Engineering Research Center Development of a Precast Floor Diaphragm Seismic Design Methodology (DSDM) Robert Fleischman, UA Clay Naito and Richard Sause, LU Jose Restrepo and Andre Filiatrault, UCSD S.K. Ghosh, S.K. Ghosh Associates, Inc.

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 DSDM Consortium DSDM Task Group PCI, IAP

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Status PCI R&D providing $200,000 in funds for project research activities. Proposal submitted to NSF GOALI Program February 7, Awaiting outcome of the review process (NSF Panel met August ). Project Original Start Date August 2003 Initial DSDM Research Meeting.

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Proposed Research Approach: Integrated Analysis and Experimentation

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Integration and Flow of Research Activities a 3a 4 Diaphragm Characteristic

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting Objectives 1.Establish consensus on a design philosophy to guide research DSDM Research #1 2.Establish guidelines for the physical scope of the research 3.Review and comment on plans for Lehigh Phase I test program Fleischman/Restrepo Sause Naito NOTE: Design approach will impact project direction; physical scope will define project outcome

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting Objectives 1.Establish consensus on a design philosophy to guide research DSDM Research #1 Applicability of Design/Analysis Methods: Beam Analogy, Strut & Tie; Stringer and Panel (Restrepo) Hollow Core details, emerging techniques and emphasis (Restrepo) Discuss importance of lateral system layout (Restrepo) Role of Elastic Diaphragm Design and Need for Detailing for Ductility in High, Moderate, Low Seismic Zones (Fleischman) Role of Web Reinforcement: compliance vs. ductility (Fleischman) Applicability of construction methods: composite, non-composite, pretopped (Fleischman)

Engineering Research Center DSDM Research Meeting #1 August 7, Role of Elastic Diaphragm Design and Need for Detailing for Ductility in High, Moderate, Low Seismic Zones DSDM Research Meeting #1 ResearcherNakakiRodriguez/ Restrepo Farrow/ Fleischman/ Sauce NEHRP Appdx. Design Force Approach Design to LFRS Ultimate Use R Factor on 1 st mode only  is function of diaphragm flexibility Higher factor for untopped Design Force   = 2.8  i = ~2   =   Nakaki: Structure overstrength factor to bring diaphragm design to the ultimate state (Squat walls use R=1). Rod/Rest: Floor magnification factor based on vertical location of the floor and influence of higher modes. Far/Flei/Sause: Overstrength factor based on diaphragm flexibility (Alternative for elastic design)

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting 1.Role of Elastic Diaphragm Design and Need for Detailing for Ductility in High, Moderate, Low Seismic Zones DSDM Research #1 Nakaki: Identifies important inconsistencies including designing diaphragm ultimate state to lateral system “first yield”. However, other factors exist in diaphragm overload (See Rodriguez et al; Fleischman et al). COMMENTS: CONCLUSIONS: Calibrate  through research. Tradeoff between  and ductility demand (and drift demands).

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting 1.Role of Elastic Diaphragm Design and Need for Detailing for Ductility in High, Moderate, Low Seismic Zones DSDM Research #1 ISSUES: Is the desired approach? –Design for a specified force level and accept ductility demands, or –Design for a specified ductility demand (including elastic) and accept force level The proper approach likely depends on: –Diaphragm span –Lateral system –Seismic Zone What is acceptable damage? What is the target seismic level?

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting One Possible Approach: Different Force levels depending on zone, span and details: DSDM Research #1 Diaphragm Classification (DC) DesignationSeismic Zones OrdinaryODA,B,C IntermediateIDB,C,D,E SpecialSDD,E,F Classify Precast Diaphragms in terms of detailing requirements.

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting Different Force level depending on zone, span & details: DSDM Research #1 Seismic Design Category Diaphragm Span ABCDEF L cl <L fd DC OD ID SDIDSD  px ** ** ee ** ee L cl >L fd DC ODIDODID SD  px ee ** ee ** ee Define applicability of diaphragms for different zones, forces and spans.

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting Different Force level depending on zone, span & details: DSDM Research #1 ClassificationODIDSD Reinforcement  detailing   Collector0.75  regular 0.6 special Chord0.9  regular 0.9 special WebShear0.75   0.6  Tension  Type A  Type B  Type C Specify strength reduction and detailing requirements for each classification

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting Objectives 2.Role of Web Reinforcement: compliance vs. ductility DSDM Research #1 ResearcherNakakiFarrow/ Fleischman Diaphragm Web Reinforcement Approach The diaphragm is designed against  M y where yield can occur in the chord or at the extreme web reinforcement. Two detailing approaches are proposed: tension resistant connector details and tension compliant web details Capacity design for web reinforcement based on comparing dynamic demands with pushover results Reinforcement Calculation Strength Criterion: Based on strain compatibility formulation in which curvature, and hence moment, is controlled by the limiting elastic deflection of the most extreme web connection or the chord steel Stiffness Criterion: Uses an effective stiffness factor based on flexure and applies it equally to the shear resistance (basis of the NEHRP force amplification factor b d [1+0.4(L eff /b d ) 2 ]/12h s )  v  = 0.6  b  = 0.9

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting 2.Role of Web Reinforcement: compliance vs. ductility DSDM Research #1 Nakaki: Method shows efficacy of tension compliance; may be overly conservative for tension resistant due to assumed debonded length COMMENTS: ISSUES: Should floors be designed as deep sections (to over 50’) with flexural strength and stiffness ONLY provided by boundary elements? Can a viable shear connection be created instead that is both tension strong/stiff and tension ductile? (distinguish between 3 types) Fleischman: Capacity design (in shear) does not directly address tension demand. What are the serviceability issues involved? Do altogether different solutions exist? How severe is the loss of a portion of the web reinforcement?

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting 2.Role of Web Reinforcement: compliance vs. ductility DSDM Research #1 CONCLUSION: This is a key issue, maybe hold off discussion until after second part of presentation.

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting Objectives 3.Applicability of construction methods DSDM Research #1 QUESTION: What are the industry’s desires in terms of: Extent of applicability of untopped diaphragms Interest in topped noncomposite Geographic Focus: emphasis on high seismic? Solutions for Hollow Core vs. Double Tees

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting Objectives DSDM Research #1 Structural System –Type –Layout 2.Establish guidelines for the physical scope of the research Diaphragm –Construction –Plan Details

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting DSDM Research #1 A.Structural System Lateral System –Wall systems –Frame systems –Dual systems Profiles –Low rise –Mid Rise –High rise Layout –Perimeter –Interior –Mixed

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting DSDM Research #1 B.Diaphragm Construction –Topped Noncomposite –Topped Composite –Untopped Precast Floor System –Double Tee –Hollow Core Construction Practice –Internal Walls –Spandrel Details –Tee Beam Details, etc.

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting DSDM Research #1 B.Diaphragm (Layout) Interior Beams Interior Cavity Irregular Floor Plans Continuous Spans Long vs. Squat

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting DSDM Research #1 C.Diaphragm Details Typical Construction Proprietary Details Emerging Details

Engineering Research Center DSDM Research Meeting #1 August 7, 2003 Meeting Objectives DSDM Research #1 Resources Existing Example Structures –Nakaki EERI: 10 story frame; 3 story wall –Englekirk/Nakaki: Typical Northridge Parking Garage –Cleland – Design Examples from Seismic Committee –PCI Handbook? ISSUE: University Researchers can follow the code in creating design but will have difficulty in producing designs that possess the typical “state-of-practice” of construction in various regions of the country SOLUTION: DSDM produce a set of prototype structures to guide the research NOTE: Certain studies (effect of # of stories) can be performed using approximate designs.