Title: Tiered Approach to PerformanceBased Seismic Design of Wood Frame Buildings
1Tiered Approach to Performance-Based Seismic
Design of Wood Frame Buildings
- Weichiang Pang1, Shiling Pei2, Hongyan Liu2, John
van de Lindt2, and David Rosowsky1
Texas AM University1 Colorado State
University2
Structures Congress 2008, Vancouver BC.
2Overview
- PBSD Background
- Tiered Approaches
- Design Examples
- Displacement-based design (DDD)
- Nonlinear time history analysis (NLTHA)
- Loss-based design (LBD)
- Conclusions
3Background
- Seismic design for woodframe structures
- Current practice and Challenges
- PBSD
- Concept
- Tools and approaches
- Displacement-based approaches, Fragility based
study, Nonlinear dynamic analysis based, IDA,
IMA, Loss analysis, etc.
4Three tiered approaches
"While no single approach to building codes can
be simple, reliable, and economical, we can have
any two of these - and maybe that's just what we
need."
-- Hamburger, R.O. (2007) Simple, But No
Simpler, Modern Steel Construction
- Tier 1 Direct displacement design (DDD)
- Objective Control excessive drifts
- Methods Modal analysis, equivalent stiffness,
database/table - Tier 2 Nonlinear time history analysis (NLTHA)
- Objective Control overall structural performance
- Methods NLTH simulation, explicit reliability
analysis - Tier 3 Loss based design (LBD)
- Objective Control economic loss
- Methods NLTH simulation loss simulation,
statistical analysis
5Numerical Example
- The structure
- A two-story single family home, approximately 220
m2 (2400 ft2). - Shearwall nail spacing to be determined
- The seismic hazard
- San Francisco, California
- Structure assumed to be founded on stiff soil
(Site Class D)
6TIER 1 Displacement-based Design (DDD)
- Three performance levels (NEESWood)
- IO(0.5) LS(2) CP(5)
- Easy-to-implement steps guide through design
process - Shearwall database or design value tables
developed based on CASHEW
7DDD method (cont.)
- Examine possible wall configurations to match the
design target points - Equivalent stiffness curve for final design
satisfies all requirements - Currently, torsional effects not included.
8TIER 2 Nonlinear time history analysis (NLTHA)
- A research tool made available to design through
easy-to-use software package (SAPWood) - Essentially can be used to design for any
structural responses (performances) - Simulation with multiple earthquake records
- Start with tier 1 result, focus on drift.
Over-strength identified.
9NLTHA (Cont.)
- Two options with NLTHA
- Perform IMA to explore the hidden load carrying
capacity - Optimize the initial design while keeping the
desired performance - More complex
- Extra information needed (building model,
earthquake records) - Torsion automatically included
- Seismic uncertainty included
- Need a software package.
10Tier 3 Loss based design (LBD)
- Loss simulation framework
- NLTH simulation with ground motion database
- Assembly based vulnerability
- Loss fragility
- Long term simulation
- Event loss (Structure, Intensity) Long term
loss (Structure, Location, Time) - Integrated in SAPWood program
11LBD (Cont.)
- A structuralized trial-and-error process
- Binary search which narrows the design quickly
- Incremental optimization refines in the target
region - Very computationally intensive, must be performed
by automated tools.
12LBD (Cont.)
- Event loss performance target
- Loss should not exceed 75 of the total house
value under an intensity level of Sa1.5 g (0.2
sec, 5 damping) with only 5 probability of
exceedance - First story altered in order to satisfy the
performance target. Require more material than
DDD and NLTHA design.
13Conclusions and recommendations
- Tiered approach represents three different levels
of possible PBSD implementations for wood frame
structures. Validity verified through numerical
examples. - DDD simple to apply and reliable, may not
provide the most optimized solution, only
controls drifts. - NLTHA provides more freedom in specifying
performance targets, design can be economical and
reliable, more involvement in modeling and
simulation, software package needed. - LBD focuses on financial losses. Can be used to
design for customized financial performance
targets. - The selection of tiers in the proposed framework
should be based on - The resources available, the accuracy needed, the
performance target type, etc.
14Acknowledgement
- This material reported in this paper is based
upon work supported by the National Research
Initiative of the USDA Cooperative State
Research, Education and Extension Service, grant
number 2005-35103-15250 with additional support
from the National Science Foundation under Grant
No. CMMI-0529903 (NEES Research) and CMMI-0402490
(NEES Operations). Any opinions, findings, and
conclusions or recommendations expressed in this
paper are those of the authors and do not
necessarily reflect the views of the sponsors.
15Thank you