Shear Provisions Research Articles

Development of the 2004 Canadian Standards Association (CSA) A23.3 shear provisions for reinforced concrete

This paper describes the development of the 2004 Canadian Standards Association (CSA) A23.3 shear design provisions for reinforced and prestressed concrete structures. These methods are similar to the 1994 standard in providing a simplified and general shear design method. They differ from previous standards by providing a direct link between these two methods and simple equations for the calculation of β and θ used in the general method rather than providing these values in a table. The paper explains the basic assumptions behind the new shear provisions, provides a derivation of the new equations, and compares designs made with the new equations to designs obtained from previous standards. In general, the new shear provisions require slightly less shear reinforcement than that required by the previous standard. The new general method is significantly easier to use, particularly with spreadsheets.Key words: shear, building codes, reinforced concrete, size effect, structural design.

Prediction of shear strength in high-strength concrete beams considering size effect

Recent research has indicated that the current American Concrete Institute (ACI) shear provisions provide nonconservative prediction for large slender beams with a low level of longitudinal reinforcement, but conservative predictions for deep beams. In the present paper, to modify these problems in the ACI shear provisions, the ultimate shear strength equation, considering size effect and arch action, is presented for computing the shear strength in high-strength concrete beams without stirrups. Three basic equations, namely those for the size reduction factor, ρ factor and arch action factor, are derived from the crack band model of fracture mechanics, analysis of previous shear equations for longitudinal reinforcement ratio and concrete strut described as a linear function in deep beams. Constants of basic equations were determined by using statistical analysis of previous shear testing data. To verify the proposed shear strength equation for each variable, about 300 experimental data were used and the proposed equation was compared with ACI 318 code, CEB–FIP model code, Kim and Park's equation, CSA 94 code and Zsutty's equation. While the proposed shear equation is simpler than other shear equations, it gives economical predictions of shear strength and reasonable safety margin.

The Seismic Shear Demand in Ductile Cantilever Wall Systems and the EC8 Provisions

The seismic shear provisions of EC8 for ductile reinforced concrete walls, serving as the lateral load resisting system in multistorey building structures are re-examined. Two aspects are considered (1) single walls, or a system comprising a number of equal-length walls, (2) a resisting system comprising walls of different lengths. It is demonstrated, in light of recent parametric studies, that the EC8 provisions for walls in the medium- and high-ductility classes (DC-M and DC-H, respectively) are both in need of revision. Possible revisions of requirements and a design procedure for a wall system are presented.

NCHRP Project 12-56, Application of Load and Resistance Factor Design Specifications to High-Strength Structural Concrete: Shear Provisions

The load and resistance factor design (LRFD) specifications in the current AASHTO LRFD Bridge Design Specifications limit the compressive cylinder strength to 10 ksi in relationships for calculating shear design strength, whereas concrete compressive strengths close to twice this level are commercially available in some parts of the United States. To overcome this limitation, allowing the same-size structural sections to span longer distances or carry higher loads, NCHRP has funded Project 12-56, Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Shear Provisions. In the experimental component of this project, 12 prestressed concrete bridge girders 52 ft long and 6 ft deep are being subjected to a uniformly distributed load until failure in shear. The primary variables in this study are concrete strength (ranging from 10 to 18 ksi), the maximum shear design stress (700 to 2,500 psi), strand anchorage details (straight, unbonded, and draped), and end reinforcement de...

Study of shear provisions for stiffened plate girders

Steel design in Canada generally follows the provisions of CSA-S16-01 "Limit states design of steel structures" (CSA 2001). The provisions in this standard governing the shear design of stiffened plate girders set limits to the choice of web thickness, girder depth, and the spacing of intermediate stiffeners. This paper reviews the influence of each of the equations that govern the shear design of stiffened plate girders. The study reveals that many of the equations are unlikely to have any effect. Of the 13 equations that could restrict the design, only 3 are likely to have any influence on a typical design. This reveals avenues for possible simplification of design procedures.Key words: anchor panel, shear design, stiffened plate girder, tension field panel.

크기효과를 고려한 복부보강이 없는 고강도 콘크리트 보의 전단강도 예측식의 제안

Recent research has indicated that the current ACI shear provision provides unconservative predictions for large slender beams and beams with low level of longitudinal reinforcement, and conservative results for deep beams. To modify some problems of ACI shear provision, ultimate shear strength equation considering size effect and arch action to compute shear strength in high-strength concrete beams without stirrups is presented in this research. Three basic equations, namely size reduction factor, rho factor, and arch action factor, are derived from crack band model of fracture mechanics, analysis of previous some shear equations for longitudinal reinforcement ratio, and concrete strut described as linear prism in strut-tie model deep beams. Constants of basic equations are determined using statistical analysis of previous shear testing data. To verify proposed shear equation for each variable, effective depth, longitudinal reinforcement ratio, concrete compressive strength and shear span-to-depth ratio, about 300 experimental data are used and proposed shear equation is compared with ACI 318-99 code, CEB-FIP Model code, Kim &Park's equation and Zsutty's equation. The proposed shear equation is not only simpler than other shear equations, it is but also shown to be economical predictions and reasonable safety margin. Hence proposed shear strength equation is expected to be applied to practical shear design.

Comparison of Eurocode 2, Model Code 90 and ACI 318-99 with regard to shear and punching provisions for footings

Code ACI 318, Model Code 90 and Eurocode EC-2 present important differences with regard to the shear strength and punching strength, this is especially shown when the steel ratio of reinforcement is low. The above mentioned is important especially in the case of footings. The author analyses the differences either in structural design or in cost for wall footings and isolated footings, in accordance with the three mentioned Codes.

Effect of Concrete Strength and Minimum Stirrups on Shear Strength of Large Members

There is currently a concern that ACI shear design procedures can be unconservative if applied to thick one-way slabs or large beams containing only minimum stirrups. This research discusses the results of 21 large beams tested to look into these concerns. Based on experimental results, this paper concludes that until the present ACI shear provisions are modified, it would be prudent to use the recent shear provisions of the AASHTO LRFD specifications as they provide a more consistent level of safety. A simple spreadsheet is described that allows these provisions to be conveniently applied.

Experimental Study on Shear Strength of High-Strength Concrete Beams

This comprehensive experimental and analytical investigation assessed the concrete component of shear resistance in beams made with high-strength concrete. The experimental program consisted of testing 24 beams (18 with stirrups and 6 without stirrups) to determine the contribution to shear resistance by the concrete component. Test data from six other investigations covering 125 specimens were also analyzed. The data from the experiments and literature were compared with the shear provisions of high-strength concrete from selected codes. When extrapolating current code provisions to determine the concrete component of shear resistance for high-strength concrete, the study found that safety margins for structural design were reduced.

Punching shear provisions for reinforced and presfressed concrete flat slabs

The validity of the CSA A23.3-94 code provisions for punching shear were compared with the punching shear results of 142 reinforced concrete flat slabs, 16 prestressed concrete flat slabs with unbonded tendons, and 17 flat slabs with unbonded prestressed and supplementary bonded reinforcement. The code prediction equations are not capable of direct verification against experimental results without using a correction factor. Using a justifiable correction factor, the CSA A23.3-94 provisions are appropriately conservative for reinforced concrete slabs but the scatter is large. However, it was concluded that the CSA A23.3-94 provisions are not conservative for prestressed concrete flat slabs. An equation is proposed to calculate the punching shear capacity of reinforced concrete and prestressed concrete slabs, which has a smaller coefficient of variation than the punching shear provisions of CSA A23.3-94, for symmetrically loaded interior columns. The critical section of the proposed method is the perimeter of the column, which is easier to justify than an arbitrary critical perimeter half the effective depth of slab from the column. Key words: reinforced concrete, prestressed concrete, flab slabs, punching shear.

Implications of soil–structure interaction effects on the NBCC 1990 base shear provisions for high-rise buildings

This study is carried out on a site-specific basis for three locations in Canada, namely Ottawa, Vancouver, and Prince Rupert. Soil models are developed to correspond to the soil classifications used to define the foundation factor, F, in the 1990 edition of the National Building Code of Canada (NBCC). Structural models are developed to represent both 20-storey ductile moment-resisting frames and ductile flexural walls. Three initial sets of actual ground motion records are scaled, in the frequency domain, to represent the postulated bedrock motions for each of the three sites. The computer program FLUSH is used to perform the numerical analyses of the various soil–structure systems. Results from the current study indicate that the code F values generally underestimate the site effects associated with the respective soil deposits, but appear to be reasonably adequate, in most cases, when soil–structure interaction effects are taken into consideration. In spite of some deficiencies in the code F values, the 1990 NBCC design base shear is shown to be quite conservative for regular high-rise reinforced concrete buildings. A simple measure to account for inertial interaction effects in uncoupled analyses is shown to provide a significant improvement, as compared to conventional uncoupled analyses, in the prediction of the coupled base shear demand. Key words: seismic, hazard, site, soil, structure, interaction, code, design, base, shear.

Combined seismic base shear and torsional loading provisions in the 1990 edition of the National Building Code of Canada

This paper evaluates the earthquake-resistant design provisions of the 1990 edition of the National Building Code of Canada (NBCC 1990) for asymmetric building structures subjected to combined lateral shear and torsional dynamic loadings arising from earthquake base excitation. A detailed parametric study is presented, evaluating the dynamic edge displacement response in the elastic range, for the side of the building which is adversely affected by lateral–torsional coupling. A series of buildings is studied, with realistic ranges of the fundamental natural period, structural eccentricity, and uncoupled frequency ratio. These buildings are evaluated under base loadings arising from a total of 45 strong motion records taken from earthquakes in North America, Mexico, Europe, the Middle East, and Southern Pacific, categorized according to site soil conditions and the ratio a/v of peak ground acceleration to velocity. The latter parameter together with the uncoupled lateral period are found to influence strongly the combined dynamic edge response, with the greatest forces on edge members arising from earthquakes with high a/v ratio in structures with natural periods below 0.8 s. In this case the NBCC 1990 loading provisions significantly underestimate the elastic dynamic response. For buildings with periods longer than 0.8 s, the conservatism of the base shear provisions leads to overestimation of combined dynamic edge response in asymmetric systems, and this is also true in the short-period range for buildings subjected to ground motions with low a/v ratio. The NBCC 1990 provisions are reasonably conservative for short-period systems subjected to ground motions with intermediate a/v ratio. Key words: earthquakes, seismic, design, response, spectra, base, shear, torsional, provisions.

Implications of the 1988 Saguenay earthquake on Canadian seismic strength specification

The November 25, 1988, Saguenay earthquake was the most significant seismic event in eastern North America over the last 50 years. Based on strong ground motion records from this earthquake, an analytical study was undertaken to evaluate the seismic design base shear provisions of the National Building Code of Canada for buildings located in the eastern regions of Canada. In light of the observed damage to masonry structures in the epicentral region, emphasis was placed on the evaluation of the codified minimum seismic strength for masonry structural systems. Key words: earthquake, ground motion, seismic design strength, code, masonry, buildings, damage, ductility.

Erratum: Evaluation of base shear provisions in the 1985 edition of the National Building Code of Canada

Erratum: Evaluation of base shear provisions in the 1985 edition of the National Building Code of Canada

Evaluation of base shear provisions in the 1985 edition of the National Building Code of Canada

A statistical analysis is performed to evaluate the base shear provisions in the 1985 edition of the National Building Code of Canada (NBCC 1985). Three sets of real earthquake records are selected to represent seismic ground motions with low, normal, and high peak acceleration to velocity (a/v) ratios. Single degree of freedom stiffness degrading systems are used as structural models; three damage indicators are employed to measure structural damage. The yield strength of the systems is specified in two different ways: (a) a single seismic response factor is used, irrespective of the a/v ratios of the input ground motions; (b) three different seismic response factors are used in the short-period range, depending upon the a/v ratios of the input ground motions, as suggested in NBCC 1985. A comparison of the statistical results of the three damage parameters for the systems designed with these two methods of strength specification indicates that the NBCC 1985 base shear provisions provide consistent control over structural damage when the structural systems are subjected to ground motions with different a/v ratios. Key words: earthquakes, ground motions, response spectra, stiffness degrading systems, seismic design, base shear, yield strength, inelastic response, damage parameters.

A proposal for the compatibility of static and dynamic seismic base shear provisions of the National Building Code

A comparison is made, based on static and dynamic base shear calculations according to the National Building Code of Canada of 1980, for four types of simple structures, namely, uniform moment resisting frame structures, uniform ductile flexural wall structures, uniform reinforced concrete shear wall structures, and unreinforced masonry wall structures. It is shown that a significant discrepancy exists between the static and dynamic base shear values, depending on the type and the fundamental period of the structure. The causes for the discrepancy and the necessity to make static and dynamic base shears compatible are discussed.

Effects of permissible shear stress on the design and construction of reinforced concrete containments

Provisions for peripheral, radial, and tangential shear have been conservatively established in the ASME Section III Division 2 Code. The design and construction of reinforced concrete containments to the shear provisions in this Code have resulted in extreme congestion of reinforcement and the associated difficulty in the placement of concrete. This is due to the low permissible shear stresses in the Code. Recent tests have demonstrated that the shear provisions are conservative. However, additional testing is required to quantify all aspects of containment behavior in shear. In this paper, those loads and load combinations that generally govern shear design are reviewed. For these loads, containment behavior is qualitatively discussed. Present Code provisions for allowable shear stresses, including Code Cases, are reviewed with illustrations provided of actual congested regions of containments designed to these provisions. The need for additional testing and for the development of new shear criteria is established.

Seismic resistance of reinforced concrete-masonry shear walls with high steel percentages

This paper summarizes test results of six heavily reinforced concrete masonry shear walls. The test programme was designed to investigate the necessity for the low ultimate shear stress specified by Masonry codes. Care was taken to accurately model good, but realistic design practice in detailing, and variables investigated in the series included steel percentage, influence of vertical load and confinement of potential crushing areas by mortar bed confining plates.
 Results are presented which clearly indicate that the maximum current code allowance for ultimate shear stress is unreasonably low. No wall suffered diagonal shear failure despite maximum shear stresses exceeding four times the maximum code level. All walls displayed stable hysteresis loops at a displacement ductility factor of 2, and the less heavily reinforced walls (designed to approximately twice code levels) were satisfactory at DF = 4. Degradation was never catastrophic and occurred due to slip of the entire wall along the foundation beam. Methods for reducing the degradation are discussed. Confining plates did not significantly reduce the degradation of the hysteresis loops, but substantially reduced damage to the walls at high ductility factors.
 Values of required ductility for walls designed to the Loadings Code are investigated, and on the basis of these and the experimental results, recommendations are made for relaxation to the ultimate shear provisions of the masonry code.

Proposed Changes in Shear Provisions for Reinforced and Prestressed Concrete Beams*

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