Presentation in support of Proposed Acceptance Criteria For Continuous or Semi- Continuous Fiber-Reinforced Grid Connectors used in combination with Rigid Insulation in Concrete Sandwich Panel Construction Dr. Sami Rizkalla February 3, 2010
Carbon Fiber Grids Carbon grids are manufactured in an automated process: High production volume High quality control Typical Nomenclature: Individual Strand Strength 4.45 kn Young's Modulus 234.5 GPa
Grids are Engineered to provide the right amount of strength in each direction. Carbon Grid Types
Carbon-Fiber Grid Installation For Prestressed Concrete Double Tee Beams
Carbon-Fiber Grid Installation Embedment and finishing machine to place the grid More precise placement for optimum performance More consistent; less opportunity for human error
Prestressed Concrete Sandwich Load Bearing Panels - Resist vertical and lateral loads - Provide building envelope - Consists of two concrete wythes and a layer of rigid foam. - Composite action achieved by shear connectors 6
Composite Action & Shear Connection Typical mechanisms include: Steel truss connectors Thermally inefficient Steel tie connectors Thermally and structurally inefficient Discrete FRP connectors Non-composite Action Concrete solid zones Thermally inefficient
Insulated Sandwich Panel Orthogonal CFRP Grid Cut at a 45-degree angle to develop truss action Structurally and thermally efficient 8
Insulated Sandwich Panel Wythe Reinforcement Exterior Interior Pilaster Typical Cross Section Carbon Fiber Shear Connector Carbon fiber grid shear connectors: - Provide composite action between wythes - Increase insulation value due to low thermal conductivity of the connector 9 9
Research At NCSU Evaluate behavior of wall panels reinforced with CFRP grids. Determine effectiveness of grid as shear mechanism. Calculate the degree of composite action achieved. Model behavior and develop design guidelines.
Experimental
Test Setup Teflon Pads Neoprene Pads Simulated loading due to lateral wind pressure
Flexural-shear failure Failure Modes
Lateral Load (lbs) Lateral Load (kn) Overall Panel Behavior Lateral Deflection (cm) 0.00 1.27 2.54 3.81 5.08 6.35 25000 111 Composite 20000 89 15000 Representative EPS Panel 67 10000 Ultimate Load 44 5000 Service Load Non-composite 22 0 0 0.0 0.5 1.0 1.5 2.0 2.5 Lateral Deflection (in)
Degree of Shear Connection
Experimental Results EPS 2 16 1.2D+0.5L r +1.6W 150
42 foot panel tests 17
Extreme Events 18 Fire testing
Finite Element Analysis CFRP grid 5.5 in. (140 mm) spacing CFRP grid 3.5 in. (89 mm) spacing 8-Node solid elements for foam and concrete 19 Truss elements for C-Grid
Analysis Theoretical composite and noncomposite load-deflection relationships were calculated following PCI guidelines. Percent composite action was determined based on deflections as follows: Calculation of I eff for non-composite behavior ACI 318-08 I eff M M cr a 3 I g 1 M M Valid only for I g /I cr < 3.0 cr a 3 I cr I g 20 (%) nc c exp x nc 100 Bischoff and Scanlon (2007) I eff 1 M M cr a I cr 2 1 I I cr g I g
Partial Interaction Theory M u M I M O F Z FAt the given curvature (%) x100 F At the full compsoiteaction 21
Panel Thickness (in) Panel Thickness (mm) Results Strain distribution for EPS2 Panel at service load 8 203.2 6 152.4 Inner wythe Compression 4 101.6 Tension Experimental Rational model FEA 2 50.8 Outer wythe Outer wythe 22 0-500 -300-100 100 300 500 Strain x 10 6
Insulated Architectural Cladding Steel-reinforced precast rib CFRP shear grid (thermal break) Insulating Foam CFRP grid secondary reinforcing Thin brick finish
Insulated Architectural Panel Vertical Back Ribs 24 Intermediate ribs attached to architectural façade with CFRP grid to avoid discoloration or shadowing
Insulated Architectural Panel Horizontal Back Ribs 25 Intermediate ribs attached to architectural façade with CFRP grid to avoid discoloration or shadowing
Panel Configuration Primary vertical rib 26 Secondary vertical rib 6 Typical Carbon fiber grid in the panel face for crack control
Manufacturing Process 27 Placement of CFRP grid reinforcement for architectural facade
Manufacturing Process Foam rib forms 28 FRP shear grid between frame and facade Steel reinforcing of structural frame
Full-scale experimental validation DC-7 Line C B3 DC-10 Line B B4 29 Full-scale testing under reversed cyclic uniform pressure loading representing extreme high-wind loads
Inward pressure (suction) Outward pressure 30
Full-Scale Experimental Validation ± 1.2 kpa cyclic loading 2.5 kpa static loading
Technical Papers Hassan, T. and Rizkalla, S., Analysis and Design Guidelines of Precast/Prestressed Composite Load Bearing Sandwich Wall Panels, Accepted for Publication, PCI Journal, 2010. Frankl, B., Lucier, G., Hassan, T. and Rizkalla, S., Behavior of Insulated Precast, Prestressed Concrete Sandwich Wall Panels Reinforced with CFRP Grid, Accepted for publication, PCI Journal, 2010. Rizkalla, S., Hassan, T. and Lucier, G., FRP Shear Transfer Mechanism for Precast, Prestressed Concrete Sandwich Load Bearing Panels, Accepted for Publication, ACI Special Publication 31, November 2009
Summary FRP can provide shear transfer mechanism without thermal breaks in precast prestressed concrete sandwich panels. Simple rational design approach can be used to determine degree of composite action Any ESR related to AC422 for the shear flow and shear modulus will be given for a specific properties of the insulation material,insulation thickness,material properties of concrete,spacing of the grid strips, orientation and strength of the grid. 33
Closing Remarks 34 Innovative use of FRP with careful analysis techniques will lead to significant advancements in design, construction and sustainability of precast concrete structures and bridges. Questions?