Abstract:In order to further study the bonding performance of carbon fiber reinforced polymer (CFRP) bar and concrete at polar low temperatures, a numerical model considering the CFRP bar surface characteristics was proposed utilizing ABAQUS. A total of 64 conditions were simulated in this study, to analyze the effect of CFRP bar diameter, rib height, rib width and concrete cover thickness on bonding on the bonding performance under low temperature conditions. The results showed that the numerical model considering the surface characteristics of CFRP bar can effectively reflect the stress transfer between CFRP bar and concrete, reflecting the damage and bonding failure mechanisms between CFRP bar and concrete at low temperatures. Low temperature significantly enhances the bonding strength between CFRP bar and concrete. At low temperatures, as the diameter of CFRP bar increases, the bonding strength between CFRP bar and concrete decreases, weakening the enhanced effect of low temperature on bonding strength. With an increase in rib height of CFRP bar, the low temperature bonding strength initially increases and then decreases, reaching the maximum value when the rib height is 8% of the reinforcement diameter. The variation in rib width of CFRP reinforcement mainly affects the shape of the bonding slip curve. Compared to specimens at room temperature, specimens at low temperature exhibit a thicker concrete cover when pull-out failure occurs.

Abstract:To investigate the shear behaviour of CFRP-concrete with surface groove subjected to chloride wet-dry cycles, single-lap tensile shear tests with different groove shapes (rectanglular, trapezoidal and inverted trapezoidal) were carried out for 0 d, 60 d and 120 d wet-dry cycles. The changes in failure mode, fracture engergy and factors influencing the maximum shear stress were examined. On the basis of experimental results, we derived the bond slip constitutive model considering dry-wet cycles and its effectiveness was validated through numerical simulations. The results show that the failure mode of the surface groove method transitions from the CFRP sheet fracture without erosion to the mixed failure and debonding failure of the CFRP sheet. Compared with EBR specimens, the interface fracture energy of 120 d wet-dry cycles reduces by 60.04%-69.42%. The maximum shear stress of the trapezoidal groove after 120 d wet-dry cycles is increased by 7.18%-9.48% compared with other surface-grooved shapes. These results indicate that the surface groove method exhibits superior shear behaviour under wet-dry cycles. The developed deterioration formula of the interface constitutive relationship is applicable for analyzing and simulating the interfacial bond behaviour of CFRP-concrete with surface groove under wet-dry cycles.

Abstract:In order to solve the problem of environmental pollution caused by coal gangue accumulation, it is a reasonable solution to use coal gangue as coarse aggregate in concrete for resource utilization with significant economic benefits. In this paper, coal gangue is used as coarse aggregate to prepare coal gangue concrete filled steel tube, and axial compression test is carried out. The design strength grade of coal gangue concrete is C40. The failure mode and failure mechanism of the component and the degree of improvement of the strength of the core concrete by the confinement of the steel tube are explored. The bond stress between the steel tube and the coal gangue concrete is studied according to the longitudinal strain distribution of the steel tube. The influence of different loading methods, diameter-thickness ratio and coal gangue replacement rate on the axial compression bearing capacity of the component was analyzed. The results indicate that loading mode A exhibits shear-type failure, while loading mode B shows waist-drum-type failure. The steel tube provides excellent lateral confinement for the coal gangue concrete. Under loading method A, the ultimate bearing capacity of specimens is higher than under loading mode B, but loading mode B significantly enhances the compressive strength of the core concrete. The primary factor influencing the ultimate bearing capacity of the coal gangue concrete filed steel tube is the replacement ratio. The steel tube coal gangue concrete effectively compensates for the low strength characteristic of coal gangue concrete.

Abstract:In order to suppress the buckling deformation and enhance bearing capacity of cold-formed steel columns, a systematic study was conducted using a combination of experimental testing, numerical simulation, and theoretical analysis on cold-formed steel-geopolymer foam concrete composite columns. The load-axial displacement curves, test process and failure characteristics of the members were analyzed. The failure modes and bearing capacity results of different types of members were compared and the effects of different factors on the axial compression performance of the members were discussed. The results show that: the ultimate bearing capacity of the composite column is 1.4 times higher than that of the CFS built-up column. When the width-thickness ratio is in the range of 60-100, the utilization rate of geopolymer foam concrete is higher. For every increase in the density of foam concrete, the ultimate load of the composite column increases by about 1.5%. From the perspective of steel consumption, the setting of symmetrical single ribs has a more significant impact on enhancing the ultimate bearing capacity of composite columns. Based on the experiment and numerical simulation, the ultimate bearing capacity of composite columns is calculated according to the calculation methods in existing relevant codes. It is found that the calculation method given by the ′Code for design of composite structures′ can roughly estimate the ultimate bearing capacity of the composite columns. Finally, a calculation method suitable for the axial compression bearing capacity of the composite columns is proposed, and the accuracy of the formula is verified.

Abstract:In order to enhance the industrialization level and repairability of prefabricated structures, a novel fully precast reinforced concrete (RC) inter-column replaceable energy-consuming joint (RECJ) was proposed and applied to the ground floor columns of frame structures in this paper. A pseudo-static reciprocating loading test was carried out on two precast column specimens connected by RECJ and a cast in situ column comparison specimen. After loading the long tenon joint specimen to an interlayer displacement angle of 1/25, the damaged connecting plate was replaced and loaded under the same conditions. The specimens were then loaded under the same conditions. The performance analysis includes the failure mode, hysteresis curve, skeleton curve characteristics, degradation characteristic of stiffness and bearing capacity, ductility and the energy dissipation capacity as well as the strain changes of the connecting steel plate and the steel bar in the column. The results showed that the damage of the bottom column of the new fully precast frame are mainly concentrated on the connecting steel plate of RECJ, while other parts of the specimen remain largely elastic. In addition, the hysteresis curve of RECJ exhibits a full and plump shape, which indicates significant improvements in energy dissipation, ductility and stiffness degradation compared to the cast in situ comparison column. Overall, the specimens with longer tenon lengths outperform those with shorter tenons, which shows better seismic performance and equivalent initial stiffness and bearing capacity to the cast in situ column. RECJ can quickly restore seismic performance of the structure by replacing damaged connection plates during major earthquakes. The stress mechanism of RECJ was analyzed, and the bending bearing capacity formula and angular deformation of RECJ during the yield and peak stages were proposed. The skeleton curve model was obtained based on the derived formula.

Abstract:In order to achieve the construction of environmentally-friendly, efficient, and highly precise modular assembled steel structure buildings at construction sites, this study introduces two types of assembled square hollow column-truss beam connections: one with diagonal braces and one without diagonal braces. Four full-scale cross-shaped specimens were meticulously designed for the purpose of conducting cyclic loading tests. The seismic behavior of these specimens was thoroughly investigated under both beam failure and diagonal brace failure modes, and the underlying causes for the occurrence of these failure modes were elucidated. Furthermore, the impact of diagonal braces on crucial aspects such as ultimate bearing capacity, ductility, stiffness, and energy dissipation capacity was comprehensively evaluated. Finally, an analysis of the mechanisms underlying these two failure modes was conducted, and the design suggestions of joints with and without diagonal braces were respectively given in combination with the failure modes and mechanical performances. Remarkably, the experimental results indicate that the specimens without diagonal braces exhibited commendable seismic behaviors in terms of plastic deformation and energy dissipation capacity. The incorporation of diagonal braces effectively transferred plastic deformation from the truss beam to the end of the diagonal brace, resulting in a significant enhancement of the connections' bearing capacity and stiffness. However, it should be noted that the plastic deformation capacity of the truss beam was constrained prior to diagonal brace failure. During the whole loading process, the connection between the column seat and the truss beam of the four specimens did not show any damage phenomenon, and there was no obvious slip phenomenon of the flange plate between the column and the column seat, which indicates that the column seat type connection was reliable.

Abstract:Previous seismic analysis of subway stations typically focused on analyzing the seismic response of intact structures. However, subway station structures are buried underground and are susceptible to chloride ion erosion. This can result in the degradation of material performance. This paper aims to establish nonlinear soil-structure interaction finite element models for subway station structures with different degrees of corrosion under chloride environments at coastal areas. The static pushover analysis method was utilized to investigate the influence of chloride ion erosion on the soil-structure flexibility ratio. Furthermore, based on nonlinear time history analysis, the seismic response of subway station structure in coastal chloride environments was analyzed. The numerical simulation results indicate that compared to the intact state, the soil-structure flexibility ratio of the structures with 10% and 20% corrosion rates decreases by 6% and 18%, respectively. However, due to the confinement of the surrounding soil, the maximum inter-story drift angle of the lower-level columns does not exhibit significant changes under the same motion. As the vulnerable component in seismic resistance, the corrosion of reinforcement in the lower-level columns leads to a decrease in their deformation capacity and load-bearing capacity. This results in a reduction of the safety factor of subway station structures by approximately 10% and 20%. The increase in the maximum inter-story drift angle of corroded columns is influenced by the site response. Under the motion with a rich low-frequency component, the significant shear deformations of the soil lead to a situation where the reinforcement in the fiber section of the columns bears more axial force. At this point, the corrosion of reinforcement will have a significant impact on the inter-story drift angle of the columns.

Abstract:After an earthquake occurs, it is a key technology to quickly generate a reasonable isoseismal map using strong motion observation data. The intensity isoseismal map generated based on source parameters and intensity attenuation law is too regular to reflect the local intensity distribution characteristics. However, the isoseismal map directly generated from the observed data by interpolation cannot reasonably reflect the source effect of large earthquakes. This article proposes an intensity field fusion Kriging interpolation method that considers the spatial correlation of seismic motion and the source effect of large earthquakes. The method utilizes the distance between points to consider the spatial correlation of intensity, and the distance between points to source to consider the source effect of large earthquakes. First, in the framework of Kriging interpolation method, Particle Swarm Optimization algorithm was used to realize the fast automatic fitting of semivariogram. Secondly, the consideration of spatial correlation and source effects was achieved through fitting two semivariogram functions with different independent variables. Finally, the interpolation results of earthquake data from Japan and China were used to verify the rationality of the method. The results show that the shape of the intensity isoseismal map obtained by the fusion Kriging interpolation method is regular, which can reflect the source effect of an earthquake, and has a good adaptability to the sparse situation of stations, meeting the requirements of rapid seismic intensity reporting. This method can provide technical support for rapid seismic intensity reporting and the drawing of seismic intensity isoseismal map.

Abstract:In response to the demand for new, energy-efficient, and efficient construction methods, a spiral rib grouted sleeve made of seamless steel pipe processed by rolling process is proposed. This type of sleeve offers advantages of low cost, simple manufacturing, and easy construction. The spiral ribs produced by the rolling process significantly improve the mechanical interlocking force between the sleeve and the grout. Building upon the research on the performance of traditional grouted sleeve connections, a middle overlap sleeve connection form is introduced. Fourteen specimens of this type are fabricated using spiral-ribbed sleeves and subjected to uniaxial tensile tests to investigate their mechanical properties. Additionally, finite element simulations using ABAQUS are performed and the results are compared and analyzed in relation to the experimental findings. The findings indicate that the sleeve connections with a 10d overlap length exhibit sufficient anchoring performance. The strain in the internal steel reinforcement within the sleeve rapidly decreases with distance from the loading end and increases with external load. Surface strains on the spiral-ribbed sleeve are relatively small, indicating adequate safety redundancy. The axial strain near the steel reinforcement is higher, while the middle section experiences mainly axial tensile strain and the sleeve ends primarily undergo circumferential tensile strain. The finite element simulation results are in good agreement with experimental results, confirming their applicability.

Abstract:To investigate the influences of parameters such as the position of post-installed rebar on the mechanical behaviors of a Type Ⅱ grouted sleeve lapping connector named APC connector (all vertical members precasted in concrete structures), a unidirectional tensile test was conducted on 36 specimens. The failure mode, ultimate bearing capacity, ductility and sleeve strain of the specimens were studied, and ABAQUS was used for numerical simulation. Test results showed that the use of anti-deflection measures effectively improved the ultimate bearing capacity and initial stiffness of the specimens. The bearing capacity and ductility of the connector were mainly influenced by three factors, namely the spacing of the steel bars, the eccentricity of the post-installed rebar, and whether the post-installed rebars were arranged tightly against the sleeve. When the post-installed rebars were arranged in the middle of the sleeve with a larger spacing between the rebars, the restraint provided by the longer side of the sleeve was weaker, resulting in a decrease in the bearing capacity and ductility of the splice. When the post-installed rebars was eccentrically positioned, it was prone to bending deformation, resulting in reduced connector bearing capacity and ductility. When the post-installed rebars was placed in close proximity to the sleeve, it was susceptible to grouting defects, resulting in reduced connector bearing capacity and ductility. When the rebars were symmetrically and tightly arranged on the long axis, the specimens exhibit the maximum bearing capacity and ductility. At the ultimate load, the longitudinal strain on the short side of the sleeve was tensile strain, but there was a compression trend, while the longitudinal strain on the long side of the sleeve was compressive strain. The absolute value of the circumferential strain on the long side of the sleeve was basically greater than that on the short side but smaller than the yield strain of the sleeve. The failure modes and ultimate bearing capacity of the simulated specimens were in good agreement with the experimental results, validating the reliability of the model. With different positions of post-installed rebars, the minimum value of the ultimate load was about 80% of the maximum value.

Abstract:During the outbreak of water blooms, extracellular organic matters (EOM) of algae accumulates in water bodies, causing great risks to water treatment processes and effluent quality. EOM is different to remove using conventional water treatment technologies, and secondary disinfection by-products may significantly affect the quality of the water supply. Therefore, it is urgent to develop efficient water treatment technologies to degrade EOM. Vacuum ultraviolet (VUV) can generate reactive oxidative species (ROS) in situ to remove organic pollutants, so it has the potential to remove EOM. In this study, vacuum ultraviolet (VUV)-activated persulfate (PS) was used to remove EOM, and its treatment efficiency, influencing factors, reaction mechanism, and impact on the formation of disinfection by-products (DBPs) were investigated, aiming to apply it to the treatment of natural algae-containing water. The results revealed that the VUV/PS system can rapidly degrade and mineralize EOM, with a removal rate of 93.7% for UV₂₅₄ and 74.1% for DOC respectively. The degradation rate of EOM significantly increases as the dosage of PS increases, and acidic conditions promote the degradation and mineralization efficiency of EOM. The coexisting HCO-₃ and Cl- in water significantly inhibit the mineralization efficiency of the VUV/PS system for EOM, while the influence of NO-₃ is relatively small. As VUV irradiation promotes the generation of ROS, the concentrations of hydroxyl radicals (HO^·) and sulfate radicals (SO^·-₄) in the VUV/PS system are higher than those in the UV/PS system. The efficient mineralization of EOM in the VUV/PS system is mainly attributed to HO^· and sulfate radical SO^·-₄. Dissolved oxygen effectively promote the degradation of EOM by facilitating the generation of ROS, primarily HO^· and SO^·-₄. After treatment with VUV/PS, the generation amount of DBPs in the subsequent chlorination disinfection process decrease significantly. The VUV/PS system demonstrates the ability to significantly reduce the mass concentrations of UV_254, DOC in water and the generation amount of DBPs when treating natural algae-containing water.

Abstract:Membrane bioreactor (MBR) has developed into efficient and mature technology for municipal and industrial wastewater treatment technologies. The wastewater treatment plants based on MBR are established and put into production all over the world with continuously increasing amount and expanding scale. As membrane fouling remains the bottleneck in wider spread and application of MBR, development of high-efficiency and low-cost methods for membrane fouling control has become a research hotspot in the field. As a typical advanced oxidation process, electrochemical oxidation (EO) is widely competent in pollutants decontamination and bacteria disinfection in aqueous environment, exhibiting attractive antifouling potential in MBR by simultaneous foulant degradation and bacteria inactivation on membrane surface. In recent years, the flourishing EO-based technologies for membrane fouling control have accelerated the innovation of antifouling methods in MBR and highlighted new thought on antifouling mechanism. To keep pace with the rapid development of MBR, comprehensive summarization and discussion of EO for antifouling research and application in MBR are urgently needed. This review firstly introduces the working mechanism of EO, and analyzes various ways involved in generation of reactive oxygen species and inhibition of membrane fouling in electrochemical oxidation MBR (eMBR). Based on the latest research progress both domestically and internationally, the operational modes and antifouling performance of eMBR were systematically discussed from the perspective of loading methods of electrode, combining methods of electrode and membrane, and fabricating material of electrode. The influencing factors of EO in inhibiting membrane fouling and existing challenges for practical application were summarized. Finally, future research prospects in eMBR were discussed and suggestions on further optimization and innovation were provided.

Abstract:Accurately acquiring real-time cooling load of internal heat sources is of great importance for developing energy-saving control strategies for heating and air conditioning systems and reducing the operating energy consumption of buildings. The delayed cooling load generated by the radiation heat transfer process poses a challenge in calculating the internal thermal load. In this paper, the radiant cooling load monitoring model of internal heat sources, represented by a 10th-order transfer function, is developed based on the analysis of heat storage-release process, heat transfer characteristics, and transfer function principle. In order to simplify the calculation process and improve the accuracy, radiant time factors are adopted to identify the parameters and reduce the order of developed models, and a transfer function of order 2 is acquired. An experimental system is built to validate the developed model and the results show an average absolute percentage error of 8.19% for the model. The developed model for thermal lag cooling load in buildings can be applied to building energy consumption monitoring platforms to achieve online load monitoring. It has theoretical significance in describing the time-delay patterns and amplitude attenuation characteristics of the delayed cooling loads. This model provides a theoretical basis for making energy-saving control strategy of the heating and air conditioning system.

Abstract:As a common natural phenomenon, icing is widespread in industrial production processes and often causes adverse effects on daily life and production. The potential hazards caused by icing in various industries could be significantly reduced or even eliminated by using ice characteristics prediction technologies. Previous studies have shown that the rate of road traffic accidents can be reduced by 65% after using ice characteristic prediction technology. Furthermore, when combined with the de-icing system, 80% of icing scenarios can be anti-icing or de-icing. To effectively address the issue of ice disasters across various industries, this review provides an overview and analysis of existing icing prediction technologies based on stationary surfaces such as road and transmission line, as well as moving surfaces such as wind turbine blade and aircraft. The results indicate that existing technologies achieve prediciton accuracies of over 80% for indicators such as ice thickness on stationary surfaces and over 70% for moving surfaces. Existing ice characteristic prediction technologies can be divided into two types, model-driven method and data-driven method, with the later showing significant potential for development. Based on the summarized ice prediction technologies applied to four simple cold surfaces under stationary and moving states, this paper further proposes key research directions in this field, aiming to provide reference and guidance for the development and optimization of anti-icing technologies on low-temperature surfaces in various engineering scenarios.