This report details Phase II of the study titled Strengthening of Bridge Wood Piling Retrofits for Moment Resistance. Phase I of the research (project

R27-082) was focused on developing a load rating method for timber piles under eccentric load and examining FRP retrofitting of pier piles.

However, Phase II focused first on numerically assessing the state of the practice of timber pile retrofitting in Illinois. The study next focused on

investigating load rating and FRP retrofitting of abutment timber piles as well as studying the long-term performance of FRP-wrapped timber piles.

Historically, timber piles have been designed for axial loads only. Under this assumption, conventional load rating procedures considered only the

effect of dead and live loads in determining the capacity of a timber pile. Unlike pier timber piles, abutment piles must resist significant lateral

forces from earth pressure and surcharge loads in addition to dead and live loads. Currently, there does not exist a separate load rating procedure

for abutment timber piles. In this study, a load rating method was developed specifically for abutment timber piles. The combined loading effects

were accounted for by using the allowable stress P–M interaction equation in the National Design Specification for Wood Construction (NDS). In

addition, a method was developed to account for the effect of FRP retrofits in the load rating. The results showed that deterioration levels as low as

10% could lead to unsatisfactory load ratings for abutment timber piles depending on the backfill soil type and equivalent fluid pressure assumed.

FRP retrofitting, however, increased the load rating of deteriorated abutment timber piles by at least 17%. FRP retrofitting techniques for abutment

piles were also examined experimentally. Three full-size timber pile specimens with different levels of deterioration were tested. A nondestructive

stress wave timing method was used to assess the condition of each specimen. FRP retrofits were designed for two of the specimens based on the

results of the condition assessment. The piles were load tested in the axial direction. First, a specified eccentric load was applied to induce a

bending moment, then a concentric axial load was applied until the proportional limit. Each pile was tested under a series of eccentric loads varying

from 10 kips to 35 kips. Timber condition normalized test results showed that the FRP retrofit was able to at least restore the properties of the piles

to their undeteriorated condition properties. Finally, the long-term performance of FRP-wrapped timber piles was studied by examining their

performance in uniaxial compression after exposure to long-term degradation. Field-extracted red oak pile specimens with different degrees of

initial deterioration were used in the study. The initial condition of the timber was assessed through stress wave timing. To simulate natural

degradation in unretrofitted and retrofitted timber piles caused by environmental exposure in a short period of time, an accelerated aging

procedure was used. The number of FRP layers and type of resin used (polyester, standard epoxy, and moisture-tolerant epoxy) were varied.

Results showed that accelerated aging induces significant deterioration in unretrofitted timber piles but the effects are relatively minor in the FRP-wrapped

specimens. It was also proven that FRP composite can significantly improve the performance of timber piles in terms of peak stress and

ductility, even after being subjected to extreme degradation.