Internal Tendons Research Articles

Closed-loop control of a tendon-driven active needle for tip tracking at desired bending angle for high-dose-rate prostate brachytherapy

Abstract Prostate cancer is the second most common malignancy in American men. High-dose-rate brachytherapy is a popular treatment technique in which a large, localized radiation dose is used to kill cancer. Utilization of curvilinear catheter implantation inside the prostate gland to provide access channels to host the radiation source has shown superiority in terms of improved dosimetric constraints compared to straight needles. To this aim, we have introduced an active needle to curve inside the prostate conformal to the patient’s specific anatomical relationship for improved dose distribution to the prostate and reduced toxicity to the organs at risk. This work presents closed-loop control of our tendon-driven active needle in water medium and air using the position feedback of the tip obtained in real time from an ultrasound (US) or an electromagnetic (EM) tracking sensor, respectively. The active needle consists of a compliant flexure section to realize bending in two directions via actuation of two internal tendons. Tracking errors using US and EM trackers are estimated and compared. Results show that the bending angle of the active needle could be controlled using position feedback of the US or the EM tracking system with a bending angle error of less than 1.00 degree when delay is disregarded. It is concluded that the actuation system and controller, presented in this work, are able to realize a desired bending angle at the active needle tip with reasonable accuracy paving the path for tip tracking and manipulation control evaluations in a prostate brachytherapy.

Experimental and analytical studies on direct shear performance of UHPC keyed joints

The keyed joint in the precast ultra-high-performance concrete (UHPC) segmental bridge (PUSB) plays a critical part in the structural behavior of the entire bridge, which requires in-depth investigations to clarify its shear performance. To this end, experimental and analytical studies on 15 UHPC keyed joints were conducted to explore the effects of the joint type, number of teeth, size of teeth, angle of teeth, and reinforcement method on the shear behavior of UHPC keyed joints. Test results presented that the failure modes were significantly affected by the teeth number and the reinforcement method, which can be classified into three primary categories (direct shear, segmental shear, and stepwise shear). The epoxied joints exhibited better shear capacity and ductility than those of dry joints, and the large-keyed joints owned higher shear capacity than the small-keyed joints under the same shear area. Moreover, the mechanisms of the two reinforcement methods were analyzed: the teeth rebars effectively improved the brittleness of the specimen, and the internal tendons significantly enhanced the shear efficiency of the specimen. Finally, considering the bridging effect of steel fiber, a calculation model was proposed for the shear capacity of the UHPC epoxied-keyed joints. The test results were in good agreement with the analysis results, indicating that the proposed model can be used to predict the shear capacity of UHPC epoxied-keyed joints.

Acoustic emission technology-based waveguide localization method for damaged internal tendons of in-service post-tensioned hollow slab bridges

Prestressing tendons are crucial load-bearing elements in post-tensioned hollow slab bridges. Damage to these tendons significantly reduces the safety, functionality, and longevity of the bridge. Regular monitoring of prestressing tendons is essential for bridge operation. Acoustic emission technology, known for its high accuracy and sensitivity to minor vibrations, is a key technique for monitoring bridge cables. This study proposes a novel dual-sensor acoustic emission localization method for detecting tendon damage in post-tensioned hollow slab bridges, utilizing waveguide technology. The effectiveness of this method is confirmed through hammering tests that simulate acoustic emission damage on operational hollow slab bridges. The proposed method, requiring only two sensors, offers a cost-effective alternative for monitoring the entire span of post-tensioned hollow slab bridges, so that effectively reduces the cost of bridge health monitoring and is easy to be promoted in actual engineering projects.

Hysteretic performance of prestressed concrete beams with AFRP tendons under cyclic loading

AbstractThis paper aims to evaluate the hysteretic performance of prestressed concrete beams with aramid fiber‐reinforced polymer (AFRP) tendons. Eight beams were constructed and tested under cyclic loading, with test variables covering the type of prestressing tendons (AFRP and steel), the ratio of internal tendons to external tendons (3:0 and 1:2) and the bond condition of internal tendons (fully bonded, partially bonded, and unbonded). Results showed that the failure of all the beams was dominated by concrete crushing and nonprestressed rebars rupturing at pure bending sections. AFRP prestressed beams exhibited commensurate bearing capacity, displacement ductility, energy dissipation and residual deformation with steel prestressed beams. The combination of internal and external tendons, and using unbonded or partially bonded tendons could improve the ductility of AFRP prestressed beams. Additionally, the finite element (FE) models of AFRP prestressed beams were developed using ABAQUS based on the coupling method under the local coordinate system. The simulated results closely matched the experimental results in terms of the failure mode and load–displacement curve. Parametric predictions, including the unbonded length of AFRP tendon, partial prestressing ratio, jacking stress and concrete strength were presented to extend the experimental works.

Teleoperated and Automated Control of a Robotic Tool for Targeted Prostate Biopsy.

This work presents a robotic tool with bidirectional manipulation and control capabilities for targeted prostate biopsy interventions. Targeted prostate biopsy is an effective image-guided technique that results in detection of significant cancer with fewer cores and lower number of unnecessary biopsies compared to systematic biopsy. The robotic tool comprises of a compliant flexure section fabricated on a nitinol tube that enables bidirectional bending via actuation of two internal tendons, and a biopsy mechanism for extraction of tissue samples. The kinematic and static models of the compliant flexure section, as well as teleoperated and automated control of the robotic tool are presented and validated with experiments. It was shown that the controller can force the tip of the robotic tool to follow sinusoidal set-point positions with reasonable accuracy in air and inside a phantom tissue. Finally, the capability of the robotic tool to bend, reach targeted positions inside a phantom tissue, and extract a biopsy sample is evaluated.

Experimental study on the shear behavior of precast concrete segmental simply supported beam with internal tendons and glue joints

Glue joints make precast concrete segmental beams with discontinuity, which is the weak link and an important part of the structure and needs to be given special attention in practical engineering. To test the shear behavior of five segmental glue joint beams and one monolithic beam, the test parameters included shear span ratios (1.2, 1.5), prestress levels (4 MPa, 6 MPa, 6.5 MPa), prestress types (unbonded prestress, bonded prestress), and beam types (segmental beam, monolithic beam). The results show that both segmental glue joint beams and monolithic beams exhibited typical brittle failure characteristics in the failure stage. The shear span ratio increased, the shear bearing capacity of the specimen decreased, and the deformation increased. The deformation of the specimen decreased when the prestress level increased. The bonded prestressed screw-thread bar improved the overall strength and stiffness of the segmental glue joint beam. The crack resistance of the monolithic beam was better than the crack resistance of the segmental glue joint beam, but the difference in shear bearing capacity between them was small. The test data were compared with the calculated values of shear bearing capacity of different formulas, and the results show that the calculated values of formulas of the American Association of State Highway and Transportation Officials (AASHTO (2003)) standard were in the best agreement with the test values. Based on the test results, the strain distribution and stress distribution of the specimens were further explored by combining the finite element method. The results show that cracks of different specimens would cross the glue joints. The yield strength of the prestressed screw-thread bar was not reached when the specimen was damaged.

Numerical Model for Flexural Analysis of Precast Segmental Concrete Beam with Internal Unbonded CFRP Tendons.

A new construction scheme was recently developed for precast segmental concrete beams by replacing steel tendons with internal unbonded carbon-fiber-reinforced polymer tendons. The discontinuous behaviors of the opening joints and unbonded phenomenon of tendons made their flexural behaviors more complicated than those of monolithic beams and members with bonded tendons. Currently, the knowledge on the structural performance of precast segmental concrete beams with internal unbonded carbon-fiber-reinforced polymer tendons is still limited. An efficient numerical model is urgently needed for the structural analysis and performance evaluation of this new construction scheme. In this paper, a new beam–cable hybrid model was proposed accounting for the mechanical behaviors of open joints and unbonded tendons. The numerical model was implemented in the OpenSees software with the proposed modeling method for joint elements and a newly developed element class for internal unbonded tendons. The effectiveness of the proposed model was verified by comparisons against two simply supported experimental tests. Then, the numerical model was employed to evaluate the flexural performance of a full-scale bridge with a span of 37.5 m. Compared with the precast segmental concrete beam with external steel tendons, the scheme with internal unbonded carbon-fiber-reinforced polymer tendons significantly improved the flexural capacity and ductility by almost 54.6% and 8.9%, respectively. The span-to-depth ratio and prestressing reinforcement ratio were the main factors affecting the flexural behaviors. With the span-to-depth ratio increasing by 23%, the flexural capacity decreased by approximately 38.6% and the tendon stress increment decreased by approximately 15.7%. With the prestressing reinforcement ratio increasing by 65.4%, the flexural capacity increased by 88.7% and the tendon stress increment decreased by approximately 25.2%.

Modeling and Operator Control of a Robotic Tool for Bidirectional Manipulation in Targeted Prostate Biopsy.

This work introduces design, manipulation, and operator control of a bidirectional robotic tool for minimally invasive targeted prostate biopsy. The robotic tool is purposed to be used as a compliant flexure section of active biopsy needles. The design of the robotic tool comprises of a flexure section fabricated on a nitinol tube that enables bidirectional bending via actuation of two internal tendons. The statics of the flexure section is presented and validated with experimental data. Finally, the capability of the robotic tool to reach targeted positions inside prostate gland is evaluated.

Numerical study on bending response of precast segmental concrete beams externally prestressed with FRP tendons

This study numerically investigates the bending response of dry key-jointed precast segmental concrete girders/beams (PSCBs) prestressed with external fiber reinforced polymer (FRP) tendons by using commercial finite element analysis (FEA) software Abaqus/CAE. The experimentally-validated model was used to conduct an intensive parametric analysis with a focus on the second-order effect. There has not been a similar numerical study of PSCBs with external FRP tendons in the published literature yet. The results showed that due to the rectilinear rigid-body bending shape, the behavior of PSCBs with external tendons was similar to that with internal tendons only if placing the deviators next to the opening joints. The second-order effect on the beam’s behavior and the harping effect on the tendon stress at deviators became more obvious when the deviators were located away from the opening joints. Both the second-order and harping effect were proportionate to the beam’s displacement. Therefore, using a high reinforcing index (ω) or a low span-to-depth ratio (L/dp) could mitigate the second-order and harping effect at the ultimate stage because the ultimate displacement of the beam decreased when increasing ω or reducing L/dp. Commonly-used CFRP tendons (Young’s modulus Ep = 145 GPa) were found to be the optimum to replace steel tendons in PSCBs with external tendons because they offered the PSCBs similar strength and ductility compared to steel tendons. The use of high-modulus CFRP tendons (e.g. Ep = 200 GPa) improved the stiffness and strength of PSCBs but greatly reduced the beam’s ductility. Lastly, the analytical analyses showed that the existing models yielded unconservative estimations of the effective depth (dpu) and stress (fpu) of external FRP tendons at the ultimate stage in PSCBs.

Consumers' attention on identification, nutritional compounds, and safety in heavy metals of Canadian sea cucumber in Chinese food market.

BackgroundBased on the consumers’ attention issues of sea cucumbers, we aimed to complete comprehensive information of commercial Canadian sea cucumbers (CCSC), which sprang up extensively in Chinese food market.ResultsCCSC were identified as Cucumaria frondosa and characterized based on the characteristics, nutritional compositions, and heavy metals. The abdomen and five internal tendons of Cucumaria frondosa were special orange. The average of soaking degree and water content, which consumers paid great attention to, was 2.8 ± 0.3 and 0.46 ± 0.09%, respectively. Proteins (56.4 ± 9.1%) and polysaccharides (12.2 ± 14.7%) were the principal nutrient component. In addition, there was a variety of free amino acids, in which arginine (70.1 ± 50.0 mg/100 g), glutamate (42.6 ± 23.9 mg/100 g), and alanine (32.2 ± 21.0 mg/100 g) were the main components. Phosphorus (P, 0.26 ± 0.05%), magnesium (Mg, 0.19 ± 0.07%), and kalium (K, 0.17 ± 0.08%) were the major mineral elements. Amount of heavy metal was within the safety limitation (5.5 ± 1.4 mg/kg). Furthermore, the active ingredients were positively correlated with size.ConclusionThe overall findings enriched the information of Cucumaria frondosa for consumers and suggested that the quality of Cucumaria frondosa was varied following commercial classification and size.

Insect Cuticular Chitin Contributes to Form and Function.

Chitin contributes to the rigidity of the insect cuticle and serves as an attachment matrix for other cuticular proteins. Deficiency of chitin results in abnormal embryos, cuticular structural defects and growth arrest. When chitin is not turned over during molting, the developing insect is trapped inside the old cuticle. Partial deacetylation of cuticular chitin is also required for proper laminar organization of the cuticle and vertical pore canals, molting, and locomotion. Thus, chitin and its modifications strongly influence the structure of the exoskeleton as well as the physiological functions of the insect. Internal tendons and specialized epithelial cells called "tendon cells" that arise from the outer layer of epidermal cells provide attachment sites at both ends of adult limb muscles. Membrane processes emanating from both tendon and muscle cells interdigitate extensively to strengthen the attachment of muscles to the extracellular matrix (ECM). Protein ligands that bind to membrane-bound integrin complexes further enhance the adhesion between muscles and tendons. Tendon cells contain F-actin fiber arrays that contribute to their rigidity. In the cytoplasm of muscle cells, proteins such as talin and other proteins provide attachment sites for cytoskeletal actin, thereby increasing integrin binding and activation to mechanically couple the ECM with actin in muscle cells. Mutations in integrins and their ligands, as well as depletion of chitin deacetylases, result in defective locomotion and muscle detachment from the ECM. Thus, chitin in the cuticle and chitin deacetylases strongly influence the shape and functions of the exoskeleton as well as locomotion of insects.

Effect of joint positions on flexural behaviors of box segmental specimens internally post tensioned under cyclic and static loadings

The goal of this paper is to get a better knowledge of effect of joint positions on flexural behavior of box segmental specimens under bending stresses. Three segmental specimens with internal tendons were produced and tested. Each segmental specimen was produced assembling three precast concrete segments and they were connected by using four post tensioning tendons. All segmental specimens were formed with dry joint type, but they different in joint positions. All specimens were tested under two types of loadings cyclic and static two point loads. The test of cyclic loading was carried out by exposure each specimen to three loading cycles. The static load test was carried out in same rate of loading that of cyclic load test and all girder specimens were tested up to failure. The loads versus deflections at specified points were recorded. Also, cracking, mode of failure and ultimate loads values were recorded as well as the concrete surface strains at the specified locations for both loadings.

Flexural behaviour of segmental prestressed composite beams with corrugated steel webs

An experimental study and theoretical calculations of the flexural behaviour of segmental prestressed composite beams with corrugated steel webs are presented. Four specimens (one monolithic and three segmental beams) are tested. Based on the experiments, the flexural strength of the segmental beams is found to be approximately 0·75 of that of the monolithic beam, and the joint types of CSWs are found to have a little effect on the load-bearing capacity of the segmental beams. Moreover, the load-bearing capacity of the segmental beams is found to maximise by increasing the ratio of internal tendons in the bottom concrete flange to external tendons. Specifically, by increasing the ratio from 2:0:4 to 2:2:2, a 31% increase in the load-bearing capacity has been gained. Additionally, it has been found that the quasi-plane assumption is valid for the segmental beams with CSWs within the elastic range. Finally, a theory-based method for calculating the flexural bearing moment of segmental beams with CSWs is presented by considering the effect of the stress increment of the prestressed tendons.

Flexural Behaviours of Box Segmental Beams with Internal Tendons Subjected to Repeated and Static Loads

The main objective of this study is to gain a better understanding of the behaviours of different types of joints when box segmental beams are subjected to bending. Five beams with internal tendons were thus produced and tested: one beam was cast monolithically as a reference beam and four were formed as segmental beams. All beams were produced using Self Compacting-Concrete (SCC) in box sections. Each segmental beam was formed by assembling three precast concrete segments with four post tensioning tendons. The segmental beams had the same general characteristics, but with different types of joints between the segments. Four types of joints were adopted in this study;-dried, epoxied, dried strengthened with carbon fibres and multi-steel shear keyed joints. All beams were tested under two types of loadings, repeated and static. A test of repeated loading was carried out by exposing each specimen to three loading cycles. Each cycle was implemented by subjecting each specimen to up to 40% of the ultimate load then releasing the loads to return the specimen to the non-loading case. The test of static loading was carried out at the same rate of loading as the repeated load test, and all girder specimens were tested up to failure. The loads versus deflections at specified points were recorded for each 5 kN. Cracking, mode of failure and ultimate load values were recorded, along with the concrete surface strains at specified locations for both loadings. The tests results for repeated loading showed that joint type had a clear effect on behaviours in the segmental beams, which had deflection readings ranging from 16 to 61% higher than that of the monolithic (reference) beam, as well as higher tensile strain than seen in the reference beam, by 8 and 67%. Similar effects of joint type were observed under static test. At the first crack loading, the segmental beams had deflections of between 8 and 94% and tensile strains of about 5 to 18% more than the reference beam. The failure modes of the tested beams were all different. Failure of the dry joint occurred in the segment interface, while the failure of each epoxied joint and joint strengthened by carbon fibres developed in the concrete adjacent to the segment interface. The steel shear keys clearly transfer the shear resistance to the concrete parts adjacent of the joints.

Odd-skipped and Stripe act downstream of Notch to promote the morphogenesis of long appendicular tendons in Drosophila.

ABSTRACTMultiple tissue interactions take place during the development of the limb musculoskeletal system. While appendicular myogenesis has been extensively studied, development of connective tissue associated with muscles has received less attention. In the developing Drosophila leg, tendon-like connective tissue arises from clusters of epithelial cells that invaginate into the leg cavity and then elongate to form internal tube-shape structures along which muscle precursors are distributed. Here we show that stripe-positive appendicular precursors of tendon-like connective tissue are set up among intersegmental leg joint cells expressing odd-skipped genes, and that Notch signaling is necessary and locally sufficient to trigger stripe expression. This study also finds that odd-skipped genes and stripe are both required downstream of Notch to promote morphogenesis of tube-shaped internal tendons of the leg.

Improved prediction of long-term prestress loss in unbonded prestressed concrete members

In this paper, an approach based on the finite element method to model the behavior of concrete beams with unbonded prestressing steel over time, and an improved simplified equation for calculating the prestress losses in statically determinate prestressed concrete members with unbonded internal tendons are proposed. Both methods take into account the effects of the concrete creep, concrete shrinkage, prestressing steel relaxation and the presence of the bonded non-prestressed reinforcement. In addition, a generalization of the Step-by-Step and the Age-Adjusted Effective Modulus methods for the time cross-sectional analysis of prestressed concrete members with unbonded internal tendons is presented. The accuracy of the proposed equation is evaluated based on the results of previous studies and is contrasted with the computational implementation of the Step-by-Step Method. As the main conclusions, we mention that the results show that the proposed equation adequately predicts the prestress loss and has higher accuracy compared to simplified existing models.

Nondestructive evaluation of grout defects in internal tendons of post-tensioned girders

Post-tensioning systems provide safe and efficient construction solutions for long span bridges. Despite the improved grouting practices over the past decade, existing post-tensioning systems may have significant amount of grout defects, which could lead to corrosion of the strands. Condition assessment of post-tensioning systems is necessary to allow bridge owners to take timely, proactive actions to mitigate or prevent further deterioration and unanticipated tendon failures. A detailed experimental study conducted to assess the performance of nondestructive evaluation techniques in detecting grout defects within internal tendons is presented herein. Nondestructive evaluation techniques that include Ground Penetrating Radar, Impact Echo, Ultrasonic Tomography, and Ultrasonic Echo are evaluated in terms of detecting the location and severity of fabricated grout defects in a full-scale post-tensioned U-girder mock-up specimen. While Ground Penetrating Radar can identify the location and profile of the internal tendons, particularly metal ducts due to strong reflections, this method did not provide any information about the defect conditions within the tendon. Both Impact Echo and Ultrasonic Echo techniques are effective in identifying the location of grout defects, but could not differentiate between water, void, or compromised grout conditions. The study clearly demonstrates the need for NDE techniques that are applicable to anchorage regions, and that are capable of estimating the severity and nature of grout defects in internal tendons.

Nonlinear finite element simulation of unbonded prestressed concrete beams

Prestressed concrete with internal unbonded tendons has been recognized as an excellent structural option for beams and slabs and is employed worlwide. Numerical solutions for the analysis of such structures are still an active field of research. This work presents a finite element model for the physical and geometrical nonlinear analysis of prestressed concrete beams with unbonded internal tendons, under short-term loading. The reinforced concrete beam is modeled by Euler-Bernoulli nonlinear plane frame elements and a total Lagrangian approach. The prestressing tendon is modeled by a single polygonal element embedded in a specified subset of the frame elements. Due to lack of strain compatibility between the concrete and the tendon at a given cross-section, the cable strain is computed from the displacements of all associated frame elements. Geometric and material nonlinearities are considered for both the reinforced concrete beam and the prestressing tendons. The internal force vector and corresponding tangent stiffness matrix of each element under large displacements are derived consistently, and novel expressions for the tangent stiffness operator which ensure the convergence rates of the Newton-Raphson scheme are developed. The accuracy of the formulation is assessed by comparison with experimental tests, with very good results.

Seismic performance comparison of precast segmental bridge girders with different cross sections and boundary conditions under vertical quasi-static cyclic testing: An experimental investigation

In this study, five 1/5-scale bridge girder specimens are tested with vertical quasi-static cyclic loading, in order to understand their performance in high seismic zones. The study is focused on the superstructures at two critical regions: (1) close to mid-span where high moments and low shears are present (2) and close to the supports where high negative moments and high shears are induced. The first case includes one precast segmental bridge box-girder, one precast segmental bridge I-girder, and one reference cast-in-place I-girder, while the second case consists of one precast segmental bridge I-girder and one cast-in-place I-girder. The ratios of the internal and external tendons are 1:1 for case 1 and 3:5 for case 2, respectively. Test results show that cast-in-place girders have better energy dissipation capacity and higher ultimate strength, but the precast segmental girders retain larger displacement capacity and self-centering capability. Internal post-tensioning tendons are subjected to more significant stress concentration at the joint locations of the precast segmental girders, while stress of external tendons is distributed more evenly. In terms of vertical loading, box-girder and I-girder possess similar hysteretic behaviors, as long as the effective widths are the same.

Assessment of an existing fully prestressed box-girder bridge

The N.S. da Guia Bridge is a 250 m-long post-tensioned box-girder bridge built in the late 1970s using the balanced cantilever method. During a routine inspection, a systematic cracking pattern that exhibited both longitudinal and transversal symmetry was detected in the webs and bottom slab, which raised concerns about the condition of the embedded post-tensioned cables. The working programme that was devised to perform the condition examination of the bridge is described. Besides a detailed visual inspection campaign and a short-term monitoring programme, non-destructive testing was also employed, most notably gamma-ray imaging of the internal tendons. Special attention is devoted to the numerical studies developed to explain the origin of the observed crack patterns. This information was crucial in order to decide on the best rehabilitation strategies. The crack pattern could be satisfactorily reproduced by taking into account the local stress conditions around the tendon anchorages, and the concerns related to the condition of the prestressed steel could be ruled out. The applied methodology constitutes an example of how detailed analysis techniques can be used in practice to help bridge owners evaluate the condition of special bridges and plan the rehabilitation intervention in a cost-effective way.