Tendon Configuration Research Articles

The contribution of the tendon electrode to M-wave characteristics in the biceps brachii, vastus lateralis and tibialis anterior.

In some compound muscle action potentials (M waves) recorded using the belly-tendon configuration, the tendon electrode makes a noticeable contribution to the M wave. However, this finding has only been demonstrated in some hand and foot muscles. Here, we assessed the contribution of the tendon potential to the amplitude of the vastus lateralis, biceps brachii and tibialis anterior M waves, and we also examined the role of this tendon potential in the shoulder-like feature appearing in most M waves. M waves were recorded separately at the belly and tendon locations of the vastus lateralis, biceps brachii and tibialis anterior from 38 participants by placing the reference electrode at a distant (contralateral) site. The amplitude of the M waves and the latency of their peaks and shoulders were measured. In the vastus lateralis, the tendon potential was markedly smaller in amplitude (∼75%) compared to the belly M wave (P=0.001), whereas for the biceps brachii and tibialis anterior, the tendon and belly potentials had comparable amplitudes. In the vastus lateralis, the tendon potential showed a small positive peak coinciding in latency with the shoulder of the belly-tendon M wave, whilst in the biceps brachii and tibialis anterior, the tendon potential showed a clear negative peak which coincided in latency with the shoulder. The tendon potential makes a significant contribution to the belly-tendon M waves of the biceps brachii and tibialis anterior muscles, but little contribution to the vastus lateralis M waves. The shoulder observed in the belly-tendon M wave of the vastus lateralis is caused by the belly potential, the shoulder in the biceps brachii M wave is generated by the tendon potential, whereas the shoulder in the tibialis anterior M wave is caused by both the tendon and belly potentials. NEW FINDINGS: What is the central question of this study? Does a tendon electrode make a noticeable contribution to the belly-tendon M wave in the vastus lateralis, biceps brachii and tibialis anterior muscles? What is the main finding and its importance? Because the patellar tendon potential is small in amplitude, it hardly influences the amplitude and shape of the belly-tendon M wave of the vastus lateralis. However, for the biceps brachii and tibialis anterior muscles, the potentials at the tendon sites show a large amplitude, and thus have a great impact on the corresponding belly-tendon M waves.

Parametric analysis of steel-concrete composite beams prestressed with external tendons

The use of external prestressed tendons in steel-concrete composite beams can improve the performance of beams by strengthening their structure, increasing the ultimate moment resistance, and reducing deflections. The present research aims to investigate the behavior of simply supported steel-concrete composite beams, prestressed with external tendons and under positive bending moment through the development of a parametric study. Firstly, for the beam strength determination, an analytical model is discussed. To predict the ultimate increment in tendon stress Chen and Gu method is used. Additionally, a numerical model that can adequately simulate the behavior of prestressed composite beams is developed using the Abaqus software. The accuracy of this model is validated through comparisons between the obtained results and existing experimental tests. Then, a parametric study is carried out to identify the influence of the following variables: positioning and shape of the tendons, initial prestressing force, and tendon and span lengths. The effect of prestressing at the steel-concrete interface is also investigated. The results of the ultimate moment from the finite element models, are compared by applying the analytical procedure. It can be concluded that all the different tendon configurations considered in the parametric study improved the ultimate moment resistance in the composite beams, but some designs are more efficient than others, increasing the resistance even more, and significantly reducing the deflections and cracking in the concrete under service loads. Regarding the analytical procedure, it was found that the method can adequately estimate the strength capacity of the beams.

Nonlinear Finite Element Modelling and Parametric Study of Prestressed Steel Box Girder

Abstract The prestressing technique is easy to apply and is generally used to strengthen steel bridges and controls their gross deflection. ANSYS has been used to establish a numerical model for the mechanical behavior of a steel box girder and prestressed by external tendons. In this paper, steel plate girders with and without strengthening technique was tested to assess the effectiveness of this technology. The results showed that prestressing improves the mechanical behavior of a girder and that its effect is proportional to magnitude of the applied external load. The results of the numerical model showed good agreement with the experimental data. A full-course simulation was conducted with ANSYS for a parametric study to analyze the influence of prestressing force magnitude, span-height ratio, and tendon configurations in increasing the effectiveness of prestressed technique.

Enhanced concrete crack closure with hybrid shape memory polymer tendons

The paper presents a new healing system that uses pre-tensioned hybrid tendons to close cracks in cementitious structural elements. The tendons comprise an inner core, formed from aramid fibre ropes, and an outer sleeve made from a shape memory PET. During the manufacturing process, the inner core of a tendon is put into tension and the outer sleeve into compression, such that the tendon is in equilibrium. A set of tendons are then cast in a cementitious structural element and heat activated once cracking occurs. This triggers the shrinkage potential of the PET sleeve, which in turn releases the stored strain energy in the inner core. The tensile force thereby released applies a compressive force to the cementitious element, in which the tendons are embedded, that acts to close any cracks that have formed perpendicular to the axis of the tendons. Details of the component materials used to form the tendon are given along with the tendon manufacturing process. A set of experiments are then reported that explore the performance of three different tendon configurations in prismatic mortar beams. The results from these experiments show that the tendons can completely close 0.3 mm cracks in the mortar beams and act as effective reinforcement both before and after activation. A nonlinear hinge-based numerical model is also described, which is shown to be able to reproduce the experimental behaviour with reasonable accuracy. The model is used to help interpret the results of the experiments and, in particular, to explore the effects of slip at the tendon anchorages and the amount of prestress force that remains after activation. It is shown that, with two of the tendon configurations tested, over 75% of the prestress potential of the tendon remains after crack closure.

Correction to: Mechanical Properties of Prestressed Concrete Members with Inclined Tendon Configuration Subjected to Uniaxial and Biaxial Loading

Unfortunately, the Acknowledgement section was incomplete in the original article. The correct version is given below.

PRESTRESSED HOMOGENIOUS STEEL BEAMS STRENGTHENED IN COMPRESSION AND TENSION – A HYPOTHETICAL CASE STUDY

The technology of prestressing steel structures is relatively an old frontier in the field of structural engineering. In spite of having many advantages over prestressed concrete, prestressed steel has not been popular in academics as well as in industry. This paper is an attempt to study the variation of Load carrying capacity for same Force Factor (FF), same Eccentricity Ratio (ER), same span and same cross-section strengthened in compression and tension.ISWB600@145 was considered for study for a span of 8m to 16m. Four types of cross-sections are considered for comparison, namely 1) I-section, 2) I-section laterally strengthened in compression and tension by welding four angle sections, 3) I-section laterally strengthened in compression alone by welding two angle sections, 4) compound girder formed by welding a plate to the top flange of an I-section. A straight tendon configuration over the whole span is considered for study. The non-dimensional design parameters like FF and ER were considered as 0.4 and 0.5 respectively.The % increase in the load carrying capacity for each case was calculated with respect to the beam without prestressing. It has been observed that welding a plate to the top flange of an I-section can increase the load carrying capacity of the I-section up to 80% when prestressed. In other words, the material of the cross-section is effectively utilized when an unsymmetrical I-section is prestressed.

Beam strengthening by external post-tensioning: Design recommendations

Buildings and bridge structures are often in need of strengthening due to deterioration of material properties or a change in design loads. External post-tensioning, in which tendons are installed on the outside of a structural member with the aid of deviators and anchorages, is an attractive strengthening method as it does not add much weight and can be carried out with minimal disruption to the operational function of the structure. An extensive programme has been carried out on simple-span and continuous beams as well as beams in reinforced concrete frames to study the effect of tendon configuration, second-order effects, and secondary and tertiary effects due to external post-tensioning. The effect of external post-tensioning on shear capacity and the use of fibre-reinforced polymer prestressing cables were also examined. This paper highlights the main findings of the study, based on which design recommendations are given and a direct design approach is proposed.

Nondestructive Radiographic Evaluation and Repairs to a Prestressed Concrete Parking Structure Following Partial Collapse

This paper presents use of radiographic imaging (X-ray) in evaluation of existing reinforcing steel and tendon configuration of a structure following a collapse and development of steel retrofit and carbon-fiber-reinforced polymer (CFRP) repairs. A collapsed section in the driving surface in a precast concrete parking deck prompted an engineering evaluation and survey of the entire deck for assessment and repairs to distressed members. Distress was identified in decking members and perimeter spandrel beams in varying forms and degrees. Repairs to the decking members involved supporting the distressed decking using supplemental steel retrofit brackets installed through the double-Tee stems containing prestressing tendons. The precise location of the tendons in the stems needed to be identified to implement this repair in order not to damage the tendons during drilling for through-stem anchors. Radiographic X-ray imaging in this application enabled locating and avoiding the tendons in the stems to support and strengthen the decking member. The supplemental steel brackets also enabled continued and improved operation of an existing expansion joint in the area of repair. Radiographic evaluation technique was also used in identification of steel reinforcement configuration in the perimeter spandrel beams exhibiting cracking at bearing locations with maximum shear. Radiographic exposures were used for evaluation of existing steel configuration and development of CFRP repairs. CFRP repairs were implemented in perimeter spandrel beams while decking surfaces were retrofitted with steel brackets to support the driving surfaces and enable continued expansion and contraction in the existing expansion joints.

Small scale experimental study of the dynamic response of a tension leg platform wind turbine

A floating Tension Leg Platform (TLP) wind turbine was constructed at scale 1/200 and its dynamic response was analysed experimentally in co-directional wind and waves. The wind turbine was Froude scaled and a new rotor was designed to yield maximum power and Froude scaled thrust at the low model Reynolds number. Physical limitations due to the large scaling ratio further meant that some structural adjustments were necessary. Nacelle and floater accelerations were measured by means of two accelerometers. The TLP was moored with four different tendon configurations and exposed to different constant wind speeds and irregular sea states as well as a range of regular waves. It was found that an increase in wind speed reduces the wave-induced floater motion but causes slightly larger nacelle displacements. Further, the orientation of the spokes relative to the direction of wind and waves influences the pitch stiffness and thereby the nacelle displacements. Inclining the tendons towards the wind turbine reduces the nacelle displacements significantly and reduces the occurrence of slack tendons, but increases the inline tilt-motion of the rotor. Application of a very stiff mooring configuration increases the occurrence of slack tendons and the magnitude of the pitch accelerations. In a robust commercial design, however, slack tendons must be avoided. The experiments demonstrate the ability of the wind turbine model and the experimental setup to give insight to the dynamic characteristics of floating TLP wind turbines.

Analytical Study on Prestressed Steel I-Beam Strengthened in Compression by Angles

Prestressed steel structures have many advantages over steel, reinforced cement concrete and prestressed concrete structures. This paper is an attempt to compare the performance of prestressed steel I-beam and that strengthened in compression by welding two angles. Iterative calculations involved in analysis were performed with the help of program developed by the authors, which takes the choice of I-section, type of beam and span required as inputs. Straight tendon configuration over the whole span was considered for comparison. The study of the variation among different parameters revealed that the load carrying capacity is not directly proportional to the prestressing force in case of an unsymmetrical I-section for eccentricity less than a minimum value. But in case of a symmetrical section, the load carrying capacity is directly proportional to the prestressing force for all eccentricities. However, it was observed that the material of the cross-section is effectively utilised when an unsymmetrical I-section is prestressed.

Getting a grip on tetrapod grasping: form, function, and evolution

Human beings have been credited with unparalleled capabilities for digital prehension grasping. However, grasping behaviour is widespread among tetrapods. The propensity to grasp, and the anatomical characteristics that underlie it, appear in all of the major groups of tetrapods with the possible exception of terrestrial turtles. Although some features are synapomorphic to the tetrapod clade, such as well-defined digits and digital musculature, other features, such as opposable digits and tendon configurations, appear to have evolved independently in many lineages. Here we examine the incidence, functional morphology, and evolution of grasping across four major tetrapod clades. Our review suggests that the ability to grasp with the manus and pes is considerably more widespread, and ecologically and evolutionarily important, than previously thought. The morphological bases and ecological factors that govern grasping abilities may differ among tetrapods, yet the selective forces shaping them are likely similar. We suggest that further investigation into grasping form and function within and among these clades may expose a greater role for grasping ability in the evolutionary success of many tetrapod lineages.

A direct design approach for strengthening simple-span beams with external posttensioning

This paper presents the analytical formulation to establish equations for the direct determination of the increase in load-carrying capacity of simple-span beams strengthened by external post-tensioned tendons. Two sets of equations--refined equations and simplified equations--are proposed. By using these equations, the tendon configuration in terms of its profile, area, and eccentricities can be determined for the strengthening of simple-span beams to carry a specified additional load. A design example is given in the appendix to illustrate the application of the method.

Prosthetic Hand Finger Control Using Fuzzy Sliding Modes

In order to improve the life quality of amputees, providing approximate manipulation ability of a human hand to that of a prosthetic hand is considered by many researchers. In this study, a biomechanical model of the index finger of the human hand is developed based on the human anatomy. Since the activation of finger bones are carried out by tendons, a tendon configuration of the index finger is introduced and used in the model to imitate the human hand characteristics and functionality. Then, fuzzy sliding mode control where the slope of the sliding surface is tuned by a fuzzy logic unit is proposed and applied to have the finger model to follow a certain trajectory. The trajectory of the finger model, which mimics the motion characteristics of the human hand, is pre-determined from the camera images of a real hand during closing and opening motion. Also, in order to check the robust behaviour of the controller, an unexpected joint friction is induced on the prosthetic finger on its way. Finally, the resultant prosthetic finger motion and the tendon forces produced are given and results are discussed.

Optimum design of prestressed concrete beams by a modified grid search method

A computer program has been developed for the optimum design of prestressed concrete beams under flexure. Optimum values of prestressing force, tendon configuration, and cross-sectional dimensions are determined subject to constraints on the design variables and stresses. 28 constraints have been used including flexural stresses, cover requirement, the aspect ratios for top and bottom flanges and web part of a beam and ultimate moment. The objective function contains cost of concrete, prestressing force and formwork. Using this function, it is possible to obtain minimum cost design, minimum weight or cross-sectional area of concrete design and minimum prestressing force design. Besides the idealized I-shaped cross-section, which is widely used in literature, a general I-shaped cross-section with eight geometrical design variables are used here. Four examples, one of which is available in the literature and the others are modified form of it, have been solved for minimum cost and minimum cross-sectional area designs and the results are compared. The computer program, which employs modified grid search optimization method, can assist a designer in producing efficient designs rapidly and easily. Considerable savings in computational work are thus made possible.

Parametric Study of Tendon Profiles in Prestressed Steel Plate Girder

The concept of prestressing steel structures has only recently been widely considered, despite a long and successful history of prestressing concrete members. Several analytical studies of prestressed steel plate girder were reported in the literature, but much of that work was not studied with reference to different parameters like tendon profile, eccentricity, partial span to full span ratio, prestressing force, load carrying capacity etc. associated with prestressing. This paper examines analytically a comparative study of various tendon configurations and prestressing parameters on over all analysis and design of prestressed steel plate girder. The output from the computer Program for analysis and design of steel plate girder prestressed with different tendon configurations are compared among each other. As a Case-study, a prototype model of Prestressed Steel Testing Frame with straight tendon has been designed, constructed and tested in the laboratory for its safe load carrying capacity and maximum deflection.

Effects of Deviators and Tendon Configuration on Behavior of Externally Prestressed Beams

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Optimal tendon configuration of a tendon control system for a flexible structure

This paper considers the optimal tendon configuration of a tendon control system for a two-dimensional, eleven-bay truss. With the criterion for optimal tendon configuration being controllability and robustness of the tendon control system, the optimal tendon configuration problem can be formulated as a constrained optimization problem which can be solved using dynamic programming; therefore, a solution to the optimal tendon configuration problem can be obtained efficiently. The robustness of the resulting tendon control system with respect to modeling imperfections is studied.

Pre‐Tensioned and Posttensioned Composite Girders

This paper deals with the analytical and experimental study of prestressed composite (steel girder with concrete slab) girders. The analysis is done for the case of simply supported bridge girder, using tendon configuration of straight, bent up, and short straight. In the development of the analytical expressions, a perfect shear connection between the concrete slab and the steel girder is assumed and the effects of losses due to creep, shrinkage, tendon relaxation, and residual stresses in the steel beam are not considered. The emphasis is placed on the stress distribution along the span under prestressing effect, and increase in initial tendon force due to application of external load. In this paper “pre‐” refers to stressing the tendon before the concrete slab is added and “post‐” to doing so after the slab is placed and ready to accept load. For this study, two girders of each 19 ft 7 in. (5,969 mm) long are tested. Calculated and observed results are then compared.

Anchor field tests in carboniferous strata

The paper discusses the preliminary findings of full scale tests on 57 anchors installed in carboniferous sediments. The site geology is briefly described together with the anchor construction and testing methods adopted. To investigate the influence of anchor geometry on failure mode, anchors ranging in overall depth from 0.75 to 12 metres were tested with grouted fixed anchor lengths of 0.75 to 6 metres. The observed effects of depth of embedment, grout surcharge, tendon configuration, interstrand spacing and tendon density on anchor performance are discussed in relation to current practice. Measurements of interfacial bond and load transmission are presented.

Optimum Design of Prestressed Plates

Optimum design of prestressed plates subjected to multiple load conditions is formulated as a mathematical programming problem. Design variables represent plate thickness, prestressing forces, and configuration and location of tendons. Using the method of equivalent load for analysis, all the constraints are expressed explicitly as functions of the variables. Based on a transformation of variables, the design problem for a given tendon configuration or tendon location is formulated with linear constraints. In the design for minimum plate thickness or minimum prestressing forces the objective function is transformed into a linear form and the problem is reduced to linear programming. Numerical examples demonstrate the application of this method.