Concrete Cross Research Articles

The Applicable Span-Height Ratio of Steel Reinforced Concrete Cross Beam Based on Deflection Control

Steel reinforced concrete (SRC) cross beam has high stiffness and seismic resistance capability, but it is difficult to determine a reasonable beam span-height ratio in engineering applications because there is no general theory in this area. In this paper, we developed a numerical model for SRC cross beam deflection simulation, in which the effect of cast-in-situ concrete floor on the beam has been taken into consideration as an effective flange of the beam. We also investigated the effect of the beam cambering limits in construction on beam deflection under different span-height ratios. The numerical results shows that seismic action and wind load have little effect on the span-height ratio, while beam cambering in construction is very favorable to decrease beam deflection. In addition, steel stiffness has great influence on the deflection of cross beam, and elastic deflection is only one fourth of the actual deflection. Therefore, the reasonable span-height ratio of SRC cross beam should be 20 to 30.

The Settlement Analysis and Reinforcement of a Cast-<i>In Situ</i> Concrete Floor

After form a removal concrete cross ribbed beam floor in a commercial plaza, the vertical cracks are discovered, and the settlement analysis and reinforcement of a Cast-in-situ concrete floor are performed. The detection of the maximum crack is 0.3mm,and the Maximum settlement of cross ribbed beam is 48mm. By theoretical analysis, improper form removal during construction stage makes the actual floor force inconsistent with the design of a load transfer, which is the main reason of the excessive settlement in the cross ribbed beam. Through the economy, ease of handling in construction and other aspects of comparative analyses, the close beam side by epoxy grout and paste the carbon fiber under the beam to reinforce the cross ribbed beam. After reinforcement, no defect is discovered in the project so far.

Estimation of the bending stiffness of rectangular reinforced concrete beams made of steel fibre reinforced concrete

A method of calculating the location of the neutral axis of a rectangular steel fibre reinforced concrete cross section before and after cracking, and its moments of inertia relative to this axis is proposed. Moreover, the method of calculating the cross section's geometrical characteristics for both the cracked stage and the uncracked stage is based on a model of fibres distribution along the length of the beam. Consequently, two algorithms for estimating the immediate and long-term deflections of steel fibre reinforced concrete beams are proposed. One of the algorithms is for uncracked beams and the other for cracked beams. The algorithms have been positively experimentally verified.

Limits to Plastic Analysis due to Size-Scale Effects on the Rotational Capacity of Reinforced Concrete Cross Sections

Reinforced concrete (RC) structures are usually designed to provide a ductile response under bending loadings. To this aim, most codes of practice impose lower and upper limits to the steel ratio in order to prevent unstable crack propagation and to avoid brittle failure due to concrete crushing without steel yielding. Within these limitations, elastic analysis with moment redistribution or even plastic analysis can be adopted for RC structures. In this context, size-scale effects are usually disregarded, leading to unsafe design conditions in the case of large structures.In the present study, the limitations of the prescriptions provided by the European and American building codes concerning the admissible plastic rotation and moment redistribution are highlighted. In particular, using a numerical algorithm based on the finite element method and on nonlinear fracture mechanics concepts recently developed by the present authors, the mechanical behaviour of the plastic hinge region of RC beams in bending is simulated. The results show that the effect of the structural dimension should be explicitly introduced in the code prescriptions for a safe structural design, by considering different design curves depending on the size-scale of the beams.

Effect of casting method and shear span-to-depth ratio on the behaviour of Ultra-High Performance Concrete cross arms for high voltage transmission lines

This paper reports on a project that is in an area of high economic and technological importance to the hydro-power utilities. Currently, most high voltage transmission line poles and their cross arms are made either from wood or steel. As an emerging technology, the project addresses an important topic on the application of Ultra-High Performance Concrete (UHPC) cross arms, in high voltage transmission poles, as a competitive alternative in today’s market to replace the existing deteriorated wood and steel cross arms. The characteristic properties of UHPC cross arms make them the ultimate materials for the construction of thin members. Given all the advantages of UHPC concrete, and the market demand for a reliable and durable solution, it is expected that these UHPC cross arms are a repetitive application. Experimental test results of an investigation on the structural evaluation of prestressed UHPC C-channel cross arms are reported in this paper. The testing program was designed to corroborate the structural capacity of the UHPC cross arms under given loading scenarios according to specifications used by the hydro-power industries. Several tests were performed to examine the effect of steel-fibre orientation around the internal ordinary steel rebars on the flexural strength of UHPC cross arms using different casting types; and to evaluate the effect of varying the shear span-to-depth (or height) ratio on the flexural and shear capacity of the prestressed UHPC cross arms.

Pushover Analysis of Shear-Critical Frames: Formulation

An analytical procedure is presented for the nonlinear analysis of reinforced concrete frame structures consisting of beams, columns, and shear walls under monotonic and pushover loads. The procedure is capable of accurately representing shear-related mechanisms coupled with flexural and axial behaviors. The formulation described herein uses linear-elastic frame analysis algorithms in a nonlinear mode based on an unbalanced force approach. Rigorous nonlinear sectional analyses of concrete member cross sections, using a distributed-nonlinearity fiber model, are performed based on the disturbed stress field model. The proposed method is distinct from existing methods in that it allows for the inherent and accurate consideration of shear effects and significant second-order mechanisms within a simple modeling process suitable for practical applications. Decisions regarding the anticipated behavior and failure mode or the selection of appropriate analysis options and parameter values, or additional supporting calculations such as the moment-axial force or shear force-shear deformation responses, are not required.

통계적 분산을 고려한 콘크리트의 역학적 특성

Dept. of Urban and Environmental System Engineering, SeoKyeong University, Seoul 136-704, KoreaABSTRACT The randomness in the strength of a RC member is caused mainly by the variability of the mechanical propertiesof concrete and steel, the dimensions of concrete cross sections, and the placement of reinforcing bars and so on . Among thosevariations, the randomness and uncertainty of mechanical properties of concrete, such as compressive strength, tensile strength, andelastic modulus give the most significant influences and show relatively large statistical variations. In Korea, there has been littleeffort for the construction of its own statistical models for mechanical properties of concrete and steel, thus the foreign data havebeen utilized till now. In this paper, variability of compressive strength, tensile strength and elastic modulus of normal-weight struc-tural concrete with various specified design compressive strength levels are examined based on the data obtained from a numberof published and unpublished sources in this country and additional laboratory tests done by the authors. The inherent probabilisticmodels for compressive and tensile strength of normal-weight concrete are proposed as Gaussian distribution. Also, the rela-tionships between compressive and splitting tensile strength and between compressive strength and elastic modulus in current KCICode are verified and new ones are suggested based on local data.Keywords : compressive strength, splitting tensile strength, elastic modulus, statistical variations, probabilistic distribution models

An automated image analysis procedure to evaluate compacted asphalt sections

A new image analysis program is presented to determine morphological and textural properties of aggregates, asphalt binder and air voids in compacted asphalt mixes. The procedure involves scanning cut sections of laboratory or field specimens and estimating volumetric properties based on a pseudo 3D algorithm. Properties that are calculated include gradation, asphalt content, air void content, amount of flat/elongated particles, distribution of particle orientations, air void profiles, and various particle shape and textural measures. Validation of the code for specimens for which reference values were available indicates generally good predictions, particularly with regard to gradation and asphalt content. The objective of the study has been to develop a robust procedure that is easy to use, cost efficient, environmentally friendly and that can be used as a means to determine asphalt characteristics for quality control and quality assurance purposes. The new analysis technique may also find application in the study of SEM resin-impregnated soil thin sections and concrete cross sections.

Experimental tests on biaxially loaded concrete-encased composite columns

This paper reports an experimental investigation of the behaviour of concrete-encased composite columns subjected to short-term axial load and biaxial bending. In the study, six square and four L-shaped cross section of both short and slender composite column specimens were constructed and tested to examine the load-deflection behaviour and to obtain load carrying capacities. The main variables in the tests were considered as eccentricity of applied axial load, concrete compressive strength, cross section, and slenderness effect. A theoretical procedure considering the nonlinear behaviour of the materials is proposed for determination of the behaviour of eccentrically loaded short and slender composite columns. Two approaches are taken into account to describe the flexural rigidity (EI) used in the analysis of slender composite columns. Observed failure mode and experimental and theoretical load-deflection behaviour of the specimens are presented in the paper. The composite column specimens and also some composite columns available in the literature have been analysed and found to be in good agreement with the test results.

Influence of Cracking on Equivalent SDOF Estimates of RC Frame Drift

Cracking, yielding, and softening of reinforced concrete cross sections influence the response of reinforced concrete structures to strong ground shaking. The accuracy of peak roof displacement estimates made using relatively simple “equivalent” single-degree-of-freedom (SDOF) models is investigated. Peak roof drifts of four multistory frames were determined by nonlinear dynamic analysis using high-fidelity models, in which cracking, yielding, and softening of components are explicitly represented in the multidegree-of-freedom model. Estimates of peak roof drift are made using low fidelity “equivalent” single-degree-of-freedom models, in which nonlinearity is represented using simple stiffness-degrading models that capture yielding and the initial stiffness of the model is set equal to the cracked stiffness. Roof drifts are examined for the four frames, each subjected to a suite of ten ground motion records scaled to five intensity levels, representing ordinary “far-field” motions. As might be expected, the influence of the uncracked stiffness on the accuracy of peak roof drift estimates was found to diminish with increasing roof drift. Of greater significance is that the uncracked stiffness had a negligible effect for roof drifts greater than approximately twice the yield drift. The simple estimates were reasonably accurate at these drift levels.

Design of Optimally Reinforced RC Beam, Column, and Wall Sections

A conjugate gradient search method is coupled with a general model for the ultimate strength of a rectangular reinforced concrete (RC) cross section. Reinforcement required to provide reliable resistance identically equal to required strengths (due to factored load effects) is determined. The total reinforcement is determined optimally, either to obtain a global minimum or to obtain a minimum subject to various constraints, such as the use of equal reinforcement on opposite faces or the use of equal reinforcement on all faces. The model is useful for the design of beam, column, and wall sections that are subjected to uniaxial or biaxial bending. Solutions are obtained directly, and make use of computing power contained within spreadsheet programs that are widely available. Avoiding the somewhat tedious hand calculations and approximations required in conventional iterative design approaches avoids errors and potentially unsafe designs, while the use of optimum reinforcement quantities advances the aim of improving the sustainability of RC construction.

Capacity of Rectangular Cross Sections under Biaxially Eccentric Loads

This paper seeks to present an analytical procedure for the determination of moment contures for rectangular reinforced concrete cross sections under assigned axial loads. The moment contours represent horizontal sections of the failure surface for assigned axial loads. The analytical approximation is obtained through a function of the type suggested by Bresler, in which, however the power exponent is not fixed but calculated on the basis of the interaction diagrams for load eccentricities along axes parallel to the axes of symmetry and to a diagonal of the rectangular cross section. Calculation of these interaction diagrams is made easy by the equivalence between their dimensionless expressions and the interaction diagrams of an equivalent square cross section of unit length side. Analytical proof of this equivalence is provided. A comparison of this procedure with interaction diagrams obtained through direct numerical integration shows that the proposed method is accurate and conservative.

Theorem of optimal reinforcement for reinforced concrete cross sections

A theorem of optimal (minimum) sectional reinforcement for ultimate strength design is presented for design assumptions common to many reinforced concrete building codes. The theorem states that the minimum total reinforcement area required for adequate resistance to axial load and moment can be identified as the minimum admissible solution among five discrete analysis cases. Therefore, only five cases need be considered among the infinite set of potential solutions. A proof of the theorem is made by means of a comprehensive numerical demonstration. The numerical demonstration considers a large range of parameter values, which encompass those most often used in structural engineering practice. The design of a reinforced concrete cross section is presented to illustrate the practical application of the theorem.

Stress Transfer between FRP Laminates and Concrete through Deteriorated Concrete Surfaces

This study investigated the mechanism of stress transfer between glass and carbon fiber-reinforced polymer (FRP) laminates and concrete beams with deteriorated surfaces. Thirty-six beams were prepared with either a solid concrete cross section, or with a weak concrete layer at the surface, simulating the state of a deteriorated surface. The beams were reinforced with glass or carbon FRP sheets and tested in flexure. Strain development in the laminate and in the concrete layers was recorded and analyzed. The mode of failure changed from shear within the deteriorated layer of concrete to delamination at the interface between the resin and the concrete in the solid high-strength concrete. A significant amount of stress was transferred between the FRP laminates and the concrete surface probably by residual frictional stresses after shear cracks developed in the deteriorated layer, leading to a remarkable load bearing capacity of these beams.

Analytical integration of cross section properties for numerical analysis of reinforced concrete, steel and composite frames

This paper presents a procedure for numerical analysis of steel, reinforced concrete or composite cross section of arbitrary polygonal shape, based on analytical evaluation of cross section properties, i.e., section resistant forces and tangent moduli. The uniaxial stress–strain relationship is supposed to be of a piecewise polynomial type, and the subdivision of the section into subregions is performed by means of a contouring algorithm. The procedure may be easily implemented into a beam–column finite element code which works with evaluation of cross section properties at the numerical integration points.

Slenderness effects on the simulated response of longitudinal reinforcement in monotonic compression

The influence of reinforcement buckling on the flexural response of reinforced concrete members is studied. The stress-strain response of compression reinforcement is determined computationally using a large-strain finite element model for bars of varied diameter, length, and initial eccentricity, and a mathematical expression is fitted to the simulation results. This relationship is used to represent the response of bars in compression in a moment-curvature analysis of a reinforced concrete cross section. The compression bar may carry more or less force than a tension bar at a corresponding strain, depending on the relative influence of Poisson effects and bar slenderness. Several cross-section analyses indicate that, for the distances between stirrups prescribed in modern concrete codes, the influence of inelastic buckling of the longitudinal reinforcement on the monotonic moment capacity is very small and can be neglected in many circumstances.

Desempenho físico-químico de metais e estruturas de concreto de redes de distribuição de energia: estudo de caso na região de Manaus

The influence of natural aging furthered by atmospheric corrosion of parts of electric transformers and materials, as well as of concrete poles and cross arms containing corrosion inhibitors was evaluated in Manaus. Results for painted materials, it could showed that loss of specular gloss was more intensive in aliphatic polyurethane points than in acrylic polyurethane ones. No corrosion was observed for metal and concrete samples until 400 days of natural aging. Corrosion in steel reinforcement was noticed in some poles, arising from manufacturing faults, such as low cement content, water/cement ratio, thin concrete cover thickness, etc. The performance of corrosion inhibitors was assessed by many techniques after natural and accelerated aging in a 3.5% saline aqueous solution. The results show the need for better chemical component selection and its concentration in the concrete mixture.

Bending Moment–Shear Force Interaction Domains for Prestressed Concrete Beams

The performance of a prestressed concrete beam, subjected to bending moment M together with shear force V, has been the object of many studies and is an important aspect to take into account in the design. Some models, proposed by researchers and international codes, evaluate the shear strength of prestressed beams by modifying the truss model by Morsch, so as to account for the different slope of stress fields in the web due to the prestressing action. More recent approaches add a strut-and-tie model to the traditional truss model. This paper generalizes a model that was previously proposed for box and I-shaped reinforced concrete cross sections of structural elements. The model, that now includes the effect of prestressing tendons, considers variable-depth stress fields applied to the cross section, subdivided into layers, and allows evaluation of normalized m-v design domains depending both on the web and flange reinforcement and on the slope of the prestressing steel tendons. The reliability of the method has been validated by comparing its numerical results to the strength provided by tests on reinforced concrete beams and on thin-webbed prestressed concrete beams, referred to in the literature. Finally, it has been used in the design of a pretensioned bridge beam to evaluate the additional reinforcement necessary in the flanges, as a function of the reinforcement provided to the web.

Mechanical Properties of Corrosion-Damaged Reinforcement

Corrosion of embedded reinforcement is the most prevalent form of degradation of reinforced concrete structures, and may impair structural capacity through loss of bar section, loss of bond between reinforcement and concrete as a result of longitudinal cracking, or loss of concrete cross section. The effect of corrosion attack on mechanical properties of reinforcement is investigated through physical tests on bars with simulated and real corrosion damage and through a simple numerical model. Bars subjected to local or pitting attack may suffer a relatively modest loss of strength but a significant loss of ductility, and this is related principally to the variability of attack along the length of the bar. The numerical model supplements experimental work through a parametric study on the influence of steel characteristics. Finally, guidelines on assessment are suggested that are derived from results reported in the paper and from elsewhere in the published literature.

Rehabilitation criteria for post-tensioned voided-slab bridges

Current rehabilitation practices for aging, post-tensioned, voided-slab bridges typically reduce the geometric properties of the concrete cross section and so permanently increase post-tensioning stresses, change primary and secondary prestress moments, and create new primary and secondary moments because the original concrete restrains shrinkage of the new concrete. These changes affect the resistance of the rehabilitated bridge at limit states specified for new construction in the Canadian Highway Bridge Design Code (CHBDC) and may cause other limit states not currently identified in the CHBDC to govern. Rehabilitation schemes should be checked for a serviceability limit state of tensile stresses due to permanent service loads that exceed the cracking strength of the original concrete, which is typically not detailed to control crack widths. Ultimate limit states to check are (i) flexural resistance over interior supports, where the total factored demand can be increased markedly by the rehabilitation; and (ii) creep-initiated failure of concrete due to permanent compressive stresses. The application of these procedures is illustrated through example calculations for a typical continuous bridge.Key words: post-tensioned concrete, serviceability, ultimate limit state, restrained shrinkage, secondary prestress moments, critical stress, cracking.