Abstract:In order to investigate the influence of the maximum aggregate size on the shear behavior of beams without shear reinforcement, 16 reinforced concrete beams subjected to concentrated loading were tested. The main parameters are the maximum aggregate size and span-to-depth ratio. Based on the test results, the failure mode, the ultimate shear capacity, the load-middle deflection curves and the relative displacement between crack lips were analyzed. Combined with a comparison of the test data and those published in the literature, the tested shear capacity was compared with the predicted value of GB 50010-2010, ACI 318-08, EC 2-02 and CSA 23.3-04. It can be concluded that the aggregate interlock is the main mechanism of shear transfer in beams without shear reinforcement, and that shear design methods should be established on the basis of accounting the critical influence of aggregate interlock on the beam-shear behavior of reinforced concrete members.

Abstract:This study investigated the effect of the seismic mitigation measure of a type of elastomeric bearing system with the sliding plate and seismic dowel. Firstly, combining the idea of the performance-based seismic and seismic guidelines of China, three performance metrics of the seismic dowel under different earthquake levels (normal service condition, frequent-occurred earthquake and rare-occurred earthquake) were proposed in terms of the seismic force of column or the displacement of the girder. Then, a detailed design methodology of seismic dowel was proposed to establish the hysteretic model and the simplified calculation formula. Finally, a medium-span beam bridge was taken as an example, six suitable earthquake records were chosen and the dynamic mode was established to apply the nonlinear time history analysis using OpenSees. The analytical results show that the proposed seismic mitigation measure can effectively reduce the displacement of the girder and the residue displacement under frequent-occurred earthquake, and it also can decrease the internal force of column dramatically.

Abstract:This paper proposed an innovative dry joint utilizing embedded steel frame (ELSF), high strength bolt (HSB), and connecting steel frame (CSF) as connecting components to connect the upper and lower precast shear wall panels properly. In order to investigate the feasibility of this novel joint and the load-transferring mechanism of the connectors, experimental study and finite element analysis were conducted firstly; and then the load-transferring route of the joint was analyzed in consideration of the manufacture error of the connectors; eventually the distribution and redistribution of the stress in the connectors from elastic stage to elastic-plastic stage were studied, and the calculation model of the stress in CSF and the calculation formulas of the shear forces transferred by HSBs were deduced. The experimental investigation and finite element analysis show the innovative joint is feasible and its load-transferring route is concise. The mechanism analysis shows the stress in the compressive zone of CSF is larger than that in its tensile zone; and the shear forces transferred by the HSBs at the compressive zone are larger than those transferred by the HSBs at the tensile zone, so the HSBs at the compressive zone slipped firstly.

Abstract:This paper focused on numerical and experimental research on mechanical behavior of thick steel plate members. Firstly, the magneto-elastic equipment was used to obtain the MP-σ curve, and the residual stress of thick plate welded joints was measured by using magneto-elastic method. Secondly, based on the ABAQUS finite element code and subroutine DFLUX, the welding procedure on the butt weld of thick steel plates was simulated. The numerical and experimental results show that: 1) the welding longitudinal residual stress is bigger than the transverse residual stress as a whole; 2) the welding longitudinal residual stress along Y axis increases with the increase of plate thickness, especially when the thickness is less than 60 mm. Moreover, coupling temperature field and stress field, and also considering damage accumulation, weld thick plate members under low-cycle loading were analyzed. The result shows that welding residual stress has a big influence on the distribution of accumulative damage under low-cycle loading.

Abstract:Bolted sphere joints in spatial grid structure are always susceptible to fatigue failure. Based on linear elastic fracture mechanics，the stress concentration factor of bolt thread was used to estimate the fatigue ultimate strength of bolted sphere joints. Based on S-N curve method, a simplified formula to estimate fatigue life of bolted sphere joints was derived by considering the effects of stress amplitude and stress ratio on fatigue life in combination with equilife curve. Compared with the existing experimental results, the predicted formulas can satisfy the engineering design requirements. On this basis, the effects of initial crack length on the fatigue lifetime of high strength bolts were studied and the influence rule was given.

Abstract:According to the current code for seismic design of prestressed concrete structures (JGJ140-2004), this paper discussed the problem of reasonable value about moment magnifying coefficients at column ends of multi-layer prestressed concrete frame structure in the 8 degrees (0.2 g) seismic grade district. Six elasto-plastic analysis models with different moment magnifying coefficients at column ends based on local fiber hinge beam element were established in SAP2000 and PERFORM-3D respectively, and the static elasto-plastic analysis (Pushover) and dynamic elastic-plastic analysis were proceeded. The analysis results show that PC frame designed by the current aseismic codes forms the beam-column hinge hybrid yield mechanism, in which column hinge occupies the priority, adverse to the earthquake. As the moment magnifying coefficients at column ends increased gradually, the seismic performance of local components and yield failure mechanism of structure showed significant improvement. If the moment magnifying coefficients of middle and side columns separately increased at 2.0 and 1.8, PC frame can form beam-column hinge hybrid yield mechanism, in which beam hinge or even beam hinge yield mechanism occupied the priority, favorable to the earthquake. Therefore, suggestions were given to improve appropriately the moment magnifying coefficients at the frame column end in the revision of code for seismic design of prestressed concrete structures.

Abstract:Dependencies of the damping scaling factor (DSF) on variables 1including duration, moment magnitude, fault distance, and local site conditions were examined from 408 acceleration time histories. Then the DSF model was derived 2that can be used to capture the influence of duration and moment magnitude. It is shown that the influence of 3duration and moment magnitude on DSF is significant, but that of 4fault distance and local site conditions is weak. Furthermore, the DSF is heteroscedastic, where the variance is a function of the damping ratio. The significant influence of 5duration and moment magnitude can be captured by inclusion of a linear magnitude term in the DSF model. The heteroscedasticity can be reflected in the standard deviation of the DSF model. The results can be directly applicable to the attenuation model for displacement response spectra of 5% damping ratio and can also provide the reference for the revisions of seismic design codes.

Abstract:The PSO technique was utilized, and the transmissibility was defined as the fitness function for the purpose of performing single optimization and multi-objective optimization of isolation parameters of 1dof and 2dof system respectively. Meanwhile, the feedback control method was considered, and the infinity norm of transfer function matrix was chosen as the fitness. The numerical results revealed that state feedback control could not further optimize the uncontrolled system based on the optimal parameters; however, recalculated operation of the isolation parameters and the controller could achieve this. Finally, the optimization gave consideration to the transmissibility of the control force in purpose of minimizing the energy consumption while optimizing the parameters. Systematic study of this paper could solve the problem of the optimal design parameters of vibration isolation system, and the importance of optimal parameter settings was discussed when control was exerted on the isolation system. Moreover, taking into account the control energy consumption while parameters optimization being performed could have some innovative for traditional isolation and control design.

Abstract:Based on the Fick's Law and Faraday's Law, the chloride-induced corrosion velocity in synthetic concrete pore solution and the time-dependent chloride diffusion coefficient in concrete were experimented by using the four-electrode sensor system. Then the chloride-induced time-dependent corrosion velocity was raised, and the pitting corrosion crack reliability model was presented considering the elastic-fracture mechanics and pitting corrosion model. The experimental results show that the mean corrosion velocity linearly increases with chloride concentration and has the largest value with the increasing of time. The corrosion velocity with time-dependent chloride diffusion coefficient is smaller than the one with time-independent coefficient. The Monte Carlo analysis of pitting corrosion crack shows that the crack is initiated on the 10th to 15th year, and the crack width is decreasingly affected by the increase of the cover and the steel diameter and the surface chloride concentration's decreasing. The study results are referred to predict the chloride-induced corrosion crack and to evaluate the durability of reinforced concrete with pitting corrosion.

Abstract:The physical and chemical properties of concrete specimens (C35) were carefully observed under high temperature (300 ℃, 400 ℃, 600 ℃, 800 ℃)and then put into cool water. After that, the concrete specimens were used for uniaxial compression test. Finally, the failure modes, strength, elastic modulus and other mechanical properties of concrete specimens were obtained. Based on the test results, the temperature and water cooling damage constitutive model of concrete materials were constructed. The four unknown parameters of the constitutive model were recognized with the differential evolution algorithm. The theoretical arithmetic stress-strain curve and experiment curve are greatly consistent. So the study result illustrates the damage constitutive model is well applicable for concrete under high temperature.

Abstract:Through experiments of corroded steel bar specimens under cycling tensile load, the effect of corrosion on mechanical property was analyzed. It's revealed that the mechanical properties and deformability decrease gradually, the yielding plateau gradually shortens or even disappears, energy-dissipation capacity decreases, which makes the anti-seismic performance of structure degenerate, even sudden collapse can happen more easily in earthquakes. Based on the test results, the constitutive model for stress-strain relationship of corroded steel bars was established, which can be used as a reference to the appraisal for residual bearing capacity, durability and seismic behavior of reinforced concrete structure for the future.

Abstract:Earth pressure measured with earth pressure cells often deviates from actual earth pressure. Earth pressure cells measurement experiments were conducted to the underconsolidated and overconsolidated soils. The experimental results show that, for underconsolidated soil, the matching coefficient is slightly greater than 1. With the increase of earth pressure, the modulus of compressibility of soil aggrandizes, and the matching coefficient decreases correspondingly. For overconsolidated soil, due to unloading, a gap between the earth pressure cell sensing plate and the soil is generated, and when the soil is reloaded, the matching coefficient is less than 1 and increases until to 1 or greater than 1 with the increase of loads and the diminution and disappearance of the gap. However, the matching coefficient decreases again if the earth pressure exceeds preconsolidation pressure. Earth pressure correction methods concerning underconsolidated soil and overconsolidated soil were proposed respectively. The corrected results conform to theoretical calculations when the presented methods were applied to the vertical earth pressure measurement correction of earth retaining walls.

Abstract:Slope instability in mountain area often causes serious accidents such as traffic jams, river diversion and significant casualties, which also brings huge economic losses and potential safety hazard. Based on the detailed geological investigation and the test analysis of the slope of the Pingxi river valley, all structural planes exposed of the slope were surveyed, also the historical forming mechanism of the slope was studied. And the research results indicate the slope is formed gradually by reconstruction in the surface and the main deformation is creep. Combined with the site survey and the basic mechanical parameters from laboratory test, the two-dimensional stability numercial modelling in different cases was carried out based on the limit equilibrium method and the strength reduction method. The minimum safety factors derived is 0.94, which can not meet the specification. As a result, a landslide reinforcement scheme was suggested.

Abstract:Based on double U-tube heat exchangers of an actual construction in Changsha, a simulation model of ground heat exchangers was built up with the help of software TRNSYS. Combining the simulation model and orthogonal design, this paper studied the factors affecting soil average temperature around double U-tube heat exchangers, and analyzed effect degree of these factors. The results showed that borehole depth, borehole spacing, borehole amount and fill thermal conductivity had different influence on soil average temperature, and borehole spacing effect was particularly obvious. Finally, value range of borehole depth, borehole spacing and fill thermal conductivity were presented orderly as follows: 60~100 meters,4~5 meters,1.7~2.1 W/(m·K).

Abstract:Based on the layer heat transfer theory, this paper tested the water temperature of the underground heat exchanger at different depth on the basis of the ground-coupled source heat pump system of a Demonstrative Building in Chongqing. After the date processing through two aspects, i.e., the daily temperature of different time and temperature difference between inlet pipes and outlet pipes, this paper compared thermal performance between the vertical double U-shape underground heat exchangers with outlet pipe insulated or not. The comparison demonstrated that: in winter, the rate of improvement in average heat transfer energy efficiency of the heat exchangers with insulated outlet tube is 14.09% in typical winter day, 23.08% in the coldest month and 40.54% in the whole cooling season compared with the heat exchangers without insulation. Meanwhile, the rate of improvement is 10.76% in typical summer day, 28.57% in the hottest month and 41.48% in the whole cooling season in summer. The insulated outlet pipe is helpful to increase heat transfer capacity of underground heat exchanger.

Abstract:This paper took rubber recycled asphalt mixture as research objects, and the low temperature bending test was conducted on small specimen beams before and after freezing-thawing process separately. The low temperature performances of rubber hot recycled asphalt mixture with different rubber powder dosages (6.4%, 9.2% and 14.1%), rubber powder sizes (20 mesh，40 mesh and 80 mesh) and RAP dosages (25%，35% and 50%) were studied. The specimens were scanned before and after freezing-thawing process based on industrial computer tomography (CT) nondestructive testing, separately, and the quantitative analysis for the volume index of specimens was presented. The result shows that the low temperature performance of rubber hot recycled asphalt mixture with 25% RAP, 80 mesh rubber powder fineness and 9.2% rubber powder dosage after freezing-thawing process has the minimal decrease. Compared with hot recycled mixture with neat asphalt, the hot recycled asphalt mixture with crumb rubber asphalt has better durability and low temperature performance. By the comparison of different CT scanning results, the enclosed air void of specimens after freezing-thawing process increased by 20.3%, and the air void number has decreased by 13.8% in 0~25 mm3 volume range and increased by 62.9% in 25~50 mm3 volume range.

Abstract:Deformation sensors were installed on truck axles and calibrated to get the relationships between the sensor readings and tire contact pressure. The truck dynamic loading was measured, and the effects of pavement evenness, vehicle speed and truck weight on the dynamic loading were analyzed. The results show that the average dynamic load coefficients (DLC) are 5%, 15%和20% for good, median, and poor ride quality index (RQI), respectively, and the maximum DLC is more than 90%. The maximum dynamic loads (MDL) are 20%, 55% and 80% more than the static load, and the changing rate of MDL can be more than 90%. DLC, MDL and its changing rate increase with speed, especially when the RQI is poor. The results presented provide the basic data for considering the dynamic load in pavement analysis and design.