Windstorm Damage – Why Buildings Fail
The "envelope" of a building consists of the walls, roof, doors and windows. Damage from high winds increases rapidly as the envelope of a building begins to break down. From the first failure, whether it's a roof panel, a broken window or a door, the internal pressure within the building increases. This force, in combination with other forces can cause the roof to lift from the building. Wind and rain can then enter the building and, if the winds are strong enough, cause structural failure of the frame of the building.
In recent years work has been done with computer models to predict the failure of various types of buildings in high winds. The structure of a building envelope is composed of various components such as walls, studs, roofing, doors, etc. The types and strength of both the components and the connections between these components is critical to predicting the performance of the building envelope.
All components of the building envelope are analyzed. Doors, windows, types of roofing, etc. Also analyzed is each type of connection. Strength ratings are assigned to each connection and component. This process is an effort to identify the weakest connections and components.
When the data is entered into the computer model, thousands of simulations can be run on every type of building, under a wide range of wind speeds and other conditions. The result is a clear understanding of how the failure of one connection places increased stress on other connections and how a series of such failures, or the failure of a single component, can lead to a breach of the building envelope and potential structural failure.
Much envelope damage is cause by wind born debris. Smaller debris travels at greater heights and greater speeds than larger objects such as lumber, which travel at slower speeds near the ground. Some surface components such as roofing tiles, glass or vinyl siding can withstand high winds alone but not with the added impact of debris.
Research on the effects of wind born debris led to a growing realization of the importance of postimpact strength of components. Previous to this research, only the preimpact strength of components has been considered. Of all surface cladding materials, glass, even fully tempered glass, is the most susceptible to small wind born debris.
Wind born debris can also have a devastating effect on external insulation and finish systems. Hard cladding materials such as vinyl siding or asbestos cement may shatter from impacts. Soft external insulation may be pulled from the building envelope. Building officials have recognized the need for improved impact resistance in the newer building codes created after Hurricane Andrew. Testing standards for research and wind resistant products have also changed to reflect the reality of an impact followed by cycles of higher and lower pressures.
Many years of research into high wind damage and wind born debris have revealed the importance of the building envelope. This research has led to several important changes in building design. First, that the design and components of the building envelope must be given the same importance as the structural frame. Second is that the critical effect of wind born debris must be addressed in the building design process. Third is the idea that the postimpact performance of building envelope components be considered equally with preimpact performance. Together, these changes will help preserve the building envelope,and help reduce building damage and failure.
Shop here for top brand name cordless power saws:
Post Footer automatically generated by Add Post Footer Plugin for wordpress.
Tags: construction, engineering, Home Improvement, structural engineering
February 17 2009 04:13 am | Home Improvement