Abstract:To achieve the ductility design of steel staggered truss framing systems and improve seismic behavior of the whole structure, this paper proposes a seismic design method for the steel staggered truss framing system by studying the design method of web members and the limit of the inter-story drift ratio. The typical failure mechanism of the steel staggered truss framing systems is analyzed firstly, and based on the expected failure mode of the chords failure in vierendeel panels, the internal force calculation model of truss members under horizontal earthquake and the adjustment method of internal force of web members under rare earthquake are proposed. Secondly, based on the expected failure mode and the ultimate deformability of truss, the composition of truss inter-story drift ratio under rare earthquake is analyzed, and the limit value of elastoplasticity inter-story drift ratio under different lengths of vi? erendeel panels are derived and proposed. Finally, the seismic design method and process of steel staggered truss framing systems under horizontal earthquake are proposed. The calculation analysis of examples shows that the seis? mic design method proposed in this paper can effectively dissipate the seismic energy and achieve the seismic design goals of“strong web member, weak chord member”and“no collapse in the strong earthquake”.

Abstract:Aiming at the problems that the effective contact area between the steel bar and concrete decreases and the bonding property becomes worse after the reinforcement is bundled, the bond anchorage property of the rein? forcement was studied through the bond anchorage tests of 57 pull out specimens and 6 beam specimens. The influ? ences of the number of rebars, test method, diameter of rebar, strength of concrete, anchorage length and the position of rebar on the bond slip performance of the bundled bars were studied. The test results show that the greater the num? ber of parallel bars, the lower the nominal bond strength; Compared with a single steel bar, the test method, anchor? age length, diameter of steel bar, concrete strength and position of steel bar have a similar influence on the bond strength of bundled bars, but the influence degree is different. Based on the test data analysis on the empirical for? mula of bond strength in design codes, it is suggested that the equivalent diameters of 2 and 3 bundled bars should be 1.41 and 1.73, respectively, so as to be used for the values of anchorage length and thickness of cover. When the thickness of cover is reduced, the anchorage length of the bundled bars can be appropriately extended.

Abstract:Aiming at the problems of insufficient identification accuracy and difficulty in collecting training samples in existing vehicle load identification method based on neural network, a vehicle load identification method based on time-frequency analysis of strain signal and Convolutional Neural Network (CNN) is proposed to identify the total weight of mobile vehicles. Firstly, the time-frequency characteristics of the strain signal are obtained by using the wavelet time-frequency transform, and the time-frequency matrix is changed into a 64×64 numerical matrix as the input data of CNN. Secondly, in order to realize the purpose of unknown vehicle load identification, the map? ping relationship between strain response and vehicle load is directly established after training a small number of nu? merical matrices by using the regression learning algorithm of CNN. Finally, through simulation tests, it is found that although the load recognition results of the CNN are affected to varying degrees under the influence of different road roughness and noise, the vehicle load can still be more accurately identified under the influence of certain road rough? ness and noise.

Abstract:In this study, a new bridge weigh-in-motion (BWIM) algorithm based on the convolutional neural net? work technology was developed for identifying the axle weights of multi-vehicles crossing the bridge. First of all, the bridge strains under vehicular loading with variable weight were simulated using the vehicle-bridge coupling simula? tion system. Then, a convolutional neural network, consisted of nine convolutional layers and two fully connected lay? ers, was developed based on an open source framework for deep learning, i.e., KERAS. The convolutional neural net? work was trained by Adam optimizer to map the relationship between the bridge strain and the vehicle weight under different scenarios, and optimized by minimizing the fitting error. Eventually, the identification accuracy of the pro? posed BWIM system was analyzed under the conditions of single- and multi-vehicle loadings. The results show that the mean identifying error of the proposed BWIM was less than 5% for both the single- and multi-vehicle scenarios, and changed slightly with the varying traveling speeds and lateral loading positions, indicating the good and stable performance of the proposed BWIM algorithm in axle weight identification. In addition, the proposed BWIM system doesn’t need a bridge influence line in advance to identify the axle weight, and therefore provides an alternative technology for bridges that are not suitable for the influence line method.

Abstract:To make good use of the widely used steel-bars truss deck in assembled steel structure buildings, the bottom rebar of the steel truss was welded to the upper flange of U-shaped steel beam as a new shear connector in this study, and the experimental study and finite element analysis were conducted on four designed specimens with different shear connectors, i.e. steel truss, angle steel, studs and their combination. The test results showed that the failure modes included bending failure and slip failure; the specimen with steel truss as shear connector can not achieve the full shear connected composite beams, and some studs can be configured to improve its composite action. The shear performance of the specimen with steel truss and stud as combined shear connector was better than that of the specimen with steel truss and angle steel as combined one. Then, finite element analysis was conducted via ABAQUS software, and the ultimate bending capacity of finite element analysis was in good agreement with the ex? perimental one. Based on the experimental and finite element analysis study, a calculation formula of ultimate bend? ing capacity of the U-shaped steel-concrete composite beam with truss deck under positive bending moment was de? rived based on the plasticity theory

Abstract:Aiming at two typical discrete optimization problems of steel frame，namely, the volume minimization with compliance constraint and the compliance minimization with volume constraint，a linear relaxation approach based on convex combination is proposed. Meanwhile, the linked discreteness of design variables is also relaxed lin? early, and the original nonlinear and nonconvex problems are recast as relaxed convex programming problems. Spe? cifically, the compliance minimization with volume constraint is reestablished as a second-order cone programming, and the volume minimization with compliance constraint is reformulated as a semidefinite programming. The global optimum solutions of two types of convex programming problems can be readily derived using existing mature optimi? zation solvers. These global optimum solutions are also the theoretical lower bound for the discrete optimization prob? lems. An example of a one-bay four-story frame is presented, and the results by the proposed approach are compared with the solutions by complete enumeration and genetic algorithm. The comparison demonstrates that the proposed approach is capable of achieving the theoretical lower bound in an efficient manner.

Abstract:The axial compression tests of 4 sets of concrete-filled steel tubular (CFST) specimens with different internal details of the longitudinal stiffeners and lattice steels were carried out. The axial compression behaviour of the CFST specimen with reinforcing lattice angles and the ordinary CFST specimen are compared and analyzed. The results show that the ultimate load bearing capacity of the specimen with longitudinal stiffeners, reinforcing lattice angles，and combined longitudinal stiffeners and reinforcing lattice angles is increased by 4.65%, 10.53% and 21.12%, respectively, compared with the ordinary CFST specimen. The failure pattern of each specimen is consistent, which is the overall instability accompanied by various local buckling of the steel tube. The small“core column”is composed of the reinforcing lattice angle and infilled concrete, which can delay or inhibit the development of con? crete cracks, and significantly improve the load bearing capacity and the ductility of members. The numerical simulation analysis on the whole process of lattice steel reinforced CFST members under axial compression is conducted. The stress development process of each component of the member is obtained. A formula for calculating the axial bearing capacity of the lattice steel reinforced CFST member is proposed. The calculation results of the formula are in good agreement with the test results, and give a conservative estimation.

Abstract:To investigate the seismic behaviour of the steel double-channel build-up member with reinforced concrete (RC) slab, quasi-static tests on four specimens with RC slabs were carried out under constant axially com? pressive load and reversed cyclic bending. The effect of the stitch spacing, the stiffener in plastic hinge region and the web depth-thickness ratio on seismic behavior of the testing specimens was studied. The experimental results in? dicate that all hysteresis curves are stable, showing excellent energy dissipation capacity and ductility. With the de? creasing stitch spacing, the strength and stiffness of specimens change insignificantly, but the ductility and energy dissipation capacity can be improved. The peak bearing capacity and initial stiffness of Specimen SJ3 are 28.42% and 22.70% higher than that of Specimen SJ1, respectively, indicating that the strength and stiffness of specimens can be improved by setting stiffeners in the plastic hinge region. The peak bearing capacity, ductility coefficient, initial stiffness and cumulative energy dissipation of Specimen SJ4 are 33.88%, 20.70%, 27.40% and 12.84% higher than those of Specimen SJ1, respectively, indicating that the seismic performance of specimens can be significantly improved by reducing the web depth-thickness ratio.

Abstract:In order to improve the accuracy of nondestructive testing methods to predict the bending strength of ancient building wood, multi-point nondestructive test was carried out on ancient Tibetan Populus cathayana bending specimens with stress wave detector and resistograph detector. By comparing the bending strength of the specimens, the correlation between nondestructive testing index and the bending strength was analyzed. The influence of measur? ing method, location and number of measuring points on the correlation coefficient, as well as the optimal combina? tion of independent variables in the multivariate model were discussed. The results indicate that the correlation coeffi? cient between nondestructive index and bending strength increases with the increasing of the number of measuring points; the stepwise regression method can quickly determine the optimal combination of independent variables in the multivariate model, while avoiding the colinearity of independent variables. Compared with the univariate linear model, multivariate linear model determined by the optimal combination of independent variables can increase the correlation coefficients and adjust R square between nondestructive index and the bending strength by 20.54% and 42.92%, respectively, which proves that the multi-point nondestructive testing method can effectively improve theprediction accuracy of bending strength of ancient building wood.

Abstract:In this study, the scanning electron microscope was employed to examine the morphology of the inter? nal original defects and microstructure of the fiber reinforced polymer (FRP) cable. The microscopic damage model of FRP cable with internal hole and interface defects was established with ABAQUS-Python platform to analyze the multi-scale mechanical behavior of the FRP cable. The results show that the equivalent elastic modulus of the fiber is mainly affected by the porosity and the length-to-diameter ratio of the hole. Specifically, the equivalent elastic modulus increases with the reduction of the holes’cross-sectional area under the same porosity and void volume. Considering the random distribution of the holes, the simulated results of the equivalent elastic modulus of fiber are higher than those obtained by the Mori-Tanaka theoretical calculation. When the length-to-diameter ratio of the holes in the fiber is less than 1, the position of the holes has the greatest influence on the equivalent elastic modulus. Based on the shear-lag theory, the equivalent elastic modulus of the fiber linearly decreases with the interface defect rate, when considering internal interface defects of materials. Based on the random failure constitutive relation of the fiber bundle, multi-scale finite element models of cable and tendon in the macro-scale were established based on the USERMAT, and the influences of micro- and meso- scale defects on the overall performance of composite materials were investigated. Finally, the simulated results of FRP tendon and cable agreed well with the experimental results by considering various Weibull parameters and the mechanical parameters of fiber bundles with internal defects.

Abstract:To compensate for the deficiency of natural sand (NS) resources during the production of selfconsolidating mortar (SCM) in the area with limited medium sand resources and promote the utilization of ultra-fine sand (UFS), this study aimed to use UFS as a substitution of medium-size sand in the production of selfconsolidating mortar (SCM) and examine the effect of different replacement ratio on the rheology of self-consolidating mortar (SCM). The results showed that there existed an critical UFS replacement ratio with regard to its influence on the rheology properties of the SCM. This is because the high water absorption capability of UFS can decrease the free water content in the SCM matrix, resulting in the deterioration of its rheological properties. However, the particle ef? fect of the UFS could improve the gradation of self-compacting mortar, allowing more free water to be released dur? ing mixing and improving the rheological properties. The viscosity and the yield stress of the SCM mixture increased as the UFS ratio increased. Also, the influence of the high water absorption of UFS on consistency was more obvious at UFS replacement ratio over 30%. Taken together, the UFS ratio should be fixed within 30% for the production of SCM with a good rheological performance.

Abstract:In order to investigate the eccentric compression performance of polypropylene (PP) fiber reinforced concrete column under the combined action of load-sulfate attack, an eccentric compression experimental research was carried out on eight PP fiber reinforced concrete columns and one ordinary concrete column. The loaddeformation curve, load- steel strain curve, and strain of column section were obtained, and the effect of different stress ratios and corrosion time on failure modes, ductility and peak load was analyzed. The results showed that the addition of PP fiber can effectively inhibit the sulfate corrosion. The increase of stress ratio was raised at first and then reduced with the peak load. As the corrosion time increased, the peak load increased first and then decreased with the decrease rate by 15.8% for time from 120 d to 150 d. Meanwhile, the ductility coefficient increased first and then decreased with the increase in corrosion time, while decreasing with the increase in stress ratio. And the coeffi? cient at 150 d was reduced by 15.79% compared with that at 60 d. Considering the damage caused by stress ratio and sulfate attack, a damage factor was introduced to establish the calculation formula of concrete compressive strength after the combined action of load-sulfate erosion. Furthermore, considering the contribution of tensile strength of PP fi? ber, an equivalent rectangular stress diagram was used. Finally, the equivalent coefficient of tensile zone was utilized to establish the bearing capacity formula for PP fiber reinforced concrete column under the combined action of loadsulfate attack. In addition, a maximum crack width formula concerning the influence of PP fibers and sulfate corrosion was also established. The theoretical results calculated by the above formulae agreed well with the test results.

Abstract:The existing studies show that reinforced concrete beams strengthened with prestressed near-surface mounted (NSM) CFRP are easy to fail by concrete cover separation due to the stress concentration at the bonded end of CFRP. In this paper, the construction details of applying gradient prestress at the end of CFRP were proposed, and a series of experiments were carried out to study the load-carrying behavior of the strengthened beams under static and fatigue loads. The test results show that under static load, the ultimate load of beams strengthened with gradually anchored prestressed NSM CFRP was increased up to 35.06%, compared with the beam strengthened with prestressed NSM CFRP. And the failure mode was changed from the concrete cover separation at bonded end into the combined failure of the concrete cover and CFRP fracture. These indicate that the strengthen method with gradually anchored prestressed NSM CFRP can significantly improve the monotonic behavior of beams, and there is an obvious bond stress peak transfer phenomenon. In addition, the fatigue life of beams strengthened with gradually anchored prestressed NSM CFRP was significantly increased, and the fatigue failure mode is changed from the concrete cover separation to the fatigue fracture of longitudinal steel bars. The details of applying gradient prestress enhances the ability of strengthened beams to resist the failure of end concrete cover, and thus improves the fatigue performance.

Abstract:The mechanism of flutter stability of open-cross-section and lower stabilizers are studied by numeri? cal calculation. The reliability of the numerical method is verified by comparing the wind tunnel test results of aerody? namic force coefficients and critical flutter wind speed. The mechanism of flutter instability and the suppression mechanism of lower stabilizers are analyzed intuitively by visual flow field. The results show that the incoming flow is separated from the upstream railing, the upstream of box room bottom and the lower inspection access road. Vortices are formed upstream and developed downstream of the girder. During this period, the aerodynamic force with the same motion direction as the girder is generated, which becomes the dominant factor of flutter divergence. The lower stabilizers are added to the girder to form stable vortices on the lower surface, which effectively suppresses the flutter divergence. By adding 1/4 lower stabilizers, stable vortices are formed between the stabilizers, and the aerodynamic force continues to do negative work in the motion cycle. However, by adding the lower central stabilizer and 1/4 lower stabilizers at the same time, the vortices formed between the upper inspection access road and the stabilizers alter? nately dominate the direction of aerodynamic force with the vortex on the upper surface. Aerodynamic forces do nega? tive work first, then positive work and eventually negative work in the motion cycle. Flutter stability of the girder is more beneficial to be improved by adding only 1/4 lower stabilizers than adding both 1/4 lower stabilizers and lower central stabilizers. The research results can provide a reference for the selection of flutter suppression measures of the same type of girder.

Abstract:The impacts of wind barrier parameters on the aerodynamic characteristics of the vehicle-bridge sys? tem are investigated to optimize the wind barrier parameters of the highway bridge. Based on wind tunnel tests con? sidering the wind barriers with different heights and ventilation rates, the aerodynamic coefficients for the bridge and the vehicle are obtained, respectively. Afterward, the lateral displacement of the bridge under testing wind speed of aerostatic stability and the critical wind speed of aerostatic instability for the vehicle running with the design speed are calculated, respectively. A multi-objective genetic algorithm (NSGA-II) is applied to obtain the related Pareto op? timal solution set. In the algorithm, the lateral displacement of the bridge and the critical wind speed for the vehicle are considered as optimal objectives. Meanwhile, the height and the ventilation rate of the wind barrier are regarded as the variables. Taking advantage of the Data Envelopment Analysis (DEA) to evaluate the relative efficiency of the individual in the Pareto solution set, the optimal parameter of the wind barrier can be determined finally. The results show that the wind barrier with the ventilation rate of 30% and the height of 3.2 m has the best performance in consid? eration of the wind-resistant effect for both the bridge and the vehicle.

Abstract:To analyze the stability and determine the support form of high steep slopes, it is important to con? firm the occurrence and location information of rock discontinuities. In order to solve high risk and low efficiency ex? isting in the traditional survey method, this paper proposed the new survey method to semi-automatically identify the discontinuities in slopes based on nap-of-the-object photogrammetry and a clustering algorithm. Firstly, M210-RTK was used to obtain high resolution digital images; the structure from motion algorithm was used to generate the de? tailed 3D models and 3D point clouds. Then, through the K-Nearest neighbor and principal component analysis algo? rithm, the set of coplanar point clouds was selected to determine the boundary range of discontinuities. Finally, the best planar equation of coplanar point cloud is fitted based on the least-squares method, and the normal vector direction of the planar equation is the basis for calculating the occurrence parameters. Validation experiments show that the accuracy of the digital surface model is better than 2cm in any direction, and the error in dip and dip direction are better than 3° and 2°, respectively. This method identified rock preferred discontinuities in the abandoned mining area of Changsha, and the influence of preferred discontinuities on slope stability was analyzed, providing the vital foundation for the slope evaluation and treatment.

Abstract:The change of porosity and the tortuosity induced by the swelling progress of Geosynthetic Clay Liner (GCL) influence the hydraulic conductive obviously. The model simulating the seepage in bentonite is established by COMSOL to investigate the effect of the expansion process of bentonite particles on the hydraulic conductive of GCL.The COMSOL simulation results showed that the maximum velocity of the boundary channel is less than that of the non-boundary channel, when the liquid passes through the pores between the bentonite particles, which is consistent with the Poiseuille equation and initially verifies the accuracy of the model. The microscopic particle velocity distri? bution law is consistent with the velocity distribution law of macroscopic fluid field. Therefore, the macroscopic hy? draulic law can be investigated in the microscopic aspect. Meanwhile, the particle expansion on the porosity and the tortuosity of bentonite is analyzed by using the particle trajectory monitoring method in COMSOL. The results showed that the tortuosity decreases with the increase of porosity, and it is exponentially functional. Based on the capillary model of porous media and the Poiseuille Formula, the theoretical prediction model of the hydraulic conductive of GCL, which can reflect the influence of porosity and the tortuosity, is proposed, considering the exponential function relationship between the porosity and the tortuosity. The theoretical calculation prediction model for predicting the hydraulic conductive of GCL is proposed. The ratio of the theoretical and experiments is between 1/5 and 5, which confirms the accuracy of the theoretical model of GCL.

Abstract:To examine the influence of cohesion and internal friction angle on surrounding rock pressure of shallow-buried and asymmetrical load tunnel under variable slopes, the thrusts on both deep and shallow sides of shallow-buried and asymmetrical load tunnel under variable slopes are obtained using limit equilibrium theory, and then the calculation methods are derived for surrounding rock pressure under variable slopes independently consider? ing cohesion and internal friction angle. The rationality of the proposed calculation methods in this paper is verified by comparison with the normative formula and existing literature. The influencing factors on the horizontal lateral pressure coefficient of the deeply buried side of the tunnel are discussed. The results show that the horizontal lateral pressure coefficient increases with the increase of the slope of the ground surface, decreases and then increases with the increase of the angle of the rock-soil, and decreases with the increase of the cohesion and internal friction angle. Besides, the split calculation of the cohesion is helpful to consider the adverse effects of the rapid changes of the me? chanical parameters (cohesion) of rock soil caused by environmental factors (such as rainfall). The internal friction angle has a greater influence on the horizontal lateral pressure coefficient of the deeply buried side of the tunnel, which shows that the split calculation of the internal friction angle is of great significance to the calculation of sur? rounding rock pressure. The relevant research results can provide a theoretical basis for the structural design of simi? lar shallow-buried and asymmetrical pressure tunnels under variable slopes.

Abstract:Based on the reflection method, superposition principle and the theory of seepage mechanics, two sim? plified calculation models for external drainage with or without grouting ring are constructed. The calculation formu? las for the inflow of the tunnel and the external drainage tunnel, and the external water pressure expression of the sec? ondary lining of the tunnel are deduced. Analytical degradation verifies the correctness and applicability of the theo? retical model and analytical formula. The parameter sensitivity analysis is carried out according to the deduced for? mula, and finally it is further tested through numerical simulation. The results show that the water inflow of the exter? nal drainage tunnel and the tunnel decreases nonlinearly with the decrease of the permeability coefficient of the grouting circle, and the external water pressure of the secondary lining of the tunnel increases nonlinearly with the de? crease of the permeability coefficient of the grouting circle, but the critical value is less than conventional drainage method; increasing the thickness of the initial support can achieve the purpose of reducing the external water pres? sure of the secondary lining and the amount of water inflow of the tunnel; the reasonable ratio of the permeability coef? ficient for the surrounding rock to the grouting circle, as well as the grouting circle to the initial support, is 15 and 100, respectively, and at the same time, the permeability coefficient of the secondary lining must be strictly con? trolled; the diameter of the drainage tunnel has a significant impact on the inflow of the external drainage tunnel. To protect the ground water resources, the external drainage tunnel diameter is recommended to be 0.2 m.

Abstract:In order to study the influence of household heat pump air conditioner air supply modes on thermal comfort, the environmental parameters, as well as 15 subjects' thermal sensation and thermal comfort, were investi? gated under the air supply modes of medium air supply, down air supply and distributed air supply in the artificial en? vironment laboratory. The results show that when the initial background temperature is 0 ℃ ，the air temperature around all human body parts can be increased quickly and evenly by the distributed air supply mode, and the overall thermal sensation and the overall thermal comfort of the subjects rise fastest, so the thermal comfort of the subject has a significant improvement. After the indoor thermal environment is stable, the temperature evenness of the distributed air supply is the minimum of 1.9 ℃, which makes the subjects in the air supply area feel warm, the local thermal sen? sation difference is the smallest, and the subjects in the other places do not feel cold. The fitting results of steady state local thermal sensation and overall thermal comfort show that the thermal sensation of the feet has a significant effect on the overall thermal comfort, the vertical air temperature difference of the distributed air supply and down air supply is less than 3 ℃，and the thermal sensation of feet can be improved in the air supply area. Thus, about 75% of the subjects are satisfied with the thermal environment. In conclusion, the distributed air supply can meet more people's requirements for thermal comfort.

Abstract:Based on the natural gas and solar energy coupled CCHP system with hybrid energy storage（heat storage/power storage），an optimization model is established from the aspects of energy saving，economy and envi? ronmental protection. The rated capacity of the prime mover，the start stop ratio of the prime mover，the solar ther? mal / photovoltaic area and the cooling ratio of the electric refrigerator are set as the optimization variables，and the quantum particle swarm optimization algorithm is used to solve the optimization model. After optimization，the opti? mal capacity and operation mode of the coupled system are obtained，and a hotel building in Guangzhou is taken as an example to verify the optimal model. The results show that the performance of the coupled system under the two optimal operation modes is better than that of the separate production system，and the performance under follow “electricity”demand mode（annual primary energy saving ratio：37.9%；annual total cost saving ratio：39.9%；an? nual CO2 reduction ratio：55.1%；overall performance：44.3%）is better than that under follow“thermal”demand mode（annual primary energy saving ratio：30.7%；annual total cost saving ratio：36.1%；annual CO2 reduction ratio：42.1%；overall performance：36.3%）.