In order to examine the effect of reinforced ring plate on seismic performance of concrete filled steel tubular (CFST) T-joints with spherical-cap gap in CFST chords, a series of hysteresis tests were carried out on 12 CFST T-joints with the chord under constant tensile load and the brace subjected to cyclic axial loading. The performance of CFST T-joints was experimentally investigated in terms of the failure mode, load-displacement hysteresis relationship and strain development. The effects of chord-to-brace diameter ratio and diameter-to-thickness ratio of the CFST chord on the hysteretic behaviour of joint specimens were compared and analyzed. It was found from the test results that the reinforced ring plate could restrain the development of plastic deformation of the CFST chord with spherical-cap gap, and counteract the unfavorable influence on the bearing capacity, stiffness, ductility and energy dissipation capacity of the CFST T-joints caused by the gap. The bearing capacity of the reinforced joint specimen was more than 12.6% higher than that of the specimen with gap but without reinforcement, and it was even more than 6.5% higher than that of the specimen without gap. It was evident that with reasonable design of the reinforced ring plate, the unfavorable influence on the seismic performance of CFST T-joints induced by spherical-cap gap might be fully compensated.
Heterogeneous multicore clusters are becoming more popular for high-performance computing due to their great computing power and cost-to-performance effectiveness nowadays. Nevertheless, parallel efficiency degradation is still a problem in large-scale structural analysis based on heterogeneous multicore clusters. To solve it, a hybrid hierarchical parallel algorithm (HHPA) is proposed on the basis of the conventional domain decomposition algorithm (CDDA) and the parallel sparse solver. In this new algorithm, a three-layer parallelization of the computational procedure is introduced to enable the separation of the communication of inter-nodes, heterogeneous-core-groups (HCGs) and inside-heterogeneous-core-groups through mapping computing tasks to various hardware layers. This approach can not only achieve load balancing at different layers efficiently but can also improve the communication rate significantly through hierarchical communication. Additionally, the proposed hybrid parallel approach in this article can reduce the interface equation size and further reduce the solution time, which can make up for the shortcoming of growing communication overheads with the increase of interface equation size when employing CDDA. Moreover, the distributed sparse storage of a large amount of data is introduced to improve memory access. By solving benchmark instances on the Shenwei-Taihuzhiguang supercomputer, the results show that the proposed method can obtain higher speedup and parallel efficiency compared with CDDA and more superior extensibility of parallel partition compared with the two-level parallel computing algorithm (TPCA).
To optimize the empirical constants in dynamic stall model and improve the prediction accuracy of airfoil aerodynamic performance when dynamic stall occurs,the influence of pressure lag and boundary layer lag time constant on the dynamic stall performance is explored,using the B-L dynamic stall model and the wind tunnel experiment in the Key Laboratory of Wind and Solar Energy Utilization Technology of the Ministry of Education at Inner Mongolia University of Technology.The main conclusions are as follows.The time constants of pressure lag and boundary layer lag have great influence on the dynamic lift coefficient,which is related to the average angle of attack.When the average angle of attack is relatively small and the flow is between the attached flow and the separated flow,appropriately reducing the time constant can make the calculated results of the dynamic stall model closer to the experimental values.When the average angle of attack is relatively large and the flow is in separated flow or completely separated flow,the time constant value can be appropriately increased.The influence of pressure lag and boundary layer lag time constant on the dynamic drag coefficient is not significant.The dynamic lift coefficient only decreases with the increase of boundary layer lag time constant in the completely separated flow process where the angle of attack decreases gradually.
Fragility functions for structural members play an important role in the FEMA P-58 methodology for the seismic performance assessment of structures. In this study, fragility functions were developed for aged reinforced columns with corroded reinforcing bars. To this end, an experimental database containing 120 specimens subjected to repeated cyclic loads was compiled from 20 previous studies. The experimental specimens were categorized into three groups: no corrosion damage (NCD), low corrosion damage (LCD), and high corrosion damage (HCD). These damage states were identified by experimental hysteretic responses in terms of the drift angle, which are linked to common methods of repair, including structural repair, structural enhancement, and component replacement. The obtained drift angles were used to fit the log-normal fragility functions of the NCD, LCD, and HCD columns. The effect of reinforcement corrosion was examined by comparing the fragility functions of uncorroded and corroded columns. According to the principles suggested by FEMA P-58, the developed fragility functions were mostly judged to have a high level of quality. The fragility medians of the corroded columns showed a clear decreasing trend along with an increasing degree of corrosion damage. However, the corrosion of the reinforcing bars had a limited effect on the fragility dispersion. The maximum differences in the exceedance probability were calculated by comparing the fragility curves for the LCD and NCD columns, which were greater than 20 % for all concerned damage states. For the HCD columns, the corrosion of the reinforcing bars led to the maximum difference in the exceedance probability, even beyond 50 %, compared to the results for the NCD columns. The above results reveal the significant effect of the corrosion of the reinforcing bars. The specific fragility functions developed for the corroded reinforced concrete columns will facilitate the seismic loss and resilience assessment of aging reinforced concrete building structures.
A series of undrained cyclic shear tests was carried out on saturated coral sands, with different initial physical states, as they were subjected to rotations of 90 degrees in the paths of cyclic stress with various initial orientations under isotropic conditions. An important finding is that the cumulative dissipated energy required for liquefaction (W-s) was significantly affected by their fines content (FC), relative density (D-r), and effective stress of consolidation (p ' 0), but was independent of the conditions of cyclic loading. W-s increased significantly with the increase in p ' 0. When FC was less than the threshold fines content, W-s increased with FC and decreased with an increase in D-r. The equivalent intergranular void ratio (e*) was introduced to reflect the effects of FC, physical states of the particles, and inter-particle contact on the physical properties of coral sand. The results revealed a unique relationship between e* and W-s at p ' 0 = 100 kPa. Furthermore, the unified model of the relation between the normalized cumulative dissipated energy and the ratio of excess pore water pressure (EPWP) followed an arc-tangent function. This model can be used to characterize the generation of EPWP with the cumulative dissipated energy of fine-grained sand under isotropic consolidation conditions.
This paper presents the mechanical behavior of T-section steel reinforced concrete (TSRC) beam under pure torsion and bending torsion. 12 TSRC beams, varying in flange aspect ratio, steel ratio, volume stirrup ratio, flange longitudinal reinforcement diameter and torsion-bending ratio, were tested. The test results indicated that the reinforced concrete beam presents brittle failure, and the steel reinforced concrete beam presents ductile failure. There is a mutual constraint between the flange, steel and concrete of the specimen, and the flange and steel significantly enhance the torsional strength and ductility of the specimen. The optimum aspect ratio of specimen flange is 2.33; with the increase of steel content, the torsional strength and ductility of the specimens increased, with an average increase of 30.99 % and 73.58 %, respectively. The ultimate torque of the specimen increases with the increase of the bending-torsion ratio, with an average increase of 7.86 %. Finally, the calculation method of cracking torque and ultimate torque of T-section steel reinforced concrete beam is proposed, and the calculated results are in good agreement with the experimental results.
Due to the existence of joints, the flexural performance of segmental assembled girders is different from that of monolithic cast girders. In order to study the flexural performance of precast segmental assembled box girder with corrugated steel webs, a static failure test on a precast segmental assembled continuous box girder with corrugated steel webs and variable cross-section and a monolithic cast continuous box girder with corrugated steel webs of the same size was carried out. The influence of the existence of joints on the deflection, strain, and prestress increment of precast segmental continuous girder with corrugated steel webs was analyzed. The parameter analysis was further carried out by the finite element method. The results showed that, at the initial loading stage, the joint had little effect on the displacement, and the deflection of the segmental assembled girder changed more rapidly than that of the monolithic cast girder. In the monolithic girder, cracks mainly occurred at the middle-support position of the middle span and pure bending sections. In the segmental beam, cracks were concentrated in the concrete on both sides of the joint. The number of cracks was relatively small and concentrated in the concrete on both sides of the joints of the loading segment and the middle support segment. The trends in the strain growth in the segmental beam and MB01 were consistent, and the values were similar. The strain growth trend of the segmental girder and the monolithic girder was consistent, and the values were similar at the initial loading stage. The external prestressed tendons in the segmental girder had a greater role in the loading process than those in the monolithic girder, and the normal stress in the segmental girder increased more rapidly during the bending process. In the ultimate loading state, the external prestressing force of the segmental girder was 2.01% higher than that of the monolithic girder. The number of segments was inversely proportional to the flexural capacity of the structure. Excessive thickness of the adhesive layer would adversely affect the crack resistance of the structure. This study will contribute to the engineering application of continuous composite box girders with corrugated steel webs.
Zhutou Puzuo joint is an important component of Yingxian Wooden Pagoda. The study on the seismic performance of Puzuo for the protection of the Yingxian Wooden Pagoda is of considerable practical importance. The impacts of structural characteristics on the seismic performances of the Zhutou Puzuo are the focus of this study. Zhutou Puzuo models of the open-layer at the 3rd to 5th story are tested by the horizontal low cycle tests. Results show that: the more the number of Pu of the models with varied structural characteristics is, the stronger the energy dissipation capacity and the greater the horizontal bearing capacity are. In positive loading, rotational deformation of the Zhutou Puzuo is the predominated deformation, while both rotational and slip deformations predominate in negative direction. The proportion of slip deformation in components decreases with the increasing the number of Pu. In the negative loading, the proportion of slip deformation increases when the number of Pu decreases. However, slip deformation increases dramatically when the ears of Sandou or Qixindou between two adjacent layers are sheared in the negative loading. The maximum proportions of slip deformation of DG-1, DG-2 and DG-3 account for 51%, 47% and 87%, respectively. The sliding components of the Zhutou Puzuo at the 3rd to 5th story are primarily located in the middle and upper portions of the model. The research can give a solid basis for the safety and rehabilitation of Yingxian Wooden Pagodas.
Based on single-phase medium theory and unsaturated porous medium theory, the vibration isolation effect of setting a single-phase solid wave impeding block (WIB) in the unsaturated soil foundation under an underground dynamic load is investigated. Using the Fourier integral transform and Helmholtz vector decomposition, the calculation formula of the dynamic response of unsaturated soil foundation under an underground dynamic load is established by combining the boundary conditions. The influence of physical and mechanical parameters such as saturation, load frequency, embedded depth of WIB, thickness of WIB, and elastic modulus of WIB on the vibration isolation performance in unsaturated soil foundation is analyzed. The results show that in the case of underground dynamic load, setting a WIB in unsaturated soil foundation could achieve a better vibration isolation effect. The surface displacement amplitude decreases significantly with the increase of saturation, load frequency, embedded depth, thickness, and elastic modulus of WIB.
To improve the deficiency of the wave input method (WIM) in expressing complex incident site waves, in this paper, a random non-uniform wave input method (RNUWIM) is derived from the use of the random incident waves and the visco-elastic boundary condition. The random incident waves are generated and adjusted by the comparison of the horizontal ground motion's response spectrum and the target spectrum, so that they are representative of the actual wavefield in project sites. Furthermore, the RNUWIM is implemented and verified by the finite element method. The result shows that the RNUWIM inherits the advantages of the WIM in simulating the wave propagation effect and the radiation damping effect. In the new method, the spatial variation of ground motions such as time delays, peak variation, and time-history shape differences can be simulated synthetically. The errors of RNUWIM in ground acceleration, velocity, and displacement at the reference point are respectively 3.23%, 0.66%, and 0.07% in one case, which proves the efficiency of the RNUWIM in seismic response analyses.
Thin-walled steel tubes are widely used in conical cylinder steel towers of wind turbines, which are prone to local buckling when the diameter-thickness ratios are large, leading to a decrease in the bearing capacity of the towers. A new structural type of longitudinal stiffened steel tube for wind turbine steel towers was proposed, and six specimens were tested under compression-bending load to study the effect of stiffeners types and diameter-thickness ratios on the compression-bending behavior of steel tubes. The experimental results showed thatwith the same amount of the steel, the stiffeners could effectively prevent the local buckling of the steel tubes, resulting in changing the failure mode of the structure and increasing the plastic development, and thus improving the strength and ductility of the steel tube. The enhancement effect of T-type stiffeners is more significant. The experimental results were also compared with the FE model to verify the accuracy of the FE results. The ultimate strength of specimens was evaluated preliminarily by using the existing specifications, showing good agreement with the test results of the unstiffened specimens, while the ultimate strength of the stiffened steel tubes was underestimated.
This paper investigates the shear performance of high strength steel reinforced ultra-high (HSSUHPC). Test were carried out on seven beam specimens with the different parameters of web steel ratio, shear-to-span ratio, and steel fibres content in volume. The failure patterns and load-displacement curves were obtained. The bearing capacity, deformation capacity and strain variation laws of UHPC, steel web, stirrups, tensile longitudinal reinforcement and tensile flange of steel were analyzed. The experimental study established the finite element model of the shear performance of HSSRUHPC beams. The results of finite element fit well with the experimental results. Then parametric analysis was carried out. The results showed two shear failure patterns for the HSSRUHPC beam: shear diagonal compression failure and shear-compression failure. The mechanical process of the HSSRUHPC beam could be divided into four stages: the elastic stage, cracking stage, strengthening stage, and failure stage. There were two peak loads for the loaddisplacement curves. As the steel ratio of the steel web and yield strength of steel increased, the bearing capacity and deformation capacity of the HSSRUHPC beam increased. The shear-tospan ratio had a significant influence on the failure pattern of HSSRUHPC beam, and with the increase of the shear-to-span ratio, the bearing capacity of the HSSRUHPC beam decreased, but the deformation capacity increased. As fibre content increased, the crack resistance and deformation capacity of the HSSRUHPC beam were improved. With the increasing width ratio between the steel flange and beam, the bearing capacity of HSSRUHPC beam increased, but the change range decreased, so it is suggested that the width ratio between the steel flange and beam should not be larger than 0.6. As the stirrup ratio increased, the bearing capacity of the HSSRUHPC beam increased, but the availability of stirrups decreased, so it is suggested the stirrup ratio should not be over 3 %.
The Bouc-Wen-Baber-Noori (BWBN) model is a modified Bouc-Wen model. The BWBN model uses a differential mathematical model to simulate nonlinear hysteretic systems. And it can well describe the pinching effect of RC structures under strong earthquakes. However, the pinching function of the BWBN model is too complex, resulting in low computational efficiency. Therefore, this paper proposes a new modified Bouc-Wen (MBW) model by constructing a simpler and more efficient pinching function on the basis of the approximate Dirac delta function. The MBW model can realize the pinching effect with fewer parameters. The validity of the MBW model is verified based on the pseudo-static test data of three RC bridge pier specimens. The genetic algorithm is used to identify the parameters of the BWBN model and the MBW model. The results show that the MBW model proposed in this study exhibits higher computational efficiency and accuracy.
This paper documents the effect of surface conditioning on the lifetime and the efficiency under typical loading conditions.The experimental work to determine the influence of the mechano-chemical surface treatment TCG on the number of cycles until mechanical damage of the contact surface and assessment of the rolling resistance in comparison to an untreated specimen is described in this paper.The surfaces of the specimen are evaluated by both optical and tactile surface measurements.The tests principle consists of the rolling of the cylindrical specimen between three loading discs, while one of them is driven by an electrical motor and at the same time, a loading force is acting upon it.Mechano-chemical surface treatments are a proven way to reduce friction and wear of components in sliding contact, especially under mixed lubrication conditions, but have so far not been considered for the optimization of the rolling resistance of bodies.
A key feature for bipedal walkers (robots and humans as well) is their stability or disturbance rejection defined as the ability to deal with unexpected disturbances.The paper by Griffin and Grizzle ( 2017) have significantly contributed to the shift from flat ground to slopes and steps when evaluating the walking efficiency of their robots.Similarly, in this contribution, based on the appropriate model of robot dynamics and control law, we examine the stability of walking-without-falling for different ground perturbations for a threelink compass gait walker.I.e., we perform the sensitivity analysis of the walking stability of underactuated bipedal walker with respect to certain disturbation using the alaska/MultibodyDynamics simulation tool.
The paper deals with numerical analysis of cable-net systems supporting large facades of prominent buildings/halls.Following the former proposal and validation of the numerical model by the Authors the current paper provides some details on the modelling in ANSYS software.Based on the previous results the embodiment of glass panes and their rigidity for the apt description of the behavior is essential.The use of geometrically nonlinear analysis for the planar cable-nets with glass laminated panes attached to the net with point-fixed bolted connections comprising glazing bolt and spider fittings is described.The preliminary parametric study concerning the net arrangement is presented.
Biomechanical computational models used more and more in medical research as well as in clinical applications need mathematical description of soft tissues with their very complex mechanical behaviour.They show large deformations with stress softening during cyclic loading, being moreover time-dependent due to their viscoelasticity, anisotropic due to fibrous structure and dependent on tissue excitation in case of muscular tissues, including smooth muscle cells in arterial walls.They are capable to adapt to the acting load (tissue remodelation) and to self-repair (healing) in case of damage or failure (rupture of fibres, etc.)This paper deals with constitutive description of passive elastic response of soft tissues to the acting load and with the ways, how the anisotropic structure of the tissue can be reflected.For this purpose, the spatial arrangement of fibres in the tissue needs to be detected and mathematically described.Lack of data on fibre arrangement in soft tissues and their interpatient variability is a major limiting factor for anisotropic constitutive description of soft tissues.Some problems related to transformation of results of mechanical tests and histological analyses of arterial tissues into parameters applicable in constitutive models are addressed as well.
Using waste and raw materials in construction materials is vital for sustainable construction. In this respect, the use of discarded tire steel fibers (DSFs) is encouraged in the construction industry to decrease pollution. On the other hand, the production of commonly used industrial steel fibers (ISFs) involves emissions of CO2. Many studies have been conducted to evaluate the influence of discarded tire steel fibers (DSFs) on concrete. It is found that using DSFs in raw form could not improve the desired properties as ISFs do. Therefore, it is expected that using both ISFs and DSFs together can help achieve the desired improvements in concrete properties for various civil engineering applications. The main objective of the current investigation is the effective use of DSFs for developing eco-friendly, sustainable concrete. This study aims to evaluate the experimental properties of fiber-reinforced concrete, incorporating hybrid fibers (DSFs and ISFs together). Concrete specimens containing 0%, 0.50%, 0.60%, and 0.70% hybrid fibers by volume fraction are prepared. The hybrid fibers (HFs) comprise 30% of industrial steel fibers (ISFs) and 70% of discarded tire steel fibers (DSF) for each proportion. The 28th-day properties are examined. The slump and densities are determined. The experimental testing includes elastic modulus, compression (CS), split-tensile (SS), and bending testing (FS). The strength properties, deflection index, residual flexure strength, energy absorption, toughness index, and cracking behavior are reported. Moreover, the water absorption and linear shrinkage are also calculated. Except for the elastic modulus test, ASTM standards are used for casting and testing. A reduction of 45% in the LS and enhancements of 9.1%, 38%, 37%, and 23% are noticed in the EM, CS, SS, and FS of HFRC in contrast to zero-fiber concrete. Significant improvements are noticed in the properties of hybrid fiber-reinforced concrete compared to zero-fiber concrete.
: Multiaxial ratcheting is a failure mode of structures characterized by the accumulation of plastic strain due to cyclic loading. Despite several models having been developed to predict multiaxial ratcheting, they often fail when validated with experimental data collected under a wide array of loading conditions. In this study, an experimental setup was developed and an autonomous testing procedure was used to experimentally analyze the evolution of the yield surface shape due to cyclic biaxial loading. Thin-walled tubular test specimens were made of 304L steel with a diameter of 40 mm and underwent axial-torsional testing using the Instron 8852 system. The total axial strain was increased from 0 to 1% while the total shear strain underwent 5 cycles with the strain amplitude of 0.5% and the mean strain of 0.5%. Three yield surfaces were measured after the straining sequence was completed. Results showed strong directional distortional hardening and good agreement between the flow vectors and the normals to the yield surface, lending support to the associative flow rule.
