Due to the high parallel efficiency, convenient handling of complex grids and the ability to handle complex boundaries, the lattice Boltzmann method (LBM) has been used for building wind load simulation in recent years. LBM large eddy simulation was employed to conduct a numerical simulation of the flow field for a high-rise structure with a twin-spiral weather radar tower. The applicability and accuracy of the LBM method in simulating structural wind pressure were tested through combined wind tunnel experiments. The non-Gaussian wind pressure distribution characteristics on the surface of the double-tower structure under multiple wind direction angles were investigated. The results show that the LBM large eddy simulation method can effectively simulate the flow field distribution characteristics of the twin-spiral weather radar tower. The change trend of wind pressure at simulated measurement points under multiple wind direction angles is consistent with the results of the wind tunnel experiment. There are significant non-Gaussian characteristics in the fluctuating wind pressure in the twin-spiral tower area. The non-Gaussian peak factor calculated based on the transformation process method is significantly greater than the value obtained from the sample assurance calculation. The local peak factor in the dual-tower area generally exceeds the recommended value of 2.5, and the local maximum value exceeds 5.0, which is significantly higher than the peak factor in the square area. The research can provide relevant references for wind load calculations and wind-resistance design of the twin-tower envelope structures.
The structural configuration of pentagonal three-four-strut alternated cable dome has the following characteristics: firstly, an arbitrary isosceles pentagonal grid is used at the ridge of upper chord; secondly, it is different from the traditional tension integral conception of Fuller, in which there are inclined multi-strut at the upper and lower chord nodes, which expands the upper chord grid and improves the stability of the overall structure. According to the joint equilibrium equation, a simple method for calculating the prestressing mode of pentagonal three-four-strut alternated cable dome is proposed with inner hole, and the general calculation formula of internal force of prestressed cable strut is derived. The formula calculation generates exact solutions. Calculations of 60 cases are carried out for different parameters of the structure, such as the number of lower chord ring cables, rise-span ratio, position of lower chord nodes and structural thickness adjustment coefficient, and the effects of different parameters on the pretension distribution of cable dome are discussed. The results of multi-parameter sensitivity analysis show that the prestressing distribution of the structure is not sensitive to the rise-to-span ratio, while the thickness-to-span ratio, the number of lower chord loops and the horizontal radius coefficient of the lower chord nodes have a greater influence and should be considered when designing the structure. The study of this paper provides a new scheme for the selection and design of cable dome.
To study the remaining fatigue strength and remaining fatigue life of existing stay cable wires with corrosion and fatigue damage, fatigue tests were conducted for steel stay cable wires under three different damage levels and no damage with similar tensile strength. Based on the fatigue fracture morphology characteristics, obtained are the characteristic parameters of corrosion pits as a fatigue crack initiation. Calculated are the stress intensity factors of corrosion pits, and investigated are the fatigue and fracture mechanisms of steel wires. The fatigue stress-life curves of steel wires with different survival probability are fitted using the least-squares method, and calculated are the reduction in remaining fatigue strength and life of stay cable steel wires . Revealed are the effects of damage degree caused by corrosion and fatigue, and the stress ratio on the remaining fatigue strength and life of steel wires . Test results show that fatigue cracks of steel wires without damage derive from the scratch on surface or slag inclusion. The fatigue cracks of existing stay cable steel wires mostly sprout at the corrosion pits with the depth more than 60 µm and the area more than 10000 µm2. The crack initiations at the corrosion pits are depended on the fatigue crack propagation threshold. The fatigue fracture of steel wires with existing corrosion and fatigue damage shows both ductile and brittle characteristics. The brittle characteristics of the fatigue fracture become more obvious for steel wires under more severe degree of the existing corrosion and fatigue damage. With the degree of existing corrosion and fatigue damage increases, the slope of the fatigue stress-life curves gradually increases, the remaining fatigue strength decreases significantly, and the fatigue limit at the inflection point of curves tends to disappear. The remaining fatigue strength of damaged steel wires decreases significantly with the stress ratio increases. With the damage degree of existing corrosion and fatigue damage increases, the remaining fatigue strength of steel wires decreases under the same stress range, and life reduction rates increase.
To analyze the structural damage characteristics of the semi-submersible platform column structure under ship impact loads and establish a safety assessment method for the column, impact experiments and numerical simulations are carried out based on structural shakedown behavior. The characteristics of the bearing capacity and indentation of the stiffened plate under the state of pseudo-shakedown are analyzed based on the quasi-static penetration test and the dynamic repeated impact test. The hardening model of the material and the damage model based on the B-W fracture criterion are developed by conducting the tensile tests, and the numerical simulations of the impact tests of the stiffened plate are carried out. The established numerical approach is applied to the impact response analysis of the column, and the critical elastic deformation energy of the column is obtained. The mass and velocity characteristics that the impact ship should meet to ensure the structural integrity of the column are given. A preliminary safety assessment guideline for the column subjected to ship impact loads is proposed, which can provide a reference for the analysis and assessment of the crashworthiness of the semi-submersible platform column structure.
The effect of train running on subgrade consists of vibration loading and intermittent loading. Conventional studies mostly focus on the effect of vibration loading, while ignore the strength and deformation recovery characteristics of soil in intermittent periods. The dynamic triaxial tests with different effective confining pressures, freeze-thaw cycle numbers, dynamic stress amplitudes and vibration frequencies were conducted to investigate the deformation characteristics of subgrade aeolian soil under intermittent cyclic load using the GDS DYNTTS. The deformation law of the freeze-thaw aeolian soil and its influencing factors under intermittent cyclic load were also analyzed. The results show that the cumulative plastic strain curves of aeolian soil include three types, e.g., stable type, developmental type and destructive type, under intermittent cyclic load. The strain accumulation of soil is largely weakened by the intermittent cyclic load, which results in a reduced deformation under continuous load. The dynamic stress amplitude is determined, by means of the extreme difference analysis method, as the most important influencing factor to the cumulative plastic strain. The effective consolidation confining pressure is the second, the freeze-thaw number is the third and the last one is the vibration frequency. The fractional-order mathematical model of the cumulative plastic strain under the intermittent cyclic load was established by using two Abel dashpot. The results are compared with the experimental results showing the model calculation results are in good agreement with the test results, which indicates that the mathematical model of fractional-order cumulative plastic strain can reasonably predict the long-term deformation characteristics of aeolian soil under the intermittent cyclic load. The research results can provide scientific basis for roadbed engineering design and disaster prevention in seasonal frozen soil area.
In cable-stayed bridges, the frequencies of adjacent cables’ local modes are close in value, resulting in the high probability of multiple internal resonances in the vertical plane. During the resonance, the coupled effect between cables transmitted by the beam, also named the coupled effect of cable-beam-cable, might intensify the cable’s vibration by changing the dynamic properties of the structure. To investigate the mechanism, considering the geometric non-linearity of the cable, a dynamic model, with eight cables and a variable-section beam, is established. The beam with multi-elastic supports in the model is reduced to a novel integrated dynamic system composed of discrete parametric lumped-mass beam segments. The dynamic equations of the model are obtained by the Galerkin method and amended by the difference methods. The modal properties of the model are solved by the eigenfunctions and verified by the finite element method. Moreover, the dynamic equations were numerically simulated by the 4th~5th-order Runge-Kutta method. The simulation results show that when the local modes of cables are “1∶1” coupled with different global modes, the vibration of cables are independent of each other, and the energy conversion only occurs between the resonant cable and the corresponding global mode. When multiple cables are simultaneously coupled to the global mode of a certain order, the phenomenon of multiple internal resonances can be observed in the model. The coupled effect of cable-beam-cable would affect the characteristics of resonated cables during the multiple resonances. Particularly, the coupled effect is mainly the excitation effect when coupled with the in-plane vertical global mode of the 7th-order. If the coupled effect was considered, the vibration amplitude of the cable would be excited to nearly twice that of the single internal resonance. Additionally, the coupled effect is inversely correlated with the distance between the cables and is positively correlated with the cable mass and the amplitude corresponding to vibration mode at the anchored position.
Proposed is a quasi-3D shear deformation plate theory that can be used for bending and free vibration analysis of functionally graded material (FGM) plates. The novelty of the theory is that it contains only four variables and takes into account the effect of thickness stretching. Based on this theory, the governing equations for the bending and free vibration problems of a functionally graded rectangular plate are derived using Hamilton's principle, and the analytical solutions of the bending displacements, stresses, and the fundamental frequencies of free vibration are obtained by using the Navier method. Comparing with the 3D theory, other quasi-3D plate theories containing more variables, and two-dimensional plate theories verifies the accuracy of the theory. Numerical results show that the theory proposed can effectively and accurately predict the bending and free vibration behaviors of FGM plates, and can significantly reduce the amount of computation.
The presence of fine polypropylene (PP) fiber with diameter ≤ 100 μm causes a fluctuation of the type I fracture strength in concrete. However, the mechanism of this phenomenon remains unknown, and the present mechanical models cannot describe the mechanical behavior of the fine PP fiber reinforced concrete (PFRC) due to the extremely expensive computational cost caused by the great number of fine fibers in matrix. To make up this gap, a mesoscopic discrete model is proposed by considering the improvement of water/cement ratio nearby PP fibers as the positive effect and the less mechanical contribution of fiber bridging force as the negative effect. The defining of the equivalent coefficient (rf) of fiber diameter makes it possible to simulate the mechanical behavior of PFRC. The numerical results show that the equivalent coefficient (rf) is recommended to be smaller than 10. The initial addition of PP fiber can increase the matrix strength, so that to slightly increase the PFRC type I fracture strength. The increase dosage of PP fiber causes the reduction of type I fracture strength due to the small strength contribution of fiber bridging force.
Seismic isolation structure system is an important means of disaster prevention and mitigation, which has developed rapidly in recent years. But its failure mechanism is different with other seismic structural system, and needs to be studied in combination with the superstructure and the isolation layer. The demand model and failure probability model of an isolated structure are established based on probabilistic safety assessment (PSA). According to the failure probability and the associated maximum damage probabilities of four failure modes of structure through vulnerability analysis, the weakest failure mode and optimized structure are found, so that the reliability of the isolated structure can be greatly improved. The demand function, failure probability function and maximum damage probability function are established based on a generic example and a practical engineering project, then the failure mechanism is studied, and the structure is optimized based on the presented theory, which shows the feasibility of the presented method.
The stress-strain relationship of recycled coarse aggregate concrete is the bridge to realize its mechanical analysis from material level to structural level, and is the cornerstone of the basic theory of recycled coarse aggregate concrete structure. The research progress made by the author's team in the stress-strain relationship of recycled coarse aggregate concrete over the years was introduced. Firstly, the influence of complex interfacial transition zones on the failure behavior of recycled coarse aggregate concrete was investigated by using the method of modeling recycled coarse aggregate, and the microscopic damage and evolutionary mechanism of recycled coarse aggregate concrete were revealed. From static to dynamic action, the experimental studies of stress-strain behaviors of recycled coarse aggregate concrete were carried out systematically under different working conditions, the influence of loading conditions on the internal force and deformation of recycled coarse aggregate concrete was investigated, and the corresponding mechanical and mathematical models were established. Furthermore, considering the temporal and spatial variability of the performance of recycled coarse aggregate, the probabilistic distribution characteristics of the mechanical response of recycled coarse aggregate concrete were found, and the stochastic damage constitutive relationship of recycled coarse aggregate concrete was proposed. Based on the obtained constitutive model, time-dependent reliability analysis and dynamic non-linear analysis of recycled coarse aggregate concrete members and structures were carried out, providing theoretical support for the safe application of recycled coarse aggregate concrete in practical engineering. Finally, relevant conclusions were extracted and future research work was prospected.
Conducting research on the dynamic shear behavior of fiber reinforced polymer (FRP)-concrete interfacial is of great significance to the evaluation and design of the impact-resistance of FRP externally strengthened concrete members. Firstly, a numerical simulation method for the dynamic shear behavior of FPR-concrete interfacial was proposed based on the concrete 3D mesoscale model and the zero-thickness cohesive elements of adhesive layer, and then it was validated through a comparison with the failure modes of bonding interface, interfacial shear stress-slip relationship and FRP strain time-histories of the dynamic single shear test and the improved notched beam impact test. Then, the experimental phenomenon of the failure interface transferred from concrete to adhesive layer due to the strain rate hardening effect of aggregate and mortar at high loading rates was reproduced. Furthermore, the influences of volume fraction of aggregate, aggregate type and mortar strength on the interfacial dynamic shear resisitance were analyzed. It indicates that the debonding loads and the peak interfacial shear stresses increase with the increase of aggregate volume fraction and mortar strength, while the aggregate type has little effect. Finally, through a comparison with the impact force-time histories, mid-span deflection-time histories and failure modes of impact tests on FRP-strengthened RC beams, it is shown that with the heterogeneity of concrete materials considered, the mesoscale model can more accurately simulate the FRP debonding failure, the shedding of concrete cover and the crack distribution of RC beams than that of the macroscale model, which demonstrates the applicability of this established method in the impact resistance analysis of FRP-strengthened RC beams.
By defining the inclined section where shear failure occurs in concrete beam without web reinforcement, the flexural behavior of the section is analyzed. And failure pattern of the section is predicted based on the bending moments in cracking and ultimate states. Then the shear capacity of the concrete beam is determined corresponding to the failing moment of the section. To simplify the calculation, a formula is proposed for shear capacity of concrete beams under concentrated loads. The rationality of the proposed formula is analyzed using test data of 680 concrete beams, and the reliability index is further evaluated by probability method. Results indicate that the proposed method is applicable for predicting the shear capacity of concrete beams without web reinforcement. The calculation results are similar to those of the relevant standards in the United Stated and Europe, and are equally conservative. The calculated shear capacity can meet the reliability index requirements of structural components that fail in brittleness with safety level II. This research can provide theoretical basis and design formula for the stipulation of new version standards in China.
In order to protect the bridge abutment from damage and destruction caused by vehicle impact, this paper proposes a new type of anti-collision energy-absorbing device to guarantee the safety of bridge abutment while absorbing part of the impact energy of the vehicle. Based on the nonlinear finite element software LS-DYNA, the numerical model of the new type of collision avoidance energy-absorbing device under vehicle impact is established, and its important energy-absorbing component - U-shaped damper is analyzed in detail. The classical low-speed impact test of steel plate and the impact test of reinforced concrete beam are simulated and verified, and the analysis results show that the numerical model used in this paper can better simulate the deflection, impact force and deformation morphology of steel and concrete under the impact. Based on this modeling method, the energy dissipation capacity and failure form of the U-shaped damper under different cross-sectional parameters are studied, the opening of the U-shaped damper is optimized, and the dynamic characteristics of ordinary bridge piers and the bridge piers protected by new anti-collision energy-absorbing devices under vehicle impact are compared. The results show that: the U-shaped damper reaches the best energy absorption capacity after the improvement of cross-sectional multi-parameter and the optimization of opening; under the effect of vehicle impact, the new type of anti-collision energy-absorbing device can play a good role in protecting the internal bridge pier columns, and it can be used in the bridge protection project.
To accurately study the influence of rock block shape on the shear mechanical properties of soil-rock mixture, proposed is a reverse reconstruction method of real rock block that can be realized only by camera and digital image processing technology, and established is a database consisting of 210 rock block models in 6 grain groups. Then, a fine modeling method of soil-rock mixture is proposed, and several different rock block sphericity models of soil-rock mixture are established, the numerical direct shear tests are carried out. The results show that: Most of rock blocks rotate along the shearing direction, resulting in an obvious "gear effect" and a "principal stress rotation"; With the increase of sphericity of rock block, the "gear failure" among rock blocks is more likely to occur, strong chains numbers and rotation angle are reduced, the thickness of the shear band becomes thinner, resulting in the reduction of the shear expansion, shear strength, internal friction angle and cohesion of the soil-rock mixture, among which the internal friction angle shows a linear decrease trend, and the cohesion decreases exponentially; In the backfill engineering, it is preferable to use the soil-rock mixture with low sphericity rock blocks.
To study the seismic control of tuned dampers for seismic isolated structures under near-fault pulse-like ground motions, the theoretical formulas for the optimal parameters of four typical tuned dampers, including tuned mass damper (TMD), non-traditional tuned mass damper (NTMD), tuned inerter damper (TID) and tuned viscous mass damper (TVMD), were compiled based on the H∞ and H2 optimization criteria. 100 near-fault pulse-like ground motions were selected as input, and the single-degree-of-freedom system was used to numerically simulate the seismic isolated structure. The effects of optimization criteria, damper type and mass ratio, period and damping ratio of seismic isolated structure, and difference of ground motions on the control effect are analyzed. The results show that the control effect of these four tuned dampers with the same mass ratio is TMD, NTMD, TID and TVMD in the order of low to high, and the design parameters should be optimized by the H2 criteria. The tuned dampers with a mass ratio of 0.1 reduce the displacement of the seismic isolation layer by 10% to 25% for the seismic isolated structure with isolation period less than or equal to 3.5 s and damping ratio less than or equal to 0.1. The control effect of the tuned dampers grows logarithmically with the increasing of mass ratio, and shows significant dispersion due to the difference in ground motions. The control effect of TVMD is significantly better than that of other conventional dampers under the condition that the element parameters are the same. The TVMD reduces or slightly increases the absolute acceleration response of the superstructure. Finally, it is recommended that the TVMD is preferred to control the seismic response of the isolated structure under near-fault pulse-like ground motions.
A time-varying fatigue reliability analysis method of steel bridges is proposed in the present study, which can consider the coupling effects of heavy loads and corrosion on the fatigue reliability of steel bridges. Taking a steel-concrete composite simply-supported bridge as an example, the investigated is the influence of average daily truck traffic, of equivalent gross vehicle weight and, of corrosivity grade on its fatigue failure probability. The calculated is the fatigue failure probability of its fatigue details under various working conditions, and the compared is the results of fatigue life calculated upon one deterministic analysis method and one reliability analysis method under various corrosion environments. The results show that: The proposed framework based on support vector regression and Monte Carlo simulation can calculate the fatigue failure probability of steel bridges quickly and accurately in corrosive environment; The increase of the average daily truck traffic, of equivalent total weight of vehicle and, of the level of environmental corrosivity will significantly shorten the fatigue life of steel bridges; The fatigue life estimated upon deterministic analysis tends to be conservative when the environmental corrosivity level is C5 and below. However, the results obtained upon the deterministic analysis may not be conservative when the environmental corrosivity reaches CX under which the environmental corrosion shall be fully considered.
Based on the advantages of ordinary flat plate shear walls (FPSWs) and of corrugated plate shear walls (CPSWs), a new type of flat-corrugated plate shear wall (FCPSW) is proposed, in which the infill panel consists of two flat panels on both sides and a corrugated panel connected by bolts in the middle. A specimen of FCPSW with a width-to-height ratio of 1.5 was designed and tested by cyclic loading, and the lateral performance, failure mode and, the collaborate lateral resistant mechanism between the flat and corrugated panels were revealed. The finite element method (FEM) was utilized to simulate the test, in which the lateral performance of FCPSWs was improved by applying the gasket plates to the bolt connection. Meanwhile FCPSWs were compared with the corresponding FPSWs and CPSWs pertaining to the lateral resistant behaviour. The wall-frame interaction in FCPSW system was investigated, including the additional bending moment to the boundary frame, the flexural rigidity requirement for the boundary frame columns, and the effect of vertical load. The test results show that: although multi-wave buckling occurred over the outer flat panel, and some bolts were detached from the panel, the lateral resistance of FCPSWs was still stable even with the storey drift angle increased to 5%. Comparison by FEA of different types of shear walls shows that: due to the interactive restraint between the flat panels and the corrugated panel, both buckling and deformation of the infill panel in FCPSWs are significantly reduced, which consequently results in high initial lateral stiffness and stable post-buckling resistance and reduces pinching in the hysteresis curve. The wall-frame interaction analysis shows that: due to the out-of-plane buckling of the flat panel and the corrugated panel being restrained, the additional bending moment acting on the boundary frame of FCPSWs is remarkably decreased. Generally, FCPSWs achieve a good lateral performance, and with flexural rigidity requirement less than that of the corresponding FPSWs, the vertical load effect is also less significant than that of the FPSW or that of CPSW counterparts.
Due to the difference in deposition and stress state, the anisotropy of natural soil is obvious. Based on Biot’s wave equation, Darcy’s Law, Lord-Shulman generalized thermoelastic theory and Riemann-Liouville integral operator, this paper adopts the normal mode analysis method to study the influence of permeability anisotropy on the saturated foundation with coupled thermo-hydro-mechanical multi-field under external loads. The normal mode analysis is a method to derive the analytical solution by using the weighted residual. By this method, the influence of anisotropy parameters and fractional order parameters on the physical variables under study is analyzed. The influences of the fractional derivative and the anisotropy of permeability coefficient on the physical variables such as dimensionless excess pore water pressure, vertical stress, vertical displacement and temperature in the foundation are mainly analyzed when the thermal load and mechanical source are considered in the upper surface. In addition, when the fractional derivative and the anisotropy parameters with the same physical meaning are taken as the same parameter, the anisotropic foundation model can be completely degraded into an isotropic saturated poroelastic foundation, which verifies the rationality of the foundation model. The results show that the variation of permeability anisotropy has obvious influence on all the physical variables except the dimensionless temperature when the thermal load is considered. It can be clearly seen from the curve with peak value that as the anisotropy of permeability coefficient increases, the peak value of the curve moves deeper to the foundation; however, it can be seen from the curve without peak value that as the anisotropy of permeability coefficient increases, the attenuation rate of the curve slows down. The research results can be widely used in the field of geotechnical engineering and have certain guiding significance for engineering construction.
To address the issues of strong independence and low generality of theoretical analysis methods for hinged floating bridges and continuous floating bridges, an elastic hinged multi-floating body model suitable for both hinged and continuous floating bridges is established through comprehensive application of the Kane method, the Euler beam theory and the potential flow theory, and the corresponding solution procedure is developed in this paper. The model validation is completed by comparing the observations and the predictions from relevant literature as well as the predicted results based on the hydrodynamic analysis software. Then, the influences of the elastic stiffnesses at the hinges on the dynamic responses of the system in calm water and wave conditions are investigated based on some case studies. The related calculation results indicate that increasing the elastic stiffnesses at the connections could nonlinearly reduce the motion responses of the system, but it will also significantly increase the bending moment at the connectors of the system, which is more pronounced when the wave frequency is relatively low. The amplitudes of heave and pitch motions of the pontoons at both ends decrease nonlinearly with the increase of wave frequency, and the motion amplitudes of the first pontoon are always greater than those of the others. In practical engineering applications, more attention should be paid to the motion response of the first pontoon of the floating bridge, and the overall dynamic characteristics of the floating bridge could be optimized through designing the elastic stiffnesses at the hinges appropriately.
Abstract: By testing the shear performance of 6 UHPC beams without Stirrups, considering the influence of steel fiber content and specimen size, and analyzing the test phenomenon, load-deflection curve and compressive strain of concrete curve arch under the shear action of the test beam, the influencing factors of the shear resistance of UHPC beams without ribs were discussed, and the test found that the size of the specimen showed a regular influence on the shear bearing capacity of the beam, and the larger the size of the beam, the smaller the nominal ultimate shear stress. When the specimen size is small, the addition of steel fiber can increase the ductility, stiffness and shear bearing capacity of the beam, but when the specimen size is large (h0≥490mm), the ductility of the beam cannot be increased; With the increase of the size of the specimen, the deformation capacity of the beam gradually decreases, the stiffness and brittleness increase, and the bridging effect of the steel fiber weakens with the increase of the specimen size. Considering the dimensional effect of concrete arch under beam shear resistance, the shear bearing capacity model of UHPC beam without ribs was derived, and the calculated value of the model was in good agreement with the experimental value, and the variability was small.