Thomas L Attard, Ph.D. Associate Professor

Department of Civil, Construction, and Environmental Engineering

Chairman, Structural Engineering & Mechanics for the Athens Institute for

Education and Research (ATINER)

The University of Alabama at Birmingham

The 6th Kwang-Hua Forum on Innovations and Implementations in Earthquake

Engineering

December 12 – 14, 2014

Shanghai, China

NEXT GENERATION HYBRIDIZED

POLYMERIC “TUNED” COMPOSITES FOR

21ST CENTURY ADVANCES IN EARTHQUAKE

ENGINEERING

PROBLEM STATEMENT AND GENERAL RESEARCH OBJECTIVE &

OUTCOME

Today‟s society is complex, variable, and high-demanding, subject to

multi-natural hazards and extreme anthropogenic loads

Objective: Develop a Pervasive damage mitigation system for

complex structures

Carbon-Fiber-Reinforced Hybrid-Matrix Composite (CHMC)

Strategy: Develop a multi-scale design solution from the molecular

level to the macro/ component/ large-scale level for various

structural components

Outcome: A systems composite that provides superior physical,

chemical, and mechanical properties to new (strengthening) or

already-damaged (retrofit) structures

NEWLY FUNDED CHMC RESEARCH PROGRAM

New 3-year funded research project for $746,709 (3 PhD

Students are sought)

Sponsor is US Army Corps of Engineers and Presidium Group of Companies

Drawbacks of many conventional fiber-reinforced epoxy systems

Lack sufficient energy dissipation and ductility

Lack fracture toughness capability

High-rate of debonding from the substrate

Suspect chemical and environmental durability

Dual polymeric hybridization alleviates many of

the above shortcomings

CHMC: Combine strong carbon-based technology with hybridized

chemical reactions

Lightweight

Design a materials system with „tune-able‟ properties. Provide:

Impact-resistance

Energy dissipation and ductility

Fracture toughness

Damping for the vibration control of elastic systems

Prevent Laminate- Substrate Debonding via an internal energy

dissipation mechanism

Excellent chemical and environmental durability

CHMC APPLICATIONS TO EARTHQUAKE-DESIGNED

INFRASTRUCTURES

DAMAGE MECHANISMS OF GENERAL LAMINATE FIBER-REINFORCED COMPOSITES

Damage Mechanisms of General

Laminate Fiber-Reinforced

Composites

Matrix cracking

Fiber–matrix debonding

Fiber breakage

Fracture of fiber

Fiber pullout

Follows fiber fracture

Separation of fiber from matrix

Develop a design standard

from the „ground-up‟

that can be utilized as a

pragmatic engineering

solution

①

②③

④

①

②

③

④

Given a non-homogeneous microstructure

Existence of numerous paths for load redistribution

The composite integrity of the CHMC depends on the accumulated sub-

critical damage rather than any single damage event

Thus, macroscopically strong solids protect integrated microscopically weak

structures

EVOLUTIONARY NATURE OF THE FAILURE CHARACTERISTICS OF VARIOUS COMPOSITES

RESULT: local damage (single crack) does not result in

catastrophic global failure of the composite

OUTCOME OF THE HYBRIDIZED CHMC

.

“ONE-STOP SHOP/ ONE-STOP SOLUTION”

An alternative mode of material failure is created

Deformable body is thus TRAPPED in a microscopically weak, but

macroscopically strong, mode of fracture … Crack propagation is precluded

Micromechanical

Behavior of the

Constituent Materials

Interaction between

Constituent Phases

Micromechanics &

Micro-scale Damage

model

Results &

Inference

Macro-scale Mechanical

Behavior of Materials

Scale-linking

Model

Large-scale Structural

Applications

Stress-strain

Behavior

Energy

Dissipation

Impact

Resistance

Engineering

Mechanics

MULTI-SCALE MODELING: ACROSS ALL SCALES

TEM

Molecular

Dynamics

Micro-structure (SEM)

Manufacturing

Process

Material Interfaces

(e.g., Fiber-Matrix)

Micro-mechanics

Stress-Strain

Vibration/

Damping

Engineering

Applications (hybrid testing)

Multi-scale modeling (across all scales) … Dimensional Scales

Fiber Push-out

Chemical

Analysis

Defects & Damage

10-9 m 10-6 m 10-1 m 10 m

Fatigue

Tolerance

Spiral Notch Torsion Test

Micro-Tens Test (polymers)

Impact resist.

HIGH-IMPACT RESISTANCE OF THE CHMC

High-Impact Tests at the ORNL (DoE)

0 10 20 30 40 50

-5

0

5

10

15

20

Fo

rce

(kN

)

Displacement (mm)

CarbonFlex

Carbon-fiber/ epoxy

Load time-histories

Carbon-fiber epoxy CHMC

(1) (2) (3) (4)

Formation of

local buckles

Progressive folding

MATERIAL DAMPING AND IMPACT RESISTANCE OF STEEL BEAMS: HIGH-FREQUENCY VIBRATION

DAMPING RATIOS:

CHMC beam 4.87%

CFRP beam 1.18%

Steel beam 0.35%

Steel CF/

Epoxy

CHMC1 CHMC2 CHMC30

2

4

6

Da

mp

ing

Ra

tio

Tes

ted

by

Fre

e V

ibra

tio

n (

%)

0.35%

1.18%

4.87%

4.29% 4.17%

0 100 200 300 400 50010-11

10-10

10-9

10-8

10-7

10-6

10-5Power Spectral Density (0.3g)

Frequency (Hz)

Pow

er-d

isp

. /H

z2

CFRP

CHMC (CarbonFlex)

Velocity Time-history

Damping Ratio vs

Thickness (CHMC)

0.00

1.00

2.00

3.00

4.00

5.00

CFRP 1/16 1/8

Dam

pin

g R

ati

o (

%)

Thickness hp (in)

Damping Ratio vs tc (CHMC)

4.00

4.20

4.40

4.60

4.80

2 3 4 5Intermittent Curing Time tc (hr)

Dam

pin

g R

ati

o (

%)

damping varying with

hp

Damping varying

with tc

0.0 0.4 0.8 1.2 1.6 2.0

-0.08

-0.04

0.00

0.04

0.08

Time (sec)

0.0 0.4 0.8 1.2 1.6 2.0

-0.08

-0.04

0.00

0.04

0.08

Vel

oci

ty (

mm

/s)

Time

(Sec)

0.0 0.4 0.8 1.2 1.6 2.0

-0.20

-0.10

0.00

0.10

0.20

Steel

Time (Sec)

Carbon-fiber/ Epoxy

CHMC (CarbonFlex)

CHMC RETROFIT OF A SEISMICALLY DAMAGED RC SHEAR WALL

n Cyclic testing of an RC shear wall specimen

n Resulting in a 3mm-wide cross-crack and crushed concrete at the two bottom

corners of the specimen

n After-test load capacity: approximately 40% of its peak value

TEST SETUP AND RESULTS -- RC SHEAR WALL

LVDT

LVDT

LVDT

Actuator to Apply Lateral Load

Hydraulic Jack to Apply Vertical Load

Bolt to Anchor the Specimen

Test Setup Lateral Force-Disp. Response

Results: CHMC retrofit of the shear wall recovered 80% of the

original load capacity, in addition to significantly increasing ductility

and confinement

-30 -20 -10 0 10 20 30

-300

-200

-100

0

100

200

300

As-it RC Shear Wall (Hysteresis)

CarbonFlex Retrfitted (Hysteresis)

As-it RC Shear Wall (Backbone)

CarbonFlex Retrfitted (Backbone)

La

tera

l F

orc

e (

KN

)

Lateral Def. (mm)

PPP

PPP

TEST SETUP AND RESULTS -- RC SHEAR WALL

Note the tremendous ductility in the

shear wall. Tremendous energy

dissipation helped stabilize the crack

growth in the wall and sustain its high

strength even after the concrete crushed.

Note also the tremendous confinement

and compression strength in the wall.

PERFORMANCE ASSESSMENT OF RETROFITTED SRC GIRDERS USING CHMC

TO DISSIPATE INELASTIC ENERGY

Fatigue Crack

Encased Steel (W-Section)

Fracture of Tensile Rebar

Repair and retrofit of Severely Damaged Steel-Reinforced Concrete (SRC) Girders

0 25 50 75 100 125 1500

100

200

300

400

500

600

700

Load

(K

N)

Deflection (mm)

B1 (CarbonFlex Retrofitted SRCC Beam)

0 25 50 75 100 125 1500

100

200

300

400

500

600

700

Deflection (mm)

B2 (CFRP Retrofitted SRCC Beam)

0 25 50 75 100 125 1500

100

200

300

400

500

600

700

Deflection (mm)

B3 (CarbonFlex Retrofitted SRCC

Beam with No Steel Welded)

B1 B2 B3

FLEXURAL LOAD TESTS – INELASTIC ENERGY DISSIPATION OF RETROFITTED SRC GIRDERS

68% of the peak load is sustained at tremendous ductility

following fracture of the welded encased steel at about 550kN

B1 – SRC Retrofitted by CHMC B2 -- SRC Retrofitted by CFRP

SEISMIC DESIGN OF OPEN-FRONT WOOD-FRAMED

STRUCTURES USING CONVENTIONAL PLYWOOD

WALLS Traditional as-is wood-home designed according to code using

plywood sheathing for shear wall construction (quasi-dynamic tests)

Displacements and accelerations are large

Nails are shown to either pop-out or withdraw from plywood sheathing

• Detachment of sheathing

• Issues of soft-story damage and insufficient force transfer

CHMC is used in shear wall construction of wood-framed structures

under quasi-dynamic loading in lieu of traditional plywood panels

Reduction of displacements and accelerations via energy-dissipation

R-factor (Response Modification Factor) increases from 6.5 (traditional

plywood sheathing) to 8.185 (CHMC sheathing)

Permit efficient story force transfer and limit soft story collapse

SEISMIC TEST RESULTS OF OPEN-FRONT

WOOD-FRAMES DESIGNED USING CHMC

SHEAR WALLS

Development of a next-generational structural composite for

extreme-load protection

“Across-the-board” pervasiveness

Advent of “tunable” properties is vehicled through dual polymeric

hybridization and material parameterization

The following properties are controlled:

Impact resistance

Damping

Fracture toughness

New three-year project has been awarded

CONCLUSIONS

SELECTED RELATED PUBLICATIONS

Zhou, H. and Attard, T.L. (2012). “Rehabilitation and strength sustainability of fatigue

damaged concrete-encased steel flexural members using a newly developed polymeric

carbon-fiber composite,” Composites Part B: Engineering, 45, 1091 – 1103.

Zhou, H., Attard, T.L., Wang, Y., Wang, J.A., and Ren, F. (2013). “Rehabilitation of

notch damaged steel beams using a carbon fiber reinforced multiphase-matrix

Composite,” Composite Structures, 106, 690 - 702.

Zhou, H., Dhiradhamvit, K., and Attard, T.L. (2014). “Tornado-borne debris impact

performance of an innovative storm safe room system protected by a carbon fiber

reinforced hybrid-polymer matrix composite,” Engineering Structures, 59, 308-319

Zhou, H., Attard, T.L., Zhao, B., Yu, J., Lu, W., and Tong, L. (2013). “Experimental

study of retrofitted reinforced concrete shear wall and concrete-encased steel girders

using a new CarbonFlex composite for damage stabilization,” Engineering Failure

Analysis, 35, 219–233

THANK YOU FOR YOUR ATTENTION

0 100 200 300 400 5001E-5

1E-4

1E-3Velocity Response as a function of frequencyPower Spectrum Density

Frequency f (Hz)

Velo

cit

y v

(f)

(m/s

)

1E-9

1E-8

1E-7

1E-6

Po

wer

December 12, 2014

FOR ADDITIONAL QUESTIONS

thoma1@uab.edu