Semester

Spring

Date of Graduation

2024

Document Type

Problem/Project Report

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Hota GangaRao

Committee Co-Chair

Ruifeng (Ray) Liang

Committee Member

Chao Zhang

Abstract

The Fiber Reinforced Polymer (FRP) composite utility poles and crossarms have been getting wider attention from the utility industries because of their advantages over the traditional wooden, concrete, and steel poles. Wood is vulnerable to fire, rot, and animal damage. Concrete poles are heavier, increasing both transportation and installation costs of the poles, in addition to limited-service life (40-50 years). Similarly, steel poles have durability and safety concerns because of their inherent corrosive nature and conductivity. These disadvantages are significantly reduced by the use of FRP composites in utility structures because of FRP’s strength, specific gravity, flexibility, non-conductivity and durability against insect damage and corrosion. In addition, FRPs are superior to steel or concrete in mechanical performance per unit weight and have better fire retardancy. Despite the surge in the adoption of the FRP utility structures, their performance against wildfire is still fully understood yet. The number of wildfires is increasing more than ever in the US, and the utility structures are collapsing due to high intensity and longer duration of wildfires. Hence, it is essential to understand the performance of the FRP utility structures against wildfire and increase their fire performance by implementing robust fire-mitigation methods.

West Virginia University Constructed Facilities Center (WVU-CFC) proposed to develop a small-scale test method to simulate wildfires for varying temperatures and duration. The simulated wildfire testing leads to a better understanding of the performance of FRP utility poles and crossarms when exposed to wildfire-induced thermal environments. The change in the mechanical properties of the FRP utility structures under simulated wildfires at elevated temperatures of around 10000 C for various flame exposure durations was first determined, and then different fire mitigation strategies were evaluated for their effectiveness in improving the performance of the FRP utility poles. The composite pole specimens studied were categorized into two Batches: Batch A and Batch B, wherein Batch A samples from four pole manufacturers were tested with and without intumescent coatings, while Batch B poles were subsequently acquired from two additional manufacturers to evaluate protection methods. These methods are the use of intumescent coating and fire protective sleeve. Crossarms were also classified into Batch A and Batch B. Batch A comprised six crossarms from different manufacturers, and Batch B consisted of just one crossarm.

For both batches, test samples were first exposed to propane gas flames regulated to be around 1000°-1100°C for 1, 2, and 3 minutes without any intumescent coating. Then, the unburnt sections of the poles from both batches were carefully coated with intumescent paint. The coated sections were again subjected to gas-regulated flames. Additionally, Batch B-sleeved poles (uncoated) were also subjected to flame aimed at the sleeves covering the pole samples. Batch A crossarm samples were subjected to flame without intumescent coating, while Batch B crossarm was subjected to flame with and without intumescent coating. Coupon test specimens were cut from the post-burn sections of both pole and crossarm samples and tested for their mechanical properties under three-point bending and short beam shear test methods as per ASTM D790-17 and ASTM D2334/D2344M-16, respectively. Then, both the bending and short beam shear strengths were compared to the strengths of unburnt poles and crossarms.

For both batches, test samples were first exposed to propane gas flames regulated to be around 1000°-1100°C for 1, 2, and 3 minutes without any intumescent (fire protection) coating. The unexposed (to fire) sections of the poles from both batches were carefully coated with intumescent paint. The coated sections were subjected to the gas-regulated flame. Additionally, Batch B-sleeved poles (uncoated) were also subjected to the flame aimed at the sleeves covering the pole samples. Batch A crossarm samples were subjected to flame without any intumescent coating, while Batch B crossarm was subjected to flame with and without intumescent coating. Coupon test specimens were cut from the burned sections of the pole and crossarm samples and tested for their mechanical properties under three-point bending and short beam shear test methods as per ASTM D790-17 and ASTM D2334/D2344M-16, respectively.

The bending strength and short beam shear strength were compared to the unburnt poles and crossarms. The results indicate that the bending strength or short beam shear strength of uncoated (unprotected) poles decreased as a function of burning duration, and their reduction trends depended on sample thickness, fiber volume fraction, fiber architecture, fiber type, filler content, manufacturing method, etc. These parameters varied from one manufacturer to another, based on burn test data of the samples. The results showed significant protection offered by coatings as well as sleeves against any degradation in mechanical properties of FRP poles and crossarm. The fire-resisting capacity is attributed to the expanding nature of the intumescent coating, which, upon exposure to fire, expands and creates a thermal insulating barrier that mitigates the degradation effect of thermal damage to the composite poles and cross arm. Furthermore, the fire-protective sleeves were deemed to have sufficient thickness to stop the penetration of the flame into the core of the poles.

Embargo Reason

Publication Pending

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Available for download on Friday, April 25, 2025

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