The “Building Code Requirements for Structural Concrete” (“Code”) covers the materials, design, and construction of structural concrete used in buildings and where applicable in nonbuilding structures. The Code also covers the strength evaluation of existing concrete structures. Among the subjects covered are: contract documents; inspection; materials; durability requirements; concrete quality, mixing, and placing; formwork; embedded pipes; construction joints; reinforcement details; analysis and design; strength and serviceability; flexural and axial loads; shear and torsion; development and splices of reinforcement; slab systems; walls; footings; precast concrete; composite flexural members; prestressed concrete; shells and folded plate members; strength evaluation of existing structures; provisions for seismic design; structural plain concrete; strut-and-tie modeling in Appendix A; alternative design provisions in Appendix B; alternative load and strength reduction factors in Appendix C; and anchoring to concrete in Appendix D. The quality and testing of materials used in construction are covered by reference to the appropriate ASTM standard specifications. Welding of reinforcement is covered by reference to the appropriate American Welding Society (AWS) standard. Uses of the Code include adoption by reference in general building codes, and earlier editions have been widely used in this manner. The Code is written in a format that allows such reference without change to its language. Therefore, background details or suggestions for carrying out the requirements or intent of the Code portion cannot be included. The Commentary is provided for this purpose. Some of the considerations of the committee in developing the Code portion are discussed within the Commentary, with emphasis given to the explanation of new or revised provisions. Much of the research data referenced in preparing the Code is cited for the user desiring to study individual questions in greater detail. Other documents that provide suggestions for carrying out the requirements of the Code are also cited.

"building code requirements for structural concrete (aci 318-11) and commentary"

Fiber-wrapping or encasement of concrete in fiber-reinforced plastic (FRP) shells significantly enhances strength and ductility of concrete columns. However, design of such hybrid systems requires an accurate estimate of the performance enhancement due to the confinement mechanism. Current design procedures are simple extensions of the models developed for conventional reinforced concrete columns. Previous studies have demonstrated that such models may not be conservative for FRP-encased concrete. A simple model is presented to predict the complete bilinear stress-strain response of FRP-confined concrete in both axial and lateral directions. The model is based on correlation between the dilation (expansion) rate of concrete and the hoop stiffness of the restraining member. The parameters of the model are directly related to the material properties of the FRP shell and the concrete core. The predicted stress-strain curves compare favorably with the results of the present study, as well as tests by others on both fiber-wrapped and FRP-encased concrete columns.

Model of Concrete Confined by Fiber Composites

External confinement of concrete by means of high-strength fiber composites can significantly enhance its strength and ductility as well as result in large energy absorption capacity. The confinement mechanism may include fiber-wrapping of existing columns as a retrofitting measure or encasement of concrete in a fiber reinforced plastic (FRP) tube for new construction. Proper design of such hybrid columns, however, requires an accurate estimate of the performance enhancement. Current design methods use simple extension of the models developed for conventional reinforced concrete columns. Results from a series of uniaxial compression tests on concrete-filled FRP tubes are compared with the available confinement models in the literature. The present study indicates that these models generally result in overestimating the strength and unsafe design. The study also shows a unique characteristic of confinement with fiber composites in that, unlike steel, FRP curtails the dilation tendency of concrete, as it re...

Behavior of Concrete Columns Confined by Fiber Composites

A uniaxial model for concrete confined with fiber-reinforced polymers (FRP), but also with steel jackets or conventional transverse reinforcement, is presented. The model, which is suitable to be i...

FRP-Confined Concrete Model

https://ira.lib.polyu.edu.hk/bitstream/10397/5409/1/01%20Analysis-oriented%20models.pdf

Analysis-oriented stress–strain models for FRP–confined concrete

An analytical model is proposed to construct a stress‐strain relationship for confined concrete. The model consists of a parabolic ascending branch, followed by a linear descending segment. It is based on calculation of lateral confinement pressure generated by circular and rectilinear reinforcement, and the resulting improvements in strength and ductility of confined concrete. A large volume of test data, including poorly confined and well‐confined concrete was evaluated to establish the parameters of the analytical model. Confined concrete strength and corresponding strain are expressed in terms of equivalent uniform confinement pressure provided by the reinforcement cage. The equivalent uniform pressure is obtained from average lateral pressure computed from sectional and material properties. Confinement by a combination of different types of lateral reinforcement is evaluated through superposition of individual confinement effects. The descending branch is constructed by defining the strain correspond...

Strength and Ductility of Confined Concrete

A mathematical model is developed to express the stress-strain relationship of high-strength concrete confined by transverse reinforcement. The model is applicable to both normal-strength and high-strength concretes, covering a strength range between 30 and 130 MPa. It incorporates all the relevant parameters of confinement that have been observed to play important roles in column tests. These parameters include the type, volumetric ratio, spacing, yield strength, and arrangement of transverse reinforcement as well as concrete strength and section geometry. Therefore, it can be used for concrete confined by spirals, rectilinear hoops, cross ties, welded wire fabric, and combinations of these reinforcements. It has been verified extensively against data obtained from column tests under concentric and eccentric loads, as well as slow and fast strain rates.

Confinement Model for High-Strength Concrete

Strength and Deformability of Confined High-Strength Concrete Columns

Experimental research was conducted to investigate the behavior of square high-strength concrete columns confined by rectilinear reinforcement. Large-scale columns with concrete strengths between 60 MPa and 124 MPa were tested under monotonically increasing concentric compression. The test parameters included the volumetric ratio and spacing of transverse reinforcement, distribution of longitudinal reinforcement and resulting tie arrangement, yield strength of transverse reinforcement, and concrete compressive strength. The results indicate that high-strength concrete columns can be confined to achieve inelastic deformabilities usually expected of normal-strength concrete columns. This is done by providing increased volumetric ratio and/or higher grade of confinement reinforcement. The results of the experimental program are presented in the paper, along with recommendations for design.

High-Strength Concrete Columns with Square Sections under Concentric Compression

Circular columns with concrete strengths in the range of 60 MPa to 124 MPa were tested under concentric compression. The columns were confined with different volumetric ratios, grades, and spacings of circular reinforcement. Tests included both poorly confined and well-confined columns. The results provided insight into the strength and deformability of circular high-strength concrete (HSC) columns and were used to generate design information for confinement of these columns. The test data indicate that HSC columns exhibit extremely brittle behavior unless confined by lateral reinforcement. The columns require higher confinement pressure than those with normal strength concrete. The additional pressure required can by provided by increasing the volumetric ratio and/or the grade of transverse reinforcement. The p(sub s)f (sub yt)/f'(sub c) ratio was found to be a suitable design parameter for confinement of circular high-strength concrete columns up to a concrete strength level of 124 MPa. Transverse spiral reinforcement of up to 1,000 MPa was observed to be effective in confining concrete. The results further indicated that circular hoops are as effective as circular spirals when the hoops are prevented from opening under lateral expansion.

Salim R. Razvi

Papers

Strength and Ductility of Confined Concrete

Confinement Model for High-Strength Concrete

Strength and Deformability of Confined High-Strength Concrete Columns

High-Strength Concrete Columns with Square Sections under Concentric Compression

Circular High-Strength Concrete Columns under Concentric Compression