Knee Bracing System Research Articles

A novel ductile CHS knee bracing system for rehabilitation of earthquake-damaged buildings: The case of Sarpol-e-Zahab (Iran) earthquake

This paper deals with a full-steel ductile Circular Hollow Section (CHS) bracing system, already employed for the rehabilitation of steel moment-resisting frames (SMRFs) damaged in the 2017 Iran Sarpol-e-Zahab earthquake of 7.3 magnitudes (Mw). The bracing device is experimentally qualified under monotonic and cyclic inelastic axial loading. It proves to have excellent ductility, energy dissipation capacity, comparable inelastic deformations under compression/tension, and stable/full hysteresis loops. A nonlinear finite element (FE) approach with element birth/death and ductile damage mechanics schemes is used to model the seismic performance of an earthquake-damaged SMRF rehabilitated with the ductile-CHS knee bracing. The results show that the proposed ductile CHS knee bracing effectively improves the seismic performance of the damaged frame. Based on experimental/numerical qualifications, the proposed CHS knee bracing may be recommended as a ductile, energy-absorbing, cost-effective, easy-to-construct, and replaceable structural device.

Evaluation of a Smart Knee Brace for Range of Motion and Velocity Monitoring during Rehabilitation Exercises and an Exergame.

Anterior cruciate ligament (ACL) injuries often require a lengthy duration of rehabilitation for patients to return to their prior level of function. Adherence to rehabilitation during this prolonged period can be subpar due to the treatment duration and poor adherence to home exercises. This work evaluates whether a smart instrumented knee brace system is capable of monitoring knee range of motion and velocity during a series of common knee rehabilitation exercises and an exergame. A total of 15 healthy participants completed a series of common knee rehabilitation exercises and played an exergame while wearing a smart instrumented knee brace. The range of motion (ROM) and velocity of the knee recorded by the knee brace was compared to a reference optoelectronic system. The results show good agreement between the knee brace system and the reference system for all exercises performed. Participants were able to quickly learn how to play the exergame and scored well within the game. The system investigated in this study has the potential to allow rehabilitation to occur outside of the clinic with the use of remote monitoring, and improve adherence and outcomes through the use of an exergame.

A novel home-based rehabilitative knee brace system is a viable option for postoperative rehabilitation after anterior cruciate ligament reconstruction: a report of 15 cases

PurposeTo investigate the functional outcomes for patients who used a novel home-based rehabilitative system during the postoperative period after anterior cruciate ligament (ACL) reconstructions.MethodsPatients undergoing ACL reconstruction surgeries were prospectively enrolled. A home-based rehabilitation system, which is composed of a knee brace with a motion tracker, a mobile app, and a web portal, was applied. Patients could complete the rehabilitation exercise through the audio guidance and the real-time tracking system which displayed the achieved motions on the user interface of the app. Feedbacks from the patients, including the International Knee Documentation Committee (IKDC) scores, were collected and uploaded to the web portal. Each patient would meet a specialized physical therapist face-to-face once a month. At postoperative 6 months, every patient received a GNRB arthrometer examination and a Cybex isokinetic dynamometer examination.ResultsA total of 15 patients (10 males and 5 females) were enrolled and followed for at least 6 months. The mean time of return to full knee extension was 1.5 months.The mean difference in laxity measured by GNRB arthrometer at 134 N significantly improved at postoperative 6 months (1.8 ± 1.6 mm) compared to that measured preoperatively (3.4 ± 1.9 mm) (p = 0.024). The peak torques of flexor and extensor muscles measured by Cybex isokinetic dynamometer remained unchanged at postoperative 6 months (p = 0.733 and 0.394, respectively). The patients’ IKDC score became smaller at postoperative 1 month (p = 0.011) and significantly improved at postoperative 6 months (p = 0.002).ConclusionUsing a home-based rehabilitative knee brace system after ACL reconstruction is a viable option as patients maintained their knee muscle strengths maintained their muscle strength and achieve similar or better knee range of motion six months postoperatively.

Experimental and parametric study of a novel braced system to improve seismic performance

Concentrically braced frames have high stiffness, but show poor ductility in terms of the buckling of compressive member. Using the yielding dampers, of which the knee-joints are a part, can improve the seismic performance of steel frames. The bracing components in this system disperse energy by adhering to the knee joint and then yielding. The role of the bracing members is to provide rigidity, while the function of the knee member is to produce ductility similar to a yielding damper. These steel dampers are inactive and installed at the connection of brace to the frame. We obtained new results by combining Y-shaped braces with knee members. In this regard, three proposed bracing frame specimens were experimentally tested at the structural laboratory. Furthermore, all of the three laboratory specimens were modeled and validated in ABAQUS finite element software, and the results confirm the optimal performance of this seismic system along with energy absorption and appropriate behavior in the stability of this design. Moreover, it shows a good capacity for energy dissipation and the knee element starts the energy absorption process faster at lower frame displacements. It increases the durability of structure against lateral loads and less force is applied to the main elements of the structure. Using a knee bracing system can be a good alternative to the brace system in terms of its ease of replacement. Reasonable agreement with the experimental results is observed. The behavior of deformation-force hysteresis curves gives good results that, the experimental and parametric experiments showed that this system will have a lot of force adjustment.

On the Evaluation of the Use of EKBs to Improve Seismic Performance of Steel Frames

In this paper a new eccentric and knee bracing system named Eccentrically Knee Brace (EKB) is introduced and its merits to increase seismic performance of the steel frames is investigated. To assess the seismic behavior of this system compared to other steel braced systems, numerical modeling using finite element software is implemented. Subjected to moderate earthquakes, the knee element exclusively dissipates the seismic energy through plastic shear distortion, while the other structural elements remain in elastic range. Under severe earthquakes, plastic deformation of the knee element will be halted by the stopper subsequently causing yielding of the link element. Finally, a simplified analytical model is derived to predict the bilinear behavior of the EKBs.

Comparison of Seismic Behavior of Eccentrically Braced Frames with Vertical and Knee Links in Retrofitting the Reinforced-Concrete Buildings with Intermediate Moment-Resisting Frame Systems

Given the fact that some reinforced-concrete (RC) buildings have not met resistance against seismic loads, it is mandatory to adopt a suitable and economically cost-efficient method to retrofit them. One appropriate method is application of steel Eccentrically Braced Frames (EBFs). This article is aimed at evaluation of seismic performance of retrofitted reinforce-concrete buildings by EBFs with single and knee links. For evaluation of modeled buildings, different editions of the Iranian Seismic Code (Standard No. 2800) were reviewed. To this end, three Moment-Resisting Frames (MRF) of four-, eight-, and twelve-story buildings with medium ductility were modeled where they were designed for seismic loads based on Standard 2800, 2nd edition. In order to evaluate buildings under modified seismic loads, models were seismically reloaded based on the Standard 2800, 3rd edition. Reanalysis showed that the stress ratios exceeded 1 in most columns. Therefore, buildings were retrofitted using EBFs with knee and single vertical links and their seismic performance were evaluated using nonlinear static analysis. Results indicate that knee bracing systems are more efficient than bracing systems with vertical link in increasing rigidity and controlling displacements, while they significantly reduce ductility. For example, application of knee bracing system in the twelve-story building can cause an 11% reduction in displacement in comparison to bracing systems with vertical links.

Experimental Study of the Lateral Resistance of Bolted Glulam Timber Post and Beam Structural Systems

AbstractTo study the lateral resistance of bolted glued-laminated (glulam) timber post and beam structures, two monotonic tests and eight cyclic tests were performed on full-scale, one-story, one-bay timber post and beam construction specimens. Four laterally strengthened structural systems were considered: a frame with an X-brace, a frame with a K-brace, a frame with a knee-brace, and a frame filled with light wood shear walls. Seismic performances were evaluated according to the experimental phenomena, hysteretic characteristics, stiffness degradation, strength degradation, and energy dissipation capacity. The results showed that the frame with an X-brace system and the frame with a K-brace system provided markedly better elastic stiffness but lower ductility. The frame with a knee-brace system showed increased elastic stiffness compared with the simple frame system and provided higher ductility compared with both the frame with the X-brace system and the frame with the K-brace system. Additionally, the...

On the characteristics and seismic study of Hat Knee Bracing system, in steel structures

In this study, a new structural bracing system named 'Hat Knee Bracing' (HKB) is presented. In this structural system, a special form of diagonal braces, which is connected to the knee elements instead of beam-column joints, is investigated. The diagonal elements provide lateral stiffness during moderate earthquakes. However the knee elements, which is a fuse-like component, is designed to have one plastic joint in the knee elements for dissipation of the energy caused by strong earthquake. First, a suitable shape for brace and knee elements is proposed through elastic studying of the system and several practical parameters are established. Afterward, by developing applicable and highly accurate models in Drain-2DX, the inelastic behavior of the system is carefully considered. In addition, with inelastic study of the new bracing system and comparison with the prevalent Knee Bracing Frame system (KBF model) in nonlinear static and dynamic analysis, the seismic behavior of the new bracing system is reasonably evaluated.

Assessment of Using of Knee Bracing in Retrofitting of Existing Steel Structures with Special Moment Resistant Frame System (Technical Note)

In this paper, non-linear behaviors of structures with special moment resistant frame were studied and possibility of using knee bracing for retrofitting of those structures was examined. For this aim, the structures that have been designed according to the second edition of Iranian seismic code (2800), were selected. Those models have 3, 5 and 7 stories. To evaluating and retrofitting of models, non-linear static analysis and capacity spectra (ATC-40) method were applied and providing of the expected performance levels in FEMA356 was studied. Results showed that the response of structures that designed according to the previous edition of code (second edition) is not compatible with the criteria of third edition. The knee bracing system was used to seismic retrofit of those structures. It would be concluded that the using of knee bracing increases lateral stiffness and improves their energy dissipating capacity. Furthermore, the results showed that the shorter knees have the highest stiffness and ductility in the structures.

Experimental and analytical studies on Buckling-Restrained Knee Bracing systems with channel sections

In this paper, Buckling-Restrained Knee Bracing (BRKB) system was developed through sub-assemblage tests. The core plate of the BRKB was restrained with two channel sections. Tests of the five BRKBs were carried out under cyclic loading as specified in the AISC (2005) Seismic Provisions. It was observed that the ductility and energy dissipation capacity of the BRKBs were mainly affected by the variables: size of core plate, size of channel sections, and size of end plate. Four out of five specimens satisfied the compression-strength adjustment factor and cumulative plastic ductility specified in the provisions. The BRKB, which showed the best performance among the test specimens, was applied to a piloti type reinforced concrete building. Static pushover and non-linear time history analyses were performed to confirm the retrofit effect. The analysis results showed that the installation of the BRKBs improved the seismic behavior of the building significantly in terms of strength and story drift.

DYNAMIC BEHAVIOR AND SIMPLIFIED MODELING METHOD FOR A TIMBER FRAME WITH KNEE BRACE DAMPERS

In this paper, wooden frames with knee brace dampers are designed, and their performance is demonstrated. Lateral dynamic loading tests are conducted in order to examine their dynamic properties. Knee brace system can add stiffness and damping to wooden house without closing its opening, which is a great advantage to reduce torsional response of structure. Simplified modeling method for passively controlled frame is also proposed, and it is based on the characteristics of the frame in two states ; without damper and with rigid damper. Dynamic property, maximum response and member's force and deformation can be predicted.

Gait changes over time in stance control orthosis users

This report presents objective motion analysis measurements of 14 stance control orthoses (SCO) users during a prospective open-enrollment 6-month clinical field trial. Participants were fitted with a Dynamic Knee Brace System (DKBS) which is a novel electromechanical SCO developed by the authors. Seven of the 14 subjects that had been prescribed but did not use a KAFO at the time of enrollment were defined as novice users. Those subjects who at the time of enrollment were using a locked KAFO for ambulation were defined as experienced users. Results showed that all subjects significantly increased peak knee flexion from 49.0 +/- 15.5 degrees to 55.9 +/- 11.4 degrees between the initial and six month tests (p = 0.02). They also tended to increase peak hip flexion from 39.6 +/- 13.4 degrees to 46.0 +/- 14.5 degrees between the 3 month and 6 month tests (p = 0.09). Novice users significantly increased velocity from 74.7 +/- 19.4 cm/s to 81.2 +/- 19.0 cm/sec between the initial and 3-month tests (p = 0.005). These same users increased stride length from 109 +/- 15.3 cm to 112 +/- 16.6 cm over the same time period (p = 0.008). Experienced KAFO users, however, tended to increase velocity from 68.8 +/- 20.5 cm/s to 83.2 +/- 16.8 cm/s at 3 months (p = 0.06). This was combined with a significant increase in cadence from 76.2 +/- 14.1 steps/min to 83.9 +/- 8.3 steps/min between the initial and 3 month tests (p = 0.05). Joint kinetics showed no changes for users over the duration of the testing period. These results indicate that KAFO users make significant gains in temporodistance measures, while changes in joint kinematics take longer to develop.

Clinical field trial of the dynamic knee brace system: A stance control orthosis

Clinical field trial of the dynamic knee brace system: A stance control orthosis

Consumer opinions of a stance control knee orthosis

Stance control knee orthoses (SCOs) have become very popular recently. However, there is little information regarding opinions of actual orthosis users. The purpose of this study was to quantify the users' opinions of a SCO, and see whether factors found important for knee orthoses in past studies hold true for a stance control orthosis as well. A standardized survey was employed as part of a larger field trial study of the Dynamic Knee Brace System, a SCO developed by the authors. The Dynamic Knee Brace System scored well in areas of effectiveness, operability, and dependability, but areas in need of improvement included weight, cosmesis, and donning and doffing. These findings match well with previous knee orthosis studies. This study shows that wearing a stance control knee orthosis can be a positive experience for an orthosis user.

Consumer Opinions of a Stance Control Knee Orthosis

Stance control knee orthoses (SCOs) have become very popular recently. However, there is little information regarding opinions of actual orthosis users. The purpose of this study was to quantify the users' opinions of a SCO, and see whether factors found important for knee orthoses in past studies hold true for a stance control orthosis as well. A standardized survey was employed as part of a larger field trial study of the Dynamic Knee Brace System, a SCO developed by the authors. The Dynamic Knee Brace System scored well in areas of effectiveness, operability, and dependability, but areas in need of improvement included weight, cosmesis, and donning and doffing. These findings match well with previous knee orthosis studies. This study shows that wearing a stance control knee orthosis can be a positive experience for an orthosis user.

Gait of stance control orthosis users

Individuals with weak or absent quadriceps who wish to walk independently are prescribed knee-ankle-foot orthoses (KAFOs). New stance control orthosis (SCO) designs automatically release the knee to allow swing phase flexion and extension while still locking the joint during stance. Twenty-one participants were fitted unilaterally with the Dynamic Knee Brace System (DKBS), a non-commercial SCO. Thirteen subjects were experienced KAFO users (average 28 +/- 18 years of experience) while eight were novice users. Novice users demonstrated increased velocity (55 vs. 71 cm/sec, p = 0.048) and cadence (77 vs. 85 steps/min, p < 0.05) when using the DKBS over the traditional locked KAFO. Experienced KAFO users tended to have reduced velocity and cadence measures when using the SCO (p < 0.10). Knee range of motion was significantly greater for the novice group than for the experienced group (55.2 +/- 4.8 vs. 42.6 +/- 3.8 degrees, p = 0.05). Peak knee extension moments tended to be greater for the experienced group (0.29 +/- 0.21 vs. 0.087 +/- 0.047 Nm/kg, p = 0.09). This report describes gait changes during the introductory phase of DKBS adoption. Experienced KAFO users undoubtedly had ingrained gait patterns designed to compensate for walking with a standard locked KAFO. These patterns may have limited the ability of those users from taking full and immediate advantage of the SCO capabilities. Also, alternate SCO systems may engender different results. Comparison studies and longer term field studies are needed to clarify benefits of the various bracing options.

Pushover tests on steel X-braced and knee-braced RC frames

Results of pushover experiments conducted on scaled models of ductile RC frames, directly braced by steel X and knee braces are presented. Test results indicate that the yield capacity and the strength capacity of a ductile RC frame can be increased and its global displacements can be decreased to the desired levels by directly adding either an X- or a knee-bracing system to the frame. X bracing can provide a stiffer bracing system but reduces the ductility of the ductile frame. Knee bracing can be employed to provide the desired ductility level for a ductile design. It is concluded that both X-bracing and knee-bracing systems may be used to design or retrofit for a damage-level earthquake. However, when designing or retrofitting for a collapse-level earthquake, knee bracing is a more effective system.

Automatic control design for a dynamic knee-brace system.

A self-contained electronically controlled dynamic knee-brace system (DKBS) has been designed and tested which allows knee flexion during swing phase, but restricts flexion during the stance phase of gait. Cardiovascular energy measurements indicate that DKBS use allowed a more energy efficient gait.

Optimization and application of a wrap-spring clutch to a dynamic knee-ankle-foot orthosis.

A dynamic knee-brace system (DKBS) has been designed which provides stance phase stability and swing phase freedom. A wrap-spring clutch controls knee flexion. Clutch optimization was performed minimizing clutch length. Kinematic tests on a normal subject using the DKBS document nearly normal dynamic knee flexion during swing (38 degrees versus 53 degrees for normal).