Abstract:To analyse size effect of high-strength concrete column under small eccentric loading, experimental analysis was carried out on 3 categories of different sizes of high-strength concrete columns under small eccentric loading. The columns' section size was 200 mm × 200 mm, 400 mm × 400 mm and 800 mm × 800 mm, respectively. Failure mode, ultimate strength, deformation capacity and cross-sectional strain distributing rules were compared to get the size effect law. The results show that the compressive failure mode and cross-sectional strain distributing rules of HSC column under small eccentric loading are basically the same, and the size effect isn't obvious. Ultimate strength and deformation capacity of HSC column under small eccentric loading have size effect obviously. With increase of section size, safety reservation of ultimate strength is reduced and deformation capacity also reduces.

Abstract:According to the theory of truss-arch model, the shear mechanism of reinforced concrete beam was analyzed, and formula of shear bearing capacity was proposed. In this formula, softening effect of concrete and the arch function were taken into account, and the coefficients in the formula were amended with experimental data. When the performance difference between the structural material and the original material is huge, the code formula of shear bearing capacity calculation is inapplicable. After the computation, the ratio of the results calculated by truss-arch model theory formula and the results calculated by the current code formula was close to 1, and the standard deviation coefficient and coefficient of variation were smaller than those of standard formula results, and the results calculated by truss-arch model formula were in good agreement with the experimental results. The collected experimental data was calculated with the shear capacity formula in ACI318-08, and the calculation results showed that United States building code was more conservative than the standard of China. The results indicate that the shear bearing capacity formula based on truss-arch model can be used for computation of shear bearing capacity of reinforced concrete beams.

Abstract:A fiber beam-column element in conjunction with zero-length elements attached to its ends was proposed to simulate the flexural and shear mechanism respectively. Based on the Limit State Material model and the Shear Limit Curve model provided by OpenSees, the nonlinear shear effect of reinforced concrete column and its coupling with the flexural effect were defined. The reliability of the proposed model was validated by means of comparisons with existing test results. Finally, a plane frame from in-situ pushover test was simulated. It is shown that the proposed method, by taking the nonlinear shear effect into account, produces satisfactory results for frame columns with shear strength and stiffness degradation, while the conventional fiber beam-column element can hardly simulate actual flexure-shear failure mechanism for columns characterized by insufficient transverse reinforcement. The proposed method is applicable for nonlinear analysis of reinforced concrete frame structures with shear deficiencies.

Abstract:An optimal distribution strategy of the energy dissipation dampers installed in the bottom stories of frame structures was put forward based on dynamic characteristics of base-isolated system. Firstly, the number of stories was defined by calculating the ratio of site characteristic frequency ω and bottom isolation stories natural frequency ωn of energy dissipation structure. Then, with regard to storey drift permissible value, the quantity and installation positions of dampers were defined through several simple calculations. 2 sets of actual strong earthquake records and 1 set of artificial acceleration time-history curve for a 10 stories frame structure were selected to conduct the time-history analysis under frequently and rarely earthquakes by ETABS software and Perform-3D software. The results show that the dynamic characteristics of energy dissipation structure in which the dampers are installed in lower stories are similar to those of base-isolated system.

Abstract:On the basis of the crack characteristics of aging RC beam bridges, the cross-section of RC simple beams with different pre-cracking levels were strengthened by the externally bonded FRP（EB-FRP）and the FRP-bolt hybrid bonding（HB-FRP）respectively to check the strengthening characteristics of HB-FRP. The flexural test with symmetrical loading on two points was conducted to study the mechanical behavior and failure mode of pre-crack beams strengthened with EB-FRP and HB-FRP. The influence of pre-cracking level on the FRP initial debonding load and FRP utilization ratio was assessed respectively. The test results show that the flexural capacity of pre-cracking beam strengthened with HB-FRP can be improved by 30%~44% compared with the one with EB-FRP. The failure mode has been changed from FRP brittleness debonding of beam strengthened with EB-FRP to obvious ductility failure of beam strengthened with HB-FRP. Furthermore, the crack distribution of RC beam has obvious influence on the FRP initial debonding load, the FRP utilization ratio and the failure mode of strengthened pre-crack beams.

Abstract:Aiming at confined concrete with stirrups and carbon fiber reinforced plastic(CFRP) respectively, the major influence factors of mechanical behavior of confined concrete under axial compression were studied based on reported experimental data. The equations for calculating the peak stress, peak strain and ultimate strain were proposed respectively for confined concrete with stirrups and CFRP. Contrastive analysis shows that the behavior of confined concrete with stirrups is better than confined concrete with CFRP in low characteristic value, whereas the conclusion is contrary in high characteristic value.

Abstract:Super-servicing reinforced concrete poles (RCP) which come from a road section in a power grid, including six pole shafts and six specimens with a mid-span steel joint, were selected as samples to conduct a flexural strength test, in which three shafts and three poles with steel joint in the middle span were strengthened by CFRP in the longitudinal direction. The mechanical behavior and failure mechanism under different CFRP layers pasted were comparatively studied. Based on the measured test data, the calculation methods of strength and stiffness were investigated, and the mathematical expression of stiffness degradation mechanism was proposed. The result shows that the final failure mode of CFRP strengthened poles is the local bond failure between CFRP material and the external concrete, and the longitudinal CFRP is snapped. The process of damage is rapid and brittleness. The mean strain of cross-section is in accord with the assumption of plane cross-section. The strength degradation of shaft specimens without strengthened is throughly serious. As for the strengthened poles, the bearing capacity and stiffness under each forcing stage are improved with different levels. The damage of strengthened specimens develops faster and more intensive than that of none-strengthened ones. When multi-aspects are synthetically considered, there is a suggestion that double layers of CFRP should be pasted along the longitudinal in the joint of the site within a certain distance, and the single layer of CFRP should be adopted in the shaft.

Abstract:Steel H-beams with corrugated webs can provide high shear-buckling resistance with very thin webs, which results in saving of steel. Common beam-to-column rigid connections are not suitable for H-beams with corrugated webs, so 2 types of rigid connections are proposed .In this paper,2 static tests of beam-to-column rigid connections of H-beams with corrugated webs were conducted. And the test results were compared with the results from finite element analysis and the results calculated from the practical design formulas to verify the validity of the results from ABAQUS FEA and reliability from the practical design formulas. Parametric studies were carried out to investigate the bearing capacity of the pinned connection with variations in the thickness of the endplate, the connecting plate and the corrugation at the breaking point.

Abstract:To reveal distribution characteristics of member initial stresses, nine experimental prototypes in span of 4 m, 5 m and 6 m were employed. To analyze effects of member initial stresses on ultimate capacity of space truss, a prototype in span of 6m was applied. Meanwhile, the results were compared with those of Abaqus nonlinear FEM which were based on elastic-perfectly plastic model and Marshall Mode. Initial stress test shows that some initial stresses approach or even exceed stability stress. It is shown that the test ultimate capacity decreases by 17.9% than that of Marshall Mode, and the safety margin of structure is just 1.25. The impact mechanism of member initial stress consists in damaging structure initial symmetry, producing member initial bending and prompting press member buckling in advance. Member initial stress must be taken into account when space truss design, especially Fully-Stress design, is conducted.

Abstract:Based on fundamental principles of the vector form intrinsic finite element (VFIFE), the basic formulas of 4-node quadrilateral membrane element were first derived in this paper. The procedure for the determination of pure nodal deformation through reverse movement was elaborated, and the method for the calculation of internal nodal forces through deformation coordinate system was presented. Feasible approaches were also proposed for several issues for 4-node membrane element, including the location statuses and the numerical integration for internal forces. A computer program of 4-node membrane element was developed. By the analysis of the numerical example, the correctness and validity of the membrane element theory and the computer program were verified. Then the approach was applied for more analysis of large deformation and large rotation problems of membrane structures, including cushion inflating and cloth draping.

Abstract:A buckling loads formula based on Generalised Beam Theory (GBT) was proposed, which could be used in non-linear elastic metallic materials thin-walled compressed members, such as stainless steel. By introducing non-linear stress-strain relations and instantaneous elastic modulus, the modifications were incorporated in the conventional GBT, and the expressions were formulated to calculate buckling loads of stainless steel members buckling in local, distortional and global modes. Compared with the existed test results, it is shown that linear elastic method cannot deal with stainless steel, while the results of proposed method are much more reliable. Moreover, the modified GBT method with deformation plasticity theories produces safer results, which could be used in determining buckling loads of non-linear metallic materials thin-walled members in compression, as well as structural design and further researches.

Abstract:Concrete pipe piles, whose internal surface is usually closed and external one is exposed to chloride environment, are widely used in marine environment. Based on Fick second law and the boundary condition of pipe pile, the analytical solution to chloride diffusion equation was deduced with the method of separation of variables. The solution comprises two parts: a stationary solution consisting of Bessel functions, and a transient solution. This is different from the traditional analytical solution that is based on semi-infinite boundary condition. Applying this result to a typical PHC pipe pile, the diffusion of chloride concentration was analyzed. Furthermore, the effects of the ratio of outer radius and inner radius, diffusion coefficient and protective concrete cover thickness on diffusion of chloride concentration were also discussed. When the ratio of outer radius and inner radius equals 1.5, the decay rate of secondary segment of transient solution is 4 times larger than that of the primary part. This example provides a computational basis for the corrosion of steel bar and some reference for durability design of pipe piles as well.

Abstract:In order to study bearing characteristics of deep rock-socketed piles (hr/b≥5), based on the test results of self-balancing test of zh12 pile in Qingdao Gulf Bridge, the bearing characteristics of deep rock-socketed piles were analyzed. The relation between sides shear resistance of the piles and its displacement socked in soft rock was researched, and the relation between end bearing resistance and displacement was studied. The hyperbolic distributions on the load transfer method were compared to them. The results indicate that Q -S curve of large diameter deep socketed pile in soft rock area declines slowly, approximately in linear distribution. According to the fitting curve based on measured results, it is feasible to fit the relationship between sides shear resistance and its displacement by using hyperbola. The parameter of 1/b also reflects the ultimate side resistance values of piles. The load-displacement curve at the top of pile is similar to the hyperbolic form. By using the parameters of a、b obtained from fitting curve, the calculated load-displacement curve on top of pile is close to the measured curve of self-balance method. At last, according to the measured results, the value range of parameterαin empirical formula was analyzed under different states of axial compressive strength.

Abstract:In recent years, the round deep foundation pits engineering gradually appears in Chengdu Plain whose strata are mainly sand-cobble soils. However, there are no proper calculation methods of earth pressure in retaining structure like this and distribution mode of the pressure is unknown. With the use of elastoplastic numerical simulation method involved in interaction between retaining piles and soil, the distribution law of earth pressure of the round deep foundation pit retaining structure is determined. The result shows that distribution of earth pressure on a pile is triangular and the maximum lies in the location of pit bottom, but the average value of the pressure is less than Rankine active earth pressure. Model tests have also been carried out so as to verify the distribution mode. As for the test model, the values obtained by the numerical simulation method are approximately similar to the experimental results in the distribution law as a whole, which to some degree suggests the rationality of the numerical simulation results.

Abstract:It is vital to get the accurate data of the shear strength parameters of gravel soil with different water content and compactedness before they conduct the stability analysis for gravel soil roadbed. Under several test conditions, a series of direct shear tests were performed by using some gravel soil samples obtained from a selected roadbed which is under the influence of water level fluctuation. The corresponding results show that the gravel soil cohesion increased as the water content of fine soil increases till it meets its peak value, then it will decrease as the water content keeps increase. However, the internal friction angle will decrease slowly with the increase of water content of fine soil in the initial phase, and then it will decrease rapidly as the water content keeps increase. And on the other hand, the fitted shear strength parameters calculated from the test data has been influenced by the pre-load values that used to prepare soil samples, especially for the condition that the pre-load value less than the normal stress value applied in the direct shear test. All in all, the fitted shear parameters will be controlled by the relationship among water content, pre-load value and normal stress.

Abstract:An analytic method was used to study the dynamic response of track system on reinforced embankment subjected to moving traffic load. Based on Biot's dynamic poro-elastic theory, dynamic analytical model of track system and reinforced embankment was established. The rails were described as an infinitely long Euler beam subjected to moving axle loads and sleepers were represented by continuous mass. Reinforced embankment embedded between track system and poro-elastic subsoil was modeled as a transversely isotropic layer. Subsoil was fully saturated poroelastic medium governed by the Biot's theory. Using the Fourier transform, the governing equations were then solved analytically in the frequency-wave-number domain. The time domain responses were obtained by the inverse Fourier transform computation. The influences of the train velocity, thickness of reinforced layer, load amplitude and reinforcement's ratio on the displacement responses of rails were carefully investigated. Computed results show that the vertical displacement of rails increases with the increase of load speed initially and decreases later. The displacement of rails with reinforced embankment is less than the ones without reinforced embankment. The displacement of rails increases with the increase of load amplitude and decreases with the increase of reinforcement's ratio.

Abstract:Cement-based material has different spalling and physical properties after exposing to different high temperatures. The spalling and physical properties of cement-based material with different additives after exposing to instantaneous high temperature were analyzed. The results show that: all samples have no spalling both at 100℃ and 300℃, but spalling completely at 600℃. The compressive strength and flexural strength of the cement-based material at 100℃ decrease by the rate of 15% and 30%, and the value at 300℃ is close to that at room temperature and decreases rapidly after exposing to 600℃. Both the compressive and the flexural strength of samples with 20% slag powder and 10% silica fume increase with the increase of the temperature when the temperature is below 300℃. SEM reflects that after exposing to 600℃ for 2 hours, C-S-H has changed into a looser structure, and the continuously cement paste is separated into segments.

Abstract:High permeability is an important characteristic of pervious concrete. For the existing permeability testing devices of pervious concrete, the specimen sidewall leakage is serious due to the large numbers of open pores on the surface of specimens. To solve the problem, a new permeability testing method for pervious concrete was developed and a composite sidewall structure with waterproof daub, flexible rubber cushion and rigid sleeve sidewall was proposed. Meanwhile, the strength and permeability of pervious cement concrete are incompatible with a reciprocal relationship. However, limited research has been conducted on the relationship between them. Effects of water-cement ratio (W/C), aggregate-cement ratio and porosity on the properties of pervious concrete, including strength and permeability, were studied. Furthermore, strength-porosity model, permeability-porosity model and strength-permeability model were established. Tests reveal that: a) There is an optimum W/C of pervious concrete, at which strength reaches the maximum; b) The relationship between the strength and W/C shows a downward quadratic curve, and the permeability is proportional to porosity and aggregate-cement ratio; c) The relationship between strength and permeability of pervious cement concrete can be well fitted with the Lorentzian function, and the strength decreases when the permeability increases, but the rate of reduction decreases gradually. The optimum combination of strength and permeability should be determined based on the specific engineering requirements in design.

Abstract:The electrical properties of fly ash, slag and limestone powder-cement paste were studied by the methods of Cyclic Voltammetry and AC Impedance Spectroscopy. The results of electrical test were fitted by equivalent circuit. The correlations between electrical parameters of paste and unevaporable water content, pore structure by mercury porosimetry were compared. The results show that there is a positive relation between the unevaporable water content and the electrical resistivity of paste. If the unevaporable water content is higher, the hydration degree is higher and the electrical resistivity of paste is higher. The electrical resistivity of paste is increased with fly ash and slag, and it is unaffected with limestone powder of 5% dosage. The resistance Rs of pore solution of paste is increased with the prolongation of hydration, and the changes of resistance Rs and the electrical resistivity are unanimous. The resistance Rp and electrical capacitance C of gel are related to C-S-H content, and there is a negative relation between the resistance Rp and electrical capacitance C of gel. The complexity of pore structure of paste is increased with the prolongation of hydration. The constant phase angle exponent P by AC Impedance Spectroscopy is decreased and the value of fractal dimension by mercury porosimetry is increased.

Abstract:In order to solve the problem that the cement-based anchoring material has low early-strength and its volume contracts obviously, it is necessary to develop anchoring material which has characteristics of early-strength, expansion, high strength etc. Based on the ettringite with characteristic of early strong and expansion, the properties of the grouting mortars modified with alunite and gypsum were studied. The results show that at early stage the expansion is rapid and expansion is stabilized at later stage. The setting time can be controlled in 0.5～1.5 hours, and compressive strength of 1 day and 3 days reaches 20 and 40Mpa, respectively. The micro-analysis shows that with the increase of curing-time there are plenty of expansive ettringite crystals and porosity decreases. The limit load test shows that the pullout force of 1metre sample at 14 days is 93 KN, which is larger than the average lever of 1.5～2 meters samples.

Abstract:In-situ experiments and investigation of evaluation indexes were performed to study the subway-induced ground-borne noise in buildings along the subway lines. The characteristics of ground-borne noise in buildings were summarized from various aspects by analyzing the experimental data. The factors such as the spectrum width, the analyzing time and background noise effect on the results of evaluation indexes, were further investigated. The correlation between different evalution indexes was analyzed, and the deficiencies of the indexes of noise evaluation in the environmental noise control codes of China were discussed.

Abstract:It is worthwhile for saving energy and protecting environment to use conductive concrete as an indoor heating engineering material. Indoor temperature is the key concern of heating system. Based on convection, radiation and Joule effect, a method to calculate temperature of concrete and indoor air was presented. The method did not need to model the air, which simplified the preprocessing. The numerical result agreed with experiment satisfactorily, with a difference of 2.40%, which proved the correctness of the model. Numerical tests of different conditions showed that electrical resistivity with higher potential than power voltage and concrete thickness was the key to increase heating efficiency.

Abstract:A free cooling unit with a pump-driven loop heat pipe was designed for internet data center (IDC), and its components and working processes were described. The experiment system for the developed prototype was built and the comprehensive studies were conducted. The experimental results demonstrate that the coefficient of performance (COP) of the unit can reach to 5.88 when the temperature difference between IDC indoor and outdoor is 10℃, and it will be 10.41 when the temperature difference is 18℃. When mass flow rate of the working fluid in the unit changes within a certain range, namely the gasification rate of the fluid being between 2% and 50%, there is no significant changes for the heat transfer capacity. And there is an approximately linear relationship between the capacity and the temperature difference. Meanwhile, with the increase of the system resistance, both temperature difference of the fluid between inlet and outlet of the evaporator and the proportion of the sensible heat to the capacity also increase.

Abstract:STEVE（Screening Tool for Estate Environment Evaluation）is a statistical model through regression analysis. It can predict the air temperature by climate and urban morphology predictors for Singapore estate, while it hasn't been proved valid in other areas. Consequently, three groups of validation tests in Guangzhou area were conducted, one using the original data in the literature and the other two using experimental data from the field measurement. It is shown that STEVE tool can meet the engineering accuracy and can be used as a simple temperature prediction model tool in urban planning and design process in Guangzhou area and other cities with similar climate conditions. Besides, the STEVE tool can be optimized further to expand its applicable scope.