Abstract:A new method was proposed for the assessment of frame structure under seismic excitation in the lab with the consideration of pile-soil interaction. In this method, an inverse model was proposed to identify the dynamic response from the substructure, the model, which relates sensor's data to the working state of the piles in the test system, was used to reduce the errors caused by uncontrollable of substructure and uncertainty of soil.Test validation was conducted by an idealized frame structure separately in this model, equivalent linearization method and the rigid foundation assumption. Numerical simulation and the tests data show that, under seismic excitations, the soil would experience plastic stage at the beginning of the excitations, and the new proposed method had a great advantage in the simulation of the pile-soil interaction. For the top displacement in the test structure, maximum displacement was found in the inverse model, followed by the equivalent linearization method, minimum in the rigid foundation assumption; however, for the drift ratio and inter-story shear, the former order was inversed.

Abstract:For a new type of string reticulated mega-structure based on the concept of beam string structure and cylindrical reticulated mega-structure, five types of cable-strut arrangements were presented, and the influence of rise-span ratio on structural deformation in different cable-strut arrangement styles was also investigated. The maximum deflection, peak value of member internal force, horizontal support reaction, distribution of deflection and member internal force, ultimate load and buckling mode of the structure were analyzed and then compared with those of the corresponding structure without cables. The results indicate that the adoption of the prestressing system can significantly improve the structural deformation, peak value of member internal force and ultimate load. The static performance and stability of the structure can be improved most effectively when the struts and cables are arranged crosswise and symmetrically along the central wide range of span of the trussed arches, which is hereby the optimal arrangement scheme.

Abstract:Based on the existing experimental data, a finite model of HDCSW with steel plate concealed bracing under low-cycle load was established reasonably with nonlinear finite element analysis software MSC.Marc. The influence of axial compression, steel ratio, height-width ratio and span-depth ratio on the capacity and deformation performance of HDCSW with steel plate concealed bracing was analyzed systemically. If the axial compression ratio is greater than 0.4, the ductility of HDCSW with steel plate concealed bracing will be obviously decreased. When the relative ratio of the steel plate concealed bracing is between 0.96 and 6.73, it will improve the ultimate bearing capacity of HDCSW with steel plate concealed bracing. The height-width ratio and span-depth ratio have a major effect on the capacity and deformation performance. The research results of HDCSW with steel plate concealed bracings have a certain reference value with elastic-plastic calculation under seismic.

Abstract:Seismic design for buildings is usually subject to various uncertainties, often severe, which have the potential to undermine engineering decisions. It is crucial that these uncertainties be accounted for in seismic design. We formulated a performance-based seismic design model that takes into account uncertainty in the seismic design spectrum of the αmax and Tg. We used info-gap theory for satisfying the critical performance requirements, while at the same time maximized the robustness to uncertainty through nested optimization. The design implications of this robust-satisfying approach were demonstrated with a three-span six-floor steel frame design example. It is shown that design preferences depend upon the performance requirements considering the trade-off between robustness to uncertainty. Also, the result reveals that the proposed method provides a novel tool for the performance-based seismic reliability design under the lack of knowledge.

Abstract:Traditional tubular wind turbine towers may result in a great increase in the fabricating, mounting and transporting cost for large wind turbine systems. A new composite tower was proposed and then the structural optimization was carried out. The new structure is composed of a lattice tower at the bottom with four-angle combined cross-section legs and the steel tube at the top. The stability coefficients curve of the four-angle combined cross-section column subjected to axial compression was first obtained by a series of ultimate bearing capacity analyses. Considering the strength, frequency and slenderness ratio as constraint conditions, the shape and section optimization of the lower lattice tower was carried out. The optimal results show that the proposed structural system can resolve the scarcity of traditional tubular steel towers in transportation and has a 34% less steel consumption.

Abstract:The utilization of the input and output dynamic signals from multiple reference hammer impact method (MRIT) for modal flexibility extraction and structural damage identification was studied. Static and dynamic experiments on a Reinforced Concrete (RC) simply supported beam and a steel-concrete composite bridge deck were designed. MRIT was conducted on the simply supported beam and composite plate under different damage states, and modal flexibility was obtained in the test, which can be used to predict the displacement under applied loading. The beam test results demonstrated that the natural frequency decreased while the damping ratio and flexibility increased with the development of damage. Changes of natural frequency can only determine the existence of structural damage, while the changes of modal flexibility can indicate the damage location and damage degree of RC beam. Steel-concrete composite slab test results demonstrated that the differences between dynamic flexibility and static flexibility match well under the linear elastic state. Three damage cases were designed to simulate the damage situation on real bridges, which are the removal of cross diaphragm, changes of boundary condition and damage of connectors. By comparing modal flexibility information before and after structural damage, the damage of steel-concrete composite slab was achieved.

Abstract:The related constitutive model is needed when using fiber model to simulate the mechanical behavior of FRP confined concrete cylinder on OpenSees platform. Based on the skeleton-line constitutive model proposed by Jiang and Teng, the test results were compared with the calculation results under different peak stresses and strains, and more precise formulas were chosen and taken into the skeleton-line constitutive model. In the constitutive model, with the confinement effect of stirrup on core concrete taken into consideration, the ultimate tensile strain of FRP under hoop tensile failure was obtained by the reduction factors of ultimate hoop tensile strain. In addition, two different constitutive models were adopted to simulate the member according to whether considering the steel fatigue through the constitutive model. Both the relationship of axial stress and strain and the relationship of lateral strain and axial stress for the structural member were obtained, and the prediction results agreed well with the test results.

Abstract:Based on a local project of the sintered brick wall reinforced with steel mesh cement mortar, pullout inspection and standard cube compressive strength test were constructed. The field test adopts nine kinds of cement mortar with a strength grade of M10, M15, M20, M25, M30, M35, M40, M45, M50. According to the test results, we have obtained the formula of compressive strength of cement mortar thin layer detected by cast-in-place pullout method，inspected the model of linear regression equation and proposed the interval estimation for the individual value of the compressive strength of cement mortar, This paper provides not only a basis for technology popularization and application of cast-in-place pullout method ,but also a basis of the establishment of relevant technical standards for cement mortar field tests.

Abstract:The non-ideal boundary conditions (neither fixed nor hinged) of arch structure were considered as an elastic constraint with certain stiffness in different directions, and the nonlinear equilibrium equation was determined by using deformation geometric relation and energy variation principle. A circular arch under radial uniform load was taken as an example to establish the relationships between the external load and the internal force, and the radial displacement. By defining the shallowness and critical constraint stiffness, the snap-through buckling and bifurcation buckling were studied and the occurrence condition and distribution range were investigated. The buckling path and critical buckling load in the proposed method were in good agreement with the results from the finite element method. And the numerical method was used to study the buckling path and critical buckling load for different stiffness of elastic constraint. The results show that the critical shallowness and the critical constraint stiffness play a fundamental role in the buckling mode and critical buckling load for circular arch.

Abstract:The aerodynamic forces on a cantilevered circular cylinder with an aspect ratio of 5 were experimentally investigated in a wind tunnel. The diameter of the cylinder d was 200 mm. The oncoming flow velocity ranged from 5 m/s to 45 m/s, corresponding to Reynolds number of 0.68×105 ~6.12×105, which covered subcritical, critical and transcritical regimes. It was found that, although the cantilevered cylinder is in uniform flow, its aerodynamic forces present significant differences at various spanwise positions, indicating a strong three dimensionality. Reynolds number has profound effect on the aerodynamic forces on the cantilevered cylinder. The critical Reynolds number is smaller for the cantilevered cylinder relative to that of 2D cylinder. In the critical regime, reduction in the drag coefficient (Cd) of the cantilevered cylinder is relatively smaller compared with that of 2D cylinder. In subcritical regime, Cd of the cantilevered cylinder is smaller than that of 2D cylinder. On the other hand, Cd of the former is larger in transcritical regime. The critical Reynolds number is different at various spanwise locations for the cantilevered cylinder. Transition from subcritical to critical regimes occurs earlier near the free end of the cantilevered cylinder.

Abstract:A OSB webbed bamboo I-shaped joist connected and fixed by epoxy resin adhesive and nails was presented. The web height, shear span ratio and web stiffener were included as control parameters to see their effect on the flexural performance of 24 OSB webbed bamboo joists. The failure process, failure mechanism, deformation and carrying capacity were investigated and the shear capacities were also discussed. The results show that the composite joists show excellent combination performance, higher stiffness and strength. Also, the shear capacity of this joist has a close relationship with the shear span ratio and web height. When the shear span ration is less than or equal to 2.0, the failure modes were characterized by shear compression failure of the OSB web panels. The web stiffeners can markedly improve the ultimate load of the joists by 3.4%~38.0%, and is helpful to ultimate displacement and initial flexural stiffness by 1.7%~12.6% and 10%~30%, respectively. The web is higher and the growth is greater.

Abstract:The integral mechanic model of the non-loading rail cable launching system was established to deal with the stiffening girders construction in suspension bridge. The rail cable segment was discretized into two-node line element. And the governing equations for the rail cable launching system, which consists of the main cable, the sling, the saddle and the rail cable, were determined. Moreover, a 1∶33 reduced-scale experimental model for the rail cable launching system of Aizhai suspension bridge was constructed. The conclusions obtained from the theoretical analysis and experiments were compared. It is shown that the results of presented calculation method match well with that from the model test. Also, the accuracy and effectiveness of the proposed method are manifested, which can be used to solve the problem about rail cable launching system and simplify the calculating process. The calculation accuracy and results for this method can be employed to the initial-state analysis. This indicates that the recommended analytical method is suitable for shape-looking calculation and analysis of the non-loading rail cable launching technology.

Abstract:There are some inconsistency issues in the evaluation results obtained by different rock mass classification quality methods. According to the combination evaluation idea, several fundamental methods were introduced to build the model for the classification of rock mass quality. The Dempster-Shafer theory of evidence is a very rigorous uncertainty reasoning method with strong capability for information fusion and reflects the consistency and conflict of different information. This paper introduced the D-S theory of evidence to establish a new synthetic rule for the building of a new model of the combination evaluation. Then, due to the combination rule of D-S theory of evidence, which is difficult to define the basic probability assignment, Euclidean distance was introduced to build a method to define the basic probability assignment, and ultimately the combination evaluation method for the classification of rock mass quality based on D-S theory of evidence was established. Finally, a practical project shows that confliction exists in the three fundamental methods but D-S theory of evidence can solve this problem.

Abstract:According to the mechanical characteristics of pile-net composite foundation of high fill section of soft soil subgrade under embankment load, this paper made an in-depth analysis of the load transfer mechanism from the top to the bottom. Firstly, embankment soil was simplified as an inside and outside column. Then, according to integral differential balance between the inside and the outside soil column, the height of the initial plane of equal settlement can be derived and the soil arch effect of high embankment fill can be reasonably simulated. Secondly, when the load transfers to the geotechnical cushion layer, thin film is used to simulate the load distribution between the pile and the soil. Based on the results of previous derivations, pile-net composite foundation can be divided into geogrid, pile and soil elements between the pile bodies. The pile and the soil between the piles were simplified as an elastic support. The pile-soil stress ratio calculation formula of the high fill section pile-net composite foundation can be derived. Finally, this paper studied the main influence parameters of the pile-net composite foundation pile-soil stress ratio in the high fill section. The results show that, with the increase of embankment height, the pile-soil stress ratio decreases, namely, with the increase of fill height pile and soil, the load distribution tends to be more uniform, but the increase of pile spacing or the compression modulus will increase the pile-soil stress ratio. Furthermore, the increase of geogrid tensile strength will cause the increase of pile-soil stress ratio, but the influence of geogrid tensile strength is small.

Abstract:According to the phenomenon of statistical relationships showing different distributions, between the area and cumulative frequency of landslides in Ⅹ,Ⅺ seismic intensity of Ms 8.0 Wenchuan earthquake, 6 sandpile model tests under seismic were conducted with the increase of seismic peak ground acceleration ranging from 0.075 g to 0.450 g. The phenomenon of statistical relationships was reproduced by the tests between the amount and cumulative frequency of sand changing from power-law distribution to lognormal distribution, then to normal distribution, with increase of seismic loading. By mathematical analysis, the decrease of the coefficient of variation is the cause of probability distribution shift between power-law, lognormal distribution and normal distribution. Observed through experiments, the performance of grains on the surface of sandpile will show different models with the increase of seismic loading. Under weak vibration, the probability that the activity will die is overall balanced with the probability that the activity will branch. A large-scale collapse occurs when there is a chain interaction between neighboring grains. It has the greatest uncertainty. Under strong vibration, most grains start independently. A large-scale collapse becomes a certain event. Therefore, the scale of collapse is transformed from the chain reaction of unstable grains triggered by self-organized effect to the independent falling of unstable grains triggered by vibrating force effect, which is the physical mechanism of the reducing of Cv. According to the above realization, the phenomenon of the relation between area and cumulative frequency changing from power-law distribution to lognormal distribution with the increase of seismic intensity of Ms 8.0 Wenchuan earthquake may be universal.

Abstract:Based on uniaxial penetration tests and unconfined compressive strength tests, the effect of loading rate, asphalt-aggregate ratio, temperature, gradation types, and asphalt types on the shear strength of gussasphalt was analyzed. Through finite element numerical calculation for a structure of steel bridge deck paving, the shear strength parameters of gussasphalt were obtained and standard curves of the shear strength under different loads were drawn, and shear strength indexes were verified with experiments. The results show that, because of its material composition characteristics, the shear strength parameters of gussasphalt present a certain special variation law under the influence of different factors. Although gussasphalt meets the shear strength requirements under load conditions, lack of cohesive force will cause shear flow deformation of the mixture. When the shear flow deformation of the mixture caused by insufficient shear strength was analyzed in gussasphalt paving design, parameters such as cohesive force and friction angle should also be considered.

Abstract:Uniaxial penetration experiments can test the shear strength of asphalt mixture effectively. In this paper, the shear mechanism of asphalt mixture was analyzed by establishing a particle flow model of asphalt mixture uniaxial penetration test. Based on the microscopic mechanism of particle flow，this paper used discrete element technique to microscopically simulate the uniaxial penetration test of asphalt mixture. The stress-strain curve of the mixture was obtained, the simulation results were validated, and then, the microscopic mechanism of the asphalt mixture in the uniaxial penetration test was revealed. This paper analyzed the effect of the penetration rate, pressure head diameter and specimen size on the test results and proposed appropriate test technical parameters based on this, which provides technical reference for the penetration test. Combined with uniaxial penetration test and unconfined compressive strength test, a method based on discrete element method to determine the asphalt mixture shear parameters was proposed. A method was provided to explore the properties of asphalt mixture by adopting the micromechanical analysis method.

Abstract:Changsha is a typical zone hot in summer and cold in winter. By using the method of experiment, natural and mechanical ventilation's flow fields and temperature fields of a VDSF, which has been built in Changsha, its features were analyzed and compared. When the glazing spacing of glass curtain was 0.10 m,0.20 m,0.30 m and 0.40 m, natural ventilation could all be realized, and the effect of the latter two's natural and mechanical ventilation was very close. Also, the positions of the blind in the heat passage were studied, and the results showed that, when the glazing spacing was 0.40 m and the blind was located in the middle position or at a distance of 0.10 m from the external wall, the effect of natural ventilation and mechanical ventilation was basically identical. In order to find out the natural ventilation's optimum glazing spacing and the best position of the blind in summer, this paper has simulated four conditions with Fluent respectively, the glazing spacing was 0.30 m and 0.40 m, and the blind was located in the middle position at a distance of 0.10 m from the external wall. The results showed that, in summer, the natural ventilation's optimum glazing spacing is 0.30 m, and the blind from the outer glass is 0.10 m.

Abstract:Due to the horizontal air duct and the improperly connected square diffuser, the airflow entering the throat of the diffuser causes large disturbance. Consequently, it makes the diffuser's air supply uneven from all sides，and eventually affects the distribution of indoor air. To study the effect of the throat structure on the uniformity of air flow, this paper, based on the computational fluid dynamic (CFD), combined practical engineering tests, calculated and analyzed the air distribution of improved diffuser under different wind speeds and proposed an improved scheme of diffuser, namely, increasing the height of the diffuser throat and setting guide vanes with adjustable angles in the throat. And an improved diffuser test platform was established to get the contrast test data through experiments and tests. The test data show that the improved guide vanes can more evenly balance the air supply of the diffuser on both sides of the perpendicular to the flow direction, so that the diffuser can easily ensure the uniformity of the wind on all sides, and the uniformity of air distribution increases significantly. As a result, the indoor comfort level is improved substantially.

Abstract:As a new energy-saving air supply mode, stratum ventilation system has not been widely applied due to inadequate theoretical support. A mathematical model based on the characteristics of the indoor air flow was established to predict the vertical temperature profile in a stratum ventilated room. By combining the characteristics of indoor air flow with mass and energy equilibrium equations, this model gave the quantitative relationship between indoor vertical temperatures and boundary conditions such as heat source, enclosure radiation and supply air parameters. A comparative study shows that the predictions of this model fit the experiment values well. The model can represent the practical vertical temperature profiles in a stratum ventilated room. The analyses indicate that this proposed model has acceptable accuracy and can be used for practical engineering designs and energy consumption analysis.