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Quality Analysis Of Grout In Post-tensioned Bridge Ducts And Study On Nondestructive Testing Methods

Posted on:2017-12-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:J B LuFull Text:PDF
GTID:1312330512459097Subject:Bridge and tunnel project
Abstract/Summary:PDF Full Text Request
The grouting quality control of prestressed ducts is an important part of the quality control of prestressed concrete project,and how to effectively detect the grouting quality of prestressed ducts has been the focus of researchers and engineers.To date,the methods that have been proved to be effective include radiography method,impact echo method and ultrasonic wave method,while the last two methods were widely used because the radiography method may lead to some security risks.The impact echo method has two shortcomings,including inability distinguish the duct which has initial defect or debonding between grout and corrugated duct case by shrinkage of grout.Concerning the application of ultrasonic wave method on grouting quality inspection,preliminary tests and numerical studies have been carried out by domestic and overseas researchers,however,systematical analysis has not been conducted on relevant parameters that affect the detection performance of ultrasonic tomography,and the relevant parameters include wave velocity difference within and outside the duct,type of corrugated duct and type of prestressed tendon.Accordingly,the main research contents of this paper are as follows:?.Experimental research and numerical simulation on impact echo method(1)Two concrete slabs with a hole to thickness ratio of 0.3 was designed and prepared,then the influence of parameters include the type of corrugated duct,longitudinal defect length,spacing of reinforcing steel bars and spacing of adjacent corrugated duct to thickness frequency of impact echo were analyzed.Experiment results showed that: under the empty corrugated duct case,the thickness frequency in the metal corrugated duct location,plastic corrugated duct location and the location of duct without corrugated duct were 0.81,0.79 and 0.80,respectively;with the ratio of longitudinal defect length to diameter of the duct of 0.5,no obvious migration of thickness frequency can be observed as compared with fullness grouted case;when the ratio of longitudinal defect length was larger than pore diameter of duct,the migration of thickness frequency ratio was larger than 10%;nevertheless,when the ratio of longitudinal defect length to diameter of duct was 2,the migration of thickness frequency ratio is still smaller than that of the duct without grouting.When the net spacing of the adjacent duct without grouting and the testing duct was larger than 0.5 diameter of duct,the evaluation of grouting state of duct was not significantly influenced by the duct without grouting.According to the results of reinforced steel bar with diameter of approximately 10 mm,the thickness frequency is basically keep unchanged as the minimum spacing of reinforcing steel bars decreases from 200 mm to 100 mm,.(2)A series of small specimens was designed and prepared,and the time variation law of thickness frequency for well grouted specimen,specimen with debonding defect and specimen with initial grouting defect were analyzed.The results showed that: the thickness frequency for well grouted specimen increased with the increase of the curing time of grout,and keeps steady as the strength of the grout tends to be stable;the time variation law of thickness frequency for specimen with debonding defect was the same as that of well grouted specimen before the grout debonding with the corrugated duct,after that,the thickness frequency of the specimen either shifted to lower frequency,or the thickness frequency invariant in the frequency spectrum with a lower low frequency peak value;the thickness frequency of initial grouting defect specimen in early curing stage was lower than that of well grouted specimen due to the defect,and the thickness frequency increased to a steady value with the increase of grout strength;when both initial grouting defect and debonding existed in the specimen,the thickness frequencies of specimens either shifted to lower frequency,or the thickness frequency invariant in the frequency spectrum with a lower low frequency peak value after the grout was debonded with the corrugated duct.(3)The three dimensional finite element model was established with ANSYS/LSDYNA,then the laws of thickness frequency of the hole thickness ratio(the Ratio of inside diameter of duct and plate thickness),the duct type,the wall thickness ratio(the Ratio of duct wall thickness and plate thickness)were analyzed.The results showed that: the ratio of thickness frequency of concrete slab without corrugated duct at all empty duct was closely related to hole thickness ratio and irrelevant to the thickness of the slab;the ratio of thickness frequency decreased with the increase of hole diameter-thickness ratio;the influence of thickness frequency of metal corrugated duct at all empty duct was greater than that of plastic corrugated duct;with the same hole thickness ratio and type of corrugated duct,the larger the wall thickness ratio,the larger the deviation of thickness frequency of at all empty duct than that at the solid position.Finally,the calculation formula of thickness frequency at all empty duct was given with considerations of all mentioned parameters,and the accuracy of the calculation formula was verified by experiments in the present study and relevant literatures.?.Theoretical and experimental research on ultrasonic tomography method(1)Defect of computing instability or low computational efficiency exists in the fundamental and improved linear travel time interpolation ray tracing algorithm(LTI)in forward modeling of ultrasonic tomography.Based on fundamental equation of LTI,law of seismic propagation and location information of node secondary source in the process of the minimum forward travel time calculation,a more efficient and stable LTI synthesis algorithm was proposed.The numerical examples showed that: for a numerical model that was a simulation of a practical engineering project,the computational efficiency of the improved algorithm proposed in this paper was about 12 times that of the most effective improved algorithm of LTI.Moreover,for a larger scale model,the proposed improved algorithm's computational efficiency was even more significant.(2)The influences of the bonding status of grout and corrugated duct,the internal and external wave velocity difference,the duct type and the type of prestressing tendon were analyzed from experimental and theoretical aspects.The results showed that: the ultrasonic tomography cannot distinguish grouting condition in the duct if the grout and the corrugated duct was debonding;when wave velocity difference within and outside the duct was relatively large,the first wave propagating time of the ultrasonic wave around the duct may be smaller than which the wave direct passing through the grout,and it is difficult to identify the grouting condition in the duct through the imaging results.Because,ultrasonic wave speed that around the metal duct propagated faster than that directly passing through the grout,the difference of imaging results before and after grouting for metal duct was less than that for plastic duct,such result indicated that the ultrasonic tomography was more suitable for plastic corrugated duct.Due to scattering attenuation at the interface of the different acoustic impedance and the limited sensitivity of ultrasonic sensor,the sensor can recognize ultrasound wave which pass through only limited steel bars.The test results showed that the ultrasonic wave can pass through 3 to 6 steel bars,and the greater the diameter of bar,the more significant contrast of the imaging results before and after grouting,the specimen with two bars in the same diameterof 28 mm,the contrast imaging results before and after grouting were significantly better than that of the built-in 16 strands of specimen.?.The comparison of detection effect of impact echo method and ultrasonic tomographyThrough the tests of two concrete slabs and a number of small specimens,the detection results between the impact echo method and the ultrasonic tomography method were compared.The results showed that: the impact echo method and ultrasonic tomography method cannot accurately determine the grouting condition if debonding existed in the interface between the grout and corrugated duct;however,the impact echo method can clearly distinguish two kinds of different grouting states include grouting and non-grouting when the internal and external wave velocity difference is large,and the effect of ultrasonic tomography was observed to be relativity poor;for the metal duct specimen,the impact echo method has a better efficiency of identifying the grouting condition in the duct than that of the ultrasonic tomography method;the detection results of the impact echo method was mainly associated with the sum area of prestressed bars in the duct,while the ultrasonic tomography method was closely related to the area of single prestressed tendons.The differences and similarities between the impact echo method and ultrasonic tomography method can be understood that these two methods were both developed on the basis of elastic wave,but the echo method was based on the transient resonance,the ultrasonic tomography was based on the minimum travel time.
Keywords/Search Tags:Prestressed Duct, Nondestructive Testing, Impact-echo, Ultrasonic Tomography, Numerical Simulation, Improved Algorithm
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