seismic design of cast-in-place concrete diaphragms...

Seismic Design of Cast-in-Place Concrete

Diaphragms, Chords and Collectors

Pramin NorachanManager, Structural Engineering Unit

AIT Solutions

DESIGN OF TALL BUILDINGS: TRENDS AND ADVANCEMENTS FOR STRUCTURAL PEFORMANCE

Pathumthani, Thailand

November 10, 2016

Presentation Outline

1. Introduction

2. Overview of Structure

3. Analysis and Design Criteria

4. Force Scaling

5. Section Cuts

6. Forces from Section Cuts

7. Diaphragm Design

Pramin Norachan 4

• Estimating the inelastic properties for a real

component is not a simple task.

• If there is substantial inelastic behavior in an

actual structure, the results of an elastic

analysis may be of uncertain value for making

design decisions, and may even be

misleading.

• As a tool for obtaining information for design,

even a crude inelastic model can be more

useful than an elaborate elastic model.

• Please keep in mind that the goal is to get

useful information for design, not to

calculate "exact" response.

PERFORM-3D is an ideal tool

for nonlinear performance-

based analysis and design,

created by

Dr. Graham H. Powell,

University of California at

Berkeley Professor Emeritus

of Civil Engineering.

Pramin Norachan 5

NEHRP

(NIST GCR 10-917-4)

ACI 318-14LATBSDC 2014

Pramin Norachan 6

Pramin Norachan 7

• Building structures generally

comprise structural elements to

support gravity and lateral loads.

• The seismic force-resisting system

is composed of vertical elements,

horizontal elements, and the

foundation.

• The vertical elements provide a

continuous load path to transmit

gravity and seismic forces from the

upper levels to the foundation.

• The horizontal elements typically

consist of diaphragms, including

collectors.

Pramin Norachan 8

• Diaphragms transmit inertial forces

from the floor system to the vertical

elements of the seismic force-resisting

system.

• They also tie the vertical elements

together to stabilize and transmit

forces among these elements as may

be required during earthquake

shaking.

• Diaphragms are thus an essential part

of the seismic force-resisting system

and require design attention by the

structural engineer to ensure the

structural system performs adequately

during earthquake shaking.

Pramin Norachan 9

Diaphragm in-plane forces:

Diaphragms span between, and

transfer forces to, vertical elements

of the lateral-force resisting system.

Diaphragm transfer forces:

Force transfers between vertical

elements which have different

properties over their height, or their

planes of resistance may change

from one story to another.

A common location where planes of

resistance change is at the grade

level of a building with an enlarged

subterranean plan (podium

diaphragm).

Pramin Norachan 10

Large diaphragm transfer

forces should be

anticipated at offsets or

discontinuities of the

vertical elements of the

seismic-force-resisting

system.

(a) Setback in the building

profile

(b) Podium level at grade.

Pramin Norachan 11

• In general, low-rise buildings and buildings

with very stiff vertical elements such as

shear walls are more susceptible to floor

diaphragm flexibility problems than taller

structures.

Pramin Norachan 12

Pramin Norachan 13

• Different parts of a diaphragm

include:

- Diaphragm slab

- Chords

- Collectors (Drag struts or

Distributors)

- Connections to the vertical

elements.

• These different parts can be

identified by considering the load

path in a simple diaphragm.

• We can idealize the diaphragm as

a simply supported beam

spanning between two supports,

with reactions and shear and

moment diagrams

Pramin Norachan 15

40-Story RC Building

[email protected]

= 128 m.

Pramin Norachan 16

Floor Framing Plan

8.0

B C D E F G H I J K M

4

3

2

1

A

8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0

88.0 m.

8.0

8.0

3.0 19

m.

Pramin Norachan 17

MaterialsExpected Strength

(MPa)

Modulus of Elasticity

(MPa)

Concrete (fc’) - Shear Walls & Columns 80.6 38,642

Concrete (fc’) – Girders, Coupling Beams & Slabs 53.8 30,649

Reinforcement Steel (fy) 484 200,000

Material Properties

Sections Properties

Members Dimension

Shear Walls b x h = 400 x 700 mm

Columns b x h = 800 x 800 mm

Girders b x h = 400 x 700 mm

Coupling Beams b x h = 800 x 800 mm

Slabs Thickness = 200 mm

Pramin Norachan 19

2014 LATBSDC

** Nonlinear fiber elements automatically account for cracking of concrete because the

concrete fibers have zero tension stiffness.

• Stiffness modifiers for RC diaphragms commonly fall in the range of 0.15 to

0.50 when analyzing the building for design-level earthquake demands

(Nakaki, 2000).

Pramin Norachan 20

Pramin Norachan 21

Pramin Norachan 22

89,604

71,465 64,639

38,983

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

H1 H2

Bas

e S

he

ar (

KN

)

Comparison of Base Shear

LRHA NLRHA

Rx = 1.4

Ry = 1.8

( )gu t

xy

Pramin Norachan 23

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3

Elev

atio

n (

m)

Story Acceleration (g)

Office Tower (Story Acceleration in X-dir.)

NLX (g)

MCEX/R (g)

Pramin Norachan 24

PERFORM 3D

(NLTHA) ETABS (RSA)

Before carrying out design checks at MCE, the linear analysis results of

ETABS were scaled to match with the nonlinear time-history analysis results

(NLTHA) from PERFORM-3D.

Pramin Norachan 25

Before scaling - load combinations for MCE level earthquakes

U1 = 1.0 DL + 1.0 SDL + 0.25 LL + 1.0 MCEX + 0.3 MCEY


After scaling - load combinations multiplied with scaling factors for MCE level

earthquakes



Pramin Norachan 27

• Define the response spectrum

function (MCE) that will be used

for analysis.

Pramin Norachan 28

• Define load cases of response

spectrum (MCE) in X and Y directions.

Pramin Norachan 29

• Scale force based on factor

obtained from floor acceleration

or base shear.

9.81/ 2 4.905

Pramin Norachan 30

• Define load combinations for

diaphragm design at MCE level.

Pramin Norachan 32

• Floor diaphragm at Story 20 will

be used as an example for

diaphragm design.

Pramin Norachan 33

• The force resultants in F11 direction on the floor diaphragm at Story 20

are shown below.

F11

F22

F11

SC-1

SC-1

Pramin Norachan 34

• Before obtaining forces, section cuts need to be defined.

SC-1

SC-1

Pramin Norachan 35

• Select elements and nodes at the cut line.

Then, assign these objects in a group.

SC-1

SC-1

Pramin Norachan 36

• Define the section cut (SC-1) by

selecting the group (SC-1).

Pramin Norachan 37

• However, for this presentation, the section cuts of

this floor diaphragm are already defined as

follows:

Pramin Norachan 38

DP-L20-01 02 03 04 05 06 07 08 09 10 11

• Section cuts for diaphragm chords and shear.

Moment

Pramin Norachan 39

F22 F22

CL-L20-01 CL-L20-02

• Locations of the

section cut for

collectors at the

core walls.

Pramin Norachan 40

• Locations of the section cut for shear friction at

the core walls.

F22 F22

SF-L20-01 SF-L20-02

Pramin Norachan 42

• For a given load case, display any stress of shell force.

F11

F22

Pramin Norachan 43

X

Y

Pramin Norachan 44

• Use the option “Draw Section Cut” to see the force distribution.

Pramin Norachan 45

• Display the results of section cut forces.

Pramin Norachan 46

Pramin Norachan 47

• Select the considered load cases and force directions.

V M

Pramin Norachan 48

V M

• Rearrange all information for design.

Pramin Norachan 49

L01

L20

L39

Pramin Norachan 50

1318

6200 73884624 3415

12719

3487 45447423 6328

1373

-1284

-6295 -7593-5038 -4446

-21749

-4518 -4957-7628 -6423

-1339

-25,000

-20,000

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

0 10 20 30 40 50 60 70 80 90

Mo

me

nt

(KN

-m)

Distance (m)

753

420181

603

932

194

933694

258 292

681

-734

-405-163

-572-865

-194

-1000-725

-276 -307

-700

-1,500

-1,000

-500

0

500

1,000

1,500

0 10 20 30 40 50 60 70 80 90

Sh

ea

r (K

N)

Distance (m)

Story

L01

Pramin Norachan 51

2911

1363416853

15022

104238612

10426

1502016887

13718

3036

-2797

-12924-15627

-13252

-8142-6165

-8145

-13250-15660

-13008

-2923

-20,000

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

20,000

0 10 20 30 40 50 60 70 80 90

Mo

me

nt

(KN

-m)

Distance (m)

1312

691

224

698

1282

177

1486

915

343611

1263

-1369

-753

-292

-771

-1354

-177

-1414

-842

-275-548

-1206

-2,000

-1,500

-1,000

-500

0

500

1,000

1,500

2,000

0 10 20 30 40 50 60 70 80 90

Sh

ea

r (K

N)

Distance (m)

Story

L20

Pramin Norachan

2498

1459818327 17048

12188 10448 1218917059 18366

14672

2604

-2852

-18565

-25412 -27429 -26998 -27242 -26998 -27440 -25452

-18639

-2958

-30,000

-20,000

-10,000

0

10,000

20,000

30,000

0 10 20 30 40 50 60 70 80 90

Mo

me

nt

(KN

-m)

Distance (m)

52

Story

L39

2092

1280

748958

1655

196

1437

715285

726

1569

-1713

-896

-354-571

-1267

-196

-1825

-1103-680

-1110

-1948-2,500

-2,000

-1,500

-1,000

-500

0

500

1,000

1,500

2,000

2,500

0 10 20 30 40 50 60 70 80 90

Sh

ea

r (K

N)

Distance (m)

Pramin Norachan 53

-30,000

-20,000

-10,000

0

10,000

20,000

30,000

0 10 20 30 40 50 60 70 80 90

Mo

me

nt

(KN

-m)

Distance (m) L01 L20 L39

-2,500

-2,000

-1,500

-1,000

-500

0

500

1,000

1,500

2,000

2,500

0 10 20 30 40 50 60 70 80 90

Sh

ea

r (K

N)

Distance (m) L01 L20 L39

Pramin Norachan 55

Chord (Diaphragm)

Chord (Diaphragm)

Collector

(Support)

Shear Friction

(Support)

Shear (Diaphragm)

Shear Wall

Diaphragm

Inertia Force = m × a

Pramin Norachan 56

Action Demand (D) Capacity (C)

Force Controlled

(Non-Critical)

Force Controlled

(Critical)

uM M

uT T 1.0

1.0

Tension & Flexure

Compression:

Shear:1.5uV V

1.5uC C

' '1.3c cf f

1.17y yf f

Materials Nominal Strength Expected Strength

Concrete

Reinforcing Steel

'

cf

yf

1.0

Pramin Norachan 57

( )uM Analysis SectionCut

Pramin Norachan 58

Tension Chord16,869uM KN m

17d m

16,869992.29

17

uu u

MT C KN

d

u s yT A f3

2992.29 102,050

(1)(484)

us

y

TA mm

f

2 27 20 ( 7 2.0 2,119 )4

sDB A mm

Pramin Norachan 59

Compression chord

3992.29 103.54

(400 700)u MPa

Use perimeter beam (400x700 mm)

Allowable stress

'0.5 0.5 53.8 10.76all cf MPa

3.540.34

10.76

u

all

D

C

Pramin Norachan 60

Pramin Norachan 61

Shear 1,485V KN 1.5 1.5 1,485 2,228uV V KN

2,228131 /

17

uVKN m

L

' (200 17,000)0.66 (1.0) 0.66 53.8

(17 1,000)

968.2 /

n,limit cvc

V Af

L L

KN m

' (200 17,000)0.17 (1.0) 0.17 53.8

(17 1,000)

249.4 /

n cvc

V Af

L L

KN m

131 / 249.4 /u nV VKN m KN m

L L

(Okay)

Pramin Norachan 62

Pramin Norachan 63

Demand Forces

992

1.5 845 1,268

u

u

T KN

C KN

u s yT A f3

2992 102,050

(1)(484)

us

y

TA mm

f

2 25 25 ( 5 25 2,454 )4

sDB A mm

Pramin Norachan 64

Compression Demand

1.5 845 1,268uC KN

22 2(800)(200)w slabA t t mm

Allowable compression

' (1.0)(0.85)(53.8)(2 200 800)(0.85) 14,634

1,000all cC f A KN

1,2680.09

14,634

u

all

CD

C C

2 wt

wt

Pramin Norachan 65

Pramin Norachan 66

1.5 1,194 1,791uV KN

u n vf yV V A f

1,791 (1.0) (484)(1.0)vfA

21,7913,700

(1.0)(484)(1.0)vfA mm 23,700

0.4625 /8,000

vfAmm mm

L

1 12@ 200DB 2

212 4 1

0.565 /200

sAmm mm

s

Shear Demand

Pramin Norachan 67

' (1.0)(0.2)(53.8)(200 8,000)(0.2) 17,216

1,000min

(1.0)(5.5)(200 8,000)(5.5) 8,800

1,000

8,800

c c

all

c

f A KN

V

A KN

KN

1,791 8,800u allV KN V KN

Allowable shear friction

Pramin Norachan 68

5-DB25 (Collectors)

(2) (6) (7) (6) (2) (4) (2) (6) (7) (6) (2)

(2) (6) (7) (6) (2) (2) (2) (6) (7) (6) (2)

7-DB20 (Chords)

1-DB12@200 (Shear Friction)

7-DB20 (Chords)

Pramin Norachan 69

Collectors Collector Connection to Shear Wall

Pramin Norachan 70

A long collector with confinement

reinforcement

Shear Friction Rebar

seismic design of cast-in-place concrete diaphragms...

Documents