最新刊期
卷 50 ， 期 6 ， 2018
- 摘要：The main reasons for earthquake damage of bridge structures are earthquake intensity and peak of near-fault velocity pulse. Compared with other bridge types, simply supported slab bridges are more likely to be damaged in the earthquakes. Gaoyuan bridge was a kind of simply supported hollow slab bridge of prestressed concrete, which was seriously destroyed in the Wenchuan earthquake in 2008. The effects of artificial boundary on the site on the accuracy of calculation results and calculation efficiency were studied carefully while the boundary was free boundary, fixed boundary, viscoelastic boundary and the artificial boundary of viscoelastic damping layer, respectively. The finite element model of Gaoyuan bridge included structure and site was established by ABAQUS, and boundary condition was the artificial boundary of viscoelastic damping layer. The effects of earthquake intensity and peak of near-fault velocity pulse on this bridge were researched. Peak acceleration of seismic wave represented earthquake intensity, and seismic wave with near-fault velocity pulse characteristic was synthesized. The results showed that when the artificial boundary of the model is the artificial boundary of viscoelastic damping layer, the reflection effect at the boundary could be effectively reduced and the accuracy of calculation results meets the basic requirements. Peak of near-fault velocity pulse is more sensitive to the seismic response of bridge than earthquake intensity. Peak accelerations of all points are improved on the site surface while earthquake intensity is raised. The earthquake damage of local structure is aggravated easily for closing to river bank and existing bedrock interface. The increase of earthquake intensity, peak of near-fault velocity pulse or peak of seismic wave displacement lead to enhance peak of span variation, relative slipping and slipping peak. Wave seismic with near-fault velocity pulse feature caused earthquake destruction in the bridge to be magnified.关键词：simply supported slab bridge;earthquake intensity;peak of near-fault velocity pulse;site effect;artificial boundary
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发布时间：2024-01-10 - 摘要：Existing steel plate shear walls could not meet the requirements of high mechanical properties and energy dissipation performance at the same time. To solve this problem, based on the origami theory three kinds of novel pre-folded steel plate shear walls were presented, which consist of origami patterns. The elastic-plastic buckling analysis of a pre-folded steel plate shear wall subjected to horizontal lateral loads under two-side connections was presented. The influences of different kinds of origami patterns on the buckling performance (such as ultimate bearing capacity, rigidity and ductility) of steel plate shear wall were studied and compared with that of flat steel plate shear walls and shear walls composed of profiled steel sheeting. The results indicated that the origami patterns has a great influence on the buckling performance of the steel plate shear walls. Origami patterns evidently reduces the rigidity of steel plate shear walls while the degree of weakening of the ultimate bearing capacity is relatively small. The ultimate bearing capacity could be weakened by up to 12.65% compared to that of shear wall composed of profiled steel sheeting. Plastic hinges firstly appears along the creases on the steel plate shear walls, and the creases guides the plasticity development process. The introduction of the origami patterns effectively avoids the overall out-of-plane instability of the steel plate and improved the ductility of the plate. The pre-folded steel plate shear walls exhibits different degrees of improvement of ductility, which is up to 8.2 times higher than that of flat steel plate shear wall and 5.2 times higher than that of shear wall composed of profiled steel sheeting. The steel plate shear wall composed of origami pattern C could form a complete folding deformation mode whose plasticity development is more uniform and sufficient. The ductility of the specimens composed of origami pattern C is about twice that of the steel plate shear walls composed of the other two kinds of origami patterns, which still has a higher bearing capacity in the later period of earthquake. The novel steel plate shear walls with plastic hinge guidance mechanism has good seismic performance, which has great energy consumption performance and good utilization prospect in the field of structural seismic resistance.关键词：pre-folded;steel plate shear wall;origami-inspired;elasto-plastic buckling;ductility
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发布时间：2024-01-10 - 摘要：Based on the research foundation of the existing equivalent model of multiple high-rise isolated structures, a dynamic response analysis method for the equivalent model of multiple high-rise isolated structures was proposed, which makes the structural response analytical solution have clear physical and engineering significance. For a simplified structure with two degree of freedom equivalent multi-layer isolation system, since the solution of the equation of motion of the multi-layer isolation structure using the strong vibration decoupling method that is widely used in practical engineering will produce large errors, the Kelly decoupling solution can greatly improve the accuracy of the solution. And for a three degree of freedom equivalent model of isolated high-rise structure, decoupling using strong decoupling method was used to analyze the error of the strong vibration decoupling method, and the results were corrected, which indicated that, the method of lifting the strong decoupling accuracy can also greatly improve the accuracy of the solution. Also, isolated structure with non-classical damping was analyzed for dynamic displacement response with standard second order oscillator to show that the existing seismic design method based on classical structure can be applied to isolated structures with non-classical damping characteristics. The method was demonstrated using example, the original multi-layer structure and the high-level structure were simplified into two degree of freedom and three degree of freedom models, respectively. The validity of the equivalent simplified model was verified by comparing the original structure with the equivalent simplified model. At the same time, the approximate decoupling solution method for non-classical damping isolation structures is simple and effective. With this method the dynamic response analysis of isolated structures becomes more complete.关键词：isolated structure;the simplified model;non classical damping;standard second order oscillator;analysis of dynamic response
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发布时间：2024-01-10 - 摘要：The mechanical properties of composite electrical equipment are better than ceramic electrical equipment and it have broad application prospects in substation or converter station. In order to research the seismic response of ±800kV composite pillar insulator, enhance the seismic level of composite electrical equipment, ±800 kV converter station composite material pillar insulator connected circuit was taken as an object, then the seismic response law of composite electrical equipment under seismic actionwas researched, the influence of the conductor stiffness and equipment stiffness on the seismic performance of the connected equipmentwere analyzed by using structural dynamics theoretical analysis method and establishing two degrees of freedom theoretical model and dynamic equation of interconnected electrical equipment. The results showed that as the stiffness of the connecting wire increases, the displacement of the high-frequency equipment is slightly larger than that of the low-frequency equipment. The greater the difference in wire stiffness, the greater the difference in seismic response between the two equipment. Under the premise of electrical function, increasing the redundancy of the wire is beneficial to improve the seismic performance of the equipment. In order to reduce the seismic response of the connected equipment, the two equipment with close frequency are interconnected as much as possible to reduce the seismic coupling effect between the equipment. Then the principle of the frequency matching and the conductor design between the composite electrical equipment were put forward, which provided reference for the seismic design of the equipment.关键词：±800 kV;composite material;electrical equipment;connection circuit;coupling effect
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发布时间：2024-01-10 - 摘要：In order to study the vibration characteristics of reinforced concrete (RC) structures during fire and to develop the method of damage assessment after fire, 4 simply-supported RC beams (L1~L4) were designed. Firstly, the finite element model of the simply-supported beams (L1~L4) were calibrated by picking up the modal information before exposure to fire. Then fire tests were conducted on L1~L4 for 60min, 90min, 120min and 150min respectively. During the fires, the structural modal information were collected, and the attenuation formula of frequency was obtained by fitting the test results. In order to study the residual stiffness and bearing capacity of L1~L4 after the fire, the dynamic tests and bearing capacity tests were carried out. Finally, based on the modal information of specimens after the fire, by taking equivalent explosion time as the damage index, the support vector machine intelligent algorithm was used to predict the damage degree of the RC beams. Based on the Standard for Appraisal of Building Structure After Exposure to Fire (CECS252—2009), a comprehensive grading of damage index for simply-supported RC beams exposure to fire was established, and the damage index grading of L1~L4 were evaluated at the end.关键词：RC simply-supported beam;vibration characteristics;fire test;damage identification;damage assessment
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发布时间：2024-01-10 - 摘要：Incidents such as fires, explosions, and impacts may cause progressive collapse of building. Since the 20th century, as terrorist activities in the world have been increasing year by year, experts and scholars around the world have begun to pay attention to the formulation of building collapse prevention codes and structural progressive collapse resistance. At present, Concrete filled steel tube column (CFST)-steel beam joints with outer ring plate have been widely used in engineering examples. However, outer ring plates occupy a large amount of building space due to welding on the outer wall of steel tubes, which affect the function of buildings, and CFST-steel beam joints with through-center construct, that is, the steel beams are wholly or partially passed through the core concretes and the steel tubes, which greatly save the use space of the buildings. In order to study the mechanism of CFST-steel beam joints with through-center construct under progressive collapse conditions, ABAQUS finite element software was used to establish five CFST-steel beam joints with through-center construct and one fully welded joint models. The resistance mechanism, deformation modes and internal forces of the joint were investigated, and the capability of progressive collapse was evaluated. The results showed that the failure mode of CFST-steel beam joints with through-center construct can be divided into two types, the collapse failure mode at the beam and the collapse failure mode at the column. The collapse failure mode at the column has better ductility and bearing capacity, but with instability. The vertical bearing capacity of the joints is mainly provided by the bending mechanism and the catenary mechanism. The bending resistance mechanism provides the early resistance and the catenary mechanism determines the ultimate bearing capacity at the later stage. The new CFST column-steel beam joint with through-center structure has good capability of progressive collapse resistance, and its index of progressive collapse resistance of joint is higher than that of the other joints with collapse failure mode at the beam.关键词：through-center construct;CFST-steel beam joints;anti-progressive collapse
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发布时间：2024-01-10 - 摘要：Severe seismic damage can be occurred in the position of significant changes of the vertical stiffness of the large chassis structure, and the mid-story isolation system can effectively solve the problem of significant changes of stiffness and mass between the chassis and the tower. A large number of numerical analysis studies have been conducted to investigate the performance of mid-story isolation structure. However, there has been a lack of experimental studies on mid-story isolation structure, and the study of the lateral–torsional coupling effect of the mid-story isolation structure with large chassis and eccentric tower has not been reported. Therefore, in order to guide the seismic design of the project, seismic response and the lateral–torsional coupling effect of the mid-story isolation structure with large chassis and eccentric tower are studied. A large chassis structure (single tower) with significance of typical engineering application and eccentric tower is established at the zone of fortification intensity 8, in which the chassis has 2 floors and the upper tower has 6 floors, the plane area ratio of the upper tower to the chassis is 1: 2.4 and the ratio of the tower height to the tower width is 1:3, I that is consistent with the typical features and conditions of such large chassis structure. According to this prototype structure, the simplify and the scaled model is built. A shaking table test and a numerical analysis are conducted by two-dimension ground motion input, and compared the results of the shaking table test and the numerical analysis. The acceleration and story drift of each story of the model are obtained. The experimental results show that the seismic response of the structure is reduced obviously by using mid-story isolation technology. Through the analysis of experimental data, it is known that the ratio of acceleration reduction and the ratio of story drift reduction for upper tower are 83.13% and 81.18% or more (Y-dir) when peak ground acceleration is 0.60g. However, the acceleration response of the chassis increases. The ratio of acceleration reduction is between –12.69% and –24.07% ( Y-dir) and the ratio of the story drift reduction is between 15.53% and 17.15% (Y-dir), so the vibration control effects of the chassis is poor. When peak ground acceleration is 0.60g, the model of the upper tower remains elastic stage but the chassis leads to the elastoplastic stage at 0.40g, and the second layer displacement of the chassis is significantly larger than that of the first layer. The results of the numerical simulation analysis for the lateral–torsional coupling effect analysis of the mid-story isolation are verified by the shaking table test. Compared with the seismic model, it can be concluded that the torsional angle of the chassis is reduced by 2/3, the torsion response of the isolation story is larger but not transmitted into upper tower, the interstory torsional angle of the tower tends to zero, and the torsional coupling effect between the tower and the chassis is not obvious. Therefore, the mid-story isolation technology is an effective method to reduce torsion effect for the building (single tower) with large chassis and eccentric tower.关键词：large chassis structure;eccentric tower;mid-story isolation;shaking table test;lateral–torsional coupling
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发布时间：2024-01-10 - 摘要：To ensure the safety of relics in museums, two new sliding relics isolation bearings were put forward, which are fixed stiffness bearing and variable stiffness bearing respectively. The " bearing-cabinet” finite element models (FEM) were established. Meanwhile, a museum FEM was established and the floor waves were extracted under different working conditions. The time history analysis of the " bearing-cabinet” FEM was carried out. The seismic isolation effect and applicability of two bearings were studied and the bearing design was completed. The results showed that the bearings can isolate the earthquake in both X and Y directions simultaneously. The variable stiffness bearing can also realize the seismic isolation target of earthquake with different intensities. The seismic isolation effect of fixed stiffness bearing and variable stiffness bearing is about 60%, 80% under the isolated floor waves and is about 90%, 95% under the non-isolated floor waves. The seismic isolation effect of variable stiffness bearing is better than fixed stiffness bearing. The design methods of two new sliding relics isolation bearings provides a necessary guidance for subsequent engineering application.关键词：sliding relics isolation bearing;fixed stiffness;variable stiffness;seismic isolation effect
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发布时间：2024-01-10 - 摘要：The accuracy of numerical substructures in structural hybrid simulation attracts more and more attention, especially when structures experience strong nonlinearity under extreme loadings. Model updating technique concerning on the accuracy of the parameters for the constitutive model is proposed to online update these parameters of numerical substructures. Due to their certain limitation, the component and sectional constitutive model for parameter updating in hybrid simulations cannot satisfy the requirements of large, complicated structures. To this end, the parameter identification of material constitutive model is proposed and applied to the hybrid simulation of RC frame structures. The identification of the parameters for concrete constitutive law and the hybrid simulation with model updating were validated through three cases of RC frame hybrid simulation. Results show that the convergence speed and stability of the parameter identification are quite good; the credibility of the hybrid simulation is highly enhanced by improving the accuracy of numerical substructures.关键词：hybrid simulation;online parameter identification;unscented Kalman filter;OpenSEES;RC frame
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发布时间：2024-01-10 -
Parametric Analysis of Seismic Performance for Bridge Bents with Buckling-restrained Braces (BRBs) AI导读
摘要：During Wenchuan earthquake, some bridge bents with double piers suffered severe damage and much attention has been paid to the seismic performance of bridge bents. Based on the structural fuse concept, the bridge bents by using buckling-restrained brace (BRB) was proposed to control its damage in transverse direction. An analytical model of single bridge bents considering the elasto-plastic behaviors of piers, the pounding response between shear keys and girders and the sliding friction behavior of laminated rubber bearing was developed. Nonlinear response history analyses were conducted with far-fault and near-fault ground motion records including velocity pulse of forward rupture directivity effect and fling-step effect. Many parameters such as the ratio of horizontal stiffness between BRBs and bents, the ratio of horizontal yielding displacement between BRBs and bents, the arrangement form of BRBs, the bent with unequal-high piers, and the intensity of ground motion were analyzed. Results indicated that the damage of regular and irregular bridge bents can be effectively controlled by using BRBs, and the rational sampling ranges of the horizontal stiffness ratio and horizontal yielding displacement ratio between BRBs and bents are found to be 0.5～2.0 and 0.5～1.5, respectively.关键词：bridge engineering;bent with double columns;buckling-restrained brace (BRB);near-fault ground motion;velocity pulse- 2508
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发布时间：2024-01-10 - 摘要：Seismic isolation has been already applied in bridges widely. It will inevitably cause large post-earthquake residual displacement between bridge superstructure and substructure. In order to effectively reduce the inertia force transferring to the pier to improve the ability of seismic isolation and reduce the damping force to improve the capability of self-centering, a new-type self-centering seismic isolated bridge system was proposed. This system was composed of a new type friction damper with self-centering function and the teflon sliding bearing instead of the traditional seismic isolation bearing. This new-type friction damper with self-centering function had stable friction force when the piston of the damper moves away from the equilibrium position. On the contrary, it had not friction force to reduce the consumption of the re-centering capacity when the piston moved to the equilibrium position. In addition, the bridge structure and the damper were connected by the cable in order to ensure that the damper was tensioned only and the superstructure could move relatively to the pier back and forth. In order to verify the validity of this self-centering seismic isolated bridge system, this new-type self-centering seismic isolated 4-span continuous bridge system and the same bridge structure with non-isolation bearings and lead rubber bearings (LRBs) were modelled via OpenSees. Then time history analysis was conducted for each model under the transverse ground motion record respectively. The pier top displacement, the relative displacement between pier and girder, and the internal forces of the pier were mainly investigated. Analytical results showed that the pier top displacement of self-centering seismic isolated bridge system is reduced to 1/8 and the internal forces at the pier bottom such as moment and shear force are reduced to 1/3 comparing with the non-isolated bridge. Comparing with the isolated bridge with LRBs, the post-earthquake residual displacement between the girder and the pier of the self-centering seismic isolated bridge system was very small, which indicates that the proposed new-type self-centering friction damper and the self-centering seismic isolated bridge system have better self-centering and seismic isolation capacity.关键词：self-centering capacity;friction damper;seismic isolation;internal force of bridge pier;residual displacement
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发布时间：2024-01-10 - 摘要：In order to improve the seismic safety and structural seismic performance of portal section of traffic tunnels in meizoseismal area, based on the research background of the Baiyunding tunnel portal in Wenchuan earthquake, a large-scale shaking table model test study on the seismic response of the soft and hard surrounding rock interface section of the tunnel portal was carried out. Firstly, the design of test scheme was introduced, including test equipment, similar design, dynamic load, dynamic characteristics and loading system. Then, the test data was analyzed, and the spatial variation law of peak earthquake acceleration (PGA), longitudinal strain, contact stress and internal force of tunnel structure during the transition from hard rock to soft rock at the soft and hard surrounding rock interface section of the tunnel portal were studied. The results showed that the development of the soft and hard surrounding rock interface section in the tunnel portal was hard rock to soft rock. The magnification factor of PGA increased from 1.04 to 1.68, the increasing multiple of longitudinal strain increased from 1.09 to 4.29, and the increasing multiple of contact stress increased from 6.34 to 32.16, the percentage reduction of minimum safety factor increased from 26.18% to 53.48%. The seismic inertia force and the forced displacement acting on the tunnel structure increased continuously with the influence of soft rock increasing, resulting in the structural safety decreasing continuously.The results of this research can provide a reference for the traffic tunnel design and the seismic fortificat in highly seismic regions.关键词：tunnel engineering;tunnel portal;the soft and hard surrounding rock interface section;seismic response character of tunnel;shaking table model test
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发布时间：2024-01-10 - 摘要：It is difficult to predict the deformation of main girder enhanced by stay cable system in the tensioning stage, and the traditional unequal interval gray model (TUIGM) has the problems of low accuracy in its application. In order to solve these problems, an improved unequal interval weight gray prediction model of main girder deformation modified by Markov chains residual was proposed. First, the girder deformation and cable force difference were taken as the original data sequence and time difference of the TUIGM respectively. Considering whether the weight distribution coefficient was introduced during the accumulation and regression process, four different gray prediction models with unequal interval weight were constructed, and the most optimal weight distribution coefficient and the prediction value of girder deformation were determined based on the similarity criterion, thus elevating the prediction accuracy. Second, the Markov chains method was adopted to reflect the random fluctuation feature of the residual sequence, made corrections to modify the prediction values of the improved unequal interval weight gray model (IUIWGM), which overcome the low accuracy of the single model, and further improved the accuracy. Finally, this model was applied to predict the deformation of main girder enhanced by stay cable system. The results showed that compared with the TUIGM, the average relative error of the model decreases by 0.47% after the weight distribution coefficient is introduced into the accumulation process. After modifying the prediction results by Markov chains method, the average relative error of the prediction model is reduced by 10.32%, which can greatly improve its prediction accuracy. Compared with the TUIGM modified by Markov chains, the average relative error of the modified model which has been optimized by the regression process decreases by 3.50%, this model has higher prediction accuracy and can reflect the development trend of the deformation of the main girder enhanced by stay cable system. The main theory of this model is grey theory and it is suitable for deformation prediction without any special requirement or limitation on the measured data.关键词：deformation prediction;gray theory;unequal interval;improved weight;Markov chain;continuous box girder bridge;stay cable system enhancement
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发布时间：2024-01-10 - 摘要：Self-centering precast concrete shear walls were constructed by using post-tensioning strands to assemble prefabricated wall panels along vertical direction. At the base of the wall, conventional reinforcing steel was used for increasing energy dissipation capability. It was concluded from the previous experimental and numerical studies that both structural damage and residual deformation for a self-centering precast concrete shear wall is insignificant, which means an resilience after a major seismic event for this type of structural system. To further investigate the performance of this system under severe earthquakes, particularly the performance for collapse resistance, two prototype structures of four and six stories were designed using self-centering precast concrete wall and conventional reinforced concrete wall as the primary lateral force resisting system, respectively. Nonlinear incremental dynamic history analyses were performed using 44 ground motions, and the results were used to establish the collapse fragility curves. On the basis of this, the collapse capacities of the above prototype structures were evaluated and compared according to the FEMA P695 standard. The analytical results showed that the self-centering precast concrete shear walls exhibit slightly larger lateral displacement than the conventional reinforced concrete shear walls because of relatively less energy dissipation capacity. However, the residual lateral displacements for the self-centering precast concrete shear walls are much less than their counterparts, indicating good self-centering capability. Based on the comparison of collapse fragility curves, it was concluded that the deformation capacity for a self-centering precast concrete shear wall is much better than a conventional reinforced concrete wall, resulting in significantly less damage after an earthquake event. The results from collapse capacity evaluation using the FEMA P695 standard indicate that the self-centering precast concrete walls investigated in this study have a similar seismic collapse capacity and safety redundancy compared to the designed conventional reinforced concrete walls, while also fulfill the requirements for structural collapse safety as prescribed in the FEMA P695 document.关键词：self-centering shear wall;precast concrete;incremental dynamic analysis;collapse capacity assessment;FEMA P695
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发布时间：2024-01-10 - 摘要：The failure mode of " strong joint weak component” resisting seismic excitation is the precondition for the frame to exert its good seismic performance. To ensure the realization of that failure mode, a energy-dissipation scheme that installs sector lead viscoelastic damper(SLVD) at adjacent core joint was proposed. For studying the effect of the SLVD on protection of core joint and seismic performance of RC frame, two two-bay and two-story RC specimens, with the same dimension, material and rebar, were designed and built. One of the specimens is the ordinary RC frame specimen and the other is the RC energy-dissipation frame specimen installed SLVD. The failure mode, hysteresis behavior, bearing capacity, strength and stiffness degradation, and absorbing-energy capacity of the RC energy-dissipation frame specimen were contrasted with the ordinary RC frame specimen by quasi-static test. The test results indicated that, compared to the serious shear damage at the joints of the ordinary RC frame specimen, slight damage occurs at the joints of the RC energy-dissipation frame specimen. Due to the excellent energy-absorbing and protection of SLVD, the emergence of cracks at the joints is delayed, the development of cracks is controlled, and the damage of the whole frame is alleviated. The SLVD plays a role of energy-dissipation haunch brace, which promotes the bearing capacity, lateral stiffness and energy-dissipation capacity of frame. The installation of SLVD changes the internal force distribution and transmission path near the joint area, which reduces the shear force and bending moment transmitted to joint area. At the same time, it also changes the force distribution of beam and column component, which should be considered at the energy-dissipation design. The installation of SLVD in joint area is conducive to the realization of the " strong node weak component” seismic design concept. The seismic performance of the RC energy-dissipation frame is better than that of the ordinary RC frame.关键词：energy-dissipation frame;sector lead viscoelastic damper;seismic performance
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发布时间：2024-01-10 - 摘要：In order to comprehensively and objectively assess water resources carrying status and to provide a theoretical support for regional socio-economic development, this study reviewed existing researches on carrying capacity of water resources, analyzed the conceptual meaning and assessment indicator system. It is indicated that red-line indexes are allocated based on the regional economic development statement, which cannot reflect water resources characteristics and the deficiency in the development of water conservancy development in that place. From the perspective of regional characteristics, this paper focused on the choice of evaluation indexes, and an assessment method was proposed based on water resources carrying potential factors such as water resources endowment, degree of development and utilization and water supply capacity of projects. Based on Cannikin Law, the evaluation system with potential indexes was proposed in this study. Taking Lijiang city in Yunnan province as example, two evaluation systems, the present one and the assessment indicator system using quantity red line and quality red line, were used to evaluate the water resources carrying capacity in Lijiang city to test all the factors and to verify the rationality and feasibility of assessment method proposed. The results revealed that the demand of regional social economic development is the main factor considered in red-line indexes allocation. While the old town district is assigned to a relatively high value in Lijiang city because it is the most developed area, the other districts can only get enough water to meet their need and further constrained their development. It is a problem for water resources management that the water use indexes only allocated in administrative regions but not in water resources regions. The results of potential indexes considering water resource endowment condition and water supply project can better reflect the real condition. In fact, Lijiang water resources condition is not bad, but it lacks of water conservancy projects and has the difficulty in water resources allocation, which causes engineering water shortage, a common problem in southwest China. Measures and suggestions for managing water resources were proposed based on the analysis of overloading causes.关键词：carrying capacity;regional characteristics;assessment method;potential indexes;Lijiang city
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发布时间：2024-01-10 - 摘要：The shear strength of expansive soil is not only influenced by the water content, dry density, vertical stress, wetting-drying cycle, crack and other factors, but also influenced by the clay content and plasticity index. However, the existing studies rarely considered the clay content and plasticity index, and thus could not systematically and objectively reflect the regularity of shear strength of expansive soil in a certain area. In order to study the effect of clay content on the free expansion ratio and plasticity index, the effect of clay content and plasticity index on the quick shear strength friction angle (including quick shear, saturated quick shear, saturated and consolidated quick shear) and residual strength friction angle of 21 expansive soils at a county of Middle Route of South-to-North Water Diversion Project, shear tests were conducted on undisturbed soil using electric strain controlled direct shear apparatus at 0.8 mm/min and ShearTrac Ⅱ reversal direct shear apparatus at 0.02 mm/min. It was founded that the free expansion ratio gradually increases with increase of clay content and then changes gently. The plasticity index exhibits a logarithmic growth relation with clay content and then changes gently as clay content increased to 33%. The shear strength of samples significantly reduces after saturating, ie. The friction angle of saturated quick shear is less than the quick shear friction angle. There is a " cure” effect of consolidation on the samples, the strength is obviously improved, ie. The friction angle of saturated and consolidated quick shear is larger than the saturated quick shear friction angle. The friction angle of quick shear, saturated quick shear, saturated and consolidated quick shear decreases with increase of clay content and plasticity index, and then changes gently with critical value about 32% and 24% ,respectively. The friction angle of residual strength decreases with increase of clay content and then changes gently. With the increase of plasticity index, the friction angle of residual strength decreases, but it is not clear whether the friction angle changes gently after decreasing. Further research is being carried out by the project team.关键词：expansive soil;clay content;plasticity index;quick shear strength friction angle;residual strength friction angle
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发布时间：2024-01-10 - 摘要：Due to the problem that local bucking is easy to occur on steel tube of concrete-filled skin steel tube (CFST) columns, the applications and researches of a new type composite column, CFST with stiffening ribs, have been reported in recent years, and the problem of CFST is expected to be solved through the change of structural form. In this paper, the effects of different types of stiffening ribs on mechanical properties of concrete-filled double skin steel tube (CFDST) columns were studied. Three types of stiffeners including single rib, triangle rib, and square rib were designed to strength CFDST columns, and three slenderness ratios of 4.0, 5.0 and 6.0 were applied for each section type of CFDST columns. The axial compression tests of CFDST columns were conducted, and full-filled strain of specimens were monitored and analyzed. Besides, the influences of different stiffener types on the ultimate bearing capacity, ductility, local bucking and load-displacement curve were investigated and analyzed. It was found that local bucking of CFDST columns with different slenderness ratios are most likely to occur from 1/8 of height to end face or from 1/8 to 3/8 of height. Compared with no-stiffener CFDST columns, the ductility of CFDST columns with stiffeners has improved greatly, and the specimens with triangle ribs show a 76% increase on average in ductility. However, the ultimate bearing capacity has different decrease. A modified formula is built and the calculated values are matched with test results well.关键词：stiffener;concrete-filled double skin steel tube;local buckling;ductility
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发布时间：2024-01-10 - 摘要：The snow-melt water is one of the most important supply sources of most rivers in the mountain area of arid area, which plays an important role on the local social and economic development, ecological environment, et al. Based on GIS spatial analysis method, the snow coverage was extracted from MOD10A2 spanning from 2001 to 2016 in the mountain region of Yarkant River basin. The annual and inter-annual variations of snow coverage in the different elevation zones were analyzed by using linear trend analysis method. The results show that: 1) Accumulation-reduction-accumulation-ablation process was presented in the annual change of the snow coverage. In spring and autumn, the snow accumulated, and it melted in summer. In winter, the snow coverage area was reduced due to the snow migration and sublimation by wind blowing. 2) With elevation interval of 200 m, the snow coverage rate in January and February showed a consistently gentle rise and fall with elevation. In March, April, November and December, it showed the same change trend. In the zone A (<3 600 m), the snow coverage rate showed gentle rise trend with the elevation. In the zone B (3 600～4 800 m) and zone C (4 800～6 000 m), significant rise trend was shown. In the zone D (>6 000 m), it showed a downward trend. From May to October, snow was totally in the melting state in the zone A, and in the gentle rise trend in the zone B and significantly rise trend in the zone C, while decreased trend in the zone D. 3) The annual variations of snow coverage rate in the zone A and zone B showed a unimodal curve, and the main replenishment period was in autumn and winter. In the zone C and zone D, the curve showed " M” type. The accumulation-reduction-accumulation-ablation process was presented, and the snow coverage area was reduced due to the migration to low attitude region and the sublimation by wind blowing in winter. The snow coverage rate was about 80% in the zone D due to the high altitude. 4) The inter-annual variation of snow cover showed a decreasing trend, especially in autumn and winter. 5) The inter-annual variation of the snow area showed a decreasing trend in low altitude areas (zone A, B and C), while it showed a weak increasing trend in high altitude (zone D).关键词：Yarkant River basin;MOD10A2;snow coverage area;snow coverage rate;elevation bands
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发布时间：2024-01-10 - 摘要：A two-story and one bay specimen of innovative PEC column (weak axis)–reduced section steel beam composite frame with end-plate connection by 1/2 scale was designed and fabricated, which represented bottom two stories of composite frame, and the pseudo-static test of the specimen was conducted to study its seismic performance. Based on experimental observation and measurements, the seismic performance as hysteretic characteristics, lateral stiffness, seismic energy dissipation and ductility, plastic damage process and ductile failure mode were analyzed. The results indicated that crimping PEC column can improve its flexural stiffness in weak axis.Plastic hinge forming location is away from beam end due to beam reduced section connection, the hysteretic loops of specimen is plump, its global drift angle, ductility coefficient and equivalent viscous damping ratio are 0.033 7 rad (push)/0.037 7 rad (pull),2.76 (push)/2.76 (pull) and 0.281. respectively with imperfection of welding, hence it owns good deformation, ductility and energy-dissipation capacity.The force-transfer mode of concrete equivalent strut in the panel zone is well captured due to end plate connection with pre-tension penetrating bolts and strengthened plate.The ideal ductile failure mode as plastic mechanism of plastic hinges are formed in all beam reduced sections and column section at bottom successively.关键词：PEC column (weak axis);reduced section steel beam;end-plate connection;composite frame;seismic performance;pseudo-static test
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发布时间：2024-01-10 - 摘要：The suction caisson can be used in offshore wind farms. Due to the long-term horizontal cyclic loadings caused by wind, waves and currents, the offshore wind turbine foundation is required to provide high horizontal bearing capacity and limit the deflection. To better meet these needs, the skirted suction caisson, consisting of an internal caisson in an external short-skirted structure, was put forward. Numerical studies were conducted with the finite element software Z_SOIL to investigate the cyclic behavior of skirted suction caissons in sand, and the influence of cyclic load ratio, load eccentricity, loading way and loading order on the accumulated displacement and stiffness were analyzed. It was found that the soil stiffness increases at the small strain stage, the hardening small strain stiffness model was adopted. Results showed that the cyclic secant stiffness does not change significantly with the number of cycles when the cyclic load ratio is less than 0.5. However, it increases with the increase of cycles when the cyclic load ratio is larger than 0.5 due to the fact that the sand around the caisson is compacted during cyclic loading. As the increase of cyclic load ratio and load eccentricity, the cyclic secant stiffness of the skirted suction caisson reduces linearly, resulting in an increase of both horizontal and vertical displacement. It was also found that one-way cyclic loading produces the largest horizontal displacement while the two-way loading produces the largest vertical displacement. Moreover, a decreasing cyclic loading causes both the largest horizontal and vertical displacement of the caisson, which indicates that the previous cyclic loading has an important influence on the bearing behavior of the caisson.关键词：offshore wind farm;skirted suction caisson;horizontal cyclic loading;cyclic secant stiffness;horizontal and vertical displacement
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发布时间：2024-01-10 -
Experimental Study on Deformation and Strength Behavior of Geotextile Reinforced Coarse-grained Soil AI导读
摘要：The influences of geotextile reinforcement layer number n on the deformation and strength properties of coarse-grained soil were investigated by using the consolidated-drained triaxial compression tests on the samples with different n (n=0～3). The experimental results showed that the axial strain at failure increases by 0.91%～2.00% under different confining pressures, with the increment of n of 1, indicating the improvement of toughness. The geotextile could inhibit the lateral deformation of soil samples. The deformation modulus increased averagely by 5 378 kPa with the increment of n of 1 under different confining pressures. The reinforcement could increase the volumetric strain at phase transition. Both points at phase transition and at failure with the same n could be fitted by lines in p–q plane. The strength indexes increased with the increase of n generally. With respect to the linear index c and nonlinear indexes such as φ0 and Δφ, its relationship with n was approximately linear, and the internal friction angle increased by 1.75 degrees with the increment of n of 1. Finally, the index of reinforcement IR was put forward by considering the description of the quantity of reinforcement conveniently, and the method to obtain IR by triaxial shear test was given. It was found that the relationships between cohesion c, pseudo-cohesion Δc (cohesion increment of reinforced earth) and IR could be fitted by lines, and with the increment of IR of 1 m–1, c and Δc increased by 9.1 kPa and 13.5 kPa, respectively. Using this parameter IR, the effect of strength increase to sands, clay and coarse-grained soil under triaxial test was analyzed and summarized. There were significant differences on the cohesion increment among these soils, where the c for sands, clay and coarse-grained soil increased by 0.07, 0.50 and 8.75 kPa with the increment of IR of 1 m–1. Based on the pseudo-cohesion principle, the relationships between c, Δc and IR were established, which can be used to evaluate c and Δc of reinforced earth directly.关键词：geotextiles;reinforced earth;coarse-grained soil;triaxial test;deformation;strength- 1983
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发布时间：2024-01-10 - 摘要：It is easy for the cracks in rock masses to propagate and coalesce under the combination of high ground stress and seepage pressure, which leads to the failure of rock masses. In order to investigate the initiation and propagation modes of 3-D crack under hydro-mechanical coupling, a numerical model was established by the 3-D fracture analysis code of FRANC3D. The numerical simulation and the corresponding laboratory failure experiments based on the transparent resin rock-like material were carried out. The applicability of different fracture criteria was analyzed by comparing it with laboratory results, and then the reliability of the model was validated. Based on the numerical simulation, the distribution characteristics of fracture parameters along the crack fronts under different loading conditions were analyzed. The influences of key factors such as water pressure and lateral stress on the angles and lengths of 3-D crack propagation were obtained. The results showed that the numerical results are in good agreement with the test results by using the optimized energy release rate criterion. The wing cracks at end points of crack long axis are the Ⅰ-Ⅱ (tensile–slip) mixed cracks, whereas the plane extensions at end points of crack short axis are the Ⅰ-Ⅱ (tensile–tearing) mixed cracks, and Ⅰ-Ⅱ-Ⅲ mixed fracture occur in the rest of the positions. The existence of water pressure significantly changes the stress distribution of crack fronts. The increase of water pressure can enhance the tensile stress and promote the tensile fracture, resulting in the crack initiation being inclined to the original surface and the propagation rates along the crack fronts tending to be uniform. The increase of lateral compressive stress can significantly facilitate tensile fracture and inhibit slip and tearing fracture. The energy release rates of crack fronts show a decreasing trend under lateral compressive stress, thus restraining the crack propagation, while the lateral tensile stress has an opposite impact on the energy release rates, which indicates that the fractured rock mass is much safer under the biaxial compressive stress state than the tensile–compressive stress state. The lateral compressive stress and water pressure jointly lead to the decrease of the deflection angle of wing crack, which changes the spatial propagation mode of crack and the macro failure pattern of rock mass.关键词：3-D crack;hydro-mechanical coupling;stress intensity factor;energy release rate;initiation and propagation modes
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发布时间：2024-01-10 - 摘要：The technique of anti-slide pile is widely applied in practical engineering as a common measure of slope reinforcement. The slope stability analysis considering its effects is of high theoretical and practical significance. Based on the upper-bound limit analysis method, 3D rotational failure mechanisms are extended by introducing new geometric parameters. The calculation framework of safety factor is established considering the equation of internal dissipation and external work rate. The minimum upper-bound solution of safety factor and the most dangerous failure mechanism are calculated through optimization procedure. Parametric studies were carried out to investigate the effects of pile location, pile spacing, slope angle, slope width on the geometry of failure mechanism and the stability of a slope reinforced with piles. The geometry of failure mechanisms is also discussed. The results demonstrate that the most effective location of the anti-slide piles is between the middle and top of the slope, which is not influenced by the slope width. With a relatively smaller slope width and a pile location close to the slope toe, the critical failure surface passes through the slope face. The farther the pile location is away from the slope toe, the closer the failure surface is to the slope face and the greater its curvature. For slopes with small pile spacing, a secondary slope failure tends to occur above the pile location. Furthermore, the safety factor of slope decreases with the increase of pile spacing. The greater the slope width is, the lower the safety factor is and the closer it is to that of a 2D slope. The failure partbecomes thicker as the pile space and the slope width turns larger. While the slope angle is small, the critical failure surface passes below the slope toe and through the slope base. Obviously the extension of failure mechanism leads to additional optimization of the results.关键词：anti-slide piles;upper-bound limit analysis method;3D failure mechanism;anti-slide safety factor
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发布时间：2024-01-10 - 摘要：The application of passivation materials to immobilize toxic heavy metals has been widely used in the remediation of contaminated soil. However, the acidification of passivated soil can reactivate the fixed toxic heavy metals. The application of passivator is limited in the long-term effect. Therefore, it is of great practical significance to study the key factors affecting soil acidification. In this study, three representative soils in southwest China were selected, their acidification degree and exchangeable acid were measured respectively, and correlation analysis was carried out to determine the internal mechanism of soil acidification. Meanwhile, SPSS software was applied to explore the effect of soil physical and chemical properties on soil acidification through multivariate statistical analysis, principal component analysis and linear regression equation. The results showed that: 1) The essence of soil acidification is mainly caused by the process of H+ and Al3+ acid ion exchange displacement base ion Ca2+ and Mg2+, Al3+ accumulation is mainly in the early stage of the reaction, its correlation with acidification is 0.567; 2) The key factors affecting soil acidification are Ca2+ element content and soil particle size. Ca2+ ion has the most influence, the principal component analysis showed that the contribution rate is 79%. While in the soil particle size composition, the percentage of clay particles has the greatest influence on acidification; 3) Passivation material selection should follow the "compensation mechanism", namely in the choice of passive components according to the physicochemical properties of soil factor, at the same time avoid adding factor which is sufficient. The quantitative analysis results provide a theoretical basis for further study on the acidification of passivated soil.关键词：passivated soil acidification;exchangeable acid;multivariate statistical analysis;principal component analysis;regression equation
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发布时间：2024-01-10 - 摘要：The state of a complex stochastic system for verification is difficult to be observed at runtime, since the cost of reliably sensing the operating state of the system is very high and the monitoring of some events can seriously affect time-related behaviors of the system. In order to perform runtime verification on such a system, a method for verifying runtime safety of a stochastic system with unobservable state was proposed. First, a runtime safety verification framework of stochastic system was constructed, in which the system model was represented by the hidden Markov model (HMM), and the negation of safety property was specified by deterministic finite automaton (DFA). Then, the product automata of DFA and HMM was used as a property verifier. Second, a construction algorithm of the verifier was proposed, which reduces the size of the verifier by eliminating the unreachable state starting from the initial state and the combined state independent of the verification property. Finally, an incremental iterative safety verification algorithm based on the verifier was proposed. Once a new observation value was received, the monitoring conclusions of the observed whole finite sequence without saving the sequence were immediately calculated. Experimental simulation results showed that the proposed method can effectively online verify the safety of stochastic systems with unobservable states.关键词：stochastic system;safety;runtime verification;hidden Markov mode
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发布时间：2024-01-10 -
Image Deblurring Method with Fractional-order Total Variation and Adaptive Regularization Parameters AI导读
摘要：In order to better recovery texture details of images, avoid the difficulty of selecting the regularization parameters when solving the image deblurring model, a novel non-blind image deblurring method by using fractional order TV (FOTV) and adaptive estimation of two regularization parameters was proposed in this paper. First, after analyzing the amplitude-frequency response of FOTV, different fractional orders of FOTV were set to the smooth (low-frequency) part and texture (high-frequency) part of the desired image, respectively, and a model of image non-blind reconstruction was modeled. Second, to effectively solve the reconstruction model and adaptively update two regularization parameters, the alternating direction multiplier method (ADMM) was used to separate the originally complex problem with two regularization parameters into two easy sub-problems. Each sub-problem has only one regularization parameter. Finally, according to the discrepancy principle, the two regularization parameters were adaptively updated and two sub-problems were solved. To test the effect of deblurring with four blurring kernels, the proposed algorithm has been applied to multiple images with smooth, edge and texture details. Compared with four traditional deblurring algorithms, the experimental results showed that the proposed algorithm can adaptively update two regularization parameters and has better deblurring performance for images with moderate texture details.关键词：non-blind image deblurring;fractional-order total variation model;adaptive regularization parameter update;texture details- 2834
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发布时间：2024-01-10 - 摘要：In the previous research on performance analysis of heterogeneous network, the distributions of base stations (BSs) and users are usually modeled as the horizontal distributions, which are not suitable for hyper-density network surrounded by dense buildings. Meanwhile, the physical layer security of the heterogeneous network is directly affected by the eavesdroppers on the vertical dimension. To address this problem, the vertical dimension of the base station antenna was adjusted, the signal-to-interference-plus-noise ratio (SINR) and the cumulative distribution function (CDF) of legitimate users and eavesdroppers was obtained by using the tilt angle, the spatial distribution of base stations and users, and the physical layer security performance of heterogeneous network was analyzed. An adjustment in three-dimensional heterogeneous network was proposed that the vertical dimension of the base station full dimension antenna is controlled.The SINR of the legitimate users and the eavesdroppers with the tilt angle of the BS antenna available were formulated, and the cumulative distribution functions of SINR were deduced according to spatial random Poisson point process distribution of the BSs and the users. Finally, the closed expressions of average secret rates of the heterogeneous network were obtained. The simulation results validated the correctness of the closed expression among the density of the small cells, the down tilt angles and the average security rates. The feasibility of the physical layer security can be improved by adjusting the vertical tilt angle. Meanwhile the reasonability of the distribution of small cells was validated.关键词：physical layer security;antenna tilt angle;average security rate function;3D stochastic geometry
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发布时间：2024-01-10 - 摘要：In order to overcome the drawbacks of basic krill herd algorithms, such as low convergence rate and poor convergence ability, a novel co-evolutionary gravitational krill herd algorithm was proposed in consider of cooperative evolution and gravitational search algorithms. First, the whole population was divided into two cooperative competitive populations to promote the population competition, and then the population was divided into three parts including employed krill herd, onlookers and scout krill herd. The population evolved according to three phases in order to enhance the population local exploitation ability. Second, the affinity for foraging motion was viewed as the gravitation inspired by gravitational search algorithm, which can make sure the direction of the search. In the last, in order to evade evolution stagnation and trap into local optimum, the physical diffusion was modified as the huddling behavior and following behavior to promote the population diversity. The trait of convergence and drift were analyzed, and the evolution performance was also analyzed in the paper. Simulation results of same and different kinds of algorithms demonstrated that the algorithm performs better than other algorithms.关键词：krill herd algorithm;co-evolutionary;gravitational search algorithm;evolution motion
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发布时间：2024-01-10 - 摘要：In order to solve the difficult problems of caused by mutual occlusion of face and face orientation, a PNMS algorithm based on penalty factors was proposed to improve the accuracy of face detection and alignment. Firstly, according to the overlap degree between face candidate windows and the corresponding detection scores of candidate windows, a non-continuous linear function and a continuous function based on Gaussian distribution were proposed and used as penalty factors for non-maximum suppression. Then the traditional non-maximum suppression algorithm was improved and replaced, and the detection score of the candidate window was redistributed. On this basis, combining the characteristics of the first two kinds of penalty factors, the continuous nonlinear function was further proposed as the penalty factor of the non-maximum suppression algorithm. Consequently, the greater the overlap value between windows, the more severe the penalty is, and the function is continuous throughout the overlapping value range. The proposed algorithm performed detailed face detection experiment verification on two face detection data sets of FDDB and WIDER FACE. The face alignment experiments were verified on the AFLW data set. The results showed that the proposed PNMS algorithms compared with other algorithms not only effectively improves the accuracy and reliability of face detection and alignment, but also solves a certain degree of face occlusion, and reduces the rate of detection failure of occluded faces.关键词：face detection;face alignment;convolutional neural network;non-maximum suppression
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发布时间：2024-01-10 - 摘要：In order to obtain a high gain, a Huygens’ metasurface was proposed as the phase shift surface (PSS) for the resonant cavity antenna (RCA) to uniformize the field phase distribution over the RCA’s aperture. The metasurface consists of two sets of split ring resonators (SRRs), which are parallel and perpendicular to the incident electromagnetic wave, respectively. The SRRs resonate with the magnetic and electric field of the incident wave, and thus the metasurface is able to manipulate the reflection and transmission of the incident wave. By configuring the dimensions of the SRRs independently, the magnetic and electric resonances can be adjusted respectively, and thereby a fast design of the PSS is achieved. To verify the proposed method, a PSS sample with an operating frequency of 5.8 GHz was designed and applied to a cylindrical RCA with a diameter of 180 mm. The RCA with the PSS was fabricated and the measurement agrees will with the simulation. The simulated and measured results demonstrated that the PSS had a phase shift range of 360° with a minimum transmission magnitude of 0.99 and the RCA with the PSS obtained a more uniform field phase distribution over the antenna’s aperture. The RCA’s gain was enhanced from 14.90 dB to 18.31 dB, and the aperture efficiency was enhanced from 25.9% to 56.7%.关键词：antennas;phase shift;metamaterials
- 2020
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发布时间：2024-01-10 - 摘要：In order to solve the problem that the soil model cannot be established accurately in the study of DC-bias, a soil equivalent resistance model based on N–1 principle was proposed, which combines the multiplemeasured data and simulation calculation of the power gridto calculate DC current distribution data in AC system. With known AC grid parameters, the multi-group distribution data of DC-bias current in AC power grid were obtained when the transmission line between two substations was put out of service in turn. The accurate equivalent resistance of soil model could be deduced by using matrix operation or genetic algorithm. A simulation example of soil equivalent resistance model was established for AC power grid near a grounding electrode, and the distribution of DC-bias current in the AC power grid was calculated while the HVDC transmission system operates under monopole ground return mode. The results indicated that the calculation data obtained from the soil equivalent resistance model are more close to the measured data. This model is less affected by the topology of the AC system and can keep the calculation error within the allowable range when the soil composition is complex. It is thus clear that the correctness of the modeling method is proved by the example. The modeling method of soil equivalent resistance based onN–1 changing principle of the power grid, avoids complicated calculation of electric field and does not need to get soil parameters. It has certain practical value in engineering projects.关键词：high voltage direct current;direct current bias;grid N–1 changing principle;soil mode
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发布时间：2024-01-10 - 摘要：The DZ125 alloy has excellent mechanical, fatigue, and high-temperature behaviors. It has been widely used in high-temperature gas turbine components. Although a lot of researches have been carried out on the fatigue problem of the DZ125 alloy, there are still few systematical studies on the fatigue crack initiation mechanism and its failure mechanism during very high cycle fatigue (VHCF) by microscopic fracture analysis. It is found that the scatter of fatigue data increases as fatigue stress decreases, and the fatigue life does not increase significantly even at a low fatigue stress (<220 MPa). The above characteristics are directly related to the change of micro-crack initiation mechanism. Under a high fatigue stress, micro-crack tends to initiate from surface or sub-surface of specimen, and the large secondary crack is the main feature of its fracture morphology. At a low fatigue stress, micro-crack is likely to initiate from interior material defects, and the existence of these defects can seriously affect the fatigue life. Persistent slip bands (PSB) lead to the formation of rough surfaces, which is the main feature at the crack tip. The main crack competes with other secondary cracks and eventually causes fatigue fractures. The results of the Murakami equation show that the average stress intensity factor at micro-crack initiation stage is 3.15 MPa·m1/2, the average stress intensity factor at the onset of unstable crack propagation is 7.7 MPa·m1/2, and the average fracture toughness (KIC) is 15.70 MPa·m1/2.关键词：DZ125 Ni-based alloy;very high cycle fatigue (VHCF);crack initiation mechanism;fractographic analysis;persistent slip bands (PSB);stress intensity factor
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发布时间：2024-01-10
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