Static Four-point Bending Research Articles

Rigidity coefficients of rubber belts for dynamic testing of modulus of elasticity and shear modulus of non-wood engineered board

To determine the appropriate stiffness coefficient k values for rubber belts used in dynamic testing of the elastic modulus and shear modulus of timber and solid wood composite materials, this study employed three different thicknesses of rubber belts. Dynamic tests were conducted on straw boards, Laminated Veneer Lumber (LVL), and Spruce-Pine-Fir (SPF) materials, and the results were validated and analyzed using static four-point bending tests. The conclusions drawn from this research indicate that the range of stiffness coefficient k values for the rubber belts obtained through dynamic testing fell between 0.05 and 0.28 N/m. The correctness of the dynamic testing method was verified through static four-point bending tests. The error levels for elastic modulus E and shear modulus G of the same type of board measured using the three different rubber belts were below 9.5% and 9.8%, respectively.

Behaviour of Innovative Concrete Sandwich Panels with Pervious Concrete Core under Flexural Bending

Research studies investigating the possibility of using new core material (other than polystyrene) in concrete sandwich panels are being reported in the literature. In this paper, lightweight pervious concrete core is proposed as a new alternative. In this paper, the flexural behaviour of concrete sandwich panels with pervious concrete core is investigated under three-point and four-point bending conditions. The geometrical variables considered are core thickness and number of shear connector lines. Test results showed that, sandwich panels without shear connector trusses failed due to separation of wythes, and the panels with shear connector trusses achieved composite action. The variables considered were found to influence the initial stiffness, cracking moment, ultimate moment, load-deflection behaviour and load-strain behaviour of the panels. Analytical study indicated that the equation given in ACI 318 underestimated the strength of the tested panels. The equation have to be modified by explicitly including the shear connector details in the equation for predicting the flexural strength with reasonable accuracy. Further experimental and analytical studies on prototype concrete sandwich panels with pervious concrete core produced using lightweight aggregates are required in view of developing design guidelines for practical applications.

Experimental Study on Flexural Behavior of RC–UHPC Slabs with EPS Lightweight Concrete Core

This paper presents an experimental investigation that focuses on the flexural behavior of an innovative reinforced concrete–ultra-high performance concrete slab with an expanded polystyrene lightweight concrete core. This type of slab is proposed to serve the semi-precast solution, in which the bottom layer is ultra-high performance concrete working as a formwork during the construction of semi-precast slab, the expanded polystyrene lightweight concrete layer is used for the reduction of structure self-weight, and the top layer is normal concrete designed to withstand compressive stress when the slab is loaded. Two similar large-scale specimens with dimensions of 6200 mm × 1000 mm × 210 mm were fabricated and tested under four-point bending conditions to investigate the flexural behavior of composite slab. Test results indicated that three different layers of materials can work effectively together without separation. The bottom ultra-high performance concrete layer leads to the high ductility of the slab and has a good effect in limiting the widening of the crack width by forming other cracks. According to design code ACI 544.4R, a modified distribution stress diagram on the composite section was proposed and proven to be suitable for the prediction of flexural strength of the composite section with an error of 3.4% compared to the experimental result. The effect of the ultra-high performance concrete layer on the flexural strength of the composite slab was clearly demonstrated, and for the case in this study, the ultra-high performance concrete layer improves the flexural strength of the slab by about 11.5%.

Finite element modeling of debonding failure in CFRP-strengthened steel beam using a ductile adhesive

Carbon fiber-reinforced polymer (CFRP) composites externally bonded to the tensile flange of the steel beam are an effective strengthening technique. Due to the apparent effect of the adhesive toughness on the debonding behavior between the CFRP and steel, this paper focuses on the CFRP-strengthened steel beam using a ductile adhesive and the adhesive selection in the strengthening work. Three-dimensional (3-D) finite element (FE) models were proposed to simulate the mechanical response of the CFRP-strengthened steel beam under a static four-point bending load. The failure of a ductile adhesive was modeled using the trapezoidal mixed-mode cohesive zone model (CZM) coded in the user subroutine (UMAT) of ABAQUS. The effectiveness of the trapezoidal CZM was validated by the experiment in the literature, and the debonding characteristics using different laminate thicknesses and lengths were clarified by the stress and damage analysis. In terms of plate-end debonding failure mode, the ductile adhesive is more appropriate for the CFRP-strengthened steel beam due to its reduced normal stress, increased mixed-mode fracture energy, and more uniform stress distribution.

Shear strengthening performance of GFRP reinforced lightweight SCC beams: Experimental and analytical study

Light weight construction using Glass Fibre-Reinforced Polymer (GFRP) bars and structural light weight concrete (LWC) have increased recently and offers a wide spectrum of advantages over traditional normal weight concrete (NWC) structures. However, the shear strengthening and rehabilitation performance of LWC beams reinforced with GFRP bars is very limited and currently there are no guidelines related to it. Therefore, this study presents the results of an experimental investigation on the shear strengthening behaviour of lightweight self-consolidating concrete (LWSCC) beams reinforced with GFRP bars. The test parameters studied in the experimental program were the longitudinal reinforcement ratio and strip configuration or orientation. A total of twelve shear deficient GFRP reinforced beams were prepared with a shear span to depth ratio of 3.12 and subjected to static four-point bending. Five beams in each series were externally strengthened with different configurations of Carbon Fibre-Reinforced Polymer (CFRP) strips and one beam served as a control specimen to compare the performance of the strengthened specimens. Crack patterns, load–displacement response curves, and strain in the external CFRP strips were recorded until the failure ultimate load. The results of the experimental study indicated that the external CFRP strips improved the nominal shear capacity of GFRP reinforced LWSCC beams, and the contribution of external CFRP strips was sensitive to the reinforcement ratio. The nominal shear capacity of the strengthened specimens increased from 33.3 to 168% compared to the control specimen. U-wraps with horizontal strips in the compression and tension zone were the most effective configuration, showing the highest increase in shear strength compared to other strengthened specimens. Moreover, the shear capacity was theoretically predicted using different Fiber-Reinforced Polymer (FRP) design standards and guidelines which were compared with the experimental results. All the FRP design standards have overestimated the shear capacity of LWSCC beams, and a modified equation with a set of recommendations was proposed based on the experimental study. In addition, a reduction factor of 0.75 is recommended for conservative design.

Experimental, numerical and analytical study to develop a design method for bending and shear resistances of 3D printed beetle elytron inspired sandwich plate (beetle elytron plate)

Beetle elytron plate (BEP) is a new type of sandwich structure inspired by the internal architecture of beetle elytra and characterized by trabeculae in the core to achieve better mechanical resistance compared to conventional honeycomb sandwich plate under lateral loads. To take advantage of this improved performance in design, this paper presents, for the first time, a series of static four-point bending and shear tests for buckling and post-buckling behaviour of small-scale 3D printed BEPs until failure. Tensile coupon tests were also carried out on the 3D printed material. The experimental results are then used to validate ABAQUS numerical modelling that previously could only be partially carried out due to a lack of experimental data. The test results confirm large increases in BEP resistances compared to conventional honeycomb sandwich plates of the same dimensions. The observed BEP failure mode under bending is post-buckling of the compressive skin. Assuming that the post-buckling stress of BEP can be calculated in the same way as conventional sandwich plate, and making use of the elastic–plastic buckling stress solution for BEP that had previously been proposed by the authors, this paper proposes a simple method to calculate the post-buckling stress of BEP for design purpose. For shear resistance, the shear buckling stress of the trabecular core of BEP can be calculated in the same way as for conventional honeycomb sandwich plate except for using the web width between the near edges of the two adjacent trabeculae. The proposed calculation methods give results in good agreement with experimental results, with the maximum difference being 8%. The difference would be even lower if the smooth 3D printed surface is under compression.

FLEXURAL BEHAVIOR OF STEEL FIBER-REINFORCED LIGHTWEIGHT AGGREGATE CONCRETE BEAMS PRESTRESSED WITH CARBON FIBER-REINFORCED POLYMER BARS

An unbonded prestressing anchorage system for carbon fiber-reinforced polymer (CFRP) tendons was introduced. Eight lightweight aggregate concrete (LWC) beams prestressed with unbonded CFRP tendons which used CFRP auxiliary reinforcements and one fabricated using normal weight concrete (NWC) were tested under a four-point bending condition. The influences of concrete type, of prestressed degree and, of clear span length on the cracking moment, on the moment-deflection response and, on the crack width were analyzed. The existing deflection and crack width models for unbonded FRP prestressed beams with steel auxiliary reinforcements were modified from the view of equivalent axial stiffness. The applicability of the modified models was evaluated based on the test results. It is shown that the serviceability limit state of the beams is mainly governed by the crack width limit. The ratios between the moment at crack width of 0.5 mm and the ultimate moment range from 41% to 52%. With the same total reinforcement amount, the increase in the prestressed degree helps delay the cracking of the specimens. Increasing the amount of the auxiliary reinforcement and of the unbonded prestressed tendons both improve the beam stiffness and restrain the propagation of the cracks. The modified Cheng’s and modified Meng’s deflection models provide accurate deflection predictions for LWC beams with unbonded prestressed and auxiliary CFRP reinforcements.

Flexural Creep Behaviour of Pultruded GFRP Composites Cross-Arm: A Comparative Study on the Effects of Stacking Sequence.

Pultruded glass fibre reinforced polymer (pGFRP) composites provide outstanding properties for composite polymer cross arms in power transmission line applications. This study has investigated the effects of various stacking sequences of fibres directions of pGFRP on flexural strength and creep behaviour. The use of static four-point bending flexural tests revealed that Stacking Sequence 2 (±45/0/90/0/90/0) had a significant flexural strength of 399.9 MPa while Stacking Sequence 1 (±45/90/0/±45) had a flexural strength of 242.5 MPa. Furthermore, the four-point bending creep experiments were performed at three distinct stress levels, notably 12%, 24%, and 37% of the ultimate flexural strength, to characterise the creep behaviour of distinct stacking sequences. Moreover, Findley’s power law equation for bending creep behaviour has revealed that the time-dependent reduction factor of Stacking Sequence 1 and Stacking Sequence 2 estimates a drop in flexural modulus of 23% and 10% respectively.

FLEXURAL STRENGTHENING OF DIMENSIONAL WOOD JOISTS WITH STEEL REINFORCEMENT

ABSTRACT Traditional approaches to the strengthening of dimensional wood roof joist systems are often intrusive and require a substantial amount of additional labour to remove ceilings or roof sections. In an effort to design a less intrusive system for reinforcing over-stressed dimensional wood joists, a roof joist strengthening system was designed consisting of a tension steel plate installed along the bottom of the existing joists with bolted side plate connections. An experimental program was conducted at the University of Manitoba to assess the viability of the reinforcement design. A total of 15 joists were tested to failure under four-point bending conditions, consisting of 5 unreinforced control joists, 5 joists with steel reinforcement, and another 5 reinforced joists with an artificial defect introduced at mid-span along the tension side. The purpose of introducing an artificial defect at mid-span was to simulate the failure modes observed at R.W. Bobby Bend School in Stonewall, Manitoba, where certain roof joists contained knots, splits or cracks along the bottom of the joist within the mid-span region. Service loads based on the applied snow and dead loads applied to these joists were calculated using the National Building Code of Canada [1] and were approximated in the experiment as 8.5 kN. The results indicated that the steel reinforcement produced a 46.8% increase in average load-carrying capacity compared to control joists, and a 33.1% increase in capacity for reinforced joists with artificial defects. The average deflection at service loads was 19.5% lesser than the deflection of the control joists, and the apparent stiffness was determined to increase by 50.0%. The results from this research support the conclusion that the steel reinforcement system for dimensional wood joists is a viable alternative to traditional systems that effectively increases the load-carrying capacity, stiffness, and ductility of the structure.

FLEXURAL STRENGTHENING OF DIMENSIONAL WOOD JOISTS WITH STEEL REINFORCEMENT

ABSTRACT Traditional approaches to the strengthening of dimensional wood roof joist systems are often intrusive and require a substantial amount of additional labour to remove ceilings or roof sections. In an effort to design a less intrusive system for reinforcing over-stressed dimensional wood joists, a roof joist strengthening system was designed consisting of a tension steel plate installed along the bottom of the existing joists with bolted side plate connections. An experimental program was conducted at the University of Manitoba to assess the viability of the reinforcement design. A total of 15 joists were tested to failure under four-point bending conditions, consisting of 5 unreinforced control joists, 5 joists with steel reinforcement, and another 5 reinforced joists with an artificial defect introduced at mid-span along the tension side. The purpose of introducing an artificial defect at mid-span was to simulate the failure modes observed at R.W. Bobby Bend School in Stonewall, Manitoba, where certain roof joists contained knots, splits or cracks along the bottom of the joist within the mid-span region. Service loads based on the applied snow and dead loads applied to these joists were calculated using the National Building Code of Canada [1] and were approximated in the experiment as 8.5 kN. The results indicated that the steel reinforcement produced a 46.8% increase in average load-carrying capacity compared to control joists, and a 33.1% increase in capacity for reinforced joists with artificial defects. The average deflection at service loads was 19.5% lesser than the deflection of the control joists, and the apparent stiffness was determined to increase by 50.0%. The results from this research support the conclusion that the steel reinforcement system for dimensional wood joists is a viable alternative to traditional systems that effectively increases the load-carrying capacity, stiffness, and ductility of the structure.

Shear strengthening of high strength lightweight SCC beams internally reinforced with GFRP bars and external CFRP strips

Last few years have seen a substantial growth in the development and application of lightweight concrete (LWC) due to its enhanced mechanical properties and economic benefits in comparison to conventional normal weight concrete (NWC). The use of LWC in infrastructure has been popularised, especially in long-span bridges and high-rise bridges due to its lower density, which significantly reduces the dead load on the structure. Carbon fibre reinforced polymers (CFRP) and glass fibre reinforced polymers (GFRP) have rapidly gained acceptance in the infrastructure industry for their desirable characteristics over traditional steel. Extensive experimental research has been carried out over to years to investigate the shear performance of externally strengthened NWC beams with CFRP (carbon fibre reinforced polymer) strips. However, very limited research has been conducted on the shear performance of GFRP reinforced LWC beams externally strengthened with CFRP strips. Therefore, the main objective of this experimental study is to investigate the shear performance of high strength lightweight self-compacting concrete (HLWSCC) beams reinforced with internal GFRP bars and strengthened with external CFRP strips. HLWSCC is the latest development in concrete technology that combines the benefit of LWC and self-compacting concrete (SCC). One control specimen and two shear deficient HLSCC beams were strengthened with CFRP strips in the shear span. The test variable studied was the strip orientation (u-wrap and 45°) and all beams subjected to static four-point bending test. Load-deflection response and failure modes were observed and recorded for all the tested specimen. CFRP strips has considerably increase the load carrying capacity of HLWSCC strengthened beam specimen. The percentage increase in nominal shear strength ranged from 58.7% to 73.4% over unstrengthened control specimen.

Evaluation of different modulus input on the mechanical responses of asphalt pavement based on field measurements

As a key input parameter of asphalt pavement design, the modulus parameters directly affect the results of pavement stress analysis. During the mechanical evaluation analysis, researchers usually use material modulus instead of structural modulus as input parameter, so the possible deviations between the field measured mechanical responses and the calculated responses are ignored in this case. Therefore, the field mechanical response and the calculations mechanical response of finite element method (FEM) with different moduli input were evaluated in this research. The field strains of each pavement layer under dynamic and static load conditions were determined by embedding the fiber Bragg grating (FBG) sensors, and the field deflection test was carried out by Beckman beam. A total of 11 types of material moduli were obtained through various modulus tests, and which were implemented in the FEM model for the strain and deflection calculation of pavement structure, and then the calculated mechanical responses were compared with the field measured mechanical responses. The results indicated that a specific modulus should be selected to ensure the calculated value effectively reflect the measured mechanical response. For the FEM calculation of dynamic strain, it is recommended to use static flexural modulus for asphalt layer and use dynamic flexural modulus for CSG layer as modulus input with average errors of 16.9% and 7.5% respectively. For the FEM calculation of static strain, it is recommended to use dynamic compressive resilience modulus for asphalt layer and use static flexural modulus for CSG layer as modulus input with average errors of 18.7% and 11.5% respectively. Besides, it is recommended to select dynamic flexural modulus or compressive modulus in static four-point bending test as the modulus input for pavement deflection analysis with the error of about 4.8%.

Mechanical Comparison of a Novel Hybrid and Commercial Dorsal Double Plating for Distal Radius Fracture: In Vitro Fatigue Four-Point Bending and Biomechanical Testing.

This study compares the absolute and relative stabilities of a novel hybrid dorsal double plating (HDDP) to the often-used dorsal double plating (DDP) under distal radius fracture. The “Y” shape profile with 1.6 mm HDDP thickness was obtained by combining weighted topology optimization and finite element (FE) analysis and fabricated using Ti6Al4V alloy to perform the experimental tests. Static and fatigue four-point bending testing for HDDP and straight L-plate DDP was carried out to obtain the corresponding proof load, strength, and stiffness and the endurance limit (passed at 1 × 106 load cycles) based on the ASTM F382 testing protocol. Biomechanical fatigue tests were performed for HDDP and commercial DDP systems fixed on the composite Sawbone under physiological loads with axial loading, bending, and torsion to understand the relative stability in a standardized AO OTA 2R3A3.1 fracture model. The static four-point bending results showed that the corresponding average proof load values for HDDP and DDPs were 109.22 N and 47.36 N, that the bending strengths were 1911.29 N/mm and 1183.93 N/mm, and that the bending stiffnesses were 42.85 N/mm and 4.85 N/mm, respectively. The proof load, bending strength and bending stiffness of the HDDPs were all significantly higher than those of DDPs. The HDDP failure patterns were found around the fourth locking screw hole from the proximal site, while slight plate bending deformations without breaks were found for DDP. The endurance limit was 76.50 N (equal to torque 1338.75 N/mm) for HDDP and 37.89 N (equal to torque 947.20 N/mm) for DDP. The biomechanical fatigue test indicated that displacements under axial load, bending, and torsion showed no significant differences between the HDDP and DDP groups. This study concluded that the mechanical strength and endurance limit of the HDDP was superior to a commercial DDP straight plate in the four-point bending test. The stabilities on the artificial radius fractured system were equivalent for novel HDDP and commercial DDP under physiological loads in biomechanical fatigue tests.

The effects of nanostructure additive on fracture strength in adhesively bonded joints subjected to fully reversed four-point bending fatigue load

Structural adhesive joints used in aerospace are usually subjected to fatigue loading rather than static loading. This study experimentally and numerically investigated the static four-point bending loads of adhesively bonded joints after fully reversed four-point bend fatigue loading where nanoadhesives – obtained by adding carbon nanostructures into aerospace grade structural adhesive – were used to bond the joints. Single lap joint specimens were produced using a nanocomposite adhesive obtained by adding 1 wt % graphene, 1 wt % carbon nanotubes-COOH and 1 wt % fullerene C60 nanostructures to a DP460 structural adhesive. AA2024-T3 aluminum alloy and carbon fiber-reinforced composites (CFRCs) with a plain weave fabric (0/90°) were used as adherend materials. First, static four-point bending tests were applied to these joints to obtain their strengths and then fully reversed sinusoidal fatigue tests were applied under a constant load amplitude, a frequency of 20 Hz and a load ratio of R = −1. Fatigue tests were performed over 1,000,000 cycles – accepted as an infinite life – at four different load levels by considering the strengths obtained from the static tensile tests. After obtaining the static four-point bending strengths of the joints to which fatigue loading was applied, the changes in the strengths of joints with and without fatigue testing were examined. The static strengths of aluminum joints bonded with nanoadhesive and subjected to fully reversed fatigue loading significant increased, depending on the nanostructure type added to the adhesive. Moreover, such increases in the strengths of joints are highly dependent on the adherend type (composite with [0/90]6 stacking sequence or AA2024-T3 aluminum).

Numerical and Experimental Investigation of Static Four-point Bending Response of Honeycomb Sandwich Structure: Failure Modes and the Effect of Structural Parameters

The aim of this study is to characterize and assess failure modes and the effect of structural parameters of honeycomb sandwich structure. The semi-finite element model of honeycomb sandwich structure under four-point bending load is established by a parametric method. Laminate delamination is exhibited by a contact algorithm with the mixed-mode damage model. Experiments are conducted to obtain load-displacement curves of honeycomb sandwich structure and thereby verify the applicability of finite element model. The failure modes of honeycomb sandwich structure have also been identified by comparing the experimental results with the numerical results. The effects of structural parameters on the mechanical properties of honeycomb sandwich structure are discussed. Results demonstrate that the overall stiffness of honeycomb structure is closely related to the honeycomb cell size such as length, height and foil thickness. In addition, the strength of honeycomb sandwich structure is sensitive to stacking sequence of composite laminate with different fiber orientation. The main failure modes of honeycomb sandwich structure are laminate fracture, delamination, core buckling and wrinkling. The achievements in this study have guiding significance to design high-performance sandwich structure.

Strengthening the Structural Behavior of Web Openings in RC Deep Beam Using CFRP.

Deep beams are more susceptible to shear failure, and therefore reparation is a crucial for structural reinforcements. Shear failure is structural concrete failure in nature. It generally occurs without warning; however, it is acceptable for the beam to fail in bending but not in shear. The experimental study presented the structural behavior of the deep beams of reinforced concrete (RC) that reinforces the web openings with externally connected carbon fiber reinforced polymer (CFRP) composite in the shear zone. The structural behavior includes a failure mode, and cracking pattern, load deflection responses, stress concentration and the reinforcement factor were investigated. A total of nine reinforced concrete deep beams with openings strengthened with CFRP and one control beam without an opening have been cast and tested under static four-point bending load till failure. The experimental results showed that the increase the size of the opening causes an increase in the shear strength reduction by up to 30%. Therefore, the larger the openings, the lower the capability of load carriage, in addition to an increase in the number of CFRP layers that could enhance the load carrying capacity. Consequently, utilization of the CFRP layer wrapping technique strengthened the shear behavior of the reinforced concrete deep beams from about 10% to 40%. It was concluded that the most effective number of CFRP layers for the deep beam with opening sizes of 150 mm and 200 mm were two layers and three layers, respectively.

Mechanical Analysis of Notch-Free Pre-Bent Rods for Spinal Deformity Surgery.

Experimental study of spinal rod as per the American Society for Testing Materials (ASTM) F2193 methodology for static and dynamic four-point bending. The hypotheses underlying this study were that the notch-free, curved rod would have a significantly higher ultimate load and fatigue strength compared with conventional notched curved rods. This study aimed to analyze the mechanical properties of notch-free curved rods compared with conventional notched rods. The goal of instrumented spinal fusion in the management of spinal deformities is to realign the spine and maintain the correction and stability in order to obtain arthrodesis. Although rod curvature could play an important role, intraoperative contouring of the straight rod induces notches into the rod, leading to decreased fatigue strength. Commercially produced titanium alloy (ϕ6.0 mm) and cobalt chromium alloy (ϕ5.5 mm) spinal rods were assessed by four-point bending tests in accordance with the ASTM F2193. Static four-point bending tests for the curved spinal rods showed that cobalt chromium alloy rods had significantly higher stiffness compared with titanium alloy rods. Notch-free cobalt chromium alloy rods had a significantly higher ultimate load than the conventional notched cobalt chromium alloy and titanium alloy rods. The dynamic four-point bending test showed that force/displacement at a minimum force at 2,500,000 cycles was larger in the notch-free cobalt chromium alloy rod than in the notched cobalt chromium alloy rod. The notch-free curved cobalt chromium alloy rod is likely to maintain its curvature after spinal deformity surgery with a decreased risk of breakage and could overcome the problems of the conventional notched rod such as breakage and spring-back. N/A.

Investigating the biomechanical function of the plate-type external fixator in the treatment of tibial fractures: a biomechanical study

BackgroundThe design of an external fixator with the optimal biomechanical function and the lowest profile has been highly pursued, as fracture healing is dependent on the stability and durability of fixation, and a low profile is more desired by patients. The plate-type external fixator, a novel prototype of an external tibial fixation device, is a low profile construct. However, its biomechanical properties remain unclear. The objective of this study was to investigate the stiffness and strength of the plate-type external fixator and the unilateral external fixator. We hypothesized that the plate-type external fixator could provide higher stiffness while retaining sufficient strength.MethodsFifty-four cadaver tibias underwent a standardized midshaft osteotomy to create a fracture gap model to simulate a comminuted diaphyseal fracture. All specimens were randomly divided into three groups of eighteen specimens each and stabilized with either a unilateral external fixator or two configurations of the plate-type external fixator. Six specimens of each configuration were tested to determine fixation stiffness in axial compression, four-point bending, and torsion, respectively. Afterwards, dynamic loading until failure was performed in each loading mode to determine the construct strength and failure mode.ResultsThe plate-type external fixator provided higher stiffness and strength than the traditional unilateral external fixator. The highest biomechanics were observed for the classical plate-type external fixator, closely followed by the extended plate-type external fixator.ConclusionsThe plate-type external fixator is stiffer and stronger than the traditional unilateral external fixator under axial compression, four-point bending and torsion loading conditions.

Finite element modeling of creep behavior of FRP-externally strengthened reinforced concrete beams

In this study, a nonlinear numerical analysis is carried out to predict the creep response of reinforced concrete (RC) beams externally strengthened using carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) laminates. The beams are tested under static four-point bending; the level of sustained service load is equal to 59% of the ultimate capacities of the un-strengthened beams. The Burger rheological model is used to evaluate the flexural creep response (compressive and tensile creep) and then to validate the findings with experimental results. It is shown that the Burger model effectively predicts the creep of CFRP-bonded RC. Furthermore, parametric studies are performed to investigate the effects of: three fiber orientations of CFRP composites (0°, 45° and 90°), the CFRP thickness, and the type of FRP (CFRP and GFRP) on the flexural creep of FRP-externally retrofitted RC beams based on the Burger rheological model. According to the numerical results, a major reduction in creep strain is obtained with the 45° orientation of CFRP. An increase in CFRP-thickness significantly lowers the creep strain. Moreover, the CFRP laminates prove to be more effective than GFRP in improving the creep response.

Experimental and Theoretical Investigation of Static and Dynamic Bending Properties of Intramedullary Nails

Kemik iliği içerisine yerleştirilerek uzun kemiklerin tedavisinde kullanılan intramedüller çivilerden en büyük beklenti kemik iyileşmesi süresince hasara uğramamaları ve yeterli yük dağılımına olanak sağlamalarıdır. Ticari olarak farklı pek çok türde intramedüller çivi olmakla birlikte bu çiviler içerisinde en çok kullanılan türlerden biri silindirik kesitli içi boş olan türleridir. Ayrıca, intramedüller çivilerin en kötü koşullarda çalışmasını referans alan birçok uluslararası biyomekanik test standardında statik ve dinamik eğilme yükleri dikkate alınmaktadır. Ancak, içi boş şekilde üretilen intramedüller çivilerin, kesit kalınlığının değişimi sebebi ile bu yükler altında özelliklerinin ne yönde değişeceği bilinmemektedir. Bu sebeple, bu çalışmada, intramedüller çivilerde kesit etkisinin intramedüller çivilerinin statik ve yorulma dayanımları üzerindeki etkileri incelenmiştir. Bu amaçla, Grade 23 Ti6Al4V ELI malzemeden imal edilen 6.2, 6.7 ve 7.2 mm kesit kalınlığına sahip içi boş geometrideki intramedüller çiviler statik dört noktadan eğme ve yorulma testlerine tabii tutulmuşlar. Testler sonrasında, intramedüller çivilerde kesit kalınlığı arttıkça hem statik hem de yorulma dayanımlarının arttığı belirlenmiştir. Bununla birlikte, statik dört noktadan eğilme deneyleri sonucunda elde edilen sonuçlar ile teorik olarak hesaplanan değerler kullanılarak; intramedüller çivilerin tasarımı aşamasında kullanılabilecek matematiksel bir model oluşturulabileceği belirlenmiştir. Ayrıca, intramedüller çivilerde kesit kalınlığı arttıkça yorulma dayanımının da arttığı ancak artan kesit kalınlığındaki artış oranı ile yorulma dayanımındaki artışın doğru orantılı olmadığı gözlemlenmiştir.