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1.
In order to investigate the fire resistance of steel columns with partial fire retardant coating damage in fire, based on the differential equation of equilibrium on each portion of steel column, the deflection of steel column after the fire retardant coating damage was derived, with the pined ends and rigid ends of the columns at elevated temperatures. The critical temperature calculation method was proposed for partial fire protection damage and axial restrained steel columns by taking the edge yielding criteria. The deflection and axial displacement were verified by finite element method at elevated temperature. With a case study, the critical temperature and relationship of axial force and temperature were obtained for pined column with axial restraint. It was shown that the axial force of the steel column at elevated temperatures was increased and the critical temperature was decreased by the axial restraint. The longer the fire retardant coating damage was and the higher the axial restraint was, the lower the critical temperature was. 相似文献
2.
The effects of the restraint stiffness ratio, the axial load ratio and the column slenderness on the buckling temperature and failure temperature of a restrained H section steel column under axial load in fire were studied with a calibrated finite element method (FEM) model. And the calculation methods of buckling temperature and failure temperature were proposed. The effect of the restraint stiffness ratio on the buckling temperature and failure temperatures could be expressed with an exponent curve while polynomial functions was appropriate for the effects of the axial load ratio and the column slenderness. The results of the proposed method were in good agreement with those by FEM method and on the safe side. 相似文献
3.
The finite element software ABAQUS is used to calculate the deformation of reinforced concrete walls under fire. The calculated results agree well with previous experimental results. Based on the finite element model, the influences of such parameters as axial load level, lateral load level, height-to-thickness ratio, wall thickness, concrete compressive strength, steel reinforcement yield strength, steel reinforcement ratio and concrete protection thickness on deformation and fire resistance of walls are analyzed systematically. It is found that, under the conditions of big axial load level or wall thickness without lateral load and small height-to-thickness ratio, the reverse deflection of reinforced concrete walls in fire is apt to occur. Within the work range of parameters in common use, the fire resistance of walls decreases with the increase of axial load level, lateral load level, height-to-thickness ratio, steel reinforcement yield strength or steel reinforcement ratio, and increases with the increase of wall thickness or concrete compressive strength. 相似文献
4.
Experiments and analysis were carried out for the axial compression performance of reinforcement concrete filled tubular steel(CFTS). The deformation capacity and ultimate load capacity were investigated with the analysis of load bearing behavior, deformation capacity and failure modes of the reinforcement CFT short columns. And the influence of reinforcement on the deformation and ultimate load capacity were analysed as well. Finally, the calculation method for axial bearing capacity of reinforcement CFT short column was discussed and a simplified calculation formula was proposed. It was indicated that the columns’ failure modes were changed and their ultimate load capacity and deformation performance were improved by reinforcement. 相似文献
5.
Based on the small deformation assumption, the equations of the laterally loaded piles influenced by the axial load were established. The effect of axial load on the lateral response of piles was studied with parameter analysis. The analysis shows that internal force and deformation of laterally loaded pile under axial loading is actually closely linked with the values of axial and lateral loads. In general, the high level axial load should be focused on. It is more significant that the effect of axial load on the internal force and lateral deflection of the upper part of flexible piles, while there is little effect on deep of long-thin pile foundation. The effect of axial load on the lateral response of pile is the largest as coefficient form of subgrade reaction increases linearly, while the effect is minimal as coefficient form of subgrade reaction is a constant. Except in case of buckling, the changes of axial load along the pile direction have little influence on the magnitudes of deflection and moment. The assumption that the axial load is constant with depth can meet the requirements of engineering. 相似文献
6.
Accurate assessment of seismic performance of reinforced concrete columns（RC columns）is significant to ensure the safety of reinforced concrete structure subjected to earthquake action. In order to derive a reasonable prediction by Pushover analysis, a calculation method for determining lateral load-deformation curve, unloading rigidity and reloading rigidity of RC columns subjected to combined flexural and shear force is proposed based on test data analysis in the PEER (Pacific Earthquake Engineering Research Center) Structural Performance Database, and the formula for calculating the equivalent damping ratio according to hysteresis loop area is also provided. In this paper, conventional section analysis techniques are employed for modeling the flexural behavior of lateral load-deformation relationship, and the modified formulas with actual data analysis are implemented for modeling the effect of shear and slip of the longitudinal bars at columns end. Unloading rigidity and reloading rigidity of the columns are determined by statistical analysis on relations between themselves and secant rigidity of the columns respectively. Finally, a single-degree of freedom (SDOF) system is taken as an example to illustrate the applications of the proposed model for developing the corresponding “capacity curve” and performing pushover analysis on columns. The influences of primary parameters, such as shear-span ratio, axial load ratio, reinforcement ratio and stirrup ratio, on seismic performance of columns are also analyzed. 相似文献
7.
Based on the determined stress-strain relationship of steel and concrete after fire, a temperature field and mechanical model of bar-reinforced concrete-filled square steel tubular columns after fire was set up with using ABAQUS, and the model has been validated by testing results. Then this paper analyzed the side of section, bar ratio, fire duration time, steel ratio and material strength parameters on the bearing capacity of bar-reinforced concrete-filled square steel tubular columns after fire. It is found that fire duration time and side of section is the dominant factor. Lastly this paper puts forward a theoretical formula of bearing capacity of bar-reinforced concrete-filled square steel tubular columns after fire, for the post-disaster restoration and provides references for the reinforcement. 相似文献
8.
Considered strength classes of concrete, ratio of structural steel to concrete, ratio of steel tube to concrete and eccentricity ratio of load, 6 test specimens of steel tubular columns filled with structural and concrete are designed. The damage phenomena of specimens are described in detail and the failure mechanism is analyzed. The results show the initial failure of the specimens are began from the yield of steel tube, the ultimate failure are ended from the buckling of steel tube caused by the expansion of core concrete. Due to the existence of structural steel, the ductility of specimens is superior to steel tubular columns. Before the yield of steel tube, the plane cross-section assumption of specimens can be put into use. The ultimate bearing capacity of specimens is increased with the increase of strength classes of concrete, ratio of structural steel to concrete and ratio of steel tube to concrete. But the ultimate bearing capacity and ductility are decreased with the increase of eccentricity ratio. 相似文献
9.
Earthquake induced dynamic axial force in reinforced concrete (RC) bridge bent columns will not only change the yield strength of the columns but also change their stiffness, which is seldom considered by the common lumped plasticity line model. Based on the fiber element model results that taking into account the influence of dynamic axial force on strength and stiffness simultaneously, the axial force stiffness interaction effect on the seismic responses of RC double column bridges was analyzed. The results show that, axial force stiffness interaction has a large effect on the seismic responses of the double column bridge in the elastic range, and it does not alter the ultimate capacity of the columns. Since the stiffness of the columns under compression and tension dynamic axial forces offset each other, the global displacement of bridge bent with equal columns is relatively unaffected by the axial force stiffness interaction, however, the differences of the column member forces are manifest. For the short column controls the global stiffness, the axial force stiffness interaction has significant influences on both the global displacement and member force responses. The influences become larger as the irregularity of the bridge bent increases, so the interaction between axial force and member stiffness should be sufficiently considered in seismic analyses. 相似文献
10.
Microencapsulated paraffin insulation mortar (MPIM) was prepared by using low melting point microencapsulated paraffin (MCP) as phase change material. The phase change temperature, enthalpy, thermal conductivity coefficient and phase change thermal storage properties were tested. The result shows phase change temperature and enthalpy of the MPIM are 33 ℃ and 13.42 J/g, respectively. The thermal conductivity coefficient decreases with the increase in the dosage of silane coupling and binder. The thermal conductivity coefficient decreases with the increase in the dosage of the MCP, and then increases. Compared with blank specimens, the heating rate and cooling rate of the MPIM is definitely lagged, and it has good thermal storage properties. 相似文献
11.
In this study, nine simplified short composite columns consisting of core CFST (concrete filled steel tube) of different diameters and outer reinforced concrete were constructed to study their compressive performance under axial or eccentric compression. The failure mode is characterized by the crush of the outer concrete. The bearing capacity increases at first and then decreases with further increase of the position coefficient. It can be concluded that position coefficient is an important structural parameter that has considerable influences on the ultimate bearing capacity of the composite columns. The outer concrete, steel tubes and longitudinal reinforcement are found to work in a cooperative manner under axial or eccentric compression when the position coefficient is about 0.5. An improved bearing capacity algorithm that takes the position coefficient into account has been proposed based on the experimental and simulation results and current technical specification in China. It has been proven to be precise and safe. 相似文献
12.
A new tie column such as core column, named as core tie column, for the substitution of cast in place tie column was used to improve seismic performance of mansonry structures. Pseudo static testes of 11 wall specimens including 6 walls constrained by core tie columns, 2 walls constrained by cast in place tie columns, and 3 walls without constraints were carried out to study the seismic deformation capacity of mansonry walls with core tie columns. The skeleton load displacement curves and the normalized skeleton curves, displacement ductility factors,drift angels of the specimens were analyzed and compared. The effects of the level of vertical compress load, aspect ratio and the wall style on the deformation capacity of the wall with core tie columns were distinguished. It is shown that the constraints effects of core tie columns on masonry wall are effective and the walls with core tie columns have good deformation capacity as those with cast in place tie columns. 相似文献
13.
In order to investigate the flexural behavior of concrete beams reinforced with high strength hot rolled bars of fine grains, static bending test on four rectangle cross section HRBF400, HRBF500 RC beams was conducted. The results show that the experimental maximum crack width under short term load meets the requirement of current code while calculated value does not meet; mid span deflection of RC beams with HRBF400 under short term load still meets the requirement of current code while RC beams with HRBF500 does not meet. Bearing capacity calculating formula under conditions of crack/deflection control was proposed and conception of component's bearing capacity utilization coefficient (BCUC) was put forward. The influences of reinforcement strength, reinforcement diameter, concrete grade, reinforcement ratio, concrete cover thickness and high span ratio on BCUC were analyzed. Within the range of economic reinforcement ratio, ductility of HRBF RC beams meets the requirement. Energy dissipation capacity of HRBF RC beams is similar to that of normal RC beams at low reinforcement ratio but it decreases faster than normal RC beams with the increasing of reinforcement ratio. Energy dissipation capacity of HRBF RC beams is higher than that of normal RC concrete beams in elastic stage and it enhances with the increasing of reinforcement ratio. 相似文献
14.
Due to the large stirrup ratio and reinforcement congest in beam-column joints, the ordinary reinforced concrete beam-column joints take inconvenience to construction. Cracked fiber renforced concrete (FRC) has strong bridge ability and better tensile performance so that it can replace part or all of the stirrups. Based on previous researches on resistance mechanism of reinforced concrete joints, a new model using FRC materials in the core zone of beam-column joints is presented. It is a kind of model in which horizontal shear supported by the diagonal strut mechanism and softening truss mechanism with a certain percentage. The calculation results of the model is compared with the existing test results. It is a bit conservative to specimens with low axial load ratio. However, the results are in line with the specimens with high axial load ratio. Therefore, the results totally demonstrate the rationality of the proposed model in this paper. Meanwhile, according to the proposed model, the shear capacity of beam-column joints can be not only calculated, it also check whether FRC compressive strength in core zone of joints and horizontal stirrup ratio meets design requirements, which has a higher practicability. 相似文献
15.
TIAN Wei ZHAO Yang XIANG Xin-an DONG Shi-lin ZHANG Wei-yu FANG Wei ZHANG An-an 《保鲜与加工》2010,(6):22-27
The stability behavior of shuttle-shaped steel lattice columns subject to combined axial force and bending moment was examined through elastic buckling analysis and geometrically and materially nonlinear analysis. Firstly, the concept of section stiffness variation ratio is proposed for shuttle-shaped lattice columns and the elastic buckling behavior is discussed. Then, the effect of bending moment on the stability behavior of lattice columns is investigated, with the emphasis on the development of axial stress, bending stress and shear stress. The influence of column component spacing and diaphragm thickness on the stability bearing capacity is also analyzed. It is shown that the elastic buckling mode of the lattice column is dependent on its section stiffness variation ratio; for lattice columns with C-shaped buckling mode, the reduction in stability bearing capacity caused by bending moment is smaller than that of columns with S-shaped buckling mode; the maximum stability bearing capacity of the lattice column can be achieved by adjusting the column component spacing, and the spacing corresponding to the maximum capacity is basically consistent with the critical spacing for transformation of C-shaped buckling mode and S-shaped mode; and it is more effective to increase the thickness of columns with S-shaped buckling mode to get larger bearing capacity. 相似文献
16.
Previous researches on shear behavior of inclined sections in reinforced concrete beams used to be carried out on a comparatively high longitudinal reinforcement ratio in the codes of various countries.However,the shear design methods based on the data obtained from these researches may have distinguished deviations.This paper studies the shear behavior on a comparatively low longitudinal reinforcement ratio.Research has indicated that different longitudinal reinforcement ratios have significant impact on the shear behavior and the development of cracks in the beams,and the shear design equation in the code applied to beams without wed reinforcement restrained maybe not safe enough. 相似文献
17.
A new reinforcement arrangement scheme was suggested to provide satisfactory seismic performance and good workmanship for the coupling beams with small aspect ratio. Coupling beams with small aspect ratio are counter flexural deep beams with both ends restrained, in which the Bernoulli hypothesis are not valid. Although their load bearing capacity can be predicted with the strut-and-tie model developed recently, how to simulate this kind of beams adopting new reinforcement arrangement is still a problem. A macroscopic strut-and-tie model is thus presented for these coupling beams. Good agreement with experimental results is achieved. 相似文献
18.
Two monolayer concrete frames with the same reinforcement, KJ1 and KJ2, were designed. KJ1 was designed to simulate low cyclic reversed loading test under weak earthquake. Besides, the fire response test, including temperature rising and lowing, was made by fixing the axial compression ratio of the column. For KJ2, the fire response test at the fixed axial compression ratio was made. The deformation response of the concrete frames in fire was studied. Comparative analysis of the apparent phenomenon, temperature curves, bearing capacity change of the frames were made based on the test results of KJ1 and KJ2. According to the simplified temperature distribution, the ultimate bearing capacity of the column under the high temperature was preliminarily determined. It is illustrated that the calculation results and finally test phenomenon are consistent according to the simplified section. 相似文献
19.
Study on the effect of cavitation on tribological performances of sliding bearing by CFD Method 
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下载免费PDF全文 Much attention has been paid to the influence of cavitation on the performance of a sliding bearing, but conventional analysis methods can not exactly describe the influence. Therefore, a reasonable cavitation method is desired, with which tribological performances of the bearing can be improved. Based on the computational fluid dynamics(CFD）and Rayleigh-Plesset(PRE）model, the influence of cavitation is studied by the commercial software CFX module. The numerical results show that both the friction force and the friction coefficient decrease, compared with the corresponding results without the consideration of cavitation effect, which is caused by the reduce in the lubricant viscosity due to the cavitation effect. With the increases in the eccentricity ratio, width diameter ratio and rotating speed, the mean vaporization ratio becomes severer. 相似文献
20.
The mechanism of shrinkage cracking is discussed with a simple member, which is fully restrained and subjected only to an axial restraining force caused by shrinkage, while a simple procedure is presented for the determination of the number and spacing of the cracks and the average crack width. With the simple model, some examples are shown to compare the provisions for minimum shrinkage and temperature reinforcement in GB 50010-2002 Code, ACI 318-02 Code and AS 3600-1988 Code. The results show that the provisions in GB 50010-2002 Code are too weak in comparison with the others. Finally, some recommendations are proposed. 相似文献