Abstract:

Abstract:Based on the damage assessment and strengthening scheme of the full-scale model which is the three-floor frame-supported reinforced concrete masonry short-leg shear wall structure, the strengthened model is tested using the substructure pseudo-dynamic testing method. The applicability of the proposed strengthening technique for the building damaged by earthquake is discussed. Thus, the seismic performance of the strengthened model is proposed to seek the strengthening technique for the structure damaged by earthquake, and it provides important reference for the post-disaster reconstruction after Wenchuan earthquake.

Abstract:Finite element software was used to simulate the internal force and deformation of high-rise pile cap-soil-structure under the wave and earthquake action. Meanwhile, wave force was calculated by using Morison equation, and the mechanical behavior of structure was simulated by inputing horizontal El-Centro wave. Then, the initial state and the state of the largest positive and negative acceleration were selected to study the structure according to the time history curve, and the displacement, bending moment, shear and axial force changes of pile foundation under wave and earthquake action were discussed, which was compared and analyzed with the structural response under the action of earthquakes solely. The result shows that the moment of front row of piles is biggest, and the force of pile bolck is the most dangerous; the axial force of the corner piles is the largest, and one of the center piles is the smallest under the action of wave and earthquake. When the wave forces and seismic forces are in the same direction, the displacement, moment, and shear force of pile bolck will be increased, on the contrary, the displacement, moment, and shear force of pile bolck will be decreased.

Abstract:In order to make fire resistance design of high strength steel columns in building structures, the numerical calculation method on load bearing capacity of high strength steel columns at elevated temperature was investigated. By taking the mechanical property of high strength steel at elevated temperature into consideration, extension was made on the inverse calculation segment length method and the program to compute the load bearing capacity of high strength steel columns at elevated temperature was performed. The program was adopted to compute the load bearing capacity. The results obtained by the program and the finite element analysis were compared and good agreement had been found. The influence of magnitude, distribution mode of residual stress and initial geometry imperfection on ultimate load bearing capacity was analyzed by employing the program. It is shown that the extended method can be is shown used to calculate the load bearing capacity of high strength steel columns at elevated temperature; the magnitude and distribution mode of residual stress had little influence but the geometry imperfection have significant influence on ultimate load bearing capacity.

Abstract:According to the theory of fracture mechanics, the mechanical model of rock-mass with multi-cracks under the action of seepage pressure was set up. Based on the principle of superposition, the formula for calculating stress intensity factor (SIF) was built. The stress intensity factor of cracks in different conditions, such as different crack distance, different crack angle and different seepage pressure, were discussed. It is suggested that, if distance between two cracks is short, the interaction of cracks has significant influence on stress field of crack tip. According to the change of relative crack location and crack angle, the different superposed stress can produce two effects, stress field strengthen and stress field weaken. The stress intensity factor would be increased when the crack tip is in the stress strengthen area; otherwise this value would be decreased. The interaction of adjacent cracks is related to the distance between two cracks. As the crack distance increases, the SIF is close to a fixed value which is calculated without considering the interaction between cracks. Therefore, when the crack spacing is larger than crack length, the interaction between adjacent cracks can be ignored. The results also show that the seepage pressure significantly affects the stress field near crack tip, and the stress intensity factor KI increases along with the increase of seepage pressure (-KI decreases).

Abstract:Based on the small deformation assumption, the equations of the laterally loaded piles influenced by the axial load were established. The effect of axial load on the lateral response of piles was studied with parameter analysis. The analysis shows that internal force and deformation of laterally loaded pile under axial loading is actually closely linked with the values of axial and lateral loads. In general, the high level axial load should be focused on. It is more significant that the effect of axial load on the internal force and lateral deflection of the upper part of flexible piles, while there is little effect on deep of long-thin pile foundation. The effect of axial load on the lateral response of pile is the largest as coefficient form of subgrade reaction increases linearly, while the effect is minimal as coefficient form of subgrade reaction is a constant. Except in case of buckling, the changes of axial load along the pile direction have little influence on the magnitudes of deflection and moment. The assumption that the axial load is constant with depth can meet the requirements of engineering.

Abstract:It is difficult to calculate the axial strain of saturated soft clay subjected to long term cyclic loading by using traditional explicit or implicit model. On the base of total stress model of consolidated-undrained shear model of saturated soft clay and considering the shakedown character of clay under small dynamic stress ratio, a shakedown model is set up to calculate the axial accumulative plastic strain. The proposed shakedown model can effectively descript the character of saturated clay displacement under cyclic loading. Because of using the equivalent method, the step of numerical integration can be chosen arbitrarily. The large numbers of calculation can be reduced, so calculation time will be saved considerably.

Abstract:The uniaxial load tests were conducted to investigate the material behavior of CFRP sheets. The results show that the probability distribution of CFRP tensile strength can be described by the three-parameter Weibull distribution. The design formulae for determining flexural capacity of reinforced concrete strengthened with CFRP sheet are proposed. The Monte Carlo procedure was applied to simulate the flexural capacity of reinforced concrete strengthened with CFRP sheet. By using the JC method, the reliability index was calculated based on the statistics of flexural capacity and load effect. After the analysis of the effect of the partial factor of CFRP sheet on the reliability index, the results reveal that the reliability index of all design points are the most close to target reliability index overall when the partial factor of CFRP sheet is 1.25，and in this condition the reliability index of three flexural failure modes achieve the target reliability index respectively. Therefore, the partial factor is suggested to be 1.25, which meets the requirement of reliability design.

Abstract:Pseudo-static tests of three one-storey spatial RC frame-shear wall structures with floor slabs were conducted to investigate their failure modes and hysteretic behaviors. The test results were compared with those of pushover analysis. It is shown that: 1) damage of the frame beams occurs later and is less than that of the shear wall and the frame columns; 2) damage of the floor slabs under lateral loading is significant in regions close to the shear wall, and tensile stresses of slabs' steel bars in these regions are much larger; 3) in comparison with the case that the floor slabs are neglected, the maximum lateral load that a frame-shear wall structure can bear is larger in the case that the floor slabs are taken into account, and the contribution ratio of the shear wall also increases; 4) shear forces carried by the frame columns with identical cross sections and reinforcement details but located at different positions are close to each other on the whole.

Abstract:Accurate assessment of seismic performance of reinforced concrete columns（RC columns）is significant to ensure the safety of reinforced concrete structure subjected to earthquake action. In order to derive a reasonable prediction by Pushover analysis, a calculation method for determining lateral load-deformation curve, unloading rigidity and reloading rigidity of RC columns subjected to combined flexural and shear force is proposed based on test data analysis in the PEER (Pacific Earthquake Engineering Research Center) Structural Performance Database, and the formula for calculating the equivalent damping ratio according to hysteresis loop area is also provided. In this paper, conventional section analysis techniques are employed for modeling the flexural behavior of lateral load-deformation relationship, and the modified formulas with actual data analysis are implemented for modeling the effect of shear and slip of the longitudinal bars at columns end. Unloading rigidity and reloading rigidity of the columns are determined by statistical analysis on relations between themselves and secant rigidity of the columns respectively. Finally, a single-degree of freedom (SDOF) system is taken as an example to illustrate the applications of the proposed model for developing the corresponding “capacity curve” and performing pushover analysis on columns. The influences of primary parameters, such as shear-span ratio, axial load ratio, reinforcement ratio and stirrup ratio, on seismic performance of columns are also analyzed.

Abstract:An improved computational method for buffeting forces of long span bridges, which substitutes the traditional wind tunnel test with the bridge segment model for CFD method, is proposed. In the case study of Tsing Ma Bridge, the pressure distribution induced by the wind field of the bridge decks was simulated. The nodal buffeting forces were computed and the local stress responses were obtained according to the CFD simulation and the refined finite element model. Preparation for buffeting induced fatigue analysis of bridges and structural health monitoring are provided.

Abstract:Two monolayer concrete frames with the same reinforcement, KJ1 and KJ2, were designed. KJ1 was designed to simulate low cyclic reversed loading test under weak earthquake. Besides, the fire response test, including temperature rising and lowing, was made by fixing the axial compression ratio of the column. For KJ2, the fire response test at the fixed axial compression ratio was made. The deformation response of the concrete frames in fire was studied. Comparative analysis of the apparent phenomenon, temperature curves, bearing capacity change of the frames were made based on the test results of KJ1 and KJ2. According to the simplified temperature distribution, the ultimate bearing capacity of the column under the high temperature was preliminarily determined. It is illustrated that the calculation results and finally test phenomenon are consistent according to the simplified section.

Abstract:By the hysteretic experiments and the finite element analysis of the proof-of-concept connections, the mechanical properties and energy dissipation capacity of the new steel beam-to-column connections are investigated. These connections are semi-rigid ones improved by adding threaded rods into the angle connections and can be designed to limit the structural damage only to the angles and threaded rods. It is found, by the comparative analysis of six connections tested with the same loading sequence, that the performance degradation of the connections may be resulted from the plastic damage, crack propagation of the angles and the buckling and fatigue crack of the rods. The rotation capacity and failure modes of the connections with threaded rods depend on the ability of anti-fatigue crack of the rods, and the better ductility the rods have, the better energy dissipation capacity the connections have. In addition, the hysteretic behavior and the deformation modes of the connections prior to the significant strength degradation or the fracture of the rods could be well simulated by the finite element method. Meanwhile, the stiffening effect from pre-stressing the angles, the plastic distribution of the angles and the degradation induced by the rod buckling were strongly verified by the FEA. Finally, the advantages and disadvantages of such new beam-to-column dissipative connections were analyzed, and the proposal for further connection improvement and in-depth study was made.

Abstract:In order to study the stress distribution effect of the webs which is under the action of vertical prestress, pairs of forces were acted on a long and narrow rectangular thin plate, and the webs stress field under the effect of vertical prestressing was simulated, with analytical solution of vertical normal stress derived and the numerical solution obtained by the Least-square method. The parameters,λ and κ, were introduced and calculated to describe vertical stress uniformity and stress level, which shows that λand κ value are more sensitive to webs vertical reinforcement spacing. On the premise of uniformity of vertical prestress and stress level, the fitting diffusion angle of vertical prestress acting on the webs is obtained and fitted by polynomial. Vertical prestress diffusion effect of the webs was tested in bridge site and analyzed by the finite element software. The results show that the webs stress diffusion is obvious, and the stress has a good uniformity at the section of H/2 but a bad uniformity at axillary and shore up.

Abstract:Base on the existing step-by-step structural damage diagnosis method, a three-step structural damage diagnosis method is developed. According to the analysis of the characteristic of genetic algorithm, a new idea of excluding the undamaged element by means of step-by-step evaluation is developed to deal with the damage diagnosis problem. In this method, sensitivity genetic algorithm is used to exclude the undamaged element step by step and residual force method is used to fix the damage district. According to the simulation research of a 2D framed structure, it is shown that the step-by-step structural damage diagnosis method can gain the ideal results when it's difficult for a single damage diagnosis method to get the good results. It is also indicated that sensitivity genetic algorithm is a good way to exclude the undamaged element step by step.

Abstract:Considering the impact of post-earthquake fire on building structures in structure design, an analysis method is proposed to analyze and simulate the response of building structures under post-earthquake fire. Based on the seismic response and thermal stress analysis, this method considers the structure seismic damage through a simplified seismic damage model, and the simulation of the response of building structures under post-earthquake fire was reached by linking the heat transfer analysis and thermal stress analysis to the results of seismic damage. A single-storey concrete frame and a multi-story concrete frame were analyzed with this method and compared with experimental results of the same concrete frame under fire without seismic damage. It is shown that the collapse mode may change for seismic damaged structures and the fire resistance decreases with the increasing of seismic damage degree.

Abstract:In order to study the particle size distribution of fine grained soil, the Malvern Mastersizer 2000 laser diffraction grain size analyzer and traditional densimeter method were used to test the clay in Hefei. According to the work principle and affecting factors of laser method, the parameters, such as the refractive index, concentration, ultrasonic displacement and time, pumping speed of the apparatus, were altered in turn. Then the influence of these control parameters on the particle size was investigated, and the best parameters for the clay in Hefei were identified. The grain size distributions measured by laser method under the best condition and traditional densimeter method were compared, which shows that laser method has a wider measuring range, higher accuracy and better repetitiveness in measuring the particle size distribution of fine grained soil.

Abstract:Based on the advanced technique of self-balancing test, the bearing characteristics of large-diameter deep rock-socketed pile（hr/d>30）, including the relation of load and displacement on top of it, side friction, the tip resistance and so on, under 10 thousand-ton load level in argillaceous area had been analyzed according to the report of static loading test on 2-piles of Balinghe River Bridge and 1-pile of Beipan River Bridge. The results indicate that Q-s curve of large diameter pile in mudstone declines slowly, and the weathering level of rock has great impact on tip resistance of pile. The ultimate bearing capacities of sandstone and dolomite in puny weathering are stronger than that of limestone in weak weathering; the side friction of pile is closely related to relative displacement of pile-soil interface, and the side resistance of pile in argillaceous dolomite needs smaller pile-soil relative displacement. Finally, the ultimate values of lateral resistance of pile and estimate of exploration report have been comparative analyzed.

Abstract:In order to analyze the large amplitude vibration mechanism of cables based on Reynolds number effect, wind forces measurement and free vibration tests were carried out on cable models with/without artificial water rivulet. In the tests, the cable models without artificial water rivulet were in different surface roughness and those with artificial water rivulet attached were in smooth surface, and artificial water rivulet was attached in different positions respectively. Wind force coefficients, Den Hartog galloping coefficients and free vibration amplitudes were obtained. It is shown that in critical Reynolds number range, there is the possibility that the special wind force coefficient characteristics and flow pattern induce vibration, and this is the possible mechanism for dry cable galloping. The roughness of cable surface can change the intensity of critical Reynolds number effect and the range of critical Reynolds number. The existence of water rivulet can change the critical Reynolds number effect. For some water rivulet positions, in certain Reynolds number range, dCF/dα＜0, vibration happens, which agrees with the Den Hartog galloping criterion. In high Reynolds number range, besides Den Hartog galloping, vibrations are relevant to significant decrease of wind force coefficients and unstable flow pattern.

Abstract:Static experiment was carried out to study rotation behavior of timber beam-column connection. The influence of length of Gongmu and position of dowel on the initial rotational stiffness of the joint was analyzed. Rules of stiffness degradation under cyclic loading were studied as well. The results show that: the moment-rotation curve of typical timber beam-column connection can be simplified as bilinear model; the initial rotational stiffness of the joint is enhanced with the increase of the length of Gongmu, and it is decreased with the inward movement of dowel; under the same conditions, the influence of the inward movement of Gongmu-beam dowel on the initial rotational stiffness of the joint is smaller than that of Dianmu-Gongmu dowel; and stiffness degrades under cyclic loading and there exists obvious transition phenomenon.

Abstract:At present, there is a lack of study on the destruction mechanism and characteristic in the investigation after gas explosion accident. The destruction and treatment scheme of two accidents happened in Shanghai were introduced. According to the precast slab and poured slab that badly damaged in the two accidents, the anti-explosion ability of the slab was obtained through theoretical calculation and numerical simulation, and then explosion overpressure was estimated. The reason why the overpressure differs little but the destruction differs much in the two accidents and the destruction characteristic of the gas explosion to the building were all analyzed. It is considered that: 1) the anti-explosion ability of the poured slab is far superior to the one-way precast slab; 2) Room with the ignition source is impacted by the overpressure directly and the damage is most serious, while the destruction of the other rooms is caused by the vibration, and its influence is smaller as the house is far from the explosion.

Abstract:The in-situ measurement of heat-transfer coefficient of external wall is the major content of building energy efficient measurement. A new test method and error assessment function were put forward. Computer simulation was conducted to analysis the influence of hot-box size, air temperature in hot box, structure and thickness of external wall on the result error to provide the theoretical guidance for test apparatus development. The results show that, size of hot-box and thickness of external wall is the major factors which decide the error in test. In-situ measurements were conducted according to the computer simulation results and show fine accuracy.

Abstract:COD and UV254 of concentrate from reverse osmosis (RO) are removed significantly by powdered activated carbon (PAC) adsorption, which makes the effluent meet the related discharged standard or further reclamation demand. First, main adsorption factors and their levels were selected through orthogonal experiments. Then adsorption isotherms and adsorption kinetics equations about COD and UV254 were obtained by single factor experiments. Finally, adsorption model of COD and UV254 removal were established via response surface methodology (RSM) experiments, in which PAC dosage and adsorption time were acted as independent variables. COD and UV254 predictive removal of RSM model were 69.7% and 82.4% respectively, and the corresponding measured values were 65.3% and 81.8% when the PAC dosage was 0.9 g·L-1 and adsorption time was 50 min. It is shown RSM models can predict COD and UV254 removal very well in the design range, which provides a comprehensive and reliable data basis for engineering application.

Abstract:To shorten the start-up period of UASB process for the low temperature municipal wastewater treatment, two lab-scale UASB reactors were employed to study the feasibility of enhanced start-up with addition of waterworks wastewater to raw water. Also the operation and biomass characteristics were investigated with comparison of conventional start-up mode. The results show that, under the water temperature of 15℃ and the initial organic loading rate (OLR) of 0.25 kgCOD/(m3·d), the UASB system can get stable condition with both the OLR escalating and enhanced mode, and the start-up period is approximate 120 days and 95 days respectively. Throughout the experiment the enhanced start-up processes preferable adaptability, which shorten 30days to achieve the OLR of 4 kgCOD/(m3·d), and higher COD removal as well as biomass growth rate (0.029 g VSS/d versus 0.043 g VSS/d) correspondingly. Compared to conventional mode, the mean diameter of granular sludge is larger and 2 mm granular sludge can be formed within 95 days by enhanced mode. The experimental results demonstrate that adding waterworks wastewater can shorten the start-up time and enhance granulation, which in turn leads to improvement in organics removal efficiency and stability of the UASB system for low temperature municipal wastewater treatment.

Abstract:Two kinds of magnesium slag from different places were added in clinker respectively to manufacture portland cement, and the essential properties of cement, such as water requirement of normal consistency, setting time and strength, were studied. The influence of magnesium slag on the drying shrinkage of portland cement was investigated. Meanwhile, effects of magnesium slag in portland cement were analyzed on the basis of XRD, DSC/TG and SEM microscopic experiments. The results show: magnesium slag plays roles in water-reducing and set-retarding as a composite material of cement; when the contents of magnesium slag range from 10%～30% (weight ratio) and 35%～40% (weight ratio), cement samples reach Composite Portland Cement 42.5R and 32.5R standard, separately; the drying shrinkage of mortar can be restrained as the contents of magnesium slag range from 30%～40%; and the structure of cement pastes is more compacted as magnesium slag reacts with the hydrations of clinker.

Abstract:Two kinds of stearic acid (SA)/ attapulgite (ATTP) composite phase change materials (PCMs) were prepared for the latent heat thermal energy storage (LHTES) in buildings or other area by the methods of fusion and immersion, using SA as PCMs and ATTP supplied by Linze of Gansu province as supporting material. The structure, thermal properties, thermal reliability and heat storage or release performance of the composite PCMs were determined by scanning electron microscope (SEM), fourier transformation infrared (FTIR), differential scanning calorimetry (DSC) and thermal cycling test analysis technique. The results indicate that the preparation method has no effect on the structure and morphologies of the composites. Two kinds of composites have same structure due to the SA adsorbed in the surface of ATTP by physical reaction. The results also show that two form-stable composites PCMs have the optimal effect for preventing SA leak from the composite emerges when the maximum load proportion of SA in the composites were 38.64wt% and 29.13wt%. The latent heats and phase change temperature were measured as 68.71 J/g and 57.3℃ for the composite which was prepared by fusion method and 51.79 J/g and 55.2℃ for the composite fabricated by immersion method, respectively. The results of DSC, FTIR and thermal cycling test are all showing that two kinds of composites have good heat storage property but the composite prepared by fusion method has a better thermal and chemical stability.