- 學位論文
敲擊回音法檢測鋼筋混凝土結構之鋼筋強度
Measurement on the Strength of Steel Bar in Reinforced Concrete Structure Using the Impact-Echo Method
摘要
本文先建立鋼筋降伏強度fy值與鋼筋對打波速CS值之迴歸方程式，然後取9根160 cm的鋼筋，各切成60 cm和100 cm段。60 cm段鋼筋用來作超音波對打量測得實際CS值，量測完畢後，並進行抗拉強度試驗得實際fy值。100 cm段鋼筋則埋入混凝土試體中，再分別以敲擊回音法和改良式超音波法量測試體之CS值，並將量測之CS值代入迴歸方程式得到預測之fy值。最後將二法量測之CS值和預測fy值分別與實際CS值和fy值作比較，以評估其準確性。為了比較二法之量測CS值及預測fy值之優劣，將二法之量測CS值分別對超音波對打CS值作t檢定，再將二法預測fy值對抗拉強度試驗之fy值作t檢定，以檢定二者是否有顯著差異。 試驗結果顯示，最佳迴歸式為二次多項式fy=-0.00667697CS2+ 74.4555CS-201457，相關係數R2=0.944，其CS值之適用範圍介於4800~5400 m/s之間，預測之fy值在2800~5600 kg/cm2之間。敲擊回音法和改良式超音波法量測之CS值與對打CS值之誤差百分比分別為-0.68%~0.49%和-0.54%~0.93%之間，平均ΔCS分別為0.329%和0.357%。另外利用標準差σ和變異係數V來檢測二法量測CS值的變異性，其敲擊回音法之σ介於20.3~34.9 m/s之間；改良式超音波法之σ介於0~58.0 m/s之間。而敲擊回音法之V於4.08×10-3~6.94×10-3之間；改良式超音波法之V於0~8.62×10-3之間。敲擊回音法之Δfy介於-5.58%~7.44%之間，平均Δfy為3.36%；而改良式超音波法之Δfy介於-4.78%~13.09%之間，平均Δfy為 3.58%。誤差皆很小，顯示二法量測之CS值和預測fy值的穩定性及準確性。最後，t檢定結果顯示，敲擊回音法量測CS值與對打CS值並無顯著差異，改良式超音波法則有顯著差異，因此，敲擊回音法量測之CS值較改良式超音波法更為準確。敲擊回音法預測之fy值與實際fy值並無顯著差異，改良式超音波法則有顯著差異，因此，敲擊回音法預測之fy值比改良式超音波法更為準確。
並列摘要
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.