Date of Award

2016

Document Type

Open Access Thesis

Department

Mechanical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Michael Sutton

Abstract

It has been documented that the sealant between asphalt roof shingles may delaminate at significantly lower wind speeds than those for which they are rated, with major consequences on safety and repair costs. In perspective, developing more resilient material systems and devising more effective installation procedures are sensible strategies to mitigate this problem. A practical approach may also entail adding a second self-sealing strip. In the first portion of this thesis, the elastic structural response of an asphalt roof shingle-sealant system consisting of individual three-tab shingles, which are bonded to the underlying shingles with two sealant strips and are subjected to uplift pressures that are produced by high wind loads, is simulated using a beam-on-elastic foundation (BOEF) model. The introduction of an additional sealant strip compared to conventional one-strip configurations is investigated to understand the effectiveness in resisting high wind loads (e.g., Category 4 hurricanes). Specifically, the two-sealant strip BOEF model is used to (a) estimate the applied energy release rate, G, along the edges of each sealant strip and (b) study the influence of sealant strips location and out-of-plane stiffness. It is found that standard three-tab shingles can be designed to optimize the position of two sealant strips, resulting in maximum G values that are approximately fourteen times smaller than those in conventional (one-sealant strip) counterparts. In addition, the maximum G values are far less sensitive to changes in sealant stiffness. The results of this study suggest that, from a mechanical standpoint, the addition of a second self-sealing strip is an efficient means to radically increase resiliency against high wind loads, and offset detrimental aging effects.

Since the sealant material is a form of bitumen, it is well known that such materials exhibit viscoelastic behavior when subjected to mechanical loads over an extended period of time. Thus, if the sealant system used in an application does not fail elastically during the early stages of loading, then its ability to sustain prolonged mechanical loading over an extended period of time without failure must be considered. This is particularly true for shingle systems when subjected to hurricane force winds that may last for several hours. Thus, the second portion of this thesis addresses the time-dependent response of the sealant material used in asphalt shingles. The viscoelastic properties of the sealant material were characterized through several creep compression tests and the use of Time-Temperature Superposition principles. The resulting viscoelastic properties were then used to create finite element analysis models in order to simulate the transient response of single and double sealant asphalt shingle structures subjected to uplift pressure loading that they would encounter during Category 4 hurricanes. Using beam elements on a viscoelastic foundation to perform simulations, it was determined that single sealant asphalt shingles will fail somewhere in between 4.1 and 4.3 hours when subjected to expected pressure loading conditions, while shingles with two sealant strips will require far more than 5 hours to approach failure conditions.

Share

COinS