BRIDGE ENGINEERING ASSOCIATION 10 th New York City

BRIDGE ENGINEERING ASSOCIATION 10 th New York City Bridge Conference August 26 -27, 2019 DEVELOPMENT AND APPLICATION OF TITANIUM ALLOY BARS FOR SHEAR AND FLEXURAL STRENGTHENING REINFORCED CONCRETE BRIDGES CHRISTOPHER HIGGINS, Ph. D. , P. E.

Overview • • • Background Experimental Test Results ASTM Specification AASHTO-LRFD Design Guide Future Directions

Strengthening Existing Bridges • Post-tensioning • Wrapping/confining Flexural girder strengthening with CFRP laminate • Carbon fiber reinforced polymer (CFRP) laminate • Near-surface mounted (NSM) • Carbon fiber reinforced polymer rod/strip • Glass fiber reinforced polymer (GFRP) rod • Stainless steel bars FRP rods and laminates fail due to bond anchorage and materials are nonductile http: //aslanfrp. com/Aslan 400/Resources/Asl an 400. pdf Strengthening with NSM CFRP strips Concerns with corrosion at surface for most metals, relatively low strength (stainless reinforcing bars) http: //aslanfrp. com/Aslan 500/aslan 500 pg 2. html 3

Ductile FRP? Environmentally insensitive material with high strength, well defined properties, good surface bonding characteristics along length, and efficient mechanical anchorages 4

Titanium Alloy Material Properties (Ti-6 Al-4 V) 1380 1030 860 690 520 Stress (MPa) 1210 340 170 Extensometer Strain (in/in) 5

Titanium Alloy Material Properties (Ti-6 Al-4 V) • Aircraft fastener quality (6% Aluminum 4% Vanadium) • Well-defined, high strength, and ductile (limited hardening->protects bond, structural fuse) • High fatigue resistance (CAFL~ 75 ksi), low notch sensitivity • Impervious to chlorides due to stable oxide layer • Coeff. of thermal expansion (8. 6 me/o. C) (8 -12 Con. and 12 St. ) • Conventional fabrication (shear, cut, and bend) • Relatively lightweight of 281 lb/ft 3 (steel 1. 7 x) • Bends facilitate anchorage 6

Strengthening – Flexure and Diagonal Tension (Shear) 26 full-scale specimens 7

Fabrication and Installation ACI 440. 2 R • Groove Spacing • Groove dimensions 8

Durability High Cycle Fatigue and Freeze-Thaw Combined Largest combined structural-environmental testing chamber Thermocouples at 0. 5, 1. 5, and 3 in. ensure temperature targets • 1. 6 million cycles @ steel stress range >50 years of life. 9

T Beam Experimental Results – Durability (s=10 in. ) Ti. AB Env. and Fatigue Base

Field Demonstration: Mosier Bridge Over I 84 DL produces MLL produces M+ 1 1

• • Results Reserve strength of Ti girder substantially exceeds factored demands Strengthening of failed girder better response than unfailed girder Predicted strength w Ti Design Reserve Capacity • Design strength of Ti girder exceeds factored demands even with conservative assumptions 1 2

30% less expensive than CFRP 1 3

ASTM Specification for NSM Titanium Main Committee: Committee B 10 – Reactive and Refractory Metals and Alloys Sub-Committee: Committee B 10. 01 on Titanium

Approved Nov. 2018

ASTM B 1009 -18 Requirements: • • • Tensile properties (Class 120 and 130) Chemical requirements Bond strength Cross-Sectional area calculation Bending requirements

Guide Balloted and Approved by COBS 2019 • “Guide for Design and Construction of Near. Surface Mounted Titanium Alloy Bars for Strengthening Concrete Structures” • AASHTO-LRFD Format • General Conditions • Materials • Construction • Installation • Design • Flexure and Shear (MCFT) 1 7

Design Guide • Conventional analysis methods • Design Ti. ABs at yield if conditions are met • Includes environmental durability factor (epoxy) • 3 Limit states for flexure and 1 for shear • Strength • Service (check bond stress at cutoffs and where retrofitted strength above base capacity) • Fatigue (not of Ti. AB but of reinforcing steel) • Comprehensive design example (shear and flexure) 1 8

BRIDGE ENGINEERING ASSOCIATION 10 th New York City Bridge Conference August 26 -27, 2019 DEVELOPMENT AND APPLICATION OF TITANIUM ALLOY BARS FOR SHEAR AND FLEXURAL STRENGTHENING REINFORCED CONCRETE BRIDGES Christopher Higgins, Ph. D. , P. E.