Emre Ercan

Identification of Historical Veziragasi Aqueduct Using the Operational Modal Analysis

This paper describes the results of a model updating study conducted on a historical aqueduct, called Veziragasi, in Turkey. The output-only modal identification results obtained from ambient vibration measurements of the structure were used to update a finite element model of the structure. For the purposes of developing a solid model of the structure, the dimensions of the structure, defects, and material degradations in the structure were determined in detail by making a measurement survey. For evaluation of the material properties of the structure, nondestructive and destructive testing methods were applied. The modal analysis of the structure was calculated by FEM. Then, a nondestructive dynamic test as well as operational modal analysis was carried out and dynamic properties were extracted. The natural frequencies and corresponding mode shapes were determined from both theoretical and experimental modal analyses and compared with each other. A good harmony was attained between mode shapes, but there were some differences between natural frequencies. The sources of the differences were introduced and the FEM model was updated by changing material parameters and boundary conditions. Finally, the real analytical model of the aqueduct was put forward and the results were discussed.

Structural health monitoring for bolt loosening via a non-invasive vibro-haptics human–machine cooperative interface

For the last two decades, developments in damage detection algorithms have greatly increased the potential for autonomous decisions about structural health. However, we are still struggling to build autonomous tools that can match the ability of a human to detect and localize the quantity of damage in structures. Therefore, there is a growing interest in merging the computational and cognitive concepts to improve the solution of structural health monitoring (SHM). The main object of this research is to apply the human–machine cooperative approach on a tower structure to detect damage. The cooperation approach includes haptic tools to create an appropriate collaboration between SHM sensor networks, statistical compression techniques and humans. Damage simulation in the structure is conducted by releasing some of the bolt loads. Accelerometers are bonded to various locations of the tower members to acquire the dynamic response of the structure. The obtained accelerometer results are encoded in three different ways to represent them as a haptic stimulus for the human subjects. Then, the participants are subjected to each of these stimuli to detect the bolt loosened damage in the tower. Results obtained from the human–machine cooperation demonstrate that the human subjects were able to recognize the damage with an accuracy of 88 ± 20.21% and response time of 5.87 ± 2.33 s. As a result, it is concluded that the currently developed human–machine cooperation SHM may provide a useful framework to interact with abstract entities such as data from a sensor network.

Dynamic Analysis of a Reinforced-Concrete Post Tensioned Wind Turbine Tower

Wind energy turbines have drawn great interest especially for the last 2 decades. Today newly developed high-power wind energy generators require long blades and tall towers with large base diameter which exceeds the allowable width for highway transportation. The tower must also be divided through longitudinal and connected on site to overcome transportation problem. In this case welding difficulties, other technological aspects on site increase the cost of steel towers. However, concrete towers precast or cast on site, becomes a competitive alternative to current steel solutions for the wind energy towers, due to its lower cost and higher durability. As the generator on top produces a variable and continues vibration the dynamic properties of the towers becomes more important than any other structures due to resonance effect. In wind turbines, inexact calculation of natural frequencies or change of natural frequencies due to concrete cracking by time may harm the whole structure. So this makes post tensioning very important for wind energy towers. Post tensioning avoids tension strength which in turn prevents fatigue cracks in concrete elements which are exposed to tension strength. In this paper, the concept of a 100 m tall modular prefabricated posttensioned high-performance concrete 3.6 MW wind generator tower is presented. In the study the finite element model of the tower is prepared and under wind and rotor loads the structural analysis of the tower is presented.

Analysis of Strengthened Composite Beams Under Flexural Stress

A steel-concrete composite beam is composed of a steel beam and concrete slap connected with shear connectors. Composite beams are highly efficient structural members in order to load carrying capacity because the tension component of the force pair originating from bending is carried by the steel profile and the compressive component is carried by the concrete slab in composite beams. In this study, numerical and experimental analysis of steel-concrete composite and strengthened steel-concrete composite beams is presented. In experimental study, one strengthened and one un-strengthened specimens are produced and tested in bending. Strengthening is produced applying carbon fiber reinforced polymers sheet to the lower flange of the steel beam and using steel fiber reinforced concrete in the concrete slab. Specimens are tested under four-point loading test. During the tests, load, deflection and strain values are collected by data acquisition system. In numerical study, the finite element models of the steel-concrete composite beams are generated and analyzed by Atena-GiD program. Comparison and evaluations are made in terms of strength, applicability, stiffness and energy consumption about the steel-concrete composite beams with carbon fiber reinforced polymers and steel fibered concrete for both numerical and experimental results.