Deformability Of Beams Research Articles

Flexural Strength and Deformability Design of Reinforced Concrete Beams

In the flexural design of reinforced concrete (RC) beams, the strength and deformability, which are interrelated, need to be considered simultaneously. However, in current design codes, design of strength is separated with deformability, and evaluation of deformability is independent of some key parameters, like concrete strength, steel yield strength and confinement content. Hence, provisions in current design codes may not provide sufficient deformability for beams, especially when high-strength concrete (HSC) and/or high-strength steel (HSS) are used. In this paper, influences of key factors, including the degree of reinforcement, concrete strength, steel yield strength, compression steel ratio, and confining pressure, are studied based on a theoretical method. An empirical formula for direct evaluation of deformability is proposed. Interrelation between the strength and deformability are plotted in charts. Based on the empirical formula and charts, a new method of beam design called “concurrent flexural strength and deformability design” that would allow both strength and deformability requirements to be considered simultaneously is developed. The method provides engineers with flexibility of using high-strength concrete, adding compression steel or adding confinement to increase deformability of RC beams.

Normalised rotation capacity for deformability evaluation of high-performance concrete beams

High-strength concrete (HSC) is becoming more popular in the construction of beams and columns of tall buildings because of its higher stiffness and strength-to-weight ratio. However, as HSC is more brittle than normal-strength concrete (NSC), it may adversely affect the flexural ductility and deformability of concrete members. Extended from a series of theoretical study conducted on flexural ductility of concrete beams, the authors would in this paper investigate the effects of some critical factors including the degree of reinforcement, confining pressure, concrete and steel yield strength on the flexural deformability of NSC and HSC beams. The deformability, expressed herein in terms of normalised rotation capacity defined as the product of ultimate curvature and effective depth, is investigated by a parametric study using nonlinear moment-curvature analysis. From the results, it is evident that the deformability of concrete beams increases as the degree of reinforcement decreases and/or confining pressure increases. However, the effects of concrete and steel yield strength are more complicated and dependent on other factors. Quantitative analysis of all these effects on deformability of beams has been carried out and formulas for direct deformability evaluation are developed. Lastly, the proposed formulas are compared with available test results to verify its applicability.

Modeling shear deformability of thin-walled composite beams with open cross-section

The present work formulates a one-dimensional kinematical model capable of assessing the statical behaviour of fibre-reinforced polymers (FRP) thin-walled beams with open cross-section. The proposed model accounts for the effects of shear deformability. Numerical results computed via finite element method (FEM) are provided and compared with the classical ones predicted by Vlasov’s theory. It is concluded that shear deformability can provoke deflections exceeding the values predicted by the classical thin-walled beam theory. Therefore, the proposed model seems to represent a viable alternative to assess the behaviour of such structures.

Deformability of concrete beams with unbonded FRP tendons

As fibre-reinforced polymer (FRP) behaves linearly until it ruptures without any yielding, the ductility and deformability of prestressed concrete beams with FRP tendons are of prime concern. This paper describes a comparative study of five existing deformability indices for unbonded partially prestressed concrete (UPPC) beams with FRP tendons. A numerical method has been developed to predict the full-range response of prestressed concrete beams with bonded and/or unbonded FRP tendons under loading, and the results agree well with experimental results reported in the technical literature. The results show that the deformability index defined as the ratio of the product of moment and deflection at ultimate to the corresponding value at cracking is consistently decreasing with the increase of combined reinforcement ratio. In addition, this index is sensitive to changes of factors that may influence the deformability of UPPC beams with FRP tendons. The present investigation also indicates that, when the ratio of neutral axis depth to the depth to FRP tendons at the critical section at ultimate is greater than 0.3, the beam would fail by crushing of concrete, which is the more favourable failure mode compared to the rupture of tendons.

SIZE EFFECT ON STRUCTURAL PERFORMANCE OF REINFORCED CONCRETE BEAMS UNDER FLEXURE

The objective of this study is to clarify the size effect on the mentioned structural performance of doubly reinforced concrete beams. A total of 16 specimens with four different scales are tested under a four-point-loading. In this experiment, effect of the amount of main reinforcement ratio and web reinforcement ratio on their structural performance is also investigated. Based on the results, it was verified that structural performance in termes of the strength and the deformability of RC beams are greatly influenced by their sizes. Non-linear flexural analysis incorporating Hillerborg's hypothesis was performed. Hillerborg introduced a model including in softening and strain localization of concrete under compression in explaining size effect on ductility.

INFLUENCE OF RANDOM CRACKS ON THE SHEAR BEHAVIOR OF REINFORCED CONCRETE BEAMS CONTAINING STEEL FIBERS

The present study is aimed at investigating the influence of random cracks on the shear behavior of RC beams with steel fibers. For this purpose, several amounts of expansion agent and two percentages of steel fibers were used. From the strain history during the curing period of time, some sort of chemical prestress could be observed due to the use of expansion agent. Random cracks were successfully created and the pattern showed different crack densities, defined as the ratio between the area of the cracks and the uncracked area of concrete, for each beam. In some cases, a significant increase in the peak load was observed. In other cases only the deformability of beams was improved due to the addition of steel fibers.

EXPERIMENTAL AND NUMERICAL ANALYSIS OF FLEXURAL COMPOSITE BEAMS WITH PARTIAL USE OF HIGH STRENGTH/HIGH PERFORMANCE CONCRETE

The paper summarises the experimental and numerical analysis of flexural capacity and deformability of structural concrete beams prepared as composite members consisting of two concrete layers made of reinforced normal concrete and high‐performance concrete (HPC). The reinforced concrete composite beams used in the tests were prepared in full scale with the cross‐section of 120 × 200 mm and the effective span of 2950 mm. The basic samples were composed in two layers consisting of high‐performance concrete as the top layer, and normal strength concrete. The results of the analyses confirm a significant improvement of structural properties of composite beams in comparison to the beams prepared totally of normal concrete, and in some cases also in comparison with the beam totally made of HPC.

Experimental and numerical analysis of flexural composite beams with partial use of high strength/high performance concrete

Abstract The paper summarises the experimental and numerical analysis of flexural capacity and deformability of structural concrete beams prepared as composite members consisting of two concrete layers made of reinforced normal concrete and high‐performance concrete (HPC). The reinforced concrete composite beams used in the tests were prepared in full scale with the cross‐section of 120 × 200 mm and the effective span of 2950 mm. The basic samples were composed in two layers consisting of high‐performance concrete as the top layer, and normal strength concrete. The results of the analyses confirm a significant improvement of structural properties of composite beams in comparison to the beams prepared totally of normal concrete, and in some cases also in comparison with the beam totally made of HPC.

Flexural Behavior and Deformability of Fiber Reinforced Polymer Prestressed Concrete Beams

After a brief review of the ductility and deformability indices currently used in the design of concrete beams reinforced or prestressed with steel or fiber reinforced polymer (FRP) tendons, a new definition of a deformability index (factor) for prestressed concrete beams is proposed. The new factor is defined in terms of both a deflection factor and a strength factor. The deflection factor is the ratio of the deflection at failure to the deflection at first cracking, while the strength factor is the ratio of the ultimate moment (or load) to the cracking moment (or load). The proposed deformability factor is verified not only by test results obtained by the writer, but also by other test results available in the literature and it appears to be a suitable measurement of the deformability of concrete beams prestressed with either FRP tendons or steel tendons.

Ductility and Deformability of Coupling Beams in Reinforced Concrete Coupled Walls

The seismic response of coupled wall structures is discussed. It is demonstrated through a review of large-scale experimental investigations of coupling beam behavior and analytic studies of coupled wall behavior that often the coupling beam ductility demand exceeds the expected available ductility. As a result, it is possible that coupled wall structures will not behave as desired in the course of a significant seismic event. Limits to the allowable degree of coupling are proposed as a remedy to this apparent deficiency. Additional design and analysis issues are discussed including reduced section properties and wall overstrength requirements.

Serviceability of Concrete Beams Prestressed by Carbon-Fiber-Reinforced-Plastic Bars

The use of carbon-fiber-reinforced-plastic (CFRP) as prestressing reinforcement for concrete structures, has increased rapidly in the last ten years. The non-corroding characteristics of CFRP reinforcement could significantly increase the service life of concrete structures. In addition, CFRP prestressing reinforcement has the advantages of high strength-to-weight ratio, good fatigue properties, and low relaxation. However, the linear elastic behavior of the material up to failure requires special design consideration to ensure sufficient deformability of the members. In this paper, partial prestressing using low-jacking stresses, is proposed for the design of concrete members prestressed by CFRP reinforcement to reduce the cost and improve their deformability. The paper summarizes a study undertaken to examine the flexural behavior of concrete beams partially prestressed by CFRP reinforcement. The experimental program consists of testing eight concrete beams prestressed by CFRP bars and two beams prestressed by conventional steel strands. The parameters considered in this experimental program are the prestressing ratio, degree ofprestressing, and distribution of the CFRP bars in the tension zone. The various limit states behavior of concrete beams prestressed by CFRP bars in terms of cracking and deflection prior and after cracking are examined. The different modes offailure and the deformability of such beams are discussed.

骨組溶接構造体の変形能からみた鋼材の降伏比一様伸び特性のあり方

A procedure to investigate the effect of work-hardening properties of steel on the deformability of welded frame-structures having the H-shape section is described. The procedure consists of the elasticplastic deformation analysis and the local buckling analysis. The analytical results have proved to agree with the experimental results. The deformation analyses of the H-shape beam were carried out for the various combinations of the yield to tensile ratio and the uniform elongation of steel.It has been shown from the analytical results that it improves the deformability of H-shape beams, such as the amount of deformation or the absorbed energy up to the maximum load, to lower the yield to tensile ratio or to enlarge the uniform elongation of steel. In case of steels having larger uniform elongation (eT>10%), it is more effective to lower the yield to tensile ratio than to enlarge the eT. Whereas in case of steels having smaller uniform elongation (eT<10%), increasing the eT is more beneficial.

Extending of the merchant-rankine formula for the assessment of the ultimate load of frames with semi-rigid joints

The influence of the actual characteristics of beam-to-column joints on the ultimate strength and the stability of steel frames is significant and no longer needs to be proved. At present, several experimental and theoretical research works are being carried out in this field. They aim on one side at a better knowledge of the non-linear behaviour of joints and on the other side at the development of numerical procedures that would take account of the non-linear characteristics of joints and would insure an accurate simulation of the response of individual members (beam or column) or of frames. The carrying capacity of non-linearly and restrained columns as well as the strength and the deformability of beams with semi-rigid joints at their ends can now be determined by means of hand calculation methods. This paper presents a hand calculation procedure for the evaluation of the collapse load of semi-rigid frames, making it possible to take account of both main aspects of a steel frame study: strength and stability. The suggested method is applied to an example, and lastly the results are compared with those obtained numerically by means of the FINELG program.

Strength and deformability of H-shaped steel beams and lateral bracing requirements

This paper is concerned with the load-carrying capacity and deformation capacity of steel beams with an H-shaped cross section. In the first half of the paper, new design formulae on beam strength and plastic deformability are proposed on the basis of statistical data analysis for experimental results obtained from the numerous beam tests which were conducted and performed in Japan. The proposed statistics and reliability based design equations were developed during the work by a sub-committee in the Architectural Institute of Japan to make a draft of the new specification for steel design based on ‘Load and Resistance Factor Design Concepts’. In the second half of the paper, bracing requirements for various types of lateral braces are discussed.