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"

Title: Sectional Analysis of Reinforced Concrete Members Degree: Doctor of Philosophy

Sectional analysis of reinforced concrete members

This paper investigates the shear strength of beams and one-way slabs without stirrups based on the opening of a critical shear crack. The shear-carrying mechanisms after the development of this crack are investigated. On this basis, a rational model is developed to estimate the shear strength of members without shear reinforcement. The proposed model is based on an estimate of the crack width in the critical shear region, taking also into account the roughness of the crack and the compressive strength of concrete. The proposed model is shown to properly describe a large set of available test data. A simplified method adopted by the Swiss code for structural concrete (SIA 262) is also introduced. Comparisons with other codes of practice are finally presented, with a highlight on the main differences between them.

Shear Strength of Members without Transverse Reinforcement as Function of Critical Shear Crack Width

The authors present a simple, unified method for the shear design of both prestressed concrete members and nonprestressed concrete members. The method can treat members subjected to axial tension or axial compression and treats members with and without web reinforcement. The derivation of the method is summarized and the predictions of the method are compared with those of the current American Concrete Institute (ACI) Code.

A general shear design method

The aims of this research were to develop a simple method for the design of fiber-reinforced polymer (FRP)-reinforced beams and to determine if a common approach for steel and FRP-reinforced members is possible. A model is presented for calculating the concrete contribution to shear strength of reinforced concrete beams. The applicability of the model is supported by comparing the computed shear strengths with the experimental strengths of 370 specimens. The shear strength equation developed from the model is simplified to yield a design equation applicable for both steel and FRP-reinforced beams. The design equation is demonstrated to provide conservative results across the range of variables known to affect shear strength.

Concrete shear strength: another perspective

Relaxation is defined as the loss of stress in a stressed material held at constant length. Another manifestation of the same basic phenomenon, creep, is defined as the change in length of a material under stress. Since no generally satisfactory quantitative relationship between creep and relaxation has been developed, relaxation tests must be carried out whenever relaxation data are required, although creep tests are simpler to perform. Relaxation characteristics of prestressing reinforcement are of interest in prestressed concrete construction, even though pure relaxation does not exist under practical conditions. Creep and shrinkage of the concrete and fluctuations in superimposed load change the length of the tendon. Nevertheless, the tendon does not deform freely and the stress in it can change. Thus, the conditions are comparable more to a relaxation test than to a creep test. The attitude toward the effect of relaxation has changed considerably over the last two decades. At first, relaxation losses were considered to be quite critical because they affected the working stresses which governed the design. At the same time, it was thought that the reinforcement reached a stable stress in a matter of a few weeks if not hours and that the relaxation losses were limited to a very small fraction of the initial stress. By the time it was established that relaxation losses could amount to as much as 20 percent of the initial stress over a long period of time, it was recognized that partial loss of prestress is not necessarilly accompanied by a loss in flexural strength. At present, a knowledge of the losses resulting from relaxation is required primarily in relation to the serviceability of a prestressed member. In this respect, it should be mentioned that the critical quantity is the remaining stress and not the loss. The recognition of this fact makes a considerable difference in the interpretation of the available test data.

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Chester P. Siess

Papers

A Study of Stress Relaxation in Prestressing Reinforcement

Investigation of prestressed reinforced concrete for highway bridges, part III, strength and behavior in flexure of prestressed concrete beams

Studies of slab and beam highway bridges : part III : small-scale tests of shear connectors and composite t-beams

Strength in shear of beams without web reinforcement

Strength and Behavior of Prestressed Concrete Beams with Web Reinforcement