Summary of the updates to ASCE/SEI 41-17
Tuesday, December 12, 2017
By Garrett Hagen, SE & Daniel Zepeda, S.E., SEAOSC Existing Buildings Committee Co-Chairs
ASCE/SEI 41 is the standard for seismic retrofit and evaluation of existing buildings, required for all federal buildings, as well as several recently passed California ordinances. There have been several important updates to the standard in the upcoming ASCE/SEI 41-17. The updates will have significant impacts on the evaluation and retrofit approach for a variety of existing buildings.
Significant revisions were included for the standard's Basic Performance Objectives, seismic hazard used in Tier 1 and Tier 2, treatment of force-controlled components, nonlinear analysis provisions, non-structural performance levels, demands on out-of-plane wall forces, modeling parameters and acceptance criteria of steel and concrete columns, and anchor testing. The summary below covers a majority of the major updates:
- Tier 1 and Tier 2 require using the BSE-2E, instead of the BSE-1E, for for Risk Category I – III BPOE.
- Both BSE-1E and BSE-2E performance objectives required to be checked for Risk Category IV BPOE.
- New nonstructural performance level, Hazards Reduced, addresses items that can have the same life safety consequences as a partial building collapse and requires that level be evaluated in the BSE-2E hazard level for the BPOE.
- Checklists changed from Life Safety to Collapse Prevention, Limited Safety, or Life Safety checklists.
- Site specific response spectra and ground motion acceleration records are developed, selected and scaled to match the requirements in ASCE 7-16.
- A 1.3 factor augments demands on force controlled actions in the LSP and LDP when the performance objective is Life Safety and higher when demands are not determined using capacity design principals.
- Minimum number of acceleration histories needed for an analysis increased to 11.
- 10 of the 11 records cannot have an “unacceptable response” for Life Safety and lower and all 11 for Damage Control and higher.
- Overstress of a critical force controlled element, using expected strengths, in any record is considered an unacceptable response. This effectively requires all critical force controlled actions be designed for the maximum force in 10 or 11 records.
- One factor that increases force controlled demands in the NSP and NDP incorporated based on the criticality of the element and another factor for Life Safety and higher performance levels.
- Out-of-plane wall force and wall anchorage force equations revised.
- The material testing requirements for concrete are revised.
- SSI provisions further restrict their use with linear procedures.
- Steel columns are classified as force controlled and the modeling and acceptance criteria for them revised as well.
- Drift limit for panel zone acceptance added.
- Modeling and acceptance criteria for concrete columns updated.
- Testing of existing post-installed anchors in concrete added, such as tilt-up wall anchors.
- Requirements for URM spandrel beams added.
- Provisions for masonry infill rewritten.
- Penalty factor added to the capacity of wood structural panel walls and diaphragms when a 2x member is present instead of the 3x member that AWC SDPWS requires, i.e. when edge nailing along panel joints is 3” or less.
- Nonstructural provisions aligned with ASCE 7-16 Chapter 13.
- Seismic isolation and energy dissipation aligned with ASCE 7-16.
- URM Special Procedure to align with the IEBC Appendix A1.