Large Slenderness Ratio Research Articles

カラマツのLVLを用いた座屈強度の評価手法に関する実験的研究

For the materials of the brace member in bearing walls of Japanese wooden houses, sawn lumber, laminted veneer lumber (hereinafter called "LVL") et al would be used commonly. Those members would be needed to resist compression and tensile force. Under the compression load, those member would be reduced the strength depending on the geometry. This phenomenon would be called buckling, and the evaluation of buckling strength is very important in structural design. In calculation of buckling strength, the Euler's method is famous and useful, so it is refered by some standard. For Standard for Structural Design in Japanese, we couldn't use that method directly, because timber material don't have the clear yield point. In our past study, we proposed a new method of evaluation method of buckling strengh, and evaluation method of yield strain from short-column compression tests. In this study, we would apply that method to LVL of Japanese Larch. For the material, the wood species is Japanese Larch, the strength grade is 100E in Japanese Agricultural Standard(hereinafter called "JAS"), and the cross-section is 45×90 mm. As a material tests, we conducted short-column compression tests and bending tests based on Japanese Agricultural Standard of plywood and LVL. We compared the yield strain from the both tests, and defined as a yield strain from short-column compression tests. The yield strain was almost 2400×10-6. Next we conducted compression tests with different length or different slenderness ratio with 50, 60, 79, 80, 100, 130, 150 and 190. From the compression tests we would get the some types of bucking strength, the one is the strength from southwell's method(σ1), the second is the maximum stress(σ2) and the last is yield buckling strength (σ3). As compared the σ1 and σ2, the both values would be almost the same. When we compared the σ1 and σ3 with large slenderness ratio, both values are almots the same. On the other side we could clear difference in both value in small range of slenderness ratio. The border would be called "limit slenderness ratio" theoretically. Then we focused on the ratio (σ2/σ3), between the 50 and 80 of slenderness ratio, we could find a difference between σ2 and σ3, and the ratio was bigger than 1.2. In the area from 80 to 190 of slenderss ratio, the ratio was almost 1.0. As a result, we could define the limit slenderss ratio was 80 in this study. In fact the elastic buckling occuered over 80 of slenderness ratio and the yield buckling occuered under 80 of slenderness ratio. Finally we would apply the Euluer's method for the evaluation of elastic buckling, Tetmjer's method and for the yield buckling. Then we could get the lower limit strength with combination of both method. In this method, we used 5% lower limit value in JAS for the Young's modulus in Euler's method, experimental 5% limit strength for the strength in Tetmjer's method.

Axial compression performance of steel/bamboo composite column

Abstract A new type of thin-walled steel tube/bamboo plywood hollow composite column with binding bars (SBCCB) that used transverse binding bars to reinforce the composite column was developed. The compression performance of 4 specimens with larger slenderness ratio was tested to examine the failure mode of the SBCCBs. The results indicated that the compression failure modes are mainly crushing failure of the bamboo plywood material, partial debonding failure of the adhesion interface and buckling instability failure; the ultimate bearing capacity of the specimens is not only related to net cross-sectional area and slenderness ratio, but also greatly affected due to binding bars. Transverse binding bars can ensure the integrity of the composite column, effectively reduce the debonding failure of the adhesion interface and significantly improve the load-bearing capacity of the SBCCBs.

Nonlinear similar design of large slenderness ratio truss boom

Nonlinear similar design of large slenderness ratio truss boom

Tests of self-compacting concrete filled elliptical steel tube columns

This paper presents an experimental study into the axial compressive behaviour of self-compacting concrete filled elliptical steel tube columns. In total, ten specimens, including two empty columns, with various lengths, section sizes and concrete strengths were tested to failure. The experimental results indicated that the failure modes of the self-compacting concrete filled elliptical steel tube columns with large slenderness ratio were dominated by global buckling. Furthermore, the composite columns possessed higher critical axial compressive capacities compared with their hollow section companions due to the composite interaction. However, due to the large slenderness ratio of the test specimens, the change of compressive strength of concrete core did not show significant effect on the critical axial compressive capacity of concrete filled columns although the axial compressive capacity increased with the concrete grade increase. The comparison between the axial compressive load capacities obtained from experimental study and prediction using simple methods provided in Eurocode 4 for concrete-filled steel circular tube columns showed a reasonable agreement. The experimental results, analysis and comparison presented in this paper clearly support the application of self-compacting concrete filled elliptical steel tube columns in construction engineering practice.

Full-scale field load testing of long drilled shafts with enlarged base constructed in marine sediment

ABSTRACTLong drilled shafts with enlarged bases are generally used to transfer heavy loads from superstructures to the underlying soils. Due to the large slenderness ratio, the load transfer mechanism for these long enlarged base-drilled shafts differs from that of a conventional drilled shaft. This paper presents field-instrumented, full-scale load tests on long drilled shafts longer than 58 m, including one straight and two enlarged base-drilled shafts in marine sediment. The field test results show that compared with straight shafts, the use of an enlarged base increases both toe resistance and shaft resistance. The drilled shafts with enlarged bases have higher load-bearing capacity. The shaft resistance and toe resistance were not simultaneously mobilized. The bottom sediment under the shaft toe has a significant influence on toe resistance and shaft resistance. Shafts having bottom sediment with a relatively large thickness exhibited lower shaft and toe resistance. Thus, the bottom sediment thickness should be strictly controlled.

휴대폰 애플리케이션을 통한 타워전망대 동적특성 분석

It is very important to calculate natural frequency of the observatory tower correctly because it is keenly affected by wind response vibration due to its large slenderness ratio, weight and small damping ratio. Additionally, suggestion equation of natural frequency being used in the design phase has considerable difference between actual measured value thereby making it inappropriate to be used in the serviceability design of the observatory tower. Therefore, this paper conducted an ambient vibration measuring on 10 observatory towers through mobile-phone application thereby calculating the natural frequency and comparing the result with the domestic and foreign standards and that of the eigen-value analysis. This paper suggested approximate equation of the natural frequency of the observatory tower; T=0.0266H. The square of the corelation coefficient is 0.940, which is high.

Aerodynamic characteristics of a spinning projectile with elastic deformation

The elastic deformation of a spinning projectile with a large slenderness ratio influences its flight stability and maneuverability. Unsteady time-accurate simulation based on a dual-time stepping method and the dynamic mesh method were used to solve the unsteady Reynolds-averaged Navier–Stokes (URANS) equations and obtain the aerodynamic characteristics of a spinning projectile given continuously elastic deformation. Archival wind tunnel experimental data were used, and grid resolution and time independence studies were carried out for numerical validation at angles of attack ranging from 2.09° to 10.4°. The aerodynamic coefficients induced by spin and elastic deformation were compared to the effect of movement frequency, deformation component, Mach number and angle of attack using Fourier transform. Numerical simulations indicate that the time-averaged values and the fluctuation amplitudes of the aerodynamic coefficients increase with movement frequency; two aerodynamic components are induced by elastic deformation, one opposite and one perpendicular to the direction of deformation; nose and body deformation have different effects on the aerodynamic characteristics; and the effective angle of attack induced by elastic deformation and rolling movement decreases as the Mach number increases, thus weakening the influence of movement on the aerodynamic forces.

Buckling Resistance of Axially Restrained Chord Members of Grid Structure at Elevated Temperatures

This paper investigates the behavior of large span grid structure exposed to a localized fire. The localized fire may generate hot smoke and thus induce non-uniform temperature distribution in the grid structure. The thermal expansion of the heated members tend to be axially restrained by the adjacent cold members thus inducing additional forces on the critical members of the grid structure. The buckling resistance of axially restrained member at elevated temperature may be obtained based on second order analysis of member with initial lateral imperfection by considering force equilibrium at deformed geometry and cross section resistance being reached. The critical temperature of the member is reached when the axial force reaches its buckling resistance. It is found that the critical temperature of members with initial lateral imperfection was higher than that without such imperfection for chord members with large slenderness ratio and high axial restraint.

Synergistic Effects of Chiral Morphology and Reconfiguration in Cattail Leaves

Cattail, a type of herbaceous emergent aquatic macrophyte, has upright-standing leaves with a large slenderness ratio and a chiral morphology. With the aim of understanding the effect of chiral morphology on their mechanical behavior, we investigated, both experimentally and theoretically, the twisting chiral morphologies and wind-adaptive reconfigurations of cattail leaves. Their multiscale structures were observed by using optical microscope and scanning electron microscopy. Their mechanical properties were measured by uniaxial tension and three-point bending tests. By modeling a chiral leaf as a pre-twisted cantilever-free beam, fluid dynamics simulations were performed to elucidate the synergistic effects of the leaf's chiral morphology and reconfiguration in wind. It was observed that the leaves have evolved multiscale structures and superior mechanical properties, both of which feature functionally gradient variations in the height direction, to improve their ability to resist lodging failure by reducing the maximal stress. The synergistic effect of chiral morphology and reconfiguration can greatly improve the survivability of cattail plants in wind.

A multibody dynamics model of contact between the drillstring and the wellbore and the rock penetration process

This article models the contact between the drillstring with large slenderness ratio and the extending rigid wellbore based on the multibody dynamics method. The drillstring is modeled as absolute nodal coordinate formulation beams with contact detection points. An algorithm is developed to locate the contact points and calculate the contact forces when the drillstring is sliding and rotating in the wellbore. This provides support force and friction for the moving drillstring and effectively confines it inside the wellbore. A rock penetration model is established based on the rock-breaking velocity equation. The governing equation for the full-hole drilling system including the drillstring and the contact model is established and solved. A rock penetration correction method is proposed to stabilize the computation and to model and simulate the slide drilling process. A field drilling process is modeled and simulated. The simulation result fits the experimental result well.

Experimental investigation on the stability of aluminium alloy 6082 circular tubes in axial compression

6082 is a relatively new alloy that currently provides the best combination of properties in 6xxx series alloys. A series of tests was conducted on the stability of heat-treated aluminium alloy 6082-T6 circular tube columns to check the reliability of buckling strength predictions of 6082-T6 alloy circular tube columns using current design rules. First, nine stub columns were tested to obtain stress–strain curves and three parameters of the Ramberg–Osgood expression (E, σ0.2 and n). The experimental stress–strain curves were in good agreement with the Ramberg–Osgood expression, and the mean value of σ0.2/n obtained from the tests was close to the Steinhardt assumption. Second, prior to column tests, the initial out-of-straightness of 15 circular tubes was accurately measured. Third, these 15 tubes, with five nominal slenderness ratios varying from 20.4 to 69.6, were tested between two pinned ends under axial compression to obtain failing modes and buckling strengths. Finally, the experimental buckling strengths were compared with the buckling strengths predicted by several current aluminium structure design codes, including the American Aluminium Design Manual (AA), Australian/New Zealand Standard 1664 (AS/NZS), and Eurocode 9 (EC9), as well as the general column curve formulation proposed by Rasmussen and Rondal [13]. These comparisons shows that the AA predictions are too conservative at small slenderness ratios, the AS/NZS predictions are unsafe at large slenderness ratios, the EC9 predictions are conservative, and the Rasmussen–Rondal formulation provides the closest and generally conservative strength predictions.

Experimental study on the fracture of lightly reinforced concrete elements subjected to eccentric compression

The objective of this work is to study the structural response of lightly reinforced concrete elements under eccentric compression from an experimental perspective. Given the difficulty of testing elements of a large slenderness ratio, an experimental campaign was carried out on columns of reduced size to facilitate material control and specimen handling, as well as to minimize the data scattering. Fifty-four micro-concrete specimens were tested to study the influence of reinforcement amount, slenderness ratio and load eccentricity. The applied load and the horizontal displacement at mid-span of the specimen (the additional eccentricity) were measured during the entire loading process, including the post-peak stage. At the same time, independent coupon tests were conducted for material characterization. Based on this study, a brittle–ductile classification according to the slenderness ratio and the initial load eccentricity is proposed. Meanwhile a methodology to evaluate the minimum reinforcement amount for reinforced concrete elements subjected to eccentric compression is formulated. In addition, the experimental results provide a valid source for modeling the behavior of lightly reinforced concrete elements subjected to eccentric compression.

The Design and Analysis of the Cooling System of NBI Thermal Shielding for EAST A# Equatorial Port

To avoid the thermal damage induced by the neutral beam to the neck tube of Experimental Advanced Superconducting Tokamak equatorial port (A#), a thermal shielding (TS) is utilized to withstand the high heat load. For the TS, the cooling system is designed including the interface with outer main loop. Several layouts of the cooling circuits are compared before a determined option. In particular, thermal–hydraulic transportation of the cooling system is investigated using a large slenderness ratio mesh model. And a discrete method for heat loading is developed. It indicates that the heat affected zones are appearing in a center gathered distribution but scattering in the surrounding area. And the central heat affected zone assumes the peak heat flux on the surfaces of the Mo tiles. This is the dominant factor to the layout of cooling pipes due to the temperature limitation of the TS materials. As a result, a non-uniform layout for the cooling pipes in the heat sinks is obtained based on the computational fluid dynamic results.

Effect of Temperature Change on Capacitance of RF MEMS Clamped-Clamped Capacitive Switch

The effects of temperature change on the pull-in behavior and on the capacitance of the RF MEMS clamped-clamped capacitive switch are quite heavy because of the larger slenderness ratio of the MEMS clamped-clamped switch beam. A one-dimensional three-stage static model with temperature change for analyzing the beam was presented based on the small displacement assumptions, in which the clamped-clamped beam was subjected to both the electrostatic forces and the temperature change. First, the model was used to calculate the capacitance of the RF MEMS clamped-clamped capacitive switch in different states. Then , the effects of temperature change on the capacitance of the clamped-clamped capacitive switch for some different geometry dimensions were analyzed. From the analysis the effect of some geometry dimensions, such as the length of the beam, the depth of the beam and so on, at different temperature changes on the capacitance can be understood and some conclusions may be useful to the design of the MEMS clamped-clamped capacitive switch with the temperature change.

Directional growth whisker reinforced Ti-base composites fabricated by laser cladding

New type Ti-base composite coatings with in-situ synthesized directional growth whiskers were successfully fabricated from a precursor mixture of titanium alloy and B4C powder by laser cladding. The typical microstructures, formation mechanism and properties of the reinforced composite coatings were experimentally studied for the purpose of developing novel hard facing coatings of titanium alloy. The results show that, there are two typical microstructures obtained in the composite coatings, i.e. the equiaxial composite structures and the columnar composite structures. The novel and interesting TiB whiskers, namely the directional growth TiB whiskers, are founded in the columnar composite structure zones. These TiB whiskers show uniform growth directions and display the characteristics of large slenderness ratio. The lengths of the whiskers are in the range of 10–30μm, but the diameters are of extremely fine size in the nanometer range. The microhardness of the coating is in the range of 430–520 HV and is about 150 HV higher than that of the substrate, which implies that these composite coatings are effectively reinforced by in situ synthesized TiB phases. The analysis shows that, solidification velocity R, temperature gradient G and direction of heat flow were the key factors to determine what kind of whiskers can be obtained.

Instrumented Static Load Test on Rock-Socketed Micropile

AbstractRock-socketed piles are often used to transfer heavy loads from a superstructure to competent underlying rock layers. The loads are transferred by the pile to the surrounding rock mass through shaft and base resistance. Several researchers have investigated the behavior of rock-socketed drilled shafts and related the uniaxial compressive strength of intact rock to pile-shaft resistance. However, the load-transfer behavior and load-settlement response of micropiles are different from those of drilled shafts because of the large slenderness ratio (pile length/pile diameter) of micropiles. This study presents results from a fully instrumented field-scale load test on a 0.2-m-diameter micropile socketed 4.2 m into limestone layers (2.7 m into weathered limestone and 1.5 m into hard limestone). The results show that practically no base resistance is mobilized until the pile-head settlement reaches approximately 7% of the diameter of the test micropile. The measured limit shaft resistance values are com...

Experimental and numerical investigation into the effect of carbon nanotube buckling on the reinforcement of CNT/Cu composites

Abstract Carbon nanotube reinforced copper matrix (CNT/Cu) composites with high strength and good damping have been developed using acid treatment, sintering processes and consolidation techniques. Strengthening of the composites as a result of nanotube buckling has been demonstrated by experimental nanoindentation tests and molecular dynamics (MD) simulations. The experimental results show that the buckling behavior of additional CNTs in the CNT/Cu composites varies with the slenderness ratio of CNTs. Specifically, this study shows that the significant buckling behavior of CNTs in the CNT/Cu composites where the shorter CNTs (with a smaller slenderness ratio) give rise to a global buckling and the slender CNTs (with a larger slenderness ratio) induce local buckling. The MD simulation results reveal that the buckling behavior of the CNTs plays a key role in increasing the mechanical strength of CNT/Cu composites by acting as a “buffer” in releasing excess strain in the Cu matrix.

Introduction of cooperating conductive components into the phosphor to improve the low voltage cathodoluminescence

In order to improve the electric conductivity of Y2O3:Eu3+ phosphor with the least amount of conductive component so as to maximize the improvement in low voltage cathodoluminescence, In2O3 and Cu nanowires (NWs) were simultaneously introduced to form Cu NWs/In2O3-attached Y2O3:Eu3+ phosphor. In2O3 and Cu NWs play different roles in the formation of electrically conductive network, i.e., Cu NWs are suitable as conductive channels for charge transmission due to their one-dimensional morphology with large slenderness ratios, while the island-like In2O3 condensates form local conductive contacts joining the adjacent Cu NWs. Meanwhile, In2O3 forms attachment between Cu NWs and the phosphor. Owing to the cooperating effects between Cu NWs/In2O3 conductive components in the phosphor, the efficiency in low voltage cathodoluminescence was significantly improved.

Determination of the Cutting Area Considering the Tool Slenderness Ratio for the Development of a 5-Axis Impeller Machining Automation CAM Module

The efficiency of applying 5-axis machining is higher for various products compared to general 3-axis machining, which is restricted to general parts and mold machining. However, impeller machining requires a large tool slenderness ratio to avoid interference with neighboring surfaces. Because such an enlargement of the slenderness ratio causes damage to the tools and deterioration of the quality of products due to the vibration of the tool, it is important to review the cutting characteristics considering the slenderness ratio and to determine the proper cutting conditions. Also, industry has attempted to develop a 5-axis machining automatic CAM module for an impeller that helps inexperienced workers to process the impeller easily by simplifying the process and options for the cutting impeller. The, current status of research on the cutting conditions considering the slenderness ratio to complete a database for a sub-module accounting for the cutting conditions among the components of an automatic CAM module is urgent. Therefore, the purpose of this work is to review the cutting characteristics that influence the cutting of aluminum alloy, the typical material of impeller parts, while also considering slenderness ratio to complete the 5-axis machining automatic CAM module of an impeller and to determine the available cutting area during the roughing and finishing operations.

Study on Capacity of High-Strength Angle Struts Connected by Single Limb

Experiment on bearing capacity of 24 Q460 high strength angle steel for compression members attached by one leg shows: the ultimate bearing capacity of the experiment value are higher than the calculated of the “Design of Latticed Steel Transmission Structures” (ASCE10-1997), on the same section in different slenderness ratio of components, the larger slenderness ratio, the higher the ratio; while on the same slenderness ratio in different sections, the greater width-thickness radio, the greater the ratio. Based on this problem, analyzing the current standard, a set of formulas based on high-strength angle struts connected by single Limb was brought, which can used for the design of the Q460 high-strength angle.