The Wood Research and Development has developed and designed a quadraxial fiber-reinforced plastic panel to retrofit the in-service utility poles damaged by natural loads over their lifetime.  This retrofit restores damaged sections to their original strength.  The Institute has conducted extensive researches, analyses and experimental testing to evaluate the stresses and the modes of failure in the utility pole due to those loading conditions.  Finite element analysis of the utility pole encased with reinforcement has determined the stresses induced in the pole due to the bending load and to the expansion of the pole with changes in moisture content.  The parameters gathered from analysis and testing were used in the design and optimization of the retrofit panel.  The product thus developed has been used in field ever since all across the United States .

The development of utility pole retrofit panel includes four stages:

a.       Identifying the design parameters.

b.      Calculating and measuring the design values.

c.       Design of Panel

d.      Optimizing the cost.

The two significant mechanical strength characteristics identified in the design of a retrofit for Utility Poles are:

a.       Longitudinal tension and compression strength to resist the stresses induced by bending of the pole.

b.      Hoop tensile stresses induced by expansion/contraction of the pole from change in moisture.

Figure 1. Full Scale Testing of Reinforced Utility Pole.

The magnitude of stresses induced in the utility pole and the retrofit panel were calculated and measured by physical testing of the pole. Full scale testing of the pole was performed by Wood Research and Development and test data was used in calibrating the finite element model.

            Figure 2. Strain Instrumentation for the Pole and Reinforcement at the Ground-line.

                              
A finite element model of the Utility Pole was developed to compare with the strain data obtained from physical testing of the pole.  The model was then used to determine stresses induced in the retrofit due to periodic changes in moisture content of the utility pole.

            Figure 3.  Finite Element Model of the Utility Pole encased with Retrofit Panel

Carbon: 

Aramid:  Small areal weights oriented in the 45^o directions to provide shear resistance. 

Fiberglass:  Oriented in the longitudinal direction to resist compressive and tensile stresses developed due to the bending of the pole.  Additional fibers also oriented in the 45^o directions to resist shear.

Optimization

The areal weights of fibers in each direction were determined using cost optimization software.  The final product thus obtained is an optimized quadraxial hybrid retrofit panel of requisite strength.

Description of the product  

The retrofit panel is wrapped around the pole in three to six layers, covering a length of five to eight feet depending upon the dimensions of the utility pole and degree of damage. Figure 4 shows the retrofit panel installed on a utility pole.  The mechanical and physical properties of the panel tested from our quality control are listed in the FiRP® Panel Specification Sheet attached.