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    • Experimental Study on Flexural Behavior of RC Beams with Lap Splices


      Abstract (157) HTML (0) PDF 23.53 M (129) Comment (0) Favorites

      Abstract:In order to investigate the influence of reinforced bar lap splices on the flexural performance of reinforced concrete beams, and verify whether the existing lap length factor can meet the limit requirements of the serviceability limit state of concrete structure design code (GB50010—2010), taking the lap length and lap percentage as variables, the flexural behavior of 16 reinforced concrete simply supported beams with lap splices under two-point concentrated load was tested. The development of cracks, crack width, crack spacing, failure pattern, flexural bearing capacity, and mid-span deflection of the specimen were observed. The test results show that the lap percentage and lap length have a great influence on the bearing capacity and deformation of the test beams, and the mid-span deflection values of the test beams all meet the limit requirements under the service state load. However, the crack width of the beams with a smaller lap length is difficult to meet. Based on the test data and considering the two parameters of lap percentage and lap length, the relationship between the maximum crack width of beams with lap splices and the maximum crack width of beams without lap splices is given, and the suggested value of the lap length factors is put forward. Based on this, the rationality of the Chinese concrete structure design code and the American ACI 318 code is discussed.

    • Vehicle Target Tracking Based on Kalman Filtering Improved Compressed Sensing Algorithm


      Abstract (158) HTML (0) PDF 22.34 M (156) Comment (0) Favorites

      Abstract:Aiming at the tracking-shift of traditional target tracking algorithms based on compressed sensing technology, a vehicle target tracking algorithm based on Kalman filtering improved compressed sensing algorithm was proposed in this paper. Firstly, the observed value was obtained by identifying the region with the highest probability of target existence in this frame based on the traditional compressed sensing target tracking algorithm. Secondly, the Kalman filter was used to predict the tracking trajectory of this frame so as to obtain the predicted value, and the Kalman filter gain coefficient was used to correct the predicted value and the observed value to obtain the final target tracking result. Finally, positive and negative samples were taken around the corrected target area to realize the updating of naive Bayes classifiers, and then the real-time updating of target tracking trajectory was achieved. The feasibility of the proposed method was verified by laboratory tests and field experiments. The average tracking error of the proposed method is reduced by 48% and 89%, respectively, compared with the target tracking algorithm based on compressed sensing technology. The tracking trajectory was closer to the real vehicle trajectory.

    • Experimental Study on Influence of Sleeve Section Size on Tensile Performance of Grouted Sleeve Lapping Connectors


      Abstract (138) HTML (0) PDF 21.28 M (80) Comment (0) Favorites

      Abstract:In order to study the influence of sleeve section size on the mechanical performance of grouted sleeve lapping connector, 39 specimens with different sleeve thicknesses and inner diameters were tested in unaxial tension, and their failure mode, ultimate bearing capacity, ductility, reinforcement and sleeve strain were studied. The results show that the failure forms of the specimens include tensile failure and pull-out failure of reinforcements. Due to the influence of eccentric loading, the effective lap length of the specimen is about 81% of the design lap length. When the inner diameter of the sleeve is the same, within a certain thickness range, the constraint of the sleeve increases with the increase of the wall thickness, and the bearing capacity of the specimen increases. When the wall thickness of the sleeve is the same, the constraint is weak when the wall thickness is small (1.5 mm). The larger the inner diameter (similar to the thickness of the protective layer), the greater the bearing capacity of the specimen. When the wall thickness is greater than or equal to 2.0 mm, the constraint is enhanced, the specimen is broken under tension, and the increase of the inner diameter has little effect on the bearing capacity. In the elastic stage, the influence of sleeve wall thickness on the bond force between reinforcement and grouting material is more obvious than that of sleeve inner diameter. The longitudinal strain of the middle section of the sleeve is tensile in the early stage of loading but gradually transforms to compressive strain with the increase of load. The circumferential strain of the middle section of the sleeve is compressive in the early stage of loading but gradually changes to tensile strain with the increase of load. The formulas for calculating the ultimate bonding stress of the connector and the critical lap length of the reinforcement are put forward, which have good applicability and can be used as a reference for practical engineering.

    • Influence of Constructional Pattern on Bending Stiffness of Composite Slab


      Abstract (111) HTML (0) PDF 8.34 M (70) Comment (0) Favorites

      Abstract:In order to meet the demand for large-span development of concrete composite slabs in recent years, a kind of composite slab filled with the lightweight aerated concrete block was proposed (i.e. CCS). Comparison tests were conducted to study the bending performance of CCSs with different parameters (longitudinal rib, filler, transverse rib) and ordinary concrete cite-in-site slab. Analyses were conducted on the mechanical parameters including ultimate bearing capacity, bending stiffness, load-rebar strain curves, and anti-slip performance. The differences in flexural properties between cast-in-site slab and CCSs were compared and analyzed; the influence mechanism of different parameter changes on the bending stiffness of CCSs was mainly studied. On this basis, the short-term bending stiffness calculation formula with different stress stages was proposed. Results show that: CCSs and ordinary concrete cite-in-site slabs share similar flexural behaviors, show evident features before failure, and their crack distribution is also nearly the same, presenting the typical bending failure mode of one-way slabs. The cracking load of the cast-in-site slab was higher than that of CCS, but the yield load and ultimate bearing capacity were lower than that of CCS. The constructional patterns of CCS have some impact on its flexural performance. According to the tests in this paper, the influencing degrees from large to small are as follow: longitudinal rib > whether filler block was exposed > transverse rib.

    • In-plane Flexural Capacity of Eccentric RHS Beam-column Joints


      Abstract (105) HTML (0) PDF 10.81 M (92) Comment (0) Favorites

      Abstract:To study the in-plane flexural performance of eccentric rectangular RHS beam-column joints, an in-plane bending test was carried out on the joints. The in-plane flexural capacity and failure modes of eccentric RHS beam-column joints were presented. The theoretical formula is improved by finite element parametric analysis, and a practical parametric calculation formula of the in-plane bending capacity of joints is established combined with regressive analysis. Results show that the failure mode of the joint is the combination of the yielding of the column flange surface and the buckling of the column web. Stiffeners can effectively improve the in-plane flexural capacity of eccentric RHS beam-column joints. Parametric analysis was carried out based on the numerical model to study the influence of the beam-to-column depth ratio, the beam-to-column depth-to-width ratio, the column width-to-thickness ratio, and the beam-to-column thickness ratio on the bearing performance of eccentric RHS beam-column joints. Increasing the beam depth and the column thickness is the most effective way to improve the bearing capacity of the joints. Finally, through numerical fitting, the calculation formula of the in-plane flexural capacity of eccentric RHS beam-column joints was obtained. The accuracy of the calculation formula is verified by comparing experimental results with numerical predictions.

    • Simplified Calculation Model of Cold-formed Thin-walled Steel Composite Wall


      Abstract (106) HTML (0) PDF 15.16 M (65) Comment (0) Favorites

      Abstract:The composite wall is the main load-bearing and lateral force-resisting component in cold-formed thin-walled steel structural systems, and the influence of the mechanical behavior of composite walls on the seismic performance of the whole building structure should be paid more attention to. Based on this, a simplified calculation model of cold-formed thin-walled steel composite walls was established. A nonlinear diagonal spring was used to simulate the shear deformation of the composite wall, and a beam-type member was set to simulate the bending deformation of the composite wall. The influence of the door and window holes can be constructed in the model. The calculation method of the axial stiffness of the diagonal spring in the simplified calculation model is derived by referring to the wall equivalent brace method recommended by the Japanese code. Combined with the pseudo-static load test of the composite wall, the correctness of the simplified calculation model of the composite wall is verified. The model meets the design requirements based on elasticity but is not suitable for the elastic-plastic analysis of structures. Finally, based on the simplified calculation model of the composite wall, the finite element model of three-storey cold-formed thin-walled steel structural building was established with reference to the shaking table test specimens. The validity of the simplified calculation model of the composite wall was verified by elastic time-history dynamic analysis, which can provide a reference for the seismic design of light-steel structures.

    • Comparative Analysis on Damage Mechanism of Two New Types of Concrete Filled Steel Tubular Lattice Wind Turbine Tower Joints


      Abstract (111) HTML (0) PDF 13.09 M (49) Comment (0) Favorites

      Abstract:This research was to find a more suitable joint form for the concrete filled steel tubular lattice wind power tower, two split spherical joints and two ellipsoidal joints were designed, and then the static test was conducted. Firstly, the failure mode of the two joints, the load-deformation curve of the web member, the stress distribution of the ball table, and the plate area of the ball table were compared and analyzed by controlling the change of the wall thickness of the ball table. Moreover, the parameters were expanded by ABAQUS. The results showed that the failure mode of the split spherical joint was the material strength failure and the plate buckling failure of the platform. Besides, the failure modes of ellipsoidal joints were the tear failure of the ball press plate and the bolt thread failure, and the elliptical joint showed higher ultimate bearing capacity. Compared with ellipsoidal joints, the stress distribution of split spherical joints was more uniform, the stress range was smaller, the material utilization rate was higher and the economy was better. When the wall thickness of the ball table increased from 6 mm to 10 mm, the ultimate bearing capacity of the two kinds of joints increased significantly; at the same time, when the stress level of the ball table of the split spherical joint decreased, the stress level of the pressure plate of the ball table increased significantly. The stress level of the ball table and the pressure plate of the ellipsoid joint decreased largely. The finite element analysis showed that the sensitivity of the ultimate bearing capacity of the joint to the wall thickness of the spherical platform was significantly reduced when the wall thickness of the spherical node and the ellipsoid node increased to 7 mm and 9 mm, respectively.

    • Characteristics and Mechanism of Longitudinal Displacement for Suspension Bridge under Vertical Loads


      Abstract (140) HTML (0) PDF 3.51 M (65) Comment (0) Favorites

      Abstract:In order to reveal the longitudinal deformation characteristics and mechanism of suspension bridges under vertical loads, the deformation characteristics of the cable under vertical loads were studied based on its deformation theory, and the analytical solutions of vertical and longitudinal displacement were obtained. On this basis, the longitudinal deformation characteristics and the longitudinal displacement of the stiffening girder for the traditional suspension bridge and the suspension bridge with central buckles are analyzed under vertical loads, the longitudinal restraint mechanism of the central buckles is subsequently revealed, and the simplified formulas to estimate the longitudinal displacement of the stiffening girder under vertical loads are deduced, respectively. Finally, the accuracy of the proposed displacement calculation formulas is verified by an example. The results show that the vertical and longitudinal displacement are coupled to each other due to the geometric nonlinear characteristics of the main cable. The main cable undergoes asynchronous longitudinal displacement, while the stiffening girder mainly moves longitudinally as a rigid body similar to the pendulum under the action of asymmetric vertical loads. The main cable, the stiffening girder, and the central buckles form a "rigid domain" area in the middle of the span as the existence of the central buckle. As a result, the longitudinal displacement of the stiffening girder decreases. The proposed method agrees well with the finite element numerical solution under different vertical load cases.

    • Fatigue Life Assessment of Corroded Cables Based on Crack Propagation


      Abstract (135) HTML (0) PDF 4.28 M (51) Comment (0) Favorites

      Abstract:The parallel wire cable is regarded as a series-parallel model with multi-crack competition, and the initial crack size of corroded steel wire is determined by a pitting non-uniformity coefficient. Based on the probability distribution of the parameters of the fatigue crack growth rate model, the fatigue life of the cable under different wire breakage rates is calculated by using the Monte-Carlo simulation method of the whole process of fatigue failure, and the calculated results are verified by the test data. The results show that the wire-breaking rate of the cable conforms to the growth law of the power series with the increase in fatigue times. When the wire-breaking rate of cable reaches about 10%, the wire-breaking rate of cable increases rapidly and loses the ability to resist fatigue load. The more the series steel wire elements are divided in the fiber bundle model, the shorter the fatigue life of the cable, but this trend gradually stabilizes with the increase of the number of steel wire elements. The fatigue life of the corroded cable follows the Weibull distribution, and the pitting effect shortens the crack initiation life of the steel wire, resulting in a significant decrease in both the average fatigue life and variability of the cable with the increase of the degree of corrosion, as well as a rapid deterioration of its anti-fatigue performance. The random load history is transformed into the repeated action of fatigue load spectrum block by the rain flow counting method. Based on the corrosion development law of steel wire, the fatigue life of cables with different corrosion degrees is calculated, and the relationship model between cable corrosion degree and fatigue life degradation under random load is established. According to the P-dc-N curve, the fatigue reliability of corroded cables can be evaluated. It is necessary to accurately grasp the defect or corrosion details of cable steel wire in the application.

    • Aerodynamic Characteristics of Two Side-by-side Square Cylinders in Biased Flow Regime


      Abstract (118) HTML (0) PDF 15.41 M (69) Comment (0) Favorites

      Abstract:The biased flow occurs when two side-by-side square cylinders are closely arranged. Wind tunnel tests are performed to investigate the aerodynamic characteristics of two side-by-side square cylinders in the biased flow regime. The Reynolds number Re is 8.0×104 and the spacing ratio T/B is in the range of 1.25~5, where T is the central spacing and B is the breath of a square cylinder. The variations of surface pressure coefficients, aerodynamic forces, and Strouhal number with spacing ratio are studied through the lateral wind tunnel tests. With respect to the biased flow regime, the temporal characteristics, spectral characteristics, and spanwise correlation of the aerodynamic forces are significantly discussed. The biased flow phenomenon mainly occurs in the range of T/B = 1.25~2, its direction is random and it disappears with the increase of spacing ratio. In the biased flow regime, the mean drag coefficients and fluctuating pressure coefficients of both cylinders are smaller than that of a single square cylinder, while the negative pressure on the gap-side surfaces of two cylinders is stronger than that on the side of a single square cylinder. Compared to the cylinder with a wider wake, the square cylinder with a narrower wake is characterized by stronger mean drag, fluctuating forces, gap-side negative pressure, and spanwise correlation of aerodynamic forces.

    • Model Size Effects on Vortex-induced Vibration Responses of a Streamlined Box Girder


      Abstract (113) HTML (0) PDF 12.17 M (59) Comment (0) Favorites

      Abstract:Aiming at the problem of model size effects on vortex-induced vibration (VIV) of the streamlined closed-box steel girders, based on the Hongqimen Bridge (HQMB) of Nansha to Zhongshan Highway, the combination method of wind tunnel tests and computational fluid dynamics is applied to carry out the investigations. Firstly, the wind tunnel experimental investigations on VIV responses of the streamlined closed-box girder segment models with two different geometric scales were conducted. Then, the numerical simulations of the fluid-structures interaction (FSI) of the streamlined closed-box girder section for VIV responses with different geometric scales were conducted. The results show that the VIV responses of the streamlined closed-box girders have obvious model size effects, where the maximum amplitudes of the main deck model with conventional geometric scale (λL=1/60) are generally larger than that of the main deck model with large length scale (λL=1/30). The numerical simulation results of the VIV responses of the streamlined closed-box girder with different geometric scales agree well with the wind tunnel test results, which verify the precision of the numerical method. Furthermore, the numerical results also indicate the ratio of length to width of the bridge girder model and the blocking ratio is not the key influencing factor on the size effects on VIV responses of the bridge girder model with closed-box streamlined section. Moreover, the VIV response of the main deck declines with the increase of the model scale ratio, and there are significant differences in the vortex shedding frequency distribution of the stationary girder model with different scale ratios.

    • Experimental Study on Shear Performance of Laminated Bamboo Lumber Nailed Connections


      Abstract (120) HTML (0) PDF 7.07 M (43) Comment (0) Favorites

      Abstract:In order to investigate the effect of the nail diameter and loading direction to the grain on the failure mode, load carrying capacity, hysteresis characteristics, stiffness degradation, and energy consumption capacity of the specimens, 50 laminated bamboo lumber (LBL) nailed connections were tested under monotonic and cyclic loadings. It is found that the failure phenomenon of the nailed connections varies greatly between different loading methods. For the specimens loaded monotonically, two plastic hinges within the nail and fiber crushing beneath the nail shank were observed. However, most nails failed in low cycle fatigue fracture due to reversed bending in the reversed cyclic loading tests, which is seldom investigated during the shaking table tests and earthquake excitation. The nail diameter is the major factor that affects the mechanical performance of the nailed connections. The load carrying capacity and the stiffness of the specimens increase significantly with the increase of the nail diameter, while the effect of the loading direction to grain is small. The load carrying capacity and stiffness of the specimens under monotonic loading are higher than those subjected to reversed cyclic loading. The load-displacement hysteresis curves of the specimens are not in plump shapes and have significant pinch phenomena at the initial loading stage. The cumulative dissipated energy of the nailed connections increases with the increasing nail diameter and decreases with the increase of the loading direction to the grain. These findings obtained can offer a theoretical reference for the design of the LBL nailed connections, and speed up its applications in the field of civil engineering.

    • Composition Design of Ultra-high Performance Seawater Sea-sand Concrete and Fiber Strengthening and Toughening


      Abstract (118) HTML (0) PDF 35.03 M (77) Comment (0) Favorites

      Abstract:This paper investigates the mix design optimization of the ultra-high performance seawater sea-sand concrete (UHPSSC) based on the simple centroid design method, and the effects of chopped ultra-high molecular weight polyethylene (UHMWPE) fiber and steel fiber on the workability and mechanical properties of UHPSSC were also studied. The experimental results indicate that the best mass fraction of cement, silica ash, and fly ash in the optimal mix design is 75%, 15%, and 10%, respectively, by comprehensively evaluating the flowability, flexural strength, and compressive strength of UHPSSC specimens. With the increase of volume fraction of chopped fibers, the flowability of UHPSSC decreases, while the flexural strength, compressive strength, and flexural toughness increase gradually. The UHMWPE fiber has a greater influence on the flowability of UHPSSC compared with the steel fiber, however, the improvement effect of steel fiber on mechanical properties is more significant. The failure mode of UHPSSC specimens under bending tests changes from brittle failure to ductile failure with the increase of volume fraction of UHMWPE fiber, and the amplitude of the second peak load is greater than the initial crack load when the volume fraction of UHMWPE fiber is 1.0%. Besides, for the specimens with both UHMWPE fiber and steel fiber mixed, the flowability of UHPSSC decreases slightly, while the flexural strength, compressive strength, and flexural toughness significantly improve. This study can provide some reference for the design and engineering application of UHPSSC.

    • Effect of Polyether Amine Grafted Graphene Oxide on Properties of Asphalt


      Abstract (115) HTML (0) PDF 2.08 M (52) Comment (0) Favorites

      Abstract:In order to improve the dispersity of graphene oxide (GO) in asphalt matrix and the performance of GO-modified asphalt, polyether amine grafted GO (PEA-GO) was synthesized, and the chemical structure of PEA-GO was characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), which verified the successful synthetization of PEA-GO. The properties of GO and PEA-GO- modified asphalt with different dosages were analyzed. The results indicate that PEA-GO shows a more obvious improvement effect on the conventional performance of asphalt than GO. At the same dosage, the penetration, ductility, and softening point of PEA-GO-modified asphalt are higher than those of GO-modified asphalt, while the viscosity of PEA-GO-modified asphalt is lower than that of GO-modified asphalt. At the same dosage, G* and G*/sinδ of PEA-GO-modified asphalt are higher than those of GO-modified asphalt. When the dosage of PEA-GO is 0.05wt.%, G* of modified asphalt is the highest, and δ of PEA-GO-modified asphalt is lower than that of GO-modified asphalt. The results show that PEA-GO is superior to GO in improving the high-temperature deformation resistance, elastic recovery ability, and anti-rutting ability of asphalt.

    • Numerical Simulation of Shield Tunneling Incorporating 3D Spatial Distribution of Strata


      Abstract (107) HTML (0) PDF 15.37 M (53) Comment (0) Favorites

      Abstract:In order to study the stratum disturbance law caused by shield tunneling under complicated stratum conditions, a simulation method of shield tunneling considering the three-dimensional spatial distribution of the stratum is proposed. This method uses the Kriging algorithm to construct a 3D geological model. The 3D geological information is then integrated into a finite element model via a conditional judgment algorithm, so as to facilitate the numerical simulation of shield tunneling with 3D geological information. According to the proposed method, a pre-processing program for the simulation of shield tunneling in complex strata is developed by C# language. A case study of the Changsha Metro Line 4 project is illustrated here. Three sections with different stratum conditions were chosen. And the excavation process of the earth pressure balance shield (EPBS) machine was simulated by pre-processing program with different proportions of extremely soft rock, soft rock, and hard rock in the shield tunneling face. Simulation results reveal that the increase in the proportion of extremely soft rock in the shield tunneling face can lead to a significant increase in the final surface settlement. Compared with the tunnel section with a 50% proportion of extremely soft rock, the final ground settlement at the full-sectional extremely soft rock was increased by 11.67 mm. This finding is consistent with the measured data, verifying the effectiveness of the proposed method.

    • Analysis on Load Transfer Behaviors of Equal-core Stiffened Deep Mixed Pile under Flexible Foundation


      Abstract (162) HTML (0) PDF 4.07 M (103) Comment (0) Favorites

      Abstract:In order to investigate the load transfer behaviors of the equal-core stiffened deep mixed pile under a flexible foundation, the stress-deformation modes of this kind of pile subjected to vertical load are analyzed first. Based on some experimental results, the double-exponential function load transfer model is introduced to characterize the interface shear softening process between the core pile and cemented soil. And the ideal elastic-plastic load transfer model is introduced to describe the interface shear deformation properties between cemented soil and the surrounding soil. The pile is then divided into several elements. Based on the load transfer method, a load transfer analysis model is established for the core pile, the cement soil pile, and the surrounding soil. And the recursive formulas used to calculate the stress-deformation behaviors of each element of the pile are further derived. A calculation flow for obtaining the distributions of axial force, side friction and interface relative displacement of the core pile, the cement-soil pile, and the surrounding soil is established by using the iterative calculation method. An analysis and calculation method for the load transfer behaviors of the equal-core stiffened deep mixed pile under a flexible foundation is thus proposed. Finally, the reliability of the proposed theoretical method is verified by comparing the calculations with the results of the field test and engineering case. At the same time, based on the calculation results, the distributions of the side friction and axial force of the equal-core stiffened deep mixed pile under a flexible foundation are discussed and obtained. The research achievements can provide guidance for the design practice of equal-core stiffened deep mixed piles under a flexible foundation.

    • Study on Microstructure Anisotropy of Kaolin under Different Hydration Environments


      Abstract (109) HTML (0) PDF 22.36 M (86) Comment (0) Favorites

      Abstract:To study the effect of different hydration environments on the microstructure anisotropy of kaolin, this paper carries out the deposition experiment of different salts, acids, and aqueous solutions for kaolin (Acti-MinR PG) produced in South Carolina, USA, and measures 13 XRD spectra with the X-ray diffractometer by rotating the χ angle of the kaolin sample from 0° to 72°. The quantitative texture analysis of XRD spectra of kaolin sediments was carried out by the Rietveld method based on MAUD software. On the basis of filling the lack of quantitative (non-qualitative) analysis method of clay micro texture, the orientation distribution was determined, and the formation mechanism of the structural anisotropy from the micro perspective was expounded. The results of the study reveal that pH and ion concentration have an effect on the arrangement of kaolin particles. With the increase of ion concentration in the salt solution, the weakening of electric double-layer repulsion makes the particles form an aggregation structure, which enhances the preferred orientation of kaolin and makes the soil show strong structural anisotropy. With the decrease of pH of the solution, the electrostatic attraction between the edge-face association promotes the formation of flocculation of particles and weakens the preferred orientation of kaolin.

    • Upper Limit Analysis of Anti-sliding Stability of a Rigid Retaining Wall in Unsaturated Soils


      Abstract (113) HTML (0) PDF 7.70 M (48) Comment (0) Favorites

      Abstract:In the previous analyses of retaining wall stability, it was assumed that the backfill soil behind the wall was saturated soil, and the influence of the suction stress effect on the sliding stability of the retaining wall was ignored, which led to the distortion of the calculation results. In view of this, based on the generalized effective stress principle, the work-energy balance equation applicable to unsaturated soils was derived, and on this basis, a method for calculating the upper limit stability coefficient for anti-sliding of the retaining wall-unsaturated soil system was proposed by using the energy method. The rationality of the method in this paper was verified by comparing the results of OptumG2 numerical software and the existing theoretical methods. And the influence of parameters such as soil shear strength, air-entry value, and seepage flow on the stability of the retaining wall was discussed. The research results show that: 1) Compared with sand, suction stress has a greater impact on the stability of retaining wall in clay, while the change of cohesion in the sand is more sensitive to the stability of the wall-soil system; 2) With the increase of air-entry value, the contribution of the suction stress to the stability of the wall-soil system decreases and eventually tends to be constant, and the influence of the suction stress on the low retaining wall is more obvious; 3) Compared with the case without suction, the stability coefficient considering suction is larger, the influence of different seepage flow on the stability of the wall-soil system is as follows: evaporation> no flow> infiltration, and the seepage flow has the greatest influence on the stability of retaining wall in clay and silt, followed by loess and sand.

    • Construction of Detailed 3D Model of Construction Site and Earthwork Survey Based on UAV


      Abstract (105) HTML (0) PDF 17.46 M (102) Comment (0) Favorites

      Abstract:Using unmanned aerial vehicle (UAV) oblique photogrammetry technology, multi-view image sequences of engineering construction sites are obtained. Ultra-high-density point clouds are formed by dense matching of structure from motion (SfM) and multi-view stereo (MVS) algorithms. The cloth simulation filtering (CSF) algorithm is used to remove the point cloud of vegetation and abandoned buildings to obtain the real ground point cloud. The earthwork volume between the two-phase point clouds based on the base design model is calculated to realize the intelligent measurement of complex earthwork engineering. Using the above-mentioned UAV method, the rapid earthwork measurement and accuracy assessment of the two construction lands at the foot of Changsha Yuelu Mountain are carried out, and a point cloud density of 538.46 million points per hectare is obtained. The error of the earthwork calculation result relative to the RTK-GNSS measurement result is 2.8%, which satisfies the requirement that the earthwork measurement error is less than 5%. This method has a good application prospect and engineering value.

    • Relationship between Fine-macro-strength of Loose Rock Pile and Surrounding Rock Pressure


      Abstract (146) HTML (0) PDF 4.51 M (42) Comment (0) Favorites

      Abstract:The surrounding rock mass of a railway tunnel in southwest China is a large porosity giant loose rock pile, which is a typical discontinuous granular material and cannot be solved by classical soil mechanics based on continuous media. In order to study the strength characteristics of loose rock piles and the stability of surrounding rock from a fine-to-macro perspective, this paper starts from the mechanical analysis of granular material mechanics on tight sands, and it is obtained that the deformation mode of the plane occlusal model of loose rock piles is point-surface contact action through the analysis. The macro-strength relationship dominated by the friction angle of the rock block elements inside the rock pile is deduced. The occlusal model between the rock mass elements of the loose rock pile is proposed, and the relationship of the occlusal force of the loose rock pile is obtained. The mesoscopic friction angle between the rock block elements has a greater influence on the macroscopic strength. Starting from the Protodyakonovco theory suitable for broken surrounding rock and combining the mesoscopic strength formula of the rock pile, the calculation method of the natural balance arch axis of the loose rock pile is obtained. The surrounding rock pressure is calculated through a railway tunnel, and its rationality is verified.

    • Experimental Study on Tensile Response and p-y Curve Characteristics of Negative Batter Pile under Top Horizontal Tension


      Abstract (154) HTML (0) PDF 10.29 M (73) Comment (0) Favorites

      Abstract:In order to study the response characteristics of the battered pile under horizontal tension, the 0°, 10°, 20° battered pile and rock socketed 20° battered pile at the pile bottom were set in the model sand, the horizontal tension load was applied on the pile top, the tension direction was opposite to the inclination direction, the horizontal displacement, strain gauge and earth pressure box strain of four model piles were tested, and the variation rules of horizontal displacement, bending moment, soil resistance and p-y curves characteristics with inclination angle and constraint conditions of pile bottom were obtained. The results show that: 1) when the pile top is subjected to horizontal tension, with the increase of the inclined angle, the horizontal displacement at the top of the negative battered pile gradually increases, and the peak value of the bending moment increases. But the peak value of the soil resistance decreases gradually, and the depth of the soil resistance peak point decreases gradually, and both the horizontal bearing capacity and the ability to resist bending of the single pile also decrease. 2) With the increase of pile bottom restraint, the horizontal displacement of negative battered pile top decreases, the peak values of pile bending moment and soil resistance decrease, and both the horizontal bearing capacity and the ability to resist bending of single pile increases. 3) The displacement mode of the model negative batter pile under horizontal tension is "rotation + bending", and the position of the rotation point is reduced with the increase of inclination angle or pile bottom constraint degree. 4) The p-y curves of 0° ~ 20° negative battered active pile can be fitted by p/pub=α(y/y50)β, and the inclination angle and pile bottom constraint degree have little effect on α. The inclination angle has little influence on the variation range of β value, and the variation range of β value decreases with the increase of pile bottom constraint.

    • Numerical Simulation Study on Forces and Wear of Shield Scrappers Used for Concrete Cutting by Discrete Element Method


      Abstract (120) HTML (0) PDF 34.42 M (71) Comment (0) Favorites

      Abstract:In recent years, cases of using shield machines to cut concrete foundations during urban tunnel construction have been increasing steadily. It is of great significance to investigate the forces and wear of the shield scrapers for the safety and efficiency of shield tunneling and the expansion of the shield machine application. Based on the previous tests, numerical simulations of using scrappers to cut concrete are performed by using the software EDEM. And the effects of the cutter parameters (the tool rake angle, tool relief angle, and tool-tip shape), the sample strength, the cut depth, and the cutting speed on the forces acting on the scrapers are investigated. And wear of cutters is also discussed based on the Archard model. Calculation results show: 1) The force on the cutters decreases with the increase of the tool rake angles. 2) The tool relief angles and the tool-tip shapes have a small influence on the forces on the cutters. 3) The force on the cutters increases with the concrete sample strength, the cut depth, and the cutting speed. The averaged calculations of the forces have good agreement with the results obtained from the tests on the whole. The most worn part is the cutter tip; more serious cutter wear is observed when subjected to a larger tool rake angle; the cutter wear amount increases with the increase of the concrete sample strength, the cut depth, and the cutting speed. The findings can provide good references for shield scrapper design.

    • Spatiotemporal Distribution of Aerosols Generated by Using Ultrasonic Scaling Instrument


      Abstract (112) HTML (0) PDF 10.47 M (51) Comment (0) Favorites

      Abstract:The study performed an on-site measurement of the spatiotemporal distribution of aerosols at the range of 0.3~10.0 μm, generated during the use of an ultrasonic scaling instrument in the dental treatment. The mass concentration and number of aerosols were monitored within 0.8 m away from the patient's mouth at three vertical heights from the floor, namely 0.8 m (the height of the patients' mouth), 0.9 m, and 1.1 m (the height of the medical staffs' mouth). The mean concentration of aerosols in the area within 0.8 m away from the patient's mouth is approximately 300 μg/m3, which is higher than the allowed thresholds in indoor spaces. This concentration is measured when a suction system with an inner diameter of 6 mm is used. Vertically, the medical staff's respiratory zone is less affected by the spattering during the dental treatment. Horizontally, the concentration of aerosols is similar along different directions and the attenuation is not obvious along the distance. Compared with powder jet handpieces, the diameter of aerosols generated by an ultrasonic scaling instrument is mostly less than 1 μm and the initial momentum of aerosols is lower obviously, indicating different levels of pollution risk of aerosols generated by different instruments. The results indicate that the present control measures, including the suction system, are not effective to prevent the spattering of aerosols generated by ultrasonic scaling instruments. New control measures should therefore be developed to limit the high risk of cross-infection in dental hospitals and clinics.

    • Research Progress and Prospect of Hail Impact Resistance of Engineering Structures


      Abstract (167) HTML (0) PDF 22.68 M (86) Comment (0) Favorites

      Abstract:Hail is one of the most serious disastrous weather phenomena, and the loss caused by hail is increasing year by year. How to reduce the hail-induced loss has become a practical problem that must be faced in the engineering field. However, the research on the hail impact resistance of structures is very limited at present. Therefore, it is of great significance to systematically investigate the theory and practice of structural hail impact disaster reduction and prevention. In this study, the mechanical properties of the hail are first summarized. Then, the experimental and numerical research status of hail resistance of engineering structures is introduced in detail. Finally, the research on the coupling effect of hail, strong wind and heavy rain and its mechanism are prospected. This study is supposed to provide the basic data and new perspectives for the research on hail resistance of structures.

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