Stochastic seismic finite element analyses of the Kömürhan Bridge, the material properties of which are described by random fields, are presented in this paper. The stochastic perturbation technique and Monte Carlo simulation (MCS) method are used in the analyses. A summary of MCS and perturbation-based stochastic finite element dynamic analysis formulation of the structural system is given. The Kömürhan Bridge, located on the 51st km of Elazığ-Malatya highway in the east of Turkey, was chosen as a numerical example. The Erzincan earthquake in 1992 was considered a ground motion, since it took place in the vicinity of the bridge. The material properties were considered to be random variables. During the stochastic analysis, displacements and internal forces of the bridge under consideration were obtained using the perturbation-based stochastic finite element method (SFEM), as well as the MCS method. The selected random variables were elastic modulus and mass density. The efficiency and accuracy of the proposed SFEM algorithm were validated through comparison with results of the MCS method.
Abstract This paper describes a historical masonry minaret, its finite element modeling, modal testing, and finite element model calibration. İskenderpaşa historical masonry minaret located in Trabzon City Center, Turkey, is selected as an application. Modal analysis is performed on the developed 3-D finite element model of the minaret to obtain the analytical frequencies and mode shapes. The ambient vibration tests on the minaret under environmental excitations, such as traffic loads and wind, are conducted. The output-only modal parameter identification is carried out by using peak picking of the average normalized power spectral densities in the frequency domain and stochastic subspace identification in the time domain. Dynamic characteristics such as natural frequencies, mode shapes, and damping ratios are determined. The finite element model of the minaret is calibrated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modeling parameters such as material properties and boundary conditions. At the end of the study, maximum differences in the natural frequencies are reduced on an average from 27 % to 5 %. A good agreement is also found between analytical and experimental natural frequencies and mode shapes after model calibration.
Historical masonry aqueducts were constructed to convey water over rivers, valleys, etc. Many of them have deteriorated due to different effects and may need to be repaired or strengthened to increase their load carrying capacities. Historical aqueducts are invaluable cultural heritage, and they require particular attention and appropriate seismic strengthening techniques including minimal intervention, better workability and reduced cost. The present study proposes filling the canal with water to improve structural seismic performance of historical masonry aqueducts. The influence of fluid–structure interaction in seismic performance improvement of historical masonry aqueducts is numerically investigated in this study. Three-dimensional (3D) finite element models of an aqueduct including without and with fluid–structure interaction are created using the coupled acoustic fluid–structure (CAS) approach. Concrete Damage Plasticity (CDP) material model adjusted to masonry units and ground motion records matched to site-dependent are utilized in the nonlinear seismic analyses. Seismic performances of the aqueduct models with and without fluid–structure interaction for the only-transverse, combined transverse and longitudinal, and combined transverse and longitudinal and vertical component cases are evaluated and compared with each other.
This paper presents finite element analyses, experimental measurements and finite element model updating of an arch type steel laboratory bridge model using semi-rigid connections. The laboratory bridge model is a single span and fixed base structure with a length of 6.1 m and width of 1.1m. The height of the bridge column is 0.85 m and the maximum arch height is 0.95 m. Firstly, a finite element model of the bridge is created in SAP2000 program and analytical dynamic characteristics such as natural frequencies and mode shapes are determined. Then, experimental measurements using ambient vibration tests are performed and dynamic characteristics (natural frequencies, mode shapes and damping ratios) are obtained. Ambient vibration tests are performed under natural excitations such as wind and small impact effects. The Enhanced Frequency Domain Decomposition method in the frequency domain and the Stochastic Subspace Identification method in the time domain are used to extract the dynamic characteristics. Then the finite element model of the bridge is updated using linear elastic rotational springs in the supports and structural element connections to minimize the differences between analytically and experimentally estimated dynamic characteristics. At the end of the study, maximum differences in the natural frequencies are reduced on average from 47% to 2.6%. It is seen that there is a good agreement between analytical and experimental results after finite element model updating. Also, connection percentages of the all structural elements to joints are determined depending on the rotational spring stiffness.
A stochastic finite element-based algorithm for probabilistic analysis of structural systems made of composite sections with random material and geometrical properties under earthquake forces is proposed in this paper. Uncertainties in the structural parameters can be taken into account in this algorithm. For the perturbation-based stochastic finite element method, only the first two moments of random variables need to be known, and is numerically much more efficient and feasible than simulation techniques. The efficiency and accuracy of the proposed algorithm are validated by comparison with results of Monte Carlo simulation method. A summary of stiffness matrix formulation and perturbation-based stochastic finite element dynamic analysis formulation of structural systems made of composite sections is given. These are followed by suitable numerical examples, which indicate that employment of such a dynamic stochastic finite element method leads to significant economical, efficient and accurate solutions for the dynamic analysis of composite structures with stochastic parameters under earthquake forces. Copyright © 2010 John Wiley & Sons, Ltd.
This investigation uses a linear elastic finite-element method to analyse the stochastic dynamic response of the Bolu tunnel in Turkey when subjected to spatially varying earthquake ground motion. The research conducts a parametric study to discover the critical magnitude of earthquake ground motion that causes tensile cracking in the reinforced concrete tunnel lining. The Drucker–Prager yield criterion determines the forces that cause cracking of reinforced elements of three cross-sections of the tunnel system subjected to spatially varying seismic ground motion. The study applies spatially varying ground-motion models, wave passage, incoherence and site response as well as the uniform ground-motion model to three cross-sections of the tunnel–soil deposit interaction system. The purpose is to determine the stochastic seismic behaviour of the tunnel. Of particular emphasis is the importance of the site response effect that arises from the difference in the local soil conditions at the different support points of the tunnel–soil deposit interaction system. The results of the analyses demonstrate that the number of cracked elements increases as the amplitude of earthquake ground motion increases. In addition, the means of the maximum values obtained from the spatially varying ground-motion case are compared with those of specialised earthquake ground-motion models. The result is proof that variations in local soil conditions have important effects on the stochastic response of tunnels.
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 Sanlurfa-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 The study presents an application of a damage detection approach for beam like structures that is based on both operational and numerical modal analyses results obtained from undamaged and damaged cases of a structure. The effectiveness of this approach is assessed by performing investigations on a column model. In the first step of this approach, the damaged member of the column is determined by comparing the mode shapes of the undamaged and damaged cases. For this purpose, the changes on the vectors defined as the differences between the undamaged and damaged mode shapes for each mode are observed. It is assumed that the abrupt change in these vectors shows the existence of the damage. In the second step, the numerical model of the column is created and calibrated according to the experimental results obtained from the undamaged case. To find the damaged section, a step-by-step analysis on the pre-identified member of the column model is performed numerically. For this reason, the natural frequencies obtained from the numerical modal analyses of the column for the damaged case are compared with the experimental results. The minimum difference between the numerical and experimental results indicates the presence of the damage on this section. The approach used in this study provides an important contribution that the number of structural members to be analyzed is limited instead of analyzing all structural members.
Finite element model updating is very effective procedure to determine the uncertainty parameters in structural model and minimize the differences between experimentally and numerically identified dynamic characteristics. This procedure can be practiced with manual and automatic model updating procedures. The manual model updating involves manual changes of geometry and analyses parameters by trial and error, guided by engineering judgement. Besides, the automated updating is performed by constructing a series of loops based on optimization procedures. This paper addresses the ambient vibration based finite element model updating of long span reinforced concrete highway bridges using manual model updating procedure. Birecik Highway Bridge located on the <TEX>$81^{st}km$</TEX> of Şanliurfa-Gaziantep state highway over Firat River in Turkey is selected as a case study. The structural carrier system of the bridge consists of two main parts: Arch and Beam Compartments. In this part of the paper, the arch compartment is investigated. Three dimensional finite element model of the arch compartment of the bridge is constructed using SAP2000 software to determine the dynamic characteristics, numerically. Operational Modal Analysis method is used to extract dynamic characteristics using Enhanced Frequency Domain Decomposition method. Numerically and experimentally identified dynamic characteristics are compared with each other and finite element model of the arch compartment of the bridge is updated manually by changing some uncertain parameters such as section properties, damages, boundary conditions and material properties to reduce the difference between the results. It is demonstrated 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 %49.1 to %0.6 by model updating. Also, a good harmony is found between mode shapes after finite element model updating.
Cable-stayed bridges (CSBs) are flexible and complex structures. Impact-induced vibrations may play an important role in the behaviours of the structural elements. Much effort has been devoted to clarifying the experimental static and dynamic responses of CSBs. However, experimental dynamic responses of the structural elements of CSBs under impact-induced vibrations have not been widely addressed in the literature. The focus of this paper is on the real experimental dynamic behaviours of cables, decks and pylons in CSBs under impact-induced vibration due to fully loaded trucks passing over a bump positioned on the deck centre. Tests were carried out on the new Kömürhan CSB under the passage of two 40 t trucks travelling at 30 km/h and passing over a timber bump of 50 mm thickness. The dynamic responses of the structural elements were recorded using load cells and two- and three-dimensional accelerometers. Forces, accelerations and frequencies of the main- and back-span cables and the acceleration responses of the deck and pylon, recorded with and without impact effects, were evaluated and compared. Significant impact-induced amplification ratios on the responses of the main- and back-span cables, deck and pylon were observed for the studied bridge.
