Joint Bars Research Articles

Study on surface waves for detection of fatigue cracks in railway joint bars

The current method of inspecting railway joint bars involves the use of high-resolution cameras to detect fatigue cracks that have undergone significant cracking exposed to the surface. The novelty of the work presented in this paper discusses the development and application of non-contact ultrasonic surface wave approach to detect and characterize near-surface fatigue cracks in the head of the railway joint bars which is not usually accessible for inspection. Simulated cracks were implanted in the head of the two different used joint bars to assess the capabilities of the ultrasonic nondestructive evaluation (NDE) surface wave approach. One of the joint bars was implanted with 3.175 mm and 6.35 mm cracks in length, while the other joint bar was implanted with 12.7 mm and 25.4 mm cracks in length. Despite the complex geometry of railway joint bars, the laboratory proof-of-concept testing conducted in an immersion water tank demonstrated that the developed non-contact surface wave approach successfully detected implanted cracks in both joint bars. The results obtained from the study indicate that a 0.5 MHz ultrasonic transducer provided the best sensitivity for detecting implanted cracks compared to 1 MHz and 2.25 MHz transducers. Similarly, test results obtained with a 0.5 MHz ultrasonic transducer, launching a surface wave from an accessible area to an inaccessible area of the joint bar (where the implanted cracks were located) yielded a significantly higher signal-to-noise ratio (SNR) than the 1 MHz and 2.25 MHz transducer.

Bond-slip model of headed bar and its application to component-based model for precast concrete joints under accidental loads

This study focused on investigating bond-slip behaviour of headed bars embedded in well-confined concrete. Test results based on eight pull-out specimens under displacement-controlled incremental loading showed that recommended development lengths from ACI318–19 are conservative in developing ultimate strength of headed bars associated with smaller slips than straight bars. Moreover, it was found that different (but sufficiently long) embedment lengths had a significant effect on the free-end slip but negligible effect on the loaded-end slip of headed bars. Additionally, the study highlighted the significance of head bearing in anchorage formation, especially during inelastic stage when bond strength had deteriorated. To address inaccuracy in predicting structural behaviour caused by inadequate anchorage strength of headed bars, a macro bond-slip model was proposed based on correlation in strain distribution obtained from the pull-out tests. Subsequently, the proposed model was incorporated into a component-based model (CBM) and validated against test results of PC joints under seismic loading. A numerical investigation using the validated CBM was conducted to study behaviour of exterior PC joints with headed bars and special detailing. These included Type X joint with X-bent bars and plastic hinge relocation (PHR), and Type A joint with an additional bar layer (ABL) in the beam-joint region, subjected to extreme loads such as seismic action or progressive collapse. The results revealed that seismic behaviour of exterior joints was governed by ductile failure of the beam at the PHR and vertical joint interface in Type X and Type A joints, respectively. Progressive collapse was primarily caused by column failure, with flexural and catenary action effectively preventing collapse. Notably, under both loading conditions, presence of ABL in Type A joint and X-bent bars with PHR in Type X joint improves flexural strength of beams at critical sections and joint shear strength, ultimately enhancing structural performance of joints. Design recommendations include replacing hooked bars with headed bars as well as implementing X-bent bars with PHR and ABL in PC joints. The authors advocate the strong-column-weak-beam design approach as an effective measure to prevent progressive collapse.

High-Strength Headed Bars in Joints of Special Moment Frames under Cyclic Loading

High-Strength Headed Bars in Joints of Special Moment Frames under Cyclic Loading

Special inspection – traditional and innovative investigation techniques carried out on the “Passignano” viaduct

The article presents some results obtained during the investigation performed by the Structural Diagnostic laboratory of the “Centro di Ricerca e Sperimentazione Stradale di Cesano” on the “Passignano” viaduct located on the Bettolle-Perugia motorway junction managed by Anas S.p.A. It was designed by Prof. Eng. Giorgio Croci in the early 1980s. The infrastructure is characterized by girders supported on two piers with two cantilevered ends. These two ends are characterized by a 45° angle section forming an inclined joint connected by No. 30 Dywidag bars. The on-site investigation consisted of the axial stress evaluation of the joint bars under dead load using two different techniques, a static load test on span No. 7 joint and, eventually test executed during exceptional 150-ton vehicle transiting on the deck.

The contribution of metal allergy to the failure of metal alloy implants, with special reference to titanium: Current knowledge and controversies.

After almost three-quarters of a century during which contact dermatologists have often struggled to comprehend the relationship between metal allergy and failure of metal-alloy containing implant, it is possible to say that a relationship does exist, particularly for cobalt and chromium, but also for nickel. There is still debate as to whether allergy develops as a consequent of failure but thenceforth contributes to it, or whether sensitisation starts first and induces failure secondarily-opinion probably favours the first. Metal-on-polypropylene articulations were associated with few metal allergic problems but now are less favoured by orthopaedists due to plastic wear products causing osteolysis and pseudotumour formation through local inflammation. New metal alloys are regularly being introduced such that interested dermatologists need to stay on top of the situation. The jury is still out as to whether the recent favouring of titanium-containing alloys will confirm them to be more inert allergenically. Case reports do show some clinical reactions to titanium-containing implants and patch test series have inferred sometimes quite a high background rate of allergy, but interpretation must be tempered by the awareness that titanium salts on patch testing have a tendency to cause irritant reactions. Blood monitoring of metal ion values is now recommended in certain situations after joint replacement and increasing levels may be an indication that allergy with joint failure can develop, in which case patch testing is indicated, and suggested series are available. Predictive patch testing, whilst generally not recommended in the past, has been introduced into some protocols often by non-dermatologists, such that it is now needed for temporo-mandibular joint and Nuss bar insertion, and it can be anticipated that this may become more commonplace in the future. One of the major current deficits for patch testers is standardised guidance on which preparation or preparations to use for suspected titanium allergy. One suggestion is 0.5% titanium sulphate in petrolatum, though experience in at least one centre suggests the use of a battery of titanium salts might be desirable.

Immediate loading of dental implants in edentulous mandibles using Locator attachments or Dolder bars: A 9-year prospective randomized clinical study.

To evaluate the long-term survival, incidence of prosthetic/technical and biological complications and the oral-health-related quality of life in patients with an edentulous mandible who were fitted with overdentures on two immediately loaded implants in the symphyseal area. Forty-six patients with edentulous mandibles received two immediately loaded implant-retained dentures with either two Locator attachments or egg-shaped bar attachments. Implant outcomes were recorded after a period of observation of 9 years and included prosthetic complications, modified gingiva index (mGI), modified plaque index (mPI), oral health impact profile (OHIP-G) and radiographic estimation of bone loss. In 2020/2021, 27 patients with 54 implants were still available for follow-up. In total, nine implants in six patients were lost. Survival was 89.1% in the bar group and 91.3% in the Locator group. Implant success was 84.6% in the Locator group and 76.9% in the bar group. The mPI values were significantly higher in the bar group than in the Locator group, whereas no difference was seen in the mGI values. During the observation period, 152 prosthetic complications occurred, but the OHIP-G score did not differ significantly. There was no difference in implant survival between Locator or joint bar attachments over a 9-year observation period. Joint bar attachments were associated with slightly more complications, while patients in the Locator group were able to maintain better oral hygiene. The study was registered in the German Register of Clinical (Trials DRKS00004245).

FATIGUE ANALYSIS OF POLYCENTRIC PROSTHETIC KNEE FOR TRANS-FEMORAL AMPUTATION

A prosthetic knee is predominantly subjected to cyclic action leading to fatigue failure during its operation. However, cyclic failure is more severe as it occurs below the yield strength and may happen even without prior indication. This study presents a cyclic structural analysis of an existing polycentric mechanical prosthetic knee by finite element simulation and its experimental validation as per the ISO 10328:2016 standard. The three-dimensional (3D) model is imported to the ANSYS 20.1 workbench to study stress distribution and fatigue life in the knee for ensuring its safety performance. The maximum von-Mises stresses developed at the front and back joint bars made of A390.0-T5 and A390.0-T6 cast aluminium are 100 and 89[Formula: see text]MPa, respectively, in both loading conditions compared to their mechanical fatigue strength of 89[Formula: see text]MPa. The maximum deformation and average number of cycles for fatigue failure are 2.66 and 2.53[Formula: see text]mm and [Formula: see text] and [Formula: see text] for simulation and experimental results, respectively. These results suggest that this polycentric knee unit has poor fatigue strength and thereby does not meet the ISO structural standard. A validation test has been performed with an average error of 4.75% between the simulation and experiments results showing higher reliability.

Bond and anchorage performance of beam flexural bars in beam-column joints using slag-based geopolymer concrete and their effect on seismic performance

An available study on the bond and anchorage performance of beam flexural bars in beam-column joints using slag-based geopolymer concrete (GC) is limited. The applicability of current design codes to beam flexural bars design in GC beam-column joints is unknown. In this study, to investigate the bond and anchorage performance of beam rebars at the GC beam-column joints and their effect on seismic performance, cyclic loading tests were performed on 2 reinforced GC interior beam-column joints and 6 reinforced GC exterior beam-column joints. The test results showed that the increase in column depth-to-beam rebar diameter ratio (hc/db) from 21 to 25 improved the bond performance of the beam flexural bars in the reinforced GC interior beam-column joints, which significantly improved the energy dissipation capacity. The limits of hc/db larger than 20 in GB50010-2010 (except seismic grade I that requires hc/db ≥ 25) and ACI 318-19 were not safe for reinforced GC interior beam-column joints. The limits of hc/db in Eurocode 8 and NZS3101 for low-strength concrete (fc′ ≤ 30 MPa) were applicable. In reinforced GC exterior beam-column joints, the bond and anchorage performance of 90˚ hooked bars was superior to that of the corresponding headed bars. Regardless of the anchorage details, the bond and anchorage performance of the reinforced GC exterior beam-column joints increased with the increase of the development length of beam flexural bars. In reinforced GC exterior beam-column joint design, the bar development length requirement of GB50010-2010 was applicable to both 90˚ hooked bars and headed bars. Eurocode 8, NZS3101, and ACI 318-19 were applicable to the development length of 90˚ hooked bars.

Wave-based analysis of jointed elastic bars: stability of nonlinear solutions

In this paper we develop two new approaches for directly assessing stability of nonlinear wave-based solutions, with application to jointed elastic bars. In the first stability approach, we strain a stiffness parameter and construct analytical stability boundaries using a wave-based method. Not only does this accurately determine stability of the periodic solutions found in the example case of two bars connected by a nonlinear joint, but it directly governs the response and stability of parametrically forced continuous systems without resorting to discretization, a new development in of itself. In the second stability approach, we pose a perturbation eigenproblem residue (PER) and show that changes in the sign of the PER locate critical points where stability changes from stable to unstable, and vice-versa. Lastly, we discuss follow-on research using the developed stability approaches. In particular, we identify an opportunity to study stability around internal resonance, and then identify a need to further develop and interpret the PER approach to directly predict stability.

Seismic behavior of novel GFRP bar reinforced concrete beam-column joints internally reinforced with an FRP tube

Due to many advantages, fiber-reinforced polymer (FRP) bars have been considered as a promising alternative to steel bars in reinforced concrete (RC) structures. The use of FRP bars in beam-column joints has been reported in the literature. However, it has been found that the energy dissipation capacity of an FRP-RC beam-column joint is dramatically lower than that of the corresponding steel-RC joint. The present study attempts to develop a novel form of FRP-RC beam-column joints with superior energy dissipation capacity. The proposed joints incorporate an internal FRP tube in the joint zone, which provides confinement to the inner concrete and shear resistance of the joint. Compared with existing reinforcement techniques using stiffeners or internal diaphragms, the proposed use of an internal FRP tube is much easier to be implemented. To demonstrate the advantages of the proposed FRP-RC beam-column joints, an experimental program consisting of 6 FRP-RC beam-column joint specimens was carried out. The effects of fiber type, thickness, and fiber orientation of the FRP tube in the joint zone were investigated. The test results in terms of failure modes, hysteretic behaviors, and energy dissipation capacities of the test specimens were discussed in detail. The test results demonstrated the efficiency of the FRP tube, especially the one with a fiber angle of ±45°, in enhancing the energy dissipation capacity of FRP-RC beam-column joints.

Load Transfer Efficiency Assessment of Concrete Pavement Joints Using Distributed Optical Vibration Sensor

This paper presents a method to assess the load transfer efficiency (LTE) of concrete pavement joints using distributed optical vibration sensors. First, a theoretical analysis of concrete pavement vibration was conducted to investigate how to reflect LTE by spectral amplitude. Second, distributed optical vibration sensor (DOVS) was applied to measure vibration around joints distributedly. Third, the corresponding processing method for DOVS data was proposed to calculate the ratio of spectral amplitude from different slabs through power spectral density (PSD) analysis. Then, field tests were conducted on nine concrete pavement slabs with three different types of joints (dummy joint, rabbet joint, and dowel bars). The deflection-based method as well as the proposed vibration-based method were employed to assess the LTE of eleven joints on two different dates. The comparative analysis results indicate the deflection-based LTE (DLTE) and the ratio of PSD (RPSD) have a strong correlation (0.871) and a slight difference (<±0.03) overall. The correlation is robust in different dates and types of joints (0.844~0.88). These findings prove the accuracy and effectiveness of the proposed vibration-based method.

Wave-based analysis of jointed elastic bars: nonlinear periodic response

In this paper, we develop two wave-based approaches for predicting the nonlinear periodic response of jointed elastic bars. First, we present a nonlinear wave-based vibration approach (WBVA) for studying jointed systems informed by re-usable, perturbation-derived scattering functions. This analytical approach can be used to predict the steady-state, forced response of jointed elastic bar structures incorporating any number and variety of nonlinear joints. As a second method, we present a nonlinear Plane-Wave Expansion (PWE) approach for analyzing periodic response in the same jointed bar structures. Both wave-based approaches have advantages and disadvantages when compared side-by-side. The WBVA results in a minimal set of equations and is re-usable following determination of the reflection and transmission functions, while the PWE formulation can be easily applied to new joint models and maintains solution accuracy to higher levels of nonlinearity. For example cases of two and three bars connected by linearly damped joints with linear and cubic stiffness, the two wave-based approaches accurately predict the expected Duffing-like behavior in which multiple periodic responses occur in the near-resonant regime, in close agreement with reference finite element simulations. Lastly, we discuss extensions of the work to jointed structures composed of beam-like members, and propose follow-on studies addressing opportunities identified in the application of the methods presented.

Optimization of Rigid Pavement

Abstract: The construction of national highways nowadays is preferred by using rigid pavements as they are durable, have the high flexural strength, can withstand different heavy axle loads, higher design span and moreover they can sustain adverse environmental conditions more efficiently with better ease. Considering their remarkable qualities, the national highways should be constructed by providing the tied shoulders and dowel bars in the transverse joints because they can better resist the fatigue accumulations on the slab with minimum safe thickness which ultimately leads to reduction in the cost of making the road efficiently. In this chapter, for the two different CBR conditions (CBR-9 & CBR-10) and three concrete mix design grades namely (M40, M45, M50) along with different shoulders and dowel bars conditions, the trial methods were carried on the IRC58 Software for bottom-up cracking fatigue analysis for single and tandem axle for day-time (6 hour) traffic and positive temperature differential and top-down cracking fatigue analysis for single, tandem and tridem axle for day-time (6 hour) traffic and negative temperature differential for evaluating the flexural stresses and cumulative fatigue damage values for the slab having dimensions of (3.5m x 4.5m). For determining the safe design, different trails on the thickness parameter of the slab were being adopted so as to get the cumulative fatigue values of BUC and TDC for single, tandem and tridem axles less than one. The results obtained showed that for which grade and CBR condition, the values of flexural stresses and cumulative fatigue damage determined is maximum. It was concluded that the rigid pavements should be constructed by using higher grades like M45 and M50 as the fatigue stresses and cumulative fatigue damage values due to variable single, tandem and tridem axle load repetitions obtained are less as compared to M40 grade. Keywords: California Bearing Ratio (CBR); Bottom Up Cracking (BUC); Top Down Cracking (TDC); Mix Design Grade Value (M), Indian Road Congress (IRC); Flexural Stresses; Cumulative Fatigue Damage(CFD)

Physical and Numerical Simulations on Mechanical Properties of a Prefabricated Underground Utility Tunnel

The “U-shaped ferrule joint bars connections” have a stable mechanical property, requiring a low level of construction accuracy and a relatively simple connection process, which significantly increase the construction speed. Based on the “U-shaped ferrule joint bars connections” technology, a new type of prefabricated concrete underground utility tunnel was proposed. This prefabricated technology realizes a formwork-free construction and vertical support-free assembly of the top plate on site. Through the full-scale model static test and numerical analyses, the mechanical properties, i.e., the crack development law and bearing capacity, were systematically investigated to validate the effectiveness of the “U-shaped ferrule joint bars connections”. The test results indicated that the performance of the “U-shaped ferrule joint bars connections” is reliable. During the loading process, the prefabricated utility tunnel experienced three stages, i.e., cracking, stiffness degradation, and ultimate failure. The numerical analysis results correlated with the test results well. The simulation results showed that the bearing capacities of the prefabricated underground utility tunnel and the cast-in-place utility tunnel were similar. The longitudinal joint connections of the prefabricated utility tunnel allow the structure as an integration to maintain favourable mechanical properties.

Influence of Misalignment Method on Performance of Dowel Bars in Joints of Rigid Pavement.(Dept. C)

Load transfer across transverse joints has always been into consideration of rigid pavement design. Steel dowels of circular cross-section were the standard load transfer device. Many problems have been related to steel dowels such as corrosion. At the same time, joints are also damaged by repeated loading over time. This research presents an experimental investigation into the comparison between the Glass Fiber Reinforced Polymer (GFRP) and steel dowel bars placed in the transverse joints of the Jointed Plain Concrete Pavement (JPCP). The main objective of this study to assess the suitability of using GFRP dowel bars as an alternative corrosion-free material to conventional steel dowels. This research contains a set of variables and conditions in which we can assess which dowel bars are the best. Among these variables is the type of material the dowel bar is made of, whether it is steel or GFRP, and the misalignment method by which the dowel bar stacks in the transverse joints. Conclusion: As expected, the use of GFRP dowel bars improved the bearing of the applied loads exposed on the specimens compared to their counterparts of the specimens with steel dowel bars by about 125%. The experimental results showed that using the horizontal misalignment method was a practical and good method to arrange the dowel bars crossing the transverse joints between JPCP slabs.

Computational Design of Planar Multistable Compliant Structures

This article presents a method for designing planar multistable compliant structures. Given a sequence of desired stable states and the corresponding poses of the structure, we identify the topology and geometric realization of a mechanism—consisting of bars and joints—that is able to physically reproduce the desired multistable behavior. In order to solve this problem efficiently, we build on insights from minimally rigid graph theory to identify simple but effective topologies for the mechanism. We then optimize its geometric parameters, such as joint positions and bar lengths, to obtain correct transitions between the given poses. Simultaneously, we ensure adequate stability of each pose based on an effective approximate error metric related to the elastic energy Hessian of the bars in the mechanism. As demonstrated by our results, we obtain functional multistable mechanisms of manageable complexity that can be fabricated using 3D printing. Further, we evaluated the effectiveness of our method on a large number of examples in the simulation and fabricated several physical prototypes.

Seismic performance of corroded reinforced concrete beam-column joints repaired with BFRP sheets

Reinforcement corrosion is one of the main reasons for the deterioration of reinforced concrete (RC) structure. Corroded RC beam-column joint experiences large deformations under the earthquake, which results in the deterioration of the seismic behavior. Although researches on the uncorroded joints strengthened with fiber-reinforced polymer (FRP) sheets have been conducted, investigations on the corroded RC beam-column joints repaired with basalt FRP (BFRP) sheets are relatively limited. In present research, seven interior beam-column joints were tested under the cyclic loading, including one reference specimen, three specimens with different corrosion rates, and three corroded specimens repaired with BFRP sheets. The seismic behaviors in terms of crack pattern, failure mode, hysteretic curve, load bearing capacity, deformation capacity, energy dissipation, and stiffness degradation were discussed. Results obtained from the test showed that: (1) the seismic behaviors of corroded beam-column joints were effectively improved by the utilization of BFRP sheets; (2) the spalling, and crushing of concrete, as well as the buckling of stirrups were delayed by the utilization of BFRP sheets; (3) the load bearing capacity, ultimate displacement, and energy dissipation capacity of corroded beam-column joints were effectively increased, and the stiffness was fully recovered to that of uncorroded joint by repairing with BFRP sheets; (4) the bond behavior between corroded bars and concrete or strains of corroded bars in beam-column joints were improved or decreased after repairing with BFRP sheets.

Influence of Misalignment Method on Performance of Dowel Bars in Joints of Rigid Pavement. (Dept. C)

Influence of Misalignment Method on Performance of Dowel Bars in Joints of Rigid Pavement. (Dept. C)

Pull-Out Behavior of CFRP Bars in Glued-In Glubam Joints

Abstract Glubam (glued-laminated bamboo) is a newly developed structural material with properties comparable to other wood and wood-based materials. Fiber-reinforced polymer (FRP) bar is an attract...

Behaviour of steel fibers reinforced exterior beam-column joint using headed bars under reverse cyclic loading

Fiber-reinforced cementitious composites have been increasingly used during recent years on beam-column joints and the introduction of headed bars is a practical solution to eliminate the congestion problem caused by hooked bars in beam-column joints. The present study emphasizes the evaluation of the performance of steel fiber reinforced concrete (SFRC) external beam-column joints (BCJ) using headed bars as an anchorage mechanism and the comparison has been made with the conventional bars which have been detailed in accordance with ACI 318-19 and ACI 352R-02. The repository of previous BCJ work has been further expanded by researching the effect of structural parameters i.e. compressive strength (C20 and C40) and steel fibers (1 and 1.5%) on the hysteresis curve, ductility, stiffness, energy dissipation, and cracking on all specimens. The experimental results have revealed that the headed bars can be significantly replaced by the conventional bars for the areas vulnerable to earthquakes due to their higher load carrying capacity with better ductility and stiffness response and reducing congestion in BCJ.