Wind damage to wood-frame houses with gable roof: Analyses of failure, building code and cost

High winds are the most costly natural hazard in the United States, and the damage is increasing due to increased housing construction and lack of improvement in wind resistance of wood-frame houses. Most post-disaster investigations conducted in the past tended to be general observations. No documented detailed analysis for the failure mechanism of wood-frame joints or calculation of damage wind speed was found. To improve the performance of wood-frame houses, an appropriate research focused on the modes of failure and the methodologies to predict wind damage is needed.; This study examines systematically the weakness of existing wood-frame houses in resisting high winds. The study points out and analyzes several failure mechanisms (modes) not usually investigated in detail, and it shows how to determine the corresponding wind speeds that produces failure.; It is assumed in this study that most of the houses failed in high winds due to failure of joints. The pertinent equations for predicting the failure of such joints under wind loads were derived first. Then, computer programs were written for analyzing the wind forces on joints. The resisting capacities of nailed joints and sheet-metal joints were calculated. The wind load data were compared with the resisting capacity of nailed joints and sheet-metal joints. It was found that the sheet-metal joints usually performed better than nailed joints in high winds. The results obtained from a comparison of wind load with joint resistance capacity determine the adequacy of each type of wood-frame joints under different wind speeds. Using information on winds given in ASCE7-88 (Minimum Design Loads for Building and Other Structures), the adequacy of various joints in various geographical regions was determined. This made it possible to determine in this study the adequacy of prescriptive requirements in U.S. building codes. The results show that the prescriptive standards agree with the performance standards in certain cases and geographical regions in the United States, and disagree with each other in other cases and regions.; Toenails are commonly used by builders and allowed by building codes due to ease of installation and low costs. In contrast, sheet-metal connectors (hurricane clips) offer higher strength but are used only in special wind regions because they are more laborious to install. This study examined the cost of using hurricane clips instead of toenails for certain wind-sensitive critical joints of wood-frame houses, and compared the incremental cost of using hurricane clips with the incremental cost of potential wind damage due to use of toenailed joints. It was found that the additional cost incurred by using hurricane clips is negligible compared to the avoided damage cost to the house due to their uses. One may conclude from this study that some prescriptive standards in contemporary building codes are unsafe and inadequate. It can also be concluded that using hurricane clips instead of toenails in many situations pays off not only from safety standpoint but also based on economics.