APPLICATION OF STEEL FIBER REINFORCED CONCRETE IN SEISMIC BEAM-COLUMN JOINTS

Masters Thesis presented by

Michael Gebman

MSCE San Diego State University, 2001

BSCE University of California, Davis, 1999

Presentation Updated: January, 2002

Presentation Overview

Problems with Joint Design

Advantages of SFRC

Previous Research & Testing

Experimental Design

Results

Analysis

Conclusion

Acknowledgements

Problem #1

During a strong seismic event, failure of beam-column joints can cause
- Structural collapse
- Loss of life

1985 Mexico City Earthquake

Collapse of an 8 level building (9/25/85)

Problem #2

Construction Technique of Seismic Beam-Column Joints is complicated by closely spaced hoops

Problem #3

Research has yet to convince authorities that it is smart and safe to use steel fiber reinforcement to
- Provide a stronger joint
- Increase hoop spacing
- Simplify construction

Advantages of Steel Fibers

Steel fibers increase
- Ductility
- Energy absorption
- Shear resistance
- Stiffness

Steel Fiber Reinforced Concrete (SFRC) after thorough mixing of fibers with plain concrete

Usage of Steel Fibers

Steel fibers glued together prior to mixing

Separation of fibers occurs during mixing to ensure uniform distribution

Types of Steel Fibers

Straight

Hooked

Paddled

Types of Steel Fibers

Deformed

Crimped

Irregular

Types of Steel Fibers

Properties - Compression

Properties - Tension

Properties - Bending

Properties - Hysteresis

Properties - Bridging Action

Plain Concrete

Load = 2,500 lb

SFRC

Load = 4,500 lb

Research & Testing

First testing conducted in 1974

Worldwide testing: U.S., Canada, China, India

Joints tested were
- Full Scale or Half Scale
- Exterior or Interior

Other Joints tested
- Knee Type Joints
- Corbels
- Frames

Two level RC Frame

Research, 1974: Henager

First testing of SFRC in beam-column joints

Tested two joints
- One with plain concrete, designed to meet ACI 318-71
- One joint with SFRC replacing hoops
  - Vf = 1.67%

Research, 1974: Henager

Found SFRC Joint to have improved
- Stiffness
- Damage tolerance
- Ductility

Concluded joint hoops could be replaced by SFRC

Research, 1986: Lakshmipathy and Santhakumar

Tested two 7-level single bay frames, at 1/4 scale
- One plain concrete frame
- One plain concrete frame with SFRC joints
  - Vf = 1%

Research, 1986: Lakshmipathy and Santhakumar

SFRC Frame had
- Ductility increase of 57%
- Cumulative energy dissipation increase of 130%

Research, 1987: Jindal and Sharma

Tested 92 knee-type joints and 8 conventional joints
- Found
  - Moment capacity to increase from 15% to 30% as volume fraction of fibers increased to 2%
  - Increase in rotational capacity for SFRC joints

Research, 1987: Fattuhi

Tested Corbels with SFRC replacing hoops
- Found significant increase in shear strength
  - For Vf = 1%, shear strength increased by a factor of 3
- Concluded further investigation would be needed

Exterior Beam-Column Joint with Corbel

Research, 1988: Olario, Ioani, and Poienar

Tested SFRC Joints built to Romanian Building Code

Tested
- Two plain concrete joints
- Six joints with SFRC
  - Vf varied from 0.5% to 1.5%

Research, 1988: Olario, Ioani, and Poienar

Found
- Ductility increase of up to 30%
- Energy increase up to 46%
- Greater stiffness
- Improved bond of longitudinal bars in joint

Research, 1989: Gefken and Ramey

Tested Seismic Joints with goal of increasing hoop spacing by using SFRC
- Tested
  - Two plain concrete joints designed to meet ACI
  - Four SFRC joints with increased hoop spacing
    - Vf = 2%

Research, 1989: Gefken and Ramey

Found
- Higher ultimate strength
- Better energy dissipation
- Better ductility
- Greater stiffness
- Less spalling

Concluded hoop spacing could increase by factor of 1.7

Research, 1991: Soubra

Examined SFRC Joint application to pre-cast construction

Tested
- Six precast beams with cast in place SFRC joint
- Used fibers of lengths 1.2-in (30-mm) at Vf = 4% and 2.1%
- Used fibers of lengths 2-in (50-mm) at Vf = 1%

Third Point Loading

Research, 1991: Soubra

Instrumentation
- Used 8 strain gages in the joint, 4 in beam

Loading
- Third point loading was applied to the specimens

Third Point Loading

Research, 1991: Soubra

Concluded
- Testing of more realistic joints would be needed
  - Third point loading subjected joint to constant moment and no shear

Third Point Loading

Research, 1992: Olario, Ioani, and Poienar

Tested SFRC joints built to Romanian code
- Four full-scale Joints and three pre-cast Joints

Found SFRC had
- Higher ultimate strength
- Better confinement
- Lower stiffness degradation
- Energy dissipating capacity increase up to 50%

Research, 1992: Jiuru, Chaobin, Kaijian, and Yongcheng

Tested SFRC joints with goal of verifying a method for calculating shear strength
- Used strain gages in the joint region
- Strain data was used to obtain bond stresses, however, no conclusions or discussion was made of the strain data

Research, 1994: Filiatrault, Ladicani, and Massicotte

Tested 4 full-scale joints
- One joint with lateral reinforcement seismic detailing
- One joint without detailing
- Two SFRC joints, both without detailing

PPT Slide

Research 1994: Filiatrault, Ladicani, and Massicotte