Amir Botros, Sami Rizkalla, Paul Zia, Gregory Lucier Department of Civil, Construction and Enviromental Engineering Precast double tees with thin stems are a widely used in parking structures and other buildings. The end supports are dapped such that the bottom of the double tee is level with the bottom of the inverted tee or ledger beam on which it is supported. The dapped connection detail is important in parking structures because the overall structural depth and floor-to- floor height need not be increased where the double tee is supported by ledge beam. • Problems Associated with Dapped End Beams 1. Cracking Problems 2. High Bearing Stresses 3. Constructability / Tolerances 1. Develop Standard and Effective Reinforcement Details for Dapped Ends. 2. Develop Rational Methodologies for Proportioning Key Reinforcement for Dapped Ends. P P FE Model For Dapped End Beam 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Vertical Dap Reaction, kips. Displacement under Load, in. L3B Specimen Experimental FE Measured Dap Reaction: 67 kips FE prediction: 65 kips Prediction/ Measured = 97 % x Cracks’ width > 0.4 mm (0.016 in) x Red zones have principal compressive strains greater than 0.002 value Re-entrant corner cracks at Crack pattern at Bond Failure Cracks Diagonal Tension Cracks Nib Region Cracks Parametric Study 5 Reinforcement Schemes 15 Parameters Studied for Each Scheme C-Shaped Vertical L Inclined L Z-Shaped Custom Welded Wire Mesh 1. Prestressing Level 2. Amount of Hanger Reinforcement, A sh 3. Shear Friction Reinforcement, A h 4. Vertical Shear Reinforcement, A v 5. Flexural Reinforcement, A s 6. Nib Prestressing 7. Length of Hanger Steel Tail, A sh’ 8. Concrete Compressive Strength, f c ’ 9. Shear Reinforcement in Full Section 10. Nib Depth 11. Friction of Bearing Pads 12. Held Back Flange 13. Flange Width 14. De-bonded Length of Strands 15. Corner Angle Construction Details 0 10 20 30 40 50 60 70 80 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Vertical Dap Reaction, kips Vertical Displacement under Load, in. Vertical L Shape C Shape Vertical Z Shape Inclined Z Shape Inclined L Shape Welded Wire Fabric • Inclined L Most efficient • C Shaped Poorest performance 0 0.005 0.01 0.015 0.02 0.025 C Shape V L Shape I L Shape V Z Shape I Z Shape WWF Crack width (in) Crack Width at Re-entrant Corner 0.0077 0.0148 0.0118 0.0230 0.0118 0.0135 Minimum Comparison between Reinforcement Schemes Typical failure of analyzed dapped end beams occurred due to diagonal tension cracking in the full depth section. Inclined schemes performed better than others in regards of strength and crack control. C-shape scheme showed poorest performance The effect of various parameters showed same trend for all reinforcement schemes. Several parameters were found to have significant effect on the ultimate strength of dapped end and in controlling cracking such as: Nib Prestressing Concrete Strength Shear reinforcement in full section 7’ 3’’ 3’ 0’’ 22’ 7’’ 7’ 2’’ P P Inclined link support Pin support 40’ 0’’ 30’’ 15’’ • Ten Beams 40’ long (20 dapped end tests) • One Full Scale 60’ long Beam Test Setup • Completing the Experimental Tests • Select the two most Efficient Reinforcement Schemes in regards of Strength and Crack control at Service Load Level. • Develop Rational Design Approach for proportioning the key Reinforcement of the Selected Schemes. Crack Pattern at Service Load Level Crack Pattern after Failure 9 Literature and Previous Tests 9 Industry Survey 9 ATENA Verification 9 Parametric Study Using ATENA 9 Proposing Experimental Program 9 Lap Splice Tests I 9 Phase 1 Report 9 Design of Full Scale Beam Specimens 9 Lap Splice Tests II ¾ Experimental program Phase 1 (Completed) Phase 2 (In progress) Re-entrant Corner Cracks Shear Cracks Splitting Cracks 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Vertical Dap Reaction (kips) Vertical Displacement, in. No Strands in Nib 1 Strand in Nib 2 Strands in Nib 3 Strands in Nib + 25% 1 Strand in Nib 3 Strands in Nib Effect of Nib Prestressing Crack pattern at service load level M4B Specimen Major DT cracking at Failure M4B Specimen Parameters Selected for Testing: • Nib Prestressing • Concrete Strength, f c ’ • Nib Depth • Length of Hanger Steel Tail, A sh ’ • Shear Reinforcement in Full Section • Flange Held Back 1- Six Reinforcement Schemes 2- Experimentally verify influence of the following six parameters: The authors would like to acknowledge the Precast/Prestressed Concrete Insitute for funding this research project in addition to providing continuous advise and guide through all phases of the research.
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Amir Botros, Sami Rizkalla, Paul Zia, Gregory LucierDepartment of Civil, Construction and Enviromental Engineering
Precast double tees with thin stems are a widely used inparking structures and other buildings. The end supports aredapped such that the bottom of the double tee is level with thebottom of the inverted tee or ledger beam on which it issupported.
The dapped connection detailis important in parkingstructures because the overallstructural depth and floor-to-floor height need not beincreased where the double teeis supported by ledge beam.
• Problems Associated with Dapped End Beams1. Cracking Problems
2. High Bearing Stresses 3. Constructability / Tolerances
1. Develop Standard and Effective Reinforcement Details forDapped Ends.
2. Develop Rational Methodologies for Proportioning KeyReinforcement for Dapped Ends.
P P
FE Model For Dapped End Beam
0
10
20
30
40
50
60
70
80
90
100
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Vert
ical
Dap
Rea
ctio
n, k
ips.
Displacement under Load, in.
L3B Specimen
Experimental FE
Measured Dap Reaction: 67 kips FE prediction: 65 kips
Prediction/ Measured = 97 %
Cracks’ width > 0.4 mm (0.016 in) Red zones have principal compressive strains greater than 0.002 value
Re-entrant corner cracks at
Crack pattern at Bond Failure Cracks Diagonal Tension Cracks
Nib Region Cracks
Parametric Study
5Reinforcement
Schemes
15Parameters Studied
forEach Scheme
C-Shaped Vertical L
Inclined L Z-Shaped
Custom Welded Wire Mesh
1. Prestressing Level2. Amount of Hanger Reinforcement, Ash3. Shear Friction Reinforcement, Ah4. Vertical Shear Reinforcement, Av5. Flexural Reinforcement, As6. Nib Prestressing7. Length of Hanger Steel Tail, Ash’8. Concrete Compressive Strength, fc’9. Shear Reinforcement in Full Section10. Nib Depth11. Friction of Bearing Pads12. Held Back Flange13. Flange Width14. De-bonded Length of Strands15. Corner Angle Construction Details
0
10
20
30
40
50
60
70
80
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Vert
ical
Dap
Rea
ctio
n, k
ips
Vertical Displacement under Load, in.
Vertical L ShapeC Shape
Vertical Z Shape
Inclined Z Shape
Inclined L Shape
Welded Wire Fabric
• Inclined L Most efficient• C Shaped Poorest performance
0
0.005
0.01
0.015
0.02
0.025
C Shape V L Shape I L Shape V Z Shape I Z Shape WWF
Crack width(in)
Crack Width at Re-entrant Corner
0.0077
0.0148
0.0118
0.0230
0.01180.0135
Minimum
Comparison between Reinforcement Schemes
Typical failure of analyzed dapped end beams occurred due to diagonal tension cracking in the full depth section.
Inclined schemes performed better than others in regards of strength and crack control.
C-shape scheme showed poorest performanceThe effect of various parameters showed same trend for all reinforcement schemes.Several parameters were found to have significant effect on the ultimate strength of dapped end and in controlling cracking such as:
Nib PrestressingConcrete StrengthShear reinforcement in full section
7’ 3’’3’ 0’’ 22’ 7’’7’ 2’’
P P
Inclined link support
Pinsupport
40’ 0’’
30’’15’’
• Ten Beams 40’ long (20 dapped end tests)• One Full Scale 60’ long Beam
Test Setup
• Completing the Experimental Tests• Select the two most Efficient Reinforcement Schemes in regards of
Strength and Crack control at Service Load Level.• Develop Rational Design Approach for proportioning the key
Reinforcement of the Selected Schemes.
Crack Pattern at Service Load Level Crack Pattern after Failure
Literature and Previous Tests
Industry Survey
ATENA Verification
Parametric Study Using ATENA
Proposing Experimental Program
Lap Splice Tests I
Phase 1 Report
Design of Full Scale Beam Specimens
Lap Splice Tests II
Experimental program
Phase 1 (Completed) Phase 2 (In progress)
Re-entrant Corner Cracks Shear Cracks Splitting Cracks
0102030405060708090
100
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Vert
ical
Dap
Rea
ctio
n (k
ips)
Vertical Displacement, in.
No Strands in Nib1 Strand in Nib2 Strands in Nib3 Strands in Nib
+ 25%
1 Strand in Nib 3 Strands in Nib
Effect of Nib Prestressing
Crack pattern at service load level M4B Specimen
Major DT cracking at Failure M4B Specimen
Parameters Selected for Testing:
• Nib Prestressing• Concrete Strength, fc’• Nib Depth• Length of Hanger Steel Tail, Ash’• Shear Reinforcement in Full Section• Flange Held Back
1- Six Reinforcement Schemes
2- Experimentally verify influence of the following six parameters:
The authors would like to acknowledge the Precast/Prestressed Concrete Insitute forfunding this research project in addition to providing continuous advise and guidethrough all phases of the research.
Related Documents
