Development of a Precast Floor Diaphragm Seismic Design

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

Status • PCI R&D providing $200, 000 in funds for project research activities. • Proposal submitted to NSF GOALI Program February 7, 2003. • Awaiting outcome of the review process (NSF Panel met August 4 2003). • Project Original Start Date August 2003 • Initial DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

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

Integration and Flow of Research Activities 1 2 a 3 a 4 2 3 Diaphragm Characteristic DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

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

DSDM Research #1 Meeting Objectives 1. Establish consensus on a design philosophy to guide research • 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) • 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) DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

DSDM Research Meeting #1 1. Role of Elastic Diaphragm Design and Need for Detailing for Ductility in High, Moderate, Low Seismic Zones Researcher Nakaki Rodriguez/ Restrepo Farrow/ Fleischman/ Sauce NEHRP Appdx. Design Force Approach Design to LFRS Ultimate Use R Factor on 1 st mode only W is function of diaphragm flexibility Higher factor for untopped Design Force Wo = 2. 8 Wi = ~2 W* = 1. 0 -3. 0 r. Wo 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) DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

DSDM Research #1 Meeting 1. Role of Elastic Diaphragm Design and Need for Detailing for Ductility in High, Moderate, Low Seismic Zones COMMENTS: 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). CONCLUSIONS: • Calibrate W through research. • Tradeoff between W and ductility demand (and drift demands). DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

DSDM Research #1 Meeting 1. Role of Elastic Diaphragm Design and Need for Detailing for Ductility in High, Moderate, Low Seismic Zones 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? DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

DSDM Research #1 Meeting One Possible Approach: Different Force levels depending on zone, span and details: Classify Precast Diaphragms in terms of detailing requirements. Diaphragm Classification (DC) Designation Ordinary OD A, B, C Intermediate ID B, C, D, E Special SD D, E, F DSDM Research Meeting #1 August 7, 2003 Seismic Zones Engineering Research Center

DSDM Research #1 Meeting Different Force level depending on zone, span & details: Define applicability of diaphragms for different zones, forces and spans. Diaphragm Span Lcl<Lfd Lcl>Lfd Seismic Design Category A B DC OD OD OD ID ID SD SD Wpx - - W* - We W* We DC OD ID ID SD SD Wpx - - We W* We C D DSDM Research Meeting #1 August 7, 2003 E Engineering Research Center F

DSDM Research #1 Meeting Different Force level depending on zone, span & details: Specify strength reduction and detailing requirements for each classification Classification OD ID SD f detailing Collector 0. 75 - 0. 75 regular 0. 6 special Chord 0. 9 - 0. 9 regular 0. 9 special 0. 75 - 0. 6 - - Type A - Type B - Type C Reinforcement Web Shear Tension DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

DSDM Research #1 Meeting Objectives 2. Role of Web Reinforcement: compliance vs. ductility Researcher Nakaki Farrow/ Fleischman Diaphragm Web Reinforcement Approach The diaphragm is designed against f. My 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: f v = 0. 6 f b = 0. 9 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 bd [1+0. 4(Leff/bd)2]/12 hs) DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

DSDM Research #1 Meeting 2. Role of Web Reinforcement: compliance vs. ductility COMMENTS: Nakaki: Method shows efficacy of tension compliance; may be overly conservative for tension resistant due to assumed debonded length Fleischman: Capacity design (in shear) does not directly address tension demand. 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) • What are the serviceability issues involved? • How severe is the loss of a portion of the web reinforcement? • Do altogether different solutions exist? DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

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

DSDM Research #1 Meeting Objectives 3. Applicability of construction methods 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 DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

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

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

DSDM Research #1 Meeting 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. DSDM Research Meeting #1 August 7, 2003 Engineering Research Center

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

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

DSDM Research #1 Meeting Objectives 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. DSDM Research Meeting #1 August 7, 2003 Engineering Research Center