Experimental Investigation of Deconstructable Steel-Concrete Shear - - PowerPoint PPT Presentation

Experimental Investigation of Deconstructable Steel-Concrete Shear Connections in Sustainable Composite Beams

Lizhong Wang, Jerome F. Hajjar

Department of Civil and Environmental Engineering Northeastern University

Mark D. Webster

Simpson Gumpertz and Heger, Inc. April 6, 2017

Sponsors

• National Science Foundation
• American Institute of Steel Construction
• Northeastern University
• Simpson Gumpertz & Heger

Acknowledgements

In-Kind Support

• Benevento Companies
• Capone Iron Corporation
• Fastenal Company
• HALFEN
• Lindapter International
• Meadow Burke
• S&F Concrete
• Souza Concrete

Image from US Energy Information Administration (2011)

Green buildings

• Material manufacture:
• Environmentally friendly, renewable and low

embodied energy materials

• Building use:
• Efficient heating, ventilating and lighting

systems

• Adaptation or reconfiguration
• End of life
• Minimum amount of waste and pollution
• Reusable and recyclable materials

Material flow of current buildings:

Extraction Manufacturing Construction Operation Deconstruction Design for Deconstruction Disposal

Sustainable Building Systems

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

End-of-life of Construction Materials

End-of-life of construction materials

Image from SteelConstruction.Info

Sustainable Building Systems

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

Composite Floor System

• Conventional composite floor systems are cost-effective solutions for multi-story buildings
• The integration of steel beams and concrete slab limits separation and reuse of the

components

• Proposed DfD System: Clamp precast planks to steel beams/girders in a steel framing system
• Both the steel members and the precast planks may be reused

Precast concrete plank Cast-in channels

Steel beam

Deconstructable composite beam prototype Clamps Tongue and groove side joint Bolts a) Plank perpendicular to the steel beam

24'' 6'' 12'' 6'' 6''

b) Plank parallel to the steel girder

12'' 12'' 12'' 12'' 12'' 6''

Precast concrete plank cross section

Design for Deconstruction

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

Test Program

• Pushout tests: evaluate a wide range of parameters and formulate strength design equations

for the clamping connectors

• Beam tests: study the clamp connector behavior and associated composite beam strength and

stiffness for different levels of composite action

Precast Concrete Planks Steel Beam Spreader system Composite beam test setup Pushout test setup Reaction Angle Precast Concrete Plank Steel Beam Self-reacting Frame

Design for Deconstruction

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

Pretension test setup

Pretension Test

• Determine the number of turns needed for pretensioning the T bolts
• Round coupons are first tested to obtain the stress-strain curve of the bolt material

Two turns and 1.5 turns after a snug-tight condition are recommended for pretensioning the M24 and M20 bolts, respectively.

Pretension Test

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions Fractured bolts M24 bolts M20 bolts

0.01 0.02 0.03 0.04 0.05

Strain (in./in.)

30 60 90 120 150

Stress (ksi)

1 1/2 turns 1 turn 2 turns 1/2 turn

Snug-tight bolts Bolt tested

0.003 0.006 0.009 0.012 0.015

Strain (in./in.)

30 60 90 120 150

Stress (ksi)

2 turns 1 turn 1/2 turn 11/2 turns

Pushout Test Setup

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

Pushout Test Configuration

Elevation View Load Plan View Load

Pushout Test Matrix Pushout Test Parameters

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

Series Specimen Test parameters Bolt diameter Number of T bolts Reinforcement configuration Shim M 2-M24-T4-RH M24 4 Heavy No M 3-M24-T4-RH-S M24 4 Heavy Yes M 4-M24-T6-RH M24 6 Heavy No M 5-M20-T4-RH M20 4 Heavy No C 6-C24-T4-RH M24 4 Heavy No C 7-C24-T4-RL M24 4 Light No C 8-C24-T4-RH-S M24 4 Heavy Yes C 9-C24-T6-RH M24 6 Heavy No C 10-C20-T4-RH M20 4 Heavy No

Three-channel specimen Two-channel specimen with shims

Steel shims

Loading protocols

• Monotonic test: Displacement control
• Cyclic test:
• Displacement control
• Emulate AISC 341-10 K2.4b “Loading

Sequences for Beam-to-Column Moment Connection”

Reinforcement pattern

• Light pattern: Contains reinforcement

designed for gravity loading only

• Heavy pattern: Supplementary

reinforcement bridges all potential concrete failure planes

Pushout Test Parameters

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

Monotonic Test Results Pushout Test Results

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

2 4 6 8 10 12

Slip (in.)

10 20 30 40 50 60

Load (kips)

M20-T4-RH

2 4 6 8 10

Slip (in.)

15 30 45 60 75 90

Load (kips)

M24-T4-RH

1 2 3 4 5 6

Slip (in.)

20 40 60 80 100 120 140

Load (kips)

M24-T6-RH

• Smaller M20 clamps are prone to rotate and cannot

hold their positions as stably as the M24 clamps

• It is recommended to reduce the rotation of the M20

clamps to maintain the bolt tension, which could be achieved by locking the clamp tails into the channels

• The strength degradation starts at a slip of 0.54 in.,

which is usually larger than the slip demand on shear connectors in composite beams

Cyclic Test Results Pushout Test Results

Abrasion on steel flanges Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6

Slip (in.)

• 80
• 60
• 40
• 20

20 40 60 80

Load (kips)

Light reinforcement Heavy reinforcement

Specimens C24-T4-RH and C24-T4-RL

• Strength reduction similar to shear studs which exhibit lower strength and ductility when

subjected to cyclic loading (25% strength reduction in design)

• The peak load reduces due to lowering of frictional coefficients and release of bolt tension,

but through pinching behavior at larger slips retains much of its strength

• Shear studs have limited slip capacity before fracture (~0.3 in.); clamps have the potential

to connect composite diaphragms and collector beams and could be designed as inelastic components to dissipate energy

Composite Beam Test Beam Test Setup

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions Composite beam # Bolt size # of channels per plank Steel beam section Reinforcement configuration Number of bolts (clamps) Percentage of composite action 1-M24-2C-RH M24 2 W14x38 Heavy 56 82.7% 2-M24-1C-RL M24 1 W14x38 Light 30 45.1% 3-M20-3C-RL M20 3 W14x26 Light 90 164.5% 4-M20-1C-RL M20 1 W14x26 Light 30 43.8% Composite beam test setup

Observed Beam Response Beam Test Results

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions Concrete crushing Deconstructed steel beam Longitudinal cracking (parallel to the steel beam) Contact between planks at ultimate deflection

2 4 6 8 10 12 14 Beam midspan deflection (in.) 15 30 45 60 75 90

Applied load(kips)

Major slip Steel beam yielding Concrete crushing at east side First bang Concrete crushing at west side

Service load Live load deflection of L/360 AISC prediction 2 4 6 8 10 12 14

Beam midspan deflection (in.)

10 20 30 40 50 60

Applied load (kips)

Slip Steel beam yielding Concrete crushing at east side First bang Concrete crushing at west side AISC prediction Live load deflection of L/360 Serivce load

2 4 6 8 10 12 14 16 Beam midspan deflection (in.) 10 20 30 40 50 60 70 Applied load(kips)

Steel beam yielding Concrete crushing at west side Concrete crushing at east side

AISC prediction Service load Live load deflection of L/360

Load-Deflection Curves Beam Test Results

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

2 4 6 8 10 12 14

Beam midspan deflection (in.)

20 40 60 80 100 120

Applied load (kips)

Discernable slip Steel beam yielding Major slip First bang Concrete crushing

Service load Live load deflection of L/360 AISC prediction

Test 1-M24-2C-RH Test 2-M24-1C-RL Test 3-M20-3C-RL Maximum slip = 0.25 in. Maximum slip = 0.32 in. Maximum slip = 0.02 in. Maximum slip = 0.35 in. Test 4-M20-1C-RL

Conclusions

• A new deconstructable composite floor system is proposed to promote sustainable design of

composite floor systems within bolted steel building construction through comprehensive reuse of all key structural components.

• Pushout tests are conducted to evaluate the effects of different parameters and formulate

strength design equations for the clamping system; composite beam tests are performed to investigate the strength, stiffness and ductility of the beams.

• 2 turns and 1.5 turns after a snug-tight condition are recommended for pretensioning the M24

and M20 bolts in the DfD plank system.

• The M24 clamps are highly robust under monotonic loading - compared to shear studs that

fracture at much smaller slips (~0.3 in.), the clamping connectors can retain almost 80% of the peak strength even at 5 in. slip under monotonic loading.

• The strength of the M20 clamps declines quickly because the clamps are prone to rotate as

the beam moves. As such, the size of the clamp relative to the channel is an important design

• consideration. Also, the slip at which the strength starts to descend is much larger than the

slip demand on the clamping connectors in composite beams.

• All the beams deflected to L/25 and behave in a ductile manner. The tested flexural strength
• f the beams is close to that predicted by the AISC design equations.

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

Thank You

Precast concrete plank Cast-in channels

Steel beam

Deconstructable composite beam prototype Clamps Tongue and groove side joint Bolts Precast Concrete Planks Steel Beam Spreader system Composite beam test setup

Test Results Pushout Test Results

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions

1 2 3 4 5 6

Slip (in.)

15 30 45 60 75 90

Load (kips)

M24-T4-RH-S Bolt head fracture Separation of shims from clamps

• 4
• 3
• 2
• 1

1 2 3 4

Slip (in.)

• 80
• 60
• 40
• 20

20 40 60 80

Load (kips)

C24-T4-RH-S

Test Results Pushout Test Results

Introduction DfD Floor System Pushout Tests Beam Tests Conclusions Complete disengagement of clamps

• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6

Slip (in.)

• 120
• 90
• 60
• 30

30 60 90 120

Load (kips)

Specimen C24-T6-RH

• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6

Slip (in.)

• 60
• 45
• 30
• 15

15 30 45 60

Load (kips)

Specimen C20-T4-RH

Frictional force Compressive Strut Tensile Tie Reaction force

Strut-and-tie model