Prestressed Concrete Cylinder Pipe Research Articles

Time-varying analytical model and mesoscopic numerical simulation of chloride ion diffusion in prestressed concrete cylinder pipe

In this paper, a time-varying analytical model for chloride ion diffusion in Prestressed Concrete Cylinder Pipe (PCCP) protective layer is established based on the separation of variables method and Bessel function. The model takes into account factors such as steam curing, pipe radius, curing age, and exposure time. Meanwhile, the mesoscopic numerical simulation is conducted on the chloride ion diffusion behavior in the PCCP protective layer, and the effects of aggregate content, interfacial transition zone (ITZ) volume fraction, and ITZ chloride ion diffusion coefficient on chloride ion diffusion are analyzed. Results show that the aggregate has inhibitory effect on the diffusion process of chloride ions, without considering the influence of ITZ. As the aggregate content increases, the average depth of chloride ion diffusion decreases linearly. In the event of both the influence of aggregate content and ITZ are considered, there is a competitive relationship between the two. The larger the diffusion coefficient of chloride ions in ITZ, the larger the average diffusion depth of chloride ions is. In addition, the correctness of the numerical model and analytical model is compared and verified by combining their calculation results. Compared with traditional chloride ion diffusion models, the smaller the pipe diameter, the more accurately the chloride ion diffusion law can be reflected by the analytical model.

Intelligent circumferential deformation prediction of structures in PCCP-E with a large diameter under internal water overpressure based on prototype experiments and Inception-ResNet-LSTM

Prestressed Concrete Cylinder Pipe (PCCP) is extensively employed in long-distance water transmission projects, owing to its notable pressure-bearing capacity and durability. Nonetheless, the operation under overpressure conditions poses a risk of structural damage and functional failure to PCCP during its service life. Consequently, accurate prediction of the deformation characteristics of overpressure operation with the structural deformation data under standard water pressure is of great importance for ensuring the safety and reliability of the project. However, it is a challenge to obtain spatiotemporal features for traditional algorithms. As a consequence, a novel deep learning model, i.e. Inception-ResNet-LSTM, is put forward to forecast PCCP deformation. It integrates the Inception, ResNet, and Long Short-Term Memory (LSTM). Based on the prototype experiments, the monitoring was undertaken on the deformations of the inner and outer concrete layers, the steel cylinders, and the prestressed steel wire under internal water pressures of 0 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1.0 MPa, and 1.15 MPa. In the case study, the deformation data of different structures are input into Inception-ResNet-LSTM to establish a model. For all the structures, the R2 (coefficient of determination) of the Inception-ResNet-LSTM model exceeds 0.97. Based on the results, it is demonstrated that the model has captured the spatiotemporal features from the monitoring data. In comparison to models based on DL and ML algorithms, Inception-ResNet-LSTM demonstrates superior performance, exhibiting heightened accuracy and enhanced generalization capabilities. It provides a new method for PCCP deformation estimation under overpressure.

Experimental study on identifying the number of wire breaks in prestressed concrete cylinder pipe based on piezoelectric sensing technology

Identifying wire breaks in prestressed concrete cylinder pipes (PCCP) has become an important research topic in recent years. Based on previous numerical studies, this paper presents the first experimental study to identify the number of wire breaks in a PCCP using piezoelectric sensing technology. During the experiment, wire breaks were simulated on a large-diameter embedded DN4000 PCCP and small-diameter lined DN700 PCCP, with a testing device designed to realise the identification method using body stress waves as a medium. Based on the analysis of the output voltage, two types of damage indices were adopted to evaluate the wire break damage. The optimal identification frequencies and corresponding damage indices were determined for different engineering application scenarios. The experimental results are consistent with those of previous numerical simulation studies, further confirming the validity of this technique.

Dynamic Response of PCCP under the Rockfall Impact Based on the Continuous–Discontinuous Method: A Case Study

Rockfalls are major geological hazards threatening prestressed concrete cylinder pipes (PCCPs) in water diversion projects. To accurately assess the impact of large deformation movements of rockfalls on PCCPs, this study utilized the continuous–discontinuous method to investigate the dynamic response of a PCCP under a rockfall. The impact mode of rockfalls, the mechanical characteristics of PCCP, and the nonlinear-contact characteristics between soil and PCCP were considered in this study. The advantages of continuous and discontinuous numerical simulation methods were utilized to establish a continuous and discontinuous coupling model of “tube-soil-rock” considering the interaction of soil and structure. The impact mechanism and process of PCCP under the rockfall were investigated by simulating the rockfall process and analyzing its spatiotemporal evolution. The influence of PCCP under rockfalls with different heights and radii was studied to clarify the effects of these two parameters on the PCCP. Combined with a practical application example of large-scale water transfer projects, there is a tendency of center flattening under static load and dynamic impact load, and the PCCP part directly below the impact point is the most dangerous. This investigation provided a comprehensive understanding of the impact mechanism of the PCCPs under rockfall. The findings of this study have significant implications for the design of the protection engineering of PCCPs and ensuring the safe operation of water diversion projects.

Sparrow search mechanism-based effective feature mining algorithm for the broken wire signal detection of prestressed concrete cylinder pipe

To enhance the capability of distributed optical fiber (DOF) monitoring system on real-time broken wire signal detection of prestressed concrete cylinder pipe (PCCP), this research proposes a novel effective parameter mining algorithm by utilizing wrapper theory and sparrow search algorithm (SSA). First, the improvement approach of SSA is investigated by applying the adaptive adjustment strategy, the Gaussian mutation perturbation, and the Tent chaotic perturbation. The subset search method is constructed based on the improved SSA (ISSA). Second, the similarity degrees of vibration signals are characterized by the Euclidean distance and the average linkage distance. On this basis, the subset evaluation criterion is established according to the classification accuracy of hierarchical clustering (HC). Finally, the prototype experiment is conducted in which the phase-sensitive optical time-domain reflectometry (Φ-OTDR) monitoring system is employed to collect vibration signals. Then, the effectiveness and the performance of the developed methodology are validated. The following results are drawn. (1) Benchmark function tests indicate that the convergence performance, the optimization ability, and the operation stability of ISSA are superior to those of SSA and the improved particle swarm optimization (IPSO). (2) The original set that has 122 feature parameters is established, and ISSA-HC, IPSO-HC, and SSA-HC extract 24, 31, and 55 effective parameters, respectively. (3) The recognition accuracies of the 3 parameter subsets are 95.83%, 84.17%, and 80.83%, respectively. The parameter subset mined by ISSA-HC has the best pattern recognition ability. This research provides technical support for the broken wire monitoring of in-service PCCP engineering. Meanwhile, it offers a foundation for further developing suitable pattern recognition algorithms to identify PCCP broken wire signals.

Effects of prestressing wire corrosion on the load response law and bearing capacity of PCCP

The corrosion of prestressed steel wires plays a crucial role in the failure of prestressed concrete cylinder pipes (PCCP). To explore the load-bearing response of prestressed steel wire corroded PCCP and the impact of prestressed steel wire corrosion on the load-bearing capacity of PCCP, a high-precision finite element model of buried PCCP with prestressed steel wire corrosion was established, and a bearing test was conducted based on this model. The results show that the corrosion of prestressed steel wires has the greatest impact on the mortar protective layer and outer core concrete, and the corrosion point at the waist of the pipe is the most detrimental to the pipeline. In addition, as the degree of corrosion of the steel wire increases, the mortar protective layer and outer core concrete at the corrosion point first crack under the action of compressive stress and internal water pressure. Finally, it was verified that the constructed bearing capacity model of PCCP with different corrosion points had high accuracy and could be used to predict the bearing capacity of corroded pipelines. This article can provide theoretical support for the structural safety monitoring and repair of PCCP in service.

Using EPS and CFRP liner to strengthen prestressed concrete cylinder pipe

The prestressed concrete cylinder pipe (PCCP) with broken wires should be strengthened to maintain the safe operation of the pipeline. A new reinforcement technology is proposed in this study: expanded polystyrene (EPS) + carbon fiber reinforced polymer (CFRP) liner. The innovative method allows CFRP to bear the internal pressure prior to PCCP, greatly improving the reinforcement effect of the pipe. A three-dimensional finite element model is established and assessed by the experimental results. Then, the mechanical properties of the PCCP when subjected to different pressures and wire breakage are analyzed under three conditions (i.e. no strengthen, strengthened by only CFRP liner, and strengthened by EPS+CFRP liner). And the improvement effect of the innovative technology on the PCCP's bearing capacity compared with the traditional method is studied. The results showed that when repaired by 8-layer CFRP liner only and EPS and 6-layer CFRP composite liner, the internal pressure bearing capacity of PCCP can be increased by 9.17% and 50.83%, respectively. Based on the elastic limit state of the pipe, the wire breakage threshold of PCCP is 65 and 89 under the cases of no repair and CFRP liner repair. For the case of EPS + CFRP liner repair, when the number of broken wires is 100, the steel cylinder does not yield.

A Simplified Limit-State Design and Verification for Prestressed Concrete Cylinder Pipes under Internal Water Pressure

Ignoring the effect of a concrete core on bearing performance, the current design of prestressed concrete cylinder pipes (PCCPs) under internal water pressure only focuses on the fracture of prestressed steel wire, while the complexity of the AWWA C304 design method leads to a strong dependence on software that cannot be sufficiently mastered by the designers. In view of these issues, a simplified limit-state design process was induced to eliminate a large number of iterative operations and was verified by a three-dimensional finite element model (FEM) with a prototype test of PCCPs under internal water pressure. Meanwhile, the bearing performance of PCCPs was investigated using the parametric simulations of the FEM. The results showed that the cross-sectional area of the prestressed steel wire is higher by about 10% than that designed using the AWWA C304 method. The FEM provides a complete evolution process of the mechanical response of the structural constituents and simulates the strain mutation phenomenon of the prototype test well. The internal water pressure of the PCCPs designed using the simplified limit-state design process has enough safety to reach 4.7 times the working pressure at serviceability and 5.5 times the pressure at the ultimate limit state. A burst in the PCCPs took place under an internal pressure greater than 6.75 times the working pressure. The result of the FEM shows that an increase in the tensile strength of the concrete core is of great significance for improving the bearing performance of the PCCPs.

Mechanical behavior of PCCPs with broken wires under complex service conditions

Buried prestressed concrete cylinder pipes (PCCPs) are subjected to the combined effects of soil cover loads, internal water pressure, and additional loads. However, there is scarce research on their mechanical performance under complex service conditions after being buried. In this study, 3D nonlinear finite element (FE) models of PCCPs and soils, along with fluid models, were developed using ABAQUS and FLUENT, respectively. Fluid–solid coupling numerical simulations of PCCPs with broken wires under complex service conditions were conducted using the MpCCI platform. The study focused on investigating the mechanical behaviors of PCCP pipes with broken wires, aiming to determine the effects of different numbers and locations of broken wires, as well as the magnitude of operating water pressure. The results shows that the number of broken wires is a crucial factor affecting the mechanical behaviors of the PCCPs; the dynamic variation of internal pressure within the pipe can cause further damage to PCCPs with pre-existing defects; when wire breakage occurs alone the springline of the PCCPs, the outer concrete core exhibited a tendency to crack before the inner concrete core. Conversely, when wire breaks occurred at the crown and invert, the inner concrete core cracked before the outer concrete core. These results provide valuable insights into the behavior of PCCPs under complex conditions and contribute to the understanding of their structural integrity. The findings can aid in the development of improved design and maintenance strategies for PCCPs, ensuring their reliable performance in underground applications.

Investigating the possibility of PCCP mortar coating leaching and the impact on drinking water quality

AbstractThe objective of this article was to investigate the potential for the dissolution and leaching of certain chemical elements from the protective mortar coatings of prestressed concrete cylinder pipe (PCCP) into drinking water in the event of leakage and how this might affect the overall quality of the water delivered to consumers. The mortars as linings are also typically used for renovation of old pipes. Samples from three frequently used mortar coating mixtures underwent immersion in water after 28 days of curing and were monitored for 430 days. The water was tested for pH levels and the presence of aluminum, chromium, lead, and iron, in accordance with the standards set for human consumption in Moroccan and other countries such as Australia, Canada, and the United States, as well as organizations such as the European Union and World Health Organization. The results indicate that the highest levels of aluminum, iron, chromium, and lead leaching occurred after the initial contact with water, gradually declining over time. Furthermore, the inclusion of silica fume and fly ash in the coating increases the potential for chemical element leaching. Additionally, preinstallation pipeline washing demonstrates its effectiveness in reducing the leaching of chemical elements into drinking water in the event of leakages. The overall results suggest that the likelihood of contamination of drinking water by leaching of chemical elements from the mortar coating in case of a leakage appears to be negligible under the studied conditions.

The impacts of CFRP widths and thicknesses on the strengthening of PCCP

Wire breakage is a regular occurrence of prestressed concrete cylinder pipe (PCCP). This research investigates the impact of fiber reinforced polymer (CFRP) width and thickness on the strengthening effect of the new technology (i.e. externally wrapping CFRP to strengthen a PCCP). Firstly, using the finite element method (FEM), a three-dimensional numerical model of PCCP is established, and the model is validated and verified using existing test data. Following that, the stress and strain changes of each material in PCCP when repaired with various CFRP thicknesses and widths are examined, as well as the improvement in PCCP bearing capacity. Finally, the impacts of CFRP thickness and width on the internal pressure threshold are investigated, based on visible cracks in the concrete core. The difference between FEM and test is 2.4% under internal working pressure. After CFRP reaches 10 layers, the growing trend of PCCP bearing capacity slows down under a broken wire ratio of 10%. The broken wire ratio has a significant impact on PCCP bearing capacity, which increases as the widths and layers of CFRP grow, although the trend gradually decreases.

Failure experiment on CFRP-strengthened prestressed concrete cylinder pipe with broken wires

The prestressed concrete cylinder pipe (PCCP) has been used widely in hydraulic engineering. However, due to hydrogen embrittlement and corrosion, the prestressing wires in PCCP can break and cause pipe failure. In this study, a retrofitting technique of using externally bonded carbon fiber reinforced polymer (CFRP) to repair PCCP was proposed. The technique is particularly useful when shutting down water is not possible. The proposed strategy was evaluated by using a full-scale PCCP with a 2.8 m inside diameter loaded with internal water pressure. First, the PCCP strains before and after repair were compared under different internal pressures. In the presence of CFRP, the strains near the broken wires significantly decreased under the same internal pressure, and the carrying capacity of the PCCP increased. PCCPs with 13 %, 15 %, and 18 % wire breakage ratios were then evaluated and compared. The strain in each material increased with increasing wire breakage ratio, and the maximum strain in CFRP was observed at the location of wire breakage. Considering the PCCP with 18 % wire breakage ratio, the section 2300 mm from the pipe end was in the linear state under an internal pressure of 0–0.9 MPa, and the PCCP reached its serviceability and elastic limit states when the internal pressure increased to about 1.0 MPa and 1.2 MPa, respectively. Finally, when the internal water pressure was increased to 1.27 MPa, which was higher than the internal design pressure of 1.12 MPa, the PCCP failed due to the rupture of CFRP.

A YOLOX-Based Automatic Monitoring Approach of Broken Wires in Prestressed Concrete Cylinder Pipe Using Fiber-Optic Distributed Acoustic Sensors.

Wire breakage is a major factor in the failure of prestressed concrete cylinder pipes (PCCP). In the presented work, an automatic monitoring approach of broken wires in PCCP using fiber-optic distributed acoustic sensors (DAS) is investigated. The study designs a 1:1 prototype wire break monitoring experiment using a DN4000 mm PCCP buried underground in a simulated test environment. The test combines the collected wire break signals with the previously collected noise signals in the operating pipe and transforms them into a spectrogram as the wire break signal dataset. A deep learning-based target detection algorithm is developed to detect the occurrence of wire break events by extracting the spectrogram image features of wire break signals in the dataset. The results show that the recall, precision, F1 score, and false detection rate of the pruned model reach 100%, 100%, 1, and 0%, respectively; the video detection frame rate reaches 35 fps and the model size is only 732 KB. It can be seen that this method greatly simplifies the model without loss of precision, providing an effective method for the identification of PCCP wire break signals, while the lightweight model is more conducive to the embedded deployment of a PCCP wire break monitoring system.

Experimental and numerical analysis of strengthening prestressed concrete cylinder pipes using a post-tensioning method

Prestress loss caused by broken wires can lead to a decline in the carrying capacity of prestressed concrete cylinder pipes (PCCPs). The strengthening of PCCPs using a post-tensioning method is becoming more and more widely utilized to restore strengthened pipes to the needed design capacity and to withstand combined loads. There is no need to drain the pipe during strengthening construction, and this strengthening actively replenishes the prestress loss caused by wire breakage at a cost-effective price. To verify the strengthening effect of this method, a full-scale test and its corresponding three-dimensional finite-element model were established. A three-dimensional numerical model of three continuous prototype pipes was established and accounted for the particularity of the bell and spigot. The numerical model of prestressing wires was optimized in two aspects, which was more in line with the actual situation. The spiral winding method instead of single winding was adopted to apply prestress, and the prestressing wires with a broken point were partitioned into two separate areas due to the bond quality between the mortar coating and the wires. The simulation and the full-scale test both contain the five processes of strengthening with external prestressed strands as follows: pressurized to working pressure→breaking the prestressing wires until visible cracks propagate→gradual depressurization to artesian pressure→the tensioning operation of strands→and pressurized to design pressure. A sensitivity analysis of the related factors of strengthening was performed through finite-element simulation to provide a better understanding of the design. The simulation results were consistent with the data on the full-scale test and indicated the rationality of this process. The strengthening of PCCP with a post-tensioning method can meet the design demand and is a feasible strengthening method. The working pressure and control coefficient of tensioning have the most significant impact on the strengthening effect. Technical recommendations and a better understanding of the application of the post-tensioning method on PCCP are provided in this study.

A time-variant model of chloride diffusion in prestressed concrete cylinder pipe (PCCP) considering the effects of curing age

Chloride penetration is considered as the most responsibility to steel corrosion for PCCP during service. Compared with ordinary concrete structures, the curing method of PCCP is generally steam-curing. Despite numerous contributions have shown that curing age has significant effect on the resistance to chloride penetration of concrete. There is still a lack of critical understanding of the curing age effect on the chloride migration in steam-cured concrete. For this reason, this paper aims to establish a chloride diffusion model suitable for PCCP. In this study, the non-steady-state chloride diffusion coefficient and chloride concentration of steam-cured concrete are measured through RCM test and chloride diffusion simulated test, respectively. The apparent chloride diffusion coefficient and surface chloride concentration are calculated based on Fick’s second law. Moreover, the instantaneous chloride diffusion coefficient was estimated. It is found that the steam-cured concrete cannot ignore the influence of curing age on the chloride penetration resistance, according to RCM test results, the non-steady-state chloride diffusion coefficient of 28 days decreased by 33 % compared with that of 3 days, while the chloride diffusion coefficient of 90 days decreased by 15 % compared with 28 days under steam curing. The larger the curing age, the smaller the chloride concentration at each depth, as well as the chloride diffusion coefficient and surface chloride concentration. In addition, it can be concluded that with the increase of exposure time, the chloride diffusion coefficient decreases gradually, while the surface chloride concentration increases gradually. Thus, the two kinds of test results and theoretical analysis were combined to establish the time-variant models of instantaneous chloride diffusion coefficient and surface chloride concentration of steam-cured concrete considering the effects of curing age and exposure time. On this basis, a new chloride diffusion model considering the effects of curing age, exposure time, the time-variant chloride diffusion coefficient and time dependence surface chloride concentration was established, which plays an important role in durability evaluation of PCCP.

Steel wire prestress analysis of large section jacking prestressed concrete cylinder pipe (JPCCP): Site experiment and numerical investigation

As one of the key factors of Jacking Prestressed Concrete Cylinder Pipe (JPCCP), stress condition of the steel wire has a significant influence on the safety and durability of the JPCCP. In this paper, the stress of the steel wire was analyzed in the process based on the in-situ test monitoring results and numerical investigation in the water conveyance project in Shanghai. According to test results, the stress losses during the entire process were ruled out and turned out to be quantized. The reduction rate of steel wire was quite high in the early stage of prestress, and gradually slowed down with the time. The relaxation of steel wire was the main influencing factor of prestress loss. The numerical model of JPCCP was established and verified by field test data. Mechanical properties and failure modes of JPCCP under high inner water pressure and under different prestress losses were analyzed. After the initial prestress of steel wire was reduced from 1048 MPa to 888 MPa, the prestress of concrete in pipe core was reduced by 15%, while the compressive stress of the outer concrete was reduced by 23%. The water pressure carrying capacity of the structure was reduced by 10%. The larger the prestress loss of the steel wire was, the earlier the concrete in the pipe core entered the plastic phase. The results indicate that the prestress loss of steel wire has a direct and prominent influence on the bearing capacity of the water pressure on JPCCP. To help tunnel designers incorporate the prestress requirement into their basis of design and structural analysis, an assessment method was also proposed.

Experimental study on the influence of scattered broken wires on the structural performance of prestressed concrete cylinder pipe

Given that the prestressed concrete cylinder pipe (PCCP) derives compressive strength from high-tensile prestressing wires, breaking of steel wires is endangering the safety of PCCP lines. To deeply explore the influence of broken wires on the performance of PCCP, two 3.4 m PCCPs with the same design parameters are tested until failure by separately cutting their steel wires in clustered and scattered manners. And this paper mainly presents the destructive test with scattered broken wires (SBWs) under the water pressure of 1.15 MPa. To collect spatially continuous strain data, four different types of distributed optical fibers are applied on five material layers of the test pipes during the production. The results show that the distribution of breakpoints is highly scattered and each broken wire regains its full tension gradually over about a 60° angle from the breakpoint when the number (ratio) of SBWs does not exceed 120 (39.6 %). As a consequence of the subsequent wire breakage, the scattered breakpoints gradually concentrate, and then mortar cracking and delamination from the wires occurs and increases the length of the wire needed to regain full tension. The numbers (ratios) of SBWs corresponding to the onset of visible cracks in the outer concrete, and mortar, yielding of the steel cylinder, visible cracks in the inner concrete, and final failure are 125 (41.3 %), 145 (47.9 %), 165 (54.5 %), 170 (57.8 %), and 185 (61.1 %), respectively. The measured sizes of breakpoint separation show that the SBWs in one wire-cutting zone has small influence on other zones. And the number of SBWs is greater than three times that of clustered broken wires at the final failure. Both the number and concentration degree of broken wires should consequently be factored into the condition assessment of PCCP. It is worth reminding that the test results obtained are not to be applied indiscriminately to other pipe designs.

Full-Scale Test and Bearing Capacity Evaluation of Large Diameter Prestressed Concrete Cylinder Pipe under Internal Water Pressure

In practical applications, the safe operation of large-diameter prestressed concrete cylinder pipes (PCCPs) depends on the loading performance under internal water pressure. However, there is lack of damage tests for the full-scale large-diameter PCCPs due to economic cost and experimental difficulty. In this paper, a full-scale PCCP with diameter of 3.2 m was tested to verify the bearing capacity for applying to an actual water transfer project. The PCCP was designed by the limit state method and manufactured in a prefabrication plant. During the test, the strains of concrete, prestressed steel wire, and mortar were detected to evaluate the limit state of bearing capacity under internal water pressure. Based on the test results and the strain analysis at the limit state, it was found that when the water pressure reached 1.9 MPa, the concrete outside the steel cylinder was at the serviceability limit state, and the prestressed steel wire was in elastic, while some protective mortar exceeded the serviceability limit state due to the appearance of visible cracks. A good accuracy of the theoretical calculation with the predicted results lower about 9.4% and 8% than tested pressures at decompression and cracking states. Moreover, the cracking pressure of concrete and bursting pressure of pipe were 2.5 and 6 times of the working pressure according to the calculation results. This indicated that the PCCP used in this study had sufficient safety in actual operation. However, it should be noted that the tensile control strain of mortar may be overestimated by the current code.

Experimental Study on External Loading Performance of Large Diameter Prestressed Concrete Cylinder Pipe

A prestressed concrete cylinder pipe (PCCP) is created with a complex composition of concrete core, welded steel cylinder, prestressed steel wire, protective mortar and anti-corrosion coating. Due to the economy and complexity of structural prototype tests, the ultimate loading test on PCCP is rarely conducted. In this paper, the three-edge bearing test was carried out on a 3.2 m diameter PCCP with embedded steel cylinder. The strains of concrete core, prestressed steel wire and protective mortar were monitored, and the distribution and width of the concrete cracks were recorded. The test results show that the cracking on the inside concrete at the crown zone occurred before those on the invert zone of the pipe. The prestressed steel wire postponed the tensile stress of out-side concrete at the springing line until subjected to the calculated cracking load (Pc). Due to the moment redistribution caused by the cracking on the inside of the concrete at the crown/invert, the protective mortar at the springing line was cracked at 1.2 Pc and exhibited visible cracking after 1.4 Pc. The prestressed steel wire reached the elastic and strength limit states of 1.4 Pc and 1.6 Pc, respectively. The PCCP designed by the limit state design method can resist the increased external loads after reaching the serviceability limit state. The final failure load of the test pipe is greater than 1.6 Pc, and there is sufficient safety in actual operation. Due to the fact that the damage to the concrete at the crown/invert zone may become a fuse of PCCP failure, the tensile stress of the inside concrete at the crown/invert zone of the PCCP should be accurately verified in the design process.

Effect of the Location of Broken Wires on Prestressed Concrete Cylinder Pipes under Working Pressure

The precise analysis of the overall mechanical performance of prestressed concrete cylinder pipes (PCCPs) with broken wires is a complicated problem. In this article, powerful finite element numerical means are applied to solve this problem. Firstly, the advantages and shortcomings of the current prestress simulation methods in the finite element analysis (FEA) literature are discussed, and the initial stress method based on a novel single-spring joint element method to model the pre-stress of wires is proposed. Then, different distributions of broken zones, including random broken distributions, are developed for two typical PCCP pipes with different wire-wrapped layers. The established nonlinear FEA model considers actual service processes such as manufacturing, installation and operation to investigate the mechanical behavior of two typical PCCP pipes with different breakage distribution regions and breakage ratios, and in particular, the overall mechanical behavior of a pipe with random breakage is determined first. To verify the accuracy of the proposed pre-stress simulation method and the established nonlinear finite element model, the overall mechanical response of a pipe before wires broke is compared with the results obtained via the specifications. The computed results under the corresponding breakage assumptions are consistent with the conclusions in the existing literature, providing important guidance for pipeline management and operation.