RELIABILITY ASSESSMENT OF ROOF SHEATHING PERFORMANCE IN LIGHT WOOD FRAME STRUCTURES SUBJECTED TO WIND PRESSURE Maral Amini 1 , Bohumil Kasal 2 ABSTRACT: This paper presents a methodology for reliability assessment of roof sheathing panels in low-rise structures for predicted wind pressure distributions. Low-rise buildings encompass the majority of the residential structures in the United States. Predominantly, this category of structures is constructed with dimension lumber. Investigations after natural disasters report that during high intensity wind pressures, low-rise buildings with wood- frame construction are at immense risks of damage with the first sign of damage initiated from the roofs. Stochastic modelling is employed to investigate the effect of random variables such as nail withdrawal capacity, and missing nails on sheathing panels due to construction malpractice. Wind pressures are obtained from a full-scale structure test conducted in New Brunswick, Canada. This study combines analytical and stochastic modelling to develop a comprehensive understanding of wind and structure interaction. The developed methodology can be used as a tool to evaluate roof sheathing performance subjected to wind load. KEYWORDS: Stochastic modelling of low-rise roofs, Roof sheathing failure, Roofs subjected to wind pressure 1 INTRODUCTION 123 In the United States a significant portion of the population resides in low-rise structures. About 95% of the residential structures in the United States are low-rise buildings constructed with wood stud framing also known as light-frame buildings (LFB). The less desirable characteristics of light-frame buildings are low resistance to negative pressures (suction) and relatively high risks of damage during high winds. Reports from insurance companies present $10-15 billion in damage from wind to low-rise buildings [1]. Inspection reports from one of the most devastating natural disasters in the United States (Hurricane Andrew, 1992) reported that the first signs of damage are initiated from the roofs [2]. More particularly, surveys have shown that typical roof damages include roof sheathing nail withdrawal and loss of roof sheathing panels due to failure to comply with the required nail spacing [3]. During high wind events, structural integrity of low-rise buildings are highly affected after roof sheathing panels are damaged. This is due to the progressive damage caused by water intrusion, breach of the building envelope, and exposure to interior 1 Maral Amini, Department of Civil and Environmental Engineering, The Pennsylvania State University, 219 Sackett Building, University Park, 16801, United States. Email: mma202@psu.edu 2 Bohumil Kasal, Department of Civil and Environmental Engineering, The Pennsylvania State University, 222 Sackett Building, University Park, 16801, United States. Email: buk13@psu.edu pressure which ultimately lead to destruction of more structural members such as the walls. Economical and social impacts of disastrous failures of low-rise structures have ascertained the need for further research on the characteristics and performance of LFB structures. It is the objective of this study to develop a better understanding of the lateral load (wind) distribution on the roof of low-rise buildings and to deliver a methodology for reliability assessment of typical North American roofs. This study employs stochastic modelling of a typical North American roof to examine the effects of variable parameters such as nail withdrawal capacity and number of missing nails on sheathing panels. Pressure measurements from a full-scale structure at University of New Brunswick (UNB) are used to develop a series of generalized functions that represent pressure variation on the roof of classified low-rise buildings. Finally, the developed pressure distributions and the stochastic analysis are used to develop an analytical model. A few related studies have been undertaken to perform reliability and fragility assessments on roofs of low-rise structures. A two-part study was carried out by Cheng and Rosowsky [4] on the reliability of light-frame roofs in high wind regions. The first part focused on presenting the differences in design standards resulting in various wind loads on selected baseline structures. In the second part of their study, a reliability index for sheathing panels was computed by using advanced first order second-moment (AFOSM) techniques [5]. Another parametric study developed roof sheathing Amini, M., and B. Kasal, 2010. Reliability assessment of roof sheathing performance in light wood frame structures subjected to wind pressure. In Proceedings from the 2010 World Conference on Timber Engineering, Riva del Garda. Italy. June 2010.