Hollow Bar Research Articles

A passive metallic damper with replaceable steel bar components for earthquake protection of structures

In this paper, a new passive earthquake damper termed as Bar-Fuse Damper (BFD) is presented for frame structures. The BFD is developed from common steel sections such as hot-rolled Square Hollow Sections (SHS), C-channels, plates and bars. It is economical, easy to install and build with no special fabrication technique. The key feature of the BFD is using round steel bars as energy absorber components that can be easily replaced in case of failure. The proposed device dissipates the energy with the replaceable bars as sacrificial elements through the flexural and tensile mechanism. The performance of several full-scale BFDs was evaluated with a series of monotonic and cyclic experiments, and the bars successfully performed their function as energy absorbers and fuses in all specimens. The effects of variations in the number, length and diameter of bars in the BFD along with the nuts arrangement were investigated in this experimental study. This study indicates that the recommended device has stable hysteretic behaviour under cyclic loads with two significant features: appropriate energy dissipation and replaceability of the fuses, which can be useful to protect the main elements of structures from plastic deformation and failure for several events. The results obtained for the BFD are promising for its use as a passive seismic damper in engineering structures in order to improve the seismic behaviour of structures as well as dissipating the earthquake energy.

Springback analysis of hollow rectangular bar of linear work-hardening material

A theoretical analysis of the springback of hollow rectangular cross-sectional bars of linear work-hardening materials under torsional loading has been carried out. By using the deformation theory of plasticity, a numerical scheme has been prepared which determines the elasto-plastic boundary in addition to springback in the bars. Finally, an analytical generalised expression relating the angle of twist and twisting moment and residual angle of twist per unit length for bars under plastic torsion is obtained.

Influence of the end cap deformation of a hollow transmission bar on the hollow split Hopkinson pressure bar test results

The deformation of an end cap was found when analyzing a hollow transmission bar with an end cap. The deformation may cause errors in hollow split Hopkinson pressure bar (SHPB) test results. Therefore, the influence of the end cap deformation on hollow SHPB test results was analyzed to guide researchers to avoid these mistakes. It is known that the hollow split Hopkinson pressure bar technique using a hollow transmission bar with an end cap is a material dynamic property testing technology, which is used to increase the amplitude of the transmitted signal by reducing the transmission bar cross-sectional area. The relation between the end cap deformation and the test results was derived. And the natural frequency of an end cap was also calculated to compare with the frequency of the interferences in test results. Several simulations and hollow SHPB experiments using hollow transmission bars with end caps in different thickness were undertaken to analyze the influence of the end cap deformation on Hopkinson bar test results. A high-frequency interference was found in a transmitted wave when the end cap was vibrating which also conform the analyzed relation between them. High-frequency interferences were also found in the experiments. The frequency of the interference in a transmitted wave (in both simulations and experiments) was similar to the natural frequency of the end cap. The vibration and the interference became weak and the interference frequency became high when the thickness of an end cap increased. When the thickness of an end cap was larger than half external diameter of the hollow transmission bar, both the vibration and the interference disappeared, however the transmitted wave introduced another kind of distortion.

Propagation behavior of the stress wave in a hollow Hopkinson transmission bar

In order to investigate the stress wave propagation behavior through a hollow elastic bar that is used in a Hopkinson-bar-loaded fracture testing system, three-point bending fracture experiments were performed in such a system. The effects of sample span and diameter and wall thickness of the hollow elastic bar on the stress wave propagation behavior were studied numerically using the software of ANSYS/LS-DYNA. The experimental results demonstrated that the incident, reflected, and transmitted pulses calculated by the finite element method are coincident with those obtained from the Hopkinson-bar-loaded fracture tests. Compared to the solid transmission bar, the amplitude of the transmitted pulse is relatively larger in the hollow transmission bar under the same loading conditions and decreases with increasing wall thickness. On the other hand, when the inside diameter is fixed, the effect of the wall thickness on the stress wave characteristics is more obvious.

Signal Gain Mechanism for a Hollow Transmission Pressure bar with an end cap

Errors in a split Hopkinson pressure bar test with a hollow transmission bar were found by analyzing the transmitted strain signal gain mechanism. To generate these errors, a hollow transmission bar with an end cap was employed and the value of the gained transmitted strain wave and specimen strain were derived. The hollow Hopkinson pressure bar technique is a material dynamic properties testing technology used to increase the amplitude of the transmitted signal by reducing the transmission bar cross-sectional area. However, since both the process of stress wave propagation and the transmitted strain signal gain mechanism in a hollow transmission bar are unclear, hollow transmission bars were used to compensate such discrepancies. In this paper, stress wave theory was used to analyze these phenomena. It was found that the transmitted wave at the variable cross section occurs many times in a hollow transmission bar and also the time lags of the transmitted waves distort the gained transmitted wave. The values of specimen strain and the transmitted wave were analyzed when a hollow transmission bar was employed. To verify the theoretical analysis, two groups of simulations of the transmitted signal gain processes with LS-DYNA have been undertaken, the results of which are in excellent agreement with the analysis results.

Magnetical hollow fiber bar collection of extract in homogenous ionic liquid microextraction of triazine herbicides in water samples.

The homogeneous ionic liquid microextraction combined with magnetical hollow fiber bar collection was developed for extracting triazine herbicides from water samples. These analytes were separated and determined by high performance liquid chromatography. The triazines were quickly extracted into ionic liquid microdroplets dispersed in solution, and then these microdroplets were completely collected with magnetical hollow fiber bars; the pores of which were impregnated with hydrophobic ionic liquid, which makes the phase separation simplified with no need of centrifugation. Some experimental parameters, such as the type of ionic liquid, ultrasonic immersion time of hollow fiber, pH of sample solution, volume of hydrophilic ionic liquid, amount of ion-pairing agent NH4PF6, NaCl concentration, number of magnetical hollow fiber bar, stirring rate, and collection time were investigated and optimized. When the present method was applied to the analysis of real water samples, the precision and recoveries of six triazine herbicides vary from 0.1 to 9.2% and 73.4 to 118.5%, respectively. The detection limits for terbumeton, ametryn, prometryn, terbutryn, trietazine, and dimethametryn were 0.48, 0.15, 0.15, 0.14, 0.35, and 0.16μgL-1, respectively.

Hollow fiber stir bar sorptive extraction for determination of phthalic acid esters in environmental and biological matrices

The purpose of this paper is to introduce a novel hollow fiber stir bar sorptive extraction for collecting and determining of phthalic acid esters in environmental and biological matrices. Shell-core ZrO2 /SiO2 composite microspheres and porous C18 silica microspheres were compared as the sorbents, which were loaded in the lumen of a microporous hollow fiber membrane. A thin stainless-steel wire was also inside of the hollow fiber membrane acting as the magnetic stirrer, thus affording the procedures like stir bar sorptive extraction to perform the active trapping of the analytes. Variables affecting the extraction (salt addition and pH of samples, extraction temperature, and time) and desorption (microwave time and eluted solvents) have been optimized. Under the optimal conditions, good linearity (r > 0.9968) of all calibration curves was obtained in validation experiments. And the limits of quantification ranged from 0.01 to 1000 ng/mL. The recoveries in different matrices were in the range of 64.90-112.60% with relative standard deviations less than 8.60%. The present work demonstrated the applicability of the developed method for the determination of phthalic acid esters in environmental and biological sample, allowing the selective extraction of phthalate esters in complex samples with low consumption of organic solvents and no sample clean-up.

Construction and testing of self-drilled soil nails

Current standards and best practice guidance recognise that testing of self-drilled hollow bar soil nails can be problematic as conventional packers and debonded lengths cannot be constructed. As a result, this causes difficulty in testing and confirming the ultimate bond resistance within the passive zone of a soil-nailed slope, and thus the design soil nail lengths. This paper provides a summary and review of the various testing procedures adopted for a soil nail construction project in Scotland. The practical design considerations, and their validation through the installation and testing of 49 sacrificial test nails, are detailed. The construction issues associated with the nail installation and testing are also outlined and discussed in light of the results obtained using different testing approaches. The aim of this case study is to report on the experiences with installation and testing of hollow bar soil nails. The objectives are to develop an initial data base of available soil–grout bond strength of hollow bar soil nails based on the several practical installation procedures used in this project and to establish areas for improvement of installation, testing and quality control in order to perform comparable pullout tests on self-drilled hollow bar soil nails.

Durability Assessment of Glass FRP Solid and Hollow Bars (Rock Bolts) for Application in Ground Control of Jurong Rock Caverns in Singapore

AbstractThis study was conducted to investigate the durability of two types of vinyl-ester/glass fiber-reinforced polymer (GFRP) rock bolts [solid and hollow (tubular) GFRP bars] that were subseque...

Hollow fiber–stir bar sorptive extraction and microwave assisted derivatization of amino acids in biological matrices

A kind of solid phase microextraction configuration combining the principles of hollow fiber solid phase microextraction (HF–SPME) and stir bar sorptive extraction (SBSE) is presented. The main feature of HF–SBSE is the use of microporous hollow fiber acting as the carrier and filter, while a thin stainless steel wire and silica microspheres in the lumen of hollow fiber respectively acting as the magnetic stirrer and the dispersed sorbents for the collection and extraction of the target analytes, thus affording extraction process like SBSE. Moreover, the prepared hollow fiber stir bar was applied to direct microextraction and microwave assisted derivatization with N,O–Bis(trimethylsilyl)trifluroacetamide (BSTFA) of four amino acids in rats’ urine and cerebrospinal fluid followed by gas chromatography mass spectrometric analysis. The limits of detection for four amino acids were found to be in the range of 0.0003–0.017μgmL−1, and all the analytes did not exhibit any lack of fit. The extraction recoveries using HF–SBSE techniques ranged from 71.8% to 102.3%. The results indicated that hollow fiber stir bar sorptive extraction was a promising technique for the enrichment and direct derivatization of analytes extracted from biological matrices without sample clean–up.

Optimal design of an extrusion process for a hinge bracket

This study considers process design in forming a hinge bracket. A thin hinge bracket is typically produced by bending a sheet panel or welding a hollow bar into a sheet panel. However, the hinge bracket made by bending or welding does not have sufficient durability in severe operating conditions because of the stress concentration in the bended region or the low corrosion resistance of the welded region. Therefore, this study uses forming to produce the hinge bracket part of a foldable container and to ensure durability in difficult operating conditions. An extrusion process for a T-shaped hinge bracket is studied using finite element analysis. Preliminary analysis shows that a very high forging load is required to form the bracket by forging. Therefore, extrusion is considered as a candidate process. Producing the part through the extrusion process enables many brackets to be made in a single extrusion and through successive cutting of the extruded part, thereby reducing the manufacturing cost. The design focuses on reducing the extrusion load and on ensuring shape accuracy. An initial billet is designed to reduce the extrusion load and to obtain a geometrically accurate part. The extruded part is bent frequently because of uneven material flow. Thus, extrusion die geometries are designed to obtain straight parts.

Discussion of “Performance of Hollow Bar Micropiles under Monotonic and Cyclic Lateral Loads” by Ahmed Yehia Abd Elaziz and M. Hesham El Naggar

Discussion of “Performance of Hollow Bar Micropiles under Monotonic and Cyclic Lateral Loads” by Ahmed Yehia Abd Elaziz and M. Hesham El Naggar

Experimental Characterization and Modified Constitutive Modeling of the Strain Rate Dependent Compressive Behavior of Adhesives

Predicting the impact performance of adhesively bonded structures requires the accurate characterization and constitutive formulation of the compressive behavior of the adhesive at dynamic strain rates. In this work, the stress–strain curves of Sikaflex adhesives are measured in uniaxial compression tests at quasi‐static and dynamic strain rates. The split‐Hopkinson pressure bar technique is modified with the hollow output bar to effectively characterize the dynamic response of the adhesive. It is found that the Sikaflex adhesive is incompressible and hyperelastic; the compressive behavior is significantly influenced by the strain rate. The strain rate sensitivity is not constant but varies as a function of the strain and the strain rate. The strain rate effect on compressive behavior is quantified and incorporated into the phenomenological hyperelastic constitutive model based on strain energy density. The modified constitutive equation accurately represents the strain rate dependent compressive behavior of Sikaflex adhesives. image

Design and Fabrication of a Ball Projecting Machine

To make a ball projecting machine which pitches various kinds of balls either soft, leather, baseball or tennis ball at desired line and length as required. It can throw the ball at predetermined speed with required spin/swing effect. Problem with the existing machines is that they are very expensive and because of very low competition they ask for extremely huge price. The project began from the research phase with the identification of basic components used in the making of bowling machine. A thorough review of the theory and operations involved in a bowling machine were studied. A basic design was plotted and after review final design was made. Fabrication was done which involved operations on lathe, milling, grinding, welding machines etc. First 2 motors were coupled with the wheels, and then it was installed on a cylindrical bar which was installed on a base plate. A drive is used which is connected with the motors. The first worm and worm wheel set is installed on the rotating shaft on top of the base plate. Second similar set is installed at bottom. A power screw is welded at bottom which allows which fits inside a circular disc which carries corresponding threads. Its rotation about those threads would provide vertical lift and fall, also rotation in horizontal plane providing height adjustment and line change respectively. Finally three hollow cylindrical bars are welded at periphery of the circular plate holding power screw to form a tripod stand. The result is an efficient working bowling machine which is relatively much cheap in manufacturing. It could project the ball at various speeds with desired spin/swing effect. It also provides the facility to project various kinds of balls.

Обзор способов получения полой заготовки электрошлаковым переплавом. Часть II

Обзор способов получения полой заготовки электрошлаковым переплавом. Часть II

Caracterización de semielaborados de aleaciones de titanio procesadas por extrusión y laminación perforación (proceso Mannesmann)

RESUMENPara la fabricación de tubos y caños sin costura se utilizan como materias primas, semielaborados huecos provenientes de procesos de deformación en caliente tales como extrusión y laminación perforación (proceso Mannesmann). A partir de los cuales y por medio de sucesivas reducciones de área a través de laminación o de trafilación se alcanzan las medidas finales solicitadas. El proceso de laminación perforación, por efecto Mannesmann, contempla la perforación de tochos cilíndricos, a través de una compresión diametral progresiva, que genera una fractura en el núcleo y facilita la perforación junto a la laminación transversal oblicua. En cambio la extrusión es un proceso por compresión en el cual el metal es forzado a fluir a través de una matriz para darle forma a su sección transversal. El presente trabajo de caracterización se realizó sobre semielaborados provenientes de ambos procesos, laminación perforación y extrusión, en aleaciones de titanio (Titanio Gr. 2 (Titanio Comercialmente Puro) y Titanio Gr. 5 (Ti-6Al-4V)). Se realizaron ensayos destructivos (tracción, aplastado y abocardado), no destructivos (inspección visual, videoscopía, dimensionales, rugosidad superficial y determinación de discontinuidades por tintas penetrantes) y macro y micro metalografías. También se evaluó la contaminación química provocada por la atmósfera del horno. Finalmente se analizaron los defectos característicos provenientes de cada proceso de deformación, su causa raíz y sus posibles soluciones.

Analyzing Stress Wave Propagation in a Hollow Bar Loaded Three-Point Bend Fracture Test Using Numerical Methods

Modified Hopkinson pressure bar apparatus is widely used to investigate the dynamic fracture behavior of materials at higher rate loading. While using a small sample for fracture toughness testing, plane strain conditions are compromised. In the current work, a large diameter two-bar/ three-point bend fracture setup is used to analyze stress wave propagation behavior within a larger cracked specimen. The experimental setup model consists of striker, incident bar, loading pin, cracked three-point specimen, span and transmission bar. The model is prepared using ANSYS software and the transient dynamic analysis technique is used to simulate the dynamic load. The effects of increased transient time on the stress wave propagation behavior within the cracked sample and the stress and strain values at the crack tip of the three-point bend specimen are analyzed. In addition, the effects of the hollow striker, the hollow incident bar and the specimen span are studied. It is found that during large specimen testing, an increase in the transient time results in the lower stress and strain values in the specimen crack-tip. The relationship of the specimen span, the striker and the incident bars with the strain values in the specimen is analyzed and a method for the three-point bend specimen testing at the higher strain rates is also proposed.

Axial monotonic and cyclic compression behaviour of hollow-bar micropiles

Micropiles are used in various applications, including low-capacity micropile networks, underpinning, and seismic retrofitting of existing foundations and high-capacity foundations for new structures. Hollow-bar micropiles have an added advantage, as they provide fast installation with a high degree of ground improvement. The current Federal Highway Administration (FHWA) design guidelines designate hollow-bar micropiles as type B, even though the FHWA construction technique is different than the technique used for typical type B, which results in an overly conservative design. In addition, the current practice for construction of hollow-bar micropiles is limited to a drilling bit / hollow-bar diameter ratio of 2.5 or less. In this paper, full-scale load tests were conducted to evaluate the suitability of FHWA design guidelines to hollow-bar micropiles installed in cohesive soil and to evaluate the performance of hollow-bar micropiles constructed with a drilling bit / hollow-bar diameter ratio of 3. Eight micropiles were constructed using 76 mm (3 in.) hollow bars (76 mm outside diameter and 48 mm inside diameter) with the air–water flushing technique and advanced to a depth of 5.75 m: six micropiles were installed using a 228 mm (9 in.) drill bit and two micropiles were installed using a 178 mm (7 in.) drill bit. All micropiles were instrumented with vibrating wire strain gauges to measure the axial strain at three stations along the micropile shaft. The load tests included four axial monotonic and four cyclic axial loading tests. The results are presented and discussed in terms of load–displacement curves and load transfer mechanism. The load test results showed that the grout–ground bond strength values proposed by the FHWA (in 2005) for type B micropiles grossly underestimate the bond strength for calculating the ultimate capacity. In addition, the toe resistance can be significant for micropiles resting on sand due to the increased toe diameter. No tangent stiffness degradation was observed in the micropile capacity after applying 15 load cycles.

A J2–J3 approach in plastic and damage description of ductile materials

This paper illustrates a methodology to improve the description of the plastic behavior and the fracture prediction for ductile materials under complex loading conditions. To this purpose, a plasticity model and a damage estimation model are proposed. The former, differently from the classic J2 plasticity theory, takes into account the effect of the third deviatoric invariant on the plastic flow. The latter assumes that damage accumulation is governed by both stress triaxiality and deviatoric parameters, and takes advantage of the new plasticity formulation. The two models rely on the same theoretical foundation, where a specific function is invoked to describe the subsequent yield surfaces and the damage accumulation up to fracture. Both have been implemented into a commercial finite element code via user subroutines. Three steel alloys have been tested under very different stress states: tensile tests on smooth and round notched bars, plane strain tests, torsion tests, and combined tension–torsion tests on hollow and solid cylindrical bars have been executed. For the last ones, several tension—torsion-loading ratios have been applied. These kinds of tests allow to explore a wide domain of the governing parameters for both models. The experimental results from tensile and torsion tests are used to calibrate the proposed plasticity model and the damage model; combined tests are used for validation purposes. The experimental–numerical comparison of global quantities made by using a standard plasticity approach confirms the need for a more accurate plastic description in the large strain range. The proposed plasticity model is able to provide a very good match until fracture for all tests available. Moreover, the damage model has the potential to take into account the experimental evidence, predicting the fracture initiation accurately. In particular, its validation by using tension–torsion tests shows to be really significant.

Performance of Hollow Bar Micropiles under Monotonic and Cyclic Lateral Loads

AbstractHollow bar micropiles are becoming a popular option for foundation retrofitting because of their fast installation and effectiveness as both a foundation system and ground improvement at the same time. This paper presents a field study and numerical investigation of the lateral behavior of single hollow bar micropiles embedded in stiff silty clay deposits. Two monotonic and six cyclic lateral load tests were conducted on four micropiles, and the results were used to calibrate/verify a numerical model that was then used in a numerical investigation. The observed load-displacement curves demonstrated that the micropile behavior was flexible and was governed by the properties of soil along a depth equal to 10 times the pile diameter. The parametric study suggested that hollow bar micropiles can carry moderate lateral loads with proper reinforcement configurations and pile head fixity condition. During cyclic loading, the micropile head stiffness degraded initially as the number of load cycles increas...