Abstract:Through the finite element software of ABAQUS， the axial compression capacity of cold-formed thin-walled steel columns with web stiffeners and staggered holes was investigated. It was found that the results of the failure modes， load-displacement curves， and ultimate bearing capacities obtained from the experiments and the finite element analysis agree well with each other， validating the accuracy of the finite element model. Based on the validated finite element model， the effects of five parameters， including hole spacing， hole shape， slenderness ratio of the column， the height of web-stiffener， and flange width-thickness ratio， on the mechanical behavior of cold-formed thin-walled steel columns with web-stiffeners and staggered holes were analyzed. The results indicate that distortional buckling is the principal failure mode for all columns. The ultimate bearing capacity of the proposed columns with staggered holes increase with the increase in hole spacing， and the increment can reach more than 10% compared to the columns with side-by-side holes. Besides， the ultimate bearing capacity of the columns tends to ascend with the increase in the height of the web stiffeners， while it is barely affected by the hole shape. Compared with the V-shaped stiffened sections， the ultimate bearing capacity of the Σ-shaped stiffened section is increased by approximately 6.5%. In addition， the ultimate bearing capacity of the columns decreases with the increase of the column slenderness ratio and the flange width-thickness ratio.

Abstract:The local compressive performance of hexagonal concrete-filled steel tubular （HCFST） columns with right angles was studied. Local compressive tests on this type of 20 HCFST columns were carried out. The effects of the end plate thickness， local compressive area ratio， and steel ratio on the local compressive performance of the HCFST column were studied. The test shows that the local compressive strength of the HCFST specimen is proportional to the thickness of the end plate and inversely proportional to the local compressive area ratio. The end plate can significantly improve the local compressive strength of the HCFST specimen. The mechanism analysis based on the numerical model shows that for the HCFST specimen under local pressure， the load is mainly taken by the concrete. The confinement of the steel tube is mainly concentrated in the corner. The steel tube of the HCFST specimen without the end plate can provide greater confinement. The shape of the loading block has a great influence on the local compressive strength of the HCFST specimen without the end plate. The steel tube can form strong confinement on the core concrete within the range of 0~1.2B （where B is the side length of the steel tube） from the loading end. The parametric analysis shows that the local compressive strength decreases with the increases of the local compressive area ratio but increases with the increase of the concrete strength or the thickness of the end plate. The steel ratio， steel strength and eccentricity have a moderate effect on the local compressive strength. Finally， a simplified predicting model of the local compressive strength of the HCFST column was proposed.

Abstract:To simplify the computational process and improve the calculation efficiency， a fast evaluation method of component importance coefficients based on the quasi-balanced matrix， which was derived from the stiffness-based component importance evaluation method， was proposed for spatial structures. By transforming the balanced matrix， the quasi-balanced matrix containing the length information of components was obtained. When the linear stiffness of each component was approximately equal and the effect of structural stress stiffening was not considered， the global tangential stiffness matrix was simplified， and the component importance coefficients were expressed only including the quasi-balanced matrix. The singular value decomposition of the quasi-balanced matrix was carried out， and the mathematical relation between the eigenvalues of the stiffness matrix and the singular values were established. Taking the product of singular values as a response， the expression of the component importance coefficient was modified so as to calculate it. Through case study on three truss examples， it was proved that the calculation results of the evaluation method of component importance coefficients based on the quasi-balanced matrix are consistent with the stiffness-based evaluation method， which shows that the proposed method is a practical and fast calculation method.

Abstract:To investigate the flexural performance of unreinforced ultra high performance concrete （UHPC） one-way slabs and square slabs， experimental studies were conducted on the slabs under locally applied loads at mid-span， respectively. Based on the test results from the present study and other literature， the tensile constitutive model of UHPC was proposed in which the influence of the characteristic parameters of steel fiber was included. Through the nonlinear sectional analysis on the slabs， an equation was developed for determining the reduction factor k of equivalent uniform stress in the tensile zone of the unreinforced UHPC slabs at the ultimate. According to the test and analysis results， a simplified approach for calculating the flexural capacity of unreinforced UHPC one-way and square slabs was presented. The results show that all the unreinforced UHPC one-way and square slabs experienced a tension failure governed by the tensile properties of the UHPC. Owing to the enhancement by the steel fibers in UHPC， the unreinforced UHPC slabs exhibited a ductile failure mode with significantly greater loads and deformations at the ultimate state as compared to those at the initial cracking state. Because the plasticity of UHPC in tension is not enough to ensure the formation of a fully plastic mechanism in those unreinforced UHPC square slabs， the upper bound solution from the yield line theory is unsuitable to predict the flexural capacity of the slabs. However， the lower-bound one from the static method of limit analysis can give better predictive results with a safer margin， and the feasibility of the developed simplified approaches for predicting the flexural capacity of unreinforced UHPC one-way and square slabs are verified well by the test results.

Abstract:To understand the compressive behaviors of the masonry columns strengthened with textile-reinforced highly ductile concrete （TRHDC）， the compression tests of 8 sets of masonry columns were carried out. The influence of different reinforcement methods， eccentricity， type of textiles， and the number of textile layers on retrofitting effectiveness was investigated based on the failure modes， load-bearing capacity， and transverse tensile strain of the strengthening layer. The results showed that the TRHDC jacket improved the integrity of masonry columns and their brittle failure. Moreover， the compressive strength of masonry columns was enhanced with the increase of glass fiber textile layers. The lateral confinement of carbon fiber TRHDC was greater than that of glass fiber TRHDC due to the high tensile strength and elastic modulus of carbon fiber textiles. Besides， the confinement effect of TRHDC was weakened by eccentricity. The analytical models were available in the literature， and codes were evaluated based on the predicting the compressive strength and corresponding axial strains of masonry columns strengthened with TRHDC. The predicted values have good agreement with the experimental results.

Abstract:Aiming at the problems that the influence of bridge deck roughness on bridge vibration is hard to remove and the low accuracy of high-order modal recognition during the current indirect measurement method based on vehicle response， this paper proposes an approach to separate the effect of bridge deck roughness and bridge vibration response by using blind source separation identification based on the acceleration response signal of the axle contact point， to identify the bridge modality. Firstly， the principle and method of obtaining the bridge vibration estimation signals by using the second order blind identification （SOBI） algorithm and taking the acceleration response signals of two groups of vehicle-bridge contact points as input signals are described in detail. Then， the bridge modal identification technology flow and framework based on vehicle response are established using signal band-pass filtering and Hilbert transform combined with the mode modification strategy of fulcrum data extension. Finally， the applicability and effectiveness of the proposed method were verified by numerical examples， and the influences of vehicle spacing， bridge deck roughness， and vehicle frequency on the applicability of the method were analyzed. The results show that the proposed method can effectively filter the influence of bridge deck roughness， achieve accurate identification of high-order modes of bridges， and show robustness under the influence of multiple key factors. Moreover， the proposed method has the characteristics of high precision， simple operation， and good applicability， which can provide a new idea for bridge modal identification based on vehicle response.

Abstract:To overcome the problems of low efficiency and poor effect when using traditional digital image processing methods to detect bridge cracks， this paper proposes an integrated bridge crack detection method that integrates deep learning YOLOv5 and U-Net3+ algorithms. By adjusting the width and depth parameters and optimizing the bounding box loss function， a crack identification and location model based on the YOLOv5 target detection algorithm is constructed to realize the rapid identification and location of bridge cracks. The U-Net3+ image segmentation algorithm combined with a deep supervision strategy and the output prediction module is introduced to train and build an efficient segmentation model of bridge cracks， and to realize pixels-level intelligent extraction of cracks. An eight-direction crack width measurement method combined with connected domain denoising， edge detection， and morphology processing is developed. And the morphology and width of cracks are measured with high precision based on U-Net3+ segmentation results. LabelImg image annotation tool is used to make a dataset containing 4 414 images to train the crack identification and location model. LabelImg image annotation tool and CFD dataset are used to make a dataset containing 908 images to train the crack segmentation model. UAV is used to capture 485 images of size 5 280×2 970 pixels， which are taken from the bridge tower. The crack images of the bridge tower are used as the test object of the intelligent crack detection model. The proposed crack intelligence detection method is applied to the above test objects， the overall precision， recall， and F1 score of crack identification and location are 91.55%， 95.15%， and 93.32%， respectively， and the overall precision， recall， and F1 score of crack segmentation are 93.02%， 92.22%， and 92.22%， respectively. The results show that the intelligence detection method of bridge cracks based on YOLOv5 and U-Net3+ algorithms can achieve high efficiency， high precision， and intelligence detection of bridge cracks， which has much research value and broad application prospects.

Abstract:The traditional Kiewitt reticulated single layer shell mesh was optimized by the method based on the Spring Force between nodes and the Laplacian Smoothing method， and two new spherical mesh forms are obtained. Firstly， the calculation principle and process of the two algorithms are introduced： the method based on the force between the nodes assumes the member as a spring， and moves the node in the direction of the unbalanced force， so as to obtain a grid （SF mesh） with a more uniform length of the member. At the same time， a smoother mesh （LS mesh） can be obtained by using the Laplacian smoothing method. Then， the Kiewitt mesh， SF mesh， and LS mesh were compared. In terms of geometric indices， the average length of the member， the change rate of member length and the shape coefficient of the mesh triangle of the three kinds of reticulated shells were compared. In terms of mechanical properties， the elastic strain energy and nonlinear stability bearing capacity of three kinds of reticulated shells under different load modes are compared. The numerical analysis results show that the SF mesh has better geometric indices than the LS mesh. In most cases， the SF mesh and LS have lower strain energy； and the stability ultimate bearing capacity of the three meshes is relatively close. On the whole， the SF mesh has the best overall mechanical properties； the LS mesh has the best mesh fluency； SF mesh and LS mesh are both better than the traditional Kiewitt reticulated shell.

Abstract:To solve the optimization problem of the position and quantity of dampers in spatial structure， a new coding method， “A-B”type digital coding， was proposed based on a genetic algorithm， which realizes the precise positioning of the optimal arrangement of dampers. The additional stiffness and damping matrix of the magnetorheological damper （MRD） were deduced， the improved genetic algorithm was proposed by adopting the H2 norm optimal control theory and the intergenerational comparison weight， and the multi-objective spatial optimization arrangement was used to develop the improved genetic algorithm program using MATLAB software. Taking a ten-story reinforced concrete frame-shear wall eccentric structure as an example， seven seismic waves were selected as dynamic time history input according to the specification， the structural displacement， acceleration， and torsion control under an optimization scheme， and three working conditions were calculated， and the development trends of different shock absorption indexes with the number of MRDs were analyzed. The results show that the value of the optimization objective function converged rapidly with the evolutionary algebra. The optimization scheme has the best control effect in the four working conditions， the shock absorption rates in the X and Y directions of the No. 88 node on the top floor reached 39.45% and 36.48%， respectively， and the structure torsion was effectively controlled. The numerical example showed the effectiveness of the improved genetic algorithm， the precise positioning of the damper arrangement of the space structure is realized， and the structure is optimally controlled.

Abstract:For the cable-damper system， the algebraic form of the transcendental frequency equation of the system is derived when the damper is located at a unit-fraction-span （1/n span of the cable）. According to the fundamental theorem of algebra， the structure of the eigensolutions of the system is discussed， and the properties of the solution are analyzed with four examples. The results show that： 1） The eigensolutions can be divided into n-1 branches. 2） Within one solution branch， all eigenvalues take an identical value in their real part （as an additive inverse of the logarithmic decrement ratio per unit time）， while their imaginary parts （meaning in physics， the frequency） form an arithmetic sequence. 3） According to the way that the frequencies vary with the damping， the solution branches can be classified as three types： The frequency of type 1 solutions is related on damping； The frequency of type 2 solutions is not affected by damping. The frequency of type 3 solutions may or may not vary with the damping， which means that a type 3 solution may behave like a type 1 or a type 2 solution， depending on the damping is under or over some certain critical value。

Abstract:A wind measurement system of a six-rotor unmanned aerial vehicle （UAV） equipped with an ultrasonic anemometer was developed and was used to carry out the wind field measurement on typical landforms such as coastal areas， agricultural greenhouse bases and dense building areas in tropical island areas. The results show that the ground roughness index， friction velocity， and ground roughness length all increase with the increase of field roughness. The wind profile of the coastal areas can adopt the exponential law or logarithmic law model， which is in good agree with the specified values of the landform in the Chinese Standard A and European Standard Ⅰ， and the turbulence intensity is significantly smaller than the existing standard value； the wind profile of the greenhouse base conforms to the exponential law model， in which the wind profile and turbulence intensity are in good agreement with the specified values of the landforms in the Japanese standard Type Ⅲ； the wind profile of dense building areas conforms to the exponential law model， in which the wind profile is in good agreement with the specified values of landforms in the American standard Type B and the turbulence intensity is in good agreement with the specified values of landforms in the Japanese standard Type Ⅳ. This research verifies the reliability of the wind measurement system of a six-rotor UAV， lays the foundation for the wind resistance design of engineering structures in island areas， and provides a new method for wind field observation， wind environment assessment， and wind energy resource utilization in complex landforms.

Abstract:To resolve the durability issues of reinforced concrete structures in the marine environment and island construction， and promote the effective utilization of seawater and sea sand resources， this study investigated the compressive performance of seawater sea sand concrete （SSC） short columns reinforced with basalt fiber reinforced polymer （BFRP） bars through axial compression tests. The influence of longitudinal reinforcement ratio and spiral spacing on the axial compression properties of the specimens was investigated. The results show that the BFRP bars reinforced SSC （BFRP-SSC） short columns fail due to crushing of the concrete followed by fracture of the spirals in the loading process， which is a relatively brittle failure mode. Increasing the longitudinal reinforcement ratio can enhance the ultimate bearing capacity of the specimens， while the influence of the spiral reinforcement ratio on the ultimate bearing capacity is not obvious. And the ductility of the specimens can be increased by reducing the spiral spacing. The calculation methods of bearing capacity of fiber-reinforced polymer （FRP） bars reinforced concrete columns in domestic and international research were compared， and the calculation of bearing capacity of BFRP-SSC short columns should consider the contribution of BFRP longitudinal reinforcement. This study can serve as a data support and theoretical basis for the design and application of BFRP-SSC short columns.

Abstract:present， sandwich insulation wall panels have been widely used in building insulation structures. However， the decorative layer of wall panels is usually made of ordinary concrete， resulting in easy corrosion of the internal insulation materials due to the cracking and falling off of the finish coat. Therefore， fiber braided mesh reinforced engineering cement-based composite （ECC） was used as the decorative layer for wall panels. And the flexural performance of this sandwich insulation composite wall panels was studied through a four-point bending test with influencing factors including the type of insulation， thermal insulation layer thickness， decorative layer thickness， the treatment method of fiber braided mesh， with or without connectors， and the angle of connectors. The results show that increasing the thickness of the insulation layer has little effect on the flexural capacity and ductility of the wallboard. But it can improve the combination degree of the wallboard. The wallboard made of expanded polystyrene （EPS） insulation board has a higher combination degree due to better bonding behavior between EPS and ECC matrix. The poor mechanical performance and stiffness of EPS make the lower flexural capacity of the wallboard. Fiber textiles processed by dipping and dipping adhesive sand can reduce the flexural capacity of the wallboard， but it can improve the bond between the ECC matrix and the fiber textile due to the process of dipping adhesive sand， thus improving the ductility of the wallboard. The existence of connectors can improve the combined performance of wall panels. Reducing the connection angle or increasing the panel thickness can improve the flexural stiffness， flexural capacity， and combined performance of the wall panel but leads to decreasing the ductility of wall panels. Finally， the calculation formula of flexural capacity of textile-reinforced ECC （TRE） sandwich insulation wallboard was deduced and the results were compared with the test ones， indicating that the proposed calculation method is feasible.

Abstract:Natural corrosion of steel bars in service structures differs from experimental artificial accelerated corrosion. For investigating the natural corrosion characteristics of steel bars in practical engineering， a batch of corroded steel bar specimens was acquired from reinforced concrete bridge decks that have been in service for more than 50 years. Precise residual surface information of the corroded steel bars was obtained by three-dimensional laser scanning， and corrosion all along the bars was described by residual cross-sectional areas. The effects of corrosion degree and bar length on longitudinal corrosion non-uniformity were studied. The probability distribution characteristics of longitudinal stochastic corrosion were studied by statistical analysis， and the corresponding probability distribution models were proposed. Results show that naturally corroded steel bars have various typical corrosion morphology. The corrosion zone and corrosion degree are random along the bars. The maximum cross-section loss ratio and variance of residual cross-sectional areas increase as the average corrosion degree increases， which indicates that the more severe the corrosion is， the more uneven the corrosion is. Bar length influences corrosion non-uniformity significantly. In the case of the same source and average corrosion degree， the non-uniformity increases with the increase of bar length. The longitudinal stochastic corrosion of steel bars has a statistical law. The probability distribution of residual cross-sectional areas of steel bars with different corrosion degrees can be accurately evaluated by the multimodal normal distribution model. In comparison， the Weibull distribution model and the unimodal Normal distribution model have a slightly poorer fitness， and are simple in form and easy to apply， which are suitable for steel bars with an average corrosion degree of less than 10%.

Abstract:The bearing capacity and seismic performance of historical timber columns can be significantly improved by the composite strengthening with near-surface mounted steel bars and wrapped carbon fiber reinforced polymer （CFRP） strips. To investigate the restoring force characteristics of composite strengthened timber columns， the cyclic loading tests on eight square timber columns were carried out considering the influence of the number of steel bars， the wrapping form of CFRP strips， and different strengthening modes. Based on the test results， the trilinear skeleton curve of composite strengthened square timber columns was proposed. And the calculation formulas of characteristic parameters such as stiffness of elastic section， hardening section and descending section， yield load， peak load， and corresponding displacement were provided. Compared with the experimental results， the correctness of the parameter calculation method was verified. According to the characteristics of specimen hysteretic curves， the hysteretic rules of composite strengthened square timber columns were determined， and the restoring force model was established. The calculated results of the model are in good agreement with the experimental results， which can better describe the hysteretic performance of the composite strengthened square timber columns.

Abstract:Adopting the improved ASTM D1037 aging method， a series of artificial aging tests with 0， 3， and 6 times of dry-wet cycling were designed for larch laminate specimens to study the effect of long-term temperature and humidity alternation on the mechanical properties of the glulam. The influences of different times of dry-wet cycling on the macroscopic characterization of glulam， micromorphology， material density， and strength indexes of the compressive strength parallel to the grain， tensile strength parallel to the grain， bending strength， and shear strength of the rubber layer was analyzed. Results show that strength indexes decreased obviously after dry-wet cycling. With the increase in the number of dry-wet alternations， the decrease of the strength indexes of the specimen increases. After 6 times of dry-wet cycling， the decline amplitude of the compressive strength parallel to the grain， tensile strength parallel to the grain， bending strength， and shear strength of the rubber layer increased in turn， within 26.75%， 29.64%， 33.57%， and 40%， respectively. Compared with the initial crack， the effect of alternating dry and wet on the bending strength is more significant. The relationship between dry-wet alternation times and the strength can be fitted by a power function. Based on the corresponding relationship between the times of dry and wet alternations and time， time-varying models of larch glulam's compressive， tensile， bending， and shear strength of the rubber layer were established.

Abstract:Based on the strain tests of similar materials in laboratory， this research focus on crushing mechanism under expansion pressure of special-shaped holes with sharp angles， such as regular triangle hole， isosceles right triangle hole and 120° top angle isosceles triangle hole. On this basis， particle flow simulation is employed to find out the optimum angle of directional cracking effect， the optimum spacing of double holes and the influence of rock strength on fracturing effect. The results show that the crack initiation and fracture time of the sample under pressure of special-shaped holes are shorter than that of round holes， and the crack development is controllable since it is always along the extension line of sharp Angle bisector. According to the change of strain， the test can be divided into three development stages. In the steady development stage， the strain growth rate in each direction has nearly no difference. In the rapid increasing stage， new fracture surfaces are formed widely and show certain directivity. In the weak stage， recurring fractures result in energy dissipation and a sharp drop in strain. The numerical simulation shows that the best orientation effect occurs when the angular spacing is 7 times the length of the equilateral triangle side， and the rock strength has a exponential relationship with the cracking effect.

Abstract:To study the water migration mechanism of granite residual soil （GRS） during evaporation and dehydration， a series of nuclear magnetic resonance tests and microscopic tests were conducted on Shenzhen GRS. In this study， the formation reasons for the dual-pore structure of GRS were analyzed. We investigated the water distribution under different degrees of saturation and proposed the mechanism of water migration in GRS. The results show that the micropore structure of GRS is formed by the cementation between iron oxide and kaolin layers； the dual-pore structure is constituted by the micropore and macropore structure which is not easily disturbed； the micropore structure and macropore structure are interconnected at high saturation， and the hydraulic connection is interrupted at low saturation； water evaporates synchronously between the dual pore structures and the supply from the macropore structure to the micropore structure decreases with the evaporation. This research can provide the theoretical basis for water migration in complex soil structures.

Abstract:Based on the theory of Bio-saturated porous media， the tapered pile was simplified into an Euler beam， and a tapered pile-soil coupling model under the horizontal steady-state vibration was established. Firstly， the potential function is introduced to solve the vibration control equation of soil around each pile section under the plane strain model. The earth pressure around the pile section of each layer is obtained by using variable separation methods and operator decomposition methods. Combining the conditions of pile-soil coupling and displacement continuity， the impedance solution of tapered pile top is obtained. The effects of wedge angle， length diameter ratio， and soil permeability on the top impedance of a wedge-shaped pile are studied based on the analysis of examples. The results show that： 1）in the low-frequency range， the impedance of the tapered pile decreases with the increase of wedge angle； 2）increasing the length of the tapered pile can improve the horizontal impedance and rocking impedance of the pile head； 3） keeping the volume and length of pile unchanged， the horizontal dynamic stiffness decreases with the increase of wedge angle in low-frequency stage， but the result is opposite in high-frequency stage； 4） the existence of liquid phase in soil has a significant effect on the dynamic impedance of pile top， and neglecting the action of the liquid phase in the soil leads to underestimating the dynamic impedance of tapered pile；5） surface soft soil reduces the dynamic impendence of the tapered pile.

Abstract:To study the propagation and attenuation characteristics of Rayleigh waves on the irregular seabed in saturated elastic half-space， a simplified dynamic model of irregular seabed sites is established with the fundamental equation of soil dynamics proposed by Zienkiewicz. By changing the boundary conditions， the Rayleigh equations are derived for the degradation model of uncovered seawater and overlying seawater when the water-soil contact interface is flat. And the dispersion and attenuation curves of Rayleigh waves under the influence of permeability coefficient， porosity， Poisson's ratio， and interface conditions are given. Based on the complex sea bed model， the effect of various factors on the dynamic response of seabed parameters， such as pore pressure and deformation during Rayleigh wave propagation， is analyzed. The results show that the soil mechanical parameters， such as elasticity modulus， permeability coefficient， and porosity， as well as the overlying water and the interface of sediment water， all affect the dynamic response of the seabed. The influence range and extent of different Rayleigh wave velocities on soil mechanical parameters differ along the soil depth. Elastic modulus and Poisson's ratio are important parameters that determine the properties of soil and are prerequisites for discussing the propagation characteristics of Rayleigh waves and the dynamic response of the soil. Their change affects the influence law of permeability coefficient， porosity， and other parameters. In the two simplified models， when the elastic modulus of the rock stratum is 6.017×1010 Pa and Poisson’s ratio is 0.38， the porosity and permeability coefficient have regular effects on the propagation characteristics of Rayleigh waves.

Abstract:Accurate selection of rock mechanics parameters has always been a key scientific problem in geotechnical mechanics and engineering area. To solve this problem， firstly， the parameters of joint spacing and quantitative block volume （Vb） are introduced， and the calculating formula of the geological strength index （GSI） is proposed based on block volume （Vb）. Meanwhile， the calculation formula of the disturbed factor for rock masses （D） based on ultrasonic velocity （Vb） is given. The above GSI value and D value are introduced into the Hoek-Brown strength criterion， and a rock mass mechanical parameter estimation method based on the block volume （Vb） and the ultrasonic velocity （Vb） of the rock mass is proposed. Firstly， the validity of the calculation of the geological strength index （GSI） based on block volume （Vb） was verified by comparing it with the existing GSI calculation method. Then， the estimation method of rock mechanics parameters based on Vb and Vp was applied to the parameter evaluation of Tianxi Expressway. And the numerical calculation results were compared with the field investigation and monitoring results， so as to verify the feasibility and accuracy of the proposed method. This method extends the application scope of the Hoek-Brown strength criterion and provides a new idea for parameter selection in the case of insufficient experimental data at the initial stage of engineering construction.

Abstract:A novel triple-tank solar water heating system with an additional makeup water tank and the corresponding control strategy were proposed based on the traditional dual-tank solar water heating system. The objective is to utilize this water tank to store solar energy to heat the makeup water under high and low solar radiation， thereby improving the solar fraction and reducing the operation time of the auxiliary heater. To evaluate its performance， a TRNSYS simulation model was established and validated by the results obtained from the experiments. Based on the model， the operation performance of the proposed system and its influencing factors were analyzed. The results showed that the annual solar fraction of the proposed system was increased by 22.42% compared with that of traditional systems. Simply increasing the volume of the make-up water tank would not necessarily result in the increase of the annual solar fraction. Therefore， when selecting the optional volume of the makeup water tank in practical applications， the annual solar fraction and initial investment should be comprehensively considered. Moreover， it was found that the proposed system could achieve a higher solar fraction than traditional systems under different water usage modes. In addition， an economic analysis was conducted for applying the proposed system in a residential building in Changsha. The results showed that annual operation cost could be decreased by 18.31%， and the payback period was 0.66 years.

Abstract:The available radiation time series employing the radiation time series method involves too few room structures and characteristic parameter numbers， which results in a large deviation of the design cooling load. Firstly， considering the commonly-used envelop structures and their characteristic parameters of buildings in China， the room samples combined with the structures and their characteristic parameters were sampled by a simple random method. Then， the heat balance method was used to calculate the radiation time series of each room sample. The main characteristic parameters that affect the radiation time series of a room are extracted by the CART algorithm， and the rooms were classified according to the main characteristic parameters. Finally， the K-Medoids algorithm is used to determine the representative radiation time series for each type of room. Using the proposed decision tree classification method， the non-solar radiation time series and the solar radiation time series of all rooms combined by the structures and their characteristic parameters were classified into twelve and eight categories， respectively. The applicability verification shows that the representative radiation time series for each category of rooms well represents all rooms in this category， which can significantly improve the accuracy of design cooling load.

Abstract:The research on the influence law of time lags and decrement factor （TLDF） characteristics for different exterior wall combinations on building peak heat transfer is of significance to reduce the peak heat transfer load and the capacity of air-conditioning system. Taking a case building as an example， EnergyPlus and orthogonal experimental design methods are used to study the change law of the TLDF characteristics and peak heat transfer cooling load of different exterior wall combinations. The results show that the external disturbance of each wall combination has different TLDF characteristics， resulting in a difference in the peak cooling load， and the maximum difference is 11.8%. An optimization method for the peak heat transfer of exterior walls is proposed， based on the fact that the peak heat transfer of different exterior walls appears at different times and can reduce the total heat transfer peak value after superposition. The peak shifting indicator （PSI） is introduced into the inner surface temperature relation of each facing wall to adjust the time lags of the wall combination. The PSI is introduced into the inner surface temperature relation of each facing wall to adjust the time lags of the wall combination. The PSI and the wall total heat transfer peak value are taken as design variables and objective functions， respectively. The optimal time lags of each facing wall are obtained by optimizing the solution， and then the optimal wall combination is obtained. The method is used to calculate the case building， and the results show that the total heat transfer peak value is reduced by 19.1% after the optimal combination of the exterior wall.