Abstract:This paper systematically elaborated the preparation method， fiber distribution characteristics， and fracture properties of directed steel fiber reinforced concrete （ASFRC） in combination with research achievements in recent years. It compared and introduced the characteristics and applicability of different methods for preparing ASFRC. By summarizing varieties of methods for determining the parameters to describe the distribution characteristics of steel fibers， it discussed the influence of different factors on the distribution of steel fibers in detail. Referring to the test method and technical standard of ASFRC fracture performance， it compared different fracture indices obtained from bending fracture tests and results. Meanwhile， it summarized the influencing factors and fracture simulation based on the existing research on the fracture properties of ASFRC. Finally， it prospected the possible research directions of ASFRC.

Abstract:To investigate the fluidity and mechanical properties of basalt fiber reinforced cement mortar （BFRCM） at different mixing ratios， the mixing ratio of BFRCM was adjusted by changing the water-cement ratio， the contents of water reducers， and the mixing ratios of long and short fibers. Fourteen groups of BFRCM samples were prepared by using 2 kinds of fiber aspect ratios， 7 kinds of basalt fiber volume dosages， 3 kinds of water-cement ratios， and 3 dosages of water-reducing agents. The fluidity， compressive strength， and flexural strength of the BFRCM at different mix ratios were analyzed， the load-displacement curve of the BFRCM after peak load was normalized， and the fracture toughness of the BFRCM after specimen fracture was quantitatively analyzed. The results show that the fluidity of the BFRCM decreases with increasing basalt fiber content， decreasing water-cement ratio， decreasing water reducer， and increasing short fiber proportion. The increase in the water-cement ratio has little effect on the compressive strength of the BFRCM but reduces its flexural strength. The application of the water-reducing agent has a certain negative impact on the compressive and flexural strength of the BFRCM. The blending of long and short basalt fibers can effectively improve the compressive and flexural strength of the BFRCM through its synergistic effect， but too much short fibers can weaken the strengthening effect of basalt fibers on the BFRCM. Increasing the content of basalt fiber and the water-cement ratio can improve the fracture toughness of the BFRCM after peak load within a certain range. However， the increase in short fiber ratios and the application of water-reducing agents negatively affect the fracture toughness of the BFRCM after peak load.

Abstract:To study the influence of steel fibers on damage and failure behaviors of ultra-high-performance concrete （UHPC） at short-term high sustained stress loading， an experimental program on creep damage and failure was proposed by using UHPC and normal concrete at the age of 28 days. The stress-strain relationship of each specimen was measured during the whole loading processing. The failure modes， irreversible strain， creep strain， and nominal Poisson’s ratio were analyzed according to the tested results. Based on the non-destructive ultrasonic test and scanning electron microscopy test （SEM）， the expansion of internal micro-cracks within UHPC specimens and the bond damage between steel fibers and matrix were characterized. The results show the high sustained stress of UHPC and normal concrete lead to the development of internal micro-cracks and lateral expansion of specimens， and finally result in the creep failure of specimens. The bridging and confinement effects provided by steel fibers can control the development of internal micro-cracks， and reduce the lateral expansion of specimens. Before sustained loading， UHPC and normal concrete have similar nominal Poisson’s ratios of 0.18~0.19. After sustained loading， the nominal Poisson’s ratio of UHPC becomes 0.28， whereas the normal concrete specimens have a higher nominal Poisson’s ratio of 0.6. When the sustained stress was higher than 0.70 f_c， creep damage of UHPC specimens occurs， which lead to the reductions in strength and elastic modulus at cycle of reloading. With the increment in sustained stress， the bond between steel fibers and matrix is damaged， and the steel fibers fail to confine the development of internal micro-cracks. As a results， the specimens are continuedly damaged and finally fail.

Abstract:To investigate the effects of grouped-stud arrangement on the mechanical performance of the post-combined UHPC （ultra-high performance concrete） composite deck， bending load tests and finite element parametric analysis based on the UHPC plastic damage model were conducted for a composite deck specimen with averagely spaced studs and a post-combined composite deck specimen with grouped-stud connection. The test results show that the failure characteristics of these two specimens are UHPC plate crushing and steel U-rib bottom yielding. The elastic flexural stiffness of the specimen with grouped-stud connection and the one with averagely spaced studs are 232 kN·mm^-1 and 213 kN·mm^-1 respectively， and the bearing capacity are 2 154 kN and 2 049 kN respectively. The maximum interface slip value of these two specimens is less than 0.2 mm before the U-rib yielding. These two specimens have the same strain distribution and strain development pattern. The cross-sectional strain distributions of the specimens approximately obey the plane section assumption. The parametric analysis results show that there is no significant change in the bearing capacity and elastic bending stiffness when the grouped-stud hole spacing is increased from 600 mm to 1 200 mm. When the grouped-stud hole size is the same， the hole spacing has no significant effect on the bonding state of UHPC bonding interfaces. The 600 mm spacing of grouped-stud holes can better ensure the safety of studs and the cross-sectional combination effect than the 1 200 mm arrangement. Comparing the flexural performance of parametric models， the longitudinal spacing of 600 mm combined with the 2×3 grouped-stud arrangement in the hole is more favorable to improve the stress state of the post-combined steel-UHPC composite deck under positive bending.

Abstract:To study the effect of steel-polypropylene crude fiber on the bending and tensile properties of ultra-high performance concrete （UHPC）， a four-point bending test was conducted to obtain different volume contents （the content of steel fiber and polypropylene crude fiber being 0， 0.5%， 1.0%， and 1.5%）. The load-deflection curve under the combination is described from the failure form， flexural strength， flexural toughness， etc.， of the specimen， and a model with high feasibility is derived from the fitting formula of the single-doped fiber to analyze the synergistic effect of the hybrid fiber. Finally， the microstructure of the hybrid fiber UHPC was observed and analyzed by scanning electron microscopy （SEM）. The test results show that the incorporation of steel-polypropylene crude fiber significantly improves the flexural strength of UHPC， with an increase range of 17.8% to 101.2%. At the same time， using the proposed method， it is found that the synergistic effect of hybrid fibers showed a positive synergistic effect when the total fiber volume content is between 1.5% and 2.0%， and the best positive synergistic effect is obtained in S10P10. In addition， compared with the specimens without fiber， the initial crack toughness of matrix specimens increases by 51.8 % to 98.2 % and 33.9 % to 48.2 % respectively with the addition of steel fiber and polypropylene crude fiber. When the content of steel fiber is 1.0% and the volume content of polypropylene crude fiber is 1.0%， the improvement to the bending toughness of UHPC is the best， which further verifies the evaluation model of fiber synergy effect. Finally， the synergistic effect and the toughening mechanism of the hybrid fiber are revealed at the micro level.

Abstract:Cable-stayed bridges， as crucial joints in transportation networks， of which the towers are vulnerable to experience plastic damage during earthquakes leading to rescue work delay. In this regard， a novel concrete material and a novel constraint device are proposed to enhance the resilience of the cable-stayed bridge system. Beside the new constraint device named SMA （shape memory alloy） cable-based restrainers which were installed in the conventional cable-stayed bridge， the new concrete material named the ultra-high property concrete （UHPC） was casted in the plastic hinges in the tower of the novel cable-stayed bridge system. Two finite element （FE） models of the conventional and innovative cable-stayed bridge systems are established， respectively. A series of far-field and near-field earthquake recorders are used to conduct the vulnerability analysis. The results show that the UHPC material and the SMA cable-based displacement restrainers can improve the resilience of the innovative cable-stayed bridge system with only a slight increase in cost， expanding the application scenarios of the UHPC and the SMA cable-based restrainer.

Abstract:Truck platooning is a traffic mode that can realize close distance following between trucks through automatic control， wireless communication， and other technologies. The decrease of gap directly leads to the increase of heavy vehicle density. Moreover， long-span bridge can accommodate a large number of truck platoons， which may affect the whole or partial structure. To study the load effect of truck platooning and mixed traffic flow composed of ordinary vehicles and truck platoons on bridge structure， and the applicability of the current design code， this paper investigated the actual test and theoretical research on truck platooning at home and abroad， and proposed a load model for truck platooning and a simulation method for mixed traffic flow based on the measured traffic flow data of long-span bridges in service. The mixed traffic flow simulation of a long-span suspension bridge was conducted， considering the actual operation condition of the bridge. In addition， the vehicle load effect level and safety of the bridge in the representative mixed traffic scenarios were studied， and the influence of truck platooning mode and mixed traffic flow on the vehicle load effect of the long-span suspension bridge was analyzed. The results show that the load effect of mixed traffic flow is significantly higher than that of ordinary vehicle traffic flow， but it is still lower than the code value. The effect value under different loading scenarios is about 35%~80% of the code value， indicating that the current code can provide a good safety margin for the global effect and partial effect of structure under mixed traffic flow with the participation of truck platooning， and that the safe service of the bridge can be ensured under the corresponding operation conditions in the future.

Abstract:A cable tray is a typical non-structural component in high-rise buildings. In order to study its seismic performance， two groups of simulated earthquake shaking table tests were conducted using full-scale models. The first group test aimed at cable trays equipped with three different types of seismic supports； the second group test aimed at an L-shaped three-dimensional cable tray with horizontal and vertical bend-way sections. Several groups of ground motions were input to the cable tray suspended on the steel platform. The damage， dynamic characteristics， displacement response， and acceleration response of the cable tray were described and analyzed. The test result shows that the seismic damage to the suspended cable tray is mainly concentrated at the joints of the main and sub beam of the tray component， and the failure of the joints causes the sub beam to fall. The displacement response and damage of cable trays with different types of seismic supports are significantly different， while the acceleration response is less different. The seismic performance of rod-type seismic support is better than that of section-steel-type seismic support. Moreover， the seismic performance of reinforced seismic support is the best. Compared with the straight section of the cable tray， the seismic damage to the bending section is smaller. Increasing the lateral stiffness of the seismic support and the strength of the main and sub beam joints of the tray component can improve the seismic performance of the cable tray.

Abstract:With the goal to develop a digital twin model with a seamless procedure for performing an intensity-based seismic resilience assessment of school buildings with self-centering modular bracing panel （SCMBP） systems on a regional scale， a computational framework comprised of sequential steps was built in the Python programming language by adopting multiple packages. The results of the analysis （e.g.， repair cost， repair time， probability of irreparability， etc.） were generated in different contexts such as graphs， tables， and multiple shapefiles containing the building footprints and resilience metrics such as repair time and repair cost at different seismic intensities that could be visualized three-dimensionally in geographical information system （GIS） software to present a more intelligible quantitative evaluation of the regional seismic loss of the building inventory with a retrofit modular bracing panel system. The steps consisted of generating the building inventory， generating simplified numerical models， response history analysis （RHA），obtaining engineering demand parameters （EDPs），estimating the quantity of the vulnerable components，probabilistic seismic loss assessments， and generating the building-specific and regional outputs. The probabilistic loss assessment was performed based on the component-level FEMA P-58 methodology by adopting the Pelicun package. As a case study， the regional seismic resilience assessment of buildings equipped with SCMBP systems was conducted by performing a study of nearly two thousand school buildings in the San Francisco Bay Area with such systems. A simplified structural model for simulating the SCMBP systems was adopted to reduce the computing time of regional-scale seismic resilience evaluation while exhibiting an identical story-shear hysteretic behavior. The effect of the key parameter of the energy dissipation ratio， β， of SCMBP systems on the resilience metrics of the school buildings was studied by performing a parametric study.

Abstract:In order to study the propagation law of blast shock wave in a flat large space such as underground parking lot， a 2D axisymmetric analysis model was established using AUTODYN software. The propagation characteristics of shock wave after 8 different masses of TNT detonated at the ground in the middle of the flat large space were analyzed. By combining the propagation cloud picture of blast shock wave and the pressure time history curve of some gauges， it is found that the shock wave will form multiple Mach waves in the propagation process， and the height of the Mach stem of the first Mach wave can reach the space net height. The height of the Mach stem of the subsequent Mach wave is small， but the propagation speed is fast， and it will eventually catch up with the first Mach wave， and converge with it. The peak overpressure at the junction is increased compared with other positions of the Mach stem. As the propagation distance increases， the influence of subsequent Mach wave waves on the first Mach wave decreases. The formula for determining the horizontal position of the critical point where the peak overpressure of the Mach wave front is constant and the corresponding maximum peak overpressure value according to the scaled clear height， and the formula for determining the average value of the maximum peak overpressure according to the plane scaled distance are given.

Abstract:To realize the maximum and low-carbon utilization of waste concrete resources， a novel full recycled aggregate concrete （FRAC） was proposed， i.e.， using the recycled coarse and fine aggregates processed from waste concrete to replace natural sand and gravel to prepare new concrete. Taking four different aggregate combinations as parameter variables， the mechanical properties， shrinkage characteristics， and uniaxial compressive stress-strain relationship of FRAC were experimentally studied. The results show that the recycled aggregate combinations have an adverse effect on the development of concrete compressive strength， especially for concrete with full recycled fine aggregate. But by adjusting the mixing proportion， the FRAC can meet the design requirement for strength grade above C30. The full recycled aggregate combination increases the drying shrinkage of concrete， especially at the early stages. When FRAC has a small deformation under uniaxial compression， the damage began to develop and accumulate obviously. By considering the initial damage and mechanical damage， a damage constitutive model for FRAC under compression was established， which could well describe its stress-strain behaviour. Finally， the future research direction of improving the mechanical properties of FRAC was prospected.

Abstract:This paper proposed a novel method for determining the stress change rate index R_s and the locking point of stress （LPS） based on a new granular sensor （SmartRock） to test the contact stress of particles inside the asphalt mixtures during rotary compaction. Three asphalt mixtures， AC-13， AC-20， and SMA-13， were selected for rotational compaction to test the contact stress of coarse aggregates. The interlocking state of mixture samples was investigated and identified from the perspective of micro-mechanics. In addition， the results of the identifications were compared with those from the traditional rotary compaction method. The results indicate that the test signals of the SmartRocks located at the top and bottom of the specimen have a spectral aliasing and harmonic interference. It is recommended to arrange the smart sensors in the middle of the specimen with less interference. For the AC-13 mixture， three compaction stages could be found. In the initial compaction stage， the coarse and fine aggregates contact and squeeze each other， and the stress and R_s of the coarse aggregates increase rapidly. As the fine aggregate and asphalt binder suspend around， the coarse aggregate begin to bear the load， and the stress of the coarse aggregate and R_s decrease and enter the creeping stage. When a stable internal structure is formed between the aggregate and the asphalt binder， the stress reaches an interlocking state. For the AC-20 mixture， the coarse aggregates quickly form an occlusal skeleton and the contact stress continues to increase under the action of external load to enter the tightening stage， resulting in the increase of stress and R_s. When the aggregates form a stable skeleton load-bearing structure， the interlocking state is reached. For the SMA-13 mixture， it would segregate due to the improper temperature. At a mixing temperature of 170°C， the particle stress amplitude fluctuates and increases non-linearly during the tightening compaction phase. Compared with the interlocking points results from the traditional method， the LPS determined based on R_s all lags behind the volume interlocking point.

Abstract:The longitudinal deformation of track slab under temperature load leads to the deviation of anchor reinforcement， which could lead to differences in the structural stress state from the design intention. To clarify the actual effect of planting reinforcement， first， the temperature deformation of longitudinal slab ballastless track was monitored， which quantitatively represented the actual deviation of anchor reinforcement. Then， the refined finite element model of embedded reinforcement anchorage of ballastless track was established， which was used to analyze the damage law of embedded reinforcement layer under different deflection conditions. Finally， the actual embedded steel bars effect of ballastless track under the coupling of anchorage reinforcement deviation and debonding was clarified. The results show that the longitudinal deformation of track slab could reach 0.946 mm. The offset of the anchor reinforcement aggravates the damage of the rubber layer of the embedded reinforcement， which is the main reason for the degumming failure of the anchor system. The damage evolution of the embedded rubber layer is vertical from top to bottom. The debonding failure between the embedded reinforcement layer and the track slab weakens the ability of the anchorage system to resist high-temperature camber deformation. When the debonding depth exceeds 200 mm， the camber of the track slab increases by 137.18%. In the evaluation of the actual effect of the embedded steel bars on ballastless tracks， it is necessary to consider the longitudinal temperature deformation of the track slab and dynamically adjust the actual maintenance plans.

Abstract:A modified environment chamber and a laser vibration meter were used to identify the modal parameters of damping treated thin plate at different temperatures. An experimental analysis was conducted to analyze the influence of temperature on the modal frequency and modal damping ratio. The results show that the temperature is negatively correlated to the modal frequency of damped thin plate， the modal damping is greatly reduced at extremely high and low temperatures. An inverse identification method based on optimization algorithm was proposed to identify the material properties of damping material. The variation of complex modulus and loss factor of damping material with temperature and frequency were identified for further verification by finite element method. The simulation results show that the resonant frequencies and response amplitude are better correlated to the measured values， by using the temperature and frequency dependent parameters to predict the vibration response of damping treated thin plate.

Abstract:In this paper， a joint simulation model of GT-suite and MATLAB / Simulink was constructed by using the calibration data of the actual engine and a collaborative control module for estimated torque feedback based on intake air and engine state parameters was established. A comparison was made between the estimation results errors of the ANN method and the Map method for estimating the steady state， transient torque variation， upshift and downshift of the engine. The results show that the Map method is more reliable under steady-state conditions， and the error of ANN method is small at low， medium， and high engine speeds， with errors of 1.31%， 1.09%， and 1.52% lower than the ANN method， and the error of the ANN method is 5.62% and 1.32% lower than that of the Map method under torque transient conditions， and 1.93% and 0.84% lower than that of the Map method under lifting conditions.

Abstract:Hydrogen energy is recognized as one of the most potential energy sources in the 21st century due to its non-polluting， high calorific value， and wide sources. As one of the forms of hydrogen energy utilization， hydrogen refueling stations are divided into gas-hydrogen refueling stations and liquid hydrogen refueling stations. Compared with gaseous hydrogen， liquid hydrogen may become the main form of utilization in the future due to its high density and high storage and transportation efficiency. In this paper， the process flow of liquid hydrogen refueling station is given. Then， the compression， gasification， storage， transportation， refueling process， equipment and risk research of hydrogen refueling station， are introduced respectively. Finally， the future of liquid hydrogen refueling in China is prospected， providing reference for the large-scale application of liquid hydrogen refueling stations.

Abstract:Aiming at the problems that traditional missing value detection methods are not comprehensive enough to analyze the multidimensional feature data and it is difficult to select the most appropriate missing value algorithm among numerous methods， this paper first designs a missing value detection method and then proposes three different concepts of missing degree to achieve the comprehensive detection of the data with multidimensional features. On this basis， it compares and analyzes the performance of different missing value imputation methods. The results show that the proposed detection method can evaluate the data with multidimensional features effectively and provide basis for the selection of missing value imputation methods.

Abstract:By combining the entropy weight method， the analytic hierarchy process （AHP）， and the technique for order preference by similarity to ideal solution （TOPSIS）， a multi criteria decision-making framework for evaluating pilots’ competency is proposed. First， based on the research of pilot competency indicators framework at home and abroad， an evaluation indicators system for pilot competency is constructed. Next， the entropy weight method is used to weigh the core competency indicators of pilots. Then， the AHP is used by experts to weight psychological competence and style competence indicators， and an integrated weight indicators system is established. Finally， based on the weight of evaluation indicators， the TOPSIS method is used to rank the pilots’ competency. The feasibility of the proposed method is verified by applying it to the competency assessment of airline pilots.