Key Engineering Materials Vols. 400-402

Abstract: Based on the analysis of reinforced concrete beams under biaxial bending, an equivalent cross-section method is proposed to calculate the shear capacity of the beams. According to the two basic equivalence principles, a biaxial flexural beam is changed into a uniaxial flexural member, and the shear strength of biaxial flexural beam is calculated as a uniaxial flexural member. Furthermore, the interrelationships among the equivalent cross-section and the neutral axis inclination as well as the ratio of depth to width of the cross-section are deduced in advance. The ratios of some typical cross-section’s equivalent dimensions to its original ones are pointed also. In order to verify the availability of the equivalent cross-section method, some academic references about the ultimate strength of biaxial flexural beams are consulted in this paper, and the shear capacity computing methods by literatures for uniaxial flexural beams are adopted in the strength calculation of biaxial flexural reinforced concrete simply supported beams with stirrups or without stirrups. The comparison between the calculation results and experimental results shows that the presented equivalent cross-section method is feasible and practical which can be used as a reference in practice design.

Abstract: Based on the common calculation methods of normal section bearing capacity of steel reinforced concrete (SRC) columns with I-shaped steel, SRC columns containing T-shaped steel are presented and their mechanical properties and failure modes are analyzed. Combining with actual engineering and current national codes, the calculation methods and formulas of ultimate moment capacity of this column are proposed and heights of the concrete pressured region in two different situations are compared, by which it can be seen that SRC columns are easier to form large eccentric compression failure when the big flange is nearer to axial force N .The bearing capacity of one SRC column with T-shaped steel is checked using above proposed formulas and the calculation results agree well with the experimental data, and finally this numerical example shows that the suggested method has good precision and reasonable application.

Abstract: Based on the theoretical analysis of steel-concrete composite П-beam’s lateral buckling, the computing model and simplified computing model on the stability of composite П-beams are brought forward. According to above two models, composite beam’s lateral buckling is studied in negative moment regions using the energy method, and the formulas which are used to calculate critical bending moment in negative moment regions in the elastic stage are deduced. Compared with other stability theories and methods, this paper represents the design correction and suggestion about the stability of composite П-beam in negative bending regions. Moreover, the simplified calculation method, which is used to compute the lateral critical buckling moment of steel-concrete composite П-beam loaded by equal-end moment, not only simplifies the computing process, the computing results also have the equivalent accuracy with numerical computing methods.

Abstract: A full test on the flexible behaviors of the long flanges and trapezoidal section high-strength concrete thin-walled box girder has been performed. The deflection horizontal distribution, strain and strain distribution of concrete and reinforced bars in the compressive flanges, strain distribution along rib height have been studied. The results demonstrate that reinforced concrete thin-walled box girder has fine flexible behavior and ductility, strain distribution along rib height agrees with the basic assume, i.e. Plane section before deforming remain plane, and the destructive experimental results disclosed the full process law of shear lag effect and equivalent calculated coefficient of compressed flange width at middle span section, which can be served as a reference for that applying elementary reinforced concrete beam theory settles the ultimate flexural capacity calculation of concrete thin-walled box girder.

Abstract: In nonlinear dynamic analyses of RC structures based on fiber-based discretization of member cross-sections, the constitutive model used to represent the cyclic behavior of reinforcing steel typically plays a significant role in controlling the structural response especially for nonductile systems. The accuracy of a fiber-section model is almost entirely dependent on the ability of both the concrete and reinforcing steel constitutive material models to represent the overall inelastic behavior of the member. This paper describes observations related to the fundamental properties of reinforcing steel such as buckling, hardening, diminishing yield plateau and growth of curvature, Bauschinger effect, and low-cycle fatigue and strength degradation that are relevant to the overall task of developing an accurate material model for use in seismic response analysis of reinforced concrete structures.

Abstract: In order to improve the constructability and meanwhile ensure excellent seismic behavior, an innovative bolted endplate connection to steel beam and reinforced concrete column (RCS) was developed, and three full scale model joints with or without floor slab were tested under simulated seismic loading. The proposed composite joint is characterized by an extended endplate which is welded to steel beam with reduced sections in factory and then bolted to reinforced concrete column using high-strength steel rods in field. The effect of material strength and concrete floor slab on the seismic behavior of joints was studied. Experimental results indicated that both specimens without floor slab exhibited good ductility and energy-dissipating ability with full plastic hinging formed at the reduced sections of steel beam. However, owing to the effect of floor slab, the beam sections became unsymmetrical and positive moment strength of the joint was increased significantly. The specimen with floor slab fractured at the weld between the bottom flange of the beam and the endplate, and the failure mode resembled what occurred during the Northridge earthquake.

Abstract: For discussing the mechanism of load-transferring for reinforced steel fiber reinforced concrete (SFRC) double-column combined six-pile caps, the large-scale general finite element software-ABAQUS is used for the tested SFRC caps with computing in the aspects of modeling, cracking load, limit load, load-deformation curve, distribution of stress in caps and cracks and etc. The results of computing is compared with the result of experiments and the comparison is indicated: The results of computing and experiments are coincided well; The destroy pattern of SFRC double-column combined six-pile caps is sheared damage or punched damage and the model of load-transferring accords with spatial strut-and-tie method (STM); The mixture of steel fiber can improve cracking load and limit load for RC caps, delay the crack for caps, block the cracks’ expansion, and enhance the cap’s ductility.

Abstract: It is difficult and important to accurately calculate single pile ultimate bearing capacity during pile foundation design. Typical computational methods on single pile ultimate bearing capacity are contrastively analyzed in this paper. Contact element method on single pile ultimate bearing capacity is relatively accurate and economical, but it isn’t used in practical projects until now because its computational process is complicated. 343 different single pile ultimate bearing capacities are calculated with the contact element method in order to study a simple computational formula based on the contact element method. All data calculated are analyzed with a linear recursive multi-analysis program which is programmed with Fortran90. A simple computational formula on the contact element method is presented based on the analysis results. The simple computational formula, the experiential formula in the code, the contact element method and the static load experiment method are respectively used to calculate single pile ultimate bearing capacity in two practical projects in order to test the simple computational formula. The results show that the simple computational formula is relatively accurate. Some advice is presented based on the analysis results.

Abstract: The thickness of the raft slab is determined by punching shear. The raft slab is commonly thick, which causes concrete volume is large. Mass concrete can bring disadvantage to the foundation. In order to increase the bearing capacity and reduce the thickness, it is suggested that the raft slab to be reinforced by steel fibers. There are five groups of specimens in this paper. S1 is the common reinforced concrete slab. S2 and S3 are concrete slabs reinforced by steel fibers broadcasted layer by layer when casting specimen. S4 and S5 are concrete slabs reinforced by steel fibers mixed homogeneously when making concrete. The punching shear tests of these slabs were done. The test results indicate that the punching shear capacity of the slab reinforced with steel fibers is higher than that of concrete slab, the stiffness and crack resistance of the steel fibers reinforced concrete slab are better than those of the common concrete slab and the punching shear of the slabs with different construction methods of steel fibers is similar. It analyses the punching shear behavior of the slab reinforced with steel fibers and suggests the ultimate bearing formula. The calculative values are coincided with the measured values well.

Abstract: Finite element method is often used to obtain exact solution in the course of internal force calculation of some complex frames which contain nodal vertical displacement such as frames with transferring layer and mega-frames with sub-structure. In the phase of scheme comparison and schematic design, methods which can quickly produce calculation results of the above said frameworks are necessary. Based on the basic principle of displacement method, this paper proposes a simple analytical method for frameworks that contain nodal vertical displacement. According to the proposal, the basic structure for calculation is the framework in which is added vertical chain-pole at relevant node; the basic unknown quantities are the nodal vertical displacement of the basic structure; the basic equation is fixed according to the equilibrium of node forces; unit vertical displacement as well as bending moment and shear diagram of the basic structure under external load are respectively obtained by using moment redistribution method; nodal vertical displacement is determined through substitution of shear force of relevant rod into the equilibrium equation of the chain-pole node; the actual internal force is determined through superposition of actual vertical displacement and internal force diagram algebra of the basic structure under vertical external load. An engineering example is introduced, which is intended to provide reference for the simple calculation for the above said complex frameworks.