çeşme, köprü gibi tarihi eserler zaman içinde doğal afetler veya canlıların tahribatları neticesinde çeşitli hasarlara maruz kalmaktadırlar.Genellikle en sık rastlanılan bilinçsiz müdahale şekillerinden biri, ahşap çatılı tarihi yığma camilerin ahşap çatısının yerine betonarme kubbe yapılmasıdır.Bu çalışmada, bu tip müdahalelerin tarihi taş duvarlı camilerin dinamik özelliklerini nasıl etkidiğinin belirlenmesini
The aim of the study is to determine the modal parameters of a prototype damaged arch dam by operational modal analysis (OMA) method for some damage scenarios. For this purpose, a prototype arch dam-reservoir-foundation model is constructed under laboratory conditions. Ambient vibration tests on the arch dam model are performed to identify the modal parameters such as natural frequency, mode shape and damping ratio. The tests are conducted for four test-case scenarios: an undamaged dam with empty reservoir, two different damaged dams with empty reservoirs, and a damaged dam with full reservoir. Loading simulating random impact effects is applied on the dam to crack. Cracks and fractures occurred at the middle of the upper part of the dams and distributed through the abutments. Sensitivity accelerometers are placed on the dams' crests to collect signals for measurements. Operational modal analysis software processes the signals collected from the ambient vibration tests, and enhanced frequency domain decomposition and stochastic subspace identification techniques are used to estimate modal parameters of the dams. The modal parameters are obtained to establish a basis for comparison of the results of two techniques for each damage case. Results show that approximately 35-40% difference exists between the natural frequencies obtained from Case 1 and Case 4. The natural frequencies of the dam considerably decrease with increasing cracks. However, observation shows that the filled reservoir slightly affected modal parameters of the dam after severe cracking. The mode shapes obtained are symmetrical and anti-symmetrical. Apparently, mode shapes in Case 1 represent the probable responses of arch dams more accurately. Also, damping ratio show an increase when cracking increases.
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.
In this paper, it is aimed to investigate the restoration effect on the structural behavior of masonry arch bridges. Dandalaz masonry arch bridge located on the 4km east of Karacasu town of Aydin, Turkey is selected as a numerical example. The construction year of the bridge is not fully known, but the bridge is dated back to 15th century. Considering the current situation, it can be easily seen that the structural elements such as arch, side walls and timber blocks are heavily damaged and the bridge is unserviceable. Firstly finite element model of the bridge is constituted to reflect the current situation (before restoration) using building survey drawings. After, restoration project is explained and finite element model is reconstituted (after restoration). The structural responses of the bridge are obtained before and after restoration under dead load, live load and dynamic earthquake loads. For both conditions, maximum displacements, maximum-minimum principal stresses and maximum-minimum elastic strains are given with detail using contours diagrams and compared with each other to determine the restoration effect. From the study, it can be seen that the maximum internal forces are consisted under dynamic loads before and after restoration. Also, the restoration projects and studies have important and positive effects on the structural response of the bridge to transfer these structures to future.
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.
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.
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.
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.
Traditional domes are obtained by double curvature shells, which can be rotationally formed by any curved geometrical plane figure rotating about a central vertical axis. They are self-supported and stabilized by the force of gravity acting on their weight to hold them in compression. However, the behavior of inverted domes is different since the dome is downward and masonry inverted domes and their structural behaviors in the literature received limited attention. This article presents a nonlinear finite element analysis of historical brick masonry inverted domes under static and seismic loads. The brick masonry inverted dome in the tomb of scholar Ahmed-El Cezeri, town of Cizre, Turkey, constructed in 1508 is selected as an application. First, a detailed literature review on the masonry domes is given and the selected inverted dome is described briefly. 3D solid and continuum finite element models of the inverted masonry dome are obtained from the surveys. An isotropic Concrete Damage Plasticity (CDP) material model adjusted to masonry structures with the same tensile strength assumed along the parallel and meridian directions of the inverted dome is considered. The nonlinear static analyses and a parametric study by changing the mechanical properties of the brick unit of the inverted masonry dome are performed under gravity loads. The acceleration records of vertical and horizontal components of May 1, 2003 Bingöl earthquake (Mw = 6.4), Turkey, occurred near the region, are chosen for the nonlinear seismic analyses. Nonlinear step by step seismic analyses of the inverted dome are implemented under the vertical and horizontal components of the earthquake, separately. Static modal and seismic responses of the inverted masonry dome are evaluated using mode shapes, minimum and maximum principal strains and stresses, and damage propagations.
Long-span cable-stayed bridges have complex and vulnerable systems, and the structural performances of in-service cables-stayed bridges are affected by many environmental factors including thermal (temperature, humidity, solar radiation), wind, rain, etc.Therefore, efficient inspection and maintenance strategies are needed to ensure their serviceability and integrity.Structural health monitoring approaches are utilized to secure the structural and operational safety of them recording different response measurements.Strain measurements offer information about stresses experienced by the bridge during its operation and are better suited to characterize the local deficiency and damage of an element than global responses.The present paper investigates the measured field strain responses of the deck, pylon, and cables of long-span cable-stayed bridges under environmental effects.The new Kömürhan long-span cable-stayed bridge with a single invert Y pylon constructed in Turkey, which was opened to the traffic in January 2021, is selected as an application.Firstly, in-service structural condition assessment of the bridge is detailly evaluated using the strain responses recorded along the deck, pylon, and cables during two periods with relatively high and low temperature.Then, the relationships between the measured strain response and environmental effects such as temperature, humidity, solar radiation, wind, and rain are determined for the cable-stayed bridge.The results provide valuable strain response knowledge about the operational conditions of long-span cable-stayed bridges in terms of serviceability, strength, reliability, and maintenance.
