Abstract:The simplified “fish-bone” model is commonly employed for the analysis of wind-induced responses of truss-stiffened suspension bridges, and one key step in establishing such a model is the calculation of the mass moment of inertia for the stiffening truss. Due to numerous members in a stiffening truss section, the calculation process of the moment of inertia is usually complicated and imprecise. Therefore, a new method is proposed based on the change in torsional frequencies of a cantilever truss girder caused by attaching the additional mass moment of inertia on the truss nodes, where the theoretical background is given, and the applicable conditions are also investigated. By taking a cantilever truss girder as an example, numerical simulation results show that the proposed method provides the best accuracy when the known mass moment of inertia is uniformly applied to all section nodes or to the nodes of chord joints, and the slenderness ratio of truss girder exceeds 20. Finally, the mass moments of inertia of stiffening truss are obtained by the proposed method, and are then used to establish the simplified “fish-bone”models for several selected suspension bridges. The torsional frequencies obtained by the simplified “fish-bone” models agree well with those predicted by their detailed models, which validates the effectiveness of this simplified method.

Abstract:A method for retrofitting the top slab of the reinforced concrete box girder with high-reinforcement-ratio UHPC is proposed in order to mitigate the loss of the capacity and durability of the bridge due to the cracking of the top slab. Test on the local models of three top slabs of the box girder is then conducted to investigate the effect of this retrofit method on the lateral flexural behavior of the top slabs under the concentrated loads. The test results show that the UHPC layer subjected to tensile stress induced by negative bending moment improves the cracking resistance and stiffness of the retrofitted slab significantly; The cracking resistance of the retrofitted slab is dependent on the elastic tensile strength of the UHPC; Compared with the unretrofitted slab, the load resistance of the retrofitted slab with the crack width of 0.2 mm increases by 255.8%; When the crack width is less than 0.27 mm, a linear relationship between the load and the maximum crack width is found. On the other hand, when the UHPC layer is subjected to compressive stress induced by positive bending moment, the cracking resistance of the slab is determined by tensile strength of the glue used for sealing cracks. Due to premature cracks in the unretrofitted part of the slab, the retrofitted slab subjected to positive bending moment exhibits a little larger deflection, but the growth rates of both the deflection and crack width of the retrofitted slab during the later period are clearly less than those of the unretrofitted slab. In addition, the top slab is well waterproofed by the compact UHPC layer. The retrofitting layer can effectively enhance the stiffness of the tested slab subjected to positive bending moment and control the crack growth. Failure patterns basically meet the expectations, and the theoretical calculation agrees well with the failure loads.

Abstract:Reliable interface connections of composite decks are important for their structural performance. To promote engineering applications of GFRP-concrete bridge decks, both the distributed sand bonding interface and the wet epoxy resin bonding interface are considered in the present study. Previous GRFP-concrete interface details are also optimized based on the double-shear test results of the GFRP-concrete composite bridge deck. Ten specimens are manufactured and tested under static loading, and the test results are compared with the previous test results. The present study shows that, with the optimized GFRP-concrete interface, the deformation of the specimens agrees with the plane deformation assumption during the loading process. The specimens show good integrity and high load-carrying capacity as well as good capability in recovering their deformations. Although brittle failure modes are observed in the specimens, large deflections occur before failure, which give some failure warning and ensure relatively high reservation of strength safety.

Abstract:The simplified calculation of the first-order longitudinal vibration period for a cable-stayed bridge is very important for the comparison of design plans and the evaluation of seismic performance. Firstly, according to the longitudinal seismic inertia force transmission of cable-stayed bridges, the double-mass model derived by flexibility method was developed to simplify the calculation of the first-order longitudinal vibration. Based on significant coupling between the longitudinal modes and vertical modes, the simplified calculation of the first-order longitudinal vibration period was then investigated by energy principle in fixed hinge cable-stayed bridges. Finally, the two formulas were evaluated by the tests on ten built-up bridges. It is concluded that these two simplified formulas were in good agreement with those predicated by finite element method. The proposed double-mass model has higher accuracy and reliability.

Abstract:In order to analyze the seismic damages of the owner-built dwellings along mountainous highway in Nepal earthquake sequence, field investigation was performed along the highway from Kathmandu to Zhangmu port. Firstly, the structural characteristics of reinforced concrete (RC) frames and masonry structures in Nepal were described. Then, the characteristics of the seismic damages of the two types of residential structures were summarized, and the damage ratios of the structures were provided according to the direct disasters and secondary disasters. The proportion of basic intact of RC frame structures is over three times that of masonry structures, but the proportion of moderate and serious damages and destruction of RC frame structures is about a half of that of masonry structures. Based on the damage investigation and statistical analysis, it is concluded that many owner-built RC frame structures are not properly designed as the requirements of the building codes of Nepal, and their construction quality is poor, but the damage degree of the RC frame structures is much less than that of the masonry structures. Moreover, as the elevation increases along the highway, the seismic damage of the dwellings has a tendency of increase. Finally, secondary disasters resulted from the earthquake aggravated the seismic damage of dwellings.

Abstract:The numerical analysis results from the finite element models through the software of ABAQUS were compared with the experimental results to verify the accuracy of finite element parameters. Tie columns, opening, vertical pressure and strength of mortar were considered to study the seismic performance of masonry walls by using the validated finite element models. Two masonry structure models with different layers were established to study the influence of structure height on the seismic performance. The results show that tie columns can improve the bearing capacity and seismic performance of the masonry wall, and the opening hole of the masonry wall reduces the bearing capacity and seismic performance of the masonry wall. The displacement ductility of the masonry wall decreases with the increase of vertical compressive stress. However, the bearing capacity of the masonry wall increases at first and then decreases with the increase of vertical compressive stress. The bearing capacity and seismic performance of the masonry wall increases with the increase of mortar strength grade, and the higher masonry structure results in more serious tensile damage．

Abstract:Two different types of horizontal connections for precast concrete shear walls are proposed and tested to evaluate their seismic performance. One is dry connection with vertical reinforcing bars anchored into the grout-filled metal bellows embedded in the precast wall, while the other is hybrid connection where the boundary elements are formed by locally placing concrete with vertical reinforcing bars lapping in the cast-in-place concrete, and the reinforcing bars placement is the same that of the dry connection. Three full-scale specimens of the dry connection, hybrid connection, and cast-in-place connection were prefabricated and tested under the low-cycle reverse loading. The measured results showed that both the precast specimens performed similarly, such as the strength, stiffness, displacement ductility, and energy dissipation capacity, and they possessed comparable seismic performance when compared with the cast-in-place specimen. Meanwhile, the seismic behavior of the hybrid connection was obviously dependent on the pouring quality of the locally placing concrete. Because of the complexity in the construction technology for the concrete placing of hybrid connection, it is difficult to ensure the quality, and the seismic performance is considerably weakened. Therefore, it is not recommended to apply the hybrid connection in precast concrete shear walls.

Abstract:Numerical modeling method was adopted to investigate the stress of uneven adhesive layer and the interfacial stresses of the beam strengthened by CFRP plate. The notch was set on the interface of strengthened beam to change the local thickness of adhesive layer. Six cases were set up according to the depth, width and location of the notch. The analysis results indicate that the peak interfacial stresses are much greater than beam without the notch when the notch is located at a short distance from the plate end. When the notch is far from the plate end, the peak interfacial stresses are barely been influenced. The peak interfacial shear and normal stresses reach the maximum values when the notch is located at around 0.83% and 1.25% of the FRP length from the plate end, respectively. With the increase of the length or depth of the notch, interfacial shear and normal stresses increase simultaneously. Both interfacial shear and normal stresses are more sensitive to the change of depth than change of length. The stress distribution of adhesive layer along the thickness-wise direction is uniform except the CFRP plate-end area. When the notch is located at the plate-end area, the notch leads to a stronger variation of stresses of adhesive layer at the plate-end area and also a more non-uniform stress distribution within the notch-area along the thickness-wise direction.

Abstract:Based on the finite element analysis software OpenSEES, substructure pseudo-dynamic test (PDT) method for frame structures was investigated. Substructure PDTs of a one-story one-bay steel frame was conducted, in which three different kinds of boundary conditions were simulated. The correctness of the PDT method was demonstrated by the agreement between the test results with complete boundary condition and time history analysis results. For one-story, five-story, and eight-story four-bay reinforced concrete frames, substructure PDTs were also conducted with three different kinds of boundary conditions. The considerable discrepancy between the test and simulation results occurs in hysteresis curve of substructure columns when only horizontal displacement boundary condition was simulated. The simulation accuracy of the hysteresis curve of substructure columns can be improved when both the horizontal displacement and rotation boundary conditions are considered. The base shear was much less affected by using simplified boundary condition, while its effect on first story drift can be ignored. The results can be used for the design of substructure pseudo-dynamic tests.

Abstract:To estimate the damage state of reinforced concrete (RC) members, a damage model was established based on stiffness degradation and fiber beam-column elements in Matlab. Firstly, the numerical analysis model of a member or a structure based on fiber beam-column elements was established in OpenSees, and the strains and stresses of fibers outputted by OpenSees were then read into the damage model established by Matlab, which estimated the damage values at fiber, section, and member levels. In the established model, fiber damages of concrete, reinforcing steel, and prestressing tendon were defined by the initial reloading modulus degradation, low-cycle fatigue law, and plastic strain, respectively. The section and member damage states were then evaluated by the degradation of the sectional bending stiffness and rod-end bending stiffness, respectively. The established model was verified by comparison with a structural test results of prestressed concrete frame subjected to cyclic loads. The results indicate that the damage model can determine its damage states accurately, and a close relationship between damage indices at various levels by using the direct stiffness method and static condensation method. Furthermore, the established damage model can be embedded in OpenSees to determine the damage states of RC members and structures directly in the future.

Abstract:An innovative composite structure, named concrete-filled RPC tube (CFRT), was presented in the paper. In this system, high-strength stirrups are arranged in prefabricated reactive powder concrete (RPC) tube, and concrete is then casted into RPC tube. Total fifteen large-scale columns were designed and conducted for axial compression test, including nine CFRT specimens, three high-strength stirrup confined concrete (HSCC) specimens and three hollow RPC tubes. Composite action between the RPC tube and internal concrete as well as the spiral stirrup spacing was considered as the main factors in tests. The results show that only slightly cracking without any spalling occurs at the RPC tube of CFRT column when axial load approaches its peak value. Meanwhile, the axial load-carrying capacity of CFRT column is higher than the sum of that of hollow RPC tube and internal concrete, indicating this composite system realizes the superposition effect. The compressive properties of CFRT columns are also improved with the decrease of spacing of stirrups. Moreover, based on Mander model and the corresponding simplifications, contribution ratio of RPC tube for load-carrying capacity of CFRT columns was quantified, and its value increased from 0.22 to 0.26 with the increasing stirrup ratio. Furthermore, a calculation method for load-carrying capacity of CFRT was proposed.

Abstract:Through NEL experimental method and scanning electron microscopy test (SEM), the resistance of chloride ion penetration in the concrete admixed with polypropylene fiber, complex minerals (fly ash/silicon ash with weight ratio of 4∶1), and polypropylene fiber under axial compressive loading or not was studied. The results show that, under no-load condition, the compactness between aggregate and cement stone improves, and the number and the width of the crevice obviously decrease in concrete specimens admixed with appropriate amount of polypropylene fiber and complex minerals. From the view of macro property, the diffusion coefficients of chloride ion decrease, and the anti-chloride ion permeability obviously increases when compared with that of the concrete admixed with polypropylene fiber or multiple minerals. The optimal proportion of the concrete for anti-chloride ion permeability is the composition of 0．1% polypropylene fiber and 25 % complex minerals co-doped. The diffusion coefficients of chloride ion slightly decrease firstly and then increase in concrete under axial compressive load. Under the same stress ratio, the chloride ion diffusion coefficient is the minimum for concrete with polypropylene fiber and complex minerals co-doped.

Abstract:To release and solve traffic jam on expressway, it is necessary to investigate the ramp metering strategy of expressway. Current specification and field data were used to build the VISSIM simulation model. The breakdown probability models of expressway ramp were established by microscopic traffic simulation, and a ramp metering strategy based on breakdown probability model was put forward. According to the mainstream and ramp volume, the breakdown probability was predicted. If the probability is higher than the threshold, the metering system turns on, and the on-ramp metering rate and cycle time are calculated. Compared with a ramp without metering strategy, the breakdown probability reduced to about 0.1, while the speed of mainstream increased by about 20 %.

Abstract:For the ground foundation influenced by the construction disturbance, the disturbance factor functions taking the shear strength and relative density as the disturbed parameters, respectively, were proposed based on the disturbed state concept. By using this function, a modified Duncan-Chang model considering the influence of disturbance was developed to provide a reference for the settlements prediction of ground foundation. Firstly, considering the stress state of ground soil, the analytical model for ground soil was established by idealizing the ground settlement to be the summation of one part caused by additional hydrostatic pressure and the other part by additional deviatory stress. Secondly, considering the stress history of ground soil, the determination method for initial deformation modulus of ground soil at different depths was provided by using the step-loading analysis method. Based on the Hooke’s law and modified Duncan-Chang model, the models to evaluate the settlement of ground foundation caused by additional hydrostatic pressure and of that by additional deviatory stress were then developed, respectively, by using the step-loading analysis method. The determination method for deformation modulus of ground soil was also given considering the additional stress effect. Finally, the proposed method was applied to a practical project case, and the corresponding settlement analysis was carried out. The results show that the proposed method has superiority and feasibility in the aspects of reflecting disturbance degree, stress state and stress history. The calculated results agree well with the prediction rule of settlement.

Abstract:The kernel functions of the boundary integral equations for thin plate were determined by the fundamental solutions for an infinite thin plate. By the discretization of the plate interior and boundary as well as the assumption of the distribution states of plate nodes and foundation reaction forces, the BEM equations of the plate can be established. Meanwhile, based on the analytical layer element solutions for layered foundations, the flexibility matrix of the foundation was obtained by a two-dimensioned Guass-Legendre quadrature. Taking into account the compatible conditions of the displacements at the soils-plate interface, the global BEM equations for the interaction problem between the layered foundation and the thin plate were then established. The solutions for the problem were further obtained by solving the global BEM equations. The accuracy of the present method was verified by comparing existing solutions with the numerical results obtained from the corresponding FORTRAN program in this study. It is observed from numerical examples that when a square thin plate is placed on a foundation, the settlement difference between the two lines perpendicular to y or x coordinate decreases as they approach the center of the plate, and the difference decreases with the decrease of the plate-soil stiffness ratio. Furthermore, the settlement discrepancy between the plate center and the midpoint of the long side is unapparent with the increasing length-width ratio, and the similar variation trend can be found between the midpoint of the wide side and angular point.

Abstract:In order to study the bearing behavior of a single pile under combined loadings of horizontal force H and torque T, a loading device was first designed to apply H and T on the pile top simultaneously. 8 groups of indoor model were tested to obtain the inner forces and deformation as well as bearing capacities of the pile shaft. The result showed that, compared with the ultimate bearing capacity of pile shaft under pure H or T (i.e., Hu or Tu), the H-T load combinations with various magnitudes and sequences (i.e., H→T or T→H) caused an obvious decrease of the bearing capacity. For example, the application of 2Tu/3 on the pile top reduced the horizontal bearing capacity by 12.4 %, while the pre-loading of 2Hu/3 resulted in a reduction of the torsional bearing capacity up to 48.5 %. Therefore, traditional superposition principles can not be used in engineering design to evaluate the bearing capacity of piles under combined loads. Considering the effects of H-T combination and subsoil constraint on the torsional bearing capacity, the torsion angles at the pile top as well as the torque and moment distributions along the pile shaft were calculated by a MATLAB-based FEM program. The predictions were also compared with the model test data.

Abstract:As weak structural planes are difficult to be simulated reasonably in large underground chamber, “element reconstruction and node separation” was introduced, and the new simulation methodology of discontinuous weak structural planes was proposed in this study. The proposed methodology was used in the actual numerical model of underground powerhouse to simulate the discontinuous weak structural planes. The reconstructed model was then imported into calculation program, and the result was compared with the prediction by conventional continuous finite element model. The comparison shows that the reconstructed model can be used in the numerical calculation, and the discontinuity feature is presented near the discontinuous structural planes. Moreover, the rules in the calculation results are consistent with the general rules, which can describe the actual occurrence mode of the structural planes. Therefore, the simulation methodology of discontinuous weak structural planes achieves the transformation into the discontinuity of the structural planes, and it provides a new way for the simulation of complex geological discontinuous weak structural planes in large underground chamber.

Abstract:This paper aims to study the characteristics of heat transfer for concrete radiant ceiling and its cooling capacity. A two-dimensional stead-state heat transfer model on the basis of simplified RC (Resistance and Capacity) Method was adopted to simulate the inner heat-transfer condition of concrete ceiling as well as the temperature fields. The calculated results showed that the cooling capacity of concrete radiant ceiling was affected by the temperature of supply water, distance of tubes and water flow rate. When the supply water temperature, flow rate and indoor air temperature ranged from 11~14 ℃, 0.26 ~0.33 m3/h and 25~26 ℃, respectively, the cooling capacity varied from 40 to 50 W/m2. The simulation models were also validated by experimental results, and the calculation error was less than 6%.

Abstract:The parameters for thermal properties of ground and grout have directly effect on the performance of ground heat exchanger (GHE). For the problem that grout thermal properties of in-situ thermal response test (TRT) need to be measured in advance and cannot be evaluated directly by calculation, this paper applied genetic algorithm to evaluate the parameters of ground and grout thermal properties simultaneously on the basis of infinite line source (ILS) model and composite media line source (CMLS) model with wall thermal resistance correction. The method was validated by in situ TRT. Compared with the measured values, the calculation relative error of borehole thermal resistance, ground thermal conductivity and diffusivity was 3.47%, 1.42% and 4.93%, respectively. The root mean square error (RMSE) of the calculated average temperature by these two models and the measured value is 0.0505 and 0.172 ℃, respectively. The results provide important reference for GHE design.