MXPA96006126A - Methods for the non-destructive evaluation of pretens concrete structures - Google Patents

Abstract

The present invention relates to a method for evaluating the condition of a cylindrical prestressed concrete tube, wherein the tube comprises at least one layer of internal concrete, a layer of prestressed wires disposed around the inner concrete layer and a layer of external mortar arranged on the prestressed wire layer, this method comprises the steps of: a) determining the frequency domain characteristics and the speed characteristics of compressed sound waves and reflected cut generated from an applied impact signal to the inner surface of the concrete layer of a tube known to be in good condition, b) to determine the characteristics of the frequency domain and the speed characteristics of compressed sound waves and reflected cut generated by an impact signal identical to the internal surface of the concrete layer of the tube being evaluated, and c) compare the signals detected in step b) with the signals detected in step a) and to determine whether the layer of pretension wires has been broken

Description

METHODS FOR THE NON-DESTRUCTIVE EVALUATION OF PRETENSED CONCRETE STRUCTURES.

D E S C R I P C I O N Field of Invention This invention is directed to methods for the non-destructive evaluation of prestressed or reinforced concrete structures. More particularly this invention is directed to methods for the non-destructive evaluation of prestressed concrete structures such as those of cylindrical prestressed concrete pipe (PCCP).

Background of the Invention Large pipes, known as main pipes for water distribution, supply the water for distribution through smaller diameter distribution pipes to the municipal communities. These large tubes have diameters typically in the range of 40.64 cm to 365.76 cm and for special projects has a diameter of up to 640.08 cm and transport the water under pressure so that the water can eventually supply under pressure to thousands of taps and other outlets .

As with other infrastructure components, the main water distribution pipes are subjected to both environmental stresses and stresses that, over time, degrade the pipeline to the point of failure. When a water pipeline fails, the results are often catastrophic, as millions of gallons of water flow into the land and undermine adjacent surface structures such as roads and occasionally constructions.

According to the above, in addition to the loss of drinking water, which is not economical to accumulate, there is the expense of repairing the main pipes, filling in the holes left by the cracks in the pipes and repairing the adjacent structures. The repair, reconstruction and restitution of damages caused by large volumes of water leaking from a single fault can cost in the scale of a few hundred thousand to millions of pesos. With the age of the structure, the number of failures that occur will increase, costing the municipalities hundreds of millions of pesos each year.

Since the water distribution pipes are buried, there is usually no effective way to monitor the condition of the walls of the water pipes from the surface of the land. Although seismic systems may reveal the place and composition of a pipe material, seismic systems are not sensitive enough to reveal the condition of the pipe walls. The radar is also now used to penetrate the surface of the earth and reveal phenomena below the surface but, like sonar, radar signals can not reveal the wall structure. In addition, the soil above the water pipeline can vary in composition and contain other structures such as rocks and varied debris that interfere with the consistency of the reflected signals. As with the PCCP there is no leakage before a crack, which explodes suddenly, the leak detection technology can not be used to identify risk conditions that can develop.

In that current technology there is no means to predict failures adequately by evaluating the pipe structure from the surface of the earth; Attempts have been made to predict tube failures by evaluating from within the tube. To date, no effective methods or devices have emerged to do this.

The only indicator of eventual tube failure is the occurrence of a longitudinal crack that appears during the last stages of a progression to pipe failure. This longitudinal crack occurs on the inner surface of the tube wall and coincides with approximately a break of 40 turns of wire at the end of the tube and 10 turns of wire at the average length of the tube. As there is only a short period of time between the appearance of this longitudinal crack and the fault, the occurrence of the crack may only be hours, weeks or perhaps several months before the break. This warning is inadequate because it carries nothing about the state of adjacent tubes that may have damages that have progressed until just before the appearance of a visual crack.

In view of the aforementioned considerations, there is a need for a provision that can evaluate the structure of a water distribution pipe and predict if and, with some degree of reliability, when a fault will occur, so that strategies can be carried out. risk management.

THE INVENTION It is a feature of the present invention to provide a method not greatly improved for assessing the condition of prestressed or reinforced concrete structures.

In a more specific aspect, it is a feature of the present invention to provide a method for evaluating the condition of pre-stressed concrete structures such as prestressed concrete cylindrical tubes used, for example, in the main water distribution networks.

In view of these and other features, the present invention is directed to a method useful for evaluating the condition of a prestressed concrete cylindrical pipe where the pipe comprises either a lined steel cylinder or a steel cylinder embedded with at least one internal concrete layer, a layer of prestressed wires arranged around the steel cylinder or a layer of concrete and an outer mortar layer disposed on the layer of prestressed wires. According to the method, compression and cutting sound waves with frequency domain characteristics and speed characteristics are generated from an impact signal applied to the inner surface of the concrete layer of a tube in good condition. The frequency domain characteristics and the velocity characteristics of the reflected compression and cut sound waves are then generated by applying an impact signal of the same intensity to the inner surface of the concrete layer of the tube being evaluated. The detected signals of the tube are evaluated and then compared with the detected signals of the tube that is known to be in good condition in order to determine if a rupture has occurred in the layer of prestressed wires.

In a more specific aspect, the tube under evaluation uses prestressed steel wire as the wire material and includes a steel membrane between a concrete core layer and a lining layer of the inner layer of the concrete.

BRIEF DESCRIPTION OF THE DRAWINGS.

Various other objects, features and advantages that are achieved with the present invention will be more fully appreciated when it comes to be better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts in the various drawings, and where: Figure 1 is a perspective view with portions in section illustrating a tube of a first configuration.

Figure 2 is a perspective view, similar to Figure 1, of a tube having a second configuration.

Figure 3 is a perspective view, partially in section, of the tube of Figure 2 monitored by an inspection apparatus.

Figure 4 is a graph showing the amplitude as a function for a sound wave propagating through a prestressed concrete cylindrical tube (PCCP) in good condition.

Figure 5 is a graph similar to figure 4, but showing the propagation of a sound wave in a PCCP tube in bad conditions.

Figure 6 is a graph showing the amplitude as a function of the frequency ode propagating in a PCCP tube in good condition.

Figure 7 is a graph showing amplitude as a function of frequency as a sound wave propagating in a PCCP tube in poor condition; Y Figure 8 is a side elevational, schematic view of a portion of the tube of Figure 2 and shows the sonic or ultrasonic waveforms propagating in different layers of concrete.

DETAILED DESCRIPTION.

Referring now to Figure 1, a PCCP tube 10 of a first embodiment known as a cylindrical lined tube is known.

The tube 10 includes a layer of internal concrete 12, a layer of steel 14 which forms what is known as a steel membrane, a layer 16 of wires consisting of rolled steel wire and finally a layer of mortar 18 which wraps the Steel reinforcing wires over areas that do not support the steel membrane.

The PCCP tube 10 is coupled to a second tube 20 PCCP similarly configured by a gasket 22. In gasket 22, there is an annular rim 24 extending from the tube 10. The rim 24 has a gasket 26 on the lower side around which the reinforcing wire 16 'is wound. steel on steel cylinder 14. The flange 24 is also superimposed on a male end 38 of the PCCP tube 20 with the gasket 26 on the flange supporting a gasket 30 on the male end of the tube 20. The junction is then covered by a layer of sealing mortar 32.

Figure 2 describes a second embodiment of the PCCP tube 30 which is differently configured from the tube 10 of figure 1 in which a steel cylinder 36 is embedded in the concrete. The tube 30 includes a core concrete layer 32, a concrete liner layer 34, a steel membrane 36 and a core layer 38. Arranged on the core layer 38 is the wire layer 40 consisting of steel reinforcing "wire" 42 wrapped around the core layer. The steel reinforcing wire 42 is in turn enveloped by a layer 30 of mortar interfacing in the soil 44 surrounding the pipe 30 and preventing the surrounding earth environment from contacting and corroding the steel wire 42.

In the embodiment of Figure 2, the tube 30 engages a second tube 50 of a similar configuration with a seal 52. At the joint 52, the concrete core 38 is re-scaled from the liner layer 34 to form a annular shoulder 54 having an annular gasket 56. The tube 50 has an opposite complementary step 58, formed by indentations in its concrete lining layer 60 with respect to the concrete core layer 62. A gasket 64 is placed on the projecting portion of the concrete core 62 and engages the packing layer 56 on the projecting annular flange 54 of the tube 30. An annular mortar bead 64 with a rib portion 66 extends between the cores 62 and 38 of concrete of the respective tubes 44 and 50 and seals the gap in the joint 52 of the tube.

In both cases, the tubes 10 and 30, the reinforcing wires 16 and 42, respectively, place the internal concrete layers 12 and 32, respectively, in circumferential compression which allows the tubes to withstand a water pressure inside the tube of the order. of 14 kg / cm. Without the prestressed steel reinforcing wire 16 or 42, the pressure inside the tubes 30 and 10 forces the steel cylinder to separate and water begins to drain through the walls of the tube, resulting in destruction of the steel. very fast tube.

When the first turn of the wire 16 or 42 is broken, as illustrated by the areas 70 and 72, a compression difference is immediately located between the portions of the concrete cores 12 or 38 compressed by the wires and the portions thereof. concrete cores that have had their compression released by breaking the wires. Over time, the stress that results between these adjacent portions of the concrete cores 12 and 38 reaches a level that exceeds the physical strength of the concrete cores 12 and 38, the microcracking 73 of the cores starting. Over time these cracks grow.

When the tubes 10 and 30 deteriorate the sides adjacent to the ruptures 70 and 72, the mortar 18 and 43 delaminates from the wires 16 and 12, respectively. More of the wire turns 16 and 42 come to be exposed to the water with soil and eventually additional wire breaks occur which in turn increases the number and rate of cracks in the concrete cores 12 and 38.

When the delamination continues, groups of wire turns 16 and 42 fall and the crack extension of the concrete cores 12 and 38 is severely increased. Since the cylindrical steel membrane 36 is relatively thin, it will break when not sufficiently supported by the concrete core 38. The break is accelerated by the holes 74 occurring in the concrete core 38 and concrete layer 34.

Normally, a sudden burst failure occurs when approximately 100 of the 16 or 42 turns of intermediate tube wire are broken. If the deterioration occurs near the joints 22 and 52, the total failure of the tubes occurs sooner due to the rupture of few, approximately 40, turns of wire 16 'or 42', which will result in failure.

Referring now to Figure 3, the apparatus 100 configured to perform the method of the present invention is schematically shown. The apparatus 100 may have a number of configurations. At the present time, the apparatus 100 may be configured as a simple hand-held device that is held against the surface 102 of the tube 30 or may be a sensory wheel vehicle that is radially urged to engage the surface 102 of both rotational and axial movements with respect to to the wall 102. The apparatus 100 is shown to be in direct contact with the surface 102 of the wall, but it is contemplated within this invention to have an apparatus traveling in water and a full tube 30, both transmitting and receiving signals through of water and tube wall so that the tube does not need to be emptied in order to be evaluated.

The inspection apparatus 100 includes an impact source 110 and at least one sensor 112. Additional sensors such as the sensor 114 can also be employed. The impact source 110 can be a simple impact of a small steel sphere discharged at a selected rate against the wall 102 to generate sonic waves or it can be an ultrasonic generator that collides with the surface of the wall 102 with an ultrasonic signal. In any case, the signals generated will have the characteristics indicated in figures 4 to 7.

Referring now to Figures 4 and 5, the amplitudes of a compression wave and a cutoff wave are plotted as a function of time for a concrete tube 30 that is in good condition.

In Figure 4, the sensor 112 is displaced 30 cm from the impact source 110. The impact occurs at time zero. The signal 120 detected by the sensor 112 is flat by approximately 70 microseconds. At 70 microseconds, the compression wave is detected. At approximately 130 microseconds, the cutoff wave is detected, resulting in an abrupt increase in the amplitude 140 of the signal. The combined amplitude of the compression and cutting waves then decays with the reflections occurring at points 142, 144 and 146. In tubes 30 having good concrete, the compression wave velocity is 34.290 cm per second and The speed of the cutting wave is approximately 20,320 cm per second, these speeds are computed by the movement of waves in the axial direction with respect to the tube.

The characteristics of the compression wave and the cutting wave that are presented in the graph of Figure 4 for tubes having good concrete are then used in a comparison to determine when a tube is in bad condition by comparing the signal of Figure 5 with the signal of figure 4.

Referring now to Figure 5, it is already evident that the signal 120 'differs from the signal 120. If the concrete in the tube 30 is decompressed because of the breaking of the turns of wire 42, then the speed of the compression wave it is reduced from about 34,290 cm per second to about 20,320 cm per second, and the cutting wave velocity is reduced from about 20,320 cm per second to about 10,768 cm per second.

How the compression wave speed is reduced, the signal 130 'of the compression wave is detected at approximately 130 microseconds instead of approximately 70 microseconds. The speed of the cutting wave is also reduced so that the cut-off signal identified by peak 140 'is detected at approximately 230 microseconds instead of at 130 microseconds. Furthermore, since the speeds of the compression and cutting wave are reduced in a tube 30 in poor condition, the reflections 142 'and 144' with the decompressed concrete occur after the reflections 142 and 144 in the compressed concrete of a sound tube . The number of detectable reflections is also reduced so that there may be insufficient signal strength to generate a third detectable reflection 146.

In addition to the delayed detection times, it is also evident that the signal peak 140 'indicating detection of the cut wave in the degraded tube is practically lower than the peak 140 which indicates the detection of the cut wave in the tube sonorous.

By comparing the detection times for the compression and cutting waves as well as comparing the amplitudes of the cutting wave, an evaluation of the condition of the tube 30 can easily be made.

Referring now to Figures 6 and 7, where the amplitude of the detected signals as a function of frequency is illustrated, it is seen that the amplitude / frequency waveforms for defective concrete (Figure 7) differ substantially from the characteristics of the amplitude / frequency waveform for the concrete of a sound tube. The reasons for this difference are evident when considering the schematic illustration of figure 8 directed to tube 30 of figures 2 and 3.

Referring now to Figure 8, it can be seen that the concrete liner layer 34 propagates a first sound wave 150 and the concrete core 38 propagates a second sound wave 152. The first and second sound waves 150 and 152 are subsequently combined to produce a composite wave 154 that passes through the steel membrane 36.

As can be seen in Figure 6, when the frequency domain is monitored by the concrete tube in good condition, the composite wave 154 resonates at approximately 10,000 Hz as evidenced by the peak 160 wave. Sound wave 152 in concrete core 38 resonates at approximately 18,000 Hz as evidenced by peak 162, while the first harmonic of composite wave 154 resonates at approximately 23,000 Hz as evidenced by peak 164. The wave 150 in the concrete liner layer 34 resonates at approximately 31,000 Hz as evidenced by peak 166, while the second harmonic of composite wave 154 resonates at approximately 37,000 Hz as evidenced by peak 168. For concrete in good conditions with the compression wave velocity of about 34.290 cm / sec and a cut-off wave velocity of about 20.320 cm / sec there is a defined frequency domain pattern compared to the frequency domain pattern for decompressed concrete that it is shown in figure 7, which indicates the probability of a future catastrophic break.

As can be seen in Figure 7, the resonance of wave 154 occurs at about 6,000 Hz as evidenced by peak 170 of the signal wave. Resonance of wave 152 in core sample 38 occurs at approximately 8,000 Hz as evidenced by peak 162 '. The peak at 160 'represents the resonant period of a weak cracked concrete zone due to delamination and fractures. This is similar to a "drum head" effect used to detect delaminated concrete by detecting with the human ear the signal of a chain drag used in the evaluation of road bridge decks. The remaining peaks 171-178 are additional evidence of cracks in which the local zones have their own resonant frequencies and also cause destructive and constructive interference from the traveling strained waves. These peaks are of a relatively low amplitude and are more numerous than the peaks of Figure 6. According to the above, comparing the frequency domains for a tube that is being evaluated (Figure 7) with the frequency domain of the tube that it is known that it is in good condition, it can be detected if wire turns 42 are broken, which results in decompressed or otherwise damaged concrete.

Clearly, by comparing the time and amplitude parameters of Figure 5 with respect to those of Figure 4 and comparing the frequency domain characteristics of Figure 7 with those of Figure 6, an illustration occurs It consists of a portion of the tube 30 that helps evaluate the tube 30 that is used for the water supply and decides when the tube 30 is replaced. As a main distribution tube includes hundreds of tube sections 30 a program of maintenance to replace degraded tube sections in poor condition first and then perhaps replace other sections after additional monitoring. The signals of Figures 4 to 7 of each tube section can be stored for subsequent comparisons to determine if degradation accelerates with time.

Using the method of the present invention, early detection of potential leaks in water distribution pipes is possible by allowing sections of the pipe that are in bad condition to be replaced before they break. A program that employs this method can therefore save millions of pesos to the water company or water equipment and at the same time reduce the minimum damage to breakage and property damage caused by catastrophic leaks in the main water distribution pipes.

Sonic / ultrasonic stress wave measurements can detect microfractures of the tube concrete that are not visible as well as macro-fractures that are visible. The process of deterioration of the concrete starts from microfractures which, with continued fatigue for any cause, coalesce and become macrofractures that lead progressively towards faults through the horizontal development of cracks that precedes the imminent failure. Since the initial microfractures occur years before the failure, a system employing the principles of the present invention is useful as a pre-alarm system for handling pipes.

From the foregoing description, one skilled in the art can easily determine the essential characteristics of this invention and without departing from the spirit and scope of the same can make various changes and modifications of the invention to adapt it to various uses and conditions.

Claims (11)

R E I V I N D I C A C I O N S

1. - A method for evaluating the condition of a prestressed concrete cylindrical tube, wherein the tube comprises at least one layer of internal concrete, a layer of prestressed wires arranged around the inner concrete layer and a layer of external mortar arranged on the pre-stressed yarn layer, this method comprises the steps of: a) determining the frequency domain characteristics and the speed characteristics of compressed sound and reflected cut waves generated from an impact signal applied to the internal surface of the concrete layer of a tube that is known to be in good condition; b) determining the characteristics of the frequency domain and the velocity characteristics of compressed sound and reflected cut waves generated by an identical impact signal applied to the inner surface of the concrete layer of the pipe being evaluated; and c) comparing the signals detected in step b) with the signals detected in step a) and to determine whether the prestressed wire layer has been broken.

2. - Method according to clause 1, wherein the speed characteristics that are determined include compression wave velocity and cutting wave velocity.

3. - Method according to clause 2, wherein the frequency domain characteristics are monitored to detect a drum head effect indicating a broken prestressed wire layer.

4. - Method according to clause 3, wherein the amplitude of the compression wave and the amplitude of the cutting wave are also determined in steps a) and b) and compared in step c) to determine if the layer of threads is broken .

5. - Method according to clause 1, wherein the inner layer of concrete includes a core layer and a lining layer with a steel membrane disposed therebetween and wherein the frequency domain characteristics are monitored for low frequencies and additional peaks which occur in stage b) in comparison with the frequencies and peaks that occur in stage a).

6. - Method according to clause 5, wherein, if the frequency domain characteristics determined in step b) have lower frequency resonances for the core layer and liner layer individually and for the combined core and liner layer that the frequency resonances detected in step a) when compared in step c), the thread layer is broken.

1. - Method according to clause 1, wherein, if the compression and cutting speeds determined in step b) are lower than the compression and cutting speeds determined in step a) when compared in step c), the Thread layer is broken.

8. - Method according to clause 1, wherein the prestressed wire layer is made of rolled steel wire.

9. - Method according to clause 1, wherein the speed of the compression wave is approximately 34,290 cm / sec and the speed of the cutting wave is approximately 20,320 cm / sec if the layer of threads is unbroken and is 20,320 cm / sec approximately and approximately 10.768 cm / sec, respectively, if the layer of threads is broken.

10. - Method according to clause 1, wherein the impact signal is a sonic signal.

11. - Method according to clause 1, wherein the impact signal is an ultrasonic signal. SUMMARY A method is provided to detect a degraded tube used in main lines of water distribution, monitored sound waves detected and observing the characteristics of those waves. The main water distribution tubes have collars around highly tensioned steel wire that hold the concrete that comprise the compressed tubes. When the steel wire is corroded by water that runs off through the mortar that encapsulates the pipe, the steel wire eventually breaks, thus releasing the compression of the concrete adjacent to the break. Sonic and ultrasonic sound waves traveling through the concrete of the tubes have different characteristics for a tube in good condition compared to the characteristics of the sound waves traveling through the tube in poor conditions due to decompression and / or other Causes. The sound waves in the tube in poor conditions travel more slowly with cutting waves that have less amplitude and reflections that occur at later times. further, the frequency domain characteristics of the tube in bad conditions differ from the frequency domain characteristics of the tube in good condition. In a tube in poor condition, resonance occurs at lower frequencies than in the tube in good condition. In addition, a drumhead effect on the tube in poor condition is evident, which drumhead effect does not occur with the tube in good condition.