Aci 318-08 Eases Testing Requirements

The American Concrete Institute (ACI) announces the release of ACI 318-08, Building Code Requirements for Structural Concrete and Commentary an essential

The American Concrete Institute (ACI) announces the release of ACI 318-08, Building Code Requirements for Structural Concrete and Commentary Û an essential standard for concrete design, construction, inspection, repair, and research professionals, Institute officials affirm. Incorporating several improvements and changes from the 2005 edition, the new publication contains latest code requirements for concrete building design and construction with corresponding commentary.

ACI 318 is a leading concrete design reference for building codes worldwide. Adoption of the updated requirements is expected in the 2009 International Building Code. Additionally, ACI 318-08 is deemed to satisfy ISO 19338:2007, Performance and Assessment Requirements for Design Standards on Structural Concrete. Notes ACI Executive Vice President William Tolley, Members of ACI Committee 318 volunteered thousands of hours to ensure that necessary updates have been made to this 2008 edition, dedicated to enhancing the safety of concrete structures.

Changes in ACI 318-08 are summarized as follows:

Chapter 1 Û 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 Û 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 Û Durability Requirements

Exposure categories and classes were adopted, replacing numerous durability-requirement tables to facilitate clear specification for intended applications.

Chapter 5 Û Concrete Quality, Mixing, and Placing

(1) The use of three 4- _ 8-in. cylinders was adopted as equivalent to the use of two 6- _ 12-in. cylinders for determining concrete compressive strength; (2) 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, (3) Flexural test performance criteria were added to qualify the use of steel fiber-reinforced concrete as a replacement for minimum shear reinforcement.

Chapter 7 Û Details of Reinforcement

(1) To avoid the misconception that no minus tolerance on cover values is given in the Code, Îminimum coverÌ was replaced with Îspecified coverÌ; (2) Class B lap splices are now required for structural integrity reinforcement; (3) Continuous top and bottom structural integrity reinforcement are required to pass through the column core; and, (4) Requirements for transverse reinforcement confining structural integrity reinforcement in perimeter beams were clarified.

Chapter 8 Û Analysis and Design Û 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 Û 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 Û 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 Û Shear and Torsion

(1) Code requirements were added to permit the use of headed stud assemblies as shear reinforcement for slabs and footings, and larger nominal shear strength was permitted for headed stud assemblies than for other forms of slab and footing shear reinforcement; (2) More stringent limits have been placed on the depths of beams that are exempted from the requirement for minimum shear reinforcement; (3) A new limit on the depth of hollow core units for which minimum shear reinforcement could be waived was established; (4) Steel fiber-reinforced concrete was added as an alternative to minimum shear reinforcement; and, (5) The upper limit on shear friction strength was significantly increased for monolithically placed concrete and concrete placed against intentionally roughened concrete.

Chapter 12 Û Development and Splices of Reinforcement

(1) Provisions were added for development length of headed deformed bars; (2) Splice length for joining bars of different sizes was addressed; and, (3) A 1.0 coating factor for galvanized reinforcement was added.

Chapter 13 Û 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 Û Walls

Slender wall panel design provisions were modified for greater consistency with methods used in design practice.

Chapter 18 Û Prestressed Concrete

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 Û Strength Evaluation of Existing Structures

Load factors for determining the required test load were modified to reflect typical modern load combinations.

Chapter 21 Û Earthquake-Resistant Structures

(1) Requirements are now presented in order of increasing Seismic Design Category; (2) New design requirements were added for most Seismic Design Categories; (3) New detailing option was added for diagonally reinforced coupling beams; (4) Design yield strength for confinement reinforcement was raised to 100 ksi in order to help reduce congestion; and, (5) Boundary element confinement requirements were relaxed.

Appendix D Û Anchoring to Concrete

Use of reinforcement in the vicinity of anchors was clarified, as were ductility requirements for anchors in seismic zones.

This fall, ACI and the Portland Cement Association will offer in-depth seminars to highlight and explain 2008 Code changes. Details of the seminars, including dates and locations, will be available in spring at ACI 318-08 also can be ordered at the web site, or by calling 248/848-3800.