CODIFYING POST-TENSIONING · CODIFYING POST-TENSIONING. 3 Important Tools Ensuring Quality and Safety in Post-Tensioned Structures ... ACI 318 Most widely used ...

Ken Bondy

CODIFYING POST-TENSIONING

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.

Current PTI SOG Activities

Combine design and analysis standard Develop simplified design method

Thank You!!!