Compression Section Research Articles

A Eurocode‐compliant design approach for cold‐formed steel sections

AbstractA Eurocode‐compliant design approach was developed for the design of thin‐walled cold‐formed steel sections which combines the AISI S100‐16‐Direct Strength Method (DSM) with the design provisions of EN 1993‐1‐3. The new design approach transfers the cross‐sectional resistance determined acc. to DSM based on numerical elastic buckling analyses on the gross cross‐section into the global member verification acc. to EN 1993‐1‐3. Additional factors were introduced to optimize the new approach, e.g., to account for the effects of the nonlinear stress distribution in cross‐sections subject to local and/or distortional buckling. Within the framework of the German research project FOSTA P1328/IGF 19964, an extensive series of tests on differently shaped, perforated, and unperforated cold‐formed sections in compression and bending were conducted which serve to analyze the buckling phenomena and the load‐bearing capacity and to validate the new design approach. In addition, a numerical model was developed, calibrated to the tests, and used for further parametric analyses on the load‐bearing capacity of cold‐formed sections.

A self-centering hybrid braced precast wall with replaceable U-shaped flexural plates: Experimental and theoretical analysis

A self-centering hybrid-braced precast wall with replaceable U-shaped flexural plates (UFPs), which is composed of a hybrid braced wall, post-tensioned (PT) strands, and steel wall toes, is proposed. The UFPs bolted inside the steel wall toes, which yield at the same thickness outside the plane of the steel plate when wall rocking, providing plastic bending energy dissipation. The steel wall toe made of H-shaped steel provided increased compressive strength and space for the installation of the UFPs. Four wall specimens with varying initial PT forces, UFPs of different thicknesses, and different dampers were investigated using low-cyclic loading tests. After replacing the UFPs, one wall was retested to assess its performance. The precast walls sustained significantly low damage and showed large self-centering capabilities. The maximum drift was up to 4.5%, which far exceeded the specified requirements, and the lateral load still maintained an increasing trend. When the initial PT force was increased, the bearing capacity, initial stiffness, and self-centering capacity of the precast wall increased. When the thicknesses of the UFPs were increased, the energy-dissipation capacity and self-centering capacity of the wall increased and decreased, respectively. The self-centering and bearing capacities of the repaired wall met the seismic requirements but were slightly lower than those of the original wall. The wall with UFPs performed better bearing capacity and stiffness than the wall with variable friction dampers (VFDs) before 1.5% drift. Additionally, the opening load of the wall, the load at the yield of UFPs, and the load at different compression sections were calculated and compared against the test results. The analysis method was able to predict the behavior of the walls reasonably well.

An BESO Approach for Optimal Retrofit Design of Steel Rectangular-Hollow-Section Columns Supporting Crane Loads

In this paper, we propose a cost-effective optimal-topology retrofitting technique for hollow-steel-section columns to sufficiently support industrial running cranes. A so-called bi-directional evolutionary structural optimization (BESO) method was encoded within the MATLAB modeling framework, with a direct interface with an ANSYS commercial finite-element analysis program, to determine the optimal topology of double external steel plates connected to columns in a 3D space. For the initial ground structure, we have adopted standard uniform double U-shaped external stiffener plates located at the top and bottom flange layers of an I-beam to box-column connection (IBBC) area. The influences of inelastic materials and the incorporated nonlinear geometry can effectively describe the premature (local buckling) failures of the columns in an IBBC area. The applications of the proposed optimal-topology BESO-based stiffening method are illustrated through the retrofitting of three hollow-steel-section columns, characterized by non-slender and slender compression sections. Some concluding remarks are provided on the pre- and post-retrofitted responses of the columns, with the results showing both the accuracy and robustness of the proposed external stiffening schemes.

Behavior of Gusset Plates Connecting Angle Sections in Compression

This paper contains experimental and numerical study on the behavior of the gusset plate in compression. Gusset plate connections are usually used for the transfer of load from one member to another, they are generally used in bridge trusses and steel braced frames. However, due to lack of technical information regarding the behavior of the gusset plate under compression, these have been under research focus. It has been seen that the gusset plate shows a buckling failure by swaying on one side as there is no out of plane restraint. In this paper, a study is initiated aimed at the gusset plate connected with the angle section on a single side. Key items that were investigated in the study were strain, strength, and displacement. A total of 5 specimens were used for the experimental investigation. The parameters which were considered for the study, the number of bolt lines and the thickness of the gusset plate. Based on the experimental results of load and strain, a numerical model was developed and compared with experimental load-carrying capacity of plate and displacements. After going through the study unpredicted behavior was observed for the two-bolt line and suggestions were given accordingly.

Recent advances in biogas purifying technologies: Process design and economic considerations

Biogas is a promising renewable energy source that is produced from biowaste and can potentially replace conventional energy resources. The economic value of biogas, which is primarily comprised of CH4, CO2, and other impurities (e.g. H2S, and N2) can be increased by upgrading and purification. This study presents the techno-economic feasibility of the cryogenic biogas upgrading process (CBioUP) based on product purities, biomethane selling prices and different refrigeration systems over 25 years of lifetime. The proposed CBioUPs is comprised of compression, refrigeration, and separation sections. Compressed biogas was liquefied in two refrigeration systems (propane pre-cooled mixed refrigerants and optimized cascade technologies) followed by a distillation separation unit. CBioUP proved its flexibility in terms of the number of distillation columns to produce low-grade CH4 (≈94.58 mol%), high-grade CH4 (≈97.13 mol%), and liquid CO2 by-product. The process's robustness to varying biogas feed composition revealed higher CO2 content would necessitate additional duty and/or equipment to enhance separation efficiency, whereas a CH4 content of ≥70% generated biomethane with a purity >99.6 mol% even in a single distillation column. CBioUP demonstrated its suitability for producing different grades of CH4 with a promising net present value (NPV) of $28.3 and $30.9 billion for low/high-grade biomethane.

Numerical Research on the NS-SDBD Control of a Hypersonic Inlet in Off-Design Mode

The overall performance of a scramjet inlet will decline while entering off-design mode. Active flow control using nanosecond surface dielectric barrier discharge (NS-SDBD) can be a novel solution to such inlet–unstart problems. NS-SDBD actuators are deployed on the surface of the internal compression section, controlling the shock waves and the separation area. Numerical simulations of hypersonic flows are carried out using the compressible Reynolds average Navier–Stokes equation (RANS), along with the plasma phenomenological model which is added in as the energy source term. Flow structures and the evolution of performance parameters are analyzed. Results show that NS-SDBD actuators are able to increase the static pressure behind the cowl shock, boosting the downstream total pressure. The compression effect becomes stronger while raising the frequency or shortening the spacing between the actuators. Under the inlet–unstart conditions, the compression wave generated by the actuator pushes the reattachment point forward, making the separation bubble longer in length and shorter in height, which reduces the strength of the separation shock. The results provide a numerical basis for the state control of a hypersonic inlet.

Seismic performance of high-strength centrifugally prefabricated RC hollow pipe columns using grouted bellows connection

The seismic behavior of high-strength centrifugally prefabricated reinforced concrete pipe columns of a practical engineering project is investigated through three 1:2 large-scale quasi-static tests. The influence of axial compression ratio and section form on their performance is evaluated. Based on the confinement effect in the high-strength centrifugally prefabricated RC hollow pipe columns, a modification to one of the most widely used confined concrete models is proposed. It can accurately predict the confined concrete behavior in the hollow pipe columns, and its accuracy is verified by numerical analysis. Finally, the hollow pipe columns are analyzed with the proposed modified confined concrete model and are subjected to different axial compression ratios. The results show that the confinement effect of single-layer transverse reinforcement on the core concrete of centrifugal prefabricated RC hollow pipe columns is not as good as that of solid pipe column, but if the neutral axis is controlled within wall of the hollow pipe columns by changing the axial compression ratio or other design parameters, they can show satisfactory ductility.

Residual compressive section capacity of filament wound carbon, glass, and basalt fibre-reinforced polymer tubes: Influence of elevated temperatures

This study investigates the residual compressive properties of various filament wound FRP tubes after exposure to elevated temperatures. Exposure temperature and fibre type were considered as the test variables. The experimental program included compression tests for BFRP, GFRP, and CFRP tubes at room temperature and after exposure to elevated temperatures up to 350 °C. A total number of 72 specimens were tested in compression. In addition, Differential Scanning Calorimetry, and Scanning Electron Microscopy were conducted on selected samples to investigate the thermal and microstructural properties of the tubes. The compressive strength of tubes, regardless of the fibre type, seemed to be affected by the competing effects of post-curing and resin matrix degradation. With respect to fibre type, for temperatures below 350 °C, BFRP exhibited the highest compression strength retention, whereas CFRP tubes showed the lowest strength retention. Temperature of 350 °C was found to be the critical temperature (the temperature that FRP loses 50 % of its load carrying capacity) for CFRP tubes, while the critical temperature for GFRP and BFRP tubes were respectively, somewhere lower than 350 °C. The maximum compressive strength reductions for BFRP, GFRP, and CFRP were 94 %, 63 % and 50 % respectively after exposure to 350 °C.

Investigation on axial resistance of steel reinforced concrete cross-shaped columns exposed to high temperature

Steel reinforced concrete (SRC) special-shaped columns have the advantages of high spatial utilization, flexible layout and good economic benefits, which are used in high-rise buildings. However, this composite structure has the disadvantages of high steel content and large fire area, which makes it easier to suffer damage in fire, and even cause the collapse of buildings. This paper presents mechanical properties of SRC cross-shaped columns exposed to high temperature. Seven SRC cross-shaped column specimens were analyzed. Temperature field distribution, failure mode, deformation and fire resistance of specimens were obtained under different axial compression ratios (0.4, 0.6) and eccentricity (0, 40, 60, 80 mm). The results showed that: (1) All specimens were in a condition of compression failure and section steel had partial bending failure with the concrete falling off. (2) The larger eccentricity and axial compression ratio were, the earlier cracks appeared, and the more cracks appeared, the more serious concrete shedding of specimen were. Moreover, the cracks were concentrated especially on the side of loading point (i.e., two sides close to the point where the applied load is located), and the cracks are adjacent to the support of specimen, which appear in the whole length of specimen. (3) Axial compression ratio had a significant influence on fire resistance of SRC cross-shaped columns, and influence of eccentricity on fire resistance was generally little compared with axial compression ratio. The fire resistance declined by 43.48–69.14% as axial compression ratio increased from 0.4 to 0.6. Fire resistance declined by 5.45–45.31% as eccentricity increased from 0 to 80 mm, and it was significantly reduced by 28.12–45.31% when axial compression ratio was 0.6. Finally, fire resistance calculation method of SRC cross-shaped column was obtained, which provided reference for fire resistance design of SRC structure.

Lagrange Optimization of Shock Waves for Two-Dimensional Hypersonic Inlet with Geometric Constraints

The present paper focuses on the Lagrange optimization of shock waves for a two-dimensional hypersonic inlet by limiting the cowl internal angle and inlet length. The results indicate the significant influences of geometric constraints on the configuration of shock waves and performances of an inlet. Specifically, the cowl internal angle mainly affects the internal compression section; the inlet length affects both the internal and external compression sections where the intensity of internal and external compression shock waves shows a deviation of equal. In addition, the performances of optimized inlets at off-design points are further numerically simulated. A prominent discovery is that a longer inlet favors a higher total pressure recovery at the positive AOA; conversely, a shorter inlet can increase the total pressure recovery at the negative AOA.

Fast characterization of biodiesel via a combination of ATR-FTIR and machine learning models

This study proposed a fast characterization method for biodiesel based on attenuated total reflection flourier-transform infrared spectroscopy and machine learning models. The concerning characteristics of biodiesel include unsaturated group content, O content, and contents of four representative esters. A total of 71 biodiesel samples were produced from a lab-scale reactor. Their spectral data and characteristics were collected and used as training data for machine learning models. The established model framework consisted of two data compression sections, a classification section, and a regression section, all of which use machine learning models, such as principal component analysis, support vector machine, artificial neural network, and random forest. The accuracy, correlation, and sensitivity of the proposed method were evaluated and optimized. Furthermore, the interpretation of the models was discussed. The results showed that the principal component analysis model was a satisfactory preprocessing procedure for the downstream classification and regression models. Under the optimal model parameters, the integrated framework could reach an average accuracy rate of 93.18% and a Pearson correlation coefficient of 0.92. Principal component number 4 and 5 showed the highest sensitivity towards the predicting results, implying that their highly weighted wavenumber ranges and the correlated functional groups played the most important role in the predicting process. The findings of this study could lead to a simple and efficient approach for characterizing the properties of biodiesel, which in turn could promote the development of similar biomass-derived liquid fuels.

A New Eurocode‐compliant Design Approach for Cold‐Formed Steel Sections

AbstractA new, Eurocode‐compliant design approach based on the Direct Strength Method (DSM) combined with EN 1993‐1‐3 was developed for the design of thin‐walled cold‐formed steel sections. The new design approach transfers cross‐sectional resistance according to DSM, based on numerical elastic buckling analyses on the gross cross‐section, into the global stability check according to EN 1993‐1‐3. Experimental investigations on various perforated and unperforated cold‐formed sections in compression and bending serve to verify the new design approach. In addition, a numerical model was developed, it was calibrated on the test results and used for further parametric analyses on the load‐carrying capacity of cold‐formed sections.

Strength of RC Beam Using Geo Polymer Concrete and Adoption Bubble Technology

Abstract: Bubble Deck technology first time in European countries provide consumption of high-density polyethylene hollow spheres to replicate the unproductive material in the mid of the slab, consequently diminishing the deceased burden and escalating the competence of the flooring. This process be used in the concrete floor system. Concrete is superior in firmness and thus is further constructive in the compression section than in the tension section. The diminution in concrete can be done by replacing the tension region concrete. Keeping the equal design in intellect, an effort has been ended to discover out the efficiency of plastic bubbles by replacing concrete in the tension region of Ordinary Portland Cement Concrete (OPCC) and Geo polymer Concrete (GPC) beam. Geo polymer Concrete does not figure calcium- silicate-hydrates (CSHs) for matrix configuration and potency like OPCC however utilizes the poly condensation of silica with alumina precursors to achieve structural potency. In this job, M25 concrete mix is used to practice both OPCC and GPC beams. The trial mix is experienced for compressive potency. Flexure test is completed for 28 days of curing of the beams.

DETERMINATION OF THE COMPRESSED FLOW DEPTH IN THE BRIDGEHEAD OF A SMALL BRIDGE

Introduction. Hydraulic calculation of bridges is one of the most important stages in determining its basic geometric parameters. Therefore, it should be based on the exact equations of hydraulics that characterize the behavior of water flow. Currently, the hydraulic calculation of a small bridge is based on an empirically established dependence, which is that the compressed depth under the bridge hc is associated with the support H approximate dependence hc ≈ 0,5H and is independent of the compression of the flow bridge crossing. In this work, it is theoretically proved that taking such a relationship between depths, you can get quite large inaccuracies in determining the depth in the compressed section hc, and hence in determining the speed in the calculated cross section of the bridgehead. Results. Based on the three basic laws of physics, namely: the law of conservation of mass (continuity equation), the law of conservation of energy (Bernoulli equation), the law of momentum (equation of the momentum change theorem), obtained an analytical relationship that establishes a relationship between compressed depth parameters hc and support H at different degrees of flow compression ε. Based on this dependence, an equation was obtained that establishes the relationship between the flow rate Q and the pressure in front of the bridge H. The obtained equation is similar in form to the flow equation through a wide-threshold spillway, with the difference that the flow coefficient m(ε) in the obtained equation depends on the degree of flow compression. Conclusions. The equation for determining the flow rate through the opening of a small bridge taking into account the flow compression is obtained. It is shown that the obtained equation coincides in form with the flow equation, which determines the flow through a wide-threshold spillway. The difference between these equations is that the flow coefficient m(ε) is a function of the flow compression coefficient ε. Using the boundary transition, it is obtained that m(ε) can vary from 1/3 √(2/3) to √0,5. Graphs are presented, which allow to analyze the change of hydraulic characteristics of the flow depending on the compression coefficient ε.

Dynamic Simulation Analysis of Carbon-Steel Hybrid Sucker Rod String in Vertical and Directional Wells

Carbon fiber composite continuous sucker rod string is more and more widely used in deep and ultradeep wells because of its light weight, high strength, and corrosion resistance. In order to analyze the dynamic problems of carbon fiber sucker rod string in actual oil wells, a transverse vibration simulation model of carbon fiber and steel (carbon-steel) hybrid rod string excited by buckling deformation in vertical wells is established with the compression buckling deformation of weighting rod. Considering the influence of wellbore trajectory and the constraint of tubing, the transverse vibration simulation model of carbon-steel hybrid rod string in directional wells under borehole trajectory excitation is also established in this paper. The finite difference method is used to discretize the well depth node, the numerical integration method (Newmark-β) is used to discretize the reciprocating periodic time node, and simulation methods for the contact and collision dynamics of rod-tubing in vertical wells and directional wells are formed. Through programming calculation, the distribution laws of transverse displacement, contact force, collision force, and bending stress of carbon-steel hybrid sucker rod string in vertical wells and directional wells along well depth are obtained. The simulation results in vertical wells show that the strong collision between the rod and tubing occurs near the bottom steel rod, while the upper load is small and the rod-tubing collision load of the upper rod of the carbon-steel hybrid rod string is much lower than that of the traditional steel rod string at the same position. Furthermore, the bending stress of the upper carbon fiber is also much less than that of the bottom steel rod. The simulation results in directional wells show that the collision phenomenon of the deflecting section and the bottom weighting rod compression section are the strongest and the rod-tubing contact pressure is also the largest. Second, the impact force of the upper carbon fiber rod is also much lower than that of the steel rod. Again, the maximum bending stress of the whole well occurs near the deviation section where the deviation angle changes suddenly. The transverse vibration mechanical model in directional wells in this paper lays a theoretical foundation and provides theoretical support for the optimal design of fracture and splitting prevention measures of carbon fiber sucker rod.

Potential for Energy Utilization of Air Compression Section Using an Open Absorption Refrigeration System

In this paper, an open absorption refrigeration system is proposed to recover part of the waste compression heat while producing cooling capacity to further cool the compressed air itself. The self-utilization of the compression waste heat can significantly reduce the energy consumption of air compression, and hence increase the energy efficiency of the cryogenic air separation unit. To illuminate the energy distribution and energy conversion principle of the open absorption refrigerator-assisted air compression section, a thermodynamic model is built and the simulation work conducted based on a practical triple-stage air compression section of a middle-scale cryogenic air separation unit. Our results indicate that the energy saving ratio is mainly constrained by the distribution of the cooling load of compressed air, which corresponds to the heat load of the generator and cooling capacity of the evaporator in the open absorption refrigerator. The energy saving ratio ranges from 0.52–8.05%, corresponding to the temperature range of 5–30 °C and humidity range of 0.002–0.010 kg/kg. It is also estimated, based on the economic analysis, that the payback period of the open absorption refrigeration system is less than one year, and the net project revenue during its life cycle reaches USD 5.7 M, thus showing an attractive economic potential.

Experimental study on effect of ductile-iron panel stiffness on mechanical properties of segmental joints of shield tunnels

In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels, as the axial force at the segmental lining decreases, the bolt load at the segmental joint increases. It is essential to adopt high-stiffness segmental joints to improve the bearing capacity and control the deformation at the joint position. When designing high-stiffness segmental joints, the selection of ductile-iron joint panel is crucial. In this study, two types of segmental joints with different joint panels were fabricated, and the effects of joint panel stiffness on the mechanical properties of segmental joints were analyzed through full-scale sagging and hogging bending tests. The results showed that the failure mode of high-stiffness segmental joint was similar to that of large eccentric compression section. According to the difference of panel stiffness, the failure modes can be specified into two types. If the stiffness is sufficient, the joint failure occurs due to the yielding of bolts; otherwise, it occurs due to the large deformation of ductile-iron joint panels. As for the design requirement of segmental joint, the stiffness of joint panel should be sufficient, i.e., the opening and failure of the joints are finally induced by the bolt deformation. Otherwise, before the plastic deformation of the bolts, the large deformation of the joint panels will occur under a bending-moment-dominant load, and the bearing capacity of the joints will greatly decrease.

The ‘grooved’ Hildoceras ammonite fauna from the Lower Jurassic (Toarcian) of the Apennines. Overview and proposal for a new species

ABSTRACT It is historically renown that morphotypes referred to Hildoceras bifrons from the Apennines (Italy) and other Mediterranean localities differ in many ways from the typical species of the Central and North-West Europe. Besides overall smaller size (usually < 40 mm), Mediterranean specimens attain marked whorl embracement, comparable to that of the kin species Hildoceras semipolitum (albeit retaining a less compressed whorl section). Relatively larger (and rare) morphotypes may show slight 'uncoiling' (resembling the typical Hildoceras bifrons), though limitedly to the final part of the adult-stage last whorl. Both the common (small-involute) and rare (larger-slightly uncoiled) morphotypes thus reveal of ambiguous taxonomic attribution either as Hildoceras bifrons or as Hildoceras semipolitum. In front of this ambiguity, the new species Hildoceras appenninicus sp. nov. is proposed for grouping 'bifrons-like' Hildoceras occurring in the Apennines and other Mediterranean localities. In contrast with previous works on this subject, definite ranges for whorl compression indexes relative to whorl diameter and embracement are provided, by this attempting at a more objective distinction of this new species from both Hildoceras bifrons and Hildoceras semipolitum. Finally, along with some biostratigraphic remarks, possible evolutionary and paleobiogeographic implications concerning the arising and spreading of Hildoceras species are outlined. lsid: zoobank.org:pub:5C2C159E-61CA-4EE0-996D-D098618B3790

Leading-to-trailing edge theoretical design of a generic scramjet

The aerospace vehicle flying at hypersonic speed, using an airbreathing propulsion system based on supersonic combustion (scramjet) technology, requires a highly integrated system without moving parts, making the propulsion system and vehicle shape indistinguishable. A scramjet uses shock waves, generated by its inlet during the hypersonic flight to provide the temperature and velocity of atmospheric air to burn the hydrogen, at the combustor at supersonic speed. The divergent exhaust nozzle accelerates the combustion products providing the thrust. A two-dimensional hydrogen-powered generic scramjet has been designed to demonstrate supersonic combustion in atmospheric flight at a Mach number of 6.8 and an altitude of 30 km. Temperature and velocity at the combustion chamber are the most important key parameters for a preliminary design. The inlet configuration must provide a temperature higher than the ignition temperature of the fuel to guarantee spontaneous combustion and the velocity must remain supersonics. The nozzle exit velocity should be higher than the vehicle flight velocity to obtain sustained flight and produce enough thrust. For this theoretical analysis, the air is considered a calorically perfect gas without viscous effects. The compressible flow is analyzed based on oblique shock waves and one-dimensional compressible flow with friction and heat addition and Prandtl–Meyer coupled to the area ratio to describe each key component of the scramjet, such as compression, combustor, and nozzle sections, respectively. The inlet mass flow and hydrogen mass flow are also critical for the scramjet design to ensure stoichiometrically combustion at the combustion chamber, generating the high flow velocity at the nozzle to produce thrust.

A simulation of energy generation from Jatropha solid residues in a power plant in Jazan city, KSA

A simulation was needed to simulate generating energy from Jatropha plants’ solid wastes in combined cycle power plants. In this study, a simulation was built to simulate energy generation from gasified Jatropha solid wastes. Solid wastes from Jatropha plants' were generated from biodiesel production to produce 1.53 kg/s biodiesel. An assumption was made these solid wastes were gasified to generate energy. Energy production was simulated using DWSIM software. Solid wastes were classified into three categories; cake, shell, and husk. The amount of cake was calculated to be 1.62 kg/s, the shell calculated to be 3.6 kg/s, and the husk was calculated to be 2.16 kg/s. Therefore, the producer gas for each Jatropha solid waste was estimated according to the literature to be 3.65 m3/s for the cake, 4.86 m3/s for husk, and 8.1 m3/s for the shell. The simulation of generating energy from the syngas was validated using experimental data from the literature. Sensitivity analysis was conducted to find the optimum conditions. The results showed that the energy produced from Jatropha waste was higher than that produced from biodiesel. From the simulation, the net energy generated in the gas turbine section was 21.34 MW and from HRSG 12.472 MW. The water flow rate in the compression section of syngas was found to be 10.18 kg/s, which was converted to steam and added more power to the power plant.