ACI 318-08 Building Code Requirements for Structural Concrete and Commentary

ACI 318-08 Building Code Requirements for Structural Concrete and Commentary

ACI 318-08 Building Code Requirements for Structural Concrete and Commentary

ACI 318-08 Building Code Requirements for Structural Concrete and Commentary is a must-have standard for all concrete design, construction, inspection, repair, and research professionals. It contains the latest code requirements for concrete building design and construction alongside the corresponding commentary, and includes several improvements and changes from the 2005 edition.

ACI 318-08 Building Code Requirements for Structural Concrete and Commentary “Everyone from engineers, architects, contractors, specifiers, and building officials, to students and professors, regularly use ACI 318,” said William R. Tolley, executive vice president of the American Concrete Institute. “Members of ACI Committee 318 have volunteered thousands of hours to ensure that necessary updates have been made to this 2008 edition, dedicated to enhancing the safety of concrete structures.”

ACI 318-08 Building Code Requirements for Structural Concrete and Commentary is a leading concrete design reference for building codes worldwide. It is expected that the updated Code will be adopted in the 2009 International Building Code (IBC). ACI 318-08 is also deemed to satisfy the requirements of ISO 19338:2007, “Performance and Assessment Requirements for Design Standards on Structural Concrete.”

This fall, the American Concrete Institute and the Portland Cement Association (PCA) will offer in-depth seminars to highlight and explain the changes in the 2008 Code. Details of the seminars, including dates and locations

The following is a summary of changes in ACI 318-08 Building Code Requirements for Structural Concrete and Commentary:
Chapter 1 – General Requirements
Design requirements for earthquake-resistant structures were changed to correlate with the Seismic Design Categories used by the 2005 ASCE/SEI 7 and the 2006 International Building Code.

Chapter 3 – Materials
New requirements for headed shear stud reinforcement, headed deformed bars, and stainless steel bars were given with appropriate references to ASTM standards.

Chapter 4 – Durability Requirements
Exposure categories and classes were adopted to replace the many tables of durability requirements in Chapter 4, making it easier to clearly specify the intended application.

Chapter 5 – Concrete Quality, Mixing, and Placing
The use of three 4 x 8 in. cylinders was adopted as equivalent to the use of two 6 x 12 in. cylinders for determining concrete compressive strength;
Due to concern that material properties may change with time, a 12-month limit was set on historical data used to qualify mixture proportions; and
Flexural test performance criteria were added to qualify the use of steel fiber-reinforced concrete as a replacement for minimum shear reinforcement.

Chapter 7 – Details of Reinforcement
To avoid the misconception that there is no minus tolerance on cover values given in the Code, “minimum cover” was replaced with “specified cover” throughout Chapter 7;
Class B lap splices are now required for structural integrity reinforcement;
Continuous top and bottom structural integrity reinforcement were required to pass through the column core; and Requirements for transverse reinforcement confining structural integrity reinforcement in perimeter beams were clarified.

Chapter 8 – Analysis and Design—General Considerations
Provisions were modified to allow redistribution of positive moments; and
A simple modeling procedure for evaluation of lateral displacements was added.

Chapter 9 – Strength and Serviceability Requirements
Strength reduction factors for spirally reinforced columns and plain concrete were raised from 0.70 to 0.75 and from 0.55 to 0.60, respectively.

Chapter 10 – Flexure and Axial Loads
The section on slenderness effects was reorganized to recognize computer analysis techniques as the primary method of evaluating second-order effects.

Chapter 11 – Shear and Torsion
Code requirements were added to permit the use of headed stud assemblies as shear reinforcement for slabs and footings. The nominal shear strength was permitted to be larger for headed stud assemblies than for other forms of slab and footing shear reinforcement;
More stringent limits have been placed on the depths of beams that are exempted from the requirement for minimum shear reinforcement;
A new limit on the depth of hollow core units for which minimum shear reinforcement could be waived was established;
Steel fiber-reinforced concrete was added as an alternative to minimum shear reinforcement; and
The upper limit on shear friction strength was significantly increased for monolithically placed concrete and concrete placed against intentionally roughened concrete.

Chapter 12 – Development and Splices of Reinforcement
Provisions were added for the development length of headed deformed bars;
Splice length when splicing bars with different sizes was addressed; and
A coating factor of 1.0 for galvanized reinforcement was added.

Chapter 13 – Two-Way Slab Systems
Dimension limits were added for the use of shear caps; and
Alternative corner reinforcement arrangement was added for two-way slabs supported by edge beams or walls.

Chapter 14 – Walls
Design provisions for slender wall panels were modified to be more consistent with the methods used in design practice.

Chapter 18 – Prestressed Concrete
The allowable concrete compression stress immediately after prestress transfer was increased; and
Requirements for structural integrity steel in two-way unbonded post-tensioned slab systems were modified.

Chapter 20 – Strength Evaluation of Existing Structures
Load factors for determining the required test load were modified to reflect typical modern load combinations.

Chapter 21 – Earthquake-Resistant Structures
The entire chapter was reorganized to present requirements in order of increasing Seismic Design Category;
New design requirements were added for most Seismic Design Categories;
New detailing option was added for diagonally reinforced coupling beams;
Design yield strength for confinement reinforcement was raised to 100 ksi to help reduce congestion; and
Boundary element confinement requirements were relaxed.
Appendix D – Anchoring to Concrete

ACI 318-08 Building Code Requirements for Structural Concrete and Commentary
Use of reinforcement in the vicinity of anchors was clarified; and
Ductility requirements for anchors in seismic zones were clarified.

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