Design Of Concrete Beams Research Articles

Shear design of concrete beams reinforced with grid reinforcement

A new method for designing orthogonal steel grids as shear reinforcement in concrete members is proposed, considering sectional stress distribution and failure criteria of concrete. The concept and formulations of this method have been applied to the analysis and design of reinforced concrete beams subjected to combined shear and bending. An accurate formula for calculation of shear reinforcement ratio is deduced, leading to innovative results. Shear strength of reinforced concrete beams is assumed as the sum of contributions from orthogonal grid reinforcements in the cracked zone and from concrete in the shear compression zone. Eleven reinforced concrete beams with grid reinforcement were tested under bending and shear to validate the accuracy of the proposed method. It was found that the proposed model predicts the experimental behaviour accurately and that grid reinforcement can enhance the shear behaviour of concrete beams.

Testing and Control for Strands Embedded in Annular Concrete Foundation Beam of Steel Archaize Tower

Combined with the design and construction of annular pre-stressed concrete foundation beam of Tiantang Site Protection Exhibition Project in Luoyang, China, this paper introduces the test process of frictional lose for annular strands. The calculation method is given to deal with the original data to get the friction coefficient of the strands. The controlling parameters such as control tensioning stress and theoretical elongations of strands are advised. The rational pre-stressing process and key indexes are confirmed by the comparison of test and theoretical circumferential stresses of the foundation beam. It is reasonable to fulfill the design requirements by strict controlling in the fields. It is believed that the process and method in this paper would give some reference for the construction of similar annular pre-stressed concrete structures.

RCStruC: A Structural Software for Design of Doubly Reinforced Rectangular Concrete Beam

Abstract - The main purpose of this experimental study is to design a structural software for the analysis of doubly reinforced rectangular concrete beams. The structural software is called RCStruC (Reinforced Concrete Structural Calculator). This study determines the performance of the structural software in terms of accuracy of the results, speed in generating results, and convenience of use. Further, this study determines whether there is a significant difference in the performance of RCStruC and the manual process of performing structural analysis. The respondents of the study were ten structural designers and practitioners in the city. Ten test runs were conducted per respondent. The findings manifested that RCStruC was perceived as very satisfactory in terms of accuracy, speed in generating results, and convenience of use. Furthermore, RCStruC was consistently perceived as very satisfactory while the manual process was generally perceived as fair. The researchers concluded that RCStruC significantly produces quicker, easier and error-free structural analysis results compare to the manual process. It is recommended that structural designers and practitioners should be encouraged to use the software package, RCStruC, to minimize errors and obtain easy and quick analysis output. Keywords - structural software, concrete beam design, concrete calculator

Effects of the Transverse Reinforcement on the Shear Behaviour of High Strength Concrete Beams

This paper presents the results of an experimental investigation dealing with the effects of transverse reinforcement on the crack patterns, the ultimate carrying capacity and the ductility of beams made of high strength concrete and normal strength concrete for comparison purposes. The test results are analyzed and compared with the shear provisions in the four major universal codes (ACI-318; BS-8110; Eurocode 2; BAEL 99). Twenty six reinforced concrete beams with and without transverse reinforcement were constructed using different shear-span to depth ratios (a/d = 1.5, 2.0 and 3.0) and different compressive strengths of concrete (44 MPa, 65 MPa and 86 MPa). The test results indicate that the presence of transverse reinforcement had controlled efficiently the crack width by enhancing the aggregate interlocking on the crack surface, increased moderately the shear strengths of the beams by factors ranging from 1.14 to 1.86, and increased appreciably the ductility of beams at the ultimate state. It should be noted, however, that the beams failed at shear strength contributions of transverse reinforcement ( Vs) considerably lower than the values predicted by the models used in the four major universal codes. This translates that the existing universal design codes may not be rationally safe against shear design of high strength concrete beams containing transverse reinforcement.

Concurrent flexural strength and deformability design of high-performance concrete beams

In the design of earthquake resistant reinforced concrete (RC) structures, both flexural strength and deformability need to be considered. However, in almost all existing RC design codes, the design of flexural strength and deformability of RC beams are separated and independent on each other. Therefore, the pros and cons of using high-performance materials on the flexural performance of RC beams are not revealed. From the theoretical results obtained in a previous study on flexural deformability of RC beams, it is seen that the critical design factors such as degree of reinforcement, concrete/steel yield strength and confining pressure would simultaneously affect the flexural strength and deformability. To study the effects of these factors, the previous theoretical results are presented in various charts plotting flexural strength against deformability. Using these charts, a "concurrent flexural strength and deformability design" that would allow structural engineers to consider simultaneously both strength and deformability requirements is developed. For application in real construction practice where concrete strength is usually prescribed, a simpler method of determining the maximum and minimum limits of degree of reinforcement for a particular pair of strength and deformability demand is proposed. Numerical examples are presented to illustrate the application of both design methods.

Minimum deformability design of high-strength concrete beams in non-seismic regions

In the design of reinforced concrete (RC) beams, apart from providing adequate strength, it is also necessary to provide a minimum deformability even for beams not located in seismic regions. In most RC design codes, this is achieved by restricting the maximum tension steel ratio or neutral axis depth. However, this empirical deemed-to-satisfy method, which was developed based on beams made of normal-strength concrete (NSC) and normal-strength steel (NSS), would not provide a consistent deformability to beams made of high-strength concrete (HSC) and/or high-strength steel (HSS). More critically, HSC beams would have much lower deformability than that provided previously to NSC beams. To ensure that a consistent deformability is provided to all RC beams, it is proposed herein to set an absolute minimum rotation capacity to all RC beams in the design. Based on this requirement, the respective maximum limits of tension steel ratio and neutral axis depth for different concrete and steel yield strengths are derived based on a formula developed by the authors. Finally for incorporation into design codes, simplified guidelines for designing RC beams having the proposed minimum deformability are developed.

Shear strength prediction for reinforced concrete beams without stirrups

Traditionally, shear design of concrete beams without stirrups has relied on empirical equations derived from laboratory experiment data. However, such methods lack a sound theoretical basis for shear failure of reinforced concrete (RC) structures due to the complexity of the failure mechanism. In the 1980s, a relatively rational model based on the modified compression field theory (MCFT) was developed at the University of Toronto and subsequently accepted worldwide; it forms the basis of shear provisions in Canadian standards and American specifications for the design of concrete structures. This paper describes further research based on the MCFT. An expression for the average shear stress across a crack was derived and a simplified equation of shear strength considering the size effect in shear was developed. The obtained equations were verified with extensive sets of experimental data from different sources (598 beams in total). It was found that the variation coefficients of the ratio of shear strength calculated using the derived average shear stress across a crack based on the MCFT and the simplified expressions to the test data was small; the mean was about 0·8. It is thus considered that the simplified expressions are suitable for shear analysis and design of RC beams without stirrups.

Analytical Modeling and Design Validation of Posttensioned Precast Concrete Coupling Beams for Seismic Regions

This paper provides an experimental validation on the analytical modeling and design of unbonded posttensioned precast concrete coupling beams. Previous test results from a series of floor-level coupling beam subassembly specimens are compared with the predicted results from a fiber-element analytical model. The test results are also used to validate an idealized coupling beam end moment versus chord rotation relationship that was developed as a design tool following basic principles of equilibrium, compatibility, and constitutive relationships. Based on the experimental and analytical comparisons, the paper presents a seismic design approach to achieve the desired lateral strength, stiffness, ductility, and energy dissipation capacity in unbonded posttensioned precast coupling beams.

Experimental Study on the Stress Increment of Prestressed Tendons of Retard-Bonded Prestressed Concrete Continuous Beams

Based on the bending experiment for two-span continuous beams of retard-bonded prestress concrete, the analysis of the stress increment of prestressed tendons is made in the loading process. The theory that the working performance of retard-bonded prestressed concrete members is as same as unbonded prestressed concrete members during the retarding period is demonstrated. It is feasible to use the formulas for the reference (Technical specification for concrete structures prestressed with unbonded tendons) to calculate σputhe ultimate stress and Δσp the Stress increment of the retard-bonded prestressed tendons and the recommended formulas are advised to use. It is also demonstrated that retard-bonded prestressed concrete members have the same working performance as bonded prestressed concrete members after the retarding period. The conclusion of this paper can provide the reference date for the design of retard-bonded prestressed concrete continuous beam.

Probabilistic assessment on flexural capacity of GFRP-reinforced concrete beams designed by guideline ACI 440.1R-06

The provisions in the guideline ACI 440.1R-06 (call ACI guideline thereafter) on the flexural design of concrete beams reinforced with glass fiber reinforced polymer (GFRP) rods are assessed from the probabilistic point of view by using the Rackwitz–Fiessler method. The assessment reveals that the design provisions in ACI guideline are really conservative. Among all resistance-related random variables, sectional width and height-to-width ratio have put significant influence on average reliability level in either failure mode. GFRP strength does not have any effect on reliability level in concrete crushing mode. Concrete strength shows a negligible effect in the failure mode of GFRP rupture. In the case of GFRP rupture, as the mean-to-nominal ratio of GFRP strength increases, the average reliability index at first increases and then decreases. Design of GFRP-reinforced concrete components subject to aggressive exposure conditions would achieve higher reliability level. As a result of the investigation on the relation between average reliability index and resistance reduction factor, a modified value of 0.81 for the factor is suggested.

Ductility Design of High-Strength Concrete Beams and Columns

High-strength concrete (HSC) is increasingly used for the construction of tall buildings and long span bridges. However, most engineers just focus on how to better utilize the strength potential of HSC and little attention is paid to ensure that the HSC structures would have sufficient ductility. In this regard, it should be noted that the current design codes, which do not provide any guidelines for ductility design, are not applicable to HSC structures. In recent years, the authors have been conducting research on how the use of HSC would affect the flexural ductility of concrete members. Herein, an overall summary of their research is presented. It will be shown that depending on the reinforcement detailing and loading conditions, the ductility of HSC structures is not necessarily lower than that of normal concrete structures. Finally, guidelines for the ductility design of HSC beams and columns, augmented with design formulas and charts, are given.

Performance-based optimal design of compression-yielding FRP-reinforced concrete beams

Abstract The application of fiber-reinforced polymer (FRP) composite in concrete structures has drawn worldwide interest recently. However, a critical drawback of the resulting structures is their poor ductility performance, due to FRP’s linear-elastic mechanical properties. “Unless ductility requirements are satisfied, FRP materials cannot be used reliably in structural engineering applications” [1] . To resolve this problem, the authors recently developed a new technology to improve the ductility of flexural members through compression yielding (CY). In the experimental and theoretical investigations that have been undertaken so far, the CY concept has proved to be not only theoretically interesting and attractive, but also practically feasible. As CY beams make use of a different avenue to deliver ductility, their design is different from that in conventional reinforced concrete theory. This paper investigates the mechanical behavior of CY structures and proposes a criterion-based optimal design methodology that directly and quantitatively addresses ductility and strength demands.

Experimental study on the shear strength of recycled aggregate concrete beams

In concrete beam design, the shear capacity of the concrete beam is of great interest because shear failure is associated with an abrupt failure mode that undermines the flexural performance of the beam. Recently, because of the increasing cost of natural resources and environmental concerns, the use of recycled aggregate (RA) in construction is becoming the standard practice. However, the effects of recycled aggregates on the shear strength of concrete have not been fully examined. In this study the effects of RA on concrete shear strength are studied experimentally by performing flexural tests on 20 RA concrete beams with various combinations of span-to-depth ratios (a/d = 1·50, 2·50, 3·25), longitudinal reinforcement ratios (s = 0·53%, 0·83%, 1·61%) and RA replacement ratios (0%, 30%, 50%, 100%). The test results indicate that the concrete shear strength diminishes by up to 30% at 100% replacement ratio compared with the natural aggregate concrete. The shear strengths of the RA concrete beams are also compared with those obtained from the existing models for natural aggregate concrete and some design considerations in using the recycled aggregate concrete are discussed.

A simplified method to obtain time-dependent curvatures and deflections of concrete members reinforced with FRP bars

The design of concrete beams reinforced with fibre reinforced polymer (FRP) bars is often governed by the serviceability limit state, in which deflections play an important role. One of the most straightforward and easiest methods for calculating time-dependent deflections is based on applying multiplicative coefficients to instantaneous deflections. These methods have been adopted by ACI.440.1R-06 and CSA-S806-02 for FRP reinforced concrete structures (RCS), introducing slight modifications with respect to steel reinforced concrete members. However, the influence of different material mechanical properties and environmental conditions are not accounted for properly. In this paper, a new method based on a simplified coefficient for the prediction of time-dependent deflections is presented. The influence of variations in environmental conditions and the mechanical properties of the materials are taken into account. The numerical predictions obtained are compared to other models available in the literature and experimental results to validate the accuracy and suitability of the methodology presented.

Experimental research on plastic design method and moment redistribution in continuous concrete beams prestressed with unbonded tendons

Determining normal ultimate load-bearing capacity is important in the design of concrete continuous beams that are prestressed with unbonded tendons. Tests on continuous unbonded prestressed concrete beams show that bending moment redistribution can occur. However, the analysis approach is far from sufficient to quantify the amount of moment redistribution to this type of beam. In this paper, an analysis approach to quantify the amount of moment redistribution is described and the concept of negative moment redistribution is introduced. Moment redistribution of two-span continuous unbonded prestressed concrete beams takes place when concrete cracking develops in the rotation of plastic hinge angle, and reaches its maximum at failure of beams. Moment considering redistribution used to calculate the ultimate load-bearing capacity at the section over the inner support is the algebraic sum of the secondary moment due to prestressing and the moment due to external loads. Two formulae of the degree of moment redistribution are proposed based on test results.

Shear capacity of continuous pre-stressed concrete bridge girders with different static systems through vertical prestressing

Shear strength requirements are not met by some existing bridge girders, and so study of this strength seems essential. Pre-stressed concrete bridge girder shear strength with and without vertical prestressing is studied in this paper. First, several prestressed concrete beam models are selected and analyzed using the finite-element method. In this regard modeling validity is evaluated based on some tests performed on an existing bridge girder in Switzerland. In the study's second part, several beam specimens are built and tested and their load-deformation curve and cracking pattern are studied. The slope of shear cracks and shear reinforcement ratio are investigated using all numerical and experimental studies and the effect of horizontal and vertical pre-stressing on the noted parameters is evaluated. The findings should be of interest to researchers as well as practicing engineers involved in prestressed concrete beam analysis and design.

Structural shear behaviour of recycled concrete with silica fume

This paper is the outcome of the second stage of studies carried out on the structural behaviour of recycled concrete. The first stage determined, using beams specimens, the shear behaviour of recycled concrete with which 50% of the coarse aggregate was replaced by recycled coarse aggregate (obtained from concrete demolition waste). This stage revealed minor differences (recycled concrete – conventional concrete) in ultimate loads and these differences were found to increase when cracking was taken into account. In this study, it was determined that the addition of 8% silica fume to recycled concrete (recycled concrete with silica fume) improved this behaviour. Moreover, the use of this material in recycled concrete produced changes in its structural behaviour similar to those induced in conventional concrete (conventional concrete with silica fume). Finally, experimental results were compared using current codes and it had been seen that all of them were conservative so t can be used for the shear design of recycled concrete beams with silica fume.

Parametric space for the optimal design of compression-yielding FRP-reinforced concrete beams

Ductility of flexural members reinforced with fiber reinforced polymer (FRP) has been a serious concern for the application of FRP in structural engineering. A new and effective structural design concept of achieving ductility for FRP-reinforced concrete beams through compression yielding (CY) instead of tensile yielding has recently been developed. The ductility of CY beams depends very much on the details of the CY zone. A previous theoretical investigation into beams with an elastic-perfectly plastic CY block has shown that an optimal level of ductility exists in certain regions of the parametric space. However, experimental investigations have found that elastic-perfectly plastic CY blocks are difficult to construct, and often the post-yield behavior features some strain hardening or softening. For this reason, the present study aims to clarify the ductility behavior of CY beams with a more general CY block model, focusing on the effects of the post-yield modulus of the CY block. The key variables of the CY beam system are first identified. Subsequently, the ductility performance of CY beams is investigated using a combination of analytical study and numerical simulation. Finally, the parametric space that produces an optimal level of ductility is further identified which could form the basis for the optimal design of CY beams. The results demonstrate that a small post-yield modulus of the CY block can be beneficial for ductility performance. However, a large post-yield modulus will significantly reduce the ductility.

Flexural Strength Design of Concrete Beams Reinforced with High-Strength Steel Bars

Current design requirements limit the allowable design strength of high-strength steel reinforcements to 80 ksi (550 MPa), which limits engineers from fully using the enhanced strength characteristics of low-carbon and chromium high-strength steel. In this paper, a methodology is presented for the flexural strength design of concrete beams reinforced with high-strength reinforcing steel that conforms to the requirements of ASTM A1035-07. The design method is based on simple analysis techniques that satisfy fundamental principles of equilibrium and compatibility. Strain limits for tension-controlled sections and compression-controlled sections are proposed that are consistent with the approach of the current and past ACI 318 Codes. The proposed method is compared with previously-reported experimental results, and the application of the proposed method is demonstrated by a numerical design example. Findings indicate that flexural members designed using the proposed design methods and criteria have comparable flexural strength characteristics with members designed according to current ACI 318 requirements, using Grade 60 (400 MPa) and Grade 75 (520 MPa) reinforcing steel.

Strengthening of reinforced concrete beams constructed with substandard steel reinforcement termination

Practical applications for the use of fibre reinforced polymer (FRP) composite materials for the seismic strengthening of reinforced concrete beams that have been constructed with a substandard beam bar termination method were experimentally investigated in this study. Results suggest that the cut-off reinforced concrete beam design does not meet the standard design codes and that if no extra shear reinforcement is arranged in the curtailed region, the beam may be subject to brittle failure . Installation of FRP plates for flexural and shear strengthening can successfully correct the deficiency. The results show that the FRP composite beams could withstand rotation levels greater than those expected to be imposed during an earthquake event.