Abstract:Shear walls are important lateral force-resistant components of high-rise building structures. To study the reliability of precast walls with openings connected by grouted sleeve lapping connectors named APC connectors （all vertical members precasted in concrete structures）， pseudo-static tests were carried out on a cast-in-place wall and two precast unequal-limb walls with an opening in which vertical reinforcements were spliced by type-Ⅰ and type-Ⅱ APC connectors. The failure modes， hysteretic behaviors， characteristic loads， deformations， strains of reinforcement and sleeve of the specimens， as well as the shear properties of bonded surfaces， were studied. The results showed that the crack development process of all specimens was basically the same， and the bending shear failure occurred in the wall limb and the coupling beam. The damage to the cast-in-place wall began at the bottom of the wall limb， while the concrete above the sleeve of the precast wall was crushed first. In addition， the failure of the outside of the wall limb of each specimen was more serious than the inside. The section at the top of the sleeve was the weak surface， and vertical reinforcements above the sleeve were prone to buckling in the failure stage， which should be strengthened during the design of the stirrup of the component. The crack load， yield load， and stiffness of precast walls were slightly higher than those of cast-in-place walls， and the peak load and strength degradation coefficient were similar， but the ductility was slightly worse. At the same loading stage， the energy dissipation capacity of all specimens was similar. The grouting joint surface of the precast walls showed reliable shear resistance， and both APC connectors can effectively transfer reinforcement stress in the precast walls. The precast shear wall with an opening spliced by APC connectors can achieve the seismic performance equivalent to the cast-in-place wall.

Abstract:To investigate the flexural performance of damaged hollow slab girders strengthened with UHPC， two hollow slab girders were designed and fabricated to perform the field full-scale experiments， and the failure modes and load-mid span deflection behavior of the unreinforced/reinforced girder were analyzed based on the comparison of field testing results. The experiment results show that the UHPC layer can effectively improve the failure mode of the damaged hollow slab girder， and the reinforced girder exhibits good flexural and deflection capacities. Compared with the unreinforced girder， the cracking and ultimate loads of the reinforced girder are increased by 11.5% and 23.8%， respectively. Moreover， the reinforcement mechanism of the UHPC layer was discussed， and the theoretical formulas were derived to determine the ultimate bending moment of the reinforced girder， and the theoretical values were compared with the experimental results. The results show that the error between the calculated values and experimental ones is only 1.1%， which verifies the accuracy of the theoretical formulas.

Abstract:Based on the unsteady characteristics of the flow field under crosswind， a numerical model including crosswind， tunnel， and train was established and the influence of tunnel type on aerodynamic pressure， flow field characteristics， and the aerodynamic load of HST in the process of leaving a tunnel under crosswind was studied. The results show that the aerodynamic pressures at the tunnel exit are the most significantly affected by the tunnel type. The change magnitude of aerodynamic pressure on the windward and leeward side of the train in a single-track tunnel （STT） are 15.7% and 22.6% greater than that in a double-track tunnel （DTT）， respectively. The blocking ratio is the primary cause of the apparent difference in aerodynamic pressure in STT and DTT under the same train type， train speed， and crosswind conditions. The distances between the separation vortex formation position and the nose tip of the head vehicle （HV） are the same， but the leeward side of the train driving out of DDT has a greater degree of flow field offset； The flow field distribution around the head vehicle and the middle vehicle （MV） are basically the same and less influenced by the tunnel type， while the tunnel type more influences the flow field distribution characteristics of the tail vehicle （TV）. The aerodynamic load of the TV is more sensitive to the tunnel type. The side force cofficient and lift cofficient amplitude of TV in DTT are 27.3% and 7.1% larger than that in STT， respectively. When an HST leaves tunnels with a crosswind， it is suggested that the effect of the tunnel type on the aerodynamic performance cannot be ignored.

Abstract:In the study of deformation characteristics of deep foundation pit excavation in a soft soil environment， the hardening elastic-plastic model is often used for analysis， such as the HSS model and MCC model. In the soft soil area of the Nanjing River floodplain， large local deformation often occurs during deep foundation pit excavation. Some soil deformation states are between small and large strains， so a single model cannot accurately predict the deformation characteristics of soil. At the same time， the BP neural network has been widely used for predicting foundation pit deformation prediction. However， in the training process， the weight threshold easily falls into the local optimal solution， which affects the accuracy of prediction. Based on this， relying on the typical soft soil deep foundation pit project in the Nanjing area， the HSS model and MCC model in Midas are used to analyze the difference in pile deformation between the two models， and the two models are linearly fused based on the least squares criterion. The fusion model can calibrate and supplement the monitoring data of the subsequent section. The BP neural network is optimized by fusing the sparrow search algorithm， and the global optimal weight threshold is obtained by fast convergence in the training process. Based on the monitoring data of the excavated section of the narrow and long foundation pit， the training is learned. The deep deformation characteristics are revealed according to the shallow excavation of the subsequent section. The predicted results are in good agreement with the measured values. The research results have important reference value for predicting the large deformation of deep foundation pits in soft soil areas.

Abstract:The design of large-diameter shield tunnels is challenging due to the complex stratigraphy. Conventional design methods relied on borehole data to identify favorable stratigraphic sections or averaged stratigraphy. However， these methods failed to depict accurately during the tunnel excavation. To address the issue， this study first proposes a new approach by constructing a coupled Markov chain model using existing borehole data to determine the most possibly crossed dominant strata during shield tunneling. Subsequently， numerical simulations with various design parameters are conducted， the standard deviation related to convergence deformation of large-diameter shield tunnels is used as the robustness index， and a robust design of large-diameter shield tunnels based on stratigraphic variability. Study results show that the dominant strata of the coupled Markov chain model provide a more precise assessment of stratigraphy for shield tunnels. Moreover， the robust design based on the refined stratigraphic condition is more suitable for practical implementation. The commonly used strata design approaches at present are optimized to guarantee that the strata chosen are close to the actual situation during tunneling， which can effectively reduce the tunnel construction cost and enable the tunnel to have better robustness.

Abstract:A consolidating method of “shell plate” aiming at the existing right-angle mutational steel crane beam is proposed， where a “shell type” steel plate with an arc is welded on both sides of the web at the variable section of the crane beam for fatigue reinforcement. The stress level of fatigue detail is reduced by increasing the stiffness of the web in variable section areas， thus improving its fatigue strength. In this paper， the fatigue performance of a right-angle mutational steel crane beam reinforced with “shell plate” is studied through a scaled fatigue test， the fatigue failure law of the crane beam reinforced with “shell plate” is analyzed， while the fatigue performance of the reinforced crane beam is evaluated. Meanwhile， taking the principal stress of the most dangerous fatigue detail of the reinforced crane beam as the basic parameter， the Sr，p-N fatigue curves of the reinforced crane beam are given. Moreover， the correctness of crack propagation simulation and fatigue life calculation of the crane beam after reinforcement is verified by the experimental results， and the fatigue crack propagation characteristics of the crane beam damage details after the “shell plate” reinforcement are further analyzed. The influence of the variation in thickness and height of the “shell plate” on the reinforcement effect is studied， which provides the reference for the crane beam reinforcement design.

Abstract:The quasi-rectangular tunnel has gradually gained popularized in engineering because of its space advantages. However， there is a lack of in-depth research on the differences between quasi-rectangular and circular tunnels in the surrounding soil layer changes， which are closely related to the buried depth of tunnels. The quasi-rectangular and circular tunnel excavation devices were independently designed and assembled， and transparent soil was used to simulate the surrounding soil layers. Particle image velocimetry （PIV） was used to accurately measure the deformation of the soil layer， and the law of soil deformation induced by the dynamic construction of quasi-rectangular and circular tunnels at different buried depths was analyzed. Experimental comparison results elucidate that the sliding surfaces of the soil deformation induced by the two types of tunnels are basically the same， which roughly conforms to the vertical sliding surface assumption of Terzaghi’s theory. The sliding angle （θ） is approximately equal to 45°+φ/2. The vertical deformation of the overlying soil layer of the circular tunnel always maintains a “V” shaped normal distribution at different buried depths， indicating the presence of a maximum value. The vertical deformation of the overlying soil layer of the quasi-rectangular tunnel changes from a “V” shape to a “W” shape as the depth of the formation increases， indicating the existence of multiple maximum settlements. This suggests that rectangular tunnels result in more uniform ground deformations compared to circular tunnels. Under the same burial depth， the maximum surface settlement induced by the excavation of similar rectangular tunnels is smaller than that of circular tunnels， especially in shallow burial conditions. The difference between both two gradually decreases with the increase of buried depth. These findings can serve as references for the design and selection of construction schemes.

Abstract:Based on the disturbed state concept （DSC）， and combined with Rayleigh distribution， the progressive load transfer characteristics of the pile-soil interface are described from a microscopic perspective. The load transfer model of pile side and pile end based on DSC theory is established， the method of determining model parameters is given， and the rationality of the model is verified. Combined with the load transfer model of the pile side and pile end， an iterative algorithm for analyzing the load bearing characteristics of a single pile is proposed， and its rationality is verified. The bearing characteristics of a single pile calculated by this method are in good agreement with the measured values of the case， and this method can reflect the hardening and softening characteristics of side resistance and end resistance. The results of variable parameter analysis show that the load transfer model of pile side and pile end based on DSC theory has good applicability to different soil layers and pile foundation construction technologies and can accurately describe the load transfer characteristics of the pile-soil interface.

Abstract:To analyze the time effect of passive pile deformation under the action of surcharge load， this paper first introduces the fractional-order Merchant model to describe the creep characteristics of the soil. Then， based on the correspondence principle and Laplace transform， the Boussinesq viscoelastic solution is derived to calculate the additional horizontal stress induced by the load. The Terzaghi arching model is used to transfer the additional stress to the pile， obtaining the passive load on the pile due to the action of the load. Next， the pile is simplified as an Euler beam on a viscoelastic Pasternak foundation， and the differential equation calculating the deflection of the pile is established. The finite difference method and Laplace inverse transform are used to solve the equation. Subsequently， by comparing the results with existing experimental data， the feasibility of the method proposed in this paper is validated. Finally， the effects of fractional-order Merchant model parameters （elastic modulus Eh of Hooke body， elastic modulus Ek of Kelvin body， viscosity coefficient η， and fractional-order order α）， surcharge load-pile horizontal distance， and surcharge load on pile horizontal displacement are analyzed. The analysis results show that the larger Eh is， the smaller the initial pile horizontal displacement is. The greater Ek is， the smaller the increment of pile horizontal displacement with time， and the greater η results in the longer time for the pile to reach the final deformation. The larger α is， the greater the viscosity of Kelvin body is. The smaller surcharge load-pile horizontal distance and larger load lead to larger horizontal displacement of piles. With increasing time， the sensitivity of pile horizontal displacement to Eh decreases， and the sensitivity of surcharge load-pile horizontal distance and surcharge load increases.

Abstract:To reveal the premature failure mechanism of polyurethane binder， it is used to optimize the formula and construction process. In this paper， by analyzing tensile strength， shear strength， bond strength， elongation at break， micro-morphology， and functional groups， the failure mechanism of polyurethane binder was summarized. The results showed that after 480 h aging， the elongation at break of hydrothermal aging was 2.44 times that of thermal oxygen aging， and the reduction ratio of bond strength and shear strength were 4.01 times and 8.95 times that of thermal oxygen aging， respectively. Moreover， the weakening effect of ultraviolet aging on tensile strength was much greater than the increase of strength after curing， and its aging rate was accelerated， resulting in an accelerated decrease in tensile strength. In addition， during the pavement construction process， it was necessary to ensure that the moisture content of cement pavement should be less than 4% as much as possible. Construction can continue after drying for about 24 h after rainfall. When the construction period is tight， a high-power floor-standing industrial fan or infrared heating truck can be used to reduce the water content of the road surface so as to ensure the construction quality of the polyurethane binder.

Abstract:A better understanding of yawed wind turbine wake characteristics could facilitate the use of a yaw-control strategy in wind farms. In this research， large-eddy simulations of the yawed wind turbine wakes were carried out. First， a simulation method based on the pseudo-spectral-based large-eddy simulation， as well as the recently developed filtered actuator disk model， was established. The feasibility and accuracy of the method were validated by the EPFL wind tunnel measurements of the yawed wind turbine wakes. Then， the turbine wakes under different yaw angles were simulated. It was found that the filtered actuator disk model could predict the velocity deficit， turbulence intensity， and wake center deflection in the far-wake region with good accuracy. Different from the non-yaw case， a “curling wake” was observed in the simulated yaw cases， resulting in an asymmetric distribution of the velocity deficit and turbulence intensity in the vertical plane. Finally， the wake flows of two wind turbines were simulated， and the yaw angles of the upstream turbine on the power performance was analyzed. The results suggest that the wind turbine spacing should not be too short. On one hand， the power of the downstream wind turbines decreases due to the wake interference induced by the upstream wind turbine. On the other hand， in the case of shorter turbine spacing， the wake center deflection of the upstream wind turbines is smaller at the location of the downstream wind turbine， and therefore， the total power increase becomes reduced. The present analysis is of guiding significance for the use of yaw-control technology in the wind farms.

Abstract:In this paper， the material point method was used to analyze the failure modes of slope， determine the slope models of shallow， middle， and deep failure modes by changing soil parmeters， and then analyze the failure process and change the law of three failure modes of slope under the consideration of soil strain softening model and different seismic loadings. The research shows that when strain softening is considered in the static calculation， the slope failure process is more complicated. After the sliding body slides along the sliding surface， the shallow failure body continues to break into fragments， the middle failure body continues to split into small blocks， and the deep failure body appears as a new layered failure zone. When strain softening is not considered in the dynamic calculation， the seismic loading does not change the failure modes of the slope but aggravates the slip and deformation of the slope and increases with the increase of the peak acceleration of the seismic loading. When strain softening is considered， the increase of peak acceleration of seismic loading changes the slope failure modes， and the friction Angle plays an important role in this process. The results can provide a reference for slope treatment and landslide prevention.

Abstract:The research background focused on the occurrence of loess roadbed landslides in northwest China in recent years. The test datas of solidified loess with different geopolymer content were measured through compaction and direct shear tests. Additionally， the microstructure of steel slag-fly ash geopolymer solidified loess was examined using the scanning electron microscope （SEM） test and X-ray diffraction （XRD） test， and the pF-Meter instrument was used to measure the matrix suction and volumetric moisture content of the solidified loess with different geopolymers content. The test datas were then imported into COMSOL Multiphysics based on the strength reduction method， and the finite element model of the solidified loess roadbed slope was created using the Richards equation of the saturated-unsaturated theory. The impact of geopolymer content and slope ratio in the roadbed layer on the overall stability of the roadbed slope before and after rainfall was analyzed. The results indicate that when the solidified loess contains 25% geopolymer， the internal friction angle increases by 62.5% compared to reshaped loess， reaching 31.2°. The cohesion exhibits a trend of initially increasing and then decreasing as the geopolymer content increases. The highest peak is reached at 81.09 kPa when the geopolymer content is 20%， which is 75.86% higher than the cohesion of reshaped loess. The stability of the roadbed slope initially increases and then decreases with an increase in geopolymer content， while it increases with a decrease in slope ratio. Under specific conditions， slope stability decreases with prolonged rainfall duration and reduces with higher rainfall intensity.

Abstract:To study the flexural performance of B/CFRP-SSRPC structures， four-point bending tests were conducted on 5 B/CFRP-SSRPC beams taking reinforcement ratio and beam section height as research factors， the influence law of research factors on the ultimate bearing capacity， mid-span deflection， and failure mode of B/CFRP-SSRPC beams was explored. The test results show that increasing the reinforcement ratio only improved the flexural performance of test beams after cracking， while increasing the beam section height improved beam flexural performance before and after cracking， and the improvement of beam flexural performance before cracking was more obvious； all test beams exhibited brittle failure， and the failure mode was closely related to the reinforcement ratio； the current design codes for FRP reinforced concrete structures in both China and the United States underestimated the flexural and shear capacity of B/CFRP-SSRPC beams， and the calculation error was affected by the failure mode and shear span ratio of the test beams， respertively.

Abstract:Green high performance fiber reinforced concrete was prepared using cellulose fiber， agricultural waste rice husk ash， and other materials. The effect of three factors， namely cellulose fiber admixture， rice husk ash admixture， and water-cement ratio， on the strength， flexural toughness， and slump of concrete were investigated by orthogonal tests， and the strengthening and toughening mechanism of rice husk ash and cellulose fiber was analyzed. The results showed that the compressive strength and splitting tensile strength of concrete decreased significantly with the increase of water-cement ratio and increased with the rice husk ash admixture and cellulose fiber admixture； the flexural initial crack strength and ultimate flexural strength of concrete increased gradually with the rice husk ash admixture and cellulose fiber admixture； cellulose fiber can not only resist cracking and toughening but also play the role of “internal maintenance”. The rice husk ash plays a micro-aggregate filling effect and volcanic ash effect in the concrete mix， which can also enhance the mechanical properties of concrete.

Abstract:To reveal the shear mechanism of the zigzag sandstone-concrete interface under constant normal stiffness （CNS） conditions from micro-scale and macro-scale aspects， several direct shear tests for the sandstone-concrete interface were conducted by self-transformation CNS shear apparatus. On this basis， discrete element numerical models simulating laboratory experiments were established by using the rigid wall substitution method. In addition， the motion of the sandstone sample was controlled by three explicit spring-based kinetic equations to ensure the dynamic balance of the system at each time step and realize the CNS loading. The rationality of the models was verified by comparing the numerical simulation and experimental results. Subsequently， 16 cases of numerical shear tests were conducted to further reveal the failure mode and load transfer mechanism of the interface from the micro-scale aspect by observing the micro-crack propagation and force chain evolution， and the effects of asperity geometries （i.e.， half chord-length λ， inclination θ） and boundary conditions （i.e.， initial normal stress σn0， normal stiffness K） on shear strength and dilation were analyzed from the macro-scale aspect. The results indicated that micro-cracks gradually propagated from the interface area to the interior of the rock in a trend of stable increase-rapid increase-decrease in growth rate， and the failure mode of the interface transitioned from wear to shear failure with increasing inclination. The shear strength increased as an exponential function with increasing λ， θ， σn0， and K.

Abstract:To study the effect of basalt fiber and cellulose fiber content on compressive， flexural， and splitting tensile strength of hybrid fiber lightweight aggregate high-strength concrete， a response surface regression model was constructed to compare and analyze the measured and predicted mechanical test values， and the optimized concrete mix ratio was obtained by combining the demand function. The results show that the regression model is effective and highly reliable， and the model can be used to analyze the test results. The interaction between the two fibers， the water-cement ratio， and the interaction between cellulose fibers have significant effects on compressive strength， flexural strength， and splitting tensile strength. The model predicts that the optimal water-cement ratio is 0.30， the cellulose fiber content is 0.90 kg/m3， and the basalt fiber content is 4.00 kg/m3. The absolute value of relative errors between the predicted and experimental strength values are all less than 5%， which indicates that the proposed model can provide a reference for multi-objective optimization of the mix ratio of hybrid fiber high-strength concrete.

Abstract:This study presents a model predictive control method based on mixed-integer linear programming， taking the chilled water storage cooling system of a data center in Guangzhou as the research object. The optimization objective of the method is to minimize the energy consumption of the cooling system. By modeling the cooling system and environmental conditions and considering energy costs and cooling system efficiency， the optimal operation strategy for chillers and the scheduling arrangement for the chilled water storage cooling system are determined. During the optimization process， this research takes into account the influence of the minimum continuous operation time of chillers on the energy consumption of the cooling system and determines the optimal value to improve stability and reduce energy waste caused by frequent chiller start-ups and shutdowns. Through an annual simulation， this method reduces the total energy consumption by 6.52% and the total operating cost by 6.93%， compared to the baseline strategy.

Abstract:Liquid desiccant dehumidifiers have received widespread attention due to their ability to utilize low-grade thermal energy and high dehumidification efficiency. However， the prediction accuracy of their mass transfer performance still needs to be improved. This article built up an experimental platform of a single-channel internally cooled liquid desiccant dehumidifier to study the effects of different parameters on its mass transfer efficiency. Meanwhile， an artificial neural network （ANN） model was established with MATLAB to predict the mass transfer efficiency of the dehumidifier. The ANN model was verified and validated with the above experimental data. The results indicated that the a mean absolute relative difference （MARD） between the predicted Sh of the ANN model and the experimental Sh was 4.07%. Compared with existing empirical formulas， the ANN model established in this paper had higher prediction accuracy. In addition， this article also used the ANN model to study the trend of Sh under different parameter changes， thereby investigating the impact of different parameters on the dehumidification performance.

Abstract:In existing IFC standard systems， there is a problem of not being able to express the unique characteristics of type-form， structure， attributes， and art in Chinese historic buildings. This paper constructs the semantic relationship diagram of bracket sets， mortise， and tenon structures based on the UML. According to the IFC four-layer frame system， the extension of corresponding component entities， relationship entities， and property sets is achieved through entity extension and property set extension. This extension is carried out in a layered manner， and the extended content is described using EXPRESS. Model files are parsed and edited using the IfcOpenShell toolkit and VScode； Solibri and Blender are used as validation platforms to verify the visualization， readability， and content of entity and attribute set information of IFC files. According to the verification results， the extension of the historic building domain proposed in this paper conforms to the extended system method of IFC， which is of great significance to realize the interaction and sharing of the structure and art characteristics of historic buildings in the information model， and can provide strong support for the information protection of historic building engineering investigation， repair， and operation-maintenance.