2014  Vol. 31  No. 3

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Overviews
Abstract:
Base isolation technology has significant advantages in the effect of vibration control, disaster reduction, as well as in social and economic benefits. The recent decades have witnessed a successful application of this technology in the field of architectural structures at home and abroad. This paper reviews comprehensively the research achievements of domestic and international scholars in terms of base isolation technology and the status of the latest development and application of isolation technology in high-rise buildings, and then summarizes the deficiencies of the current isolation technology research, hoping to provide a reference for further researches. Meanwhile, through the elaboration of the progress and deficiency of isolation technology, the direction of the development of this technology in Chinese high-rise buildings has been discussed, and it will promote the application of isolation technology in Chinese high-rise buildings to some extent.
Methodologies
Abstract:
The pounding behavior between adjacent girders is the main cause of the local damage or even collapse of bridges during an earthquake. In order to analyze the seismic pounding responses of bridges reasonably, a comparative analysis on the computational precision and application conditions of different contact element models in the seismic pounding analysis of bridges is made, based on the developed refined simulation platform FENAP. Four contact element models, including the linear spring, Kelvin-Voigt, Hertz and Jan-Hertz-damp models are lead in the FENAP, and a platform for seismic pounding analysis of structures is built. The influence of difference contact element models on the pounding responses of structures is comparatively investigated through the numerical verification and the numerical simulation of model tests under sine waves and earthquake excitations. The results indicate that the developed platform for the seismic pounding analysis of structures has a good precision and efficiency. Among the four contact element models, the Kelvin-Voigt and Jan-Hertz-damp models have higher computational accuracy and applicability, and the linear spring and Hertz models are only suitable for approximately elastic pounding cases with high restitution coefficients due to the inconsideration of the energy loss during a pounding process.
Abstract:
Conventional design of steel plate shear walls (SPSWs) assumes that 100% of the story shear is resisted by each infill panel, and the contribution of boundary frame is neglected. However, analysis results show that if the moment-resisting frame is used as boundary frame, whose contribution can not be neglected. Plastic collapse mechanisms of SPSWs subjected to lateral loads and design methods of SPSWs with moment-resisting frame were investigated in this paper. The design equation of vertical boundary elements (VBE) considering axial force was derived through mechanical analysis of horizontal boundary elements (HBE) and VBEs, and the shear distribution equation between infill panel and boundary frame was then determined. The feasibility of shear distribution equation was verified through the analysis of several one story, one bay SPSWs structures. Two 9-story SPSWs structures were designed separately by the conventional design method and the proposed design method considering boundary frame. Seismic performances were then evaluated by nonlinear time history method. For both designs, the maximum average story drifts of structures meet the requirements of Chinese seismic code, indicating the effectiveness of the proposed method. For the design using the proposed method, the total weight of steel is reduced by 6.48% compared with the conventional design, indicating the proposed procedure is more economic.
Abstract:
C1 natural element method for couple-stress (CS) theories was constructed when C1 natural element method was applied to CS theories. Considering the fact that the thickness of film is on the micron scale, which is close to the material characteristic length scales, the size effect of interfacial shear stress between film and substrate was studied. Numerical results illustrated that with decrease in the film thickness, normalized interfacial shear stress (defined as the ratio of the shear stress in the CS theories to that in the classical theories) decreased gradually, while the size effect became stronger gradually. For a given bonding strength, the shear stress in the CS theories was less than that in the classical theories, which implied that it is hard to debond in the CS theories.
Abstract:
The buckling analysis of long plates with two longitudinal edges either restrained by rotational springs or torsional stiffeners under uniform shear is presented using Rayleigh-Ritz method and numerical finite element analysis (FEA). By introducing generic non-dimensional parameters, i.e., orthotropic material parameters, restraint coefficients and buckling coefficients, the buckling formulas of long plates with two kinds of restraints are obtained using curve fitting technique. The analytical buckling formulas of long plates with two longitudinal edges restrained by torsional stiffeners can also be obtained by adapting the fitted formulas of long plates with two longitudinal edges restrained by rotational springs with a critical aspect ratio. The accuracy of the present approximate analytical formulas is validated with the numerical FEA and available solutions in the literature, and excellent agreements are reached.
Abstract:
An interfacial spring element model (ISEM) is employed to simulate the strength of concrete under uniaxial compressive loading. In this model, the concrete was considered as a composition consisting of aggregate, matrix, interfacial transition zone (ITZ) and initial defects in ITZ at meso level. The distribution and contents of the initial defects, and the ITZ properties parameters are discussed, accordingly which, the range of meso-parameters are suggested. The results show that the compressive strength of concrete decreases with the increase of the ITZ initial defects. When the initial defects in ITZ achieves to 30 percent of ITZ elements, the numerical simulation results of concrete compressive strength agree well with the experimental results.
Abstract:
Dynamics of plates, as well as its vibration control, is an important research topic in the design of engineering structures. In this paper, based on Hamiltonian formulism using the refined dynamic equation of thick plates, the vibration control of plate structures is investigated. By satisfying the boundary conditions of plates, vibration modes of thick plates were obtained. The independent modal space control was applied to achieve the active vibration control of cantilever plates. The calculated results were compared with those based on Mindlin plate theory. The results were analyzed and discussed through a comparison with numerical simulations. The research results of this paper can be applied to the analysis of structural dynamics and vibration control in modern engineering.
Civil Engineering
Abstract:
Composite soil nailing with pre-installed micro-piles is a type of economical and effective support system for deep excavation. The study on its design analysis method is however far behind current engineering practice. In this paper, the constitution and working performance of this type of composite soil nailing is first discussed, then the calculation methods for its global stability and deformation are studied and simplified calculation methods have been proposed. For the global stability checking, it is suggested to use the passive resistance force on a maximum characteristic-length of 2.5 times for the pile, which reflects the pile stiffness relative to the soil, to consider the contribution of the micro-pile to the global stability. A formula for the calculation width of piles under lateral loading is also given. Thereafter, a relatively simple method has been put forward for the stability analysis, which is proved to be reasonable through comparison with finite element calculation and some analysis of practical engineering projects. For the calculation of displacements of the excavated pit wall, a relatively simple and clear method has been proposed based on the incremental calculation method and the theory of a beam on elastic foundation by the careful consideration for the deformation mechanism of this type of supporting system. The calculation model, together with the load and stiffness parameter determination method, is established, and the validity of the method is also proved by the comparison with finite element analysis and field measurements.
Abstract:
In order to investigate the overall buckling behaviour and design method of Q420 high strength steel (HSS) angle columns under axial compression, a finite element model is developed through the finite element software ANSYS, which is validated against the test results and is utilized to undertake a large amount of parametric studies. The effects of the imperfections and Y/T ratio of steel on the overall buckling behaviour are elucidated, and the applicability of current design methods is analyzed. It is found that the effect of geometric imperfections is significantly related to the column slenderness and failure mode, and the effect of residual stresses is related to the column slenderness, whilst that of Y/T ratio is very slight. Design approaches for the overall buckling design method allowing for the local buckling are suggested for Q420 HSS angle columns, which contributes to the improvement of current steel structural design code, and has a potential application of HSS structures.
Abstract:
Ten large-scale specimens were designed based on hollow pier prototypes with rounded rectangular cross section used in high-speed railways. Hysteresis curves and failure mechanisms were obtained from cyclic loading tests under constant axial loading. The influence of each design parameter on the energy dissipation capacity and ductility of the specimens was further analyzed, and the shear performance of piers was evaluated using two empirical seismic shear capacity equations. Test results show that all specimens failed in flexure with flexure-shear cracks commonly observed at the bottom of the piers. The hysteresis curves had significant pinch and the skeleton curves rose slowly from concrete cracking to yielding. The displacement ductility reduced and the bearing strength increased with the increment in axial-load ratio and longitudinal reinforcement ratio. No pronounced effects of the volume-stirrup ratio on the ductility were observed due to the relatively low volume-stirrup ratio of the specimens. The longitudinal reinforcement ratio had notable effects on the shapes of hysteretic curves. Furthermore, increasing the longitudinal reinforcement ratio significantly improved the energy dissipation capacity of the specimens.
Abstract:
Snow loads are important in the design of large span latticed shell structures, and the distribution of snow on roof is non-uniform due to the effect of wind and temperature. Thusly, the problem how to determine the most dangerous snow distribution on single-layer spherical latticed shells is valuable. A method of location combination is provided in this paper to solve the above problem. In first step, the roof is divided into 8 sectors in the radial direction and snow loads are applied at different sectors considering all kinds of permutations and combinations, then the limited bearing capacity of the latticed shell was calculated and the most dangerous snow distribution in the radial direction was determined. In second step, the roof is divided into 6 locations in the circular direction and snow loads are applied at different locations considering all kinds of permutations and combinations, then the limited bearing capacity of the latticed shell was calculated and the most dangerous snow distribution in the circular direction was determined. In third step, the dangerous snow distributions in the radical and in the circular direction are combined together and the most dangerous snow distribution on spherical latticed shells can be determined. Results show that when the snow loads are applied at the outer two circles in the half-span roof, the limited bearing capacity of the latticed shell is lowest, which decreased 24.8% and 16.3% compared with full-span and half-span snow loads respectively.
Abstract:
In the research on the collapse of the structures under strong earthquake, the nonlinear dynamic behavior of tall reinforced concrete (RC) structures is influenced by the characteristics of the foundation soil. The assumption of a fixed-base model for this type of structure might not adequately represent their seismic response. Therefore, the seismic performance evaluation should take into account the soil-structure interaction (SSI). In this study, the seismic performance of a 10-story RC frame with fixed-base and flexible-base conditions is evaluated. The characteristics of the flexible-base models cover three types of soils, namely, soft soil, medium soft soil and medium hard soil. The ATC-40 spring model is adopted to represent the soil condition. The analysis results reveal that the roof displacement will be magnified when considering SSI. The inter-story drift angle in the first story will be increased obviously, and will be smaller in the second and above stories compared with the fixed-base model. The failure point will change from the bottom to the top of the column in the first story compared with the fixed-base model, while the distribution of plastic hinges will be concentrated in the lower stories, which reduces the capacity resistance of the frame.
Abstract:
The distributed monkey algorithm is established for the optimal sensor placement of multi-degree- of-freedom large structures. Firstly, the problem that the original monkey algorithm can only solve the problem of continuous variables is overcome by introducing the dual-structure coding method. Then, a new method is proposed that assigning large number of individual monkeys generated by the initialization to multi-group of monkeys in a specified way and performing the parallel search. Considering that the original monkey algorithm is able to step out local optimum while the harmony search algorithm has better local search capability, the two-step search algorithm is adopted based on the basic harmony search algorithm by collecting the preliminary optimum gotten by each group of monkeys as the original harmony memory to obtain the final sensor placement scheme. Finally, the parametric sensitivity analysis and the selection of sensor placement schemes are performed on the Dalian International Trade Mansion. The results show that the distributed monkey algorithm has better global search capability and it is applicable to the sensor placement of multiple-degree-of-freedom large structures.
Abstract:
Micromechanics-based fracture criteria of structural steels can be used to predict ductile fracture initiation with large scale yielding and no initial flaw. High-fidelity finite element analyses were carried out on ten welded connection specimens between the steel tube column and beam flange under monotonic tensile loading. The calibrated micromechanics-based fracture criteria, including Stress Modified Critical Strain (SMCS) model and Void Growth Model (VGM), were used to predict fracture initiation for each specimen. Good agreements were found between the predicted results and the test results. Therefore, it is applicable to use the micromechanics-based fracture criteria to predict ductile fracture initiation of connections under monotonic loading. Subsequently, the VUMAT subroutine was developed in ABAQUS software by the authors. By taking the SMCS and VGM as fracture criteria, the post-fracture load-displacement curves of two welded connection specimens between the steel tube column and beam flange that fractured at different locations were traced by deleting the failure elements one by one. The predicted results agree well with the test results, which indicates that these micromechanics-based fracture criteria and associated simulating techniques can be used to carry out collapse analysis of steel structures under extreme events.
Abstract:
Using an analytical method, the harmonic vibration characteristics of viscoelastic soil and lining structure are presented in the frequency domain. Firstly, the soil skeleton is treated as a viscoelastic medium with the fractional derivative constitutive relations. By the viscoelastic theory, the analytical solutions for the displacement and stress of the fractional derivative type viscoelastic soil are obtained, subject to a harmonic axisymmetric load. Secondly, the lining is treated as a homogeneous elastic medium. The lining is equivalent for a thin shell structure. The motion equation of the lining structure is established by the Flügge theory of a thin shell. The dynamic interactions of fractional derivative viscoelastic soil and the shell are analyzed. The expressions of undetermined coefficients are based on continuity conditions. Thirdly, the analytical results are compared with the analytical solutions from current existing literatures. Finally, the system dynamic characteristics are analyzed for different parameters of the soil and the lining by the numerical examples. It is shown that the system dynamic responses with a thin shell are greater than those with homogeneous elastic lining conditions; the response amplitudes decrease gradually as the modulus ratio between soil and lining increases. The parameters of fractional derivative constitutive have great influences on the system dynamic characteristics.
Abstract:
In order to study the numerical simulation method of the joints of reinforced concrete frame, numerical simulation is performed by using the Beam Column Joint element in the finite element software OpenSEES in this paper. Two principal factors have been investigated, including the inelastic shear behavior of concrete and the anchoring and slipping behavior of longitudinal reinforcement in the core area of joint. This element in OpenSEES is used to simulate a reinforced concrete side joint and five middle joints under low cyclic loading. The comparison of simulated result and experimental result indicates that the proposed model can be used efficiently in simulating the nonlinear response of joints.
Abstract:
The aerodynamic derivatives were expressed by the fluctuation pressure on the plate surface through rational simplification. The influence of fluctuation pressure distribution characteristics on the aerodynamic derivatives was studied by using of numerical simulation method based on the fluid-solid loosely coupled calculation strategy and existing fluid software user defined function (UDF). The influence of aerodynamic derivatives on the model vibration and aerodynamic coupling phenomenon were explained at micro level. The study shows that aerodynamic coupling flutter derivative which produced different action on the flutter depended on the model surface fluctuating pressure distribution. So the main factor of model flutter was determined by the fluctuating pressure distribution. The main component of fluctuation pressure was drifted to the model windward side in the flutter critical state, which caused the center of torsional vibration move forward and not coincide with the geometric torsion level.
Abstract:
An innovative concrete reinforcing technique of prestressed high strength steel wire (steel wire rope) mesh (PSWM) is presented. Approximate full-scale tests of 24 concrete circular columns strengthened with PSWM and 2 contrast columns were put forward to research the strengthening effects of main experimental parameters of the steel wire spacing and the prestressing level of steel wire under axial loading. The test results show that the peak stress and strain of the strengthened columns are 83% and 95% greater than those of the contrast columns. By raising the steel wire prestressing level, the reinforcing effect is improved; with steel wire spacing decreased, strengthening effect is greatly improved. The formula of peak stress & strain and 2 kinds of stress-strain full curve relationship models of the columns strengthened with PSWM were proposed. The calculated results agree well with the experimental ones and a theoretical support for related research. The presented technology is an attractive, nondestructive, and efficient reinforcement technology, worthy of popularization and application.
Abstract:
In this study, the early-age tensile stress development and cracking potential were investigated on cement paste and concrete. It was found that the cracking potential is closely related to the shrinkage rate rather than the shrinkage magnitude. A unique relationship was found exist between the shrinkage rate and cracking time for cement paste. The cracking time was then expressed as a function of a relative humidity (RH) drop rate and the aggregate content of mixtures. This study proposes a new methodology for evaluating cracking potential and has implications for mitigating early-age cracking in concrete members.
Abstract:
Based on the differential equation of shear-beam lateral free vibration and the up-right cantilever shear-beam model on a rigid half space, a spring-shear beam model is developed and the implicit analytic solution and recursion formula for single and random multi-layer site are derived, considering the elasticity of a half space. The influence to the calculation results of site natural frequency in the rigid half space assumption is analyzed by the spring- shear beam model. Results show that the error of calculation caused by rigid half space assumption decreased with the increase of modulus ratio and soil thickness. For common practice sites, if the covering layer thickness is not very small, there will be a good calculation precision using traditional shear beam method with a rigid half space.
Abstract:
The aseismic behavior of new type steel reinforced concrete (SRC) columns was simulated based on the finite element software, and the calculated results were compared with experimental results to ensure the correcteness of the simulation model. Furthermore, with abundant simulations, the effect of loading paths, the cycle times of displacemensts, the amplitude increment of displacements and variable axial forces were studied on aseismic behavior of the new type SRC columns. Because a biaxial coupling effect exists in the column, the aseismic behavior of the columns under a biaxial cyclic loading path is much lower than those under a uniaxial cyclic loading path, which indicates that the aseismic behavior of the column is influenced significantly by the loading path. Before reaching the yield load, the skeleton curves are not significantly influenced by the cycle times of displacements, but significantly influenced after the yield load. The more cycle times of displacements the smaller the peak load as well as the corresponding horizontal displacement and the displacement ductility ratio are reached, but its energy dissipation is larger. The effect of the increment of displacements on aseismic behavior of the columns under a biaxial cyclic loading path is much more significant than those under a uniaxial cyclic loading path. The yield displacement, yield load, and displacement ductility ratio are increased with the increase of the increment of displacements, but the energy consumption is decreased. The column under a variable axial force shows asymmetry apparently, and it is more adverse than the one under a constant axial force in the aseismic behavior.
Abstract:
A new kind of the self-centering post-tensioned precast connection (simplified as PTED) is proposed based on the concept of the earthquake resilient structure. The PTED connection is composed by precast beams, columns and angles that are connected by frictional high-strength bolts and tendons. Tendons, beams, columns and angles could be recognized as the components of the connection. In order to study the effect of components on the performance of the connection, a series of the low reversed cyclic loading tests were conducted. Firstly, tests of a PTED connection were made for studying the seismic performance of the integral connection. Subsequently, tests on the same connection were repeated to study the seismic performance of the connection with replaced new angles. Respective contributions of the angles and tendons to the performance of the connection were also investigated by the tests. The test results show that the combined effect of PT connection and ED connection consist of the overall performance of the PTED connection; the connection not only has good self-centering capacity but also performs well in energy dissipation; in general, beams, columns and tendons remain elastic and could be reused if the story drift is not more than 4%; in addition, damage of the connection concentrates in the angles themselves that are replaceable; seismic performance of the connection with replaced new angles is basically the same as the original one.
Abstract:
A Buckling-Restrained Brace (BRB) is an energy dissipation device of metal yielding and its advantages include the stable energy dissipation capacity, easy construction and fabrication with the low cost, etc. This paper presents the low-cycle fatigue tests of three partly-welded BRB specimens. The torsional buckling failure modes of the unstrained yield segment at the end of the BRB’s core brace are discussed and the theoretical formula is compared with the experimental results. Test results show that the plastic torsional buckling induces the failure of the BRB, which should be focused on and taken as an important failure mode. The effect of the BRB’s axial deformation on the torsional buckling failure is significant. When the axial deformation is larger, the critical stress of the plastic buckling is decreased and the actual axial stress is increased. Furthermore, the theoretical formula can accurately predict the torsional buckling occurance of an unstrained yield segment.
Abstract:
Based on the current seismic design specification, the additional damping ratio formula has been derived when lead dampers are mounted to a bilinear model structure which can be simplified as a single-degree -freedom system. The additional damping ratios under different seismic levels are studied. The results show that the additional damping ratio varies with the increment of the structural deformation. Before the structure yields, the additional damping ratio is increased at first and then decreased, while its elastic potential energy reduces after the structure yields. The additional damping ratio provided by the well-designed lead dampers increase with the increment of the structural deformation. The lead damper design principles and methods are also discussed.
Abstract:
In order to enhance the seismic behavior of reinforced concrete (RC) columns more efficiently, a method to strengthen concrete columns by using steel bar/wire mesh mortar (FS)was proposed. Nine RC square columns were produced. They were divided into three groups, namely FS strengthed columns, steel bar mat mortar (S) strengthened columns and a unstrengthed control column, respectively. A comparative experimental study under constant axial loading and lateral cyclic loading was carried out. Seismic bearing capacity, ductility, failure modes and hysteretic characteristics of all columns were tested, and the influence of reinforcement ratio, strengthening method and axial load ratio on the seismic behavior of tested columns was analyzed. The results show that the energy dissipation capacity of FS strengthened columns is significantly higher than that of the S strengthened columns and that of the unstrengthed control column.
Abstract:
In order to optimize the meridian curve of hyperboloidal cooling towers (HCTs), its influence on the dead weight effects and wind load effects of HCTs was illustrated through comparative analysis according to the slope of meridian curve and internal forces. An explanation for the Ferrybridge accident was also represented on the basis of the influence mechanism. Influence of the meridian curve can be classified into three types, local defects, existing of straight line and global curve. Local defects include fluctuation and leap of the slope of meridian curve which exacerbate internal forces, but it can be eliminated by minor changes of the local meridian curve. At the place where the meridian curve changes into straight line, the meridian axial force under wind loads will leap and then aggregate downward along the height in straight line. The aggregation is related to the length and slope of the straight line, and is not always adverse for mechanical performance; properly designed, the straight line in meridian curve may be more beneficial to mechanical performance than traditional hyperbolic curve. However, the latitude axial force in straight line will be aggravated under wind loads, so the local buckling problem should be examined carefully according to the BSS approach.
Abstract:
The Holmquist-Johnson-Cook (HJC) model is a computational model for describing the dynamic constitutive behaviours of concrete. In this paper, the HJC model was extended to describe the dynamic behaviours of rock. In order to rationally determine the parameters of HJC rock constitutive model, the relationship between the cohesion parameter and the cap model parameters was derived firstly based on the plastic yield surface theory. Secondly, the strength, pressure and strain rate constants were obtained based on the tri-axial compression test, the Hugoniot experiment, and the Hopkinson pressure bar experiment. Thirdly, the projectile penetration tests on Salem limestone targets were numerically simulated by using finite element program LS-DYNA, and the obtained parameters values were verified by comparison between the depth of penetration obtained from experiments and numerical simulations. Furthermore, the sensitivities of 19 parameters related with the HJC model were discussed, and the approach for acquiring HJC model parameters of general rocks was recommended. The proposed method was verified by comparing the penetration depth between the simulation results and the projectile penetration tests on high strength granite and Sidewinder tuff.
Abstract:
Aiming at the shortage of strain localization analysis on anisotropic sand, a non-coaxial theory was employed to improve constitutive model. The isotropy assumption in traditional plastic potential theory caused deficiencies that constitutive model can not describe non-coaxial features and can not give a better description of stress-induced anisotropy. To overcome such deficiencies, a three-dimensional non-coaxial critical state constitutive model for anisotropy sand is proposed with introduction of non-coaxial plasticity theory. In the view of the geometric relationship of micro fabric and stress state, the improved model can describe variation of sand state under the principal stress axes rotation condition, while the dilatancy and hardening law of model is a function of sand state. After amended with non-coaxial plasticity theory, the model can describe the non-coaxial features and stress-induced anisotropy, and the model with bifurcation theory can analyze the strain localization of anisotropy sand under different deposition angle and confining pressure condition. The improved model is verified against the results of simple shear and plane strain tests for Toyoura sand.
Abstract:
Based on the Unit Cells theory and the shear displacement theory, the pile-to-pile elastic coupling principle of mirroring image method was introduced, and shear displacement cell mode was built for analyzing the load transfer of piles in large pile group. The generalized shear displacement analytical expression was deduced by introducing the generalized shear displacement concept, which can be explained as a superposition of shear displacement and relative slippage of pile-soil interface. The iterative solving method was presented based on the pile tip displacement coordination condition. An case analysis reveals the effects of sparse piles space and the load level on the settlement-reducing property of sparse pile foundation. The load-displacement transfer characteristics of sparse piles and foundation are described. The contact mechanism of the sparse-pile foundation working property of the pile top relative displacement and the stiffness of the pile end bearing layer is explained. The validity of the model and the flexibility of the algorithm are also verified.
Abstract:
Tests on concrete filled steel tube column under pure torsion and compression-torsion cyclic load were carried out. The hysteretic curves from the tests were compared with the predicted results calculated by the laminated tubes model, and good agreement was found. Based on the laminated tubes model, the torsion mechanism of concrete filled steel tube columns was analyzed and discussed, including the internal force distribution, strain change regulation and main influencing factors. According to the results from laminated tubes model, a simplified formula suitable for practical design were proposed by the regression method for calculating the torsion capacity and axial load-torsion capacity interaction relations.
Abstract:
Textile-reinforced concrete has gained increasing popularity due to its favourable properties, namely corrosion resistance, anti-high temperature, better ability in anti-crack, ease and speed application and minimal change in geometry. The eccentric compression experiments of short columns strengthened by TRC on side were conducted under mainly different parameters, specifically in eccentricity, the load history and numbers of fibre sheet layers. The experimental results show that: the method strengthened by TRC on side is suitable for the big eccentricity column and the strengthen effect shows increasingly powerful with eccentricity; load history is harmful to strengthen effect, and the strengthen effect decreases while the load history increases; It is useful to increase strengthen effect by adding fibre sheet layers in some extend, but it shows decreasing trend. Finally, based on the related existing study and test data, the formula of calculating ultimate bearing capacity is proposed, and it shows a satisfactory agreement between the calculated and the experimental results.
Mechanical Engineering
Abstract:
It was shown in current literatures that the performance of a dry friction damper would significantly change while the excitation level varies. This phenomenon originates from the non-linear nature of friction, and as a consequence, there is only one most suitable excitation level for an individual dry friction interface. The present work is devoted to extend the working range of a dry friction system with respect to the excitation level, by introducing multiple dry friction interfaces into the host structure. The torsional vibration of the host structure is considered, modeled by the Lumped Parameter approach and the Coulomb assumption. Firstly, the feasibility of such a system is discussed based on the derived non-dimensional dynamic equations. Secondly, an enhanced time/frequency alternating method is proposed, with a full consideration of the relative motions which could possibly happen in each dry friction interface. It is proved through a numerical integration method, that the proposed method is a precise and rapid tool for the solution of nonlinear systems in a frequency domain. The dynamic behavior of such a system was investigated via several groups of parameters, including the number of dry friction interfaces, the critical frictional forces and damper mass and etc. At last, the damping characteristics of a 2-interface system and a 3-interface system are presented respectively, showing the procedure of designing such a system.
Other Engineering Disciplines
Abstract:
The performance of inflatable antennas critically depended on the shape accuracy of the membrane reflectors. Based on the non-linear finite element method, this paper explores the effects of boundary perturbations on the shape and stress of inflatable antenna reflectors of different focal-length-to-diameter ratios and diameters, as well as the reasons for these effects. Three kinds of distributions of boundary are focused on, including uniform distribution, local distribution and waveform distribution. The sensitivity analyses are respectively conducted. The effects of three kinds of boundary perturbations are compared in effect region, effect extent, sensitivity value and wrinkling. The study shows that: the effects of uniform and waveform perturbations act on the whole reflector. In the edge effect regions, the translation and curvature change of surface coexist. In the central regions, only the translation occurs. The effect of local distribution is limited to a local area. Among three kinds of perturbations, the uniform perturbation imposes the largest effect on the shape accuracy. However, the local distribution and waveform distribution have higher sensitivity values. All kinds of distributions except outward uniform distribution lead to wrinkling in effect areas. In addition, the influences of focal-length-to- diameter ratios and diameters are discussed. Based on the work presented, suggestions are given on proper strategy in passive and active control of the shape accuracy of inflatable antenna reflectors.