Analysis of the window damaging mechanism in windstorms



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Texas Tech University


Studies of the behavior of window glass in windstorms have revealed that significant numbers of window glass failures may be attributed to windborne missiles. In addition to detailed discussions of the role of windborne missiles in window failure incidents, the presentation includes (1) an analysis of the character and dynamic properties of the damaging missile, (2) an analysis of window glass response to wind pressure acting in conjunction with missile impact, and (3) a discussion of the innovative process through which results of the investigation must pass in order to reach professional practice.

Surveys of 54 rooftops in two urban areas suggested that large quantities of loose gravel present a potential hazard to adjacent glass curtain walls in multistory buildings. Dynamic analyses of the average rock size (0.61 gm) reveal that windspeeds in the 80-120 mph range can easily lift and propel roof gravel at speeds up to 90 fps -- missile speeds that are well within the range of impact speeds that will break glass.

Extensive treatments of window glass response under conditions of uniformly distributed wind pressure acting in conjunction with small missile impact constitute the second major part of the presentation. Theoretical and experimental methods are employed to evaluate the response of two representative sizes of square glass windows (1 sq ft and 6 sq ft) to impacts from two representative sizes of missiles (0.61 gm and 5.55 gm) under several conditions of superposed wind pressure. Theoretical methods are advanced which characterize the response phenomena, and which permit predictions of failure modes. Experimental evaluations are presented to verify the theoretical characterizations of response, and to provide specific information regarding glass breakage phenomena under the loading conditions considered. It is concluded from these analyses that: (1) statistically average roof gravel missiles will break window glass at mean minimum impact velocities in the 40-60 fps range, (2) the presence of wind pressure coincident with missile impact will reduce the mean minimum impact velocity necessary for failure under certain missile size and glass geometry conditions, and (3) The presence of wind pressure coincident with missile induced glass fracture will assure total shattering of window glass panels in a high precentage of such impact incidents.

The final part of the presentation contains discussions of important technological factors identified by the research and an outline of the innovative process involved with integrating the research into professional practice. It is concluded that roof gravel is available, it menaces glass windows in multistory buildings, and it can be lifted and propelled by winds with sufficient momentum to break windows. Conclusions related to glass failure mechanisms in windstorms have long range implications for the development of new glass design procedures. Development of these procedures and their acceptance by the architectural and engineering professions will involve a long "innovative process." It is concluded that additional research, extensive professional involvement, and active involvement with the building code and standard activity will be required to move new glass design technology into professional practice.



Windstorms, Windows, Glass -- Research