The investigation of dynamic response for civil engineering structures largely depends on a detailed understanding of their dynamic characteristics, such as the natural frequencies, mode shapes, and modal damping ratios. Dynamic characteristics of structures may be obtained numerically and experimentally. The finite-element method is widely used to model structural systems numerically. However, there are some uncertainties in numerical models. Material properties and boundary conditions may not be modeled correctly. There may be some microcracks in the structures, and these cracks may directly affect the modeling parameters. Modal testing gives correct uncertain modeling parameters that lead to better predictions of the dynamic behavior of a target structure. Therefore, dynamic behavior of special structures, such as minarets, should be determined with ambient vibration tests. The vibration test results may be used to update numerical models and to detect microcracks distributed along the structure. The operational modal analysis procedure consists of several phases. First, vibration tests are carried out, spectral functions are produced from raw measured acceleration records, dynamic characteristics are determined by analyzing processed spectral functions, and finally analytical models are calibrated or updated depending on experimental analysis results. In this study, an ambient vibration test is conducted on the minaret under natural excitations, such as wind effects and human movement. The dynamic response of the minaret is measured through an array of four trixial force-balanced accelerometers deployed along the whole length of the minaret. The raw measured data obtained from ambient vibration testing are analyzed with the SignalCAD program, which was developed in MATLAB. The employed system identification procedures are based on output-only measurements because the forcing functions are not available during ambient vibration tests. The ModalCAD program developed in MATLAB is used for dynamic characteristic identification. A three-dimensional model of the minaret is constructed, and its modal analysis is performed to obtain analytical frequencies and mode shapes by using the ANSYS finite-element program. The obtained system identification results have very good agreement, thus providing a reliable set of identified modal properties (natural frequencies, damping ratios, and mode shapes) of the structure, which can be used to calibrate finite-element models and as a baseline in health monitoring studies.
This paper addresses field investigations of the performance of masonry buildings during the October 23 (Erciş) and November 9 (Edremit), 2011, Van earthquakes in Turkey. Erciş and Edremit are villages respectively located 90 km and 18 km from the city of Van in Turkey. Ground accelerations and response spectra for these earthquakes are discussed. A total of 28,000 buildings were damaged or collapsed in the city center and surrounding villages after the Erciş earthquake. This number increased to 35,000 after the Edremit earthquake. Almost all masonry buildings were affected in the region. Most of them in the area were constructed of random or coursed stone walls with no reinforcement to support heavy clay tile roofing over wooden logs. A large number of such buildings were heavily damaged or collapsed. Cracking and failure patterns are examined and interpreted according to current provisions for earthquake resistance of masonry structures. From the field investigations, it is shown that damages had several causes, among them site effect, location and length of the fault, and poor construction quality. In addition, the two earthquakes hit the masonry buildings within 17 days, causing progressive damage. A large number of nonengineered masonry buildings completely collapsed or were heavily damaged. Most of those in the affected area were not designed and constructed in accordance with the Turkish Earthquake Resistant Design Code.
This paper presents an algorithm for structural reliability with the response surface method. For this aim, an approach with three stages is proposed named as improved response surface method. In the algorithm, firstly, a quadratic approximate function is formed and design point is determined with First Order Reliability Method. Secondly, a point close to the exact limit state function is searched using the design point. Lastly, vector projected method is used to generate the sample points and Second Order Reliability Method is performed to obtain reliability index and probability of failure. Five numerical examples are selected to illustrate the proposed algorithm. The limit state functions of three examples (cantilever beam, highly nonlinear limit state function and dynamic response of an oscillator) are defined explicitly and the others (frame and truss structures) are defined implicitly. ANSYS finite element program is utilized to obtain the response of the structures which are needed in the reliability analysis of implicit limit state functions. The results (reliability index, probability of failure and limit state function evaluations) obtained from the improved response surface are compared with those of Monte Carlo Simulation, First Order Reliability Method, Second Order Reliability Method and Classical Response Surface Method. According to the results, proposed algorithm gives better results for both reliability index and limit state function evaluations.
In this study, dynamic characteristics of a laboratory bridge model are determined by operational modal analysis using frequency and time domain methods. For this purpose, a reinforced box girder concrete bridge model is constructed in laboratory conditions. The bridge deck consists of a main span of 3 m and two side span of 1.5 m each. The structural system of the model bridge consists of deck, piers and foundation. The total length of bridge deck is 6 m and width of bridge deck is 60 cm. Ambient vibration tests are conducted to the model bridge to identify its natural frequencies, mode shapes and damping ratios. Natural excitations such as wind and impact hammer are used to vibrate the model bridge. Vibration data is gathered from bridge deck. Measurement time, frequency span and effective mode number are determined by consider similar studies in literature. Sensitivity accelerometers are placed to collect signals from the measurements. The signals collected from the tests are processed by operational modal analysis; and the dynamic characteristics of the bridge model are estimated using enhanced frequency domain decomposition (EFDD) method in the frequency domain and stochastic subspace identification (SSI) method in the time domain. The dynamic characteristics obtained from both methods are found to be close to each other. Maximum 2.68% differences are obtained between natural frequencies for the first mode. Modal assurance criteria values are between 0.85-1.00. This shows that EFDD and SSI results are almost overlapped. It can be concluded that the both of enhanced frequency domain decomposition and stochastic subspace identification methods are very useful to identify the dynamic characteristics of the bridge model.
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.
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.
The aim of this study is to determine the dynamic characteristics of long reinforced concrete highway bridges with post-tension tendons using analytical and experimental methods. It is known that the deck length and height of bridges are affected the dynamic characteristics considerably. For this purpose, Berta Bridge constructed in deep valley, in Artvin, Turkey, is selected as an application. The Bridge has two piers with height of 109.245 m and 85.193 m, and the total length of deck is 340.0 m. Analytical and experimental studies are carried out on Berta Bridge which was built in accordance with the balanced cantilever method. Finite Element Method (FEM) and Operational Modal Analysis (OMA) which considers ambient vibration data were used in analytical and experimental studies, respectively. Finite element model of the bridge is created by using SAP2000 program to obtain analytical dynamic characteristics such as the natural frequencies and mode shapes. The ambient vibration tests are performed using Operational Modal Analysis under wind and human loads. Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI) methods are used to obtain experimental dynamic characteristics like natural frequencies, mode shapes and damping ratios. At the end of the study, analytical and experimental dynamic characteristic are compared with each other and the finite element model of the bridge was updated considering the material properties and boundary conditions. It is emphasized that Operational Modal Analysis method based on the ambient vibrations can be used safely to determine the dynamic characteristics, to update the finite element models, and to monitor the structural health of long reinforced concrete highway bridges constructed with the balanced cantilever method.
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.
Vibration based damage detection is very popular in the civil engineering area. Especially, special structures like dams, long-span bridges and high-rise buildings, need continues monitoring in terms of mechanical properties of material, static and dynamic behavior. It has been stated in the International Commission on Large Dams that more than half of the large concrete dams were constructed more than 50 years ago and the old dams have subjected to repeating loads such as earthquake, overflow, blast, etc.,. So, some unexpected failures may occur and catastrophic damages may be taken place because of theloss of strength, stiffness and other physical properties of concrete. Therefore, these dams need repairs provided with global damage evaluation in order to preserve structural integrity. The paper aims to show the effectiveness of the model updating method for global damage detection on a laboratory arch dam model. Ambient vibration test is used in order to determine the experimental dynamic characteristics. The initial finite element model is updated according to the experimentally determined natural frequencies and mode shapes. The web thickness is selected as updating parameter in the damage evaluation. It is observed from the study that the damage case is revealed with high accuracy and a good match is attained between the estimated and the real damage cases by model updating method.
Abstract The aim of this paper is to determine the earthquake behaviour of the Kömürhan Highway Bridge, located at the 51st kilometre of the Elazığ-Malatya highway over the Fırat River, after finite element model updating using operational modal analyses. Finite element models of the bridge are built with the SAP2000 program to obtain analytical dynamic characteristics such as natural frequencies and mode shapes. The ambient vibration tests are performed using operational modal analysis under traffic loads to attain experimental dynamic characteristics. Vibration data is gathered from both the box girder and bridge deck to compare the results. Measurement time, frequency span, and effective mode number are determined following similar studies and literature. The peak picking method in the frequency domain is used for output-only modal identification. The finite element model of the bridge is updated by changing some uncertainties in the parameters such as material properties and boundary conditions to eliminate the differences between analytical and experimental dynamic characteristics. An analytical model of the bridge after finite element model updating is analyzed using the 1992 Erzincan, Turkey earthquake record, which occurred near the region, to determine the earthquake behaviour of the bridge. At the end of the study, the maximum differences in the natural frequencies are reduced on average from 10 % to 2 %, and a good agreement is found between analytical and experimental natural frequencies and mode shapes by model updating. Also, the variation of internal forces such as bending moment, axial forces, and shear forces for the bridge deck and columns are presented in detail.
This paper provides an overview on some of the latest advances in the applications of fiber reinforced polymeric (FRP) composites in construction. The paper focuses on three main inter related review areas, namely; (i) Repair and rehabilitation of concrete, steel, masonry and wood structures using composites, and (ii) All-composite structural applications that includes buildings and bridges, and (iii) Latest development on design codes, materials specifications, design manuals and national and international standards for composites used in civil infrastructure applications.
