Earthquake Resistance of Modern Masonry Construction - SEAoT

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Earthquake Resistance of Modern Masonry Construction - SEAoT

EARTHQUAKE RESISTANCE OF MODERN MASONRY CONSTRUCTION

Richard E. Klingner, University of Texas at Austin

SEAoT Annual Meeting Austin, Texas October 29-31, 2009

Earthquake Resistance of

Modern Masonry Construction

NSF NEES Small - Group Project

( October 2006 through September 2010 )

Prof . Richard E . Klingner

The University of Texas at Austin

klingner@mail.utexas.edu

State Conference

SEAoT

Austin , TX

October 31 , 2009

1

Main points

1. Wall - type masonry structures are simple to

design

2. The MSJC Code and Specification is the

technical basis for masonry design in the

US

3. Low - rise masonry structures designed and

constructed according to the MSJC Code

and Specification can resist very strong

earthquakes

2

a dynamic treat . . .

1. Wall - type masonry

structures are simple to design

almost

3 g !

3

4

Steps in simplified design of

masonry structures

• starting point for design

• design of vertical strips in walls perpendicular

to lateral loads

• design of walls parallel to lateral loads

• design of lintels

• simplified analysis for lateral loads

• design of diaphragms

• detailing

units of

concrete or

fired clay

steel

reinforcing

bars

grout

grout

mortar

. . . typical

materials in

reinforced

masonry

5

6

1


EARTHQUAKE RESISTANCE OF MODERN MASONRY CONSTRUCTION

Richard E. Klingner, University of Texas at Austin

SEAoT Annual Meeting Austin, Texas October 29-31, 2009

Starting point for wall - type

masonry structures

NO BEAMS OR COLUMNS

( example of

direction of span )

vertical reinforcement of

#4 bars at corners and

jambs

Essential function of walls in

resisting gravity loads

bearing walls resist

axial loads ( concentric

and eccentric ) as

vertical strips

Horizontal reinforcement

of two #4 bars in bond

beam at top of wall ,

and above and below

openings ( two #5 bars

over openings with span

> 6 ft )

7

non - bearing walls

resist concentric axial

load as vertical strips

8

Essential function of walls in

resisting lateral loads

Effect of openings . . .

walls parallel to lateral

forces act as shear

walls

bond beams transfer

reactions from walls to

horizontal diaphragms ,

and act as diaphragm

chords

Effective

Width of

Strip A

Strip A

Effective

Width of

Strip B

Strip B

Effective

Width of

Strip C

Strip C

vertical strips of walls perpendicular to

lateral forces resist combinations of axial

load and out - of - plane moments , and

transfer their reactions to horizontal

diaphragms

9

Width A

Width B

Width C

10

. . . Effect of openings

Design of vertical strips in

perpendicular walls

Openings increase original design

actions on each strip by a factor

equal to the ratio of the effective

width of the strip divided by the

actual width

moments and axial forces due

to combinations of gravity and

lateral load

M = P e

Actions in Strip B

⎛ EffectiveWidth B ⎞

= Original Actions



⎝ Actual Width B ⎠

M = P e / 2

M wind

11

12

2


EARTHQUAKE RESISTANCE OF MODERN MASONRY CONSTRUCTION

Richard E. Klingner, University of Texas at Austin

SEAoT Annual Meeting Austin, Texas October 29-31, 2009

. . . Design of vertical strips in

perpendicular walls

Design of parallel walls . . .

Φ P n

moment - axial

force interaction

diagram ( with the

help of a

spreadsheet )

moments , axial forces and shears

due to combinations of gravity

and lateral loads

P

V

M u , P u

h

Φ M n

13

14

. . . Design of parallel walls

. . . Design of parallel walls

Φ P n

moment - axial

force interaction

diagram ( with the

help of a

spreadsheet )

sufficient lateral

capacity comes from

wall density

shearing resistance

V +

n

=

V

m

V

s

M u , P u

16

Φ M n

15


M

⎞⎤


⎠⎦

u

'

Vnm

= ⎢4.0

−1.75

⎜ ⎥ An

fm

+ 0. 25

Vu

d ⎟

v





P

u

Design of lintels . . .

. . . Design of lintels

( example of

direction of span )

moments and shears

due to gravity loads

M

V

u

u

w l

=

8

w l

=

2

2

17

neutral axis

A s

shear design : provide

enough depth so that

shear reinforcement is

not needed

d

A

s

flexural design :

M

u

≈ φ f ×0.9 d

y

18

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EARTHQUAKE RESISTANCE OF MODERN MASONRY CONSTRUCTION

Richard E. Klingner, University of Texas at Austin

SEAoT Annual Meeting Austin, Texas October 29-31, 2009

Distribution of shears to shear

walls . . .

Classical analysis of structures

with rigid diaphragms

• classical approach

• determine whether the

diaphragm is “rigid” or

“flexible”

• carry out an appropriate

analysis for shears

• locate center of rigidity

• treat the lateral load

as the superposition of

a load acting through

the center of rigidity ,

and a torsional

moment about that

center

19

20

Simplified analysis of structures

with rigid diaphragms . . .

. . . Simplified analysis of

structures with rigid diaphragms

V

32 ft

32 ft

4 ft

8ft

8 ft

8ft

4 ft

• consider only the

shearing stiffness ,

which is proportional

to plan length

• neglect plan torsion

21

V

32 ft

32 ft

4 ft

8 ft

8 ft

8 ft

4 ft

V =

V

left

right

32 ft

( 32 + 4 + 8 + 4)

( 4 + 8 + 4)

ft

( 32 + 4 + 8 + 4)

=

× V

ft

total

× V

ft

total

2

= V

3

total

1

= V

3

total

22

Classical analysis of structures

with flexible diaphragms . . .

. . . Classical analysis of structures

with flexible diaphragms

• distribute shears according to tributary areas

of the diaphragm , independent of the

relative stiffnesses of the shear walls

32 ft

half half

32 ft

V

4 ft

8 ft

8 ft

8 ft

4 ft

V

V

left

right

1

= V

2

1

= V

2

total

total

23

24

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EARTHQUAKE RESISTANCE OF MODERN MASONRY CONSTRUCTION

Richard E. Klingner, University of Texas at Austin

SEAoT Annual Meeting Austin, Texas October 29-31, 2009

Simplified diaphragm analysis

design for the worse of the two cases

2 / 3 V

1 / 2 V

V

32 ft

32 ft

4 ft

8 ft

8 ft

8 ft

4 ft

1 / 3 V

1 / 2 V

Design of diaphragms

• Diaphragm shears are resisted by the total

thickness or the thickness of the cover

alone ( for non - monolithic diaphragms ) .

Diaphragm moments are resisted by

diaphragm chords ( bond beams ) .

V = w L / 2

L / 2

M = w L 2 / 8

25

w

26

. . . Details

• wall - diaphragm connections

• design of lintels for out - of - plane loads

between wall - diaphragm connections

• connections between bond beam and walls

• connections between walls and foundation

2. The MSJC Code and

Specification is the technical

basis for masonry construction

in the US

27

28

Masonry Design Codes in the US

Technical

Organizations

MSJC

develops

provisions

ANSI process ( balance of interests , letter ballots ,

resolution of Negatives , public comment )

Industry

Groups

MSJC

Code

model codes

reference

ICC

those

( International

provisions

Building Code )

NEHRP

Other Model

Codes

( NFPA )

ASTM

( Material

Specifications )

MSJC

Specification

( QA ,

materials ,

execution )

3. Low - rise masonry structures

designed and constructed

using the MSJC Code and

Specification can resist very

strong earthquakes

local authorities

adopt those

model codes Building Code

( legal standing )

( contract between society and the designer )

( part of a civil

contract

between owner

and contractor )

29

30

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EARTHQUAKE RESISTANCE OF MODERN MASONRY CONSTRUCTION

Richard E. Klingner, University of Texas at Austin

SEAoT Annual Meeting Austin, Texas October 29-31, 2009

Seismic design of masonry is

state -of -the -art

important results so far

• NSF -NEES small -group

project

• October 2006 through

September 2010

• involves four universities

plus masonry industry

• headed by UT Austin

31

• low-rise reinforced concrete masonry buildings

with clay masonry veneer ( meeting MSJC

Code and Specification for SDC D ) resist

earthquakes above MCE without collapse

• seismic response of buildings and veneer is

generally consistent with performance

expectations

• seismic response is well predicted by nonlinear

dynamic analysis and static design tools

32

what’s coming

project objectives

• project objectives

• project participants

• seismic response of low - rise buildings

• reinforced concrete masonry with clay

masonry veneer

• experimental and analytical work

• key observations

• important points

33

• performance - based design of new masonry

and masonry veneer

• study seismic performance of masonry veneer and

veneer connectors

• examine inelastic behavior of low - rise reinforced

concrete masonry structures

• propose refinements to performance - based design

provisions for new masonry and masonry veneer

• educate the profession and the public

34

project participants

structures studied

• University of Texas at Austin

• Richard E . Klingner , Seongwoo Jo ( GRA )

• University of California at San Diego

• Benson Shing , Hussein Okail ( GRA )

• Washington State University

• Char Grimes , Katherine Keane , David McLean

• North Carolina A&T State University

• Mark McGinley , Eric Johnson ( GRA )

• Help from masonry industry

35

• backing system of

wood-stud frames or

reinforced concrete

masonry ( CMU )

• clay masonry veneer

( attached to backing

system using

connectors ) improves

esthetics and thermal,

acoustic and water -

penetration resistance

36

6


EARTHQUAKE RESISTANCE OF MODERN MASONRY CONSTRUCTION

Richard E. Klingner, University of Texas at Austin

SEAoT Annual Meeting Austin, Texas October 29-31, 2009

masonry veneer connectors

seismic response

• wood - stud frames

• corrugated connectors

• rigid connectors

• reinforced concrete masonry

• adjustable connectors

• tri-wire connectors

37

• in - plane CMU

walls govern the

seismic response

of the building

• in - plane veneer

slides and rocks

• out -of-plane

veneer acts as

added mass

direction of

shaking

38

reinforced concrete masonry

with clay masonry veneer

experimental work ( 1 )

• experimental work

• analytical work

• key observations

• important points

• quasi - static tests of

wall segments

( UT Austin )

• shaking - table tests of

wall segments

• shaking - table tests of

complete structure

in - plane

out - of -

plane

39

40

experimental work ( 2 )

experimental work ( 3 )

• quasi - static tests of

wall segments

• shaking - table tests of

wall segments

( UCSD )

• shaking - table tests of

complete structure

out -of -plane

in - plane

• quasi - static tests of

wall segments

• shaking - table tests of

wall segments

• shaking - table tests of

complete structure

( UCSD )

41

42

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EARTHQUAKE RESISTANCE OF MODERN MASONRY CONSTRUCTION

Richard E. Klingner, University of Texas at Austin

SEAoT Annual Meeting Austin, Texas October 29-31, 2009

analytical work ( OpenSees )

a construction treat . . .

• develop nonlinear analytical models for each

element

• reinforced concrete masonry

• clay masonry veneer

• veneer connectors

• predict quasi - static and shaking - table

response

• refine models using quasi - static and shaking

- table results ( in progress )

43

44

a dynamic treat . . .

response sequence . . .

almost

3 g !

45

• Design - basis earthquake

• PGA 0.67 g : no damage

• Maximum considered earthquake ( MCE )

• PGA 1.01 g : no damage

• PGA 1.68 g : flexural cracking of walls

• PGA 1.79 g : rocking and sliding of in - plane veneer

• PGA 2.69 g : sliding of in - plane CMU

• PGA 2.69 g : damage to CMU and veneer

46

important results so far

Main points

• low-rise reinforced concrete masonry buildings

with clay masonry veneer ( meeting MSJC

Code and Specification for SDC D ) resist

earthquakes above MCE without collapse

• seismic response of buildings and veneer is

generally consistent with performance

expectations

• seismic response is well predicted by nonlinear

dynamic analysis and static design tools

47

1. Wall - type masonry structures are simple to

design

2. The MSJC Code and Specification is the

technical basis for masonry design in the

US

3. Low - rise masonry structures designed and

constructed according to the MSJC Code

and Specification can resist very strong

earthquakes

48

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