External Bars Research Articles

Deformation and cyclic behavior of partially-restrained energy dissipaters with yielding end connections

Partially-restrained Energy Dissipater (PED) is a metal hysteresis dissipative device and exhibits an excellent low-cycle fatigue performance. Each PED typically consists of an inner core and an outer restraining member. The inner core is manufactured from a steel rod, forming a milled portion (the fuse) to dissipate energy and two intact external portions (external bars) to connect with structural members. External bars were expected to remain elastic in prior studies and the cyclic responses of PEDs with yielding external bars were hardly discussed. In this paper, a total of eight PEDs were designed and tested to comprehensively investigate the hysteresis responses of PEDs with yielding external bars. The three variable parameters of the test were loading patterns, the unrestrained length of the external bar lur and the cross-sectional area ratio ρ of the fuse to the external bar. The test results illustrated that most of PEDs exhibited stable cyclic performances after external bars yielding and two failure modes were observed, including fuse fracture and end bending. Besides, a larger area ratio ρ significantly improved the low-cycle fatigue life and energy dissipation capacity of PEDs, meanwhile it increased the demand on the flexural stiffness of the external bar to avoid end bending. Finally, an analytical model was established for the deformation of the external bar and a design criteria was presented to avoid the end bending failure of PEDs with yielding end connections

Joint strengthening by external bars on RC beam-column joints

Column strengthening is a very common practice for improving the seismic performance of reinforced concrete frame structures or repairing damage after a seismic event. Several methods are employed for column strengthening, which can improve column strength by preventing its shear, bending or compression failure. However, not all methods allow column strengthening connections between adjacent floors, thus the beam-column joint strength could be limited by the column-joint interface capacity. This work aimed to analyse two joint strengthening designs, for which an experimental campaign of eight full-scale beam-column joints strengthened with steel caging, and subjected to cyclic and gravity loads, was carried out. As access to joint panels is very complex in existing structures, joint strengthening consists of external solutions: vertical or diagonal bars and capitals connecting columns. The results showed that these techniques significantly increased beam-column joint strength and highlighted that failure can be undesirably transferred to the joint. Vertical bars prevented the bending failure of the column-joint interface, but failure occurred at the joint in this study. Diagonal bars can also prevent joint failure.

Numerical analysis of the hydrodynamics induced by rotating ring electrode using κ-ε models

The dynamic rotating rings electrode (RRE) has proven to be an efficient configuration for removing contaminants. The flow induced by the complex geometry of the RRE was analyzed by computational fluid dynamics (CFD) and the multiple reference frame approach (MRF), rotational speed in the range of 75–500 rpm. Assessment of the three κ-ε type models (standard, renormalization group theory (RNG) and realizable) to solve the turbulent flow was performed. The results show that the realizable model provides a more adequate physical description of the flow than the other models. The global flow was analyzed using integral parameters such as the average flow, circulation time, pumping number, and power number. The local flow was examined qualitatively through velocity profiles and streamlines. The effect of simulating two different positions (0° and 45°) of the RRE moving walls concerning the baffles when using the MRF approach was evaluated. The flow pattern is predominantly radial because the electrode external bars propel the fluid to the lateral tank wall. Besides, the external bars promote regions of high deformation in the fluid that produce vortices. It was found that the result at 0° is in good agreement with the experimental results of mixing time.

Punching shear strengthening of flat slabs with CFRP on grooves (EBROG) and external rebars sticking in grooves

The main objective of this study is strengthening of flat slabs in punching shear with a new model. For this purpose 15 numerical samples include a control and 14 strengthened defined and nonlinearly analyzed up to failure. The strengthening method is new method of grooving in two orthogonal direction (x and y axes of slab plan) and then mounting the external bars (sticking) in one direction and FRP in EBROG (externally bonded reinforcement on groove) method in another direction. The results showed the great efficiency of the method so that the punching shear capacity of strengthened samples increased between 28 and 62% compare to control one. Also the mode of failure changed in strengthened specimens from shear to flexure–shear and the punching critical area was broader and developed from the loading point. In the grooving method the sticking bars yielded in all specimens and the FRP tensile strain was closer to rupture strain compared to EBR.

STRESS-STRAIN STATE OF REINFORCED CONCRETE BEAMS STRENGTHENED WITH A NEW EXTERNAL STEEL STRUCTURE

The study presents a new structure for strengthening of one-span reinforced concrete beams in rectangular cross-section using external steel bars. The specific feature of the proposed strengthening is the unloading of the compressed upper zone of a beam with simultaneous compression of its lower stretched zone. The article considers some variants of making the strengthening structure with rigid and flexible reinforcement elements for faster tension of external bars, and the variant including only flexible elements. It provides a design scheme and method for such reinforced beams. The study provides experimental research data on the series of beams with different parameters of the strengthening structure in the form of «bending moment – deflection» and «bending moment - deformation of concrete» dependencies.

RC beams retrofitted using external bars with additional anchorages-a finite element study

Study on flexural retrofitting of RC beams using external bars with additional intermediate anchorages at soffit is reported in this paper. Effects of varying number of anchorages in the external bars at soffit were studied by finite element analysis using ANSYS 12.0 software. The results were also compared with available experimental results for beam with only two end anchorages. Two sets of reference and retrofitted beam specimens with two, three, four and five anchorages were analysed and the results are reported. FE modeling and non-linear analysis was carried out by discrete reinforcement modeling using Solid65, Solid45 and Link8 elements. Combin39 spring elements were used for modeling the frictional contact between the soffit and the external bars. The beam specimens were subjected to four-point bending and incremental loading was applied till failure. The entire process of modeling, application of incremental loading and generation of output in text and graphical format were carried out using ANSYS Parametric Design Language.

Finite Element Analysis of Bearing Capacity of RC Beams Retrofitted with External Bars

For enhancing the flexural strength of existing reinforced concrete beams provision of external bars at the soffit of the beam is identified as one of the cost effective and easy to execute method. This paper discusses the finite element modeling and nonlinear analysis of reinforced concrete beams with additional external reinforcing bars at the soffit level using ANSYS 12.0 software. Finite element modeling of reinforced concrete beams is carried out using discrete reinforcement modeling and the results are compared with experimental results of twenty numbers of beam specimens under four-point bending. SOLID65, SOLID45, and LINK8 elements were used finite element modeling of the beam. COMBIN39 spring elements were used for simulating the frictional contact between the soffit and the external bars. Wide range graphical display of the results such as deflected shape of the beam, strain variation along the length and depth of the beam and crack propagation at various loading stages were generated by creating a batch file using ANSYS parametric design language.

Experimental investigation on the performance of RC beams strengthened with external bars at soffit

This paper presents the findings of the comprehensive experimental investigation on the use of non-prestressed external reinforcing bars at soffit of the RC beams for enhancing the flexural strength. Based on the encouraging results of the preliminary experimental study conducted by the authors, a comprehensive experimental investigation was carried out by testing 20 numbers of RC beams with varying internal and external bar ratio in order to further explore the viability of this technique. External reinforcing bars technique has already been used by keeping the reinforcement at the sides of the beam using deflectors, mechanical anchoring devices and with strengthening end anchorage zones. The reported technique uses external reinforcing bars at the soffit, which eliminates the need of deflectors, and the anchoring was done by adopting a very simple technique, which eliminates the use of mechanical anchoring devices. The proposed technique is found to be cost effective, easy to execute, enhances moment carrying capacity and effective in deflection and crack control.

Study on Shear Behaviour of Concrete Beams Prestressed with External CFRP Tendons

Based on independent research and development of a CFRP tendons wedge-type anchorage, the shear tests of six CFRP external prestressing concrete beams were done. Among them, CFRP external tendons of three pieces were installed in straight line while other pieces were installed in curved line. The results of experimental research show that shear behaviour of concrete beams prestressed with CFRP external tendons are the similar process to the traditional prestressed reinforced concrete beams. They go through the elastic stage, the stage of crack extension, the yield stage of internal hoop reinforcements at the intersection of inclined cracks and the failure stage. When external CFRP tendons are arranged in the same situation, the cracking load and the shear capacity of concrete beams prestressed with CFRP external tendons reduce gradually along with the increase of shear-span ratio,.When shear-span ratio is equal, the cracking load and the shear capacity of concrete beams prestressed with curved arrangement of CFRP external tendons are larger than those of concrete beams prestressed with straight arrangement of CFRP external tendons. Compared with traditional concrete beams prestressed with external steel bars, due to elasticity modulus and shear modulus of CFRP tendons are both smaller than those of steel bars, the mid-span deflection of concrete beams prestressed with CFRP external tendons at the time of shear failure is bigger than that of traditional concrete beams prestressed with external steel bars under the same circumstance.

New records of two trypetesid burrowing barnacles (Crustacea: Cirripedia: Acrothoracica: Trypetesidae) and their predation on host hermit crab eggs

Acrothoracican barnacles of the genusTrypetesaare obligate symbionts of hermit crabs that burrow into the gastropod shells occupied by their hosts. In the present study, hermit crabs were examined for the presence of trypetesids, based on collections from the United States, Jamaica, and the Philippines made between 1997 and 2008. Shells from Jamaica and New York containedTrypetesa lateralis, a trypetesid previously documented from central California.Trypetesa lateralisis redescribed based on light and scanning electron microscopy, showing the presence of an external mantle flap and asymmetrical opercular bars diagnostic for this species. The mean prevalence of trypetesids in Jamaica was 8.3% and most barnacles were associated withCalcinus tibicen; in New York the barnacles were found in 1.6% of shells occupied byPagurus longicarpus. Specimens from the Philippines were identified asTrypetesa spinulosa(formerly known only from Madagascar) based on the presence of their diagnostic orificial palps. The mean prevalence ofT. spinulosain the Philippines was 3.7% and most barnacles were associated withCalcinusspp. Hermit crab eggs were observed in the guts ofT. lateralisfrom Jamaica andT. spinulosafrom the Philippines. In both of these regions the trypetesids were found significantly more often in shells occupied by female hermit crab hosts (80–87% with females). These findings suggest the barnacles be classified as transient parasites. The biology of trypetesids is reviewed and a key to the family is provided. Further studies are needed to determine if egg predation occurs in all trypetesids and the impacts on hosts.

Behavior of Strengthened Composite Castellated Beams Pre-stressed with External Bars: Experimental Study

The behavior of composite castellated beams strengthened using different configurations and subjected to external pre-stressing is studied experimentally. A total of ten specimens divided into three groups were considered. The first group consisting of four specimens represented the reference castellated beams without any strengthening configuration subjected to different pre-stressing ratios where one specimen has been taken as a control specimen without any pre-stressing. The second group consisting of three specimens represented the same configuration of the castellation, but additional vertical stiffeners were used at all web-posts and subjected to different pre-stressing values. The third group consisted of three specimens of partially encased composite castellated beams with the same castellation. Three pre-stressing ratios were used, namely 0, 25 and 50 %, respectively, of the yield strain of the external steel bars. The connection between the concrete slab and the castellated beam was considered as perfect connection where the slip between both of them was prevented using properly designed shear connectors. The ultimate strength, vertical mid-span deflection, strain on both concrete and steel and the strain on pre-stressed bars were recorded and analyzed. The experimental data showed the unfavorable influence of the external pre-stressing on the global behavior of composite castellated beams unless greater attention is paid to the end zone of the beam. On the other hand, partial encasing of the web of the steel section showed significant increase in the ultimate capacity and decrement of the vertical deflection of the beam. Furthermore, the pre-stressing effect manifests its affirmative effect for concrete section in comparison to the steel one.

Nonlinear Analysis on Flexural Behavior of Externally Prestressed Composite Beam

Steps loading method was used to caculate the whole bending process of a composite beam loaded verticaly in order to accurately analyze the bending performance of composite beams. It has taken into account a variety nonlinear constitutive relations of different materials and based on the layered-step sections transformed method. The displacement of external prestressed steel bars were expressed with rotation angles at anchor points using finite bar elements method. This method is proved reasonable and reliable by comparative analysis of the calculating and the experimental results. It is feasible to analyze the forces and deformations of composite beams which were effcted by nonlinear material factors with layered-step sections transformed method.

Flexible Fixation and Fracture Healing: Do Locked Plating ‘Internal Fixators’ Resemble External Fixators?

External and internal fixators use bone screws that are locked to a plate or bar to prevent periosteal compression and associated impairment of blood supply. Both osteosynthesis techniques rely on secondary bone healing with callus formation with the exception of compression plating of simple, noncomminuted fractures. External fixation uses external bars for stabilization, whereas internal fixation is realized by subcutaneous placement of locking plates. Both of these "biologic" osteosynthesis methods allow a minimally invasive approach and do not compromise fracture hematoma and periosteal blood supply. Despite these similarities, differences between the two fixation methods prevail. Locked plating "internal fixators" allow a combination of biomechanical principles such as buttressing and dynamic compression. Periarticular locking plates are anatomically contoured to facilitate fixation of articular fractures. They allow for subchondral stabilization using small-diameter angular stable screws as well as buttressing of the joint and the metaphyseal component of a fracture. Biomechanically, they can be far stiffer than external fixators, because subcutaneous plates are located much closer to the bone surface than external fixator bars. External fixators have the advantage of being less expensive, highly flexible, and technically less demanding. They remain an integral part of orthopaedic surgery for emergent stabilization, for pediatric fractures, for definitive osteosynthesis in certain indications such as distal radius fractures, and for callus distraction.

Flexural retrofitting of RC beams using external bars at soffit level – An experimental study

Throughout the globe, huge stock of buildings become vulnerable to damage due to aging, rebar corrosion, and natural hazards, particularly earthquake. Section enlargement, bonded steel plating, external post-tensioning and FRP composites wrapping are some of the techniques being widely followed to retrofit various structural elements. Each technique has at least one or more number of limitations. High cost, difficulty in execution, reduction in headroom, loss of aesthetic value, increase in self-weight, careful surface preparation, de-bonding failure are some of the innate limitations of these techniques. A maiden attempt has been made by the authors to devise a new technique to retrofit RC beams with external reinforcement. The proposed method overcomes most of the drawbacks of the above said existing methods. Some work has already been reported on external reinforcement by keeping the reinforcement at the sides of the beam using deflectors, mechanical anchoring devices and strengthening end anchorage zones. The reported technique in the present work overcomes all the drawbacks of the above method. The authors propose the external bars to be kept at the soffit level of the beam section, thus eliminating the use of deflectors, mechanical anchoring devices and making it amenable, simple and effective. Additional advantages of the present technique are the enhanced moment carrying capacity, reduced deflection and crack width and improved ductility.

An experimental study on the flexural behaviour of RC beams strengthened with high-strength bars

External unbonded strengthening offers advantages in speed and simplicity of installation over other strengthening techniques. Unlike externally bonded steel plate or carbon fibre sheet, surface preparation of the concrete for installation of a high-tension bar is not required and installation is not affected by environmental conditions. An anchoring pin or anchoring plate is installed at the end of the beam to connect the high-tension bar to the concrete beam. The deviators are used so that supplementary external bars follow the curvature of the tested beam. The main test parameters are the section area of strengthening bar, the depth of deviator and the number of deviators. The current paper provides a general description of the structural behaviour of beams strengthened using the technique. The test results of a strengthened beam are compared with those from a reference specimen. It is shown that the reinforcing technique can provide greater strength enhancements to an unstrengthened beam and that the provision of deviator enhances efficiency. The ultimate moment of the specimen with two deviators was higher than that of specimens with one deviator.

고장력 인장봉으로 보강된 RC보의 휨거동에 관한 실험적 연구(2)

The external unbonded strengthening offers advantages in speed and simplicity of installation over other strengthening techniques. Unlike externally bonded steel plate or carbon fiber sheet, surface preparation of the concrete for installation of high-tension bar is not required and installation is not affected by environmental conditions. Anchoring pin or anchoring plate are installed at the end of beam to connect the high-tension bar to concrete beam. The deviator are used in order that supplementary external bars would follow the curvature of the tested beam. A set often laboratory tests on reinforced concrete beam strengthened using the technique are reported. The main test parameters are the section area of strengthening bar, the depth of deviator and the number of deviators. The paper provides a general description of structural behavior of beams strengthened using the technique. The test result of strengthened beam are compared with those from a reference specimen. It is shown that the reinforcing technique can provide greater strength enhancements to unstrengthened beam and that the provision of deviator enhances efficiency. The ultimate moment of specimen with two deviators was higher than that of specimens with one deviator. It is also shown that the external bars enhance strength of beams in shear.

The assessment of bar chewing as an escape behaviour in laboratory mice

AbstractThe ability to measure objectively how an animal perceives its home environment is essential for improving the housing and husbandry conditions of laboratory animals. Chewing at cage bars by a rodent may reflect the animal's desire to escape from its home cage and thus provide a measure of the relative aversiveness or inadequacy of different housing conditions from the animal's viewpoint. To assess whether bar chewing by laboratory mice is an escape behaviour, adult male and female ICR-(CD-1) mice were housed individually or in same-sex groups of three in modified shoebox-type cages. Cages had two sets of external bars in the side walls, an equivalent set of bars fixed internally and a Perspex lid. One set of external bars opened daily, allowing the mice to escape into a larger arena. All mice showed a strong preference for chewing at external bars over those that were internal to each cage. After one week of experience, mice also preferred the external bars that opened daily to those that did not open. Behaviour directed towards the cage lid declined over time as the mice experienced the new escape route in the cage side. Interest in the external bars correlated positively with time since last escape. Results confirm that bar chewing reflects an attempt to escape the cage and explore the surrounding area and may provide a suitable behavioural measure of perception of the cage environment for use in welfare assessment.

Strengthening reinforced concrete beams with external unbonded bars: experimental investigation

In an earlier study the authors outlined a strengthening technique for reinforced concrete beams using external unbonded reinforcement. It was shown that the technique could provide useful enhancements in load capacity in all but heavily reinforced cross-sections. The technique offers advantages in speed and simplicity of installation over other, established, strengthening techniques. The earlier work used deflectors in order that supplementary external bars would follow the curvature of the original beam. If these deflectors could be dispensed with, further simplifications could be made in installation procedures. A more extensive programme of physical testing and associated modelling of behaviour has now been performed in order to further explore the capabilities of the technique and to determine the circumstances under which deflectors should be installed. The paper provides a general description of structural behaviour of beams strengthened using the technique. Results of 27 physical tests on strengthened reinforced concrete beams are reported and compared with those from a further eight reference specimens. It is shown that the technique can provide greater strength enhancements to lightly reinforced sections and that provision of deflectors enhances efficiency. The danger of sudden collapse is found to be no greater than that for equivalent conventionally reinforced beams. The various parameters which affect strength enhancements attainable with the technique are reviewed.

Strengthening reinforced concrete beams with external unbonded bars: theoretical investigation

The paper describes the development of a numerical model for analysis of beams retrofitted with external unbonded reinforcement. The experimental phase of the investigation is described in a companion paper, which also outlines the advantages of the method. Because external reinforcement is not bonded to the beam throughout its span, but is anchored only at the ends, normal plane section behaviour assumptions cannot be used. The numerical model is based on section analysis, and incorporates non-linear material behaviour and non-linear geometric effects. The model is first validated against results from an experimental programme comprising 35 physical tests on laboratory specimens. The model is then used to supplement the experimental study by exploring parameters which could not receive adequate experimental coverage. The influence of the shape of the bending moment diagram and of span/depth ratio, parameters which were not adequately explored in the experimental investigation, are reported. Deflectors we...

Strengthening reinforced concrete beams with external unbonded bars: experimental investigation

In an earlier study the authors outlined a strengthening technique for reinforced concrete beams using external unbonded reinforcement. It was shown that the technique could provide useful enhancements in load capacity in all but heavily reinforced cross-sections. The technique offers advantages in speed and simplicity of installation over other, established, strengthening techniques. The earlier work used deflectors in order that supplementary external bars would follow the curvature of the original beam. If these deflectors could be dispensed with, further simplifications could be made in installation procedures. A more extensive programme of physical testing and associated modelling of behaviour has now been performed in order to further explore the capabilities of the technique and to determine the circumstances under which deflectors should be installed. The paper provides a general description of structural behaviour of beams strengthened using the technique. Results of 27 physical tests on strengthened reinforced concrete beams are reported and compared with those from a further eight reference specimens. It is shown that the technique can provide greater strength enhancements to lightly reinforced sections and that provision of deflectors enhances efficiency. The danger of sudden collapse is found to be no greater than that for equivalent conventionally reinforced beams. The various parameters which affect strength enhancements attainable with the technique are reviewed.