Examples were done with both fixed-base and flexible-base
foundations to show the differences. In this case, the braced frame
met the acceptance criteria in the flexible-base model, but not in
the fixed-base model.
NSP with Nonlinear SpringsNSP with Fixed Base
Subdiaphragm chord evaluation in the roof of the tilt-up
building example Examples show evaluation of all the various
components and connections in the braced frame building example
FEMA P-2006 3: Performance Objectives and Seismic Hazards
3-13
0.00.10.20.30.40.50.60.70.80.91.0
2E/2N 1E/1N
Figure 3-4 Ratios of BSE-2E to BSE-2N and BSE-1E to BSE-1N for
short period spectral acceleration at various citiesassuming Site
Class D.
Figure 3-5 Ratios of BSE-2E to BSE-2N and BSE-1E to BSE-1N for
1-second spectral acceleration at various citiesassuming Site Class
D.
0.00.10.20.30.40.50.60.70.80.91.0
2E/2N 1E/1N
ASCE 41-17 Revision
Revisions have been made to the Tier 1 and Tier 2 procedures in
ASCE 41-17 to address concerns of some professionals that the ratio
of the BSE-1E to BSE-1N was so small that evaluations conducted
only using the BSE-1E Seismic Hazard Level would be significantly
less conservative than those done using ASCE 31-03 and not provide
thecommensurate performance atthe BSE-2E Seismic Hazard Levelas the
BPOE indicates.
For example, in New Madrid, Missouri, for Site Class D and short
period spectral acceleration, where the BSE-1E to BSE-1N ratio is
0.16, the BSE-2E to BSE-1E ratio is nearly 8, while the ratio of
Collapse Prevention to Life Safety m-factors is 1.3. This is
addressed in ASCE 41-17 by requiring the use of the BSE-2E Seismic
Hazard Level for the BPOE in the Tier 1 and Tier 2 procedures.
3.3.4 Site-Specific Procedure for Hazards Caused by
GroundShaking (ASCE 41-13 § 2.4.2)
ASCE 41-13 requires site-specific hazard procedures for Site
Class F andnear-fault Site Class E. However, for very significant
structures, where there is some concern about local hazards, or
when acceleration time histories are needed for nonlinear dynamic
analysis, a more comprehensive site-specific
Chapter No.
FEMA Building Type
Risk Catagory Location
Level of Seismicity
Performance Objective
Analysis Procedure
Evaluation/Retrofit Procedure
6 PC1 II Anaheim, CA High BPOE LSP Tier 1 and Tier 2
7 W1a III San Jose, CA High BPOE and Partial Retrofit
LSP Tier 1 and Tier 3
8 S1 II San Francisco Bay Area, CA
High BPOE LSP,LDP, NSP
Tier 1, 2, 3
9 S2 III Charlotte, NC Moderate Immediate Occupancy at
BSE-1N
LSP, NSP Tier 1 and Tier 3
10 C2 II Seattle, WA High BPOE LSP Tier 3
11 C2 II Seattle, WA High BPOE NSP Tier 3
12 URM II Los Angeles, CA High Reduced Special Procedure
Special Procedure
13 URM II Los Angeles, CA High BPOE LSP Tier 3
Tier 1 screening deficiencies for URM building Flowchart to
illustrate in-plane URM wall evaluation
FEMA P-2006 11: Concrete Shear Wall (C2) with Nonlinear Static
Procedure 11-1
Chapter 11
Concrete Shear Wall (C2)with Nonlinear Static Procedure
11.1 Overview
This chapter provides discussion and example application of the
Tier 3 systematic evaluation and retrofit procedures of ASCE 41-13
(ASCE, 2014)on the same 1950s three-story concrete shear wall
building studied inChapter 10 of this Example Application Guide
using the linear static procedure (LSP). The example in this
chapter applies the nonlinear static procedure (NSP) to the
building, as NSP is another analytical approach of the ASCE 41-13
Tier 3 systematic evaluation procedure. The followinginformation
regarding the building is provided in Chapter 10 and will not
berepeated in this chapter: building description (Section 10.2.1),
Tier 1screening and mitigation strategy (Section 10.2.2), seismic
design parameters and Performance Objective (Section 10.2.3), and
data collection requirements (Section 10.3).
This example demonstrates three-dimensional nonlinear modeling
ofreinforced concrete shear wall structures, determination of the
targetdisplacement for the NSP, performance evaluation of
reinforced concrete shear walls and columns with the NSP, and
three-dimensional explicitmodeling of foundation components,
including kinematic interaction and radiation damping
soil-structure interaction effects. Additionally, the seismic
performance of shear wall elements is compared between the LSP and
NSP, as well as NSP results obtained from fixed-base and
flexible-base models. The sections of this chapter are organized as
follows:
• Section 11.2: This section highlights the following aspects of
a three-dimensional analytical model for the reinforced concrete
shear wallbuilding:
o Fiber section for reinforced concrete shear walls
o Nonlinear constitutive stress-strain relations for concrete
andreinforcing steel materials
o In-plane shear stress-strain relations for reinforced concrete
shearwalls
o Nonlinear plastic hinge model for reinforced concrete
columns
Example Summary
Building Type: C2
Performance Objective: BPOE
Risk Category: II
Location: Seattle, Washington
Level of Seismicity: High
Analysis Procedure: Nonlinear Static (NSP)
Evaluation Procedure: Tier 3
Reference Documents:
ACI 318-14
FEMA 440
Example flowchart in the Guide to illustrate foundation modeling
methods in ASCE 41
Three-dimensional model and force-displacement curve used to
determine target displacement in the concrete shear wall example
building
Description of soft story deficiencies in the tuckunder example
building
Summary of Examples Covered in the Guide
FEMA, through the ATC-124 project series, and with assistance
from SEAOC, sponsored development of an Example Application Guide
offering guidance on the interpretation and use of ASCE 41-13. The
Guide is co-branded with FEMA and SEAOC. SEAOC members assisted in
determining the scope of the Guide and reviewed examples.
The purpose of the Guide is to provide helpful guidance on the
interpretation and the use of ASCE 41-13 through a set of examples
that cover key selected topics. The comprehensive, two-volume,
936-page Guide covers topics that commonly occur where guidance is
believed to be beneficial, with topics effectively organized and
presented such that information is easy to find. Commentary
provides context, rationale, and advice.
Audience/Goals The target audience for the Guide is both
practicing engineers and building officials who have limited or no
experience with ASCE 41 and those engineers and building officials
who have used these documents in the past but have specific
questions. It is assumed that the user has seismic design
experience and a working knowledge of seismic design concepts.The
document includes guidance for lower and higher seismic hazard
levels.
Project Approach and DevelopmentTo ensure success of the Guide,
the project team:• Reviewed sample precedent documents• Organized a
user survey (initial stage) and focus group (draft review
stage) to gain insight into usability of the document• Engaged a
consultant to develop consistent graphics for use within the
Guide
Design for Ease of Use• User survey resulted in 100+
recommendations• The project team determined the following would
lead to ease of use:
– Detailed examples – Substantial use of over 275 graphics
including 3-D pictures of
deficiencies
– Consistency in example presentations/use of standard format–
Topics vs. full design examples: both shorter topic examples
together with longer full-building examples– Commentary: some
level of commentary without excessive
amount of text or overly opinionated discussion– Flowcharts that
would be nice to have in ASCE 41-13– Clarification of primary vs.
secondary elements and
force-controlled vs. deformation-controlled actions– Matrix
relating ASCE 41-13 sections to the Guide
• Focus group from the target audience of engineers with
seismicexperience but no or little ASCE 41 experience evaluated
documentorganization and user aids, writing clarity and style, and
design examplepresentation
Detailed Examples For each of the detailed examples, there is a
standard presentation approach which includes a description of the
building, site seismicity, weight takeoffs, performance objective
and analysis procedure selection, data collection and material
testing, and determination of forces and displacements. The
buildings are located in different parts of the United States to
present a range of seismicity. The focus is on the linear static
procedure (LSP) as this is the most common analysis procedure,
although some examples include the linear dynamic procedure (LDP),
and the nonlinear static procedure (NSP). Most examples use the
Basic Performance Objective for Existing Buildings (BPOE) as this
is the most common Performance Objective, but the URM Special
Procedure example and an Enhanced Performance Objective for the
steel braced frame are included.
Figures shown to the right illustrate the detailed example
buildings in the Guide and some of the issues covered.
Introduction to the Guide
The Guide is organized via the following topics:• Introduction•
Guidance on Use of ASCE/SEI 41-13• Performance Objectives and
Seismic Hazards• Analysis Procedures• Foundations• Detailed
Full-Building Examples• Changes from ASCE 41-06 to ASCE 41-13• FEMA
P-2006 vs. ASCE 41-13 Index
The Guide’s physical layout is also vital to meeting the goals
of the project in that it enables ease of use via the following:•
Wide margins on pages to allow for blue
boxes providing summaries, useful tips and commentaries. Green
margin boxes identify key changes from ASCE 41-13 to ASCE 41-17 and
their implications.
• Ample, but judicious use of graphics to illustrate
calculations and comments and reduce sole reliance on text.
• Flowcharts have been used in the Guide toillustrate more
complicated issues or the proper sequence of steps to follow.
• See examples to the right.
Guide Content and Layout
Based on experience with using ASCE 41-06 and ASCE 41-13, the
following general advice, tips, and guidance are offered. Some
examples include the following:
• ASCE 41 is not always organized in a sequential way, nor were
the provisions holistically developed (with the exception of the
Special Procedure for Unreinforced Masonry).An evaluation is
performed on a component-by-component basis, which often requires
jumping between chapters for analysis provisions, component
strengths, and acceptancecriteria. In the examples of this Guide,
the starting point in ASCE 41 and reference sections related to the
next steps are indicated.
• It is important to read all associated text and table
footnotes in the associated chapter in ASCE 41 rather than simply
applying the equations. For example, there are manyinstances where
the text and footnotes significantly alter m-factors or when
certain equations are not applicable.
• ASCE 41 uses displacement-based design. Thus, the inelastic
response of a building is primarily about deformation compatibility
and ductility on a component level. Section2.2 of this Guide
discusses this in more detail.
• Understanding component behavior and whether an element is
classified as force-controlled or deformation-controlled are
essential.• Wood evaluation and retrofit design in ASCE 41 requires
determination of various failure limit stats and can take more
effort than ASCE 7.• Boundary conditions can make a significant
difference in resulting behavior mechanisms and analysis results.•
Some seemingly straightforward equations actually require detailed
iteration and parallel calculations to complete, such as
determination of target displacement for the
nonlinear static procedure.
General Advice, Tips, and Guidance
FEMA Oversight Mike MahoneyAndrew HersethWilliam T. Holmes
ATC Management and Oversight Jon A. HeintzAyse HortacsuVeronica
Cedillos
Project Technical CommitteeBret Lizundia, Project Technical
Director | Rutherford + ChekeneMichael BraundJim CollinsRon
LaPlanteBrian McDonaldMark Moore
Project Review PanelDavid BiggsAnthony CourtRoy LoboJames
ParkerRobert PekelnickyPeter SomersWilliston Warren
Working GroupRyan BogartLawrence BurkettCasey ChampionAlex
ChuJie LuoSteve PattonKylin Vail
IllustratorChris Tokas
SEAOC Reviewers Russell BerkowitzJonathan BuckalewLachezar
Handzhiyski Kari KlaboeJeremiah LegrueDion MarriottRose McClureBen
MohrBrian OlsonJim ReberAndrew Shuck Fred Turner
Focus Group Marshall Carman Joseph R. JonesValerie MartinRyan
McDaniel Meghann Riedner
Project Participants
Detailed Examples
Challenges and Solutions
Careful location and sizing of the BRBFs and cantilever columns
was necessary to achieve torsional balance, minimize loads
transferred between pavilions, and reduce drift at the canopy edges
to acceptable levels. Because the northwest end of the canopy is
highly eccentric to the building, rigorous analytical effort was
needed to prevent it from affecting the rest of the design. Column
sizes and the elevations of the column bases were varied to tune
the lateral system for optimal performance in wind and seismic
conditions.
Special detailing addressed the different geometries of the
pavilion roofs. In some cases, the high roof slopes steeply enough
to connect to the low roof, creating complicated interstory drift
situations across the footprint.
Initial architectural canopy forms included a variety of double
curvature bends of different radii in the HSS girders. R+C worked
with the steel fabricator and roller to select optimal joint
locations, reduce complicated curves, and simplify bending, saving
significant costs and while achieving the desired architectural
form.
We developed special details for skewed and sloped moment
connections at wide flange columns in the building and where canopy
tubes join at highly acute angles. To create more intriguing canopy
forms, canopy columns are typically offset from girder
intersections. The top of the column narrows to a smaller section,
providing a more elegant connection.
All canopy framing is architecturally exposed structural steel.
Specifications defined two levels of AESS, so that tighter shop and
field tolerances and higher quality member surface and weld
preparation and finishes were targeted at critical locations for
fit-up and aesthetic importance, with less stringent and more
economical requirements at less sensitive locations.
To address gravity moments from offset columns, torsional
demands from curving members, and large wind and seismic demands,
the HSS-to-HSS joints are all made with moment connections.
Connection details use different strategies and sizes of continuity
and through plates, providing increased tolerance where desired by
the erector.
The team built a full sized mockup of cladding, glazing, and
canopy. HSS joint mockups were created and tested with oversight by
the inspector who would check future production welds. R+C and the
erector developed project specific welding techniques and fit-up
procedures to account for observed joint tolerances and to minimize
weld distortion.
Together with Front, R+C detailed infill beams to provide a
fixed connection at one end and a special connection at the other
end. The adaptable special connection remains fixed
Torsional Balance
Sloped Roofs + Connecting Diaphragms
Efficient Bending of HSS Sections
Complicated Geometry
Architecturally Exposed Structural Steel
Joints + Tolerances
Mockups
Infill Beams
SEAONC/SEAOC 2020 Excellence in Structural Engineering
Awards
FEMA P-2006 Example Application Guide for ASCE/SEI 41-13 Seismic
Evaluation and Retrofit of Existing Buildings with Additional
Commentary for ASCE/SEI 41-17
Primary vs. secondary elements Force-controlled actions (FCA)
vs. deformation-controlled actions (DCA)
