Engineering Research Center Development of a Precast Floor Diaphragm Seismic Design Methodology (DSDM) Robert Fleischman, UA Clay Naito and Richard Sause,

EngineeringResearchCenter

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.


DSDM Research Meeting #1August 7, 2003

DSDM Consortium

P ro d uce r M em b e rs

U n ive rs ity o f C a lifo rn iaS a n D ie go

Jo se R e stre po , P IA n d re F ilia tra u lt, C o -P I

P ro d uce r M em b e rs

L e h igh U n ive rs ityC la y N a ito , P I

R ich ard S au se , C o -P I

In d u s try A d viso ry P a n e l

In d u stry L ia isonS . K . G h osh , C o -P I

U n ive rs ity o f A rizo naR o b e rt F le isch m anC o n so rtium L ea d er

DSDM Task Group

PCI, IAP



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.



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Side Walls

Load Cell

Floor Diaphragms

Shake Table

ReactionWall

Steel Base withCantilever Outriggers

6 ft – 6 in

Proposed Research Approach:Integrated Analysis and Experimentation



Integration and Flow of Research Activities

1

2

3

2a

3a

4

Diaphragm Characteristic



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



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)



1. Role of Elastic Diaphragm Design and Need for Detailing for Ductility in High, Moderate, Low Seismic Zones

DSDM Research Meeting #1

Researcher Nakaki Rodriguez/ Restrepo

Farrow/Fleischman/Sauce

NEHRP Appdx.

Design Force Approach

Design to LFRS Ultimate

Use R Factor on 1st mode only

is function of diaphragm flexibility

Higher factor for untopped

Design Force = 2.8 i = ~2 = 1.0-3.0

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)



Meeting1. 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) .



Meeting1. 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?



MeetingOne Possible Approach: Different Force levels depending

on zone, span and details:

DSDM Research #1

Diaphragm Classification (DC)

Designation Seismic Zones

Ordinary OD A,B,C

Intermediate ID B,C,D,E

Special SD D,E,F

Classify Precast Diaphragms in terms of detailing requirements.



MeetingDifferent Force level depending on zone, span & details:

DSDM Research #1

Seismic Design Category

Diaphragm Span

A B C D E F

Lcl<LfdDC OD OD OD ID ID SD ID SD SD

px * * e * e

Lcl>LfdDC OD ID OD ID ID SD SD

px e * e * e

Define applicability of diaphragms for different zones, forces and spans.



MeetingDifferent Force level depending on zone, span & details:

DSDM Research #1

Classification OD ID SD

Reinforcement detailing detailing detailing

Collector 0.75 0.75 regular 0.6 special

Chord 0.9 0.9 regular 0.9 special

Web Shear 0.75 0.75 0.6

Tension Type A Type B Type C

Specify strength reduction and detailing requirements for each classification



Meeting Objectives

2. Role of Web Reinforcement: compliance vs. ductility

DSDM Research #1

Researcher Nakaki Farrow/ Fleischman

Diaphragm Web Reinforcement Approach

The diaphragm is designed against 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

ReinforcementCalculation

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 steelStiffness 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]/12hs)

v= 0.6

b= 0.9



Meeting2. 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?



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.



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



Meeting Objectives DSDM Research #1

• Structural System– Type– Layout

2. Establish guidelines for the physical scope of the research

• Diaphragm – Construction– Plan

• Details



MeetingDSDM Research #1

A. Structural System• Lateral System

– Wall systems– Frame systems– Dual systems

• Profiles– Low rise– Mid Rise– High rise

• Layout– Perimeter– Interior– Mixed




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.




B. Diaphragm (Layout)• Interior Beams

• Interior Cavity

• Irregular Floor Plans

• Continuous Spans

• Long vs. Squat




C. Diaphragm Details• Typical Construction

• Proprietary Details

• Emerging Details



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.

Documents

Engineering Research Center Development of a Precast Floor Diaphragm Seismic Design Methodology (DSDM) Robert Fleischman, UA Clay Naito and Richard Sause,