Compression Reinforcement Research Articles

Research on Seismic Performance of Core Wall in Hybrid Structure

The ductility of primary lateral resisting member, i.e. Core wall is analyzed using finite element program ADINA. The influencing factors like aspect ratio, concrete grade, axial compression ratio, reinforcement ratio,boundary confinement and reinforcement ratio of boundary element etc. are considered in the analysis. Based on the aforementioned research, some suggestions for the design of core wall in hybrid structure are proposed.

Research on Seismic Performance of Core Wall in Hybrid Structure

The ductility of primary lateral resisting member, i.e. Core wall is analyzed using finite element program ADINA. The influencing factors like aspect ratio, concrete grade, axial compression ratio, reinforcement ratio,boundary confinement and reinforcement ratio of boundary element etc. are considered in the analysis. Based on the aforementioned research, some suggestions for the design of core wall in hybrid structure are proposed.

Tests of Mechanical Characteristics of Steel Fiber Reinforced Concrete Wall-Beams Simply Supported

The characteristics of crack load, failure load, crack and deflection of steel fiber reinforced concrete wall-beams simply supported have been studied though the tests of 12 steel fiber reinforced concrete wall-beams simply supported specimens. The upper steel of joists changing from tensile reinforcement to compressive reinforcement, neutral axis moving from joists to walls and phenomenon of stress redistribution in wall-beams with the increase of external load have been found; the optimum mixing amount of steel fiber has been determine and the increase rate of crack load and failure load comparing steel fiber reinforced concrete wall-beams simply supported with ordinary ones has been raised. It is good for the practical constructions application that steel fiber increases the ductility of simply supported wall-beams.

Flexural ductility design of high‐strength concrete beams

SUMMARYIn the seismic design of a reinforced concrete (RC) structure, it is necessary to provide not only sufficient strength, but also adequate flexural ductility. This is particularly important to the design of RC beams cast of high‐strength concrete that is inherently more brittle. Eurocode EN1998‐1 directly specifies such minimum flexural ductility. To provide adequate flexural ductility to RC beams, Chinese code GB50011 limits the normalised depth of simplified rectangular stress block at peak resisting moment, whereas American code ACI 318–08 requires that the tension steel strain at peak resisting moment shall not be smaller than 0.004. The essential parameters identified for effective flexural ductility design of RC beams include the maximum difference of tension and compression reinforcement ratios and maximum normalised neutral axis depth at peak resisting moment, as they help to guarantee various flexural ductility requirements. Their relationship with the flexural ductility is studied using a rigorous full‐range moment–curvature analysis procedure. Empirical formulae and tables are also developed to facilitate flexural ductility design of RC beams. A comparison shows that the allowable differences of tension and compression ratios may be smaller than those specified in Eurocode 8 particularly for those cast of high‐strength concrete. Copyright © 2011 John Wiley & Sons, Ltd.

Theoretical and experimental serviceability performance of SCCs connections

The Self Compacting Concrete, SCC is the new generation type of concrete which is not needed to be compacted by vibrator and it will be compacted by its own weight. Since SCC is a new innovation and also the high strength self compacting concrete, HSSCC behavior is like a brittle material, therefore, understanding the strength effect on the serviceability performance of reinforced self compacting concretes is critical. For this aim, first the normal and high strength self compacting concrete, NSSCC and HSSCC was designed. Then, the serviceability performance of reinforced connections consisting of NSSCC and HSSCC were investigated. Twelve reinforced concrete connections (L = 3 m, b = 0.15 m, h = 0.3 m) were simulated, by this concretes, the maximum and minimum reinforcement ratios p and p\' (percentage of tensile and compressive steel reinforcement) are in accordance with the provision of the ACI-05 for conventional RC structures. This study was limited to the case of bending without axial load, utilizing simple connections loaded at mid span through a stub (b = 0.15 m, h = 0.3 m, L = 0.3 m) to simulate a beam-column connection. During the test, concrete and steel strains, deflections and crack widths were measured at different locations along each member. Based on the experimental readings and observations, the cracked moment of inertia (Icr) of members was determined and the results were compared with some selective theoretical methods. Also, the flexural crack widths of the members were measured and the applicability for conventional vibrated concrete, as for ACI, BS and CSA code, was verified for SCCs members tested. A comparison between two Codes (ACI and CSA) for the theoretical values cracking moment is indicate that, irrespective of the concrete strength, for the specimens reported, the prediction values of two codes are almost equale. The experimental cracked moment of inertia (Icr)exp is lower than its theoretical (Icr)th values, and therefore theoretically it is overestimated. Also, a general conclusion is that, by increasing the percentage of p, the value of Icr is increased.

Test and Design of Tensile-Compression Prestressed Concrete Beam

In this paper, the tensile-compression prestressed concrete beam was researched, and gets deflection of the beam subjected to load. Then, the beam was analyzed by the finite element method of ANSYS software. The test and analysis results show that the beam has a good flexibility and the phenomenon of stress concentration were appeared in ends concrete of pre-compressed steel tube. The pre-compressed steel tube control stress is 0.5 times the nominal value of steel tube, the concrete pre-tensile stress can be obtained effectively by relaxes pre-compressed steel tube. This paper further optimizes the dosage of pre-tensile tendon (Ap), pre-compressed steel tube (AT), tensile reinforcements (As)and compression reinforcements (A`s).The results from example show that the concrete structure of tensile-compression prestressed can reduce the pressure area height of the beam effectively and solving conventional prestressed concrete structure excessive or cannot reinforcement in pressure area.

Assessment of the flexural capacity of RC beam/column elements allowing for 3d effects

The paper describes an experimental investigation of the deformational response and the stress conditions developing in the compressive zone of reinforced concrete beam-like structural elements in bending and bending combined with axial force. The results obtained confirm the findings of earlier work and demonstrate that the compressive zone at its ultimate-limit state is characterised by the development of triaxial rather than uniaxial–as widely considered–stress conditions. These findings form the basis for introducing a simple modification in the method currently used for calculating flexural capacity and it is shown that, by complementing the proposed method with an approach that takes into account the effect of yielding of the compression reinforcement on structural behaviour, it is possible to achieve predictions of flexural capacity which are considerably closer to experimentally established values than the values obtained through the use of currently adopted methods.

FE analysis of reinforced concrete corbels with enhanced continuum models

The paper presents quasi-static FE-simulations of the behaviour of short reinforced concrete corbels with and without shear reinforcement. Concrete was modelled with the aid of three various constitutive continuum models: an isotropic elasto-plastic, an isotropic damage and an anisotropic smeared crack approach. To ensure the mesh-independent numerical results and to describe strain localization, a characteristic length of micro-structure was introduced by means of a non-local theory. To simulate the behaviour of reinforcement, an associated elasto-plastic constitutive model with isotropic hardening was assumed. The effects of a characteristic length, bond between concrete and reinforcement, tensile and compressive fracture energy and shear reinforcement on strain localization were carefully investigated. The numerical results were compared with corresponding laboratory tests.

Theoretical and Numerical Analysis on Membrane Effects of RC Slabs

When a RC structure is laterally restrained, the load resistance is enhanced due to the membrane effects. A simplified membrane action theory was proposed by modifying the Maximum Membrane Force Design Method (MMFM) to predict the resistance-deflection curves of restrained slab RC structures, in which the total strain plastic theory and strain rate plastic theory were combined and a serial of explicit formulae were derived. A better agreement was observed between the test data and the analytical results predicted by the proposed theoretical method, comparing with MMFM and numerical results conducted by ABAQUS. It is demonstrated that the proposed theory is validated and the steel bar at compressive zone has definite influence on the load carrying capacity, and cannot be neglected in the case of high compressive reinforcement ratio.

Model for post-yield tension stiffening and rebar rupture in concrete members

A tension stiffening model is presented which enables the calculation of average tensile stresses in concrete, after yielding of reinforcement, in reinforced concrete elements subjected to uniaxial tension, shear or flexure. To determine the average tensile stress–strain relationship for concrete, a crack analysis approach is employed taking into account the bond mechanism between concrete and deformed reinforcing bars, and numerical analyses are conducted to determine the tensile behavior of reinforced concrete members including post-yield response. Analytical parametric studies are conducted to determine the influence of various parameters including concrete compressive strength and reinforcement yield strength, ultimate strength, hardening stress, and hardening strain. Analysis results obtained from the proposed model, when compared to experimental results for uniaxial members, indicate good agreement for structural behavior after yielding of reinforcement. The proposed model makes it possible to accurately calculate reinforcement stresses at crack locations and, thus, average strain conditions which result in rupture of reinforcement. This leads to more realistic predictions of the uniaxial, flexural, and shear ductility of reinforced concrete members.

Effect of steel corrosion and loss of concrete cover on strength of deteriorated RC columns

In this paper, the effect of reinforcement corrosion and loss of concrete cover on structural behavior of bridge columns is quantified by developing moment–axial load (M–P) interaction diagrams using modified analysis procedure and advanced deteriorated material models. The results of this study suggest that corrosion of steel bars on the compression side of column section reduces the effective depth, and causing more reduction than left side or tension side deterioration, in compression controlled region. However, in general, corrosion of tension reinforcement causes more strength reduction than corrosion of reinforcement in compression or left/right side reinforcement, particularly, in tension controlled region.

Discussions on the Maximum Longitudinal Reinforcement Ratio as a Ductility Requirement for Reinforced Concrete Beams by the Code of Practice for the Structural Use of Concrete 2004 and Recommendation of Alternatives

The Code of Practice for the Structural Use of Concrete 2004 has limited the tension reinforcement ratio in reinforced concrete beams contributing to the lateral load resisting system to 2.5% (under the heading ‘ductility’) which is based on the phenomenon that high tension reinforcement ratio in a reinforced concrete beam will lead to low ductility of the beam. This phenomenon is explained in this paper, together with the parallel one that high compression reinforcement ratio will conversely lead to high ductility. For comparison purpose, ductility is quantified by the ‘ductility factor’, the criteria and the mathematical determination of which are also explained in this paper. Proposals of increasing the compression steel ratios are discussed so as to allow the maximum tension reinforcement ratios to exceed 2.5%, while keeping the ductility factor not inferior than that implied by the Code (under the prescribed limits of reinforcement ratios in the Code). The purpose is to allow smaller structural sizes...

43 Targeting PI3K: where are we?

This paper presents a numerical study on structurally continuous steel decking concrete slabs subjected to fire. This is an important subject for improving the fire design methods of this type of elements. Slabs with tension, compression and/or both steel reinforcement types have been tested. The results of twelve full-scale slab fire resistance tests carried out by the authors have been used in the calibration of the numerical models. Despite the compression rebars being more thermally protected, the use of tension rebars proved to be a good design solution, because just from the initial 5 min of fire, a detachment of the steel deck was registered. In this sense, slabs without tension rebars performed like a non-reinforced concrete slab. The detachment of the steel decking suggests that this type of slabs should not be fire designed as a composite element. There is no interaction between the steel decking and the concrete just from the beginning of the fire exposure. Nevertheless, when the steel decking detaches and stops contributing to the mechanical resistance of the slab, it continues to work as a thermal barrier. Another important conclusion is that the simple calculation method of EN 1994–1-2 needs an update for taking into account these phenomena. A new methodology for the mechanical and thermal design of these slabs in case of fire is proposed.

THE EFFECT OF SOLID PARTS ON THE NON-LINEAR BEHAVIOR OF ONE WAY RIBBED SLABS

Non-linear behavior of one way ribbed slabs was introduced in this paper. The 3D-FEM model through (ANSYS) program has been used to accomplish this study. In this research the effect of width of middle solid part, the area of compression reinforcements of middle solid part and the width of edge solid parts on the behavior of one way ribbed slabs were studied. The ultimate load, the cracking load, the strain of concrete, stress of steel and deflection were calculated as well as mode of failure was observed. The best ratio of the width of middle solid part to the span of slab and the effect of existence the edge solid parts were concluded.

Bar Buckling in RC Columns Confined with Composite Materials

The onset and evolution of bar buckling at the plastic hinge of old-type reinforced concrete (RC) columns confined with composite material [fiber-reinforced polymer (FRP) and textile-reinforced mortar (TRM)] jackets was investigated experimentally and analytically in this study. The interaction between composite jacket (or concrete cover, for unconfined concrete) and embedded longitudinal compression reinforcement at the onset and evolution of bar buckling was achieved through strain measurements of the compression reinforcement. Moreover, the implementation of a recent stress-strain confinement model, which relates lateral with axial strains, allowed the description and monitoring of the axial-lateral strain relationship at the base of the columns throughout the evolution of bar buckling. Based on the aforementioned model and the experimental measurements, the postbuckling behavior of columns was related to the jacket stiffness. Finally, a semiempirical expression that gives the drift ratio of RC columns at the onset of bar buckling was modified herein for the case of FRP- or TRM-jacketed columns.

A generalisation of the Hillerborg's model for the analytical evaluation of ductility of RC beams in bending

In this study, a generalised analytical model for the evaluation of the plastic rotations of reinforced concrete beams in bending is proposed. To this aim, the pioneering Hillerborg's model is here extended by taking into account also the contribution of reinforcement in compression. Moreover, a detailed comparison with the experimental results by Bosco and Debernardi on three-point bending reinforced concrete beams by varying the reinforcement percentage and the size-scale of the structural elements is carried out. This permits study of the influence of the parameter β, related to the length of strain localisation of concrete in compression, on the ductility response and how to tune this parameter according to experiments. The proposed generalisation of the Hillerborg model is then suitably applied to over-reinforced concrete beams in bending, where concrete crushing is the prevailing non-linearity; it is shown that the model is able to capture the phenomenon of size-scale effects.

Experimental research on standard cracking patterns in reinforced concrete members subjected to pure bending

The present study analyzes the suitability of the formulas proposed in EHE, Eurocode 2 and ACI Building Code 318 for crack control in reinforced concrete by testing 14 full-scale beams subjected to pure bending. It also explores the effect of varying parameters such as diameter, steel ratio and compression reinforcement arrangement and analyzes the fit between the above theoretical procedures and the experimental findings (less favourable than expected in some cases). The article also discusses the considerable impact of certain parameters, such as steel ratio, on crack control, and the scant effect of parameters such as diameter, reinforcement spacing and the arrangement of compression reinforcement. Pursuant to the results obtained in this study, possible variations on existing formulas are evaluated, specifically on the formula exhibiting a tendency that came closest to reflecting the test results (EC-2), with a view to improving the fit between that formula and the experimental results.

Compressive strength loss and reinforcement degradations of reinforced concrete structure due to long-term exposure

Degradations due to long-term weathering actions on a reinforced concrete structure were investigated. Compressive strength and reinforcement corrosion developments of a prototype RC structure were monitored for 6 years using destructive and non-destructive tests which include periodic coring, compressive strength, rebound hammer, ultrasonic pulse velocity, carbonation, half-cell and tensile strength tests. Eventually, results have shown that more than a quarter of peak compressive strength can be lost within 5 years of continuous exposure. Corrosion of the exposed bars within the range of the testing period was also observed to be quite alarming. Thus, defects caused by prolonged actions of environmental factors may pose serious threats on the integrity of partially completed structures especially abandoned projects.

Behavior of Full-Scale Glass Fiber-Reinforced Polymer Reinforced Concrete Columns under Axial Load

Most current design guidelines and codes do not allow glass fiber-reinforced polymer (GFRP) bars to be used as compression reinforcement. This study investigates the compressive behavior of longitudinal GFRP bars in reinforced concrete (RC) columns. An experimental campaign on full-scale GFRP RC columns under pure axial load was undertaken using specimens with a 24 x 24 in. (0.61 x 0.61 m) square cross section. The results showed that the GFRP RC specimens behaved similarly to the steel RC counterpart when the longitudinal reinforcement ration is equal to 1.0%. The use of longitudinal GFRP bars was not found to be detrimental to the performance of RC columns, but the contribution of GFRP bars to column capacity was significantly lower than that of the steel bars in the steel RC counterpart. The 3 inch spacing of the GFRP ties strongly influenced the failure mode by delaying the buckling of the longitudinal bars, initiation and propagation of unstable cracks and crushing of the concrete core. Considerations for including GFRP reinforced columns in current ACI practice are discussed.

Engastamento parcial de ligações viga-pilar em estruturas de concreto armado

Neste trabalho são apresentados os resultados experimentais de ensaios em ligações viga-pilar de concreto armado realizados na Escola de Engenharia de São Carlos - USP. Os referidos resultados experimentais concentram-se nas rotações relativas entre os elementos viga e pilar, importantes para a determinação da relação momento-rotação das ligações e da caracterização do comportamento semi-rígido das mesmas. Os dados experimentais foram obtidos a partir de ensaios de ligações viga-pilar de extremidade. A influência da resistência à compressão do concreto e da taxa de armadura transversal na região dos nós de pórtico sobre as rotações relativas foi analisada. Os resultados experimentais foram confrontados com o modelo teórico proposto por Ferreira [1] para ligações com engastamento parcial, permitindo uma avaliação da porcentagem de engastamento alcançada pelas tipologias de ligações monolíticas abordadas neste trabalho.