Abstract:To clarify the wind-induced dynamic disaster mechanism of membrane structure, this paper analyzed the research progress of field test, aero-elastic model wind tunnel test and numerical simulation method of Fluid-Structure Interaction (FSI) problems, and discussed the latest research results on the additional aerodynamic force and aero-elastic instability mechanism of membrane structure. It was shown that by the limitation of field test equipment, similar theory of aero-elastic model and FSI simulation method, the research on the observation and simulation of practical membrane structure was still relatively few. As for the aero-elastic instability mechanism of membrane structure, it was believed that the aero-elastic instability of membrane structures was related to the vortices formed near the membrane surface, which was manifested as a significant attenuation of the total damping of the structure. However, the research results were based on the vibration phenomena observation of the simple membrane structure in the approximate uniform flow field, which was quite different from the actual project. The following aspects are suggested for researches: similarity analysis method and error correction technique of similarity theory of aero-elastic model wind tunnel test; key technology of numerical simulation of FSI problem of large-scale membrane structure; research on the aero-elastic instability mechanism of membrane structure that based on various research means including field test, aero-elastic model wind tunnel test, numerical simulation method, analytical theory, and so on; the wind-resistant design method of membrane structure, which is acceptable for designers to consider the FSI effect.

Abstract:Optimizing arrangement of prestressing tendons is a crucial aspect for calculation and design of frames with interior large-span neighboring two exterior small-spans. To maximize the capacity of critical section, prestressing tendons required in interior large-span are often arranged as continuous curve and extended as horizontal straight line to the side columns in two neighboring small-spans. This arrangement generates only upward prestress equivalent load in interior large-span, which could balance the vertical load in interior large-span effectively. While both of interior large-span and two neighboring exterior small-spans were concerned together as a single flexural member, and prestressing tendons were arranged as continuous curves, thus the equivalent load due to tensioning tendons would effectively balance the vertical loads both in interior large-span and two exterior small-spans. This arrangement can optimally realize the concept of load balancing. For a typical project, the differences in distribution and amplitudes of combination moment, major moment and second moment between two types of prestressing tendon profiles under the same conditions were analyzed. The influences on flexural capacity of normal section of two profiles were compared, and the rationality of continuous multi-curvature parabola profile in frames with interior large-span and neighboring exterior small-spans was validated.

Abstract:A novel set of prestressing system for U-straps of FRP was developed for shear strengthening of RC beam to restrain debonding failure, realize active reinforcement and achieve efficient utilization of FRP.It included self-locking anchorage, angle steel and device for connecting and tensioning. The single point loading tests of 5 RC beams with full-sized rectangular section were carried out, among which one remained unstrengthened, and the other four were strengthened in shear using unbonded prestressed U-straps of CFRP.The feasibility of the technique was verified and the influence of prestress on the behavior of RC beams shear-strengthened with unbounded prestressed CFRP U-straps was discussed.The experiments show that the system can provide reliable prestress for U-straps of FRP and transform the conventional debonding failure of FRP to the tensile failure.Prestressing can obviously inhibit the occurrence and development of main diagonal crack and the stiffness degradation after cracking. The level of prestress has a significant influence on the inclination angle of the main diagonal crack and the number of U-straps of FRP directly involved in shear resistance, but it has a little effect on the effective strain of these fibers.But the shear-strengthening effect cannot keep becoming better with the increase of the prestress.In this experiment, the maximum shear capacity of the strengthened beams is reached with a prestrain of 0.001.Based on the test data, a new expression was proposed for shear capacity of the strengthened beams using unbounded prestressed U-straps of CFRP, in which the influence of the vertical average prestress on the inclination of the main diagonal crack was considered.The predicted capacities are in accordance with the test results.

Abstract:Promoting the application of high performance material in modern bridge structures in order to meet the rapid development of high-speed railway technology, 10 pre-stressed reactive powder concrete (RPC)-normal concrete (NC) composite beams and 1 pre-stressed pure NC beam were designed and fabricated to investigate the flexural ductility of composite beams with the high performance material RPC, which was evaluated by the displacement ductility ratio at mid-span of composite beam. In this paper the effect of the height of RPC, the pre-stress ratio and degree of NC were mainly considered on the flexural ductility of composite beam. The results show that the sectional reinforced index decreases and the flexural displacement ductility ratio increases with the increasing height of RPC. Both the pre-stress ratio and flexural ductility increase with the increasing of steel strand number. The flexural ductility increases with the grade of upper NC as the brittle failure feature is not obvious. The deformation capacity of composite beam after the appearance of peak load increase, and the flexural ductility is significantly better than NC beam because of the excellent mechanical properties of RPC and the effect of steel fibers. It can be observed that the RPC has both high strength and good ductility. The fitting formula to calculate the flexural ductility of composite beams was proposed simultaneously based on the test results.

Abstract:The inclined reinforcements are configured in low-rise reinforced concrete shear wall with single row of steel bars and low reinforcement ratio, which can limit horizontal shear slip at the bottom construction joints and development of diagonal cracks on the wall. To investigate optimization design method of reinforcements for low-rise concrete shear wall with single row of steel bars and inclined reinforcements, the cyclic loading tests of 5 shear walls with different reinforcement design were carried out. The failure characteristic, hysteretic property, load-carrying and deformation capacity, stiffness degradation, energy dissipation and reinforcement strain were compared and analyzed. The results show that the seismic performance of shear wall with inclined reinforcements is better than the wall without inclined reinforcements, because the inclined reinforcements can control the shear deformation effectively. If inclined reinforcements are reasonably allocated, energy dissipation capacity of low-rise concrete shear wall can be significantly improved and higher performance price ratio of structural wall can be obtained.

Abstract:To evaluate the seismic behavior of semi-assembled shear wall with single row of steel bars and the application effect of recycled concrete in the precast shear walls, four I-shaped semi-assembled concrete shear wall specimens with single row of steel bars were designed. This type of specimen consisted of an upper precast concrete shear wall with reserved holes at the bottom, a foundation beam with single row of button-head steel bars, slurry layer between the precast shear wall and the foundation beam, and cast-in-place concealed columns between longitudinal and transversal walls. Button-head steel bars extending from the surface of the foundation beam were anchored in the reserved holes of the precast shear wall, with high strength grouting material filling the holes. Specimens were tested under cyclic reversed loading and different axial compression. Failure character, bearing capacity, stiffness, energy dissipation were compared, and the results show that: under the horizontal load, horizontal crack and a small slip appear in the joint connection between the precast shear wall and the foundation beam, X-shaped cracks distribute in the precast wall; with the increase of axial compression ratio, the bearing capacity of specimens is improved, but the ductility is reduced; the failure mode and mechanical properties of recycled concrete specimens are similar to those of normal concrete specimens; the semi-assembled shear wall structure with single row of steel bars has the advantages of simple structure, convenient construction and good seismic performance, and it can be used in low-rise and multistory residential structures.

Abstract:To analyze the nonlinear mechanical behavior of concrete U-shaped thin-walled beams under pure torsion, a nonlinear analysis model was suggested based on Vlasov's elastic theory for open thin-walled beams, space truss model and numerical method of differential equation. Aiming at the character that Saint Venant torsion and warping torsion coexist in open thin-walled members, the nonlinear analysis models of the Saint Venant torsion stiffness and warping torsion stiffness of U-shaped cross-section were respectively derived, and nonlinear analysis model of open thin-walled members in pure torsion was derived. The nonlinear material constitutive laws of concrete and steel bars, the geometric nonlinearity of open thin-walled members, and the coupling effect of Saint Venant torsion and warping torsion were considered in the derived nonlinear analysis model. The corresponding analysis program was developed by using the derived nonlinear analysis mode under pure torsion. And 5 existing RC U-shaped thin-walled experimental members under pure torsion were analyzed with the derived nonlinear analysis model. Nonlinear analysis results correspond well with the experimental data. Analysis results confirm that the nonlinear analysis model derived here is correct. The derived nonlinear analysis model is simple and precise, the torsion nonlinear responses of concrete U-shaped thin-walled beam can be analyzed by the derived nonlinear analysis model, and it will provide a technical reference for the engineering design of such concrete members.

Abstract:Subjected to extreme load actions, local damages will be initiated. Since the initial local damages can be transferred between different elements, global progressive collapse may be occurred and leads to large economic loss and human casualty. To assess structural resistance of progress collapse, the alternate path method, which includes nonlinear static analysis technique and nonlinear dynamic analysis technique, is commonly used to analyze the global resistance of the damaged structure with one element removed. This paper aims to investigate the main influence factors on the nonlinear dynamic analysis technique used in the alternate path method. A reinforced concrete frame structure that was designed according to the current Chinese codes was selected as the study case. The effects due to different failure time of a frame column, different gravity load distributions, and different applying ways of dynamic loads on the structural dynamic responses caused by a sudden removal of column were examined. The results show that the variation of column failure time has a significant effect on structural nonlinear dynamic response. When the column failure time reaches 0.5 times of structural natural period, the corresponding dynamic effects on structural nonlinear responses almost disappear. Different gravity load distributions (i.e., full bay distribution and damage-bay distribution) do not affect structural nonlinear dynamic responses obviously. Applying dynamic load after column removal consequently amplifies the nonlinear dynamic response of the structure, while the scale of amplification is limited.

Abstract:To analyze the nonlinear hysteretic behaviors of RC frame structures under reversed cyclic loading, a new element of reinforced concrete beam-column joints, super DOF element, was presented. The element edges were divided into "joint plane" and "beam-column plane" at the joint-column interface and joint-beam interface. The inelastic mechanism of joint core was represented by the four-node plane stress element. The anchorage failures of beam and column longitudinal reinforcement embedded in the joint were determined by eight springs between "joint plane" and "beam-column plane". The proposed element has four exterior nodes and four interior nodes. There are two degrees of freedom on each interior node. There are three degrees of freedom on each exterior node, coinciding with ones of typical beam element, so the element is suitable for use together with typical hysteretic beam-column line elements in two-dimensional nonlinear analysis of reinforced concrete structures. The element is implemented as a four-node twenty-degree-of-freedom element through moving the degrees of freedom on the interior nodes to ones on the exterior nodes. The simulated data were compared with tests, and the results indicate that the ultimate strengths and hysteretic pitching behaviors analyzed by the element are well agreement with the test ones and the computer time is short. It concludes that the proposed element is suitable for use in simulating response of building joints under cyclic loading.

Abstract:Taking an 80-meter-span singer-layer reticulated dome which has been constructed in the Shenbei New District as an example, the natural frequency characteristics and dynamic response of the singer-layer reticulated dome under different peak seismic loads were analyzed with the FE software ANSYS. Based on the data of the numerical analysis and the test of the joints, the bending performance of bolt-ball joints were obtained and introduced into the seismic response analysis considering the joint stiffness. Different structural models were established to investigate the effect of the structure model changes, including strengthening the local members and joints and installing maintenance materials on the surface of the structure. The results show that the constructed 80-meter-span singer-layer reticulated dome has a good seismic performance, but the local hole on the structure is the obvious weak area. It is suggested that the welded ball joints should be used around the hole, and the members around the hole should be strengthened. The seismic performance of the structure will be reduced by installing maintenance materials on the surface, and the maximum displacement of the reticulated dome increases by 140.1%, and the maximum internal force increases by 77.8% under the rare earthquake action. A divergence trend of the curve can be found in the time-displacement curve of the structure, showing the possibility of a whole collapse of the structure.

Abstract:To investigate the overall structural stability of the steel heavy truss and obtain stability coefficient under vertical loadings, the finite element models were established using ABAQUS program. The nonlinear analysis was carried out by introducing the initial geometric imperfection of the steel truss obtained through the linear elastic buckling analysis. The effect of the out-plane slenderness ratio of top chord on the stability of the steel truss was discussed to form the stability coefficient formula. Results show that the stability coefficient increases faster with the decreasing of the out-plane slenderness ratio of top chord, and buckling failure transits to strength failure when the out-plane slenderness ratio reduces to a specific value. Furthermore, the influence of steel strength, unequal sections of top and bottom chords, loading positions and depth-span ratios were studied, and the revised stability coefficient formula was suggested by a selected enveloping curve.

Abstract:To study the plate-assembly effects on the local buckling loads and ultimate strength of cold-formed thin-walled C-sections, the cross-sectional deformation of each plate of the C-section with respect to local buckling was analyzed and an analytical web local buckling model was proposed considering the plate-assembly effects. Based on the energy method and equilibrium conditions, an analytical formula for thin-walled compressed C-sections was derived. The derived formula was verified by the finite strip method and the Chinese code GB 50018—2002, respectively. The ultimate strengths of 21 cold-formed C-section columns under compression were calculated by adopting the analytical formulae in the direct strength method and compared with the test results and the results calculated by the Chinese code GB 50018—2002, respectively. The results show that the derived formula is reasonable and reliable for the local buckling loads, whereas the Chinese code brings out systematic errors, namely conservative results for the depth of web to width of flange ratio less than 4.5 and unsafe results for the depth of web to width of flange ratio more than 4.5. As for the ultimate strength, the results from the proposed method agrees well with the test results, which indicate that the proposed method is reasonable and reliable. In contrast, the Chinese code are conservative with respect to the tests results and the difference between the Chinese code and the test result increases as the depth of web to width of flange ratio increasing.

Abstract:Long-term strength is one of important properties to predict the long-term stability for rock engineering. New methods for determining the long-term strength that could be called limit strain method and inflection point method were proposed based on the isostrain-rate creep curve. To verify these methods, the traditional tests and muti-stage creep tests were carried out to analyze the creep behavior of greenschist in Jinping Ⅱ hydropower station. On the basis of the tests and proposed methods, the long-term strength under different confining pressure were obtained. Combining with the creep curves, the value of limit strain and stability time of deformation were also obtained in the solving process of long-term strength. The research results show that: the long-term strength can be determined by these two methods and the results meet the empirical value. The ratio of long-term strength and instantaneous strength were 66.9% (uniaxial), 68.0% (confining pressure 10 MPa), 79.6% (confining pressure 40 MPa). Therefore, the two proposed methods are reasonable and the ratio of long-term strength and instantaneous strength increases with the increasing of the confining pressure, and the confining pressure is one of the important aspects that influence the long-term strength.

Abstract:Content of sulfate ions is relatively high in saline soil that can deteriorate the bearing capacities of bored pile and related studies are rarely reported. To clarify the evolution rules of bored piles' vertical bearing strength and the effects of pile length and pile radius on bearing strength after sulfate attack, bearing capacity evaluation model of bored pile was established based on the sulfate corrosive reactions and mechanism in sulfate corrosive condition. By combination with cases, the evolution rules of side resistance, end resistance and pile compressive strength were studied. The influences of pile diameter and pile length on bearing properties were analyzed and compared. The results show that the side resistance, the end resistance and the pile compressive strength change after sulfate corrosion. The side resistance of pile depends on stress redistribution and concrete deterioration around pile caused by sulfate corrosion products, and is also affected by the length and diameter of pile. The end resistance reduces with increasing depth of sulfate corrosion because the effective area decreases after corrosion. The compressive strength of pile decreases rapidly during sulfate corrosion process. It concludes that increase of pile diameter can enhance the resistance ability against deterioration, and the pile diameter increase can enhance the anti-sulfate corrosion ability for pile foundation design in saline area.

Abstract:To study the mechanical responses induced by undrained expansion of a cavity in natural clay soils, considering the K₀-consolidated property and the stress history of the natural saturated clay, as well as the relationship among the radial, tangential, and vertical stresses, an elasto-plastic analytical solution to the undrained cylindrical cavity expansion in K₀-consolidated saturated natural clay, which was under the initial stress anisotropic condition, was derived based on the modified Cam-clay (MCC) model, large-deformation theory and the elastic-plastic boundary conditions. The solution presented in this paper was verified by the well-documented numerical solution and compared with the previous initial stress isotropy assumption based solution. The effect of the K₀-consolidated property and stress history on the stress fields and the plastic radius during the cavity expansion process was discussed in detail. The results show that the present closed-form elasto-plastic solution matches the numerical solution fairly well, and the present solution can be reduced to the initial stress isotropy assumption based solution. The K₀-consolidated property has a significant effect on the stress fields around the cavity during the cavity expansion process, especially on the limit cavity expansion pressure. The effect of the initial stress anisotropy on cavity expansion increases with the degree of the initial stress anisotropy. This paper provides a theoretical benchmark for pile installation and pressuremeter test in natural clay soils.

Abstract:Comparing with intact rock, the mechanical characteristics of non-persistent closed jointed rock mass have relatively large differences. A revised self-consistent method was used to consider the coupling between different damages, as a result, the compound constitutive model was deduced for non-persistent closed jointed rock mass under uniaxial compression. Based on the correlation between additional strain energy increment and damage strain energy release, the equivalent linear crack as jointed crack damage evolution trajectories was adopted, and then the additional strain energy for micromechanical damage, initial joints and jointed crack damage evolution was respectively calculated. In accordance to the Betti energy reciprocity theorem, a self-consistent method was introduced to account for the correlation among cracks, moreover, an approach for adding joints one by one was utilized to correct the traditional self-consistent method, in which the compound damage constitutive model was deduced in regard to different stages during uniaxial compression. The theoretical calculation results of the proposed model were compared with in-house experimental results in existing literature. The results show that: the theoretical calculation results are consistent with the experimental results. With the increase the number of joints, the initial elastic modulus and peak load show a downward trend, and the reducing value is in the same extent; there are significant impacts for the damage evolution of joints crack damage on the mechanical characteristics of the rock mass. The theoretical stress-strain curve and peak load for joint fissure damage evolution are consistent with in-house experimental results, which apparently verify the correctness and reasonability of the compound damage constitutive model.

Abstract:As a light steel structure, the horizontal lateral resistance is an important parameter for the aseismic design of container house, while there is no reliable theoretical calculation formula. To provide reference for design and improve the theoretical system of corrugated skin structure, this paper deduced the calculation formula of lateral stiffness of container house. Different from the traditional skin structure using bolt connections, the side wall plate and steel frame of container house are connected by welding, the shear stress distribution and deformation composition in plane vary greatly, and the key point of solution is to analyze the diaphragm effect of corrugated plate under the welding boundary condition. Based on the energy theory and ABAQUS finite element simulation, the ideal lateral stiffness under uniformly horizontal distributed load and the local deformation under concentrated load at the top corner fitting were analyzed respectively. Then the calculation formula of lateral stiffness was derived, and it was verified by the experimental data. The results show that: under the concentrated load, the local deformation is much larger than the overall lateral displacement and the local effect ranges with the beam stiffness and the specifications of the container. In practical engineering, it is effective to increase the beam's effective sectional area or the amounts of connecting components for reducing the local deformation and improving the whole lateral stiffness.

Abstract:Due to the need of the function as a construction, container houses are usually required opening treatments in practical engineering, which will influence the whole lateral stiffness significantly. To get the lateral stiffness theoretical calculation formula of container house with openings, this paper studied the reduction factor from the influence of openings on the corrugated skin structure welded on four sides. Based on the diaphragm theory of Europe, the forms of openings were limited and the corresponding calculation formula of the reduction factor was deduced. Then the finite element model built with ABAQUS was adopted to verify the theory, and for the three limitations which were most easily to be exceeded (the height\\shape of window and the position of door) were analyzed. Through the existing experimental data, the proposed finite element model was verified. The results indicate that the window type openings cause the obvious stress concentration at the place close to openings, so corresponding deformation increases and overall lateral stiffness is reduced, while the reinforcement of openings can effectively reduce this tendency. In practical engineering, a circular window should be considered firstly instead of rectangle one, the smooth and symmetrical shape of which can weaken the stress concentration compared with the rectangle shape under the premise of the same area. Door shaped opening is sensitive to the position, and it should be center layout to reduce obvious local effect.

Abstract:To establish standard system of fabricated container structure and obtain its mechanical characteristics, static mechanical analysis and seismic analysis were made on six sets of structures according to existing codes based on a typical plan of container building. The influence on structural performance by adding beams and columns or tension cables was also studied. The results indicate that: container building system is sensitive to wind load, which controls the section of members and seismic action is not a dominant factor; the effort to enhance lateral stiffness of container building by adding local columns and beams is not useful, while adding lateral tension rod can strengthen the structural lateral stiffness effectively. Finally, a connected joint used in container building was analyzed by multi-scale analysis. The results indicate that this joint can work well under every working condition and provide a technical reference of joint selection in similar container buildings.

Abstract:To investigate the overall stability of stainless steel axial compression member with welded box-section, the nonlinear finite element simulation of the stainless steel axial compression members was conducted by ANSYS. By comparing the simulation results with the experimental results, the accuracy of the finite element (FE) model was verified. The initial geometric imperfections, section residual stress, mechanical properties, section width-to-thickness ratio and slenderness ratio which affect the overall stability of the member ultimate bearing capacity were parametrically analyzed by the proposed FE model. The results show that the mechanical properties and slenderness ratio of member are key influential factors on the ultimate load. A new three-section formula for calculating the overall stability coefficient has been proposed by data fitting, which can accurately predict the overall stable bearing capacity of stainless steel axial compression members with welded box-section.

Abstract:To study the comfort of "Building-Bridge Integration" station hall structure under various dynamic loads and the applicability of the existing vibration norms, a large passenger railway station was tested under pedestrian load and transit train load, meanwhile field investigation were implemented to study crowd disturbance response under the vibration level. This paper established comfort quantitative indicators, which is suitable to evaluate the annoyance rate of "Building-Bridge Integration" structure, based on different load styles and structure spans, used the existed annoyance rate model considering the fuzziness and randomness. Results indicate that partial region vibration level is under perception value, practical annoyance rate is 2%; partial region vibration intensity exceeds 70 dB, theory annoyance rate is 50%, but practical annoyance rate is 2%, traditional comfort evaluation standard can't accurately evaluate this structure type. Annoyance rate model can quantify annoyance rate under any vibration intensity, the vibration limit is between 75-90 dB, the result based on measured data is consistent with ISO standard in vibration response description, which make up deficiency of present comfort standard about long span"Building-Bridge Integration".

Abstract:To deal with the problem of stress concentration and component failure at the right-angle area of I-shaped combined steel lead damper, an oval steel-lead damper (OSLD) composed of steel and lead was presented, which had advantage of simple manufacture process and good energy dissipation capacity in the two horizontal directions. Plane stress analysis of the steel plate of OSLD was performed. The mechanical property tests of OSLD were carried out, and the nonlinear analysis model was established by ANSYS, of which results were compared to the test results. The shaking table tests of a six-storey steel frame structure model with and without OSLDs were performed and compared. Research results show that the numerical simulation results are in agreement with the test results, which indicate that the method of establishing numerical model is correct. The OSLD has full hysteresis curves and good energy dissipation capacity, and the OSLD has well vibration control effect of seismic responses on multi-storey structure.

Abstract:To study the relationship between spectral energy and vortex motion or turbulence scale, wind pressure distribution characteristics of different rise-span ratio and low height of the saddle roof surface were investigated when the flow was perpendicular to the windward wall through the rigid model wind tunnel pressure tests. Then the study focused on the high point, middle point and low point wind measuring point column respectively, and their wind pressure spectra were discussed. Results show that the maximum wind suction is at the location of the low windward point, and the wind pressure gradient changes greatly. The saddle rise-span ratio is mainly embodied in the rear of two-thirds area of the roof of wind pressure, and the severer wind suction occurs with the greater the curvature. The greater the windward side height is with the higher the wind suction. The wind suction has maximum change near the low point of the windward. In high and middle windward point the wind pressure spectrum is the narrowband distribution and low frequency plays a leading role at the front windward, however, the high frequency band energy of back area is greater than that of the front area. The wind is characterized by wide distribution and the high frequency energy increases gradually as the development of flow downstream.

Abstract:To investigate the influence of turbulence characteristic, structure dimension and separation distance on spanwise correlation characteristics of fluctuating along-wind loads acting on the rectangular building, the surface pressure fluctuations on a rigid model with rectangular cross-section were measured synchronically in the simulated atmospheric boundary layers. The distribution characteristics of coherence function of fluctuating along wind loads and oncoming turbulence were also studied. The correlation of unsteady along-wind loads and wind fluctuations, and the fluctuating pressures acting on windward side and leeward side were compared through present experiments. A modified expression of a coherence function of fluctuating along-wind loads on rectangular high-rise building was proposed by considering various parameters, including windward width of structure, spatial spacing and incoming wind characteristics. The measured results show that the fluctuating along-wind loads are more correlated than the wind fluctuation. The correlation of fluctuating pressures on windward side is weaker than that of overall unsteady drag forces in the case of model whose width exceeds the stream wise dimension. The weak correlation of fluctuating wind pressure on leeward side can't be ignored at a small separation distance. So the conventional coherence model of turbulence is unsafe for predicting the fluctuating along-wind loads of the high-rise buildings.

Abstract:To explore the vulnerability of different part of a reinforced concrete cooling tower in service, numerical simulation analysis was carried out. The software ABAQUS was selected to establish analysis model. According to the field conditions where the structure locates in, a range of reasonable ground motion records were selected and then incremental dynamic analysis was conducted. Material strain and peak ground acceleration were selected as engineering demand and intensity measure parameters, respectively. The structure was divided into 13 regions in the height direction, and the damage states of the structure were divided into five levels. Unidirectional, bidirectional horizontal and three-dimensional seismic action were respectively exerted to the bottom of the structure, the regression analysis on the structure response was performed. The probabilistic seismic demand model of the structure was established, and the partitioned vulnerability curves of different parts were obtained. The analysis results show that: the damage probability of the upper tower is relatively small and the herringbone pillars' damage probability is significantly higher than the other parts of the structure. The herringbone pillars at the bottom are the most injury-prone part, which can be reinforced according to the actual needs, and the seismic performance of the upper tower is excellent.

Abstract:To analyze the reliability of the multi-circle ground motion attenuation model, of which the rationality has been demonstrated by the ground motion attenuation relation analysis of the Wenchuan earthquake, the measure of dividing fault and getting sub-source epicentral distance were studied based on NGA database. The multi-circle ground motion attenuation relationship of NGA database was fitted, and the types of fault, hanging/foot wall and coverage thickness on fitting ground motions were discussed respectively. The fitting results of multi-circle model have been compared with that of NGA model (BA08), and the difference between the two results was analyzed. The results show that the multi-circle model gives a good fitting result for spatial distribution of ground motion of NGA database. Due to the simple form and high precision, the multi-circle model with specific theoretical basis would have further development through this project.

Abstract:In most countries or regions of the world, observed strong ground motion data is not enough, which makes it difficult to develop empirical attenuation relations statistically. To overcome this bottleneck, this paper discussed the progresses to build seismology based regional ground motion attenuation relationship there, the importance of estimating the values of regional parameters, stress drop Δσ in source spectrum, Q₀ and η in quality factor, and two distances R₁ and R₂ in geometric attenuation term were emphasized, and the idea and approach to acquire these five values were presented by means of an joint inversion of small earthquake records (M_w=3.5-4.5, focal depth≤30 km) from regional digital monitoring network. Based on these parameters, regional attenuation relations were built and examined by the strong ground motion data (M_w≥4.5, focal depth≤30 km). The result matches the observed strong ground motion data well for the northeastern region of Japan and it is also good for earthquakes with magnitude 5 and 6 in Sichuan and Yunnan regions of China where there are not enough data for checking, but it is larger than the observed data for earthquakes with magnitude 7 and distance further than 100 km. The feasibility of the proposed method is shown through three cases.

Abstract:To determine the relationship between magnetic memory signal and tensile stress and the influence of geometric size of the specimen on the surface magnetic field, static tensile tests on plate specimens made of Q345 low alloy steel with different thicknesses were performed. The variation regularities of surface magnetic signals of specimens with three thicknesses under different tensile stresses were investigated using the magnetometer TSC-1M-4. The test results show that the magnetic memory signal is positively correlated with tensile stress in the elastic stage but weakly correlated in the plastic stage. Compared with the normal component, the tangential component is more sensitive in characterizing the local yielding of the specimen. The early plastic deformation and stress concentration zone can be predicted via the abnormal magnetic change of the tangential component. Under the same stress level, the specimen thickness has a negative correlation with the surface magnetic intensity and no influence on the variation trend.

Abstract:Based on the theories of bounding surface and multiple surface, a three-surface cyclic constitutive model, which is applicable for engineering because of the simple form and less parameters, was established to describe metal material behavior under the triaxial cyclic loadings. The plastic strain was decomposed into plastic strain 1 corresponding to a bounding surface model and plastic strain 2 corresponding to a single yield surface model. An evolution formula of the distance between the current stress and the image stress on the bounding surface was developed, which makes the plastic modulus calculation be coupled with the kinematic hardening rule through the consistency condition of the yield surface. As the hardening parameter, the plastic strain was calculated according to the associated flow rule. Compared with the classic bounding surface models, it has a concise form, and compared with the modified kinematic hardening rule models, it has less parameters. The existing experimental results about stable metal material U71Mn under uniaxial cyclic loading were adopted, and four mechanical behaviors were considered. The ratcheting were simulated by the model considering the effect of mean stress and stress amplitude under asymmetrical stress cycling, and the maximum strain amplitude memory effect was analyzed under symmetrical strain cycling. The calculated results agree well with the experimental results, which means the proposed model provides a new method to study the constitutive relation.