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.
With the recent advances in computer technology and digital simulation software, it is now possible to rapidly and accurately build computer models for complex linear and nonlinear dynamic systems. MATLAB is a unique system that can be used for structural and earthquake engineering problems. This study presents MATLAB tools developed for numerical process of all steps of dynamic vibration test of structures. The functions of the tools are processing the signals obtained from forced and ambient vibration tests of structures, determining the dynamic characteristics of structural systems, and automatically updating the analytical finite element (FE) models. The software group is composed of three programs named as SignalCAD, ModalCAD, and FemUP. The SignalCAD program is developed for processing raw measured data obtained from forced and ambient vibration tests of engineering structures. The ModalCAD program is developed for dynamic characteristic identification and validation procedure. The peak picking method, complex exponential method, and polyreference time domain method are used for modal identification process. The FemUP program is developed for automatically updating the numerical models of structures compared to modal testing results. Each program has a unique graphical user interface and is designed as user friendly. The possibilities of the programs are demonstrated with the model vibration test of a steel cantilever beam. The obtained results are compared to the analytical model, and the FE model is automatically updated, whereas the experimental model is considered as the reference model. Finally, it is seen that MATLAB can be used as a scientific programming platform in all vibration test and modal analysis applications.
The effects of restoration on the experimental dynamic characteristics of historical masonry Molla Siyah Mosque in Trabzon, Turkey, are investigated in this paper. Firstly, the initial situation and the implemented restoration works of the mosque are mentioned in detail. Then, the experimental dynamic behaviors of the mosque before and after the restoration are obtained by using the Ambient Vibration Tests. High sensitivity seismic accelerometers with cables are used during the tests. The collected signals are evaluated by Enhanced Frequency Domain Decomposition Technique, and experimental natural frequencies, mode shapes and damping ratios of the mosque are determined for the initial and restoration cases. The obtained results are compared with each other and restoration effects on the dynamic behavior of the mosque are discussed in detail
Abstract The effects of the sediment on the earthquake response of concrete gravity dams subjected to horizontal and vertical asynchronous ground motion are investigated including dam-reservoir-sediment-foundation interaction in this paper. Dam-reservoir-sediment-foundation interaction is modeled by the finite element method. The equations of motion of the dam-reservoir-sediment-foundation system are determined using the Lagrangian approach. Solutions are obtained for dam-reservoir-foundation and dam-reservoir-sediment-foundation systems separately. Parametric studies were conducted in order to investigate the effects of the variation of Young's modulus and thickness of the sediment on the dam response. Seismic wave velocities of 250, 3000 m/s and infinite are used in calculations. It is observed that stresses near the dam crest decrease considerably when the sediment is included in the analyses. The variation of the values of Young's modulus and thickness of the sediment influences the stress component slightly. Keywords: Concrete gravity damsedimentfluid-structure interactionearthquakesasynchronous ground motionseismic wave velocityfinite element methodLagrangian approach
The focus of the present paper is to determine the effect of compressibility of the fluid on the stochastic dynamic response of fluidstructure systems by using Lagrangian approach. Variable-numbernodes two-dimensional fluid finite elements were programmed in Fortran language by the authors and incorporated into a generalpurpose computer program for stochastic dynamic analysis of solid systems, STOCAL. A two dimensional fluid-structure interaction problem is selected for numerical example. The influence of the compressibility of the fluid is investigated by increasing the value of the bulk modulus of the fluid. Results obtained from Lagrangian approach are compared with each other and those of the Westergaard approach.
There are several idealizations in numerical analysis of structures. In the joints and supports, which is usually assumed to be pinned or rigid, semi-rigid connection should be considered to obtain more realistic, reliable and also economical results. In this study, rotational spring stiffness-connection ratio relation is clearly explained and revealed. A finite element program SEMIFEM is developed in FORTRAN language for the numerical analysis. This program provides to define semi-rigid connections in terms of rotational spring stiffness or connection ratio simultaneously. In the numerical applications, rotational spring stiffness - connection percentage relation of the semi-rigid connected structural members is submitted. Semi-rigid connections are considered in column-to-foundation connection of a portal frame, beam-to-column connection of a prefabricated structure, steel brace connection to reinforced concrete (RC) frame of a steel X-braced RC frame and truss member connection to joint of a steel truss system. The variation of moment, shear force, axial force, displacement and stress is investigated in a selected axis of the structures. Numerical examples are performed with respect to connection percentage of the related structural members by using finite element method. According to finite element analysis results, the degree of the semi-rigid connection is important as much as its existence in the design phase. This study reveals that the effect of semi-rigid connections on structural systems shows different variations from structure to structure.
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.
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.
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 updated finite element model of K<TEX>$\ddot{o}$</TEX>m<TEX>$\ddot{u}$</TEX>rhan Highway Bridge on the Firat River located on the <TEX>$51^{st}$</TEX> km of Elazi<TEX>$\breve{g}$</TEX>-Malatya highway is obtained by using analytical and experimental results. The 2D and 3D finite element model of the bridge is created by using SAP2000 structural analyses software, and the dynamic characteristics of the bridge are determined analytically. The experimental measurements are carried out by Operational Modal Analysis Method under traffic induced vibrations and the dynamic characteristics are obtained experimentally. The vibration data are gathered from the both box girder and the deck of the bridge, separately. Due to the expansion joint in the middle of the bridge, special measurement points are selected when experimental test setups constitute. Measurement duration, frequency span and effective mode number are determined by considering similar studies in literature. The Peak Picking method in the frequency domain is used in the modal identification. At the end of the study, analytical and experimental dynamic characteristic are compared with each other and the finite element model of the bridge is updated by changing some uncertain parameters such as material properties and boundary conditions. Maximum differences between the natural frequencies are reduced from 10% to 2%, and a good agreement is found between natural frequencies and mode shapes after model updating.
Abstract This paper presents the earthquake response of the Kömürhan cable-stayed bridge with a single pylon and steel deck which was exposed to the Elazığ-Sivrice earthquake (Mw = 6.8) on January 24, 2020, while it was under construction. The distance from the epicenter to the bridge is approximately 40 km. 82% of the Kömürhan bridge was completed during the Elazığ-Sivrice earthquake in 2020. The spectral accelerations of Elazığ-Sivrice earthquake are approximately 2.5 times greater than those of the design earthquake (72-year) considered in the construction stage. In this paper, the characteristics of Kömürhan cable-stayed bridge and Elazığ-Sivrice earthquake (Mw = 6.8) are first presented. Then, a 3D numerical finite model of the Kömürhan cable-stayed bridge under construction is created. Modal and seismic responses of the deck, pylon and cables of the bridge under construction are compared for the load combinations including the design (72-year) and the Elazığ-Sivrice earthquakes. The result shows that under the 2020 Elazığ-Sivrice earthquakes, the maximum vertical displacements, axial forces, bending moments of the deck and the cable forces were three time more than the design value using the 72-year design hazard. Nevertheless, despite the significant increase in the structural response, no visual damage was observed on the structural element. This shows the robust design of the Kömürhan cable-stayed bridge.
In this paper, the development of a new optimization software for finite element model updating of engineering structures titled as FemUP is described. The program is used for computational FEM model updating of structures depending on modal testing results. This paper deals with the FE model updating procedure carried out in FemUP. The theoretical exposition on FE model updating and optimization techniques is presented. The related issues including the objective function, constraint function, different residuals and possible parameters for FE model updating are investigated. The issues of updating process adopted in FemUP are discussed. The ideas of optimization to be used in FE model updating application are explained. The algorithm of Sequential Quadratic Programming (SQP) is explored which will be used to solve the optimization problem. The possibilities of the program are demonstrated with a three dimensional steel frame model. As a result of this study, it can be said that SQP algorithm is very effective in model updating procedure.
The effects of the uniform and spatially varying ground motions on the stochastic response of fluid-structure interaction system during an earthquake are investigated by using the displacement based fluid finite elements in this paper. For this purpose, variable-number-nodes two-dimensional fluid finite elements based on the Lagrangian approach is programmed in FORTRAN language and incorporated into a general-purpose computer program SVEM, which is used for stochastic dynamic analysis of solid systems under spatially varying earthquake ground motion. The spatially varying earthquake ground motion model includes wave-passage, incoherence and site-response effects. The effect of the wave-passage is considered by using various wave velocities. The incoherence effect is examined by considering the Harichandran-Vanmarcke and Luco-Wong coherency models. Homogeneous medium and firm soil types are selected for considering the site-response effect where the foundation supports are constructed. A concrete gravity dam is selected for numerical example. The S16E component recorded at Pacoima dam during the San Fernando Earthquake in 1971 is used as a ground motion. Three different analysis cases are considered for spatially varying ground motion. Displacements, stresses and hydrodynamic pressures occurring on the upstream face of the dam are calculated for each case and compare with those of uniform ground motion. It is concluded that spatially varying earthquake ground motions have important effects on the stochastic response of fluid-structure interaction systems.
