Abstract:According to experimental sectional flutter derivatives, indicial functions are used to simulate the self-excited loads of a bridge deck section, and their recursive formulas that are essential in the implementation of FE analysis procedure are given. The procedure of time-domain flutter analysis, which is achieved by APDL language, is performed by the ANSYS software. Numerical results show that geometric nonlinearities have a negligible effect on the flutter threshold, but show a significant effect on the post-flutter properties. When geometric nonlinearities are included, the post-flutter ultimately leads to a limit cycle oscillation (LCO) with very small amplitude compared with a formidable divergence resulted from a linear method. Furthermore, the analysis results show that, in the case of linear analysis, the energy stored in the structure increases continuously as time progresses. However, this energy is limited in a quite low level (LCO state) when geometric nonlinearities are involved. Compared with the traditional divergence and catastrophic collapses, LCO results in significant cumulative damage. In view of this, other factors, such as the material strength and fatigue properties, are indispensable for further evaluation of the security and stability of bridge structures.

Abstract:In order to investigate the applicability of reactive powder concrete (RPC) and carbon fiber reinforced polymer (CFRP) in long span cable-stayed bridges, two cable-stayed bridges with the same span-length, 1100m, are designed for comparison. One is composed of steel stay cables, steel main girder, and ordinary concrete tower, while the other is composed of CFRP cable, RPC main girder and RPC tower. Dynamic properties and wind-resistant performances of the two schemes are analyzed and compared by using the finite element method. The results show that the two schemes show insignificant differences in fundamental natural frequencies, but the flutter stabilities for the RPC girder of the bridge with CFRP cable, RPC main girder and RPC tower is improved. The buffeting response displacement can be much reduced when the RPC girder and CFRP stay cables are employed. Natural frequencies of CFRP cables reach as high as 2 times of those of the steel cables. Compared with the steel cable, the vortex-induced vibrating amplitude of CFRP cables increases. However, the amplitudes of both schemes are very small, and hence they could have no effects on the structural safety. Rain-wind vibration amplitudes of CFRP cables can be as low as half of those of the steel cables. Moreover, critical wind speeds of the former are higher than the latter. In general, as far as the wind-resistant performance is concerned, RPC and CFRP can have an advantage over the traditional 3409 steel material in applications to long span cable-stayed bridges. In view of this point, it is feasible to apply high-performance materials, RPC and CFRP, to long span cable-stayed bridges.

Abstract:In order to study the influence of nodal rigid zone on the dynamic responses of a steel-concrete composite trussed girder bridge under high-speed train, one railway bridge is taken as a numerical example and the self-developed software TRBF-DYNA is utilized to calculate the dynamic responses of train-track-bridge coupled system. The whole three-dimensional model of the track-bridge subsystem is established by using finite element method, where each vehicle of the train is modeled as 31 degrees of freedom model by applying the rigid-body dynamics theory, and the spatial rolling contact model is used to simulate the interaction between wheel and rail. Firstly, the influence of nodal rigid zone on the bridge vibration characteristics is studied. Then, the effects of the nodal rigid zone and running lane on the vehicle running safety indexes and dynamic responses of local steel truss webs and global bridge are investigated. The analysis results show that the nodal rigid zone improves the stiffness of the bridge. Meanwhile, the maximum vertical displacement and vertical acceleration of the bridge are reduced by 30.00%~35.15%. Moreover, the internal force of steel truss webs increases significantly, particularly the bending moment increases up to 90.41%~224.02%, and the nodal rigid zone has little influence on the safety indexes of vehicle. Compared with single-lane driving, the dynamic responses of the bridge with double-lane driving are markedly increased, and the peak value of the lateral and vertical accelerations are increased by 114.29% and 100%, respectively. Stress of the steel truss webs increases, but it is not linearly increased according to the number of running lane. It is suggested that the influence of the nodal rigid zone should be considered in the evaluation of the dynamic responses of steel-concrete composite trussed girder bridges.

Abstract:By introducing two non-dimensional parameters related to the cable tension force and sag, in-plane nonlinear equations for motion of the suspended cable considering the temperature effect were derived. Firstly, the nonlinear partial differential equation was discretized by the Galerkin method. Then, the approximate solutions of the second and third order single mode super-harmonic resonances of the suspended cable were obtained by the multiple scales method, and the corresponding frequency response equations were also derived. Finally, the effect of temperature variations on the single mode super-harmonic resonances of the suspended cable with three different sag-to-span ratios was illustrated by the numerical calculations. The numerical results show that: in the case of small sag-to-span ratio, the nonlinear vibration characteristics would be changed by a certain degree of the temperature change quantitatively and qualitatively, the softening and hardening spring behaviors are changed, and it means that the degree and direction of the frequency response curves are changed. The single/multi-values of the excitation-response amplitude curves are also varied by the temperature variations. However, with the increase of the sag-to-span ratio, only some quantitative changes are found under the thermal effect. With the increase of the temperature change, the frequency response curves are bent to the left much more, and the softening spring characteristic is also increased. Moreover, due to the initial tension force of the suspended cable, the effects of warming and cooling conditions on the vibration characteristics of the suspended cable are not symmetric.

Abstract:The issue related to multi-model structural identification (MM St-Id) was experimentally researched based on sampling method of Bayesian theory. The concept and basic framework of MM St-Id method based on Bayesian theory were introduced, and then, the Markov chain - Monte Carlo simulation (MCMC) was utilized to build finite element (FE) model libraries. Since MCMC is not easy to converge and it has low calculation efficiency when the parameters have high dimensions, an improved MCMC sampling method for MM St-Id was introduced. The Matlab-Strand7 Application Programming Interface (API) strategy can be used to update the parameters of large structural FE model automatically. After the calibrated FE model libraries were established, they can be used to predict the responses based on the posterior probability distribution of the FE models. In order to verify the feasibility and effectiveness of the proposed theory, a numerical example of a simply-supported beam and an on-site large concrete-steel tubular truss arch bridge St-Id were investigated based on Bayesian theory and response prediction. A simple model St-Id method -genetic algorithm (GA) was used for comparison. The results showed that the proposed MM St-Id method based on Bayesian theory was much better in structural response prediction.

Abstract:For quantitative evaluation of fire endurance, this paper presented a prediction method on the fire endurance of post installed rebar beams exposed to elevated temperature. It was based on equivalent section method, which regarded initial sections as ladder sections by strength reduction of concrete and reinforcement under high temperature. The simplified calculation theory about the mechanical properties of members at ambient temperature and the calculation formula of the ultimate strength of single anchored rebar in fire were used. The feasibility of the theoretical calculation was evaluated through a comparison between the results obtained by the prediction method and the experimental measurements. The results showed that the fire endurance calculated by formula agreed well with the test data with the error of 15%, equivalent to about 15 mins. It was feasible to use this method to predict the fire endurance.

Abstract:To study the dry connections in precast shear wall structure, this paper presented a welded connection approach for precast shear wall vertical joint based on an existing advanced prefabricated composite wall system. By manufacturing and testing 5 specimens under monotonic static loadings, the shear pattern and deformability of the dry connection were studied. The results showed that the welded connection has a good shear patterns and deformability. The failure of the specimens began with the concrete cracks around the joints, and shear failure ultimately occurred in the connecting steel plates and anchor bars. Then, detailed analysis and comparison of material parameters were conducted by using finite element analysis software ABAQUS. It was observed that shear pattern of the welded connection was mainly determined by shear resistance of connecting steel plates, shear resistance of anchor bars, and compressive resistance of the concrete around pre-embedded steel plate, while longitudinal reinforcement, stirrup and pre-embedded steel plate had limited impact. It is concluded that this welded connection approach can be utilized for the vertical joint of precast shear wall.

Abstract:In order to understand the effects of endplate thickness, bolt diameter, bolt pretension, thickness of column flange, steel grade of endplate and fire temperatures on the behavior of high-strength steel beam-to-column endplate connections, a design concept that thin high-strength steel plate is used to replace the general thick steel plate is deeply discussed, and this paper presents a parametric analysis by using finite element modeling. The results presented herein show that with the increase of the endplate thickness, the initial rotation stiffness and peak moment increase, but the rotation capacity decreases. With the increase of the bolt diameter, the initial rotation stiffness, peak moment and rotation capacity increase. With the increase of the bolt pretension, the initial rotation stiffness increase, but no difference of the peak moment and rotation capacity occurs. With the increase of the column flange thickness, the initial rotation stiffness decrease, but the peak moment has no difference and the rotation capacity slightly decreases. With the increase of the steel grade of the endplate, the initial rotation stiffness remains, the peak moment increases and the rotation capacity remains when the steel grade of the endplate doesn't exceed Q460, while the rotation capacity decreases observably when the steel grade of endplate exceeds Q460. A proper design using a thinner high-strength steel endplate can achieve the similar load-bearing capacity and comparable or even higher rotation capacity, in comparison to a connection with thicker mild steel endplate, no matter at ambient temperature or after fire. Further, the failure mode of the endplate connections may be changed after fire, even from a ductile failure mode to a brittle failure mode.

Abstract:Exterior concrete wall panels are becoming one of the main building envelope wall for prefabricated steel frame structures as well as ordinary steel frame buildings, and the effect of exterior concrete wall panels on the natural period of steel frames cannot be ignored. The calculation method for the fundamental natural period of steel frame buildings in current design codes are summarized, and the feasibility of these formulas for steel frames with exterior concrete wall panels is evaluated by comparing the empirical results with the test data of a full-scale steel frame structure with autoclaved lightweight concrete(ALC) panels and the field measured data of a steel frame school building with precast concrete wall panels. The results show that empirical formulas considering the effect of wall materials can predict the natural period in a reasonable precision. Based on the field measured natural periods of the steel frames with exterior concrete wall panels, the empirical formula for estimating the fundamental natural period of the steel frame structures with exterior concrete wall panels is put forward. The structural height is adopted as independent variable in the empirical formula, and the fundamental natural period is a power function of the structural height. The results obtained from the empirical formula have little discreteness and agree well with the field measured data. The empirical formula may provide a reference to engineering designers.

Abstract:To screen out the basin long-period ground motion inputs, which could be used for the seismic design of supper high-rise buildings in basin, the formation mechanism of long-period ground motions was explained. Then, the dominance of surface wave in long-period ground motion was analyzed, and an approach to extract the coda waves of ground motions, which were dominated by surface waves, was put forward. Finally, the discriminant criterion of long-period ground motion was proposed through statistical analysis based on the characteristics of coda waves. The results demonstrate that the propagation, overlapping, and frequency-dependent amplification of the surface waves are generated by conversion of body waves at the boundaries of deep sedimentary basins, and plains are the main formation mechanism of long-period ground motions. The surface wave components in the coda waves of long-period ground motions are responsible for the maximum responses of long-period structures, such as supper high-rise buildings. The discriminant criterion of long-period ground motion is concluded that: the predominant period of velocity response spectrum (Tp) of ground motion is larger than 2 s, in addition, the ratio of the amplitude in the predominant period of velocity response spectrum associated with the extracted coda waves and original wave is greater than 85%.

Abstract:High-Frequency-Pressure-Integration tests were carried out in a wind tunnel by using rigid models to investigate the effects of architectural surfaces on the wind load acting on the cantilever roof, with emphasis on the height of ribs and the space of waves. The test results show that in the range of the selected parameters in this paper, the height of ribs doesn't change the mechanism of wind load, but the space of wave affects the mechanism to some extent when inflow and waves are intersected, resulting in the variations of the PSD of wind load and the wind direction of the maximum wind pressure case. When the height of ribs increases, the maximum wind suction keeps the same (wind direction is 0°), but the maximum wind pressure decreases (wind direction is 110°). When the space of waves increase, the maximum wind suction also keeps the same (wind direction is 0°), but the maximum wind pressure deduces (wind direction is 130°), especially on the part of wave.

Abstract:For wall jet model with co-flow used in the downburst, four turbulent models were used to analyze the flow characteristics of the wall jet with co-flow, including the average wind velocity profile and Reynolds stress at different developing stages. The results show that the prediction of the modified Reynolds stress model (RSM) is in close agreement with the experimental data. The modified RSM is effective and accurate for the wall jet with co-flow, and it is also used to investigate the effects of ratio of the wall jet bulk velocity and co-flow velocity on the wall friction coefficient and mean wind velocity profile. It is found that when β increases from 0.1 to 0.3, the mean velocity increases with the velocity ratio, the maximum velocity degradation becomes slower gradually, the wall friction coefficient decreases more rapidly, and the interaction between inner layer and outer layer is decreased.

Abstract:A new hardening non-Gaussian model based on Zhao and Lu model was proposed, by comparative analysis of the Winterstein's hardening model, and Ding and Chen model. Skewness error and kurtosis error of the new hardening non-Gaussian model are smaller than the existing hardening response models. The maximum Skewness error and kurtosis error is 0.311, 0.479, respectively. It is indicated that the proposed new hardening non-Gaussian model has good accuracy. At the same time, the proposed model extended the application range of the Zhao and Lu model. Finally, the new hardening non-Gaussian model was applied to simulate the hardening non-Gaussian processes, and Monte Carlo simulation method for the first passage probability of hardening structural responses was developed. Numerical example show that the proposed method has good precision for estimating the first passage probability of hardening structural responses. The long-span roof of Hanzhou New Train Station and the aqueduct of South to North Water Transfer Project were given for illustrating the use process of the proposed method.

Abstract:To control the cost of trough condenser, uniform design method was adopted to optimize its structure. Displacement and stress were considered as constraints, triangular truss’s rod sizes and the wing’s rod sizes were taken as quantitative parameters, and the initial tension of cable was set as qualitative parameter. Then, according to the optimized parameters, the three-dimensional model of trough condenser including steel types, quantity, length, quality and other information was established by BIM technology to calculate the cost of steels. The result indicates that uniform design method can be used to optimize the structure of condenser with qualitative and quantitative factors. Under the constraints, the cost of the condenser is reduced by 11.76% and the amount of steel is saved by 11.86%, which shows that the optimization is effective. The proposed method has a certain reference value for the complex optimization problems including quantitative parameters and qualitative parameters. The cost of steels according to the 3D BIM information model further proves the feasibility of the method.

Abstract:To analyze the moment-rotation relationship of the representative asymmetric mortise-tenon joint to through-tenon joint with gap, an embedment model of joint was constructed. The moment-rotation calculation formula of through-tenon joint was deduced by establishing the relationships of forces, materials and geometries. Existing tests approved that the theoretical calculation results agreed well with the test results. Furthermore, the effects of the gap g and the friction coefficients μ on bending moment and initial rotation stiffness of the joint were analyzed quantitatively, and the results showed that: the positive and negative initial rotation stiffness of the through-tenon joint decreased with the increasing gap g, and there is a linear change between them. The bending moment and rotational stiffness of the joint increased as the friction coefficient increased under the positive and negative loading, and they have a significant change, especially when the joint yields. Gap in joint is a main influence factor on the bending moment and rotational stiffness of the joint, and the influence of friction coefficient on the bending moment and rotational stiffness of the joint is slightly less than that of the gap. The study in this paper provides theoretical basis for the mechanics analysis of ancient timber framed buildings.

Abstract:To study the flexural capacity of internal prestressed glulam beams, the relevant conclusions of experimental research at home and abroad were summarized, the methods to predict the failure mode and the formula of the flexural capacity were proposed based on Bazan's constitutive relation model, the plane-section assumption and the limit strain analysis method. The computation examples demonstrated that the calculated results according to the formula were in reasonable agreement with the experimental data. The relationship between the flexural capacity and the effective tensioning force was studied, and it showed that the effective tensioning force could determine the failure mode, and the mechanical property parameters of the compressive zone were the key influencing factors of the relationship. The internal force of the tendons under tensile failure mode or compression failure mode was approximately linear with the effective tensioning force. The upper and lower limit of the effective tensioning force were defined, which indicates that the tendons yield when the failure happens, and tension failure and compression failure occur simultaneously. The analytical solutions of the upper and lower limit were also provided.

Abstract:In order to study the effect of saturation on the creep characteristics of transversely isotropic rock, creep experiments were conducted on transversely isotropic slate under saturated and dry state employing the RYL-600 microcomputer control rock rheometer by means of hierarchical incremental loading method. Some conclusions are drawn from these experiments as follows: There are four deformation stages, i.e., instantaneous elastic deformation stage, initial creep stage, constant creep stage and accelerated creep stage, under water-saturated and dry conditions. The instantaneous elastic modulus of water-saturated slate samples is less than that of dry samples under the same loading condition. Creep rate is steady, and there is no remarkable difference of the creep rate between water-saturated and the dry at low stress level. However, creep rate increases rapidly with the increasing load, and there is the opposite situation in two cases at high stress state level. The failure stress of water-saturated slate specimen is less than that of dry slate samples, and failure stress curves both present U-shape with the increase of bedding angle.

Abstract:The contradictory problem that “blocking” the solar radiation in summer and “receiving” the solar radiation in winter for buildings thermal design should be considered in hot summer and cold winter zone in China. In this paper, the typical building in hot summer and cold winter zone was analyzed by theoretical deduction, simulation calculation and experiment validation in order to obtain the effect of different envelope design parameters on internal and external surface temperature changes and heat/cold load demand. The results show that when the solar radiation absorption coefficient decreases from 0.9 to 0.3, the external surface temperatures of envelopes are reduced significantly, and the largest declines of the maximum temperature and the average temperature are 20.2 degrees and 6.9 degrees (roofs), respectively, but there is no change of the internal surface temperatures. By reducing the solar radiation absorption coefficient, building cooling load demand in summer can be decreased significantly, and nearly no effect on heating load in winter. The building heating load in winter can be reduced by increasing the thermal resistance of walls and roofs, and the thermal resistance and energy savings are approximately linear, but the effect of the thermal resistance on the building cooling load is less than building heating load, and there are “anti-saving” risks. This study is valuable, and will be helpful to design building envelopes and heat insulation so as to realize energy consumption reduction of the air conditioning in the whole year in hot summer and cold winter zone.