Compression Section Research Articles

Flexural Behavior of Normal and Lightweight Concrete Composite Beams

This paper presents an experimental study of the behavior of Normal Concrete Beams (NCB) and composite beams with lightweight foamed concrete (CB), reinforced with steel bar measuring 2 f 8 mm in the compressive section and 2 D 16 mm in the tensile section, shear steel bar f 8 mm. The sample consisted of two normal concrete beams (NCB) and two composite beams with lightweight foamed concrete (CB). The main variables in this study are the type of concrete, the type of steel bar and the flexural behavior. The beam samples were tested by two-point loading, failure mode and crack width were observed. The results showed that the flexural process of normal concrete blocks (NCB) and composite beams with lightweight foamed concrete (CB) was almost the same. There is no slip failure at the combined interface, the flexural capacity of the composite beam with lightweight foamed concrete can be calculated based on the statics analysis and plane-section assumptions. To calculate the ultimate capacity of a composite beam with lightweight foamed concrete is to convert a section consisting of more than one fc' to an equivalent section consisting of one fc'. Furthermore, it is validated by calculating the theoretical moment capacity and comparing the theoretical moment capacity of the experimental results. The results of the flexural test, composite beam with lightweight foamed concrete (CB) showed ductile deflection behavior, diagonal crack patterns, and low flexural capacity of the beam (NCB). Doi: 10.28991/cej-2021-03091673 Full Text: PDF

The Association of Working Duration with Lung Function and Chest X-Ray Results in Ceramic Industry Workers of Company X, Mabar Medan

Background: Ceramics industry workers are often exposed to silica materials from ceramics. The aim of this study was to determine the association between silica exposure withlung function test and chest x-ray (CXR) results of the workers. Methods: This was an analytical study with cross-sectional design conducted in the Ceramic Industry X in Mabar, Medan City. The dust level in the work station was measured using Personal Dust Sampler. Lung function was measured by spirometry and CXR was evaluated using the ILO interpretations. Results: About 35 male workers were included as subjects, divided into 3 working stations namely precompression section of 11 subjects (31.4%), compression section of 13 subjects (37.1%) and 11 subjects (31.4%) in the sintering section. Dust levels in each work location are 24.8, 29.2, and 6.11 respectively. Of all subjects, 9 (25.7%) had respiratory symptoms, 21 (60%) had restriction in lung function and 8 (22.8%) had abnormal CXR (6 pneumoconiosis and 2 tuberculosis). There were no association between dust levels with lung function and CXR (P>0.05), but there was a significant correlation between duration of work with lung function. The FEV1 and FVC values of subjects working <5 years were 87.6% and 87.2%, while of those working ≥5 years were 68.1% and 68.7%, respectively (P<0.001). There were no correlation between working duration and pneumoconiosis finding in CXR (P=0,69). Conclusion: The prevalence of pneumoconiosis among ceramic worker exposed with silica dust was 22.8%. There was a significant relationship between duration of work and decreased lung function, but there were no correlation between dust level in the workplace with lung fuction and CXR, and sobetween working duration and pneumoconiosis finding.

CFD simulation for the internal pressure characteristics of an oil-injected twin-screw refrigeration compressor

3• A 3D model of an oil-injected twin-screw compressor was simulated with CFX. 3• The CFD model accounted well for the pressure in both time and frequency domains. 3• The highest pressure pulsation acted on the inner surface of the rotor housing. 3• The fluid hammer effect was found at the oil injection outlets. The internal pressure characteristics of an oil-injected twin-screw refrigeration compressor was studied using a full 3D CFX model, and the hexahedral moveable meshes of the twin-screw domain were generated by the professional mesh tool SCORG. The gas pressure throughout the whole working process was investigated to disclose its distribution feature. The working pressure at different locations, such as the inner surface of the screw rotor housing, the oil injection paths, the male screw groove, the internal suction and discharge flowing paths, were all captured and analyzed. The simulated pressure inside the screw working chamber agreed well with the experimental results in both time and frequency domains. The pressure pulsations in the compression section acting on the inner surface of the screw rotor housing presented higher levels than the data in the other domains. The highest pulsation level occurred on the location where could record the whole discharge process of the internal ports. Under the high oil flowrate conditions, due to the different influences of the fluid hammer effect, the pressure pulsation increment of the axial oil injection outlet was much larger than that of the radial oil injection outlet. The orifice on the oil path could help reduce the influence of the fluid hammer. Finally, several suggestions were given based on the simulation findings.

Effect of the chloride environmental exposure on the flexural performance of strengthened RC beams with self-anchored prestressed CFRP plates

Carbon fibre-reinforced polymer (CFRP) plates are widely used to strengthen reinforced-concrete (RC) structures. At present, most studies focused on the short-term performance of strengthened RC beams with a prestressed CFRP plate, and very limited information is available on their durability, which is of importance in certain cases, such as high-piled wharfs and bridges in marine environments. This study investigates the effects of chloride environment exposure on the flexural performance of strengthened RC beams with self-anchored prestressed CFRP plates. In total, seven RC beams, four of which were strengthened by a self-anchored prestressed CFRP plate, were fabricated and tested under three-point bending. The testing parameters included 25% and 40% prestress level of the ultimate tensile strength of the CFRP plate, 5% and 10% tensile steel rebar corrosion ratio of mass loss and 10% and 20% anchor corrosion ratio in the chloride environment. The evolution of time-dependent prestress losses in the strengthened beam was determined, and the flexural behaviour of the strengthened beams was analysed. A theoretical model is proposed to predict the flexural strength of prestressed CFRP strengthened RC beams in a chloride environment. The experimental results indicated that the coupling of the corrosion expansion of the metal anchor and rebar in the chloride environment had a large negative effect on the flexural performance of the beams strengthened by the self-anchored prestressed CFRP plates. After exposure to the chloride ion solution, the failure mode of the RC beams strengthened by the prestressed CFRP changed from concrete crushing in the compression section to anchor pullout. The proposed model, which considered the effect of a chloride environment to predict the flexural strength of the strengthened beams, agreed well with the test results.

Investigation of the Mechanical Integrity of Prismatic Li-Ion Batteries Under Multi-Position Indentation

Abstract Understanding the mechanical, thermal, and electrical properties of prismatic lithium-ion batteries (LIBs) is vital to battery safety design, which is key to electric vehicle safety. This study investigated prismatic LIBs subjected to multiple-position indentation loading. The side face of an intact prismatic LIB cell is divided into 15 compressed sections. Experimental results indicate that indentation loading of all sections could initiate thermal runaway. Among the sections studied, that near the positive terminal shows the highest risk of thermal runaway, whereas that near the top-right corner is relatively safe. Failure mode analysis reveals that short circuits may result from contact between the positive and negative current collectors.

Investigating local buckling in highly slender elliptical hollow sections through analysis of 3D-printed analogues

Tubular structural members with slender cross-sections are susceptible to failure through local buckling of their tube walls. Previous numerical studies of steel elliptical hollow sections in compression predicted the local buckling modes and the ultimate loads of particularly slender specimens, with the results used to calibrate design methods for slender elliptical sections. Although these numerical parametric studies were conducted across a wide slenderness range, it was only possible to validate the models against experimental results in the low slenderness range since commercially-available steel EHS are intended to satisfy non-slender geometric limits prescribed by structural design codes. Such limitations to the experimental scope are circumvented in the present study through testing of highly-slender specimens produced using additive manufacturing techniques. A total of eight specimens of various cross-sectional aspect ratios and tube wall thicknesses were fabricated at London South Bank University using additive manufacturing techniques, which were then tested in compression; the observed load-deflection behaviour, ultimate loads, longitudinal strains and failure modes are discussed. Through appropriate rescaling of relevant parameters, design predictions for the ultimate load of the 3D-printed analogues are obtained using a design method intended for use with steel elliptical hollow sections. It is shown that the design predictions are safe-sided when compared to the present experimental results, with the accuracy generally increasing with aspect ratio and slenderness.

Performance of Two Types of High Speed, High Efficiency ‎Axisymmetric Intakes

Performance of two axisymmetric air intakes are compared at conditions suitable for Mach number range from 2 to 8. First is the Busemann intake and second is the reversed isentropic nozzle. The isentropic nozzle is built by the method of characteristics. The contour of this nozzle is taken as a compression surface for the incoming flow. Performances of these two intakes are compared by comparison of both viscous and inviscid CFD calculations at Mach 6. Viscous flow calculations show that the total pressure recovery in compression section is 0.8316 in the Busemann intake and 0.869 in the reversed isentropic nozzle intake.

Exergy analysis of vapour compression-absorption two-stage refrigeration cycle

In this work, the exergy analysis of vapour compression-absorption two-stage refrigeration cycle has been performed. While NH3-H2O has been used as fluid pair in the absorption section, NH3 has been used in the vapour compression section. To improve the performance of the cycle, it is possible to reduce the total damage by focusing on the parts that cause high exergy damage. Therefore, the detailed exergy analysis has been made for different operating conditions (generator temperature, condenser temperature and intermediate pressure) of the cycle. The exergy destruction rates of each component were calculated and compared. As the generator temperature increases, the highest exergy destruction rates are seen in the generator. The generator exergy destruction rates increase with increasing condenser temperature. Also, the performance coefficient (COPcyclegen) and the exergy efficiency (e) of the novel cycle have been investigated for different the intermediate pressures. The performance coefficient (COPcyclegen) increases as the intermediate pressure increases. Maximum value of the exergy efficiency is obtained at the intermediate pressure of 516.015 kPa. With this cycle, it is possible to refrigerate down by using alternative energy sources. Also, the refrigeration system is environmentally friendly because environmentally safe fluids are used in this cycle.

Investigation of tooth crack opening state on time varying meshing stiffness and dynamic response of spur gear pair

In the traditional calculation model of mesh stiffness, the tooth root crack is commonly assumed to be in a closed state. However, the gear tooth crack will open under the action of mesh force in the meshing process, the mesh stiffness of the cracked tooth and the dynamic response of gear system is thus different from the closed crack case. There almost no studies have been done to investigate the influence of tooth crack open state on mesh stiffness and dynamic response. Thus, this paper presents an improved mesh stiffness calculation model of the cracked gear, in which the effective compression section and the neutral layer of the cracked tooth are re-evaluated considering the crack opening state. Then, the accuracy of the proposed model is verified by the finite element method (FEM), and the differences of mesh stiffness and statistical indicators of the dynamic response between the proposed and traditional models are further studied. The mesh stiffness calculation results show that the proposed model achieves a higher accuracy than the traditional model. And its precision gradually increases as the crack grows, which can be improved by 2.35% in the case of large crack (48.38% crack) when compared to the traditional model. The fault response signal obtained from the traditional model yields a larger amplitude than the actual situation, which will lead to errors of the statistical indicators used for fault diagnosis, in particular, the RMS value can be up to an average percentage difference of 11.98% under the large crack (48.38% crack). It is concluded that the proposed model has a higher accuracy for calculating the mesh stiffness of the cracked gear and can be further used to serve the fault diagnosis and detection of the gear system.

Evaluation of Two-Column Air Separation Processes Based on Exergy Analysis

Cryogenic air separation processes are widely used for the large-scale production of nitrogen and oxygen. The most widely used design for this process involves two distillation columns operating at different pressures. This work focuses on the selection of suitable cryogenic air separation process by evaluating seven alternative designs of the two-column air separation process based on detailed exergy analysis. The feed conditions (500 tons/h, and 50% relative humidity of air), product purities (99 mole% for both nitrogen and oxygen), and operational conditions (pressures of both distillation columns) are kept same in all designs. The two cryogenic distillation columns in each configuration are heat-integrated to eliminate the need for external utilities. Steady-state simulation results are used to calculate the exergy efficiency (%) of each equipment as well as its contribution toward the overall exergy destruction rate (kW) of the process. The results show that the compression section is a major source of exergy destruction, followed by the low-pressure column, and the multi-stream heat exchanger. A Petlyuk-like configuration, labeled as C1, provides the lowest exergy destruction rate.

Design of fixed-ended octagonal shaped steel hollow sections in compression

In recent years, octagonal steel hollow sections (OctHSs) have attracted significant interests from researchers and engineers, and OctHSs have been employed in civil engineering applications. However, designs of OctHSs are not included in structural steel design codes. This paper therefore presents comprehensive numerical analyses on the stub column behaviour of OctHSs. A database of 46 stub column tests reported in 6 sources were collected. Different fabrication routes, steel grades and cross-sectional slenderness were covered. Finite element (FE) modelling was carried out to replicate the test observations. The validated FE models were subsequently adopted to conduct an extensive parametric study to supplement the test database. Existing design methods in North American specifications, ASCE standard, Eurocode, Australian code and recently published literature were thoroughly discussed and evaluated. It was found that existing design methods are not applicable to the design of OctHSs. New cross-sectional slenderness limits and modifications to the existing design methods were then proposed. The cross-sectional resistance obtained from different design methods were compared with test and FE results. The applicability of the modified design methods was confirmed by statistical analyses. The reliability of the modified design methods was finally verified through reliability analyses. Results indicate that the modified design methods can be used to accurately predict the resistance of OctHSs with accepted safety levels.

Experimental Research on Concrete Beams Reinforced with High Ductility Steel Bars and Strengthened with a Reactive Powder Concrete Layer in the Compression Zone.

The article describes four-point bending tests of three reinforced concrete beams with identical cross-sections, spans, and high-ductility steel reinforcement systems. Two beams were strengthened in the compressed section with a thin layer of reactive powder concrete (RPC) bonded with evenly spaced stirrups. Their remaining sections, and the third reference beam, were made of ordinary concrete. Measurements of their deflections, strains and axis curvature; ultrasonic tests; and a photogrammetric analysis of the beams are the main results of the study. For one of the beams with the RPC, the load was increased in one stage. For the two remaining beams, the load was applied in four stages, increasing the maximum load from stage to stage in order to allow the analysis of the damage evolution before reaching the bending resistance. The most important effect observed was the stable behaviour of the strengthened beams in the post-critical state, as opposed to the reference beam, which had about two to three times less energy-absorbing capacity in this range. Moreover, thanks to the use of the RPC layer, the process of concrete cover delamination in the compression zone was significantly reduced, the high ductility of the rebars was fully utilized during the formation of plastic hinges, and the bending capacity was increased by approximately 12%.

Large Scaphitid Ammonites (Hoploscaphites) from the Upper Cretaceous (Upper Campanian–Lower Maastrichtian) of North America: Endless Variation on a Single Theme

We describe three species of large scaphitid ammonites (Ammonoidea: Ancyloceratina) from the Upper Cretaceous (upper Campanian–lower Maastrichtian) of the Western Interior of North America. Each species occurs as two dimorphs, referred to as macroconch and microconch. All three species share a similar pattern of ornamentation consisting of long, thin, nonbifurcating ribs on the adoral part of the phragmocone, suggesting that they constitute a single monophyletic clade. Macroconchs of Hoploscaphites crassus (Coryell and Salmon, 1934) are characterized by a globose whorl section, with closely spaced ventrolateral tubercles on the body chamber, usually persisting to the aperture. Macroconchs of Hoploscaphites plenus (Meek and Hayden, 1860) differ from those of H. crassus in having a more subquadrate whorl section with flatter flanks, and fewer, larger, and more widely spaced ventrolateral tubercles. Macroconchs of Hoploscaphites peterseni, n. sp., closely resemble those of H. crassus, but differ in being nearly circular in side view with a more compressed whorl section. All three species lived at approximately the same time in the same general area and depositional environment. They are abundant in the Baculites baculus Zone but also occasionally occur in the B. eliasi Zone and possibly lower part of the B. grandis Zone. They are present in the Pierre Shale of east-central Montana and east-central Wyoming, the Lewis Shale of south-central Wyoming, and the Bearpaw Shale of northeast Montana. It is possible that these three species represent subspecies within a single species or a “flock” of very closely related species, similar to the “species flocks” observed in modern cichlid fishes.

Evaluation of Structural Performance of Concrete Beams Strengthened with Carbon Fiber Sheets and No-Slump Concrete

In this study, the compression and tensile sections of existing concrete were reinforced using carbon fiber sheet (CFS) and no-slump high-strength, ductility concrete (NSHSDC) to evaluate the structural response of the reinforced concrete. From the experimental test results, the CFS showed a low energy dissipation ability when reinforced at both the compression and tensile sections. However, the NSHSDC reinforcement exhibited high energy dissipation and the lowest deflection under maximum load at both the compression and tension sections. The NSHSDC without reinforcement in the compression section, and concrete reinforced with CFS, exhibited lower load resistance and concrete compression failure. Furthermore, a linear relationship between the compression reinforcement and structural performance was observed, which demonstrated the high load resistance and excellent structural performance of the member reinforced with NSHSDC at both the compressive and tensile sections.

Spatial Transverse Vibration Simulation Model of Axially Moving Sucker Rod String under the Excitation of Curved Borehole

The mechanical model of transverse vibration of sucker rod string (SRS) in directional well is simplified to the transverse vibration model of longitudinal and transverse curved beam with initial bending under borehole constraints. In this paper, besides considering the excitation of alternating axial load on the transverse vibration of SRS, it is proposed for the first time that curved borehole is also the main excitation for the transverse vibration when the SRS moves reciprocating axially in the borehole. Based on the elastic body vibration theory, the transverse vibration mathematical model of SRS with initial bending under borehole constraints is established. In this model, the curved borehole excitation caused by the axial motion and the alternating axial load excitation is considered. Besides, the elastic collision theory is applied to describe the constraint of tube on the SRS transverse vibration in this model. Then the fourth-order Runge–Kutta method is used to calculate the transverse vibration of SRS in directional wells. The simulation results show the following: (1) The simulation results of the three simulation models in this paper are different. The results indicate that the curved borehole excitation caused by the axial motion and the alternating axial load excitation is the main excitation for the SRS transverse vibration. (2) In directional wells, the rod and tube contact along the well depth, and the dangerous sections locate at the deviation section of the borehole and the compression section of the rod. On the whole, the contact force between rod and tube in deviation section of borehole is larger. The transverse vibration of the compression section of the rod is the most violent.

Optimization of Heat and Mass Transfer Process in Single Screw Floating Fish Feed Extruder

To optimize the extrusion conditions of locally developed single screw floating fish feed extruder. A factorial experiment in completely randomized design was employed to study the effect of extrusion variables: feed moisture content (20, 30, and 40% wet basis), screw speed (158.5, 245, 334 rpm), die size (4, 6, 8, mm) while checking for their effect on Product temperature of the feed produced. Product temperature is strongly related to the extrusion process parameters under study. Product temperature decreased with increasing moisture content. Optimum condition was found at 74.11⁰C at the feed section, 80.83⁰C at compression section and 85.15⁰C at metering section, screw speed at 330.5 rpm, feed rate at 0.6 kg/min, die size at 7.47 mm, moisture content at 39.87%, particle size at 1.1., and the coefficient for the final model is 0.93 which indicated that the model is good. The extruder was found to be cost efficient for floating fish feed production. Thus, model-fitting using response surface methodology was performed to examine their effect on product temperature. Quadratic coefficients fit the extrusion data very well, better than linear models. The equations relating the various dependent and independent variables were established to predict the performance of the machine.

Behavior of concrete-filled steel tubes subjected to axial impact loading

Investigations on concrete-filled steel tubular (CFST) members under static loads have been extensively reported. Still, limited researches have been conducted to investigate the behavior of CFST columns subjected to axial impact loading. This paper presents an experimental study on dynamic behaviors of twelve square and rectangular CFST stub columns subjected to axial impact loading using a drop-weight test apparatus. The instantaneous force and deformation states were recorded during the impact tests. Finite element (FE) models were established and verified using the experimental results and existing research data, in which the strain rate effects of steel and concrete were fully considered. Then the effects of cross-section shape, steel strength, concrete compressive strength, steel ratio and impact energy condition on the dynamic responses of the CFST stub columns were studied using the FE models. The experimental and analytical studies indicate that the circular CFST stub columns perform better than the square and rectangular ones. While, little difference can be found between the square and rectangular CFST stub columns. For all the three shaped CFST stub columns, the average platform impact force increases and the deformation decreases with the increase of steel strength, concrete compressive strength, steel ratio and section area. Based on the parameter studies, a simplified design method was proposed by establishing the relationship between the maximum axial displacement and the impact energy condition to predict the deformation response of CFST stub columns under axial impact.

Flexoelectric effect on electric potential in piezoelectric graphene-based composite nanowire: Analytical and numerical modelling

In this work, an analytical model was developed to study the distribution of electric potential in a graphene reinforced nanocomposite (GRNC) nanowire. The electromechanical responses such as electric potential and deflection of cylindrical GRNC cantilevered nanowire were investigated. Moreover, the conservative fully coupled finite element (FE) models were developed to validate the analytical predictions. Analytical solution shows that the piezoelectric potential in the GRNC nanowire depends on the transverse force, but it is not a function of the force acting along its axial direction. The electric potential in the tensile and compressive sections of nanowire is antisymmetric along its cross-section, making it as a “parallel plate capacitor” for nanopiezotronics applications such as nanogenerator and piezoelectric field effect transistor due to potential drop across the nanowire which assists as the gate voltage. The predictions of potential distributions across the GRNC nanowire considering piezoelectricity show better agreement with FE predictions. Outcomes of the current work reveal that the flexoelectric effect on the electromechanical behavior of GRNC nanowire is noteworthy and cannot be ignored.

Research on the Coupled Axial-Transverse Nonlinear Vibration of Sucker Rod String in Deviated Wells

The coupled axial-transverse nonlinear vibration simulation model of sucker rod sting (SRS) in deviated wells is established. Based on the simulation results, the nonlinear vibration phenomenon of SRS is analyzed, and the influence of centralizer arrangement on the nonlinear vibration of SRS is discussed. The mechanical simulation model of the coupled axial-transverse vibration of SRS in deviated wells can be simplified to the coupled axial-transverse vibration model of longitudinal and transverse curved beam with initial bending under borehole constraints. In this paper, when establishing the simulation model of the coupled axial-transverse vibration of SRS, it is proposed that the bending borehole trajectory is a main excitation of the vibration of SRS. Based on the theory of elastic vibration, a nonlinear dynamic simulation model of the coupled axial-transverse vibration of SRS in deviated well is established. Then the fourth-order Runge–Kutta method is used to solve the simulation model. The nonlinear vibration phenomenon of the SRS is studied by example analysis. The simulation results show that: (1) the simulation curve of polished rod dynamometer card is in good agreement with the test curve, and the error value of polished rod maximum load and minimum load is within 5%, which shows that the coupled axial-transverse vibration simulation model of SRS established in this paper has high accuracy. (2) When the centralizer is not arranged, the chaotic motion of SRS mainly occurs in the compression section of SRS, which shows that the instability of SRS is the main reason for the chaotic motion of SRS. (3) The arrangement of centralizer can improve the bending rigidity of SRS, restrain or even eliminate the chaotic motion of SRS.

Measurement of the length of vertebrobasilar arteries: A three-dimensional approach

Under the assumption that neurovascular compression can be caused by elongation or kinking of the artery, we measured the length of each section of the vertebrobasilar artery, compared the lengths between various age groups, and evaluated the involvement of the arterial sections in brain stem compression in 1000 cases. The lengths of the posterior inferior cerebellar artery (PICA)-union of both vertebral arteries (union), union-anterior inferior cerebellar artery (AICA), AICA-superior cerebellar artery (SCA), and union- superior cerebellar artery were measured using an arterial length measuring tool applied to three-dimensional images. The presence of arterial compression of the brain stem was also evaluated. The mean age of the participants was 66.8 ± 12.9 years, and 44.8% were men. Intraclass correlation coefficients for both inter-rater reliability and intra-rater reliability were high in all sections. The vessel lengths of left AICA-SCA (P < 0.001), left union-SCA (P < 0.0001), left PICA-union (P = 0.03), right AICA-SCA (P = 0.002), right union-SCA (P < 0.0001), and right PICA-union (P = 0.04) increased with age, but each R2 was less than 0.05. Brain stem compression by PICA or vertebral artery was identified in 13.8% of cases. The proportion of the presence of brain stem compression was significantly higher in the cases with arterial elongation than in those without (P = 0.01). Vessel length increased with age, but age had a relatively small impact on the elongation of vertebrobasilar arteries. Brain stem compression might be caused by kinking of the artery rather than arterial elongation.