Abstract:In order to study the influence of external platform width on wind loads of large-span buildings, wind tunnel tests of six rigid models with various platform widths were carried out. In particular, the characteristics of mean wind pressure coefficient and fluctuating wind pressure coefficient were studied. The test results show that the enlargement of platform widths increases the mean wind loads. The mean wind loads change from small to large and to small again with the increase of platform width. The most unfavorable situation occurs when the platform width is 12 meters, and its growth rate reaches 33%, while its growth rate is 20% when the platform width is 20 meters. Meanwhile, the increase of platform widths increases the fluctuating wind loads. The most unfavorable situation takes place when the platform width is 12 meters, and its growth rate reaches 11%, while its growth rate is 8% when the platform width is 20 meters, and the rate is lower than 5% in other cases. The fluctuating wind loads on the leeward side decrease when the width of platform increases. The maximum decrease reaches 7% when the platform width is 20 meters.

Abstract:The relative oscillation between the strands of the suspension bridge hangers could be effectively mitigated by means of rigid spacers, but the hanger-spacer system may experience overall translational or torsional vibrations. In this paper, based on a four-strand hanger of the Xihoumen Bridge, the ANSYS software was utilized to establish three kinds of computational models for the hanger-spacer-damper system, and a series of free vibration analyses were carried out to study the characteristics of the universal curve for the torsional modes considering the effects of support stiffness and damper stiffness. The results show that the universal curves are affected by the torsional modes, and a unified universal curve cannot be used for the design of the dampers for different torsional modes. The realizable maximum damping ratio for torsional mode and its corresponding damper coefficient reduce with the decrease of the support stiffness. However, the realizable maximum ratio for torsional mode decreases with the increase of the damper stiffness, but its corresponding damper coefficient increases.

Abstract:Laboratory model tests on steel piles embedded in cohesive soil were carried out to study the transformation law in relation to ultimate uplift capacity and displacement patterns of uplift piles subjected to oblique loads. The test results show that the side of the pile near the oblique load is always under pressure, while the other side is in tension all the time, which differs from the uplift pile subjected to vertical loads. After reaching the ultimate capacity, soil in some depth is cracked only around the side close to oblique load. The failure surface occurs below the top of the pile. The failure area on the earth surface is distributed as a fan, whose range becomes larger with the increasing inclination of loads. Meanwhile, the ultimate capacity of piles increases with the increase of the inclination angle. On this basis, the calculation model of uplift piles subjected to oblique loads and the formula of failure surface around the pile were established based on the failure mode. Moreover, according to the analysis on the equilibrium conditions of the soil element, a formula for estimating the oblique capacity of uplift piles in clay soil subjected to oblique loads was also proposed. The predictions agree well with the test results so that the formula can be used in practical engineering.

Abstract:The soil resistance is a nonlinear function varying with depth, and it is related to the effect of location in slopes. The simplified model for a pile-column bridge pile and the total potential energy equation of pile-slope system were presented by considering the slope effect. The analytical solution of the critical load and calculated length were derived based on the energy method. In this respect, verification between the measurement and theoretical solution was conducted by dissimilar conditions in plain and slope. The parametric study shows: the increase of the Young's modulus of the pier column or decrease of its free length enhances the stability of the pile foundation; the appointed elastic modulus of pier column corresponds to an optimal column-height, and the best stability is achieved while the ratio is in the range of 0.3 to 0.4. Moreover, a key conclusion from observations is that the bridge pile should be located at the slope with the gradient less than 35° for safety. However, the correlation between m and α is of significance so that it needs to be further investigated.

Abstract:This paper studied the vehicle dynamic performance of orthotropic steel deck (OSD) bridge at fatigue details, based on a series of field tests on a 35 t 3-axle calibrated tractor across Fochen New Bridge (a three-span continuous steel box-girder OSD bridge) as well as finite element analysis. The results of the field tests were first filtered to remove the noise signal. The strain range and cycle times of each strain gauge were then obtained by using rain flow method. The impact factors of fatigue details were eventually calculated. The research shows that in both the crawl case and general speed case, the OSD bridge has obvious vehicle-bridge coupling vibration. Due to the differences in local stiffness and geometric construction at each fatigue detail, the impact factors at each fatigue detail exhibit different values. For instance, the impact factors of steel deck, U-rib, and cut-out in diaphragm are 0.219, 0.245, and 0.394, respectively, which are all larger than 0.15 specified by “Orthotropic Steel Bridge Design and Maintenance Guide” and AASHTO specification. Therefore, the current vehicle design specification underestimates the vehicle dynamic response of the OSD bridges.

Abstract:The finite element software ANSYS was used to investigate the nonlinear stability of single-layer spherical latticed shells with hexagonal connection form. Firstly, a reasonable grid layout was determined by analyzing and comparing the stability of two types of honeycomb spherical latticed shells. A large scale parametric analysis was then carried out, including the influences of the span, raise-span ratios, grid size, initial geometric imperfection, asymmetric load distribution, and material nonlinearity on the stability behavior of honeycomb spherical latticed shells. The results show that the grid of typeⅠexhibits better overall stability capacity for two kinds of grid configurations of single-layer honeycomb spherical latticed shells. It is also suggested that the span should not exceed 40 m. The overall stability of the net shell is better and material utilization is higher, when the rise to span ratio is close to 0.25 and the bar length is about 2 meters. Meanwhile, the material nonlinearity has a great effect on the stability of the bearing capacity for single-layer honeycomb spherical latticed shells, and the bearing capacity of latticed shells is decreased by 50%. However, the critical load of latticed shells is reduced by 52% when the initial defects reach 1/150 of the span. Moreover, it is found that the reticulated shells are not sensitive to the asymmetric loads.

Abstract:In order to unify the discrimination method of failure members in progressive collapse analysis for large-span spatial grid structures, the selection method of probable range for the important members was put forward based on the failure modes of buckling and strength. A novel analytical method, known as multiple responses, was then introduced based on the primary scope. This proposed method was eventually implemented in the mechanical analysis of the main stadium for the Universiade Sports Centre. The arrangement of the important members for folded-plane latticed shell structures was established. It is found that the computation results agree with the design results well. It is shown that the novel analysis approach is suitable for the evaluation of the structural performance of the important members in large-span spatial grid structures. The deficiency of current methods that single structural response is only considered is made up. The problem that the unified standard is not given for the members to be removed of spatial grid structures in progressive collapse analysis is also solved. Moreover, the alternate load path method will have extensive applications.

Abstract:In the shear strengthened reinforced concrete (RC) beams by externally bonded fiber reinforced polymer (FRP) composite, there are some main shortcomings including low fiber utilization, premature debonding, and stress hysteresis of the FRP, etc. In order to address these problems, this paper independently developed a novel prestressing system for U-shaped FRP sheet in shear strengthening, which consists of three parts: anchor device, tension device, and steel angle. The design method of component size and the prestress construction technology were presented. Furthermore, a prestressing system for 2-ply and 50-mm-wide FRP sheet was designed and manufactured. One bearing capacity test of linear FRP sheet and eight prestressing loss tests of shear-strengthened FRP strips were conducted in this system. The test results show that: the prestressing system can effectively anchor FRP and result in rupture failure; fiber strength increases up to 96.1%; design method of component size is safe and reliable; prestressing construction technology can exert different prestress values to FRP strip based on the uniformity and symmetry of the strip stress; the system is applicable to exert the prestress more than 244.84 MPa to the FRP; and the long-term prestress loss ratio is about 15%.

Abstract:Based on the secondary development platform of OpenSEES software, this paper studied the restoring force model of unbonded partially prestressed concrete beam sections. According to the statistics of experiments and theoretical analysis, the moment-curvature hysteretic model of the section for unbonded partially prestressed concrete beams was established, and planted into Material class in the software of OpenSEES by compiling Visual C++ programs, which is used for the nonlinear analysis of unbonded partially prestressed concrete structure without iterative calculation of stress increment for unbonded prestressed tendon. The crucial problem of stress analysis for unbonded partially prestressed concrete structure was then solved. Moreover, under displacement control, this paper considered the nonlinear beam-column element based on flexibility to calculate the moment-deflection hysteretic curves of unbonded partially prestressed concrete beams under low cyclic reversed loading on the basis of established restoring force model. The calculation results are reasonably identical to experiment results, which indicates the reliability of established restoring force model, and provides theoretical basis for the nonlinear analysis of unbonded partially prestressed concrete structures.

Abstract:Based on the existing experimental investigation on RC frame with a column removal, the three-dimensional finite element simulation with a combination of separated and integral models for a four-story two-span RC frame structure was established by using the finite element software AUTODYN, and analyzed through three stages. The effect of gas-solid interaction was considered to simulate the dynamic response and failure modes of RC frame due to the removal of reinforced concrete columns under explosion loads. In the numerical simulation, the strain rate effects were also taken into account for the dynamical constitutive behaviors of the materials. In the case of the failure of the corner column or the short side column under blast loads, the failure modes of the column and the dynamic displacement of the beam-column joints from FE models agreed well with the experimental results. Meanwhile, the failure process of the column removal and the influence of the longitudinal-steel in the column on the dynamic response of the RC frame structure were examined. Moreover, the simulation results indicate that the way adopting separated and integral models in the plastic and elastic deformation region, respectively, not only ensured the authenticity and adaptiveness of the simulation of the RC frame under column removal, but also reduced substantial computational effort. Therefore, this developed model can provide a reference for the further studies on the parametric analysis and collapse mode control of RC frame structures under blast loads.

Abstract:In order to improve seismic performance of interior joints in the recycled concrete frame structures, silica powder and hybrid fiber were used to improve the seismic performance of recycled concrete. Under the same axial compression ratio, and with the same reinforcement ratio and recycled aggregate replacement ratio, four interior-joints of the frame columns were manufactured by different amount of silicon powder and hybrid fiber. Low cyclic lateral loading tests were performed to study and compare the failure mode, hysteretic behavior, ductility, energy dissipation, and deformation characteristics between the common recycled concrete and enhanced recycled concrete. The test results show that the recycled concrete interior-joints experienced four stages including initial crack, general crack, ultimate state, and damage. Meanwhile, the performance of enhanced recycled concrete is superior to that of common recycled concrete, such as the failure pattern, hysteresis curve, ductility performance, deformation, and energy dissipation, especially in terms of failure pattern and ductility. Additionally, with the increase of silicon powder and mixed fiber content, the improvement effect has a downward trend, while due to the application of silicon powder mixed with hybrid fiber, the seismic performance of the recycled concrete interior-joints is obviously improved. Therefore, this enhanced recycled concrete can be applied to the structures in the seismic fortification regions.

Abstract:The pressure measurement of rigid model for long-span spherical shells structure was conducted at TJ-3 wind tunnel laboratory. Firstly, the non-stationary characteristics of wind pressure signals were verified by the run theory. Secondly, the wind signals of 1∶200 model structures were decomposed in the different scales by discrete wavelet transform, and the time-history curves of wavelet coefficients were obtained. For the quantitative analysis of intermittent characteristics of wind, the distribution of scale energy, intermittent factors, and intermittent energy were analyzed and compared. The studies show that wind field category had great influence on the stationary characteristics of drag coefficient and Z-direction lift coefficient as well as the intermittent energy ratio and intermittency factor in high scale region, but had small influence on the scale energy ratio of wind coefficients in the different scales. In the different scales, the overall drag coefficient presents positive correlation with Y-direction lift coefficient and negative correlation with Z-direction lift coefficient. In addition, the correlations between overall drag coefficient and Y-direction lift coefficient increased with the increase of scales.

Abstract:In order to make an intensive study of the failure mechanism of rectangular footings adjacent to slope, a three-dimensional and bilateral failure mode was established, which fully considered the influence of the shear strength of inside soil in the foundation and the double asymmetrical features. Moreover, a simplified construction method of the rigid-motion blocks collapse mechanism was proposed, which could not only effectively reflect the three-dimensional end effect but also avoid complex coordinate and surface integral calculation, and it is more convenient for practical engineering. Based on the failure mode, the upper limit analysis theory was then introduced, and a new analysis approach of ultimate bearing capacity of rectangular footing adjacent to slope was put forward. Meanwhile, the solving of the bearing capacity was realized by using the SQP optimization theory. Finally, the feasibility and rationality of the research approach proposed is showed through the comparison analysis with the current research as well as the ABQUS finite element results.

Abstract:In order to evaluate the effectiveness of existing engineer measures for wide permafrost subgrade in Qinghai-Tibet plateau, a finite element (FE) model of temperature field of permafrost subgrade was first constructed by FE software ABAQUS and the secondary development platform. The temperature fields of normal subgrade, rock embankment, EPS insulation layer subgrade, and composite subgrade were then analyzed and compared with the help of the FE model. Furthermore, the change rules of melting depth for four kinds of subgrades were studied. The results demonstrate that the temperatures of the subgrades with different cooling engineer measures all change periodically over time, but the mean annual temperature rises. Under the same condition, the temperature of composite subgrade is the lowest, and its thermal stability is the best. When the width increases, the melting depth of normal subgrade rises linearly, and the melting depth of rock embankment shows a three-stage rising trend, while for EPS insulation layer subgrade it is a two-stage rising trend. Meanwhile, the melting depth of composite subgrade rises with the increase of the width, but the variation is very small. The mere EPS insulation layer or rock embankment is ineffective, while the insulation-gravel composite subgrade has excellent performances on the cooling effectiveness of wide subgrade in permafrost region.

Abstract:In order to study the wind characteristics along bridge axis at multi-pylon cable-stayed bridge site with high piers in mountainous terrain, two three-dimensional anemometers and two two-dimensional anemometers were installed on the bridge deck. The time-varying mean wind speeds of the non-stationary winds were obtained by wavelet analysis method. The mean wind and turbulence characteristics measured along the bridge axis were analyzed. The results demonstrate that the mean wind speeds and wind direction changed in the same trend along the bridge axis. The turbulence characteristics measured along the bridge axis, such as turbulence intensities, gust factors, and integral scales also changed in the same trend. Meanwhile, the mean longitudinal turbulence intensities were higher than the values recommended by wind resistant design specification for highway bridges, while the values of longitudinal turbulent wind spectrum measured along the bridge axis were lower than the specification spectrum at low frequencies and close to the specification spectrum at high frequencies. The values of vertical turbulent wind spectrum measured along the bridge axis were lower than the specification spectrum at low frequencies and not close well to the specification spectrum at high frequencies.

Abstract:In order to solve the unstressed configuration of beams, the accurate computation element disintegration theory, named as geometric method and zero-loads method, was created based on the theory of nonlinear second order beam-column theory and CR-UL total deformation theory. The basic parameters of unstressed configuration of beam were firstly solved by using the geometric information and corresponding element resistance of the objective configuration. The full unstressed configuration of component element was also confirmed by using the geometric method as coordinate transformation. The zero-loads method as converse calculation based on these basic parameters was then proved to be effective. Moreover, a program was compiled to verify the above two methods. The results show that the geometric method for full unstressed configuration of beam elements in this paper could be executed efficiently without the finite element model of full structures, and the zero-loads method could be executed efficiently under the condition of impeccable geometric nonlinear program.

Abstract:By using the improved iteration model for train-bridge coupled system, the analysis model of train-track bridge vertical random vibration based on Pseudo Excitation Method (PEM) was established. PEM was applied to transform the random track irregularities into the superposition of a series of vertical harmonic irregularities, while the iteration calculation was applied to solve the equation of the train-bridge coupled system. Taking a five-span simply-supported beam bridge passed through by a CRH2 high-speed train as numerical example, the accuracy and efficiency of the improved iteration model for train-bridge coupled system was verified. The results show that the calculation efficiency of the improved model is about 5 times that of the conventional model under the same calculation accuracy. The mean value and the root mean square (RMS) of the vertical random vibration response for train-track-simply supported beam bridge, which are caused by deterministic load and track irregularities, respectively, were calculated. It can be seen that the vertical displacement of the bridge is mainly controlled by the weight of the train, but the excitation of track irregularity has little effect on it. The vertical acceleration of the bridge and car bodies are significantly influenced by track irregularities, and the improvement of the track condition can effectively improve the riding comfort. The RMS of the train-bridge coupled system random vibration and the discrete of the vibration caused by track irregularities increase with the acceleration of train speed.

Abstract:To reduce the cost of bar splice, a new type of grouted sleeve was developed with standard seamless steel tube through cold rolling techniques. Based on this sleeve, twelve coupler specimens were prepared and tested under cyclic load as well as incremental tensile load. The structural performance of this novel grouted splice was then studied. The test results showed that the strength and deformation of the splices could satisfy the requirements specified in the JGJ107-2010. Due to the cyclic loads, the ultimate bond strength declined by about ten percent of the specimen strength under direct tension test. Meanwhile, because of the confinement provided by the sleeve, the residual bond strength of the bond failed specimen is greater than 50 percent of the ultimate tensile strength. Moreover, it is found that the number of the concentric ribs at each side of the sleeve should not be less than three, and it should be increased properly for the improvement of tensile capacity requirement of the splice.

Abstract:Large wind turbine system is a periodic time-varying system with rigid-flexible coupling multi-bodies. The traditional finite element method cannot solve the singular stiffness matrix produced by the rotation of blades. However, the vector form intrinsic finite element method can effectively solve the geometric deformation of elastic continuum, the nonlinear or discrete constitutive model, the coupling motion of continuum and rigid body, and so on. In this study, a solver program of space beam elements was developed by the vector form intrinsic finite element method with MATLAB code, and verified by two typical examples where one is a cantilever method with a dynamic force acting at the end, and the other is an Euler beam rotating around a fixed axis. The integrated simulation of wind turbine system that consists of tower, rotor blades, and nacelle was then established, and its dynamic response of free vibration under parking was analyzed. The natural frequencies of the turbine system were obtained by modal parameter identification, and they agree well with the results obtained by traditional finite element method. Moreover, the weighted amplitude wave superposition method and proper orthogonal decomposition method as well as B-spline surface interpolation were employed to obtain the wind time series of wind turbine under the normal operation condition. The wind-induced dynamic response of wind turbine system was also calculated by vector form intrinsic finite element method. The results reflect the periodic influence of gravity on the internal forces of blades and the interaction between blades and the tower.

Abstract:A finite element model of the photovoltaic module with different component parameters was established and Von Mises stress of crystalline cell was calculated using ANSYS software. The effects of wind pressure and shear modulus variation of EVA were taken into account in the analysis. The analysis results show that 1) the stress distribution in the cell agrees with the theoretical results(i.e., the maximum stress occurs at the center of the cell and the stress decreases nonlinearly toward the cell edges, and the stress in the cell increases nonlinearly with an increase of shear modulus of EVA); and 2) the composite layer that consists of EVA, cells, and TPT exhibits a little effect on the rigidity of the module, when it is subjected to wind loads and flexural deformation occurs approximately at the neutral surface of the panel.

Abstract:Many factors affect the tunnel temperature field in cold region. An unsteady heat transfer calculation model was established based on finite difference method. Taking the Nan Shan railway tunnel in cold region as an example, the othogonal test method, which takes the average temperature of tunnel lining internal nodes, lining temperature of a certain section, and longitudinal frozen length of tunnel entrance as index, respectively, is applied to carry out sensitivity study of the influencing factors on tunnel temperature field. The results show that there are some local differences in the ranging of sensitivity of each factor under different indexs. Overall, the tunnel depth, wind direction in tunnel, tunnel section size, wind speed in tunnel, wind temperature of entrance, and thermal conductivity coefficient of surrounding rock are the main factors affecting the tunnel temperature field, while the surrounding rock density and specific heat of surrounding rock are the secondary factors affecting tunnel temperature field. In the antifreezing design of the tunnel in cold region, except the unchanged factors such as the surrounding rock density, surrounding rock specific heat, surrounding rock heat transfer coefficient, thermal conductivity of surrounding rock, and wind temperature of tunnel entrance, sufficient attention should be paid on the design parameters that affect significantly the tunnel temperature field including the tunnel depth, wind direction in tunnel, wind speed in tunnel, and tunnel section size.