Abstract:In order to study the seismic performance of steel reinforced ultra-high strength concrete frame structure, three quasi-static cyclic tests of steel reinforced super-high strength concrete frames with one-story and one-bay were carried out. The global failure modes as well as the local failure at the bottom column-end under low-cycle reversed load were examined. The hysteretic and skeleton curves were analyzed, and the strain of the beam end and column bottom was evaluated. Meanwhile, the loading and displacement values at different stages were evaluated, and the global deformation of the entire structure was further understood through the development of local strains. Furthermore, the strength, ductility, and energy-dissipation capacity of the frame structures were obtained through the tests. The test results show that the steel reinforced ultra-high strength concrete frames exhibit good ductility and energy dissipation capacity, showing little discrepancy between forward reverse ductility coefficient, slow degradation of strength and stiffness, and plump hysteretic curve. It is also concluded that most of the earthquake energy is dissipated in columns, while the constraint effect of beams improves the global stability of frame structure as well as energy dissipation capability especially after the load-carrying capacity decreases to 80 percent of the ultimate load, which provides the effective load-carrying capacity in structures under severe earthquakes, and thus sudden collapse of the frame structure can be avoided.

Abstract:In order to study the seismic behavior of composite concrete and double steel plate shear walls with binding bars, sixteen specimens were tested under reversed cyclic lateral load, and the numerical simulation by using the analytical software OpenSees was also conducted for the composite concrete and double steel plate shear walls. On the basis of experimental and numerical analysis, the main parameters affecting on the seismic behavior of the composite shear walls were evaluated. All the results indicate that the factors of aspect ratios, axial compression ratios, and binding bar spacing significantly affect the seismic behavior of the composite shear walls. As the aspect ratios of the composite concrete and steel plate shear walls increase, the initial stiffness, peak load, yield load, post-yield stiffness, and energy dissipation capacity decrease obviously. The axial compression ratios exhibit an effect on the degradation of the post-yield stiffness. In addition, the close spacing of binding bars can improve the bearing capacity and energy dissipation capacity of the composite shear walls, and reduce the degradation of the post yield stiffness.

Abstract:Based on the dynamic theory of taut string and Euler beam as well as the dynamic equilibrium conditions at the joint of cable and beam, the in-plane free vibration theory of a cable-stayed beam was established. The transfer matrix method and boundary conditions were considered to solve the eigenvalue problem of the in-plane free vibration of a cable-stayed beam structure. Meanwhile, a finite element model of the cable-stayed beam was also developed to verify the proposed theory and method. he predictions by the proposed method match well with those of the finite element analysis. Finally, the parametric analysis was conducted, which shows that the fundamental dynamic properties of the cable-stayed beam are improved by replacing steel cables with CFRP cables.

Abstract:Based on the Euler-Bernoulli beam theory (EBT), a new model for free bending vibration problems of rotating tapered beams using spline finite point method (SFPM) was investigated. The beam was discretized by a set of uniformly scattered spline nodes along the beam axis direction instead of meshes, and the displacement field was approximated by the cubic B-spline interpolation functions. Both of the variations of cross-sectional dimension and the rotating centrifugally stiffened effect were considered in the proposed model, and the global stiffness and mass matrices of the structures were deduced based on the Hamilton principle. Computer programs were compiled to study the dynamic properties of rotating tapered beams. The finite element model (FEM) for the rotating tapered beams by using ANSYS was also built for validating the proposed model. The results show that the present results agree very well with the results of other reported literatures and the FEM, and the proposed model has the advantages of good computational accuracy, high modeling efficiency, simple boundary conditions, and convenience for compiling computer program. It is capable of studying the free bending vibration of rotating tapered beams with the variation of boundary conditions, taper ratios, cross-sectional types, rotating speeds, and hub radius. Both the taper ratios and rotating speeds have important roles on the dynamic properties of rotating tapered beams through parameter analysis.

Abstract:In order to fully use the seismic bearing capacity of sliding piers to improve the seismic performance of continuous bridges，the acceleration activating locking dowel was developed and installed between the piers and beams. To investigate the principal influencing factors on the damping effect of the locking dowel and optimize the damping performance of the locking dowel, taking a seven-span continuous bridge as an example, five test parameters including acceleration activating thresholds, locking clearance, pier height, site condition, and connection stiffness were studied. On the basis of the principle of the orthogonal experiment design, five levels for each factor and twenty-five text schemes were considered. The primary and secondary influencing factors on damping effect were obtained by the extreme difference analysis. Furthermore, the influences of the activating threshold range and connection stiffness on dampingeffect were analyzed. The investigation results indicate that the acceleration of the pier top and the natural vibration period of the pier are closely related, and the acceleration activating thresholds can be determined from the natural vibration period of the pier. Moreover, the damping effect of the device is significantly influenced by the connection stiffness.When the connection stiffness increases, the damping effect is improved.

Abstract:For better understanding of the mechanical property and constitutive relation of carbonated concrete under cyclic load, cyclic load and monotonic load tests were carried out on prism specimens. Considering the effect of section sizes on carbonated concrete member, the hysteresis loop and skeleton curve of the specimens were obtained, and the effects of carbonization on specimen failure mode, concrete strength, elasticity modulus, peak strain, and ultimate strain were analyzed from carbonation rate perspective. It's revealed that, because of the accumulated internal damage under cyclic load, the stress-strain curve of carbonated concrete decreased significantly, and the ductility was less than that under monotonic load. Furthermore, the peak strain of carbonated concrete decreased a little, peak stress increased, and ultimate strain decreased with the increase of carbonization depth. Based on the test results, under the consideration of carbonation rate and the introduction of the parameters at stress-strain curve descending branch, the stress-strain constitutive relation of carbonated concrete under cyclic load was established, which agreed well with the experimental values.

Abstract:To accurately predict the shear capacity of square concrete filled steel tube (SCFST) columns, a theoretic model was established based on modified compression field theory. In this model, compatibility and equilibrium relationships were taken to consider the axial-flexure-shear interaction, and a general formula of shear capacity of SCFST was deduced by dissecting shear mechanism. Due to two different failure modes observed in previous tests, two different failure criterions were given respectively. The proposed model was applied to the 17 existing column specimens, which predicted well the shear capacities of the test specimens. The results show that the proposed model not only can be utilized to evaluate shear capacity of SCFST subjected to axial force, flexural moment, and shear force, but also can be employed to verdict different failure modes. The calculation results of the proposed model are credible, and the model is effective.

Abstract:To study the axial constraint effect on fire resistance of partially encased concrete column (PEC column), an experimental study and a numerical simulation were carried out. Two unprotected PEC columns were tested under ISO-834 standard fire. The two columns were bent in strong axis subjected to axial load and eccentrically compression load, respectively. The distribution of temperature field on the cross-sections, axial and lateral deformations, fire resistance, and failure modes of the specimens were recorded and presented. The test results show that the restrained column applied end moment exhibits higher lateral deformation rate than that of the axially loaded column, and the failure modes are obviously different. The fire resistance of the restrained column applied with end column is higher than that of the axially loaded column under the same load ratio. Generally, fire resistance limits of the two PEC columns are all short. Moreover, a comparison between numerical analysis and test results shows good agreement. Therefore, the numerical model provides sufficient accuracy to predict the fire resistance of the restrained PEC columns, which could be used for further parametric analysis.

Abstract:To obtain the elastic horizontal displacement spectra that can be applied to displacement-based seismic design, the influences of moment magnitude, rupture distance, and site classes on the displacement spectra were examined using the ground motion prediction equation of Campbell and Bozorgnia. The deficiencies of design spectra in existing seismic design code of buildings (GB 50011-2010) were pointed out and an elastic horizontal displacement spectra model using double parameters, peak ground acceleration (PGA) and peak ground velocity (PGV), was proposed to compensate for the deficiencies. The results show that the starting period of the constant displacement plateau (TD) is an important parameter to determine the spectral shape of the displacement spectra. It is mainly affected by moment magnitude and is increased significantly with the increases of the moment magnitude. The peak ground velocity-to-acceleration (PGV/PGA) ratio is strongly dependent on the moment magnitude, and thus the significant influence of the moment magnitude can be captured by the inclusion of the PGV/PGA ratio in the model. The proposed model is capable of fitting real displacement spectra and can be applied to the seismic design codes by providing the peak acceleration and velocity zonation maps for each seismic precautionary level and giving the peak acceleration and velocity site amplification factor corresponding to the each level in the seismic design codes. The results can provide the reference for the revisions of seismic design codes in our country.

Abstract:An information management system for structural behavior monitoring, named MIMS, was developed based on big data technology. The system performance was improved by using three layered browser/server architecture and multi-server coordination mechanism. To satisfy the requirements of big data processing, mongoDB database was employed in the data management platform, and the structure and format of the database were discussed. The developed system was applied to the structural behavior monitoring of Ningbo South Station, and the interfaces were illustrated. The application results of the system show that approximately 10 GB data can be remotely received every day, and the massive monitoring data can be processed efficiently.

Abstract:To investigate the fatigue performance of anchor plates, a composite beam cable-stayed bridge was taken for example in this study. A loading model in the new standard for steel bridge and the rain-flow method were applied to gain fatigue load spectrum, combined with a three dimensional finite element model to identify the typical structural details and fatigue stress spectrum of anchor plates. Initial surface cracks were imported in the typical details, and stress intensity factors of crack tips were calculated. The stress intensity factor and crack size were regressed by substituting in Paris formula, which were integrated to gain the fatigue life of typical structural details. The assessment of fatigue life for anchor plates based on fracture mechanics was then established. The results show that the fatigue life for anchor plate based on fracture mechanics is over 100 years, satisfying the requirement of design and utilization; the crack is developed very slowly in the early time, but when it reaches 10 millimeters, 50% to 80 % of its fatigue life is consumed. Therefore, reinforcement should be timely applied to the anchor plates.

Abstract:On the basis of the mechanism of stiffness degradation and torsional divergence in long-span suspension bridges subjected to static wind, two criterions have been reasonably chosen for the evaluation of torsional divergence in smooth flows and turbulent flows, respectively. In a concerned bridge immersed in smooth flows, taking into account the easy estimation of the deformation conformation and the simple evolution rule of main cables, the vertical displacement at the mid-location of main cables was adopted as a criterion to estimate the stiffness degradation and torsional divergence. When the vertical displacement reaches a critical value, the phenomenon of aerostatic torsional divergence will occur. In the case of turbulent flows, however, the bridge structure will experience complicated and stochastic dynamic responses in a form of multiple modal coupling. Consequently, the criterion used in smooth flows is not applicable to this case. To this end, a new criterion based on the identification of the length of the main cables in time domain was put forward. The criterion can be described as that, when the minimum value of the main cable length indentified in the whole time domain reaches the value being equal to or very close to the zero-strain length, the bridge will be affected by the intermittent torsional divergence because of the softening of the main cable subsystem. It is shown that, using some static and dynamic finite element analyses, the phenomena of the aerostatic torsional divergence behavior of long-span suspension bridges in different types of field flows can be well explained with this new criterion.

Abstract:Based on long-term monitoring data in Nanjing No.3 Yangtze River Bridge, a long-term trend assessment and dynamic early warning method on the girder deflection of the steel cable-stayed bridge with statistical theory was proposed. First of all, the variation characteristics of the deflection with temperature were analyzed. The data of 0:00-1:00 at night was selected. The influence of vehicle load was removed, but the integral temperature effect was considered. The reference value of the deflection due to dead load was obtained. Secondly, the assessment was implemented by the linear moderate model and grey correlation analysis according to actual fact. Taking the data from 2007 to 2010 as an example, the results show that the established methods are consistent with long-term trend and helpful for the further inspection of bridge defects. Finally, two-stage (yellow and red) early warning line was set up based on a certain guarantee rate. Considering the influence of traffic volume variance and cumulative damage, the dynamic warning line was established. Two samples of period before and after the snowstorm in 2008 and traffic volume growth were taken for verification. The results show that the proposed dynamic warning line not only can be effectively applied to the daily operation or emergency situation, but also achieve synchronous update according to the actual condition of the bridge.

Abstract:A dynamic experiment for CRTSⅡ slab ballastless track - bridge system under the train running condition was carried out. The dynamic response of CRTSⅡ and standard 32m simply supported prestressed concrete box girders was measured under CRH380A-001 trains traveling at the speed of 285 to 350 km/h. Through the field collection and data analysis, the vertical and transverse acceleration amplitudes of the rail, track plate, base plate, and beam panel were obtained. The vertical and transverse absolute displacements of the pier top were also obtained. The results show that abrupt wave crests appear, as the acceleration of each structure increases fast and then reduces significantly when the train speed reaches about 295 km/h. At that time, the vehicle induced acceleration response of the rail-track plate-base plate-beam panel has a significant decline trend, and the vibration attenuation is relatively obvious. Furthermore, the simplified method for computing the dynamic deflection of a girder was analyzed based on the measured natural frequency and damping ratio of the girder, and the calculated values are close to the measured ones. The study results can provide the basis for improving the numerical analysis model and verifying the calculation results.

Abstract:To solve the problem of insufficient consideration of interlayer contact state between leveling course and asphalt pavement, a new interlayer contact factor was adopted in this paper. Based on the semi-contacted bi-layer beam mechanical model, a calculation formula was derived, and the bending test on a bi-layer beam was designed to determine the interlayer contact factors under different concrete surface treatments and spraying volume of modified asphalt condition. Meanwhile, the mechanical responses were analyzed by using the analysis software ANSYS under different interlayer contact states. The results show that the interlayer contact state under artificial chiseling treatment is the best, and the maximum value of the interlayer contact factor is 0.607． The stress state of the asphalt pavement structure in the continuous layer contact state is obviously worse than that of the complete continuous contact condition. Taking the shear stress of asphalt pavement under cutting groove measure as an example, the maximum stresses in XY and YZ directions are 0.412 MPa and 0.421 MPa, while the stresses are 0.195MPa and 0.222 MPa under the complete continuous contact condition, and the former are larger than the latter by 111% and 91%, respectively. It shows that the complete continuous contact condition is not reasonable in the design of deck pavement structure． Compared with the fully continuous state, the stress state of asphalt pavement is obviously deteriorated, which indicates that the layer of the pavement layer and the layer of the asphalt overlay can be enhanced when the pavement is laid.

Abstract:In order to analyze the improvement effects of rubber particles on low temperature performance of epoxy asphalt mixture, the low temperature performance of the epoxy asphalt mixture with different rubber particles volume content was studied choosing the rubber particles with appropriate shape feature and hardness, based on the flexural strength, flexural strain, flexural stiffness modulus, temperature of brittle point and strain energy density. The moisture susceptibility and high temperature performance of epoxy asphalt mixture with different rubber particles volume content were then validated by laboratory tests. The results show that the less the flat and elongated particle contents of rubber particles are, the greater the Shore A hardness of rubber particles is, the better the compaction effect and raveling resistance of rubber particles epoxy asphalt mixture are. The influence of rubber particles on flexural strength, moisture susceptibility and high temperature performance of epoxy asphalt mixture is not significant. However, the rubber particles with appropriate content can significantly increase the low temperature deformability of epoxy asphalt mixture, which can reduce the temperature of brittle point for epoxy asphalt mixture, and improve the low temperature performance of epoxy asphalt mixture. Compared with the epoxy asphalt mixture without rubber particles, the strain energy density of the epoxy asphalt mixture with rubber particles volume content of 5% is increased to 108.0 % at -15 ℃.

Abstract:In order to evaluate the segregation level of bituminous pavement quickly and effectively, the digital image processing technique was adopted in studying the heterogeneity of bituminous pavement. The drawbacks of common evaluation methods on image processing of bituminous pavement segregation were firstly discussed, and a new method of evaluating the bituminous pavement segregation was proposed, which is based on the analysis of the macroscopic construction width of the concave area in pavement texture. This method is to get the binary image by taking photos of the concave areas in macroscopic construction, and defines the average width of the related concave area in the binary image as the macroscopic construction width K of bituminous pavement, and then builds a model based on the construction width K and depth TD to evaluate the aggregate segregation level of bituminous mixture. It is found that the construction width K is correlated with the conventional construction depth measured by the traditional manual sand patch method, which better characterizes the aggregate segregation level of bituminous pavement.

Abstract:The retaining structures including the balance weight retaining wall were set up outside the new embankment unilaterally in mountain region highway embankment widening reconstruction. The finite element software phase2 was used to build a detailed numerical model for describing the interaction between soil and wall, which introduced the joint element. Based on two-step approach, the nonzero displacement constraints were imposed on metope to simulate translational and rotational (RBT) active extraversion deflection of the retaining wall. The effect of the different deformation amount of active extraversion deflection in the retaining wall on the embankment differential settlement was analyzed. The results were verified and compared with the test results of geotechnical centrifuge model. It shows that the rigid retaining wall is interacted and interdependent well with the new and old embankment. Additional differential settlement, which is caused by the active extraversion deflection of retaining wall, is 51% to 67 % of total differential settlement when the ratio of the extraversion value to wall height is 1% to 3 %.

Abstract:An electrical floor heating system was designed by using carbon fiber tapes (CFT). The heating performance and economic applicability of the heating system were also analyzed. The heating system was constructed in a bedroom with good heat insulation, and the temperature sensors were arranged at the layers of the floor and near the floor for 24 h duration tests. Temperatures at specified locations were monitored and analyzed to study the performance and the energy consumption of the heating system. The results showed that the CFT electrical heating system could keep the indoor temperature constant within the preset range; the temperature gradient in lateral direction was within 3 °C when the carbon fiber tapes were reasonably arranged in the floor. Meanwhile, compared with that of the traditional heating methods, the economic applicability of the proposed heating system was also studied. The results show this CFT electrical heating system has the advantages of less construction cost, medium operation cost and less overall cost.

Abstract:The Kriging model was introduced to detect and diagnose the faults in the chillers of building air-conditioning systems. This model was built and validated by using the normal data from ASHRAE RP-1043. The methods of T-statistic and exponentially-weighted moving average (EWMA) were compared by the sensitivity of performance indexes. The results show that the EWMA can achieve better performance sensitivity. Combined with the EWMA, Kriging model and the rules of fault diagnosis, the chiller faults like condenser fouling, refrigerant overcharge, refrigerant leakage, non-condenser gas, reduced evaporator water flow rate, and reduced condenser water flow rate were diagnosed using the measured data from ASHRAE RP-1043. The diagnosis results show that the chiller faults at different levels can be accurately and efficiently detected and diagnosed by using the Kriging model.