Abstract:To study the dynamic responses of a tridimensional parking structure subjected to vehicle impact, a multi-scale and refined finite element models of the tridimensional parking structure were established based on ANSYS/LS-DYNA finite element software. The accuracy and efficiency of these two models were compared, and the applicability of the multi-scale model was verified. Based on the multi-scale model, the dynamic responses of the tridimensional parking structures were examined, and the influences of various factors, such as the impact velocity, vehicle mass, impact position, and working condition were investigated. Additionally, the impact force was studied and compared with the allowances given in Chinese code, American code, and European code. The results indicate that the vehicle impact has a local effect on the tridimensional garage; the impact velocity and vehicle mass have a great influence on the dynamic responses of the tridimensional garage, while the impact position and working condition present no obvious effect; the impact velocity has a greater influence on the impact force. However, when the impacted column is failed, the peak value of the impact force would not change with the increase of the impact velocity and vehicle mass; for the tridimensional parking structure subjected to vehicle impact, the values of the impact force given in Chinese code and Europe code are not reliable in some cases, but the value given in American code is safe.

Abstract:After fire, residual forces and deformations are re-developed inevitably in steel structures, and it may cause more dangerous consequence than that in fire condition. Beam-column connections are very important parts for the whole structure. In order to reveal more information about high strength steel flush endplate connection, an experimental study on mechanical behaviour of high strength steel flush endplate connections was carried out. Seven flush endplate connections were tested after cooling down from 550°C. The final deformation, moment-rotation curves and failure mode of high strength steel flush endplate connections were obtained and compared with those of mild steel flush endplate connections. Moreover, the provisions of Eurocode 3 were validated with the test results. It is found that a thinner high strength steel endplate can achieve similar residual load-bearing capacity and comparable or even higher rotation capacity after fire, in comparison with a connection with thicker mild steel endplate. Meanwhile, the provisions of Eurocode 3 for plastic flexural resistance of endplate connections are applicable when used to predict the behavior of high strength steel flush endplate connection after fire.

Abstract:To complement the insufficient experimental study on the mechanical behavior of aluminum alloy at low temperature, tensile tests of Chinese structural aluminum alloy 6082-T6, 6N01-T6, 6061-T6, and 6061-T4 under constant low temperatures were carried out, and their mechanical properties including the ultimate tensile strength, nominal yield strength, elongation rate and section shrinkage were obtained at different temperatures that range from -120 to 20 ℃. It is found that material hardening of the aluminum alloy occurs at low temperatures, leading to the increase of the ultimate tensile strength and nominal yield strength. However, the change rule of the elongation rate and section shrinkage is not clear. The increasing factor formulae of the mechanical properties for the 4 kinds of aluminum alloy at low temperatures were derived through a numerical fitting method. Moreover, the fitting formulae were compared with the corresponding formula prescribed in American standard. The results demonstrate that the American standard method provides more conservative estimation

Abstract:This paper presents a new I-V type sandwich panel structure for civil building wall and plate, and uses the nonlinear finite element software LS-DYNA to study the explosion protection properties of I-V type sandwich panel under the combined loading of close-range blast wave and fragments. In terms of three aspects of mass loss, energy absorption and vertical peak displacement response, the influence of the explosive proportion distance, explosive initiation position on the protection effect of sandwich panels and the actual protective performance of sandwich panels were studied. The results show that the ratio of explosive distance has great influence on the protective performance of I-V type sandwich panels. The damage degree of different explosive initiation points to I-V type sandwich panels is different, and the number of initiation points in axial direction can not significantly increase the damage degree of I-V sandwich panels. There is only a small amount of detached concrete and no reinforcement exposed on the front surface, while on the back surface, no concrete falls off and no reinforcement exposes with lesser plastic deformation area，and there is no penetrating damage to the whole with the protection of I-V sandwich panels. The damage degree of the reinforced concrete slab with I-V sandwich panel is far less than that of the unprotected concrete slab.

Abstract:The downburst outflow wind field was modeled by plane wall jet, and the co-flow was used to simulate the translation of downburst. Based on the computational fluid dynamics（CFD） method，the velocity profile of steady downburst was simulated with Reynolds stress model（RSM），and then a high -rise building model was put into the wind field to study the surface pressure distribution. The velocity profile from the numerical analysis results matches well with the empirical models as well as the plane and radial wall jet experiments. The pressure distribution characteristics of the building model in plane wall jet flow is in good accordance with the results of the imping jet experiment. The pressure coefficient decreases when the downstream distance increases. The pressure coefficient decreases with the increase of wall jet inlet turbulence intensity. When the half-width of the downburst velocity profile is higher than 1.45 times height of the building, the pressure distribution in wall jet flow is similar with that in boundary layer. Co-flow mainly has influence on the structure in the lower part. The wind direction of wall jet has little effect on the maximum pressure.

Abstract:In order to study the inter-story lateral stiffness damage and identification of ancient wooden structures under strong earthquakes, the inter-story lateral stiffness, lateral displacement response and the sensitivity of displacement to stiffness were analyzed by the shaking table test of an ancient timber frame with a scale ratio 1:3.52. Based on the simplified mechanics model considering the column sliding, the structural state equation and observation equation were deduced. Considering the influence of noise, the lateral stiffness was identified by means of Partial Least Squares-Singular Value Decomposition （PLS-SVD） and Extended Kalman Filter （EKF）. The analysis results show that the ratio of inter-story lateral stiffness gradually decreases with the increase of seismic damage. The damage of column layer is especially sensitive to the increase of lateral displacement. The identified error of the lateral stiffness is about 10% without damage. Under the damage condition, the identified error of the lateral stiffness is about 15%~20%. Through the lateral stiffness identification of Bell Tower of Xi'an, it indicates that the method of PLS-SVD and EKF has high accuracy and good applicability, and can provide a theoretical basis for monitoring the change of lateral stiffness and offering warning before structural collapse.

Abstract:Hoop head tenon-mortise joint is extensively adopted in an ancient timber structure in Guangfu, which is different from straight tenon-mortise joint or dovetail tenon-mortise joint in terms of mechanical performance. To analyze the mechanical properties of hoop head tenon-mortise joint，mechanism analysis was carried out and the moment-rotation calculation formulae were also derived, while the formulae were verified by experimental results. Using the formulae，the factors affecting the relationship of moment-rotation of hoop head tenon-mortise joint were investigated. The results indicate that within the range of parameters, the initial rotational stiffness and ultimate bending moment increase with the increase of the column diameter, mortise width, friction coefficient and unilateral compression width between tenon and mortise，while the ultimate bending moment increases with the increase of beam height, but the initial rotational stiffness is only slightly affected by the beam height. The results of this study can serve as a theoretical foundation for mechanical analysis as well as for seismic research of ancient timber structures in Guangfu.

Abstract:The steel-UHPC lightweight composite deck is a novel bridge deck pattern that consists of an orthotropic steel deck（OSD） and a thin ultra-high performance concrete（UHPC） layer. In order to reveal the effect of UHPC layer on the performance of the OSD, field measurement was performed for Fengxi Bridge to evaluate the stress ranges in the typical detail categories of the OSD with/without UHPC layer, respectively. Before the field measurement was conducted, the global finite element model of Fengxi Bridge was developed to determine the instrumented sections. Then, a triaxial loading vehicle, according to the loading scheme，was arranged to run on the bridge deck with/without UHPC layer at a low speed, respectively. The field measurement data of the typical detail categories were collected and sorted. Finally, a local finite element model of Fengxi Bridge was built to compare with the field measured results. The field measurements show that the stress response of the typical detail categories are significantly reduced after installment of UHPC layer. For the detail categories related to the steel deck（i.e., rib-to-deck weld, deck splices, and deck of rib-to-deck at diaphragm joint），the stress range decreased by about 75% ~ 90%；for the detail categories related to the trapezoidal rib（i.e., rib splices, weld end of rib-to-diaphragm joint, and rib of rib-to-deck at diaphragm joint），the stress range decreased by about 65% to 80%; for the detail categories related to the diaphragms（i.e.，cut-out on diaphragm, diaphragm base metal at cut-out transition, and diaphragm of rib-to-deck at diaphragm joint），the stress range decreased by about 20% to 50%. Meanwhile, with the decrease of the distance from detail categories to top surface, the contribution of UHPC layer to the stress reduction of the detail categories was significantly increased. The results of the local finite element model agreed well with the measured results, and the similar rules were obtained. The field measured results of this paper provide the reference data for the application of steel-UHPC lightweight composite bridge deck.

Abstract:Using initial parameter solutions and transfer matrix method，the finite element formulation for restrained torsion of a thin-walled box girder was presented. The equivalent nodal forces of distributing torque and bimoment acted on an element were also derived. Based on the displacement solutions of the finite element method for restrained torsion, a new algorithm for calculating the flexural-torsional moment was developed. The relevant stiffness matrix and fixed-end forces for distributing torque and bimoment acted on the element were established. It facilitated the calculation of normal stress and shear stress. The examples show that the calculation results of the proposed method agree well with the theoretical solutions, which proves that the stiffnesses for restrained torsion, equivalent nodal forces for distributing torque and bimoment acted on element as well as new algorithm for flexural-torsional moment are exact.

Abstract:In classical elasticity theory with different modulus, the constitutive equations based on the direction of principal stress can only represent the relationship between the principal stress and principal strain in the main stress direction and cannot reflect the stress-strain behavior in other directions, and the mechanical essence of the problem on different modulus in tension and compression cannot be characterized effectively. Therefore, according to the constitutive equations based on the direction of principal stress，the generalized elastic laws were deduced by the rotation formulas of stress and strain under different Cartesian coordinate system, which are constitutive equations with different modulus in tension and compression. With theoretical verification, both the nonlinearity and anisotropy property of bi-modulus materials were revealed by the generalized elastic laws. Furthermore, it can also degenerate to the classical bi-modulus elasticity law, which implies that the constitutive law for material with different modulus in tension and compression is special cases of the obtained results. With respect to the indistinct issues about the shear modulus and the assumption of the ratios between Poisson's ratio and Young's modulus, bimodulus material point under pure shear state was investigated. It is shown that, in the rectangular coordinate system based on the maximum or minimum shear stress direction, the relation between shear stress and shear strain is linear. In other words, the shear modulus keeps invariant；besides，the hypothesis is proved that the ratio of tensile Poisson's ratio to tensile modulus is equal to the ratio of compressive Poisson′s ratio to compressive modulus under pure shear state, combining with the geometric relationship of pure shear deformation in differential element.

Abstract:The existing method is difficult to consider the actual state of geogrid ribs under loading, which could underestimate the settlement of the geogrid-encased stone column (GESC) composite foundation. In order to solve this problem, in this paper, the unit cell concept was employed as the objects in the analysis, while it was assumed that GESC together with soil was elastic materials and evenly deformed. Stone column was constrained by geogrid and earth ring at the same time, while the earth ring can be considered as a ring with earth pressure at rest provided by soil outside and bulging pressure caused by the stone column installed inside. Hook's law was then introduced to gain the stress-strain formula of the unit cell. Then, a different method of settlement calculation of GESC composite foundation was established. The rationality of the results of this method was verified by an engineering example and also compared with the existing method. The result demonstrates that the method agrees well with the engineering example. Through the comparison with the existing method, it is found that the relative error between the calculated value and measured value is +5.70%, which demonstrates the method presented in this paper is safer and more accurate as a result of the combined top loading and lateral deformation of GESC. The parametric study shows that the replacement ratio has a significant influence on the controlling settlement of composite foundation, and the increase of the replacement ratio can effectively reduce the pile - soil ratio and settlement of composite foundation when a certain level load is applied.

Abstract:Laboratory direct shear test and pullout test were conducted focusing on biaxial geogrid (SS20) and triaxial geogrid（TX160） to investigate the deformation and geogrid-soil interface behavior. The displacements of geogrid specimens were recorded at 4 sections in the pullout test. The development of geogrid-soil interface shear stress, geogrid deformation, shear dilatancy/shrinkage behavior and interface parameters were analyzed, and the effect of test methods on the testing results was also investigated. The results show that the interaction between the geogrid and soil of TX160 concentrates at the vicinity of pullout end. However, this interaction is well developed along the full length of SS20 specimens. Meanwhile, this interaction of TX160 can be better enhanced with the increase of vertical stress compared with that of SS20. Both the peak and residual friction angles of SS20 case are greater than that of TX160 case, while the cohesion is just opposite. The vertical stress has obvious effect on the geogrid-soil interface strength parameters obtained from both the direct shear test and pullout test. Thus, the vertical stress adopted in the test should be determined based on the actual stress status of the geogrid for engineering application.

Abstract:To explore the effect of thermal oxidative aging intensity on the properties of asphalt, different times of the rotating thin film oven test (RTFOT) and RTFOT + pressure aging vessel (PAV) aging tests were applied to asphalt. The conventional physical properties and dynamic shear rheological properties of asphalt samples were tested before and after aging. Additionally, the viscosity harmonic method was used to determine the amount of rejuvenating agent in order to restore the asphalt performance under different thermal oxidative aging to the matrix asphalt. The test results show that the physical properties of asphalt are significantly changed after different thermal oxidative aging intensity. The dynamic shear rheological test results exhibit that the increase ratio of asphalt complex modulus （G*） decreases obviously after the certain aging degree, and finally, the G* approaches a stable value. It is found through physical and rheological properties that, for Changlian 70# asphalt, 3 times RTFOT aging intensity is equal to the RTFOT + PAV aging intensity. In addition, through viscosity harmonic method selecting rejuvenating agent dosage, it can be found that the recycling asphalt′s G* can restore to the level of matrix asphalt，the penetration is slightly lower than the matrix asphalt，but the ductility is improved obviously. Additionally, the softening point is higher than that of matrix asphalt. At the same time，the phase angle（δ） at low temperature can be restored to the level of matrix asphalt, but it cannot be restored to the level of the matrix asphalt at high temperature.

Abstract:Taking the rock nature joint surface as the research object, the morphology of joint surface was measured and 3D shape of the joint surface was established. On the basis of this, five parameters were calculated and the correlation between parameters was studied taking the root mean square value（RMS） as benchmark. Selecting three morphology parameters, the method of fuzzy mathematics was used to quantify the roughness of joint surface, and the roughness was classified. Meanwhile, the correlation between the morphology parameter and roughness index was studied. The results show that the average height of the central line is proportional to its RMS. The relation among the ratio of kurtosis coefficient, skewness coefficient, micro convex angle and RMS of mean height of centerline is power functions. The results of quantitative classification of roughness show that the quantitative classification index and friction coefficient and friction angle have obvious positive proportional linear relationship. It can be used for the estimation of joint surface friction. The relation among the ratio of friction coefficient, friction angle, the quantitative classification index and RMS of mean height of centerline is also power functions. Through the quantitative function relationship between the parameters, the correlation coefficient can be obtained, and then the estimation of surface roughness and friction force of the joints can be realized.

Abstract:Based on the heat transfer process of orifice plate and the exergy analysis method of traditional mental radiant panel and convective air-conditioning terminal, the algorithm of room input exergy for air carrying energy radiant air-conditioning system（ACERS） was proposed. The exergy cost analysis model of ACERS was established by exergy cost analysis method. The unit exergy cost of three radiant air-conditioning systems including ACERS, capillary radiant air conditioning system and a combined system of split air conditioning with floor radiant air conditioning，was compared under the premise of thermal comfort. The results show that the unit exergy costs of capillary radiant air conditioning system are 1~3 times higher than that of ACERS in office buildings. The unit product exergy cost for the year of a combined system of split air conditioning with floor radiant air conditioning is 1.2 times higher than that of ACERS in residential building. It is found that the overall exergy economic performance of ACERS is superior to the other two radiant air-conditioning systems, which is of great significance for future engineering application of ACERS.