Abstract:To analyze an excavation engineering adjacent to high-filling surcharge loads, an equivalent stiffness method was applied to calculate the deformation of secant piles which were used as the retaining structure of foundation pit. And only the flexural capacity of reinforced concrete piles was taken into account when the secant piles were considered as the isolation piles. In the second case, the flexural capacity of plain concrete piles was ignored. The in-situ measurements revealed that both stability of the filling soil and safety of the foundation pit were satisfied in the excavation engineering adjacent to the high-filling surcharge load. Secant piles, as a new kind of retaining structure, are suitable for isolating the stress caused by the adjacent overloading, ensuring the stability of landfill soil and the safety of excavation engineering.

Abstract:As one of common reinforcement measure, cement mix pile is widely used in soft ground treatment of road widen project, while relevant studies on reinforcement range is insufficient. According to the one side road widening project, the cross-section of deep soft ground is analyzed. When fill is simplified as trapezoid load, the conclusion that reinforcement depth of cement mix pile should greater than load breadth can be gained by addition stress distribution. Based on the numerical simulation of different reinforcement measures, the slope stability, road settlement and horizontal deformation are influenced greatly by reinforcement range. Comparison research indicates that when the soft ground from slope toe to road shoulder is strengthened, the improvement effect is obvious. The numerical simulation and field monitoring resules show that reinforcement measure is suitable. Meanwhile, this study can provide reference to similar project.

Abstract:Based on the static liquefaction of granular materials, an elastoplastic static liquefaction constitutive model was proposed in the framework of critical state soil mechanics. The yielding surface and hardening rules were obtained by integrating the contact force of the model proposed by Chang and a non-associate flow rule was adopted as well. The model has taken the state dependent dialatency law and the effect of initial density to the stress-strain relationship into consideration. The parameters of the model are simple and have certain physical meanings. The predicted results obtained by the model have a good agreement with the undrained triaxial test of Toyoura sand and sand-silt mixture.

Abstract:Based on Biot's theory, the longitudinal vibrations of a single pile in saturated viscoelastic soil are investigated in the frequency domain subject to the harmonic load. By the Novak plane strain model, the control equations for the saturated viscoelastic soil are derived. Regarding the pile as the one-dimensional rod model, the vibration equation of the pile is established. Based on the continuity conditions of the pile and soil, the dynamic stiffness and dynamic damping of the pile top are obtained. It is compared with the solution for Novak, and the influence of different physical parameters of the pile and soil on the longitudinal vibrations of the soil and pile system is examined. It is shown that the dynamic characteristics of the pile in the dry soil as well as the saturated soil have some differences; the resonance effect of dynamic stiffness factor and equivalent damping is obvious weakening with the increase of the ratio of the length to radius of the pile. The resonance effect and natural frequency are increasing when the modulus ratio of the pile to soil increases; the interaction coefficient of the flow-solid and the damping ratio of soil skeleton have few influences on the responses.

Abstract:To study the influence of stress path on the long-term deformation, creep tests of dredger fill in Tianjin Binhai New Area in three different stress paths, namely decrease p paths (DEP)、constant p paths (CNP) and increase p paths (INP) respenctively, were carried out by using the WF stress paths tester and grading loading method. The results showed that under the same deviate stress conditions, the creep strain decreased in three kinds of stress paths of DEP, INP and CNP in turn, deformation rate of stable stage in the procession of creep increased according to the three kinds of stress paths of DEP, CNP, INP. The pore water pressure were negative in the procession of creep with decrease p and constant p stress paths, and decreased along with the deviate stress increase. However, in the procession of creep with increase p stress paths , the pore water pressure increased with the increase of deviator stress. The long-term strength in decrease p and constant p stress paths was higher than that in increase p stress paths. Finally, the effect is better by using quadratic polynomial to fit stress-strain isochronous curve of the three stress paths.

Abstract:Collapsible loess was collected from a suburban district of Shanxi, China. Dynamic model experiments of different hammer blows were designed to simulate the in-situ test on collapsible loess. The model experiments results showed that the density and shear strength parameters of the soil specimens increased with the increase of blows while the collapsible coefficient of the loess decreased with the increase of blows. However, after eight blows, the vertical displacement, the density, the internal friction angle and the cohesion of the loess were tend to be constant, and the collapsible coefficient was less than 0.015 that means the loess is stable. Furthermore, scanning electron microscope was used and SEM image analysis program was established to study the micro-structure of the specimens. The analysis of results showed that small pores in the soil increased with the increase of the blows; before compaction the content of pores with an equivalent pore diameter under 16 μm was 92.6%, the content of pores with an equivalent pore diameter larger than 16 μm was 7.4% and the content of pores with an equivalent pore diameter less than 4 μm was 66.9%. After ten blows, there were nearly no pores with an equivalent pore diameter larger than 16 μm, while the content of the pores with an equivalent pore diameter less than 4 μm was 81.8%. According to quantitative analysis, the relations between the blows and the plane void ratio, and the equivalent pore diameter were established. Meanwhile, the relations between the collapsible coefficient and the plane void ratio, the equivalent pore diameter were established.

Abstract:To get the spatial distribution characteristic of roadway's surrounding rock stress, circular section roadway was taken as a case study. The solution of stress was got by using complex function method, and roadway's surrounding rock stress field was analysed after the solution of mapping space was transformed into the solution of roadway space. As a result, the visual diagram of stress field distribution of roadway's surrounding rock was obtained, which could describe intuitively stress distribution of roadway's surrounding rock at any position. Considering the influence of different radius and side pressure coefficients on surrounding rock stress field, the following conclusions have been obtainded: the peak value and direction of circular roadway's surrounding rock stress has nothing to do with the radius; when side pressure coefficient is less than 1/3,the roof can produce tensile stress; when side pressure coefficient is more than 3, the surrounding rock in two sides can produce tensile stress. And the change rule of hoop stress, radial stress, shear stress and the maximum and minimum of stress have also been generated.

Abstract:Double-track railway over-cross tunnels were stuied by numerical simulation and regression analysis. A series of research on the influence of the construction of newly built tunnel to the existing one in different surrounding rock grades was carried out. According to the numerical simulation, 48 mechanical models were established, which considered various clearance, rock conditions and different construction sequences（building above or beneath existing one）. Based on regression analysis on the calculation results from the 48 models, the deformation prediction formulas for the existing tunnel's surrounding rocks and ballast bed were deduced. According to the high-speed rail allowed standard of roadbed deformation during operation, the minimum clear distance value by which the existing tunnel's operation would not be affected was recommended. Some analysis on the surrounding rock pressure's variation of the existing tunnel caused by new tunnel construction was done. Taking the variation amplitude as the evaluation criteria, a critical value of influenced clearance for railway over-crossing tunnels project is provided. Meanwhile, the results found that the tunnel cross the building had a smaller impact on itself compared with that of the tunnel which goes through the building.

Abstract:The 3D Goodman element is used to simulate segments' cracks in one section of shield tunnel in Guangzhou. Mechanical and deformation characteristics of segment structure responded to varied depth of cracks is analyzed in this paper. Meanwhile, research on coefficient of lateral earth pressure, soil coefficient and ground water level on mechanical and deformation characteristics is carried out. The research result shows that along with the increase of cracks' depth, the tensile stress, pressure stress reach the maximum value while the increment is not too much. However, when the depth equals to the thickness of segment, the reinforcements' tensile stress has increase sharply, even exceeded the allowable value. Moreover, the maximum number of tensile stress, horizontal and vertical convergent value of shield tunnel segment with cracks increase with the reduction of the coefficient of lateral earth pressure and soil coefficient, and increase with the increase of ground water level as well. Specific repair measure has been taken to segments' cracks in this section of shield tunnel based on the conclusions. In general, this section of shield tunnel is stable and safe now, and there is no longer new cracks appeared.

Abstract:The foundation for offshore wind turbines is subjected to vertical loading caused by structural weight and horizontal loading and moment due to wind- or wave-induced loading. Furthermore, it sustains torque from rotor blades. Based on the framework of hypoplasticity theory, the available general yield function and plastic potential function, a macro-element model for circular shallow foundations on sands under six-degree-of-freedom combined loading has been developed. In this model, to correctly reproduce the mechanical response of offshore foundations under cyclic loading, the concept of equivalent inter-granular strain is introduced into the relationship of generalized forces as well as its corresponding displacements. The performance of the proposed macro-element model is demonstrated by comparing the model predictions with available experimental data from a series of model tests.

Abstract:In order to investigate the fire resistance of high strength steel beams made from Q460, the method to compute temperature distribution of high strength Q460 steel beams was derived and the temperature distribution was calculated by using finite difference method. The modified equations of temperature for components of steel beam were proposed. According to critical moment at room temperature and mechanical properties of high strength Q460 steel at elevated temperature, the critical moment and stability checking coefficient were obtained by analysis. The load bearing capacity and critical temperature as well as stability factor were studied by using equivalent stiffness method through considering the effect of temperature gradient on stiffness.

Abstract:In the previous companion paper, the fire resistance of high strength steel beams made from Q460 was theoretically studied. The methods to obtain temperature distribution, critical moment, critical temperature and stability coefficient were presented. The temperature distribution and load bearing capacity was analyzed by finite element method, and the validation was evaluated by comparison of results between theoretical computation and finite element analysis as well as experimental results. The comparison was made between Q460 steel beam and mild Q235 steel beam and the difference on fire resistance was obtained. A simplified approach for fire resistance of high strength Q460 steel beams was proposed and an example was given to show the application and reference of the approach.

Abstract:It is assumed that concrete compressive stress of the cross-section compression zone is linear distribution when the cross-section of high-strength concrete shear wall reaches yield situation. Based on the plane section assumption, the yield curvature formula of shear wall section is obtained by using moment - curvature analysis method. The parameters affecting yield curvature of high-strength concrete shear wall are studied by using the yield curvature formula. The results show that longitudinal reinforcement yield strain is the most vital factor of the yield curvature in addition to axial load ratio. When axial load ratio is larger, both wing walls of shear wall section have larger impact. The yield curvature formula is presented, considering the impact of axial load ratio, boundary reinforcement yield stress and both ends of wing walls of shear wall section based on the regression analysis of calculation results. On this basis, the vertex yield displacement formula of high-strength concrete shear wall is proposed, and the calculation results of formula correspond well to the vertex yield displacement experimental values of the 12 high-strength concrete cantilever wall. The formula is also suited for the vertex yield displacement of comment concrete shear wall.

Abstract:Under the salt frost environment， the flexural behavior of reinforced concrete was studied. The bearing capacity and deformation performance of the beams were analyzed by comparing with the reference beam(undamaged) and beams subjected to 25，50，75 and 100 salt freeze-thaw cycles respectively. The results showed the plane section hypothesis still was satisfied for the concrete strains of frost beam section, and the mechanical characteristics of frost beam was similar to reference; The main reason to affect the beam bearing capacity under salt freeze-thaw environment was the concrete cover scaling in the compressive zone. Secondly, it was the reduction in concrete strength, while the degradation of bond properties between rebar and concrete was not a dominated factor; the deformations of concrete beam increased mainly due to the reduction in concrete strength, the damage of concrete cover and the degradation of bond properties. In addition to the number of freeze-thaw cycles, the positions of freeze-thaw damage and the load level affected the degree of reduction in beam stiffness.

Abstract:In order to realize the variation of structural dynamic characterics due to neighbor structures in buildings, the surface structure is idealized as an equivalent single degree of freedom system with rigid base whose site consists of a single homogeneous layer. The dynamic characteristics of three-dimensional structure-soil-structure interaction system, including two identical structures, are investigated to identify the additional effects caused by the presence of a second structure. When comparing the data from the soil-structure system with only one structure and the structure-soil-structure system, two close natural frequencies with opposite phase modes are identified. Therefore, the term twin-frequency is proposed. Next, the value of twin-frequency varying with the frequency ratio of structure to soil is discussed. Meanwhile, the relative distance between two structures and the ratio of foundation width to soil thickness are covered. The data will be used to consider the coupling effects of soil on the dynamic characteristics of structure-soil-structure systems. Finally, a numerical case of seismic response of the structure-soil-structure system is calculated under traveling wave excitations. The numerical results indicate that the twin-frequencies cause beatings of the structures as well as ground motion.

Abstract:Due to the large stirrup ratio and reinforcement congest in beam-column joints, the ordinary reinforced concrete beam-column joints take inconvenience to construction. Cracked fiber renforced concrete (FRC) has strong bridge ability and better tensile performance so that it can replace part or all of the stirrups. Based on previous researches on resistance mechanism of reinforced concrete joints, a new model using FRC materials in the core zone of beam-column joints is presented. It is a kind of model in which horizontal shear supported by the diagonal strut mechanism and softening truss mechanism with a certain percentage. The calculation results of the model is compared with the existing test results. It is a bit conservative to specimens with low axial load ratio. However, the results are in line with the specimens with high axial load ratio. Therefore, the results totally demonstrate the rationality of the proposed model in this paper. Meanwhile, according to the proposed model, the shear capacity of beam-column joints can be not only calculated, it also check whether FRC compressive strength in core zone of joints and horizontal stirrup ratio meets design requirements, which has a higher practicability.

Abstract:On the basis of Hollow Flange Beam (HFB) which is proposed by Australian researchers, a new pattern triangle hollow flange beam (THFB) is presented. According to the experimental test and finite element simulation, the failure processes of THFB and traditional I-beam under concentrated load are compared, and then the obvious differences between the failure modes of these two type beams are founded. The local buckling is easily occurred for the THFB, while overall instability is easily occurred for traditional I-beam, and THFB possesses have better bending performance and twist resistance than those of traditional I-beam. with the experiments, finite element analysis is carried out by FE software ANSYS, and the FE results agree with the test results. Based on FE models, the parameter analysis is carried out for THFB. The parameters mainly include the thickness of top flange, the width of top flange, the thickness of web and the yield strength of steel. The change rule of the bearing capacity of THFB with different parameters can be achieved by parameter analysis. Finally, based on the above results, the applicability of the calculation formula of Eurocode3 to compute the bearing capacity of THFB is discussed. The results show that it is safe and reliable to adopt the calculation formula of Eurocode3 to compute the bearing capacity of THFB, Whilst the estimation is relatively conservative.

Abstract:A comprehensive estimate scheme employed multiple parameters is proposed for quality grade of recycled concrete coarse aggregate based on grey clustering theory. In the scheme, seven parameters are selected as comprehensive evaluation indices according to Recycled Coarse Aggregate for Concrete of China. The parameters are apparent density, porosity, sturdiness, crushing index, micro-mist content, silt content and water absorption respectively. Secondly, weighted similarity method is adopted to determine the objective weight, and divide the quality grade into four grey ranks according to characteristics of grade assignment interval of the indices. Then, whitening weight function is employed to make an estimate model, by which the quality grade estimate result of recycled concrete coarse aggregate can be achieved through compute of grey clustering coefficients. Finally, a case study is adopted to verify the practicability of the proposed scheme.

Abstract:The mechanical properties, hydration products, and pore structure of SSC(super sulphated cement) were tested with universal test machine，XRD(X-ray diffraction), SEM(scanning electron microscope) and MIP(mercury intrusion porosimetry), which were compared with P·O 42.5 and slag cement. Results show that the main hydration products of SSC are ettringite, C-S-H gel and little gypsum crystals, while without calcium hydroxide; SSC hardened paste has smaller threshold pore diameter, the most probable pore diameter, middle pore diameter and average pore diameter, and has lower porosity and higher density, which can effectively promote the 90-day strength increase of SSC paste.

Abstract:To solve the flow instability and adjustment difficulty of filtering dirt-removing device in the sewage source heat pump system, which affect the efficiency of heat exchanger, semi-flooded rotary orifice sewage auto-strainer was generated. According to establishing the mathematical model, the effect is analysed of pollutant concentration and liquid level height of sewage and rotation period of orifice plate to filtered flow rate, filtered load and filtering surface block coefficient. The result shows that: in the certain condition of sewage liquid level height and orifice plate rotation period, the increase of sewage will decrease the filtered flow rate of orifice plate, and increase filtering surface block coefficient; The effect of pollutant concentration change in the sewage to orifice plate filtered flow rate could be adjusted by regulating the sewage liquid level height and orifice plate rotation period, and the moderating effect of orifice plate rotation period is better than that of sewage liquid level height.