Measurement on the Strength of Steel Bar in Reinforced Concrete Structure Using the Impact-Echo Method

• Main Authors: Wei-Ting Hung, 洪偉庭
• Other Authors: Chi-Hsing Wu
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/62235791379637597647

碩士 === 國立屏東科技大學 === 土木工程系所 === 99 === Firstly, the paper established a regression equation of steel yield strength fy vs its pressure wave velocity CS measured by opposite face. Several 160-cm steel bars with different strength were cut into a 60-cm piece and a 100-cm piece for each. The 60-cm pieces were measured the CS by placing detectors oppositely on two ends of the steel bar using an ultrasonic device to obtain the actual CS values, and then performed the tensile strength test to obtain the actual fy values. The 100-cm pieces were cast in concrete specimens. The impact-echo method and the improved ultrasonic pulse-wave were then employed to perform the surface measurement on the specimen to measure the CS of steels in the specimen. These measured CS values were then substituted into the regression equation to predict the fy values. The measured CS values and the predicted fy values by these two methods were compared with the actual CS and the fy values to evaluate their accuracies. For comparing these methods, the measured CS values by these two methods were performed t-test with the actual CS values respectively. The predicted fy values by these two methods were performed t-test with the actual fy values respectively. The test was to see there is significant difference between them. The test results shows that, the best correlation regression equation is a 2nd order polynomial equation fy=-0.00667697CS2 +74.4555CS-201457. The correlation coefficient R2=0.944. The applicable range of CS value is in 4800~5400 m/sec. The predicted range of fy value is in 2800~5600 kg/cm2. The error of the CS measured by the impact-echo method and the improved ultrasonic pulse-wave method measured are in the ranges of -0.68%~0.49% and -0.54%~0.93% respectively. The average error ΔCS are 0.329% and 0.357% respectively. The standard deviations σ of the CS measured by the impact-echo method are only in a range of 20.3~34.9 m/sec. The σ of the CS by improved ultrasonic pulse-wave method are only in a range of 0.0~50.0 m/sec. The coefficients of variation V of the CS measured by the impact-echo method are only in 4.08×10-3~6.94×10-3, while the V of the CS by the improved ultrasonic pulse-wave method are only in 0.00×10-3~8.62×10-3. The error Δfy by the impact-echo method are in -5.58%~7.44%. The average error Δfy is 3.36%. The error Δfy by the improved ultrasonic pulse-wave method are in -4.78%~13.09%. The average error Δfy is 3.58%. All the Errors are quiet small. The results show the accuracy and stability of the measured CS and the predicted fy by these two methods. Finally, the t-test shows that, the CS values measured by the impact-echo method have no significant difference with the actual CS, while those by the improved ultrasonic pulse-wave have significant difference. Therefore, the CS values measured by the impact-echo method are more accurate than those by the improved ultrasonic pulse-wave method. The fy values predicted by the impact-echo method have no significant difference with the actual fy, while those by the improved ultrasonic pulse-wave have significant difference. Therefore, the fy values predicted by the impact-echo method are more accurate than those by the improved ultrasonic pulse-wave method.and those measured directly on steel bars are well within 1.0%. The error percentages between the predicted fy values and the tensile strength fy values are in -4.8%~13.1%. The average error is 3.6%. The test results well show the accuracy of the proposed method.