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- MakaleYayıncıda açık erişim2019An experimental study on the compressive response of CFRP honeycombs with various cell configurations
Pehlivan, Levent; Baykasoğlu, Cengiz
The experimental investigation on the compressive response of carbon fiber reinforced polymer (CFRP) honeycombs with various cell configurations was carried out in the present work. The CFRP honeycomb specimens were manufactured by corrugation technique, in which the prepreg CFRP sheets were first corrugated into the certain shape using corrugated aluminum moulds under heat and pressure, and then the corrugated CFRP sheets were glued and stacked to construct honeycomb specimens. Twenty-seven groups of specimens were experimentally tested to examine the effects of cell geometry (i.e., square, circular, and hexagonal), cell wall thickness and height on the quasi-static out-of-plane crushing performance of the honeycombs. The square, circular, and hexagonal honeycomb specimen groups were designed to have almost the same weights. The results showed that the cell wall thickness is an significant parameters on the overal crushing response of the CFRP honeycombs while the out-of-plane compressive strenght of the honeycombs is generally independent of the height. It is observed that the hexagonal specimen groups have generally superior crushing performance in comparison with the square and circular counterparts due to their large double foil bonding surfaces. The experimental results also revealed that the crushing properties of the honeycomb structures with the core densities of 157–282 kg/m 3 could be increased more than two times with the appropriate selection of cell configurations.
- MakaleYalnız künye2016Retrofitting Effect on the Dynamic Properties of Model-Arch Dam with and without Reservoir Water Using Ambient-Vibration Test Methods
Altunisik, Ahmet Can; Günaydin, Murat; Sevim, Baris; Bayraktar, Alemdar; Adanur, Suleyman
Continuous health monitoring and regular condition assessment is of vital importance for engineering structures in general and especially for arch dams. These structures can be exposed to many different loads such as earthquake, blast, wind, ice, and water pressure, which may cause deterioration and loss of structural integrity. Such development may have severe economic consequence and, more importantly, may present a serious risk to public safety. Therefore, the structural behavior of arch dams must be monitored at regular intervals during their service life, although the overall failure rate of these dams is around 1%. Experimental measurements by ambient vibration test methods are among the most commonly preferred inspection techniques for the evaluation of structural performance and safety. The aim of this research is to examine the retrofitting effect on the dynamic properties of a damaged arch dam model, with and without reservoir water, after retrofitting with high-strength structural repair mortar and carbon fiber reinforced polymer composite material. To this end, an arch dam-reservoir-foundation model was built. In the study, ambient vibration tests were carried out for three test-cases to determine changes in dynamic properties, such as natural frequency, mode shape, and damping ratio before and after retrofitting. The three cases were (1)a severely damaged dam with full reservoir (Case-A), (2)a repaired dam with full reservoir (Case-B), and (3)a strengthened dam with full reservoir (Case-C). In addition, all the measurement tests were repeated with an empty reservoir to extract the effect of water. Data for the ambient vibration tests were gathered from the dam body during vibrations by natural excitations. These excitations were provided through small impacts, and the response signals were measured by sensitivity accelerometers placed at the crest points. To obtain the experimental dynamic properties, the enhanced frequency domain decomposition method in the frequency domain was used. Comparisons of experimentally identified dynamic properties for the damaged and the retrofitted dam showed that the retrofitting application affected the structural behavior of the arch dam considerably. It was very effective in restoring the structure's original dynamic properties.
- MakaleYalnız künye2015CFRP composite retrofitting effect on the dynamic characteristics of arch dams
Altunişik, Ahmet Can; Günaydin, Murat; Sevim, Bariş; Bayraktar, Alemdar; Adanur, Süleyman
The purpose of this study is to investigate the effect of retrofitting dynamic characteristics of a damaged laboratory arch dam model, subsequently repaired with high-strength structural mortar and strengthened with composite carbon fiber reinforced polymer. This study constructed in laboratory conditions is a prototype arch dam-reservoir-foundation model. Five test cases of ambient vibration on the arch dam model illustrate the changes in dynamic characteristics: natural frequency, mode shape, and damping ratio, before and after retrofitting. The ambient vibration tests collected data from the dam body during vibrations by natural excitations which provided small impacts and response signals from sensitivity accelerometers placed at crest points. Enhanced Frequency Domain Decomposition Method in the frequency domain extracts the experimental dynamic characteristics. At the end of the study, experimentally identified dynamic characteristics obtained from all test cases have been compared with each other. Apparently, after the retrofitting, the natural frequencies of the dam body increased considerably, demonstrating that the retrofitting, including repairing and strengthening is very effective on the flashback of initial dynamic characteristics.