Contrast Analysis of Mechanical Behavior of Confined Concrete with Stirrups and CFRP Under Axial Compression

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.     

Mechanical Properties of Regional Confined Rectangular Concrete Columns under Axial Loads

Based on experimentthatal results,we conclude that confinement in regional confined concrete(RCC) columns is more efficient than that in normal confined concrete(NCC) columns.As loads increase,NCC column sections tend to become round;the corner concrete in the core area may break;and,the strains of external stirrups tend to drop slightly after the peak load.RCC columns,however,remained thoroughly rectangular and the stirrup strain increased steadily.The failure mode of RCC columns was totally different from that of NCC columns.While NCC columns tended to fail in shear,followed b a rapid drop in load carrying capacity,the RCC columns developed gaps in their midsections and the columns separated into several slender columns.After a long deformation period,the RCC columns retained approximately 40% of their load carrying capacity.It can be expected that this characteristic may benefit the anti-seismic capacity of structures.     

FEA About Capacity of Resisting Explosion Inside of Short Concrete Column With Steel Tube Confined

With the development of offense and defense strategy in future war and the application of high tech weapon, the demand is much improved to the resistibility level of defense engineering. LS-DYNA3D software is adopted to simulate the situation causing by the explosion of the commonly short concrete column and Short Concrete Column with Steel tube confined. The comparison includes chamber causing by explosion and nodes' displacement. The results show that steel tube-confined concrete structure can confine the displacement of core concrete, improve the structure's capacity of resisting explosion effectively, and enhance structure's elasticity and firmness.     

The Experimental Study on Size Effects on Axial Compression Performances of Reinforced Concrete Column under Repeated Load

The size effects on axial compression performances of reinforced concrete column under repeated load are needed. Specimens were designed and tested in accordance with the relevant similarity, whose geometric dimensions are: 400 mm×400 mm×1 200 mm, 600 mm×600 mm×1 800 mm and 800 mm×800 mm×2 400 mm. The result of the experiment, the failure characteristics, crack development process, strength, peak stress, peak strain and stiffness of various specimens were comparatively analyzed. The results show that, within size range of this test, size effect exists on performances of columns.     

Stress-Strain Model of FRP-Confined Concrete Column under Axial Compression

Stress-strain mathematical model of FRP-confined concrete plays an important role in civil engineering, and it should be well understood. Based on first region slope, turning point coordinate and third region slope, the development of stress-strain curve of FRP-confined concrete column is analyzed, and conditions which ideal mathematical model need to meet are point out. A new composite exponent-line model is proposed, which overcomes the weakness of conventional model and is available for both hardening and softening type stress-strain curves. Approaches to determine parameters of the proposed model are presented. Finally, the capability and accuracy of the proposed model in predicting the complete stress-strain process of FRP-confined concrete under axial compression are demonstrated through comparisons between predictions of the proposed model and test results.     

Experimental Research on Mechanical Behavior of High-strength Concrete Short Columns Confined with Stirrups

Based on the test of high strength concrete (HSC)short columns confined with stirrups 8 under axial loads and 6 under small eccentric loads, the influence of stirrups confinement on stressstrain relationship and related parameter under monoaxial compression are studied, and the effect of the type of stirrups, stirrup ratio, etc. on the HSC columns ductility is analysed. Besides, the strength and deformation behavior of HCS columns under small eccentric compression are explored.Based on the experimental study, the complete stress-strain curves of confined HSC and the formula for calculating the related parameter are presented in this paper.     

Stress-Strain Relationship of Circular Concrete Columns Confined with Lateral Pre-tensioned FRP

The active confinement for the core concrete can be provided by lateral pre-tensioned FRP, the stress hysteresis of FRP can be avoided, and good confinement effect for concrete columns can be got. It must cause large error if adopt the calculated model and constitute model of concrete columns confined with non-pretentioned FRP. The initial confined stress and effective confined stress associated with the lateral pre-stress were introduced. According to the test results and finite element simulation, the calculated model on peak stress, peak strain, ultimate stress and ultimate strain of circular concrete columns confined with lateral pre-tensioned FRP were proposed, and the initial elastic modulus of circular concrete columns confined with lateral pre-tensioned FRP was analyzed. Based the exiting stress-strain models of circular concrete columns confined with FRP, the three linear stress-strain model of circular concrete columns confined with lateral pre-tensioned FRP was recommended, and good agreement between theoretical and test results is achieved.     

Deformation Capacity of FRP Confined Reinforced Concrete Circular Columns under Simulated Seismic Loading

The accurate calculation of the deformation capacity of structures is very important to performance-based seismic design, which satisfies the explicit deformation demands. The method to evaluate drift capacity of fiber reinforced polymer (FRP) confined reinforced concrete circular columns under simulated seismic loading is focused. Firstly, the moment-curvature relationship of FRP confined sections of reinforced concrete (RC) circular columns is simulated by numerical analysis. It is found that the calculated ultimate curvature is significantly less than the test result, and the difference is controlled by the axial load ratio of the tested columns. According to the numerical and the test results, an equation is proposed to modify the calculated ultimate curvature. Based on this, the drift capacity can be predicted with the equivalent plastic hinge method. The calculated result agrees well with the test result when FRP amount is low, but it is significantly larger when FRP amount increases. Finally, the main parameters exerting influences on the drift capacity of the FRP-confined RC circular column are analyzed.     

Experimental Analysis on Bending Capacity of Unbonded Prestressed Concrete Beams with HRBF500 Steel Bars

The bending capacity tests on ten simple supported beams were conducted to investigate the damage characteristics, prestress increment, beading capacity and displacement ductility of unbounded prestressed concrete beams with HRBF500 steel bars. The results show that the HRBF500 steel bars has yielded before the limit state. The concrete in compression zone crushes upon the broken of the beams, which shows a sudden damage mode. The measured ultimate stress increments of unbounded tendons are in linear relationship with the comprehensive reinforcement ratio index, while the values of the ultimate stress increments are obviously higher than those values specified in the code GB50010-2010, and the average ratio of predicted values to testing values is about 0.35. The mid span deflection upon yielding of the beams is large, while the displacement ductility is bad and the average value of the displacement ductility ratio is 1.67. The displacement ductility ratio decreases with the increases of the comprehensive reinforcement ratio index. Based on the experimental results, the proposed calculation formula of ultimate stress increments of unbounded tendons was established, and it is in good agreement with the experimental results when the testing value is less than 450 MPa.     

Experimental Analysis of Size Effect of High-strength Concrete Column Under Small Eccentric Loading

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.     

Test and Finite Analysis to Non-strong Column and Weak Beam Concrete Frames

Through the test of two concrete frames under vertical load and nonlinear finite programme analysis,the performances of strong beam with weak column and equal strength column and beam are studied,such as ultimate load,deflection,displacement ductility,redistribution of internal force.When the reinforcement is proper,the research proved that strong beam with weak column" and "equal strength column and beam" have better displacement ductility and can realize full redistribution of internal force,the width of cracks and deflections can satisfy the rules of code for design of concrete structures.     

A Review of Concrete Damage Constitutive Models

The existing constitutive models of concrete are mainly based on the framework of the classic elastic -plastic models which are rigorous on mathematics, but not coordinated with the failure mechanism of concrete. Researchers of different countries proposed various kinds of damage constitutive models based on the irreversible thermodynamics theory to describe the damage behavior of concrete. This paper presents a review of different models for concrete,analyzes the characteristics of each representative model and studies the scope of their application. On the basis of the review of existing concrete damage models, some new methods can be provided for further research on damage constitutive models.     

Integration Strategy for Thermal-Elastic-Plastic Models of Concrete under Plane Stress

Plastic strain was determined at multiple time increments.The strain was caused by stress and temperature.The yield function in high-temperature states is the function of temperature and plastic strain.The calculation efficiency would be decreased and much more calculation would be needed if a conventional method,such as the radial return method,was used.In the case of axial stress states,the temperature path was difficult to determine at various time intervals.Initial value equations were obtained with the Drucker-Prager function of plane stress concrete.This method can solve the previously mentioned problems efficiently when used with the Runge-Kutta integration strategy.A program was developed with an updated co-varying coordinate finite element method based on the S-R decomposition theorem.Computational results show that the integration strategy is highly accurate and efficient.     

舍饲青年杜泊公羊行为习性研究初报

选用4只舍饲青年杜泊公羊连续进行3昼夜行为习性观察，结果表明：试验羊昼夜采食193.3±35.5min，反刍409.4±40.3min，卧息541.6±23.2min，自由活动245.7±42.3min，其它行为50.0±4.7min，反刍与采食时间比为2.1:1.0。反刍、卧息多发生在夜间（p<0.01），采食多发生在白天（p<0.01），白天与黑夜排粪、排尿时间差异不显著(p>0.05)     

The Effect of Axial Compression on the Prestressed Concrete Frame under Vertical load

For prestressed frames, the axial compression ratio will affect not only the ductility of structures but also the structural internal force.Based on the computer-calculation for four groups of 24 prestressed frames combined with the references, in this paper, the effects of axial compression ratio on the prestressed frames are studied and discussed through three aspects: the second-order effect, the axial deformation of frame-columns and the comparison with ordinary concrete frames.The study results show that the effects of axial compression ratio on the prestressed frames and the ordinary concrete frames are basically consistent, but there are some self-born characteristics.As a whole, the effect of axial compression ratio on the prestressed frames is more notable than that on the ordinary concrete frames, but under common situation the effect is small.