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"

Computational modelling of impact damage in brittle materials

Modeling of the evolution of distributed damage such as microcracking, void formation, and softening frictional slip necessitates strain-softening constitutive models. The nonlocal continuum concept has emerged as an effective means for regularizing the boundary value problems with strain softening, capturing the size effects and avoiding spurious localization that gives rise to pathological mesh sensitivity in numerical computations. A great variety of nonlocal models have appeared during the last two decades. This paper reviews the progress in the nonlocal models of integral type, and discusses their physical justifications, advantages, and numerical applications.

Nonlocal integral formulations of plasticity and damage: Survey of progress

The effects of blending fibers on the tensile behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete (UHP-HFRC) are investigated. Four types of steel macro-fibers (of differing length or geometry) and one type of steel micro-fiber are considered. In producing the specimens, the volume content of the macro-fiber was held at 1.0%, whereas the volume content of the micro-fiber varied from 0.0% to 1.5%. The overall shape of tensile stress–strain curves of UHP-HFRC is primarily dependent upon the type of macro-fiber, although the addition of micro-fibers favorably affects the strain hardening and multiple cracking behaviors. UHP-HFRC produced from macro-fibers with twisted geometry provides the best performance with respect to post cracking strength, strain capacity and multiple micro-cracking behavior, whereas UHP-HFRC produced with long, smooth macro-fibers exhibits the worst performance.

Tensile behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete

A mechanical explanation of the phenomenon of punching shear in slabs without transverse reinforcement is presented on the basis of the opening of a critical shear crack. It leads to the formulation of a new failure criterion for punching shear based on the rotation of a slab. This criterion correctly describes punching shear failures observed in experimental testing, even in slabs with low reinforcement ratios. Its application requires the knowledge of the load-rotation relationship of the slab, for which a simple mechanical model is proposed. The resulting approach is shown to give better results than current design codes, with a very low coefficient of variation (COV). Parametric studies demonstrate that it correctly predicts several aspects of punching shear previously observed in testing as size effect (decreasing nominal shear strength with increasing size of the member). Accounting for the proposed failure criterion and load-rotation relationship of the slab, the punching shear strength of a flat slab is shown to depend on the span of the slab, rather than on its thickness as often proposed.

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Punching shear strength of reinforced concrete slabs without transverse reinforcement

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 results of a test series on the punching behavior of slabs with varying flexural reinforcement ratios and without transverse reinforcement are presented. The aim of the tests was to investigate the behavior of slabs failing in punching shear with low reinforcement ratios. The size of the specimens and of the aggregate was also varied to investigate its effect on punching shear. Measurements at the concrete surface as well as through the thickness of the specimens allowed the observation of phenomena related to the development of the internal critical shear crack prior to punching. The results are compared with design codes and to the critical shear crack theory. From that comparison, it is shown that the formulation of ACI 318-08 can lead to less conservative estimates of the punching strength for thick slabs and for lower reinforcement ratios than in the test results. Satisfactory results are, on the other hand, obtained using Eurocode 2 and the critical shear crack theory.

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Punching tests of slabs with low reinforcement ratios

The traditional approach of codes of practice for estimating the punching strength of shear-reinforced flat slabs is based on the assumption that concrete carries a fraction of the applied load at ultimate while the rest of the load is carried by the shear reinforcement. Concrete contribution is usually estimated as a fraction of the punching strength of members without shear reinforcement. The ratio between the concrete contribution for members with and without shear reinforcement is usually assumed constant, independent of the amount of shear reinforcement, flexural reinforcement ratio, and bond conditions of the shear reinforcement. The limitations of such an approach are discussed in this paper and a new theoretical model, based on the critical shear crack theory, is presented to investigate the strength and ductility of shear-reinforced slabs. The proposed approach is based on a physical model and overcomes most limitations of current codes of practice. Its application to various punching shear reinforcement systems is also detailed in the paper and its results are compared to available test data.

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Applications of Critical Shear Crack Theory to Punching of Reinforced Concrete Slabs with Transverse Reinforcement

1 Introduction and Theoretical Basis.- 1.1 Introductory Remarks.- 1.2 Fundamentals of the Theory of Plasticity.- 1.2.1 Material Behaviour.- 1.2.2 Limit State Theorems of the Theory of Plasticity.- (a) Static Solution.- (b) Kinematic Solution.- 1.3 Engineering Methods.- 2 Stress Fields for Simple Structures.- 2.1 Introduction.- 2.2 Beams with Rectangular Cross-Section Subjected to Bending and Shear.- 2.2.1 Deep Beams, Concentrated Loads.- 2.2.2 Deep Beams, Several Concentrated Loads.- 2.2.3 Deep Beams, Distributed Load.- 2.2.4 Beams with Medium Slenderness Ratio, Concentrated Loads.- 2.3 Beams with I-Cross-Section Subjected to Bending and Shear.- 2.3.1 Slender Beams, Concentrated Loads.- 2.3.2 Slender Beams, Distributed Load.- 2.3.3 General Case, Practical Design.- 2.3.4 Beams of Variable Depth.- 2.3.5 Compression Flange.- 2.3.6 Tension Flange.- 2.4 Members Subjected to Torsion and Combined Action.- 2.4.1 Introduction.- 2.4.2 Warping Torsion (Open Cross-Sections).- 2.4.3 Circulatory Torsion.- 2.4.4 Circulatory Torsion Combined with Bending and Shear.- 2.5 Brackets.- 2.6 Coupling Beams.- 2.7 Joints of Frames.- 2.7.1 Corner Joint, Compression on the Inside.- 2.7.2 Corner Joint, Tension on the Inside.- 2.7.3 Joints of Frames with Three Connecting Beams.- 2.7.4 Joints of Frames with Four Connecting Beams.- 2.8 Beams with Sudden Changes in Cross-Section.- 2.9 Walls.- 2.9.1 Shear Walls.- 2.9.2 Diaphragms.- 2.10 Three-Dimensional Example.- 3 Material Strengths and other Properties.- 3.1 Reinforcing Steel.- 3.2 Concrete.- 3.2.1 Uniaxial Stress State.- 3.2.2 Three-Dimensional Stress State.- 3.2.3 Concrete with Imposed Cracks.- 3.2.4 Cracks: Aggregate Interlock.- 3.3 Force Transfer Reinforcement - Concrete.- 3.3.1 Anchorage of Reinforcing Bars.- 3.3.2 Splices of Reinforcement.- 3.3.3 Force Deviations.- 4 Additional Considerations for the Development of Stress Fields.- 4.1 Remarks on Plastic Design Applied to Reinforced Concrete.- 4.1.1 Behavior of Statically Indeterminate Beams.- 4.1.2 Selection of the Inclination of the Compression Field in the Web of Beams.- 4.1.3 Redistribution of Internal Forces and Ductility Requirements.- 4.2 Procedure for Developing Stress Fields.- 4.2.1 Introduction.- 4.2.2 Spreading of Force in a Wall Element Loaded in Tension.- 4.2.3 Spreading of Force in a Wall Element Loaded in Compression.- 4.2.4 Further Cases.- 4.3 Impaired Strength through Wide Cracks.- 4.4 Stress Distribution in Highly Stressed Compression Zones.- 4.4.1 Introduction.- 4.4.2 Stress Fields for Beam-Columns.- 4.5 Prestressed Beams.- 4.5.1 Beam with straight cable.- 4.5.2 Beam with curved cable.- 4.5.3 Anchorage zone of pretensioned beams.- 4.5.4 Unbonded prestressed beams.- 5 Plane Stress, Plate and Shell Elements.- 5.1 Plane Stress Elements.- 5.2 Slab Elements.- 5.3 Shell Elements.- 6 Outlook: Computer Programs.- References.

Aurelio Muttoni

Papers

Punching shear strength of reinforced concrete slabs without transverse reinforcement

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

Punching tests of slabs with low reinforcement ratios

Applications of Critical Shear Crack Theory to Punching of Reinforced Concrete Slabs with Transverse Reinforcement

Design of Concrete Structures with Stress Fields