TP24-07 A Comparison of the New LRFD Design Standard for FRP and Current ASD Practices

Field erected stick built cooling towers until the early 1980’s, were principally constructed of pressure treated wood products.  Until the 1980’s the lumber of choice had been old growth Redwood.  Due to certain environmental concerns though, old growth Redwood became difficult to obtain and Douglas-Fir became the common choice of material.  It was also at that time that Pultruded Fiberglass (FRP) started to make inroads into the cooling tower market. As FRP was becoming more popular, CTI developed STD-137 which was first published in 1988.  This new standard defined physical properties for the pultruded products along with the mention of mechanical properties, design criteria, workmanship, and inspections.  CTI continued with development of reference material for use with FRP with the publication of ESG-152 “Structural Design of FRP Components” in 2002.  This guideline provides some of the basic design information for use in designing a cooling tower using Allowable Stress Design (ASD) philosophy. This paper will compare the design of a cooling tower using ASD with the ASCE standard “Load and Resistance Factor Design (LRFD) for Pultruded Fiber Reinforced Polymer (FRP) Structures” which as of this writing has been approved and is awaiting publication. It will also touch on the limit state design standard that has been approved in Europe by the European Committee for Standardization.