209 publications from this institution
Seismic assessment of existing engineering structures in earthquake zones is very important. This paper presents seismic assessments of a highway bridge and an arch dam using non-destructive tests under ambient vibrations. Firstly, finite element models of these structures are developed and analytical dynamic characteristics are attained. Secondly, experimental measurements under ambient vibrations are performed and dynamic characteristics are extracted using Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods. Experimental and analytical dynamic characteristics are compared and finite element models are updated to eliminate the differences. Lastly, the seismic assessments of the selected structures are performed using the updated finite element models under earthquake ground motions.
This paper describes a historical arch bridge; its analytical modelling, modal testing and finite element model (FEM) updating. For this purpose, Senyuva historical arch bridge which is built in 1696 and located in Camlihemsin, Rize, Turkey, is selected as an application. 3D FEM of the bridge is modelled using ANSYS software to obtain analytical dynamic characteristics such as natural frequencies and mode shapes. Then, operational modal analysis using ambient vibrations is performed to attain dynamic characteristics experimentally. Human walking and wind are used as natural excitation. The output-only modal parameter identification is carried out using the Peak Picking method in frequency domain and the Stochastic Subspace Identification method in time domain. After, analytically and experimentally identified dynamic characteristics compared with each other and FEM of the historical bridge is updated to minimize the differences between modal parameters by changing uncertain modelling parameters such as boundary conditions. As a result, differences between the natural frequencies are reduced from 27% to 3% and good agreement is found between analytical and experimental dynamic characteristics after FEM updating.
This paper presents the analytical modeling, modal testing, and finite-element model updating for a two-span masonry arch bridge. An Ottoman masonry arch bridge built in the 19th century and located at Camlihemsin, Rize, Turkey is selected as an example. Analytical modal analysis is performed on the developed 3D finite-element model of the bridge to obtain dynamic characteristics. The ambient vibration tests are conducted under natural excitation such as human walking. The operational modal analysis is carried out using peak picking method in the frequency domain and stochastic subspace identification method in the time domain, and dynamic characteristics (natural frequencies, mode shapes, and damping ratios) are determined experimentally. Finite-element model of the bridge is updated to minimize the differences between analytically and experimentally estimated dynamic characteristics by changing boundary conditions. At the end of the study, maximum differences in the natural frequencies are reduced on average from 18 to 7% and a good agreement is found between analytical and experimental dynamic characteristics after finite-element model updating.
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.
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 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.
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.
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 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.
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.
