Abstract:Fire resistance of Concrete-filled RPC tube (CFRT) columns were investigated by experimental study. Seven large-scale CFRT specimens were performed by heating test and axial compression test after elevated temperature. The test parameters included control temperature, volumetric stirrup ratio and stirrup arrangement mode. The test results showed the spalling of concrete was not observed during elevating temperatures. The compressive performance of CFRT column after high temperature decreased with the rising control temperature. Both increasing the volumetric stirrup ratio and arranging double layers of spiral hoops were effective measures for improving the mechanical properties of the CFRT columns after high temperature. Compared with the existing test results, the residual load carrying capacity ratio of the CFRT after elevated temperature was higher than that of the ordinary steel-confined column. The CFRT columns exhibited excellent fire resistance.

Abstract:To investigate the bond performance of reinforcement and concrete components under high temperature, twenty-five central pull-out test specimens and other eight specimens for temperature field test were casted. The corresponding standard cube compressive specimens were also casted for concrete tensile splitting strength test under different temperatures. After exposed to 100 ℃, 200 ℃, 400 ℃, and 600 ℃, the tensile splitting strength of the cube specimens and the bond properties between rebar and concrete were tested immediately to simulated the concrete circumstance and reinforcing steel performance under high temperature. The strength of rebars which underwent temperature cycle loadings was tested after its cooling. The strength of rebar, tensile splitting strength of the cube specimens, and the bond performance between rebar and concrete under different temperatures were recorded. According to the temperature test results, a simplified test method of the bond strength between reinforcing bar and concrete under high temperature was proposed. The effect of high temperature environment on bond performance between rebar and concrete was analyzed from the perspective of the mechanical properties degradation of materials, and the influence of high temperature on bond stiffness was studied by the method of tangential bond stiffness. The experimental results show that the strength of rebar after high temperature shows little change below 400 ℃, the tensile splitting strength of concrete decreases linearly with temperatures and the variation trend of bond strength under high temperature is similar to the tensile strength of concrete. The results present two different relationships between bond stiffness and temperature by the slip of 0.015 mm.

Abstract:The tests of 9 composite concrete-filled square thin-walled steel tubular (CCFSTST) columns with longitudinal stiffeners under eccentric compression were carried out. The test results indicated that the load-carrying capacity decreased with the increase of eccentricity and slenderness ratio, but increased with the increase of core concrete strength. Based on the finite element model verified by the test results, the working mechanism of CCFSTST columns was studied and the parametric analysis was conducted. It can be found that the confinement of the outer steel tube is focused on the corners of the cross-section, the majority of the load is resisted by the concrete and the ductility of the composite column is enhanced by filling core concrete. With the increase of the steel yield strength, steel ratio of inner concrete-filled steel tube and diameter to width ratio, the abscissa and ordinate values of the equilibrium point in the relative axial compression versus relative moment relationship decreased, but they increased with the increase of concrete strength. Meanwhile, with the increase of slenderness ratio, the axial compression versus moment relationship trended to be a straight line. Finally, the simplified model was proposed to predict the load-carrying capacity of CCFSTST columns under the eccentric compression.

Abstract:In order to investigate the effect of fiber volume content on tensile characteristic of Ultra-High Performance Concrete (UHPC), 6 groups of “8” shape specimen were designed, and uniaxial tensile test was performed after 28 days standard curing, the complete tensile stress-strain curves were gotten, the effect of fiber volume content on tensile strength, peak strain and toughness of UHPC were analyzed. Test results show that the fiber volume content can be as much as 5% without workability problem, its tensile strength and peak strain are 8.50 MPa and 1 619 με respectively; with the fiber volume content increase the tensile strength, peak strain, compressive strength and toughness increase as well, the uniaxial tensile constitute of UHPC was finally proposed based on the test results. The results of this paper provide a reference for the application of UHPC material.

Abstract:Tensile mechanical properties of two and three layers basalt fabric reinforced cementitious matrix composite（BFRCM） with different volume fractions (0,0.5%, 1.0% and 1.5%) short carbon，alkali-resistant glass and steel fiber, were tested utilizing a MTS loads frame . The experimental results show that an obvious increase in crack stress is observed in all case when short carbon, glass, steel fibers had been added, and volume fraction exists an optimal value. Within the range of 0~1.5% content, the crack stress increases, reaching a maximum at 1.5%, with increasing volume fraction for 2 layers BFRCM. For 3 layers BFRCM with short carbon or steel fibers, the crack stress firstly increases and then decreases with increasing volume fraction, but the crack stress increases, peaking at 1.5%, with increasing volume fraction for 3 layers BFRCM with short glass fibers. Short carbon and glass fibers cannot increase load-bearing capacity of BFRCM, but a pronounced increase in load-bearing capacity is observed with short steel fibers，reaching a maximum at 1.5% for 2 layers BFRCM and 0.5% for 3 layers.

Abstract:Taking a cable dome with new compound form whose span longer than 100 m in China as a study subject, the construction technology of this project was analyzed in 4 aspects: controlling of dimensional error of ring beam and cable; sequence of structure installation; sequence and method of tensioning; and controlling and simulation of construction process. This paper focused on analyzing the influence degree of different error level of ring beam and cables on the internal force of cable dome, and put forward the corresponding treatment measures. The research shows that adjustable cables used for outmost ridge cables and outmost diagonal cables can eliminate the construction error of ring beam, while cable random error can be reduced through optimizing field placement. Step-by-step hoisting and synchronous tensioning method can avoid large displacement of members, and prestress level is proposed to ensure the coincidence of the actual cable force and the design value.

Abstract:The hysteretic behavior of aluminum alloy is fundamental for studying the seismic behavior of aluminum alloy structures. A total of three different loading protocols, including cyclic ascending, cyclic alternating and cyclic tensile, with the maximum strain amplitude up to ±4%, were adopted for the 6082-T6 and 7020-T6. In order to avoid buckling, the small gauge specimen with length-to-diameter ratio of 1.5 was adopted. The comparison of monotonous tensile results between the small gauge specimen and standard specimen revealed that the error of the two specimens was very small, which indicated the feasibility of the adoption of the small gauge specimens. The stress-strain relationship and hysteretic behavior of aluminum alloy were also obtained by cyclic loading test. The obtained results show that the aluminum alloy has good hysteretic behavior and ductility, and the load protocol influences its skeleton curve to a certain extent.

Abstract:This paper focuses on the development of steel tubular scaffold with couplers in construction, based on Revit, through the aid of Revit API. The specific method is to create required family members of the scaffold by using C# as the programming language. Revit API can automate the rivial modeling of scaffold, which can assist the designers to build the moulding in short time, and meanwhile integrate the computing functions of scaffold into Revit. This program finally achieves the functions of scaffold safety calculation and intelligent modeling. Moreover, taking a specific instance to illustrate the stability and applicability of this method, this program can realize a 3D visualization model of scaffold in a short time, which satisfies the engineering requirement and provides rich engineering information. Finally, it significantly improves the work efficiency of the designers and constructors.

Abstract:At present，there is no bridge design code to guide the fatigue design of beam with corrugated steel webs. In order to study the fatigue design and evaluation methods of this structure, constant amplitude fatigue load tests of 7 beams were performed, and the basic fatigue data were obtained. Based on the FEM sub model method and the linear extrapolation method recommended by the IIW, the hot spot stress concentration factor of model beams was calculated. The fatigue performance of tested beams in this paper and other two tests was estimated by the hot spot stress method. The results show that the hot spot stress method is safe in evaluating the fatigue test results of the beams with corrugated steel webs and the 100 FAT class is recommended for fillet welds in this structure. The parameter analysis indicates that the largest hot spot stress and its concentration factor is greatly influenced by steel flange thickness and web corrugation angle, and they decrease with the increment of steel flange thickness and increase with the increment of web corrugation angle, while they are less affected by the web corner radius and decrease with the increment of web corner radius.

Abstract:Fatigue damage and atmospheric corrosion lead to the degradation of cable performance, which affects the lifetime safety risk of the cable-stayed bridge. In order to investigate the influence of cable resistance degradation on the system reliability of cable-stayed bridges, a series-parallel probability model of the cable resistance was established. A framework for time-variant system reliability evaluation of cable-stayed bridges was presented based on machine learning. Both a typical bridge and a long-span cable-stayed bridge were selected as prototypes to investigate the influence of the cable degradation on their structural system reliability indices. Numerical results show that the dominant failure sequence of the short-span bridge with short-spacing cables changes from the bending failure of girders and pylons to the tensile failure of cables due to the cable corrosion. As a result, the structural system reliability significantly decreases in the period that the cable reliability is inferior to the one of the critical girder. For the long-span bridge with long-spacing cables, the system reliability index decreases to the threshold value 5.2 in the 29-year service period taking into account both fatigue and corrosion.

Abstract:As part of the untreated fillings of concealed Karst cave with internal pressure behind tunnel are complex and influenced by the seasonal precipitation and sudden precipitation, the increase of internal pressure can affect the stability of the structures near the tunnel, and may easily lead to the instability of tunnel primary support structure. Scaled model tests based on a 3-lanes highway tunnel were carried out to investigate the stability of tunnel excavation nearby Karst cave with internal pressure. Characteristics of the tunnel convergence, internal force of steel arch, surrounding rock pressure behind primary support and surrounding rock strain were analyzed to study the effect of position and pressure on the stability of the tunnel. The results show that, under the specific cavity size and spacing, tunnel lost stability firstly for Karst cave in the inverted arch. The convergence of the tunnel near the Karst cave increases with the increase of the pressure and changes suddenly when reaching the critical internal pressure, and the primary support loses its stability. The increase of pressure leads to the obvious increase of the bending moment of steel arch, and increases the axial force of steel arch evenly. Finally, the steel arch reaches the yield state, meanwhile, primary support becomes instability. Surrounding rock pressure behind the primary support near Karst cave increases obviously and leads to the uneven stress of primary support with the increase of Karst cave internal pressure.

Abstract:Model of shield tunnel considering the shearing dislocation was used to investigate the effect of the new shield tunnel undercrossing on existing tunnels. In light of the fact that the additional stress along the central axis of the existing tunnel was caused by the bulkhead additive thrust, the friction force between shield and soil, and grouting pressure in the process of undercrossing shield tunnel construction, the lining ring of shield tunnel was regarded as a series of short elastic foundation beams connected by shear spring. An equation was developed by the principle of minimum potential energy, and three-dimensional change process of the vertical deformation, shear force and dislocation between rings with the excavation of the new tunnel were worked out. The research shows that the vertical displacement value calculated by the proposed method combined with the shearing dislocation model and the principle of the minimum potential energy agreed well with field test data. The dislocation of the segments where the vertical displacement is the maximum is close to 0. The maximum value of segment ring's dislocation and shearing force appears at the inflection point of vertical displacement curve. With the excavation of the new tunnel, the vertical deformation, shear force and dislocation between rings of existing tunnel increased and finally stabilized.

Abstract:To investigate the mechanism of tire-pavement partial hydroplaning, finite element numerical method was applied to establish 175-70-R15 tire model and water-air composite model. Coupled Eulerian-Lagrangian method was applied to establish the three-dimensional numerical model of patterned inflation tire hydroplaning. The simulation investigated the influence of water film thickness and tire velocity on the mechanical responses of tire and discussed the impact of tire motion state on the partial hydroplaning process. The results show that, with the thicker water film, the water lifting force increases, while the longitudinal force provided by pavement decreases, which means that the tire enters into the complete hydroplaning earlier. With the increase of tire velocity, the longitudinal water drag force increases, which occurs more obviously when the water film becomes thicker. The relationship between water lifting force and water film thickness and tire velocity is regressed into an equation. It is determined that tire with ABS enters complete hydroplaning earlier than that in free rolling statement.

Abstract:Energy equation of two-parameter foundation - rigid plate system was established by using energy method based on the basic theory of Pasternak model. In the principle of the minimum potential energy, the relationships of foundation coefficient, foundation size, load and surface displacement of soil were obtained. The foundation coefficient expression was obtained by solving the equation system which was established with two rigid plates loading test of different size based on the above relationships and the existing determining rules of foundation coefficient. Four sandy soil-rigid plate loading tests were performed to verify the validity of this method, where the circular plates with diameter of 0.3 m and 0.6 m, and square plates with the size of 0.54 m × 0.54 m and 0.71 m ×0.71 m were used. Examples of calculating foundation settlement and considering the influence of adjacent foundation were given to illustrate the engineering significance of the two-parameter foundation model, and empirical values of two-parameter foundation coefficient for clayey soil and sandy soil were estimated for the popularization and application of the two-parameter foundation model.

Abstract:To investigate the stress dependency of the dynamic resilient modulus (MR) of remodeled-loess, the dynamic triaxial tests were conducted under 16 stress paths, 3 degree of compactions and 4 water contents. The research results show that the effect of deviatoric stress and confining pressure are more significant than the bulk stress when the water content is higher, while the effect of deviatoric stress and bulk stress are more significant than confining pressure when the water content is lower. For the loess with low compaction degree, MR is significantly affected by the water content under low deviatoric stress conditions, while for loess with high compaction degree, MR is significantly affected by the water content under high deviatoric stress conditions. MR is significantly affected by deviator stress and bulk stress when ω<ωopt, while, it is significantly affected by deviator stress and confining pressure when ω≥ωopt. In view of this, a two-phase prediction model of MR is proposed based on the Ni mode which adopts different stress control parameters at different humidity stages, so as to express the performance parameters of loess subgrade accurately.

Abstract:To quickly and accurately compute the borehole fluid and ground temperature, a new thermal response factors (referred as δ-function) was proposed to calculate the ground temperature response of bore field to a unit rectangular heat pulse. The proposed model is based on the existing models for the long δ-term simulation of vertical heat exchanger. In this paper, the δ-function was combined with the fast Fourier transform to improve the computation speed of the δ-function. Then, the response factor and algorithm were compared with the δ- function in terms of accuracy and computation time. The results show that when combined with the fast Fourier transform, the g-function not only has the same precision with that of the g-function, but also has significantly faster computation speed than that of the g-function. It only spends shorter than 90 seconds to complete the 30 year hourly simulation of a 5×8 bore field.

Abstract:To obtain the material parameters of typical bamboos and explore the distinction between bamboo and timber as well as among different bamboo products, flattened bamboo panel (FB), bamboo laminated lumber (BSB), plybamboo (BMB), bamboo scrimber (BFB), bamboo particleboard (BPB), and bamboo OSB (BOSB) were systematically tested for thermal and hygric physical properties based on the material parameter requirement of heat-air-moisture transfer model (HAM model). The items included density calculation and vacuum saturation test for basic properties, sorption test for moisture storage properties, capillary absorption test, water vapour transmission test and drying test for moisture transport properties, thermal analysis for heat storage properties, thermal conductivity test, surface light and thermal properties test for heat transport properties. The test results initially formed a data basis of thermal and hygric physical properties that could provide support for the bamboo application in the building envelope. The comparison with 18 reference timbers showed that the moisture storage and moisture transport properties of bamboo were generally lower, while the thermal storage coefficient that characterized heat storage and heat transport properties were higher. The comparison among 6 bamboo products showed that modification treatment improved the homogeneity, broadened the spectrum of material properties, and strengthened the distinction with timber.