Seismic Design Recommendations for PT Slab-Column … Convention/S2-2... · Practical design guide...

Seismic Design Recommendations for PT Slab-Column Connections

Thomas Kang, Ph.D., P.E.

Assistant Professor, Univ. of Oklahomass sta t o esso , U o O a o a

Punching during Northridge EQ. (1994; Four Seasons Bldg., Sherman Oaks, CA)

Localized damage in PT flat plate systemsafter shake table tests (Kang and Wallace, 2006)

2008 PTI TECHNICAL CONFERENCE SESSION 2 - SEISMIC DESIGN RECOMMENDATIONS FOR PT SLAB-COLUMN CONNECTIONS THOMAS KANG, PH.D., P.E.

(C) COPYRIGHT POST-TENSIONING INSTITUTE, ALL RIGHTS RESERVED of 35

PT Background and EffortsEducation, Research, and ServicesEducation, Research, and Services

PhD / P tPhD / P t dd UCLA C tl t hi tUCLA C tl t hi t OUOUPhD / PostPhD / Post--doc. doc. –– UCLA, Currently teaching at UCLA, Currently teaching at OUOU

PTPT ResearchResearch

Shake table tests & modeling of PT flat plate systems (Ph.D.)Shake table tests & modeling of PT flat plate systems (Ph.D.)Cyclic tests of Isolated PT conn. (PostCyclic tests of Isolated PT conn. (Post--doc.)doc.)Development of PT conn design models (PostDevelopment of PT conn design models (Post doc / Now withdoc / Now with OUOU))Development of PT conn. design models (PostDevelopment of PT conn. design models (Post--doc. / Now with doc. / Now with OUOU) )

Professional Services in Professional Services in PTPT AreaArea

Ed. Subcomm.: ACI 352.1REd. Subcomm.: ACI 352.1R--XX (Seismic design of PT conn.)XX (Seismic design of PT conn.)Ed. Subcomm.: ACI 369.REd. Subcomm.: ACI 369.R--XX (Modeling of PT conn. XX (Modeling of PT conn. –– ASCE 41)ASCE 41)Ed. Subcomm.: Practical design guide for PT bldg. (PTIEd. Subcomm.: Practical design guide for PT bldg. (PTI––BD)BD)

2

Recently joined ACIRecently joined ACI--ASCE 423 Comm. to serve.ASCE 423 Comm. to serve.



University of Oklahoma

3



OKC Downtown OKC Downtown

4Norman Norman



Donald G. Fears Structural Eng Lab

5



PT Flat Plate Systemsy



PT Flat Plate SystemsVery popular in North America, except for NYCVery popular in North America, except for NYC

As intermediate moment frames (w/ nonAs intermediate moment frames (w/ non special Bspecial B C framesC framesAs intermediate moment frames (w/ nonAs intermediate moment frames (w/ non--special Bspecial B--C frames C frames or bearing walls)or bearing walls)

As nonAs non--participating frames w/ core wallsparticipating frames w/ core wallsAs nonAs non participating frames w/ core wallsparticipating frames w/ core wallsATC 63: allows 30% lat. resistance by perimeter flat platesATC 63: allows 30% lat. resistance by perimeter flat plates

Longer spanLonger span--toto--thickness ratiothickness ratiog pg pBetter seismic performanceBetter seismic performanceEasier to construct, and costly efficient (materials, time)Easier to construct, and costly efficient (materials, time)

Careful design considerationCareful design consideration

ShortShort-- and longand long--term cracking controlterm cracking control

7

ShortShort-- and longand long--term cracking controlterm cracking controlEarthquakeEarthquake--resistant design for PT connectionsresistant design for PT connections



Non-participating frames

Flexural design for gravity loads

Punching shear design / lateral drift capacity check

Moment transfer in flexure

I t di t PT l b l tiIntermediate PT slab-column connections

Earthquake-resistant shear reinf. detailsq

8



Tendon Layouts – Gravity Analysisy y y

Banded in one dir., distributed in the other dir.Banded in one dir., distributed in the other dir.

If same loading & geometry, same If same loading & geometry, same AApsps and ecc. for and ecc. for both layoutsboth layouts

Flexure design for gravity loadsFlexure design for gravity loads

3D FE l i ( i l f )3D FE l i ( i l f ) l dl d3D FE analysis (commercial software) 3D FE analysis (commercial software) –– commonly usedcommonly used

As availableAs availableD l i h i l l d dD l i h i l l d dDeals with irregular plans and secondary momentsDeals with irregular plans and secondary moments

Hand cal. possible Hand cal. possible –– at least should reat least should re--check by handcheck by hand

9



Hand Cal. / Check for Flexure

Using design Using design PP , , PePe , and “service” , and “service” MMgravgrav & & MMsecsec

Service Service MMgravgrav & & MMsecsec from FE software or per PTI manualfrom FE software or per PTI manual

W ki t h k t l j t ft PTW ki t h k t l j t ft PTWorking stress check: at early age, just after PTWorking stress check: at early age, just after PT

MMePP gravii sec++−−=σ

Working stress check: at service loadsWorking stress check: at service loads

SSAc

+σ

SMM

SeP

AP grave

c

e sec++−−=σ

10

c



Strength Check – At ultimate

Strength check: at ultimate (using “design” Strength check: at ultimate (using “design” MMgravgrav & & MMsecsec))

⎞⎛⎞⎛sec_22 +≥⎟

⎠⎞

⎜⎝⎛ −+⎟

⎠⎞

⎜⎝⎛ −= gravuysppspsn MadfAadfAM

f ′

p

cseps

fffρ300

000,10 where′

++=

Recent research (Kang and Wallace, 2008; Recent research (Kang and Wallace, 2008; PTI journalPTI journal) ) revealed that revealed that ffpsps Eq. is conservative for PT “slabs”.Eq. is conservative for PT “slabs”.pp

ffpsps can be used at any location/section of PT members.can be used at any location/section of PT members.Experimentally verified (shake table testsExperimentally verified (shake table tests

11

Experimentally verified (shake table tests Experimentally verified (shake table tests –– Kang and Wallace, 2008; Kang and Wallace, 2008; PTI journalPTI journal))




30

35) 200 a)

LC3 (Run 4)+ drift ratio:W direction (see Fig 1)

(Kang and Wallace, 2008; PTI journal)

20

25

stre

ss (k

si

150

200

ress

(MPaW direction (see Fig. 1)

+ change in tendon stress:Increase in tensile stress

At peak lateral loadΔ = 22 ksi

10

15

20

tend

on s

100

tend

on s

t

5

10

Cha

nge

in

50

hang

e in

t

After Run 44.1 ksi

(28 3 MPa)

-5

0C 0 Ch

-5 -4 -3 -2 -1 0 1 2 3 4 5

(28.3 MPa)

12

Mean Drift Ratio (%)

Δ = 12-15 ksi @ 3% driftΔ = 8-10 ksi

@ 2% drift




30

35) 200 a)

LC4 (Run 5)

(Kang and Wallace, 2008; PTI journal)

20

25

30

tress

(ksi

)

150

200

ress

(MPaAt peak lateral load

Δ = 22 ksi

15

20

tend

on s

t

100

tend

on s

tr

5

10

Cha

nge

in

50

hang

e in

t

-5

0C 0 Ch

-5 -4 -3 -2 -1 0 1 2 3 4 5Mean Drift Ratio (%)

13Δ = 12-14 ksi @ 3% driftΔ= 7-10 ksi

@ 2% drift




Punching shear design / lateral drift capacity checkcapacity check


Intermediate PT slab-column connections

Earthquake-resistant shear reinf. details

14



Drift-induced Punching of PT Conn.• Pimanmas et al. (2004)

– Static, cyclic PT i t iPT interior

Drift ratio at punching = 2%

5.0/ =cug VV φ cug φ

Loading directionLoading direction

• Kang and Wallace (2005; 2006; 2008)• Kang and Wallace (2005; 2006; 2008)

– Dynamic, PT systemswith shear reinforcement

15

Drift ratio at punching = 4.5%33.0/ =cug VV φ



Drift-induced Punching of PT Conn.• Han et al. (2006a)

– Static, cyclic PT i t iLoading Direction PT interior conn.

Drift ratio at punching = 4%4.0/ =cug VV φg

• Han et al. (2006b)

– Static, cyclic PT exterior conn.

16

Drift ratio at punching = 3.3%35.0/ =cug VV φ



Drift-induced Punching

Stress-induced punching

V u)

p g

Drift-induced punching due to potential

Dem

and

(V punching due to potential shear-strength degradation

She

ar D

r city

(Vn)

She

arC

apac

17Ductility (μ)

0 1 2 3 4 5



Connection Punching Shear DesignFirst, punching design only for gravity loads without shear reinf. First, punching design only for gravity loads without shear reinf.

per ACI 318per ACI 318--08, Ch. 1108, Ch. 11

Deform. compatibility check (lateral drift capacity check)Deform. compatibility check (lateral drift capacity check)per ACI 318per ACI 318--08, S21.13.608, S21.13.6

RC

cug VV φ/

RC

18

If design story drift ratio of the system If design story drift ratio of the system >> drift limit, drift limit, min. shear reinf. should be provided per 21.13.6.min. shear reinf. should be provided per 21.13.6.



PT Connection Drift Limit

0.08

0.09Lateral drift limit for RC ConnectionsLateral drift limit for PT ConnectionsRC without shear reinf. (Kang and Wallace, 2006)PT ith t h i f t

Best-fit line for RC interiorconnections

0.06

0.07

unch

ing

PT without shear reinforcement connections without shear reinforcement Specimens with slab span

-to-thickness ratio of 17

g0.04

0.05

ratio

at p

u

Best-fit line for all PT connections without shear reinforcement

g

0.02

0.03

Drif

t r

PT

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.01RC

19

Gravity shear ratio, (Vu /φVc)

ACI 352.1R-XX (Kang et al., 2008; PTI journal)cug VV φ/



Design Story Drift Ratio

Design story drift ratio of PT flat plate systems Design story drift ratio of PT flat plate systems = that of SFRS (Special walls / SMRF)= that of SFRS (Special walls / SMRF)( p )( p )

, where , where RR is for SFRSis for SFRSsu RΔ= 7.0δ

Should use UBCShould use UBC--97 to get 97 to get δδuu , according to ACI 318, according to ACI 318--0808S21.1; S21.1; δδuu = design drift expected for DBE= design drift expected for DBE

ConservativelyConservatively, can use IBC, can use IBC--06 to get (06 to get (ΔΔaa//hhxx) ) related to related to MCEMCE

ACI 318: “LifeACI 318: “Life--safety” under DBEsafety” under DBE

F “ ll ti ” d MCEF “ ll ti ” d MCE SSt I t it bt I t it b

20

For “collapse prevention” under MCE For “collapse prevention” under MCE SStr. Integrity bars tr. Integrity bars



ALTERNATIVELY,ACI 318ACI 318--08, S21.13.6(a)08, S21.13.6(a)

Limit AnalysisLimit Analysisyy

Max possible unb. moment, Max possible unb. moment, MMunb unb = = MMn,slabn,slab–– + + MMn,slabn,slab

++

ff MM ; Plug; Plug MM intointo bcMV γffpsps MMn,slabn,slab ; Plug ; Plug MMunbunb intointo

UseUse φφ = 0.60 (instead of 0.75) per S9.3.4 to account for= 0.60 (instead of 0.75) per S9.3.4 to account forc

unbv

o

un J

cMdb

Vv γ+≥

21

Use Use φφ 0.60 (instead of 0.75) per S9.3.4 to account for 0.60 (instead of 0.75) per S9.3.4 to account for shear strength degradation @ shear strength degradation @ δδuu



Shear Strength of PT Conn.ACI 318ACI 318--08: PT Interior 08: PT Interior ≠≠ PT Exterior Conn. PT Exterior Conn.

0 9(Kang et al., 2008; PTI journal)

0.7

0.8

0.9

2 )

0.5

0.6

(MP

a1/2

Eq. (11-36)

of ACI 318-05

0.3

0.4

c / (f

' c)1/

2

Gravity loading tests (connections, frames) Eq. (11-33)

0.1

0.2v c Interior connections under lateral loadsExterior conn. with banded PT under lateral loadsExterior conn. with distributed PT under lateral loads

of ACI 318-05

22

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

fpc / (f'c)1/2 (MPa1/2)



Shear Strength of PT Conn.ACI 352.1RACI 352.1R--XX: PT Interior = PT Exterior Conn.XX: PT Interior = PT Exterior Conn.

⎞⎛ ′ 5.3 where,3.0psi ≤+⎟⎠⎞

⎜⎝⎛ +′= ppopccpc VdbffV βλβ

Kang et al. (2008); Kang et al. (2008); PTI JournalPTI Journal –– Higher (Higher (vvcc + + vvss) for PT ) for PT conn. conn. with any shear reinf. with any shear reinf. (incl. headed studs) than (incl. headed studs) than that for RC conn.that for RC conn.

dbfVVV ⎟⎞

⎜⎛ ′≤+= psi8λ dbfVVV ocscn ⎟

⎠⎜⎝

≤+= psi8λ

dbfV ⎟⎞

⎜⎛ ′≤ i3h λ

23

dbfV occ ⎟⎠⎞

⎜⎝⎛≤ psi3where λ






I t di t PT l b l tiIntermediate PT slab-column connections


24



γfMunb in Effective “Transfer” Widthγf unb

No adjustment in No adjustment in γf permitted by ACI 318 for PT conn.permitted by ACI 318 for PT conn.

For banded layout, always OKFor banded layout, always OK

For distributed layout, may not be OK with 1 or 2 tendons For distributed layout, may not be OK with 1 or 2 tendons and bonded reinfand bonded reinfand bonded reinf.and bonded reinf.

Based on the test data (Han et al., 2006a; 2006b), Based on the test data (Han et al., 2006a; 2006b), had NO problems for PThad NO problems for PThad NO problems for PThad NO problems for PT

i.e., Effec. transfer width seems larger than i.e., Effec. transfer width seems larger than cc22 + 3+ 3hh (RC), (RC), ibl d t i d 3D i t it b PTibl d t i d 3D i t it b PT

25

possibly due to improved 3D integrity by PT.possibly due to improved 3D integrity by PT.



Non-participating frames




Intermediate PT slab column connectionsIntermediate PT slab-column connections


26



Lateral AnalysisYou may need to use different softwareYou may need to use different softwareEffective slab width method (ASCE 41, Chapter 6)Effective slab width method (ASCE 41, Chapter 6)( )( )

αlαl2 l2

αβl2Dynamic tests (Kang and Wallace 2005); α = 0 70 β = 2/3Dynamic tests (Kang and Wallace, 2005); α = 0.70, β = 2/3

Interior bay (uni-axial shaking)

ASCE 41 (2007); α = or Design aid tables (Allen & Darvall 1977)⎟⎟⎞

⎜⎜⎛⎟⎠⎞

⎜⎝⎛ + 1

112 lc

27

ASCE 41 (2007); α or Design aid tables (Allen & Darvall, 1977)

β = 1/2 Constant (vs. β = 1/3 for RC)

⎟⎠

⎜⎝⎟⎠

⎜⎝ 2

1 3 l



Linear Lateral Analysis1.2DL + 1.6LL (no EQ)& 1.2DL + 0.5LL

1.0E per IBC-06

Col. – per ACI 318-08, S10.10.4.10 7E I

Effec slab width (Effec slab width (αβαβEE II l bl b) based on ASCE 41) based on ASCE 41

0.7EcIg

28

Effec. slab width (Effec. slab width (αβαβEEccIIslabslab) based on ASCE 41) based on ASCE 41Also, ACI 318Also, ACI 318--08, S8.8, S10.10.4.1, R13.5.1.2, R21.2.2, R21.1.208, S8.8, S10.10.4.1, R13.5.1.2, R21.2.2, R21.1.2



Flexure, Punching Shear DesignMoment and shear demands due to design forcesMoment and shear demands due to design forces

Design conn. such that i) & ii) Design conn. such that i) & ii) c

unbv

o

un J

cMdb

Vv γ+≥ 6.0≤

c

u

VVφ

per ACI 352.1Rper ACI 352.1R--XXXX

VV //φφVV can be greater than 0 6 IF design drift ratio (can be greater than 0 6 IF design drift ratio (δδ ))

29

VVuu//φφVVcc can be greater than 0.6, IF design drift ratio (can be greater than 0.6, IF design drift ratio (δδuu) ) should not exceed the drift limit (S21.3.6.8)should not exceed the drift limit (S21.3.6.8)..






Intermediate PT slab column connectionsIntermediate PT slab-column connections


30



EQ-Resistant Design of Shear Reinf.gACI 352.1RACI 352.1R--XX (Kang et al., XX (Kang et al., PTI JournalPTI Journal ) )

h3>==< d2

2=< d

should be locateds<= /2<=0.75dshould be locatedbetween 0.5 and 0.85away from the column face

d d

31



ShearbandsACI 352.1RACI 352.1R--XXXX

Verified from static testsVerified from static tests

-8 -6 -4 -2 0 2 4 6 8 Drift ratio [%]

60(a) C0

-8 -6 -4 -2 0 2 4 6 8 Drift ratio [%]

15(b) PS2.5 Primary (CP) Secondary(LS)Primary (CP) Secondary

(LS)Verified from static testsVerified from static tests(Pilakoutas and Li, 2003) (Pilakoutas and Li, 2003) & seismic tests of RC conn.& seismic tests of RC conn.(K d W ll i(K d W ll i ))

0

20

40

l loa

d [k

N]

0

5

10

load

[kip

s]

Conversion: 1 kN = 0.2248 kips

(Kang and Wallace, in(Kang and Wallace, in--press) press)

-60

-40

-20

Late

ra

-10

-5

Late

ral

Experimental data

Primary (CP)Secondary

(LS)Secondary Primary

ab

-8 -6 -4 -2 0 2 4 6 8 Drift ratio [%]

-8 -6 -4 -2 0 2 4 6 8 Drift ratio [%]

-15Experimental dataFEMA 356 modeling curves (LS) (CP) c

32

Test specimen with thin plate

stirrups (spacing = 2.5")



Str. Integrity (Collapse Prevention)

New ACI 318New ACI 318--08, S18.12.6 & 18.12.708, S18.12.6 & 18.12.7,,

Two tendons in both dir.Two tendons in both dir.or 2 tendons in one dir. + min. bottom reinforcing or 2 tendons in one dir. + min. bottom reinforcing bars in two dir.bars in two dir.

A bit conservative ACI 352.1RA bit conservative ACI 352.1R--XXXX

in each dir.in each dir.usm f

llA 5.0 21

φω

=

33

yf φ



SummaryNonNon--participating Sparticipating S--C FramesC Frames

Deform compatibility check (lateral drift check) or limit analysisDeform compatibility check (lateral drift check) or limit analysisDeform. compatibility check (lateral drift check) or limit analysisDeform. compatibility check (lateral drift check) or limit analysis

Intermediate SIntermediate S--C FramesC Frames

2D linear lateral analysis 2D linear lateral analysis –– Effec. slab width methodEffec. slab width method

Contact InformationContact InformationContact Information Contact Information

[email protected]@ou.eduhttp://www cees ou eduhttp://www cees ou eduhttp://www.cees.ou.eduhttp://www.cees.ou.edu

PTI Journal PTI Journal (Kang and Wallace, 2008)(Kang and Wallace, 2008)

PTI JournalPTI Journal (Kang et al 2008)(Kang et al 2008)

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PTI JournalPTI Journal (Kang et al., 2008)(Kang et al., 2008)or after the session...or after the session...



0400800

12001600

train

[μs]

Questions?RC

10 12 14 16 18 20 22 24 26 28 30Time [sec]

-1600-1200

-800-400

0

Mic

ro S

t

CL

blue, dotred, lineRC-Run4-FL1NW (Top Bar Strains)

Questions?

Thank you !!

[ ]

PT

Thank you !!

RC

35 PT



Seismic Design Recommendations for PT Slab-Column … Convention/S2-2... · Practical design guide...

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