Abstract:Based on the vertical compressive static load and pile mechanics tests of 6 large diameter mud-walled bored piles in fully weathered and strongly weathered granite gneiss foundation, including three post-grouting piles in side, the bearing behavior, deformation properties and impact factors are analyzed and the corresponding test data are then compared with the current recommended value of code and survey report. The results show that the Q-s curves of the large-diameter rock-embedded mud-walled bored piles, which are with length-diameter ratio of 25~34 and rock-embedded depths of 5D~8D, present slow type. Compared with no post-grouting piles, the ultimate compressive capacity of post-grouting piles increases by 16.7%~25%, the maximum settlement decreases by 35.1%~65.6%, and the rebound rate increases by 13.1%~82.4%. Besides, the control effect of pile top settlement is remarkable. Under the experimental conditions, the bearing capacity and deformation characteristics of the six test piles are greatly affected by the aspect ratio and the rock-embedded length. Nevertheless, the side resistance in rock-embedded section and side-resistance sharing ratio of the grouting piles is less influenced by the aspect ratio and the rock-embedded depth. The end-resistance sharing ratio of the six test piles and side-resistance sharing ratio of no post-grouting pile is highly affected by the rock-embedded depth.

Abstract:Based on Fick's second law of diffusion, the chloride diffusion equation in reinforced concrete (RC) pipe pile was developed considering the effects of environment temperature and chloride binding. The experimental study on the effect of environment temperature on chloride diffusion in RC pipe pile was conducted in this paper. RC pipe piles with different water-to-cement (w/c) ratios (0.30, 0.45 and 0.55) were exposed to 5% chloride salt spray for 32 days at different exposure temperatures (21, 30, 50℃). Based on the experimental results and proposed model, the chloride concentration profiles, surface chloride concentration, apparent and effective diffusion coefficients, activation energy and binding capacity values of RC pipe piles with different w/c ratios at different exposure temperatures were explored. The experimental results show that the free chloride concentration, surface chloride concentration, apparent and effective diffusion coefficients increase with the environment temperature. The binding capacity increases significantly with the increase of environment temperature from 21 to 30℃. However, the binding capacity decreases slightly when the environment temperature increases from 30 to 50℃. It could be concluded that the chloride diffusion into RC pipe pile follows the Arrhenius theory due to the linear distribution of the log-variation of apparent diffusion coefficient with the inverse of absolute temperature.

Abstract:In this work, the deformation resistance and energy dissipation of rock rings were investigated by using the 4D lattice spring model (4D-LSM). Firstly, the 4D-LSM was verified against existing experimental and numerical simulation results in terms of the influence of rock ring size on the failure pattern and strength. On this basis, empirical relationships of the influence of various factors, e.g. the porosity, heterogeneity, and thickness-diameter ratio, on the deformation resistance and energy dissipation of the rock ring were derived from numerical tests with the 4D-LSM. When considering the large deformation, it was found that the failure pattern of the rock ring would be different from the classical experimental and numerical observations. Moreover, different empirical relationships between the deformation resistance and energy dissipation as well as the material ultimate deformation were derived compared to these numerical tests considering small deformation only. Finally, the failure pattern, deformation resistance and energy dissipation of a composed structure made up from an array of rock rings were studied. Numerical results reveal that these relationships obtained for the single rock ring are also applicable to the composed structure.

Abstract:Considering an inclined rough retaining wall under the general conditions such as curvilinear fill, cohesive soil and uneven surface load, the functional extreme-value isoperimetric model about passive earth pressure is deduced based on the force equilibrium equations of the sliding mass. Then, the model can be transferred into a functional extreme-value problem with two undetermined functions by introducing Lagrange undetermined multiplier. According to Euler equations, Logarithmic spiral slip surface and normal stress distribution along the slip surface are obtained. Combined with the boundary conditions and transversality conditions, the conditional functional extremum problem of passive earth pressure involves searching the minimum of unconstrained optimizations of function with two unknown Lagrange multiplier. Results show that the passive earth pressure resultant force is minimal when the point of resultant force is on the lower bound and it increase nonlinearly as the point of resultant force moved up to the upper bound for general soil. Accordingly, the slip face evolves from logarithmic spiral face to plan. Although the magnitude of passive earth pressure reaches maximal that is the same with result calculated from Coulomb's theory, the application point of earth pressure is not at 1/3 height of the retaining wall. In addition, curvilinear fill and uneven surface load have significant effect on both the magnitude and location of application point of passive earth pressure.

Abstract:Aquitard with uneven thickness and discontinuities commonly occurs in thick-overburden dam base in Northwest China. The seepage field in dam foundation is affected by the thickness, discontinuity form and opening size of the aquitard, which is needed to be studied in depth. In this paper, based on the seepage theory of unsaturated soil and seepage solution in Seep/w, we aim to obtain the influence of thickness and continuity of a aquitard in the middle position on the discharge per unit width and exit gradient, and compare with engineering practices. Results show that discharge per unit width and exit gradient decrease as the aquitard thickness increases. The influence of aquitard thickness on seepage field decreases in order of semi-closed cut-off wall, suspended cut-off wall and totally enclosed cut-off wall. The semi-closed joint anti-seepage system formed by aquitard and cut-off wall at the upstream is of the best control effect, followed by aquitard that opens at the downstream, case in which opens at both the upstream and downstream is the worst. The discharge per unit width and exit gradient increase with the opening length of aquitard. But at the upstream seepage system, since the weak layer only plays a weak role in water separation, therefore the opening length has little influence on seepage field. It is suggested that a semi closed joint anti-seepage system formed by cut-off wall and downstream aquitard is a doable measure, which can avoid the adverse condition that opens of aquitard both at the upstream and downstream. It is found that, compared with the monitoring result, the simulating error meets the codes. Therefore, the calculation method and conclusions of this paper are reliable.

Abstract:At present, the most common method to evaluate the health service and safety reliability of urban shield metro structures is limited to static analysis. In this paper, by applying the concept of Pair-Copula to Bayesian networks, the multi-joint probability distribution of evaluation index was obtained by constructing PCBN (Pair-Copula Bayes Network) structure, which is capable of identifying parameters' dependencies accurately and high-precision reconstruction. Based on the three kinds of failure modes, the correlation analysis and safety evaluation of shield metro structure nodes were conducted. The implicit information in monitoring data was exploited to characterize the risk status of the shield metro structure. As an example, an empty pushing section of Wuhan Metro Line 3 is used to build a PCBN model. Results show that the metro safety status obtained by the PCBN model is in good agreement with the actual risk information in the subway project, demon strating the accuracy and practicability of the PCBN network model proposed in this paper.

Abstract:Control of pollutant migration is the prerequisite for the reuse of contaminated soil. Considering the properties of contaminated saline soil and the mechanical demand in engineering utilization, lime and fly ash were chosen optimally as treated materials. The influence of lime and fly ash on adsorption-desorption behaviors of oil contamination in inshore saline soil were studied via static and dynamic tests. Results indicate that:under the individual action of lime and fly ash, the oil adsorption rate is increased by 26% and 14%, respectively, and it increases by 39% as combine. As a conclusion, lime and fly ash can effectively increase adsorption rate and improve adsorption rate of oil contamination. Adsorption kinetics of saline soil, lime + saline soil, fly ash + saline soil, lime + fly ash + saline soil on oil contamination conform to the dynamic nonlinear equation of Lagergren second-level dynamics. The adsorption equilibrium time of saline soil was 400 min and it reduced to 60 min for lime and fly ash. Lime and fly ash is beneficial to adsorb the free oil which cannot be adsorbed by saline soil. The adsorption isotherms of saline soil, lime + saline soil, fly ash + saline soil, lime + fly ash + saline soil are non-linear Freundlich models. Adsorption of oil contamination for lime + fly ash is an irreversible chemical process, which can help to reduce the influence of ambient temperature and enhance stability.

Abstract:Seven buckling-restrained braces were designed to verify the influence of different connection modes and structure modes on hysteretic behavior of buckling-restrained brace.They include two connections of the bolt connection and the articulated connection, three kinds of core material section form of "Ten" glyphs, "T" shape "and" one "glyph, two kinds of core material production method of end welding type and middle cutting type, and two combinations way of along the core material longitudinal full-length welding and only in the working section welding. In this paper, the load capacity, secant stiffness, energy dissipation coefficient and ductility of buckling constrained support are analyzed by the quasi-static loading test. The tests results show that the hysteretic curves of 7 specimens are full and stable,with energy dissipation ability, and the bearing capacity, energy dissipation coefficient and ductility increase with the increase of load displacement, and the secant stiffness decreases with the increase of load displacement. The restoring force model is of the typical bilinear characteristics and the connection mode and the structural characteristics possess no obvious effect on the hysteretic performance of buckling constrained support. The ratio of material properties, generosity and clearance and thickness of the core material are the main factors influencing the hysteretic performance. The results show that the two angles have synergistic work performance. Improving welding quality and increasing the radius of curvature of the transition arc near the limit card are the key factors to enhance the hysteretic performance of the end welded and the central cutting buckling constrained support.

Abstract:Based on the unified strength theory, the axial ultimate bearing capacities of composite L-shaped steel tube short columns filled with steel-reinforced concrete (CLSC-SRC) under three-dimensional stress were analyzed in this paper. According to characteristic of section shape, the column was firstly divided into one rectangle and one square steel tubular columns filled with steel-reinforced concrete. Then, considering the influence of width to thickness ratio on steel tube and a concrete strength reduction factor was introducect with scale effect. Because nonuniform constraint of the long and short edge of the steel tube was equivalent to the uniform constraint of the circumferential direction, a formula for calculation of axial compressive bearing capacity of CLSC-SRC can be developed. Finally, the formula for calculating the compression bearing capacity of the steel bone L-shaped concrete-filled steel tubular long columns was proposed referring to the code for design of steel structure. The proposed fomula was validated by comparing the calculation results with the corresponding test data. Results show that the proposed foumulations are correct and reasonabce. The effects of the parameters and Pull pressure ratio of Material and Osseous rate were obtained in the theoretical analysis. More importantly, the proposed formula has good applicability and extensive applications, offering a useful supplement to existing formulas obtained from experiments.

Abstract:In order to investigate the strengthening effects of different types of FRP sheets on the mechanical properties and failure modes of square concrete columns, 1/4 arc was adopted to replace the traditional second-degree parabola to distinguish the effective confinement area from weak area. Then the shape coefficients were improved and unified into one for purpose of engineering application. The performance of the five strength models after improvement was evaluated based on the analysis of 138 experimental columns strengthened by different types of FRP sheets. Satisfactory agreements between the improved models and the experiments were found. In order to extend the application range of the improved models, 8 BFRP jacketed concrete columns were further tested. Result shows the improved models is capable of predicting the bearing capacity of BFRP jacketed concrete column in predicting the load capacities of such columns was confirmed.

Abstract:Wood truss connected with metal plate is an important structural component widely used in modern timber structures. A new type of girder truss was developed and its bearing capacity and anti-deformation ability of light wood truss were studied. According to multi-stage loading test method specified in Standard for test methods of timber structures (GB/T 50329-2012), the deformation of 3 kinds of wooden trusses under standard design load and the ultimate bearing capacity during the destructive loading stage were compared. The test results showed that ultimate bearing capacity of wood truss is more than twice the standard design load which means the truss has great safety margin. During the course of design, the bearing capacity of the metal plate joints of the timber truss must be strictly checked to meet the basic requirements of corresponding bearing capacity of the truss. Several single trusses combined into girder truss by wooden dowel which have great synergistic effect can effectively solve the instability of the single truss. Wooden dowel joint is an effective connection for girder truss, which makes the bearing capacity of girder truss exceeds the sum of several single trusses and anti-deformation ability much better than single ones.

Abstract:Damping matrix of mixed structure no longer satisfies the classical damping condition. In such a case, the modal superposition method may become invalid. The advantage of hysteretic damping model is that energy consumption is related to external excitation frequencies in each cycle. At the same time, the calculation results of time-domain are stable. However, it does not meet the principle of energy conservation. By the equivalence of energy dissipation and damping power in each cycle, damping coefficient of hysteresis damping model can be modified. Subsequently, an improved hysteretic damping model and its own modal superposition method of mixed structure are proposed in this paper. The characteristics of improved hysteretic damping model response spectrum are firstly analyzed. Then, the most unfavorable combination of seismic effects could be calculated. Based on the improved hysteretic damping model, SRSS method for seismic analysis of mixed structure is performed. Results show that seismic effects of the improved hysteretic damping model are more significant than that of viscous damping model, and the increase is about 15%~20%.

Abstract:Based on social force model which is combined statistics and analysis of crowd motion characters and body motion parameters in the field of transportation and biodynamic, vibration comfort of long-span corridor under stochastic crowd load is studied and stochastic crowd motion is simulated.The critical parameters such as pace and landing position are obtained in different densities, the stochastic crowd model is built and the peak acceleration is calculated.The study shows, peak acceleration is closely related to the pacing frequency, and pedestrian velocity becomes large along with increase of pedestrian density while the acceleration response of structure increased initially and then decreased. By the relationship curve of structure peak acceleration and pedestrian density the pedestrian density interval in which the structure suffering vibration serviceability problems can be found.

Abstract:Regarding the problem of bridge girder's flutter under influence of wind-driven rain, the rainfall similarity laws are firstly established in terms of raindrop impact and surface ponding respectively, according to the characteristics of wind-driven rain and bridge main girder's vibration, besides, the selection principle is also discussed. Then, several typical main girder sections, which are frequently used in long-span bridges, are selected as examples to investigate the influence of wind-driven rain on flutter derivatives and flutter occurrence process by sectional model tests. Results show that there is no significant regularity between the flutter aerodynamic derivatives of the main girder and the rainfall intensity, as the variation of each derivative is almost the same. Comparatively, the variation of derivative caused by rainfall is increased with the wind speed. However, the general variation trend of the flutter aerodynamic derivatives with wind speed is not changed. When the test rain intensity is 120 mm/h, the critical wind speed of the flutter model raises about 20%~30%. Considering the similarity law proposed in this paper, the effect of rainfall on wind-induced flutter characteristics can be ignored.

Abstract:Based on SST K-ω turbulent model, aerodynamic measures of 2D-corner-cutoff square cylinder were simulated under all yaw wind angles, at Re=5×10⁴.The aerodynamic coefficient, lift frequency spectrum, strouhal number were studied after adding aerodynamic measures,which showed good agreement with other experiment test. The research results show that when wind yaw angle α ≤ 25°,the lift coefficients show a decreasing trend and increase greatly after adding fins;α>25°,The lift coefficients are on the rise and aerodynamic measures can't influence it. Drag coefficient increase after adding aerodynamic measures and the minimum of drag coefficient is at α=5~10°. Different vortex shedding pattern include different vortex-shedding frequency when the wind yaw angle is changing and vortex shedding isn't always simple harmonic wave. St number will diminish after adding aerodynamic measures and the maximum St number is at α=5°~15°.

Abstract:In the cyclic loading test of column or shear wall with the axial compression load, frictional force exists in the roller of steel hinges or the sliding rail, which is connected to the vertical actuator for applying axial force. The measurement of lateral load would be higher than its actual value due to this friction. On the basis of experimental research and finite element simulation, the variation characteristics and quantization method of the friction were investigated. In order to eliminate the influence of material nonlinearity and calculate geometric nonlinearity accurately, two steel columns were designed and cyclic loading tests under elastic situation were carried out. Besides, a finite element model which can accurately calculate the second-order effects was established on the OpenSees platform. Based on experimental and numerical results, the frictional forces were calculated, the method of determining the friction coefficient was proposed, and the influence of friction on the experimental results was evaluated. It was revealed that the frictional force caused by the devices for applying axial force was mainly affected by the axial compression force, while the top displacement of columns was of weak influence. As the axial compression force increases, the frictional force increases and the friction coefficient decreases. However, the maximum frictional force or the minimum friction coefficient converges. In cyclic loading test of the reinforced concrete columns with axial force of 350~900 kN,the measurement error of column top horizontal force caused by friction is 5~13 kN approximately.

Abstract:In order to accurately locate the fault sensor position in the structural health monitoring system, a sensor fault localization method based on the cumulative residual contribution rate is proposed. Based on the basic principle of principal component analysis, the data collected by the sensor under the vehicle load or the ground pulsation excitation are divided into the main element space and the residual space, and the fault is detected by SPE statistic. Furthermore, the residual contribution value is further deduced, and the cumulative residual contribution rate index is proposed. It improves residual contribution graph, also improves the accuracy of fault location. And sensor fault location is extended to simultaneously locate two fault sensors. The numerical simulation results show that the principal component analysis can accurately identify the four kinds of common sensor faults. The cumulative residual contribution rate not only better locates the single sensor fault, but also accurately locates the faulty position when the two sensors fail simultaneously.

Abstract:The manual arrangement, which has some defects such as low utilization rate of production area, time-consuming and low leakage, was mostly adopted in traditional localization of prefabricated concrete (PC) elements in industrial production. Building Information Modeling (BIM) technology is applied in the industrial production of PC elements to improve the degree of management informatization, and thus the problems mentioned above can be solved to some extent. A parametrized modeling standard was developed and a PC information model was created using Revit software and the minimum horizontal line algorithm was improved. On the basis of information, the algorithm was used to arrange components, so as to improve the degree of information and productivity of PC components.

Abstract:This paper aims to study the effect of single-doped steel fiber, monofilament polypropylene fiber and cellulose fiber on compressive strength and flexural toughness of concrete. The compressive strength and flexural toughness of concrete specimens were firstly tested under different volume fraction of fibers, and the variability of test results was then analyzed. The test results show that the compressive strength of the three kinds fiber reinforced concrete are 26.7%, 6.1% and 11.1% higher than that of normal concrete respectively. The average retention tate of secondary compressive strength are 77.0%, 45.7% and 58.0%. The flexural toughness index I₂₀, Nemkumar index PCSm, and toughness ratio R_x of fiber reinforced concrete are 4.2 times, 3.1 times, 2.6 times, and 19.9 times, 9.8 times, 6.9 times, and 4 times, 3.4 times, 2.7 times higher than of normal concrete respectively, which these based on load-deflection curves, Nemkumar method and bending-tension stress-strain curves, The results of the variability analysis show that the compressive strength of concrete is less than the flexural toughness after the incorporation of fiber. Meanwhile, the coefficient of variation of flexural toughness of concrete obtained from Nemkumar method and bending stress-strain curves is less than that of load-deflection curve method. Overall, the compressive strength and flexural toughness of steel fiber reinforced concrete are the most significant with the smallest coefficient of variation, and the compressive strength of cellulose fiber reinforced concrete and the flexural toughness of polypropylene fiber reinforced concrete are relatively significant.

Abstract:In order to study flashover phenomenon of special fire in building under construction, a fire energy conservation equation was first established in this paper. Then,the critical temperature of thermal smoke during the flashover was determined by the catastrophe potential function based on the swallowtail catastrophe theory. Finally, the software FDS was adopted to simulate the fire flashover considering different construction scenarios, so that the corresponding fire characteristic parameters can be obtained. The results show that different fire combustible materials at different construction stages lead to different flashover time points. With the increase of ventilation velocity, the rate of fire heat release increases slowly, whereas the visibility of smoke increases rapidly. In addition, the fire characteristic parameters are highly related to the fire sources. Thus, flashover is more likely to occur in narrow space, leading to an obvious chimney effect, especially for the unclosed stairwell.