seismic rehabilitation using infill wall systems · frame precast infill wall system. existing...

Seismic Rehabilitation using

Infill Wall Systems

Robert J. Frosch

Non-Ductile Frames

• Columns and Beams

– Inadequate capacity

• Flexure

• Shear

– Lack of confinement

– Lack of column tensile lap splices

• Beam-Column Joints

– Lack of confinement

– Inadequate joint shear capacity

– Strong beam – Weak column

Economical Rehabilitation

• Construction Cost

• Construction Time

• Maintain Building Operations

Total Rehabilitation Cost

Rehabilitation Techniques

• Increase frame ductility and strength

– Frame jacketing

• Reduce seismic stresses

– Braces

• Change lateral load system

– Infill Wall

Infill Wall

New footing

Reinforcement

Dowels

Interface Dowels

Field Experience

Objectives

• Eliminate interface dowels

• Eliminate extensive formwork

• Eliminate large volumes of concrete

– Movement

– Placement

• Increase column tensile capacity

– Without jacketing

Precast

Panels

Steel Pipe

Grout Strip

Reinforcement

Existing

Frame

Precast Infill Wall System

Existing Column

Precast Wall

Post Tensioning

Grout Strip

Post TensioningDucts

Column Tensile Capacity

Precast Infill Wall

• Ease of Construction

• Ease of Fabrication

– Avoid Protruding Bars

• Provide Force Transfer

– Shear Keys

Model Test StructureP

P/2

6 in. Wall

4 in. Wall

8’

8’

16’

Precast Panels

Panel Installation

Shear Lug

Grouting

Grouting

Completion

Before After

Rehabilitation

Frame Test

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

-0.3 -0.2 -0.1 0 0.1 0.2 0.3

Total Drift (%)

Ba

se S

hea

r (k

ips)

300

Total Drift (%)

Ba

se S

hea

r (k

ips)

Infill Wall Test 1: Flexural HingePost Tensioning = 237 kips

-300

-200

-100

0

100

200

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

Splice Failure

2 - 1” Bars2 - 1” Bars

2 - 1 1/4” Bars2 - 1 1/4” Bars

Splice Failure

-300

-200

-100

0

100

200

300

-1000 -500 0 500 1000 1500 2000 2500

Micro-Strain (in./in.)

Ba

se S

hea

r (k

ips)

Decompression LoadColumn PT: Test 1 (PT = 237 kips)

e PT

PTe

VDC = 85 kips

Decompression

Load

Total Drift (%)

Ba

se S

hea

r (k

ips)

Infill Wall Test 2: ShearPost Tensioning = 507 kips

-500

-400

-300

-200

-100

0

100

200

300

400

500

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

2 - 1” Bars

2 - 1 1/4” Bars

2 - 1” Bars

2 - 1 1/4” Bars

Splice Failure

4 -1” Bars4 -1” Bars

Cracking Pattern

Benefits

• Provide an economical system for strengthening RC buildings

• Decrease damage costs from an earthquake

• Decrease nonstructural damage

• Increase life safety

-500

-400

-300

-200

-100

0

100

200

300

400

500

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

Total Drift (%)

Ba

se S

hea

r (k

ips)

Analysis of Wall BehaviorTest 2

Decompression

Load

P.T. Model

Ig,Ag

P.T. Model

Icr,AgP.T. ModelP.T. Model

Flexural Design

• Capacity Controlled by Post-

Tensioning System

• Provide Adequate Anchorage of

Post-Tensioning System

Splice Failure

MPost Tensioning

d

T

Anchorage

( )2

n

aM T d= −

V/3

V/3

Panel Shear Panel Shear ≥≥ Pipe YieldPipe Yield

φ Vn ≥ α Vn

Panel PipeV/3 V/3

V/3

Joint Capacity Joint Capacity ≥≥ Pipe YieldPipe Yield

µ = 1.4

Vn = Avf fy µJoint

φ Vn ≥ α Vn

Joint Pipe

ACI ShearVn

Panel⇒

Wall Component Design

V

General Design Requirements

• Minimum Design Forces according to UBC or NEHRP recommendations

• Monolithic Behavior

• Shear Strength Sufficient for Flexural Hinge Formation– R consistent with codes

– R = 1 if shear control

• Assess Effects of the Change in Lateral Load System

Shear Design

Splice FailureV

Vn = Σ Vn

Pipe Vn = Pipe Yield Strength= 0.6 As Fy

dw

df

Frame SideFrame Side

Wall SideWall Side

pp

∅∅o

do

d

(Bearing Stress)(Area) ≥ Pipe Capacity

Provide Adequate EmbedmentProvide Adequate Embedment

fb ∅od d ≥ α Vn

Pipe

Pipe

8'

8'

16'

Front Elevation Side Elevation

P

P

1

2

Large-Scale Model Test Structure

Research Goals

Determine minimum design and detailing requirements for the precast wall system.

Provide a rational analysis method of precast infill-frame interaction.

Gain a better understanding of shear transfer in concrete.

Gain a better understanding of concrete - steel pipe shear transfer.

-60

-40

-20

20

40

60

80

100

-0.25 -0.2 -0.15 -0.1 -0.05 0.05 0.1 0.15 0.2 0.25

Load (

Kip

s)

Displacement (Inch)

Panel Connection TestSpecimen PC-AL-A

VVariables

Panel Connection Test Specimen

• Shear Key Configuration

• Shear Key Size• Vertical Strip Steel

• Panel Spacing• Grout Strength

-80

-60

-40

-20

0

20

40

60

80

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

Displacement (in.)

Lo

ad

(kip

s)

Panel Connection TestSpecimen PC-5 (2#3)

Loa

d (

kip

s)

0.4-80

-60

-40

-20

0

20

40

60

80

100

120

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3

Displacement (in.)

2 #3 BarsSpecimen PC-5

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

Displacement (in.)

4 #3 BarsSpecimen PC-9

Effect of Vertical Reinforcement

Panel Connection Results

• No significant effect of shear key size, configuration, and panel spacing

• Failure controlled by weaker of grout strip or precast panel

• Vertical reinforcement affects peak and residual capacity

• Residual capacity reliably estimate by shear friction

V

Frame Connection Test Specimen

• Pipe Embedment Length• Vertical Strip Steel

• Grout Strength

Variables

-80

-60

-40

-20

0

20

40

60

80

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

Displacement (In.)

Lo

ad

(kip

s)

Frame Connection TestSpecimen FC-2 (2 1/2” XS)

Frame Connection Results

• Embedment of pipe determined by concrete bearing on projected area

• Residual capacity determined by shear yielding of shear lug

Out-of-Plane Resistance

• Continuous vertical reinforcement

• Shear lugs

• Boundary element constraint

– In-plane compression

developed under bending

w