3 Important Tools Ensuring Quality and Safety in Post-Tensioned Structures
Codes Specifications Certification
Building Codes for Post-Tensioned Concrete
ACI 318 – “Building Code Requirements for Structural Concrete” Chapter 18 – Prestressed Concrete
Shear covered in Chapter 11 Governs the design of almost all elevated post-
tensioned concrete buildings in the USA And in many other parts of the world (318S)
PTI Well Represented on ACI 318
4 full voting members of 318 are members of PTI TAB
3 full voting members of 318 are members of PTI Board of Directors
PTI Executive Director is a voting Subcommittee member
ACI 318
Most widely used building code in the world Incorporated into all U.S. model building codes
for concrete design IBC (Chapter 19)
Does not govern post-tensioned slabs-on-ground (Section 1.1.7) Refers to PTI
Significant Recent 318 Code Changes
Moment redistribution (18.10.4) Cracking moment requirement (Mn≥1.2Mcr)
waived for all post-tensioned members with unbonded tendons (18.8.2)
Clarification on prestressed shrinkage and temperature reinforcement (7.12.3)
Eliminate requirement for stress limitation (0.74fpu or 0.82fpy) in field of prestressing steel immediately after transfer (18.5.1(b))
BIG Change Coming ACI 318-14 will be completely reorganized
Member-based with Chapters on: One and two-way slabs Beams Columns Walls Foundations “Toolbox” Support Chapters (analysis,
materials, durability, seismic)
All Requirements for Each Type of Member…
Contained in one chapter Will make code easier to use
No searching for code requirements now distributed throughout the code
Revisions will be easier to make and use Will be a 2011 “Supplement” in old format
Slabs-on-Ground
Nonprestressed slabs-on-ground foundations permitted to be designed by ACI 332-08 (see ACI 318 Section 1.1.4)
Post-tensioned slabs-on-ground (on expansive soils) governed by IBC Section 1805.8.2 “Slab-on-Ground foundations”
IBC Section 1805.8.2
Moments, shears and deflections permitted to be determined by: “PTI Standard Requirements for
Analysis of Shallow Concrete Foundations on Expansive Soils”
Design of post-tensioned foundations by: “PTI Standard Requirements for
Design of Shallow Post-Tensioned Concrete Foundations on Expansive Soils”
IBC Section 1805.8.2
Permits analysis and design by “other methods” that address: Soil-structure interaction Deformed shape of soil support Plate or stiffened plate action Center lift and edge lift swell
conditions
For All Practical Purposes…
IBC requires design of post-tensioned slab-on-ground foundations on expansive soils by PTI Standards.