Renewal of Aging and Deteriorated Infrastructure

Using Titanium Alloy BarsChristopher Higgins, Professor, Oregon State University

Overview

• Introduction, Background, and Motivation

• Laboratory Test Results from Full-Scale Specimens• Shear Strengthening• Flexural Strengthening• Seismic Retrofits

• Field Implementation

• Conclusions

Punch Magazine, 1891

During the 1950 and 60’s:• Post‐war construction boom• Reinforced concrete widely used• Advent of standardized deformed reinforcing 

steel bars produced poor details• Design codes were not conservative 

Now:• Visual distress, changes in use, extend life• Using modern design codes to assess

Results:• Replace, limit loads, retrofit

Retrofit:• Want environmentally insensitive material 

with high strength, well defined properties, and efficient mechanical anchorages ‐> Titanium

Introduction

Titanium?

It is too expensive

It only for aircraft or medical devices….

Titanium Alloy Material Properties (Ti-6Al-4V)

5

Fy=145.4 ksi (0.2% offset)Fu=158.1 ksiFu/Fy=1.07 (Y=0.93)E=15,120 ksi11% Elongation

Titanium Alloy Material Properties (Ti-6Al-4V)

• Aircraft fastener quality (6% Aluminum 4% Vanadium)

• Well-defined, high strength, and ductile (limited hardening->protects bond, structural fuse)

• High fatigue resistance (CAFL~ 70 ksi), low notch sensitivity

• Impervious to chlorides due to stable oxide layer

• Coeff. of thermal expansion (8.6/oC) (8-12 concrete and 12 steel)

• Conventional fabrication (shear, cut, and bend)

• Relatively lightweight of 280 lb/ft3 (steel 1.7x)

Experimental Work (gravity loads)• Full‐scale tests with typical 

proportions and materials from legacy designs

• Shear specimens: 10  (3 control)#2 TiABs

• Flexure specimens: 10 (3 control)#5 TiABs

• Fatigue and freeze‐thaw exposure: 3  (2 shear, 1 flexure)

4 ft height, 24 ft long, 20,000 lb

Durability High Cycle Fatigue and Freeze-Thaw Largest combined structural-environmental chamber Thermocouples at 0.5, 1.5, and 3 in. ensure temperature targets 1.6 million cycles @ steel stress range >50 years of life

8

Time

Tem

pera

ture

(C

)

6/1/2016 4:34:00 PM 6/2/2016 12:34:00 AM-10

-5

0

5

10

150.5 in. embedment1.5 in. embedment

3 in. embedmentAmbient

Ti-NSM Retrofit Installation• Cut grooves in concrete• Drill holes at ends of groove• Shear bars to length• Heat to ~480˚C• Bend• Epoxy into grooves

Grooves with holes for hooks Bend hooks

Apply epoxy

Warm work

Shear Strengthening

36M Grade 420

36 in

6 in

42 in

14 in

#4 Grade 40

6mm TiAB

#11 Grade 60

Shear span~=10 ft m

4 ft

Double Leg Single Leg

Shear Results

Midspan Deflection (in)

Shea

r (ki

ps)

0.0 0.25 0.5 0.75 1.0 1.25 1.50

50

100

150

200

250

Control

Ti w Epoxy1Ti w Epoxy1+FTG

T Beam Flexure Details

T.45.Ld3: Baseline Specimen

T.45.Ld3.NSM‐Ti: 10 in. stirrup spacing

T.45.Ld3.NSM-Ti Failure (s=10 in)

Flexural Results with Durability

TiAB Env. and FatigueTiAB

Base

First Field Application: Mosier Overcrossing Interstate 84• Built in 1952

• Serves a nearby quarry

Test Plan Prior to Field ImplementationThree (3) specimens:

1. Mosier 1: As-Built

2. Mosier 2: Strengthen after failing reinforcing steel anchorage (designer’s assumption)

3. Mosier 3: Strengthen with reinforcing steel anchorage intact

Searched mill certifications to locate bars that best matched strength curves of original design. Used smaller sized Grade 420 (60) rebar to match development length of intermediate grade steel (280 MPa (40 ksi))

Experimental Results: Mosier 1

Experimental Results: Mosier 3

Results

• Design strength of Ti girder exceeds factored demands even with conservative assumptions

Des

ign

Reserve Capacity

297 kN-m

Mosier 1 As‐built

Mosier 2: Failed 1st

Mosier 3

30% less expensive than CFRP

Common design details of pre-1970’s columns

24 db to 36 db

2 ft thick

Seismic Retrofitting

• Insufficient tie reinforcement (#3 @ 12 in.)

• Lap-splice lengths of 24 db to 36 db

• Large bar sizes (#11; square and round)

• Longitudinal rebar placed at column corners

• Grade 40 steel (275 MPa)

• f’c = 3300 psi (22.7 MPa)

• Provide confinement (increase ductility)

• Remove splice deficiency (control

strength loss)

• Rocking column behavior (reduce

residual drift/restoring force)

• Control foundation forces

Seismic Retrofit Design Objectives

8 ft

12 ft

#3 @12”

36”

24”

6 ft Square

36”

8 ft

Experimental Set-Up

Elevation View

Actuator 110 kip +/‐ 10 in

Axial load  200 kip, 150 kip Active Control

No. of Cycles

Drif

t Rat

io (%

)

Col

umn

Drif

t (in

ches

)

0 20 40 60 80 100 120-10 -9.60

-5 -4.80

0 0.00

5 4.80

10 9.60

Observed Performance Control SpecimenControl specimen: progression of lap-splice failure

C2-LRTHeight of Retrofit = 1.67ls

B

A

Retrofitted Specimen Details

7.5” deformed tail15” deformed end

Ligament Construction Details

Spiral Construction Details

TiAB Spiral Reinforced Concrete Shell

Retrofitted specimens: Damage progression

Titanium Observed Performance

Short Column Response

Typical TiAB Retrofit

10.9 y 7.6 y

Plastic Hinging above the retrofit shell

Stainless Steel

Control

No ductility

Short Column (Cumulative Energy)

Cumulative Energy Dissipated in Each Cycle (kip-in)

Cumulative Energy Dissipated in Each Cycle (kip-ft)

Effe

ctiv

e C

olum

n D

rift/

y (fo

r ref

eren

ce

y = 0

.4 in

.)

0

0.00

1000

83.33

2000

166.67

3000

250.00

4000

333.33

5000

416.67

6000

500.00

7000

583.33

8000

666.67

9000

750.00

10000

833.33

0

2.5

5

7.5

10

12.5

15

17.5

20

22.5

Unretrofitted Square ColumnUnretrofitted Diamond ColumnStandard Retrofitted Square ColumnStandard Retrofitted Diamond ColumnRetrofitted Square Column with Ti Spirals only

ConclusionsTitanium's well‐defined material properties, high strength, ductility, environmental and fatigue durability, and ability to fabricate mechanical anchoragesmake Ti‐6Al‐4V alloy bars an excellent alternative for strengthening and renewal of civil infrastructure

Cost for performance is highly competitive, less expensive than CFRP, and can do things that CFRP cannot

Design guide is available with AASHTO‐LRFD framework for shear and flexural strengthening, seismic forthcoming, as is an ASTM Specification

Acknowledgements Oregon Department of Transportation and Federal Highway Administration

Perryman Company, Houston, PA

Graduate Assistants: Laura Barker, Deanna Amneus, Eric Vavra, Jonathan Knutdsen, and Sharoo Shresta

Undergraduate Assistants: Kyle England, Brandon Zaikoski, Caleb Lennon, Liam Kucey, Tyler Redman, Anthony Quinn, Jonathan Roy, Spencer Maunu, and Lance Parson

The findings and conclusions are those of the authors and do not necessarily reflect those of the project sponsors or the individuals or companies acknowledged.