modeli SAP2000 programi kullanilarak olusturulmus ve dinamik karakteristikler analitik olarak elde edilmistir. Operayonel Modal Analiz yontemi kullanilarak koprunun dinamik karakteristikleri deneysel olcumlere dayali olarak belirlenmistir. Deneysel olcumler sirasinda titresim hareketi olarak tasit yukunden yararlanilmistir. Olcum verilerinin karsilastirilabilmesi icin hem kutu kesit icerisinden hem de tabliye uzerinden olcumler alinmistir. Olcum suresi, frekans araligi ve etkin mod sayisi daha once yapilmis benzer olcumlerden faydalanilarak belirlenmistir. Olcumlerin degerlendirilip dinamik karakteristiklerin elde edilmesinde frekans ortaminda Piklerin Secilmesi yontemi kullanilmistir. Calisma sonunda, analitik ve deneysel olarak elde edilen dinamik karakteristikler birbirleriyle karsilastirilmis, malzeme ozellikleri ve sinir sartlarindaki degisimler dikkate alinarak koprunun mevcut durumunu yansitan gercek sonlu eleman modeli elde edilmistir.
The structural performance evaluation is presented of 90 reinforced concrete (RC) buildings that collapsed during the October 23 (Erciş) and November 9 (Edremit), 2011, earthquakes in Van, Turkey. A total of 35,000 buildings are damaged or collapsed in the city center and surrounding villages after the Erciş and Edremit earthquakes. Almost all the RC buildings are affected in the region. To evaluate the structural performance of the collapsed buildings, the buildings are evaluated according to structural system properties, specification properties, material properties (concrete and reinforcement steel properties), and soil properties. The results showed that a large proportion of nonengineering RC buildings completely collapsed or were damaged heavily. Most of the RC buildings in the affected area are not designed and constructed in accordance with Turkish code. Also, it was found that 26% of the buildings do not have a building license, 66% of the buildings' ground floors were used as a commercial or retail space, 36% of the buildings lacked any structural design, 57% of the buildings were not constructed in accordance with their structural drawings, 74% of the structural drawings did not have any detail drawings and beam/column confined zones, the concrete used in many buildings did not have adequate compressive strength, aggregate dimensions were larger than the maximum aggregate diameter for concrete, 60% of the buildings were constructed with unribbed reinforcement steel, and the majority of the buildings (85%) did not have any geotechnical report.
The structural assessment of historic timber mosques is a challenging process with many uncertainties such as strength and stiffness of structural members, joints and boundary conditions. The analytical models of timber mosques must be calibrated using experimental dynamic characteristics for reliable structural evaluation and accurate interventions. This paper aims to determine the experimental dynamic characteristics such as frequency, mode shapes and damping ratios as well as developing empirical frequency formulas for historical timber mosques. Seven historical timber mosques having different geometrical dimensions in the East Karadeniz Region in Turkey are selected for this purpose. Experimental dynamic characteristics of the selected mosques are determined by using Ambient Vibration Testing and the Enhanced Frequency Domain Decomposition (EFDD) method. The experimental dynamic behaviors of the selected mosques are initially compared using the obtained natural frequencies, mode shapes and damping ratios. Then, empirical natural frequency formulas for the first three modes based on mosque geometrical dimensions have been developed by regression analysis. The proposed frequency formulas were observed to be very consistent with the results measured.
Abstract This paper describes a Turkish style reinforced concrete minaret, its finite element model, modal testing, finite element model updating and earthquake behaviour, before and after model updating. The minaret of a mosque located in Trabzon, Turkey is selected as an application. A three‐dimensional (3D) model of the minaret and its modal analysis is performed to obtain analytical frequencies and mode shapes using ANSYS finite element program. The ambient vibration tests are conducted on the minaret under natural excitations such as wind effects and human movement. The output‐only modal parameter identification is carried out by Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods in Operational Modal Analysis software and in doing so, dynamic characteristics (natural frequencies, mode shapes and damping ratios) are determined. A 3D finite element model of the minaret is updated to minimize the differences between analytical and experimental modal properties by changing some uncertain modelling parameters such as material properties and boundary conditions. The earthquake behaviour of the minaret is investigated using 1992 Erzincan earthquake before and after finite element model updating. Maximum differences in the natural frequencies are reduced from 21% to 8%, and good agreement is found between analytical and experimental natural frequencies. In addition to this, it is realized that finite element model updating is effective on the earthquake behaviour of the minaret. Copyright © 2008 John Wiley & Sons, Ltd.
Historical masonry stone mosques with timber truss roofs were widely constructed all over the world. Due to the complex structural behaviors of this type of building, it is difficult to determine natural frequencies during the seismic safety evaluations numerically. The article aims to develop simplified natural frequency formulas based on ambient vibrations for the historical masonry stone mosques with timber truss roofs. Fourteen masonry stone mosques with timber truss roofs built in the Eastern Black Sea Region of Turkey are selected for the study. Experimental natural frequencies, mode shapes and damping ratios of the selected mosques under ambient vibrations are determined using the Operational Modal Analyses. Ambient vibration-based simplified natural frequency formulas based on the geometrical dimensions for the masonry stone mosques with timber truss roofs are obtained by using the statistical regression analysis. The proposed formulas for the first three frequencies are verified with the control data.
