TIMBER REPAIRS WITH FRP

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1 TIMBER REPAIRS WITH FRP by Vijaya (VJ) Gopu, Ph.D., P.E Associate Director External Programs, LTRC Matthew G. Stuller Endowed Professor, UL Lafayette Formosa Plastic Endowed Professor Emeritus, LSU 2018 Louisiana Transportation Conference February 26, 2018

2 Background FRP systems have been used in the field to repair timber piles, but highway engineers lacked tools to predict strengths of variety of FRP systems in the market.

3 Objectives Determine the failure modes of FRP repaired timber piles Determine the ultimate strengths related to these failure modes for a variety of FRP systems via laboratory testing

4 Organization of Presentation Failure Modes Test Development and Methodology Analysis and Discussion Conclusions

5 Failure Modes of FRP Wrapped Timber Timber compression: Piles Assumed failed in a rehabilitation situation (zero capacity) FPR/timber bond failure Slippage would allow significant deflection in the pile under loading Local compression of wrap Local compression failure in FRP would result in dramatic strength reductions Euler buckling of wrap Spans not long enough to experience Euler buckling Neglected for the purposes of this study

6 Materials: Glass FRP Wraps System Fabric Resin Tensile (psi) Fyfe Uni (27 oz/yd^2) Epoxy 83,400 Sika Uni (27 oz/yd^2) Epoxy 88,800 Aquawrap Bi (22 oz/yd^2) Polyurethane 45,400 Phenolic Bi (18 oz/yd^2) Phenol Formaldehyde N/A Simpson Strong Tie Uni (27 oz/yd^2) Epoxy 56,000

7 Materials: Timber Specimens Creosote Treated 10 to 12 Diameter Cut by hand with chain saw Cuts produced were not square or flat due to the lack of a guiding mechanism. Influence of the non-square cuts will be discussed.

8 Push out Tests (bond shear) Objective: determine relationship between bond length and bond shear strength to be used in future designs Tests Conducted: Each FRP system on new creosote treated pile samples 6 and 12 bond lengths Three layers of wrap Comparison of bond capacity with capacity of new timber piles

9 FRP Shell/Grout Bonding Study Evaluated bond shear strengths of timber grouted in FRP shells Pushed out timber until bond slippage

10 Bond Test (Push Out) Development Wet layup fabrics are not stiff enough to hold shape therefore a removable mold is required to produce the gap FRP can crush prematurely on hard surfaces requiring supplemental support at the base

11 Basic Bond Test

12 Bond Test Configuration by

13 Compressive Failures Occurred when bond strength passed compressive capacity of wrap Effected samples: 12 Aquawrap Adjusted for in other systems with additional wraps around the gap region Failure was test method related Field installation will not have bearing surface failures

14 Eccentric Loading Non-square loading surface from cutting led to uneven load distribution through the bond Resulted in premature failures Effected system: 12 Phenolic Elastomeric padding added to correct eccentricity on one sample

15 Primer/Resins System Viscosity Working Time Primer Timber Retained on Wrap after tests Fyfe cps 6 hour Epoxy Phenolic cps 1 hour Phenolic Deeper (1/8" - 1/4") Superficial (< 1/32") Aquawrap Prepreg 30 minute Water Very Limited

16 Summary of Influences Factor Samples Influence Resin/Primer Aquawrap (All) Limited timber failure Fabric Stiffness Compressive Failure Aquawrap (All) Aquawrap (12") Lack of full surface bond No bond failure Eccentric Load Phenolic (12") Reductions up to 6 kips

17 Average Results System Strength (psi) Capacity (kip) 6" 12" 6" 12" Failure Mode Fyfe Timber Aquawrap Bond Phenolic Timber Simpson Timber Sika Timber For a 10 pile, design capacity is around 96 kips Timber failure indicates FRP bond exceeds timber strength No system provides enough shear strength Longer bond lengths increase capacity but decrease strength Non-linear relationship

18 Pull-off Tests Objective: correlate tensile bond strengths to shear bond strengths Tests Conducted: Each FRP system on new pile samples Establish tensile pull off strength of FRP to timber bond Compare to bond push out testing Baseline timber strength on new piles Establish tensile pull off strength of timber Comparison to previous field data

19 Type Pull Off Summary Strength (psi) COV Typical Failure Mode Timber % Timber Fyfe % Timber Sika % Timber Aquawrap 28 45% Bond Phenolic % Timber In Service 36 25% Bond/Timber Each system tested on a single timber sample

20 Comparison with Push Out System Pull off Pushout Avg of 12 & 6 Fyfe Aquawrap Phenolic Similar influences present as bond pushout More pull off tests will be conducted to determine how different timber substrates influence the pull off values

21 Compression Tests Objective: determine relationship between wrap thickness and compressive strength Tests Conducted: Axial compression of each FRP system cast into hollow shells Three and Five layers of wrap Tensile coupon testing of each FRP system Three layers of wrap Comparison of compression and tensile strengths Comparison of lab strength values with published values Comparison of compressive capacity with capacity of timber piles

22 Compression Tests Created 9 diameter hollow shells Lengths roughly 24 Molds as shown were used

23 Compression Test Configuration

24 Cause: Eccentricities Off-centered placement of shell in Instron Result: Uneven distribution of loading Lowered compressive strengths Effected system: Fyfe A (placed off center)

Wrinkles created during wrapping Cause: Oversaturation of resin in fabric Difficult to secure oversaturated wraps to smooth mold Stricture

25 Wrinkles created during wrapping Cause: Oversaturation of resin in fabric Difficult to secure oversaturated wraps to smooth mold Stricture wrapping pulled fabric into wrinkle Result: Longitudinal misalignment of fibers Lowered compressive strengths Effected system: Fyfe C, D, F

26 Wrinkles

27 Eccentricities Cause: Non-square cuts during trimming of shells Result: Uneven distribution of loading Lowered compressive strengths Effected system: Sika B, D (non-parallel surfaces)

28 Failure Modes of Compression

29 Summary of Influences Factor Samples Influence Wrinkles Off Center Loading Fyfe C, D, F Reduced capacity by 20-30% Fyfe A Reduced capacity by up to 45% Non-Parallel Loading Surface Sika B, D Reduced capacity by 45, 20%, respectively Influences caused reductions Will be taken into account with knock down factors in final designs

30 Compression Results Three Five System Stress (psi) Load (kip) Stress (psi) Load (kip) Fyfe 14, , Sika 13, , Aquawrap 3, , Phenolic 5, , Simpson 11, Excluding those results with reduced values due to influences

31 Fabric Density and Wrap Thickness Assumption: fiber failure should control Systems with more fibers in the longitudinal directions should have equivalently higher capacities Comparing % of fabric density in longitudinal with Fyfe/Sika Phenolic: 50% and 55% (3 and 5 layers) Aquawrap : 61% to 67% (3 and 5 layers) Comparing % of compressive strength with Fyfe/Sika Phenolic: 33% and 50% (3 and 5 layers) Aquawrap : 21% and 34% (3 and 5 layers) Conclusions: More than three wraps of phenolic to develop compressive strength due to thinner fabric Aquawrap results reaffirms de-bond failure Fabric density in longitudinal direction (oz/yd^2) System 3 layer 5 layer Fyfe/Sika Aquawrap Phenolic 27 45

32 Coupon Testing

33 Compression vs Tension Assumption: Fiber Failure Compression and tension results should same strength order Fyfe -> Sika -> Aquawrap -> Phenolic Results: Compression results did not follow same trend as tensile Fyfe -> Sika ->Simpson -> Phenolic -> Aquawrap Conclusion: Compressive strength of Aquawrap determined by resin debond not fiber failure System Compression Tension Difference Fyfe 14,511 59,719-76% Sika 13,809 43,579-68% Simpson 11, Aquawrap 3,018 35,436-91% Phenolic 4,716 32, %

34 Differences between published values System Tested Published Difference Fyfe 59,719 83,400-28% Sika 43,579 88, Aquawrap 35,436 45,400-21% Phenolic 32,692 N/A N/A Tension strengths lower due to: Fyfe and Sika coupons had 1/3 of fibers in the off axis No post curing Lower fiber volume fraction Compression testing to be completed to compare with published compressive strengths

35 Full Scale Rehabilitation Simulation

36 Rehabilitation Specimen Preparation Securing pile on pipe Trimming of foam Final sample

37 Rehabilitation cont.

38 Rehabilitation Simulations System Ultimate Comparing Compress Stress (psi) Bond Stress (psi) (Did not Fail in Bond) Failure Mode Load (lbf) Rehab Shell Rehab Pushout Fyfe 49,733 7,698 14, Phenolic 20,953 4,843 5, Compre ssion Compre ssion AquaWrap N/A 5, * 56 Bond Sika 44, , * 204 Simpson 12,500 11, Compre ssion Compre ssion * Conservative shear areas used. Precise shear stress unknown. Aqua wrap failed in bond, possibly due to poor wrapping. All other specimens failed in compression.

39 Rehabilitation Failure Modes Fyfe displayed lower strength: Stress concentration at the edge Varying wrap thickness around perimeter due to wrapping Overlap of seams Acetone used to dissolve the foam caused damage to composite Phenolic displayed higher strength: Thicker wrap Fabric overlaps were longer then the shell samples Closer to four wraps

40 Aged Bond Evaluation Purpose: Evaluate the effects of saturated/dry tide cycles on bond capacity. Samples saturated for 6 hours, air dried for 6 hours 4 month duration(sept 2017-January 2018) Specimen: Same as 12 bond specimens

41 Aged Bond Comparison System Strength (psi) Capacity (kip) Failure Mode Aged Original Aged Original Fyfe N/A Aquawrap N/A Phenolic N/A Simpson N/A Sika N/A

42 Filler Evaluation Purpose of Fillers: Seal cracks and fill voids due to rot and deterioration. Types of Fillers Crack fillers: high viscosity putties and resins, seal external cracks Bulk fillers: Low viscosity resins, combined with sand to fill large voids Injection fillers: Low viscosity resins, fill voids behind composite wraps

43 Crack Fillers Fillers: Elmers ProBond Wood Putty Simpson Strong Tie- Crack Pac Flex H20 Resin Sikadur 31 Hi-Mod Gel

44 Bulk Fillers Fillers: Phenolic Resin Rimline Polyurethane Foam Sikadur 35, Hid- Mod LV Resin/Sand Mixture

45 Injection Fillers Fillers: Sikadur Injection Gel Simpson Strong Tie Crack Pac Flex H20 Polyurethane Sikadur 35 Hi-Mod Lv Injection Fillers

46 Conclusions: Bonding The greater the bonding area, the higher the capacity (kips) but the lower the bond strength (psi) The Fyfe system displayed the best bond strengths for both push out and pull off tests indicating a superior resin system A possible explanation for the higher bond strengths is greater timber penetration due to the low viscosity and longer cure time of the resin when compared to the other systems Aquawrap displayed lower bond strengths which are attributed to a lack of a primer and rigidity of the wraps The phenolic systems did not show increases in capacity despite the increase in bond length None of the bond strengths were adequate to achieve the capacity of a new timber pile, although the 12 Fyfe bond was close to the pile capacity Bond tensile tests results correlated well with the bond shear strength and is a useful field verification test

47 Conclusion: Compressive Strength The more layers of wrap utilized was directly proportional to the compressive strength provided. The Fyfe, Sika, and Simpson systems provided the highest capacities with failure in the fibers The Phenolic system also failed in the fibers, and the strength is attributed primarily to a lower longitudinal fiber density, although the 3 layer samples may have had insufficient thicknesses to achieve their expected strengths. Aquawrap experienced debond between wrap layers and consequently had the lowest strengths. Five layers of Fyfe and Sika systems should be able to provide enough capacity for the wraps while more evaluation is needed to determine the number of layers for the other systems.

48 Conclusions: Aged Bonding Specimens were swollen due to water saturation This swell due to water increased bond strengths due to normal forces Thus, water saturation provides a mechanical advantage increasing pile capacity

49 Conclusions: Fillers Each type of filler worked well Crack fillers cured quickly and completed sealed cracks Bulk fillers were able to fill over 90% of internal cavities Injection fillers flowed well to small cavities Lessons learned are being incorporated into guide documents.

Use of FRP to Strengthen and Repair Marine Structures

Use of FRP to Strengthen and Repair Marine Structures ICRI Spring Convention March 2016 Presented by: Julie A. Galbraith, P.E. Simpson Gumpertz & Heger, Inc. www.sgh.com Presentation Outline The marine