November 2014

The PUC Meets in Burlingame, CA

The Provisions Update Committee (PUC) of the Building Seismic Safety Council (BSSC) met September 16-17 in Burlingame, California, to continue assessing proposals to update the National Earthquake Hazards Reduction Program’s (NEHRP) 2009 NEHRP Recommended Seismic Provisions for New Buildings and Other Structures. Specifically, the PUC assessed the results of remaining items of Membership Organization (MO) Ballot 2 not addressed at its last meeting in May, the results of MO Ballot 3 and PUC Ballot G to be conducted in November.

Following the two-day PUC meeting, the BSSC Board of Direction met by teleconference on October 7 and voted to allow MO Ballot 3 (except for an item on rigid-wall flexible diaphragms) and the remaining MO Ballot 2 proposals reviewed by the PUC to be included in the 2015 NEHRP Provisions, and to conduct MO Ballot 4 following a successful PUC Ballot G.

PUC Ballot G, the last ballot of the five-year cycle for the development of the 2015 Provisions, is intended to address recently identified significant problems in the design response spectrum, with longer period values judged to be significantly un-conservative in high-hazard locations and short period values conservative. The PUC will review the results of PUC Ballot G in a November 25 web meeting, and the results of MO Ballot 4 in a final meeting in Burlingame on February 10, 2015. MO Ballot 4 also will include a proposal on accidental torsion, and a revised proposal on rigid-wall flexible diaphragms. This will be followed on February 11 by a meeting to present the 2015 Provisions to the BSSC membership and the broader seismic community. The results of the PUC and MO ballots will be passed onto the BSSC Board of Direction for affirmation.

Over the summer, the 50 BSSC member organizations that represent the building industry assessed MO Ballot No. 3, which is based on PUC Ballot F. All items passed. Earlier in the spring, the MOs passed all items in MO Ballot 2, based on PUC Ballots C, D and E. Previously, the Board also accepted MO Ballot No. 1, which will be included in the 2015 NEHPR Recommended Seismic Provisions. Membership Ballot No. 1 addresses adoption of ASCE 7-10, its Supplemental No. 1 and Commentary, Chapter 24 on simplified provisions, and Chapter 22 on seismic maps for Guam and American Samoa.

Along with MO Ballot 1, the proposals in MO Ballots 2 and 3 will be used to develop the three parts of the Provisions: proposed changes to ASCE 7-10 Minimum Design Loads for Buildings and Other Structures (Part 1); changes to the ASCE 7-10 Commentary (Part 2); and resource papers on special topic in seismic design (Part 3). MO Ballot No. 2 addresses the following for chapters of ASCE 7-10:

Chapters 11 – Seismic Design Criteria

Diaphragm Design Force Level
Revisions to Site Factors Fa and Fv
Revisions to Site Factor Fpga
Site Specific Ground Motion Procedures

Chapter 12 – Building Structures

Diaphragm Design Force Level
Vertical Seismic Load Effect
Maximum Ss Value in Determination of Cs
Number of Modes
Combined Response
Scaling Design Values
Structural Modeling
Foundations on Liquefiable Sites

Chapter 15 – Non-Building Structures

Tanks/Vessels Supported on Structural Towers

Chapter 16 – Seismic Response History Procedures (entire chapter)
Chapter 17 – Seismically Isolated Structures (entire chapter)
Chapter 18 – Structures with Damping Systems (entire chapter)
Chapter 19 – Soil-Structure Interaction (entire chapter)
Chapter 22 – Seismic Ground Motion Long-Period Transition and Risk Coefficient Maps

Uniform Hazard Commentary

MO Ballot 3 addresses the following:

Chapter 11 – Seismic Design Criteria

Spectral Acceleration Parameters

Chapter 12 – Building Structures

Alternative Structural Systems
Substitute Components
Foundation Strength Design
Linear Modal Response
Simplified Design Procedure for Bearing Wall or Building Frame Systems

Chapter 14 – Material Specific Seismic Design and Detailing Requirements

Precast Diaphragm Design

Chapter 17 – Seismically Isolated Structures

Steel Ordinary Concentrically Braced Frames in Isolated Buildings
Steel Grid Frames

Chapter 22 – Seismic Ground Motion Long-Period Transition and Risk Coefficient Maps

Updated Design Maps

MO Ballot 3 also addresses the intent of the Provisions and Part 3 resource papers on performance, diaphragm design and Sect. 21.2 max-direction factors.

In all, the 2015 NEHRP Provisions will address changes to half of the sections in the seismic chapters of ASCE 7-10. The 2015 Provisions will provide complete replacements for Chapters 16, 17, 18 and 19 of ASCE 7-10.