Abstract:Based on the present situation of masonry structure and the development of housing industrialization, We proposed an invonative unbonded post-tensioned precast concrete composite wall to develop a new structure form in the low-rise civil construction. We studied two specimens with various levels of pre-stressing were studied experimentally by the quasi-static test system to investigate the seismic behavior of the composite wall and obtained the seismic behavior indexes of corresponding specimens. The results show that the walls have better bearing capacity and good ductility. They could meet the application requirements of the low-rise building in eight-intensity area and be used as an alternative of masonry load-bearing wall structure. We also presented some suggestions about the structure forms of the compostie wall.

Abstract:Small-span-to-depth-ratio coupling beams of shear wall can be formed with a crack in the middle to prevent from shear failure and improve the seismic performance. Three coupling beams with same small-span-to-depth-ratio were tested under cyclic loading. Comparing the results of slotted coupling beams with other coupling beams of different forms of reinforcement, we analyzed the seismic behavior of the slotted coupling beam, including failure pattern, hysteresis loop, strength degradation, stiffness degradation, ductility and energy dissipation. We simulated skeleton curve of specimens' hysteresis curve by using ABAQUS and compared the simulation result mith the experiment result. The results show that slotted coupling beams with small-span-to-depth-ratio have good performance of bearing capacity and deformation.They can be constructed conveniently and economically. Besides, with the good seismic performance, small-span-to-depth-ratio coupling beams could prevent from shear failure effectively and be applied well in practical engineering.

Abstract:We carried out horizontal low cyclic loading tests of four all-welded double beam-column inner joints to study the seismic performance of the double beam-column inner joints of the steel intimated ancient building. We studied the mechanical performance of the double beam-column inner joints according to the loading process and failure pattern of the specimens under the action of lateral forces, and divided the double beam-columns into two kinds,which were the box section beam and I-shaped section beam,according to different section forms of beam.Based on unique structural features of the intimated ancient building,we divided the joint core area of each specimen into three regions,which were upper core zone, middle core zone and lower core zone. By measuring the shear strain within the scope of every area,we analyzed the mechanism performance and failure modes of the joints under lateral forces, and established the diagonal strut mechanism. The experimental results and theoretical analysis show that the failure mode of the double beam-column joints of the intimated ancient building is mainly for the shear failure along the diagonal of the lower core area. So we presented a modified formula of shear bearing capacity of double beam-column inner joints considering the axial compression ratio and the cross section of the beams.

Abstract:We used the optical surface measurement technology to collect the pitting surface data of steel plate specimens subjected to laboratory accelerated corrosion, and discussed on trends of pitting characteristics with the increase of corrosion time by establishing 3D contour pictures of surface data of corroded steel with different corrosion time. For the corroded steel plate mainly with local corrosion, calculations showed that the average depth of pitting corrosion was approximately equal to the average depth of corrosion, and the tendency of the average depth of pitting corrosion with time could be described by a new Weibull function. The pitting section loss ratio, which was perpendicular to the force direction of steel plate, showed a normal distribution, and the relationship between the model parameters and the average depth of pitting corrosion was established. The probabilistic yield strength deterioration model relating to the corrosion ratio was discussed.

Abstract:Using prismatic specimens of concrete, we examined the uniaxial compression stress-strain curve of ordinary concrete (mixture C43F10), ordinary shotcrete (mixture S43F10) and steel fiber reinforced shotcrete (mixture S43F10SF50) with the same mixture by using the accelerating freeze-thaw method. By fitting the relationship between parameters and the number of freeze-thaw cycles, the stress-strain curve of specimens under damaging was calculated. The test results show that with the increase of freezing and thawing cycles, the peak stress is low and has a liner relation with the freezing and thawing cycles. However, the peak strain is bigger and demonstrates an exponential relationship. The peak stress of shotcrete decreases more slowly than that of ordinary concrete, and that of shotcrete with steel fiber reduces much more slowly. We also observed and analyzed the microstructure and pores of specimens after damage by using scanning electron microscope and the mercury intrusion method. The result shows that with an increase number of freeze-thaw cycles, the amount of micro-creaks and pores and the diameter of pores increase by the effect of osmotic pressure and frost heave pressure while the specimens' density decreases. In the same situation, there are only several connected capillary pores in steel fiber reinforced shotcrete, which is consistent with macro-mechanical properties.

Abstract:The accelerated high-temperature test was carried out to understand the influence of rehydration of unhydrated cement under different curing temperature and W/B on the performance of ultra high performance concrete(UHPC) with the test of loss on ignition method,mechanic performance, deformation test, RCM and carbonation test. The results show that the rehydration of unhydrated cement in UHPC could be accelerated effectively when the curing temperature was 60 ℃.The bound water content was stable in 90 d. With the increase of age, UHPC would first shrink and then expanse. It would have a downside on the development of its performance in 90 d, such as flexural strength, resistance to chloride ion permeability and carbonation resistance. There was no obvious change of compressive strength. Moreover, the lower W/B, the higher increased percentage of bound water content of UHPC in 90 d, the greater expansion value, and the higher the flexural strength loss rate.

Abstract:We carried out load testson five groups of recycled concrete beam specimens of different corrosion rates to explore the recycled concrete structure durability,and analyzed the influence of different corrosion rates on steel bar strain,local bond stress, load-slip and the ultimate bond stress of recycle concrete beam specimens. The results show that lightly corrosive cracks appeared in the bottom of the beam when rebar corrosion rate was greater than 3%.The strain curve was flat when the corrosion rate of reinforcing steel bar was greater with the anchor position under the breaking load. The distribution of local bond stress along the anchor section was bimodal distribution, and peak mainly concentrated near the loading end and the free end. The slippage phenomenon happened first on the position near the loading end, and delayed away from the loading end. With the increase of rebar corrosion rate, ultimate bond strength increased first and then reduced and slip value increased under the ultimate load.

Abstract:We used two kinds of industrial waste of Fly ash and blast furnace slag as major raw materials, and modules of sodium silicate ranging from 1.2 to 1.8 as the activator to manufacture geopolymer. We conducted the orthogonal experiment in five-factor and four-level form, and studied water to binder ratio (W), alkali-activator proportion (S), blast furnace slag replacement ratio (B) and the module of sodium silicate (M) on the four essential properties including the fluidity, setting time, compressive strength and tensile bond strength of the geopolymer used in green materials for construction mending. The relation between mix design and performance index of the green repair material were investigated by range analysis and factor analysis. By synthetic analysis, an excellent geopolymer-based green material for construction mending could be manufactured when W, S, B and M were 0.28, 0.14, 0.4, 1.2, respectively.

Abstract:Based on creep relaxation properties of the early-age concrete and concrete creep experimental data of different proportions strengths and loading age conditions, we carried out a comparative study of models for predicting creep CEB-FIP model, Muller model, B3 model and the presented Burgers model. The results show that, the CEB-FIP model has the best adaptability; Muller model is good for the creep prediction of high strength concrete; and the B3 model, which is based on the solidification theory, overestimates the creep for early-age concrete and shows poor accuracy. The results of the comparative study verify the physical significance and experience data range of parameters, as well as the rationality and applicability of the presented Burgers model with variable coefficient and four parameters.

Abstract:We studied the effect of different amount of basalt fiber on the splitting strength, bond strength and other mechanical properties of shotcrete under the context of tunnel heat-harm by using a combined method of model test, approximate simulation wet shotcrete technique, quantitative analysis and microscopic testing. Then we compared mechanical properties of shotcrete with different amount of basalt fiber both under standard curing and dry heating curing, and added silica fume and steel fiber into shotcrete to find an effective way to solve heat-harm. The results show that the basalt fiber added to the shotcrete can increase the strength of the shotcrete and resist cracks, which improves the fragility of shotcrete. Moreover, in dry and hot environment, a small amount of basalt fiber added can improve the mechanical properties of shotcrete. When the mixing amount of basalt consists of 0.1 percent basalt fiber and 5 percent silica fume, the mechanical properties of shotcrete is the best, and 0.2 percent basalt fiber added can also improve to a certain degree. In practice, adding moderate amount of basalt fiber and silica fume into shotcrete can reduce the damage of concrete under heat-harm.

Abstract:To study the complete stress-strain curve of stirrup confined recycled concrete under uniaxial loading, we tested on nine circular column specimens of recycled concrete which have a diameter of 500 mm and a height of 1 500 mm. In this test,we used a servo-hydraulic test machine with a capacity of 20 000 kN for displacement and loading control. The main test parameters are longitudinal reinforcement ratio, the spacing and diameter of stirrup, and applied strain rate. The results show that the spacing of stirrup and stirrup ratio have great influence on the ductility of specimens. The peak stress of specimen increases 114% when the applied strain rate increases from 0.000003/s to 0.0033/s. The complete stress-strain curve of recycled concrete is similar to that of normal concrete but the descending branch is stiffer than that of normal concrete, which means that the recycled concrete is more brittle than normal concrete.

Abstract:Based on simplified stress-strain relationship of fiber reinforced concrete and the plane section assumption and equilibrium equation, the curvature of reinforced concrete columns with fiber reinforced concrete in plastic hinge region under different ultimate state was derived. Then, the distribution force in the cross section was obtained by calculating the curvature under different ultimate states. By taking the distance of the cross section centroid axis, the moment expressions of reinforced concrete columns with fiber reinforced concrete in plastic hinge region at crack load point, yield load point, peak load point and ultimate load point were attained. The calculated values agree well with the experimental results.

Abstract:Strong earthquake has adverse impact on the petrochemical steel structures of refinery and lead to large economic losses and serious secondary disasters. We studied a reformer reactor of a large refinery, built the finite element model and set viscous dampers to reduce the seismic risk of petrochemical structures based on their characteristics. Then we analyzed the influence factors, including location, quantity and the damping parameters of the viscous dampers. The results show that the inter-story force and inter-story displacement angle of the floor where the viscous damper was setted decrease significantly, and the damping effect with setting viscous damper in the bottom is greater than that in the middle and upper part. Besides, the inter-story force and inter-story displacement angle decrease when the number of viscous damper increases, but the decrease amplitude reduces gradually. In addition, the influence of damping coefficient on the damping effect of the petrochemical steel structure is greater than that of the damping index. So the damping coefficient should be given priority to consider in the structure design for better seismic performance.

Abstract:We studied the progressive collapse performance of cylindrical latticed shell and its failure modes indifferent load distribution and boundary conditions. By using the sensitivity assessment index based on the ultimate bearing capacity of components, the influence of imperfection and buckling of compressive rods on the sensitivity index of the rods and nodes. The results show that in the four-side boundary condition, the full uniform-distribution load is mainly controlling. Nodes at the mid-span are the sensitive components and the adjacent rods are the key components. In two-side longitudinal boundary condition, the half uniform-distribution load is basically controlling. The largest sensitivity index of the rods and nodes are found at 1/3 span, and the smallest is adjacent to the support. Considering the structural imperfection, the important coefficients of the rods and nodes increase by 41% and 53% respectively; and considering the effect of buckling of compressive rods, increase by 45% and 62% respectively. So we can optimize the progressive collapse performance of cylindrical latticed shell by strengthening the key components.

Abstract:To improve the durability and stability of subgrade on service, we aimed to research on a scientific method for filling subgrade with completely decomposed granite soil under the hot and humid condition in south. Wet heavy compaction test and California bearing ratio test were conducted on the completely decomposed granite. The results show that the moisture content of completely decomposed granite was more similar to natural moisture content than the optimum moisture content under the maximum bearing capacity. Swelling experiment was carried out to obtain the regularity of density decay by variation of initial moisture content. The modified consolidation test was applied to analyze the deformation properties on the maximum bearing capacity and the maximum dry density status respectively. The results show that compared to maximum dry density condition, the resistance of deformation and the stability on the maximum capacity status was enhanced. Moreover, the experimental subgrade filling with completely decomposed granite was constructed on the maximum bearing capacity status. The in-situ bearing plate test and compactness test were conducted, and the results show that the compactness could totally meet the demand of lower road bed which is the 94% compactness region. To meet the design modulus of the subgrade that the pavements demands, we proposed a method of stiffness compensation based on principle of equivalent deformation to ensure the stiffness and the durability of the completely decomposed granite subgrade effectively.

Abstract:A series of dynamic triaxle test on soft soil in Tangshan Binhai area was carried out to understand the horizontal dynamic characteristics of the soil around the offshore wind power pile foundation under wave load. The influence of confining pressure, dynamic stress amplitude and vibration frequency on horizontal dynamic characteristics of soft soil were studied. The results show that the horizontal dynamic strength of soft soil increases with the increase of confining pressure increases,and decreases with the increase of vibration. When the dynamic stress amplitude increases, the vibration times decreases. The horizontal dynamic strain ε_d increases with the increase of vibration frequency, and the larger the dynamic stress amplitude is, the more significant the growth is. The change agrees well with that of the Monismith model. The change of the horizontal dynamic modulus of soft soil is significantly influenced by the dynamic stress amplitude. When confining pressure decreases, dynamic modulus decreases. The Caofeidian soft soil has distinct structural horizontal dynamic characteristics. Under different confining pressures, the damping ratio shows an increasing trend when dynamic stress amplitude increases.

Abstract:It is very difficult to apply a uniform impact (explosion) loads on the structural member in the laboratory. We presented an innovative loading apparatus using a drop hammer impacting on the airbag to simulate the uniform loads,and proposed a two-DOF (degree-of-freedom) analytical model. The fundamental mechanical equation, boundary conditions and solution method were given and verified. A fine finite element model was established and the loading effects on the divided area were compared to verify the feasibility of presented apparatus. Some key factors of the dynamic loads were also discussed, including stiffness, load duration and damping ratio.The results show that the presented apparatus can be applied to simulate the uniform dynamic loads with choosing parameters,which provides a possibility for experiments simulating blast loading in the laboratory.

Abstract:Atmospheric corrections were conducted with the MODTRAN4+ model for 49 TM data from 1990 to 2010 in Fuzhou. Multi-temporal trajectories of major land cover type were derived from NDVI images. The trends of Mean NDVI were analyzed. To investigate the influence of different data combination on the classification and detection accuraly of different methods,induding maximum likelihood classification, support vector machine, artificial neural network, and object-oriented methods, and compared the deteetion methods before and after adding a sample, the areas converted from cropland to built-up land were added to the learning sample. The results show that the object-oriented method is the most accurate method compared with other methods for a small sample. By using the method, the classification accuracy improves up to 3.53% and 4.24% for different data combination and different season respectively.Adding NDVI data and the sample of changing features improves 3.54% of the whole classification accuracy and 4.24% of drawing accuracy of the buid-up land.