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.
This paper aims to determine the dynamic characteristics, such as natural frequencies, mode shapes and damping ratios, of two different domed structures, namely Hamza Paşa Mausoleum and Kavak Meydan Fountain, built in the sixteenth century by experimental methods. The experimental dynamic characteristics are used to develop initial analytical models and update these models. Analytical models of the structures are constituted using finite element theoretical software, and dynamic characteristics are determined analytically. The experimental measurements are carried out by operational modal testing under environmental loads, which are wind and traffic loads, and the dynamic characteristics are identified experimentally. Vibration responses are collected from the dome's outer surface for Hamza Paşa Mausoleum and the dome pulley's inner surface for Kavak Meydan Fountain. Measurement time, frequency span, and effective mode number are determined by considering pretest measurement results. At the end of the study, analytical and experimental dynamic characteristics are compared with each other and the finite element models of these domed structures are updated by changing material properties and boundary conditions.
This paper presents the finite element calibration of Berke Arch Dam by using Operational Modal Testing. Achievement of this purpose involves structural vibration characteristics of Berke Arch Dam using analytical and Operational Modal Analyses. Therefore, the study has two parts — analytical and experimental. In the analytical part of the study, the authors developed a 3D finite element model of Berke Arch Dam-reservoir-foundation system using ANSYS software, and analytically determined vibration characteristics such as natural frequencies and mode shapes. In the experimental part of the study, sensitive accelerometers were placed to several points of Berke Arch Dam, and ambient vibration tests were conducted over four days to obtain dynamic characteristics. The Enhanced Frequency Domain Decomposition technique is used to estimate natural frequencies, mode shapes and damping ratios of the Berke Arch Dam experimentally. Results showed that there were some differences between analytical and experimental natural frequencies of the dam. Therefore, an analytical model of Berke Arch Dam was calibrated to minimize these differences by changing material properties. Analytical results obtained from the calibrated model mainly conform to those of the experimental model.
In this study, the earthquake damage response of the concrete arch dams was investigated including dam-reservoir interaction. A continuum damage model which is a second-order tensor and includes the strain softening behavior was selected for the concrete material. Fluid-structure interaction problem was modeled by Lagrangian approach. Sommerfeld radiation condition was applied to the truncated boundary of reservoir. The improved form of the HHT-<TEX>${\alpha}$</TEX> time integration algorithm was used in the solution of the equations of motion. The arch dam Type 5 was selected for numerical application. For the dynamic input, acceleration records of the 10 December 1967 Koyna earthquake were chosen. These records were scaled with earthquake acceleration scale factor (EASF) and then used in the analyses. Solutions were obtained for empty and full reservoir cases. The effects of EASF and damping ratio on the response of the dam were studied.
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.
This paper presents the reliability analysis of the frame structures with semi-rigid connections. For this purpose, the SEMIFEM finite element program that is capable of dealing with the semi-rigid connections is coded in FORTRAN. Then, this program is connected to the reliability algorithm. The direct coupling method, which is a combination of the reliability method and finite element method, is utilized to determine the reliability indexes and probabilities of failure for the structure. The first order reliability method (FORM) is the one favored in the present reliability analysis. Two sets of steel framed structures are analyzed; each of four and eight stories, consisting of a portal frame and three types of concentrically braced frames. Concrete compression strength limit state in reinforced concrete (RC) columns, steel strength limit state in steel braces and inter-story drift limit state are considered in reliability evaluation. According to the limit states, X braced frames are determined as the safest structures, while the portal frames are regarded as the most unsafe structures. As the connection percentage increases, the safety of the structure increases in terms of inter-story drift and steel strength limit states, but decreases for concrete compression strength limit states.
The traditional destructive tests in damage detection require high cost, long consuming time, repairing of damaged members, etc. In addition to these, powerful equipments with advanced technology have motivated development of global vibration based damage detection methods. These methods base on observation of the changes in the structural dynamic properties and updating finite element models. The existence, location, severity and effect on the structural behavior of the damages can be identified by using these methods. The main idea in these methods is to minimize the differences between analytical and experimental natural frequencies. In this study, an application of damage detection using model updating method was presented on a one storey reinforced concrete (RC) building model. The model was designed to be 1/2 scale of a real building. The measurements on the model were performed by using ten uni-axial seismic accelerometers which were placed to the floor level. The presented damage identification procedure mainly consists of five steps: initial finite element modeling, testing of the undamaged model, finite element model calibration, testing of the damaged model, and damage detection with model updating. The elasticity modulus was selected as variable parameter for model calibration, while the inertia moment of section was selected for model updating. The first three modes were taken into consideration. The possible damaged members were estimated by considering the change ratio in the inertia moment. It was concluded that the finite element model calibration was required for structures to later evaluations such as damage, fatigue, etc. The presented model updating based procedure was very effective and useful for RC structures in the damage identification.
Abstract Dynamic characteristic identification provides an important insight about structural behavior of steel structures. The experimental modal analysis is used to detect dynamic characteristics and consists of several phases. First, forced-vibration tests are carried out, spectral functions are produced, 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, forced-vibration testing is conducted on the steel footbridge by using an impact hammer. Low-amplitude broadband excitations are applied using an impact hammer to excite the bridge. The excitation force and measured responses are processed by passing them through a band-pass filter to obtain frequency-response functions, cross-power spectra, auto-power spectra, power spectral densities, and spectrograms. The system-identification procedure is based on input–output measurements. The obtained system-identification results are compared with the analytical results, which were obtained in a different previous study. A very good agreement is observed, thus providing a reliable set of identified modal properties (natural frequencies, damping ratios, and mode shapes) of the structure. The good correlations between analytical and experimental analyses show that no anomalies are detected along the structure. The experimental mode shapes are similar to what is expected from this type of structure. There is not any unexpected mechanism that changes the dynamic characteristics of the system.
The paper investigates the structural performance of a seven-story reinforced concrete (RC) building that collapsed during the Van (Turkey) earthquake on October 23, 2011, using nonlinear static and dynamic methods. The selected RC building has two blocks and was designed according to the Turkish Earthquake Code (TEC) in 1975. The site investigation included sections and steel detailing and soil and concrete properties taken after the earthquake. The pushover and nonlinear time history analyses of the building were completed using the existing plan and test and observation data. It is concluded that the building collapses both analysis types.
