Tendon Failure Research Articles

Detection of tendon breaks in prestressed concrete structures using coda wave interferometry

AbstractTendon breaks significantly threaten the safety of prestressed concrete structures. Failure of embedded tendons does not necessarily indicate as surface cracks, demonstrating the need for early detection methods. This paper presents a novel ultrasound‐based approach for detecting and localizing tendon breaks using coda wave interferometry. Already few embedded ultrasonic transducers form a robust monitoring network able to detect subtle changes in the structure. To demonstrate the feasibility of detecting tendon breaks, a post‐tensioned concrete beam was fabricated at Ruhr University Bochum, Germany. A break of a centric and eccentric tendon was artificially created by drilling from the outside. Both were successfully detected and localized through characteristic changes in the ultrasound results without any evidence of damage on the concrete surface. Measurements with fiber optic sensors validate the ultrasonic findings and provide insights into the re‐anchoring behavior after tendon failure.

Transmission length of multiwire tendon in existing post-tensioned concrete structures

The paper presents unique research on real-scale post-tensioned concrete crane girders dismantled from an existing hall structure. The study aimed to determine the transmission length for bonded prestressing tendons in an anchorage failure situation, a critical factor for proper assessment of the safety of many building structures, mainly those built between the 1950s and 1980s. The results of the tests indicated the feasibility of prestressing force transmission from a 12Ø5 mm Freyssinet-type tendon to the element via bond stress, with implications extendable to the other 18Ø5 mm tendon type prevalent at the time. The key factor affecting transmission efficiency is the quality of tendon duct grouting, with good quality cement injection resulting in transmission length as short as 800 mm. Furthermore, a computational model for the transmission length of prestressing force in post-tensioned concrete members has been developed similarly to the Model Code 2020 for pretensioned concrete. The level I of approximation enables quick transmission length estimation, whereas refined analysis is possible with the level II approach. The developed model and the research findings facilitate a comprehensive assessment of the post-tensioned concrete members in anchorage or tendon failure scenarios. As a result of the analyses carried out, optimal strategies for the further use of the structures can be proposed, fostering a step towards sustainable management.

Redundancy and reliability levels of post-tensioned and grouted concrete cross-section in case of tendon failure

Since the 1960 s and 1970 s, the prestressing steel used on post-tensioned concrete (PTC) bridges has been known to be susceptible to stress corrosion cracking (SCC). This can result in brittle rupture of the prestressing steel. Objective of this study is to evaluate the reliability levels achieved with assessment method developed for verifying crack behaviour before failure in cross-section of PTC bridges with cross-section loss of prestressing steel. Additionally, the study aims to investigate of tendon loss on crack before failure behaviour. This paper applies a reliability analysis for methodology based on robustness analysis on crack before failure behaviour in PTC with deteriorating prestressing steel. The analysis involves examining cross-sections with various design criteria. The effects of choices made in designing the PTC structure are analysed and noted to have a significant impact on the safety margin of the structure, while the deterioration of prestressing steel does not significantly decrease the ductility of the cross-section if certain conditions are met. The use of stricter serviceability limit-state (SLS) criteria used in past design results the greater safety margin for the structure in the event of tendon loss, which therefore makes it beneficial for structural redundancy in the ultimate limit state (ULS).

Monitoring tendon breaks in concrete structures at different depths using distributed fiber optical sensors

Unannounced tendon breaks are a dreaded failure mechanism in concrete bridges. The failure of single wires or tendons does not necessarily cause cracking of the concrete. Thus, the damage cannot be detected by visual inspection. But, in the case of tendons bonded in concrete, re-anchoring causes characteristic local strain fields: tensile strains occur between the crack edges while three-dimensional compressive strains develop in the area around. On the surface, these strains are small and depend, e.g., on the concrete stiffness, the depth of the tendon inside the member and the anchorage length. Such strain fields can be measured by fiber optical sensors on the surface in two dimensional grids. By evaluating the backscatter of emitted light beams, minimal strain changes (uncertainty: ±1 µm/m) can be detected in quasi-continuous resolution (0.65 mm pitch). An experimental investigation on a prestressed concrete beam with bonded tendons is presented. Gradually, three tendons of 10.5 mm diameter were mechanically cut to simulate failure, while longitudinal strains were measured on a 2D grid at the surface. With a prestressing force of 64.5 kN and up to a depth of 25 cm breaks of the tendons could be detected. They caused strains about 10-15 µm/m at the surface at maximum. For varying tendon positions, the effect of depth on the strain is investigated by two sided measurements. As the distance between the break and the concrete surface increases, the strain significantly decreases but remains detectable. In the future, the results enable deeper analyses of the most influential parameters. The final aim remains to precisely detect the position and number of failed wires or tendons just from the strain signal at the surface.

Indirect Head of the Rectus Femoris Tendon as a Graft for Segmental Hip Labral Reconstruction: An Anatomic, Radiographical, and Biomechanical Study in Comparison With Iliotibial Labral Reconstruction

Background: The indirect head of the rectus femoris (IHRF) tendon has been used as an autograft for segmental labral reconstruction. However, the biomechanical properties and anatomic characteristics of the IHRF, as they relate to surgical applications, have yet to be investigated. Purpose: To (1) quantitatively and qualitatively describe the anatomy of IHRF and its relationship with surrounding arthroscopically relevant landmarks; (2) detail radiographic findings pertinent to IHRF; (3) biomechanically assess segmental labral reconstruction with IHRF, including restoration of the suction seal and contact pressures in comparison with iliotibial band (ITB) reconstruction; and (4) assess potential donor-site morbidity caused by graft harvesting. Study Design: Descriptive laboratory study. Methods: A cadaveric study was performed using 8 fresh-frozen human cadaveric full pelvises and 7 hemipelvises. Three-dimensional anatomic measurements were collected using a 3-dimensional coordinate digitizer. Radiographic analysis was accomplished by securing radiopaque markers of different sizes to the evaluated anatomic structures of the assigned hip.Suction seal and contact pressure testing were performed over 3 trials on 6 pelvises under 4 different testing conditions for each specimen: intact, labral tear, segmental labral reconstruction with ITB, and segmental labral reconstruction with IHRF. After IHRF tendon harvest, each full pelvis had both the intact and contralateral hip tested under tension along its anatomic direction to assess potential site morbidity, such as tendon failure or bony avulsion. Results: The centroid and posterior apex of the indirect rectus femoris attachment are respectively located 10.3 ± 2.6 mm and 21.0 ± 6.5 mm posteriorly, 2.5 ± 7.8 mm and 0.7 ± 8.0 mm superiorly, and 5.0 ± 2.8 mm and 22.2 ± 4.4 mm laterally to the 12:30 labral position. Radiographically, the mean distance of the IHRF to the following landmarks was determined as follows: anterior inferior iliac spine (8.8 ± 2.5 mm), direct head of the rectus femoris (8.0 ± 3.9 mm), 12-o’clock labral position (14.1 ± 2.8 mm), and 3-o’clock labral position (36.5 ± 4.4 mm). During suction seal testing, both the ITB and the IHRF reconstruction groups had significantly lower peak loads and lower energy to peak loads compared with both intact and tear groups (P = .01 to .02 for all comparisons). There were no significant differences between the reconstruction groups for peak loads, energy, and displacement at peak load. In 60° of flexion, there were no differences in normalized contact pressure and contact area between ITB or IHRF reconstruction groups (P > .99). There were no significant differences between intact and harvested specimen groups in donor-site morbidity testing. Conclusion: The IHRF tendon is within close anatomic proximity to arthroscopic acetabular landmarks. In the cadaveric model, harvesting of the IHRF tendon as an autograft does not lead to significant donor-site morbidity in the remaining tendon. Segmental labral reconstruction performed with the IHRF tendon exhibits similar biomechanical outcomes compared with that performed with ITB. Clinical Relevance: This study demonstrates the viability of segmental labral reconstruction with an IHRF tendon and provides a detailed anatomic description of the tendon in the context of an arthroscopic labral reconstruction. Clinicians can use this information during the selection of a graft and as a guide during an arthroscopic graft harvest.

Use of a Krackow suture technique with PEEK barrel augmentation for subscapularis repair is stronger than use of a Mason-Allen suture technique

BackgroundIn total shoulder arthroplasty, the subscapularis tendon is routinely mobilized, by tenotomy, peel, or lesser tuberosity osteotomy, to visualize the joint and allow proper implant positioning. Careful mobilization of the subscapularis is undertaken to achieve an anatomic tension-free repair. This cadaveric study tests the biomechanical differences of 2 repair techniques of the subscapularis peel (SP) compared to the classically described technique. We hypothesize that adaptation of this SP technique using a custom-designed polyether-ether-ketone (PEEK) barrel in the bicipital groove may further stabilize suture repair of the subscapularis. MethodsTwenty paired cadaveric shoulder specimens underwent SP and repair via transosseous suture fixation. The PEEK barrel used was a laboratory prototype designed for the study (Catalyst OrthoScience, Naples, FL, USA). Five specimens were repaired using a traditional Mason-Allen suture; their paired shoulders were repaired using the PEEK barrel and a Mason-Allen suture. Five specimens were repaired using the Krackow suture; their paired shoulders were repaired using the PEEK barrel and a Krackow suture. Mechanical testing was performed using a uni-axial materials testing system with primary outcome of gap displacement and secondary outcomes of maximum load to failure and method of failure. ResultsThe Krackow repair method with and without PEEK augmentation was significantly stiffer than the Mason-Allen repair method with and without PEEK augmentation (P < .001 across all groups). Adding augmentation changed the strength of the Mason-Allen repair without achieving statistical significance (P = .0925). Intergroup differences in cyclic displacement were not statistically significant. The Krackow repair methods had higher mean maximal load at failure than the Mason-Allen repairs of 534 ± 108 N and 266 ± 98 N, respectively (P < .001). Maximum load at 5 mm displacement was significantly different across groups (P = .004). Methods of failure in the Mason-Allen technique groups included knot and tendon failure, and in the Krackow technique groups included suture failure and lesser tuberosity fracture. ConclusionRepairing the subscapularis with a Krackow suture is significantly stronger than a Mason-Allen repair in stiffness as well as load to failure. The results reported here compare a Krackow suture with a more common Mason-Allen suture configuration, and demonstrate the application of PEEK augmentation to subscapularis repair techniques. This study can guide surgeon selection of an ideal subscapularis repair technique for stemmed or stemless total shoulder arthroplasty.

Degradation of structural safety levels in prototype balanced beam systems

Post-tensioned balanced beam structures are very sensitive to natural deterioration and excessive environmental attacks, which can lead to relatively rapid drops in safety levels. Since partial failure or corrosion of pre-stressing tendons can be difficult to detect, the strategy of last resort to ensure that safety levels are acceptable remains to perform a mechanical load test, with the risks that this entails. In the case of some iconic balanced beam systems, destructive investigations are further limited by the need to comply with the deontological standards valid for cultural heritage structures. The capacity and robustness of balanced beam systems can therefore be estimated by relying primarily on accurate mechanical models and sensitivity analyses against scenarios that may degrade safety. To this end, reference models can be corroborated by information from various sources, including experimental campaigns and archives. This study, in particular, focuses on the evaluation of the residual capacity offered by Morandi's prototype balanced beam scheme, to aid prognosis, and possibly support “decision-making” for possible reuse. Finally, an experimental and numerical application to the most complex post-tensioned concrete balanced beam system ever designed by Riccardo Morandi is presented, i.e. the roofing system of Pavilion V of Torino Esposizioni dating back to the late 1950 s.

Comparison of Suture Types and Techniques in Achilles Tendon Repair: An Ex Vivo Biomechanical Animal Experiment.

The ideal suture technique and type in tendon repair remain unclear. This biomechanical study aimed to assess the biomechanical characteristics of three techniques-modified Kessler (mKE), modified Krackow (mKR), and modified tension Bunnell (mtBU)-in sheep Achilles tendon tear repair using three suture types-polypropylene, polyester, and ultra-high-molecular-weight polyethylene (UHMWPE)-which are also compared. Sixty-three Achilles tendons harvested from sheep were transversely hacked as a replacement for rupture in a standardized measure and repaired using mKE, mKR, and mtBU techniques with No. 2 polypropylene, polyester, and UHMWPE sutures. Biomechanical parameters, such as Young's modulus, ultimate strength, and strength to the 5-mm gap, were recorded for statistical analysis. The mtBU technique with UHMWPE use resulted in increased ultimate strength, strength to 5-mm gap, Young's modulus, and quantity of specimens with low clinical failure modes compared with the other techniques with other suture materials. Furthermore, mtBU has the lowest thickness at the repair side of the tendons. This approach showed tendon failure during maximal traction testing, whereas the mKE and mKR techniques had polyethylene and polyester suture failures. The UHMWPE suture was significantly superior to the other sutures in each technique in terms of strength and durability. The mtBU technique using UHMWPE suture showed better biomechanical results, implying that this repair might be more appropriate to obtain early mobilization after tendon ruptures.

Experimental study of tendon failure analysis for a TLP floating offshore wind turbine

This paper describes an experimental study conducted on a multi-column tension leg platform (TLP) floating offshore wind turbine (FOWT). A prototype model of the TLP FOWT supporting the NREL 5-MW wind turbine with a scale ratio of 1:50 is tested under various wind and wave conditions at the State Key Laboratory of Coastal and Offshore Engineering at Dalian University of Technology, China. This work has particularly focused on the tendon failure and its impact on the dynamic response of the FOWT. Free decay tests, regular wave tests, wind-wave combined tests and tendon failure tests are conducted using different environmental parameters.The results suggest that natural periods, dynamic responses of the platform, and forces in the tendons satisfy the design requirements. The analysis indicates that the impact of tendon failure on the platform surge, heave and pitch responses are found to be insignificant. When one of the tendons is broken, the adjacent tendons experience a significant increase in tensile force; and, the maximum tensile force in the remaining tendon is found to increase by about 130%. The overstepping of the minimum breaking load as recommended by the design standard DNV GL is not reached, and this indicates that the safety of the system is ensured even during the harshest failure condition.

Inspection for Voids in the Grout below the Protective Duct of an External Post-Tensioning Bridge Tendon Using a THz A-Scanner

Grout voids in the tendons of a post-tensioning bridge reduce their strength. Grout voids are also severe flaws causing corrosion of the steel strands in the tendons. Detecting voids during construction and operation of the tendons is essential to prevent tendon failure, which is critical to bridge safety. This study presents a method for inspecting external tendons for voids in the grout below the protective duct pipe using terahertz electromagnetic waves. Due to low attenuation in the high-density polyethylene duct and the large reflectivity difference between the duct/grout and the duct/void interfaces, terahertz waves are suitable for detecting voids in the grout inside tendons. For this study, we developed a mobile frequency-domain terahertz A-scanner that can be used to measure terahertz A-scan data in real time. It is shown that the mobile terahertz A-scanner can be used to assess the area of the grout void in external bridge tendons.

An Experimental Study on the Deterioration Behaviour of External Tendons Due to Corrosion

An external tendon failure of the PSC box girder was found due to corrosion in South Korea, and the maintenance authorities promoted a study on evaluation and maintenance methods. One of their concerns was to confirm that the tendons were constantly available through repair when voids or minor corrosion were found in ducts. This study, thus, conducted external tendon experiments with insufficient grout filling and corrosion, and the resulting decrease in deterioration behaviours was investigated. The corrosion was accelerated during the experiment, and the strains and prestressing force were measured. The test results indicated minimal reductions in prestressing force and strain as the corrosion was induced, followed by significant fluctuations when a corroded wire ruptured. Prior to the rupture, the strain development was approximately 130 µε. However, after the rupture, the strain increased significantly, reaching a maximum of 4,296 µε in compression and 2,776 µε in tension. It was also confirmed that enough grout ratio to strands resulted in meaningful stress redistribution among the strands and that the wire rupture caused various strain development due to impact load. Based on the test result, a method for corrosion monitoring after re-grout was also proposed using low-power sensing and strain gauges.

Experimental investigation on the fatigue performance of multi-tendon basalt fiber reinforced polymer cable

The fatigue performance of fourteen basalt fiber reinforced polymer (BFRP) cables, each containing 37 tendons with a diameter of 4 mm, was investigated. Four testing schemes were employed to examine the failure mechanism and factors affecting fatigue behavior, including manufacturing technology, tendon surface shape, and anchoring method. The findings suggested that the fatigue life of the cable was controlled by the tendon surface shape, and subsequently affected by both anchoring method and manufacturing technology. The pretension method can eliminate the wedge action of the load transfer component (LTC). The splitting failure of ribbed tendons usually initiated from transverse cracking of resin matrix and eventually leaded to continuous interface debonding. Interlayer splitting in tendons can be avoided by adjusting the outer fiber from bending to flattening, which improves the tensile stiffness of the cable with round tendons under cycle load. The cable can achieve 2 million cycles while maintaining a stable deformation state, which is achieved by using round tendons in combination with a variable-stiffness LTC composed of epoxy resin and glass microfibers. The variable-stiffness LTC effectively alleviated stress concentration at the loading-end cable. The static anchoring efficiency of the cable with round tendons reached 110% after undergoing 2 million cycles.

Recent failures of external prestressing grouted tendons: when the ducts take on water…

AbstractThe article describes recent cases of tendon ruptures by corrosion and investigations carried out on some bridges in France. Several causes related to HDPE ducts have been identified such as damages during handling, threading and tensioning of strands, defective connection of the duct to the anchorage, damage during construction or operation, low quality of HDPE material, etc. These cases of tendon rupture exclusively concern ducts injected with cement grout. To our knowledge, no structure built after the application of the 2001 circular [1] (prohibiting cement grout for the injection of external prestressing) is currently exhibiting major disorders.A warning note on existing structures with external prestressing has been updated by Cerema in November 2018 [2]. It describes the diagnosis methodology based on analysis of documentation, thorough visual inspection, destructive and nondestructive investigations. New non‐destructive techniques such as guided‐wave ultrasonic technique and magnetic leakage field test using permanent magnets and induction coils are presented. Innovative methods of local repair of the ducts are also described. Finally, different protective devices are analysed in terms of worker safety in the event of a sudden failure of tendon.

Partial ruptures of the distal triceps tendons show only slightly lower ultimate load to failure: a biomechanical study

ObjectivePartial ruptures of the distal triceps tendon are usually treated surgically from a size of > 50% tendon involvement. The aim of this study was to compare the ultimate load to failure of intact triceps tendons with partially ruptured tendons and describe the rupture mechanism.MethodsEighteen human fresh-frozen cadaveric elbow specimens were randomly assigned to two groups with either an intact distal triceps tendon or with a simulated partial rupture of 50% of the tendon. A continuous traction on the distal triceps tendon was applied to provoke a complete tendon rupture. The maximum required ultimate load to failure of the tendon in N was measured. In addition, video recordings of the ruptures of the intact tendons were performed and analysed by two independent investigators.ResultsA median ultimate load to failure of 1,390 N (range Q0.25—Q0.75, 954 – 2,360) was measured in intact distal triceps tendons. The median ultimate load to failure of the partially ruptured tendons was 1,330 N (range Q0.25—Q0.75, 1,130 – 1.470 N). The differences were not significant. All recorded ruptures began in the superficial tendon portion, and seven out of nine tendons in the lateral tendon portion.DiscussionPartial ruptures of the distal triceps tendon demonstrate a not statistically significant lower ultimate load to failure than intact tendons and typically occur in the superficial, lateral portion of the tendon. This finding can be helpful when deciding between surgical and conservative therapy for partial ruptures of the distal triceps tendon.

The application of mechanical load onto mouse tendons by magnetic restraining represses Mmp-3 expression

ObjectivesMechanical loading is crucial for tendon matrix homeostasis. Under-stimulation of tendon tissue promotes matrix degradation and ultimately tendon failure. In this study, we examined the expression of tendon matrix molecules and matrix-degrading enzymes (matrix metalloproteinases) in stress-deprived tail tendons and compared to tendons that were mechanically loaded by a simple restraining method.Data descriptionIsolated mouse tail fascicles were either floated or restrained by magnets in cell culture media for 24 h. The gene expression of tendon matrix molecules and matrix metalloproteinases in the tendon fascicles of mouse tails were examined by real-time RT-PCR. Stress deprivation of tail tendons increase Mmp3 mRNA levels. Restraining tendons represses these increases in Mmp3. The gene expression response to restraining was specific to Mmp3 at 24 h as we did not observe mRNA level changes in other matrix related genes that we examined (Col1, Col3, Tnc, Acan, and Mmp13). To elucidate, the mechanisms that may regulate load transmission in tendon tissue, we examined filamentous (F-)actin staining and nuclear morphology. As compared to stress deprived tendons, restrained tendons had greater staining for F-actin. The nuclei of restrained tendons are smaller and more elongated. These results indicate that mechanical loading regulates specific gene expression potentially through F-actin regulation of nuclear morphology. A further understanding on the mechanisms involved in regulating Mmp3 gene expression may lead to new strategies to prevent tendon degeneration.

The Effect of Pulling Angle on Rotator Cuff Mechanical Properties in a Canine In Vitro Model.

The objective of this study was to examine the effect of pulling angle on time-zero mechanical properties of intact infraspinatus tendon or infraspinatus tendon repaired with the modified Mason-Allen technique in a canine model in vitro. Thirty-six canine shoulder samples were used. Twenty intact samples were randomly allocated into functional pull (135°) and anatomic pull (70°) groups (n = 10 per group). The remaining sixteen infraspinatus tendons were transected from the insertion and repaired using the modified Mason-Allen technique before being randomly allocated into functional pull or anatomic pull groups (n = 8 per group). Load to failure testing was performed on all specimens. The ultimate failure load and ultimate stress of the functional pulled intact tendons were significantly lower compared with anatomic pulled tendons (1310.2 ± 167.6 N vs. 1687.4 ± 228.2 N, p = 0.0005: 55.6 ± 8.4 MPa vs. 67.1 ± 13.3 MPa, p = 0.0334). For the tendons repaired with the modified Mason-Allen technique, no significant differences were observed in ultimate failure load, ultimate stress or stiffness between functional pull and anatomic pull groups. The variance of pulling angle had a significant influence on the biomechanical properties of the rotator cuff tendon in a canine shoulder model in vitro. Load to failure of the intact infraspinatus tendon was lower at the functional pulling position compared to the anatomic pulling position. This result indicates that uneven load distribution across tendon fibers under functional pull may predispose the tendon to tear. However, this mechanical character is not presented after rotator cuff repair using the modified Mason-Allen technique.

Programmable DNA Hydrogel Provides Suitable Microenvironment for Enhancing TSPCS Therapy in Healing of Tendinopathy.

Tendon stem/progenitor cells (TSPCs) therapy is a promising strategy for enhancing cell matrix and collagen synthesis, and regulating the metabolism of the tendon microenvironment during tendon injury repair. Nevertheless, the barren microenvironment and gliding shear of tendon cause insufficient nutrition supply, damage, and aggregation of injected TSPCs around tendon tissues, which severely hinders their clinical application in tendinopathy. In this study, a TSPCs delivery system is developed by encapsulating TSPCs within a DNA hydrogel (TSPCs-Gel) as the DNA hydrogel offers an excellent artificial extracellular matrix (ECM) microenvironment by providing nutrition for proliferation and protection against shear forces. This delivery method restricts TSPCs to the tendons, significantly extending their retention time. It is also found that TSPCs-Gel injections can promote the healing of rat tendinopathy in vivo, where cross-sectional area and load to failure of injured tendons in rats are significantly improved compared to the free TSPCs treatment group at 8 weeks. Furthermore, the potential healing mechanism of TSPCs-Gel is investigated by RNA-sequencing to identify a series of potential gene and signaling pathway targets for further clinical treatment strategies. These findings suggest the potential pathways of using DNA hydrogels as artificial ECMs to promote cell proliferation and protect TSPCs in TSPC therapy.

Experimental and numerical investigation on flexural behavior of concrete beams strengthened by different NSM tendons

To comprehensively study the flexural behavior of RC beams strengthened by means of near-surface mounted (NSM) technology, 142 simply supported concrete beams strengthened in flexure with a wide variety of NSM materials, including fiber reinforced polymers (FRPs) and metallic materials were collected from previous experimental studies. The effects of the material properties and number of NSM reinforcements on the failure modes of beams strengthened with the NSM system were analyzed. The enhancements in the load-bearing capacity, ductility, and energy consumption capacity of beams were discussed. By classifying the NSM strengthening materials into brittle reinforcement and ductile reinforcement, the results demonstrated that beams strengthened with brittle NSM reinforcement were prone to premature brittle failure modes, as beams strengthened with only one FRP tendon easily failed through rupture of FRP, and those with more than one tendon were prone to debonding failure. Whereas beams using ductile materials were more likely to fail in a ductile manner. A numerical analysis was performed to predict the maximum strength of beams strengthened with different materials and prestress levels. Conservative prediction was observed for beams that failed by concrete crushing, and overestimated prediction was observed for beams governed by debonding failure or rupture of NSM tendons.

A pilot study on lengthening potentials and biomechanical effects of double and triple hemisection on tendon with slide lengthening

The current study explored the slide-lengthening potentials of double and triple hemisections and the biomechanical effects of different inter-hemisection distances. Forty-eight porcine flexor digitorum profundus tendons were divided into double- and triple-hemisection groups (Groups A and B) and a control group (Group C). Group A was divided into Group A1 (distance between hemisections were the same as Group B) and Group A2 (distance between hemisections corresponded to the greatest distance between hemisections in Group B). Biomechanical evaluation, motion analysis, and finite element analysis (FEA) were performed. Failure load of intact tendon was significantly highest among groups. When the distance was 4 cm, the failure load of Group A increased significantly. When the distance between the hemisections was 0.5 or 1 cm, the failure load of Group B was significantly lower than Group A. Tendon elongation and failure load of Group B were significantly lower than those in Group A when the greatest distance between hemisections was the same. Consequently, Double hemisections had a similar lengthening ability to that of triple hemisections with the same distance, but better when the distances between extreme hemisections matched. However, the driving force for the initiation of lengthening may be greater.

Galvanic corrosion and cathodic protection of re-grouted, post-tensioned (PTd) concrete systems

Grouted post-tensioned (PTd) concrete systems are widely used in long-span segmental bridges with a target service life of 100+ years. However, the usage of inadequate grout materials and grouting practices have resulted in the formation of unwanted air voids in the duct, which in turn led to premature corrosion (say, within about 20 years) of strands and failure of tendons. Also, the re-grouting/repairing of void regions have led to localized corrosion of strands at the interface between the dissimilar base-grout (usually carbonated) and repair-grout. This study aims (i) to quantify the galvanic corrosion at the void region in a PTd system re-grouted with a dissimilar grout and (ii) to develop cathodic protection system to protect PTd anchorage regions. Specimens simulating the re-grouted strand-grout-air (SGA) interface were prepared with prestressing steel wires and cementitious grout. The macro-cell current (galvanic current) between the prestressing steels embedded in carbonated base-grout and repair-grout indicated that galvanic corrosion can be possible at the SGA interface – reducing the long-term structural reliability of re-grouted PTd bridges. In addition, the feasibility of galvanic anode cathodic protection system to protect PTd anchorage regions was assessed. For this, a proof-of-concept study was conducted to validate that a thin layer of grout around the strand will be sufficient for a galvanic anode (connected to the end of the strand at outside the tendon anchorage) to protect the strand portions inside the duct/anchorage.