http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Gucunski, Nenad,Kee, Seong-Hoon,La, Hung,Basily, Basily,Maher, Ali Techno-Press 2015 Structural monitoring and maintenance Vol.2 No.1
One of the main causes of a limited use of nondestructive evaluation (NDE) technologies in bridge deck assessment is the speed of data collection and analysis. The paper describes development and implementation of the RABIT (Robotics Assisted Bridge Inspection Tool) for data collection using multiple NDE technologies. The system is designed to characterize three most common deterioration types in concrete bridge decks: rebar corrosion, delamination, and concrete degradation. It implements four NDE technologies: electrical resistivity (ER), impact echo (IE), ground-penetrating radar (GPR), and ultrasonic surface waves (USW) method. The technologies are used in a complementary way to enhance the interpretation. In addition, the system utilizes advanced vision to complement traditional visual inspection. Finally, the RABIT collects data at a significantly higher speed than it is done using traditional NDE equipment. The robotic system is complemented by an advanced data interpretation. The associated platform for the enhanced interpretation of condition assessment in concrete bridge decks utilizes data integration, fusion, and deterioration and defect visualization. This paper concentrates on the validation and field implementation of two NDE technologies. The first one is IE used in the delamination detection and characterization, while the second one is the USW method used in the assessment of concrete quality. The validation of performance of the two methods was conducted on a 9 m long and 3.6 m wide fabricated bridge structure with numerous artificial defects embedded in the deck.
Thermal strain behavior and strength degradation of ultra-high-strength-concrete
Lee, Y. W.,Kim, G. Y.,Gucunski, N.,Choe, G. C.,Yoon, M. H. Rilem Publications 2016 Materials and Structures Vol.49 No.8
<P>With the increasing application of high-strength-concrete (HSC) in high-rise-buildings for which structural safety performance is needed. However, the thermal mechanical behavior of HSC exposed to fire differs from that of normal-strength concrete (NSC). HSC is known to show different thermal strain behavior and strength degradation from NSC. It is needed to consider the thermal strain of HSC at elevated temperature under loading condition. In this study, the thermal strain behavior and strength degradation of HSC when exposed to elevated temperatures under loading conditions were examined experimentally. The compressive strength, thermal expansion, total strain, and hightemperature-creep at elevated temperatures were evaluated. To evaluate the thermal expansion of HSC at elevated temperatures, HSC with compressive strengths of 80,130, and 180 MPa concrete were heated to 700 degrees C at a rate of 1 degrees C/min. The total strain and high-temperature-creep were measured under the loading condition of 25 % of the compressive strength at room temperature. The experimental results clearly showed that the strength degradation of HSC increased with the higher compressive strength at elevated temperature. Thermal expansion occurred consistently regardless of the strength level without loading. However, 180 MPa concrete failed while being heated to around 300 degrees C. The transient creep had a large influence on the high temperature-creep as the HSC was heated at elevated temperature while under a load. It is considered that the reduced amount of aggregate and increased binder content make extremely density matrix in HSC, and it is particularly evident as the compressive strength increased.</P>
Evaluation of concrete degradation depending on heating conditions by ultrasonic pulse velocity
Hwang, Euichul,Kim, Gyuyong,Choe, Gyeongcheol,Yoon, Minho,Gucunski, Nenad,Nam, Jeongsoo Elsevier 2018 Construction & building materials Vol.171 No.-
<P><B>Abstract</B></P> <P>As the mechanical properties of concrete subjected to high-temperature heating decrease due to continuous degradation, it is necessary to evaluate the integrity of concrete in real time. Hence, the degradation monitoring (continuous integrity evaluation) of concrete subjected to high-temperature heating was examined by employing ultrasonic pulse velocity. In this study, the mechanical properties and the ultrasonic pulse velocity in concrete subjected to high-temperature heating were evaluated for ordinary-strength to ultra-high-strength concrete. To measure the ultrasonic pulse velocity in concrete during high-temperature heating, transducers were contacted to the top and bottom surfaces of the concrete specimens using SUS bars. This enabled monitoring of concrete degradation due to heating. In a range of 200–300 °C, it was confirmed that the thermal strain coincides with the static fracture strain at room temperature. The cracks generated during heating and the expansion of the cracks after cooling were clearly confirmed by continuous measurement of the ultrasonic pulse velocity. The cracks generated at temperatures up to 300 °C had little effect on the decrease in compressive strength. However, it was confirmed that the elastic modulus continuously decreased, because the cracks generated during heating and expanded after cooling led to strain increase at the peak stresses. Therefore, the evaluation method proposed in this study is anticipated to allow the integrity evaluation of concrete at high temperature heating.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Concrete of similar compressive strengths has different UPV depending on elastic modulus. </LI> <LI> UPV can measure expansion of crack width in concrete by cooling. </LI> <LI> UPV can decreases sharply during heating when thermal strain exceeds static fracture strain. </LI> <LI> Proposed method is anticipated to allow integrity evaluation of concrete during heating. </LI> </UL> </P>