209 publications from this institution
An accurate numerical analysis of the behavior of long-span cable-stayed bridges under environmental effects is a challenge because of complex, uncertain and varying environmental meteorology. This study aims to investigate in-situ experimental structural behavior of long-span steel cable-stayed bridges under environmental effects such as air temperature and wind using the monitoring data. Nissibi cable-stayed bridge with total length of 610m constructed in the city of Adıyaman, Turkey, in 2015 is chosen for this purpose. Structural behaviors of the main structural elements including deck, towers (pylons) and cables of the selected long span cable-stayed bridge under environmental effects such as air temperature and wind are investigated by using daily monitoring data. The daily variations of cable forces, cable accelerations, pylon accelerations and deck accelerations with air temperature and wind speed are compared using the hottest summer (July 31, 2015) and the coldest winter (January 1, 2016) days data.
The study investigates ambient vibration based model updating effects on the seismic behavior of a RC tall building subjected to far and near-fault ground motions. A 17-storey building built in Giresun, Turkey is selected as an application. Firstly, 3D initial finite element model of the selected building is created and determined analytical dynamic characteristics. Then, experimental dynamic characteristics of the building (frequencies, mode shapes, damping ratios) are determined by Operational Modal Analysis Method using the ambient vibration test data. According to experimental results, initial finite element model is calibrated by using boundary conditions and material properties. Initial and calibrated finite element models of the building are analysed under far and near-fault ground motions. Two models are compared with each other in terms of displacement, velocity, acceleration, base bending moment, base shear force, compressive and tensile stresses.
Abstract In this study, the dynamic behavior of a model building for different damage cases is studied based on the changes in the natural frequencies and mode shapes. The damage is assumed to occur on the walls and at the column-ends of the first story, because they are generally affected by earthquakes, explosions, etc. A ½-scale three-story reinforced-concrete (RC) building model is constructed in the laboratory. Different damage cases are applied to the model gradually by using mechanical cutting equipment. The wall damage is assumed to reach the interior of the walls and the column-end damage is created by removing the cover of columns. The ambient vibration tests are performed by using the operational modal analysis method under unknown random impact loads. The accelerometers are placed on the columns in the transverse and longitudinal directions to get the responses of the model in these directions. It is observed that the natural frequencies, corresponding mode shapes, and modal damping ratios of the building model vary depending on the damage location and damage extent. The natural frequencies show a decreasing trend with damage, and for the last damage case the natural frequencies are 60 % lower than for the undamaged case. In addition, the mode shapes are affected considerably by wall damage.
This study determines the water length effects on the modal behavior of a prototype arch dam using Operational and Analytical Modal Analyses. Achievement of this purpose involves construction of a prototype arch dam-reservoir-foundation model under laboratory conditions. In the model, reservoir length was taken to be as much as three times the dam height. To determine the experimental dynamic characteristics of the arch dam using Operational Modal Analysis, ambient vibration tests were implemented for empty reservoir and three different reservoir water lengths. In the ambient vibration tests, the dam was vibrated by natural excitations provided from small impact effects and the response signals were measured using sensitive accelerometers. Operational Modal Analysis software process signals collected from the ambient vibration tests, and Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification techniques estimated modal parameters of the dams. To validate the experimental results, 3D finite element model of the prototype arch dam was modeled by ANSYS software for empty reservoir and three different reservoir water lengths, and dynamic characteristics of each model were determined analytically. At the end of the study, experimentally and analytically identified dynamic characteristics compared to each other. Also, changes on the natural frequencies along to water length are plotted as graphs. Results suggest that reservoir water complicates the modal behavior of the arch dam significantly.
Abstract This study presents earthquake performance analysis of the Torul Concrete-Faced Rockfill (CFR) Dam with two-dimensional dam-soil and dam-soil-reservoir finite element models. The Lagrangian approach was used with fluid elements to model impounded water. The interface elements were used to simulate the slippage between the concrete face slab and the rockfill. The horizontal component of the 1992 Erzincan earthquake, with a peak ground acceleration of 0.515g, was considered in time-history analysis. The Drucker-Prager model was preferred in nonlinear analysis of the concrete slab, rockfill and foundation soil. The maximum principal stresses and the maximum displacements in two opposite directions were compared by the height of the concrete slab according to linear time-history analysis to reveal the effect of reservoir water. The changes of critical displacements and principal stresses with time are also shown in this paper. According to linear and nonlinear time-history analysis, the effect of the reservoir water on the earthquake performance of the Torul CFR Dam was investigated and the possible damage situation was examined. The results show that the hydrodynamic pressure of reservoir water leads to an increase in the maximum displacements and principal stresses of the dam and reduces the earthquake performance of the dam. Although the linear time-history analysis demonstrates that the earthquake causes a momentous damage to the concrete slab of the Torul CFR Dam, the nonlinear time-history analysis shows that no evident damage occurs in either reservoir case.
Abstract. In this paper, it is aimed to determine the finite element model updating effects on the structural behavior of long span concrete highway bridges. Birecik Highway Bridge located on the 81stkm of Sanliurfa-Gaziantep state highway over Firat River in Turkey is selected as a case study. The bridge consist of fourteen spans, each of span has a nearly 26m. The total bridge length is 380m and width of bridge is 10m. Firstly, the analytical dynamic characteristics such as natural frequencies and mode shapes are attained from finite element analyses using SAP2000 program. After, experimental dynamic characteristics are specified from field investigations using Operational Modal Analysis method. Enhanced Frequency Domain Decomposition method in the frequency domain is used to extract the dynamic characteristics such as natural frequencies, mode shapes and damping ratios. Analytically and experimentally identified dynamic characteristics are compared with each other and finite element model of the bridge is updated to reduce the differences by changing of some uncertain parameters such as section properties, damages, boundary conditions and material properties. At the end of the study, structural performance of the highway bridge is determined under dead load, live load, and dynamic loads before and after model updating to specify the updating effect. Displacements, internal forces and stresses are used as comparison parameters. From the study, it is seen that the ambient vibration measurements are enough to identify the most significant modes of long span highway bridges. Maximum differences between the natural frequencies are reduced averagely from %46.7 to %2.39 by model updating. A good harmony is found between mode shapes after finite element model updating. It is demonstrated that finite element model updating has an important effect on the structural performance of the arch type long span highway bridge. Maximum displacements, shear forces, bending moments and compressive stresses are reduced %28.6, %21.0, %19.22, and %33.3-20.0, respectively.
Abstract In this paper the development of interactive and comparative dynamic characteristic identification software titled as the ModalCAD is described. The software is developed for vibration monitoring of civil engineering structures and constructed by using MATLAB, which is a mathematical tool developed by The Mathworks. The modal analysis of structures consists of four distinct steps: Data collection, digital signal processing, determination of the modal parameters (eigenfrequencies, damping ratios, mode shapes, and modal scaling factors) with modal data presentation/validation and model updating. The ModalCAD software is a powerful tool that deals with modal parameter identification and validation procedure. The ModalCAD offers extensive functionalities for the visualization and processing of the measurement data, the identification of system models, and the determination and visualization of the structure’s modal parameters. The program disposes of a graphical user interface, which what makes it very intuitive and easy to handle. The most common modal parameter estimation techniques have been used in the ModalCAD. The Operating Vectors method, Complex Exponential method, and Polyreference Time Domain method are implemented in a user-friendly way. By pushing buttons the user is guided through the whole process of input-output and output-only modal analysis: Preprocessing the data, system identification, extracting modal parameters, animating mode shapes, and evaluating model validation tools. The possibilities of the program are demonstrated with a three dimensional frame model. It can be said that the ModalCAD software can be used as a scientific tool in future structural health monitoring studies of researchers.
The present paper presents a stochastic seismic analysis of fluid and fluid–solid systems by using Lagrangian approach. For this reason, authors have programmed variable-number-nodes two-dimensional isoparametric fluid finite elements in fortran and have incorporated into a generalpurpose computer program for stochastic dynamic analysis of structure systems, stocal. For numerical examples, a rigid fluid tank and a fluid–solid interaction system are selected. Natural frequencies from the modal analyses of the fluid and fluid–solid systems are compared with those of analytical and numerical solutions. S16E component of the Pacoima Dam record of the San Fernando Earthquake in 1971 is used as a ground motion. The mean of maximum values from stochastic analysis are compared with deterministic analysis results
On 6 February 2023, two major earthquakes struck Türkiye, with their epicenters in the Pazarcık (M7.7; focal depth: 8.6 km) and Elbistan (M7.6; focal depth: 7 km) districts of Kahramanmaraş city. Most of the dams in the earthquake region remained structurally safe and stable. However, 17 dams in Türkiye and 1 dam in Syria were damaged during the 2023 Kahramanmaraş earthquakes. The main objective of this study was to better understand the real seismic behaviors of the dams during the two mainshocks and significant aftershocks. An earthfill dam, a concrete-faced rockfill dam (CFRD), and a roller-compacted concrete (RCC) dam constructed in the disaster area were selected to identify the real seismic behaviors of different types of dams during strong earthquakes. Acceleration records measured at the crest, right and left abutments, and foundations of the selected dams during the 2023 Kahramanmaraş earthquakes were taken into account to determine the real seismic behavior of the dams before, during, and after the earthquakes. The results of this investigation provide valuable insights into the real seismic behaviors of different types of dams in the vicinity of fault lines during strong earthquakes.
