Significance and Use
5.1 This standard procedure facilitates determination of the thickness of a glass construction required to resist a specified design load with a selected probability of breakage.
5.2 For optical purposes, ATCT cab glass typically utilize only annealed glass products. For this reason, some specifying authorities mandate its use and prohibit heat-strengthened and tempered glass in control cabs. This standard procedure therefore addresses the following glass constructions: annealed monolithic, annealed laminated, and insulating glass fabricated with annealed monolithic or annealed laminated glass, or both. In cases where the specifying authority approves the use of heat-strengthened or fully tempered glass in the control cab or in areas where optical characteristics do not apply but are deemed critical to the facility operation, the NFL values obtained from standard may be adjusted using appropriate Glass Type Factors (GTF) and procedures for their use as specified in Practice .
5.3 Use of these procedures assume:
5.3.1 The glass is free of edge damage and is properly glazed,
5.3.2 The glass has not been subjected to abuse,
5.3.3 The surface condition of the glass is typical of glass that has been in service for several years and is significantly weaker than freshly manufactured glass due to minor abrasions on exposed surfaces,
5.3.4 The glass edge support system is sufficiently stiff to limit the lateral deflections of the supported glass edges to less than 1/175 of their lengths. The specified design load shall be used for this calculation, and
5.3.5 The center of glass deflection shall not result in loss of edge support. Typically maintaining center of glass deflection at or below the magnitude of three times the nominal glass thickness assures that no loss of edge support will occur.
5.4 Many other factors affect the selection of glass type and thickness. These factors include but are not limited to: thermal stresses, the effects of windborne debris, excessive deflections, behavior of glass fragments after breakage, seismic effects, heat flow, edge bite, noise abatement, potential post-breakage consequences, and so forth. In addition, considerations set forth in federal, state, and local building codes along with criteria presented in safety glazing standards and site-specific concerns may control the ultimate glass type and thickness selection.
1.1 This practice covers the determination of the thickness of glass installed in airport traffic control towers (ATCT) to resist a specified design loading with a selected probability of breakage less than or equal to either 1 lite per 1000 or 4 lites per 1000 at the first occurrence of the design wind loading.
1.2 The procedures apply to common outward sloping cab glass designs for which the specified loads do not exceed 15 kPa (313 psf).
1.3 The procedures assume control tower cab glass has an aspect ratio no greater than 3.
1.4 The procedures assume control tower cab glass has an area no less than 1.86 m2 (20 ft2).
1.5 The use of the procedures assumes the following:
1.5.1 Monolithic and laminated glass installed in ATCTs shall have continuous lateral support along two parallel edges, along any three edges, or along all four edges;
1.5.2 Insulating glass shall have continuous lateral support along all four edges; and
1.5.3 Supported glass edges are simply supported and free to slip in plane.
1.6 The procedures do not apply to any form of wired, patterned, etched, sandblasted, or glass types with surface treatments that reduce the glass strength.
1.7 The procedures do not apply to drilled, notched, or grooved glass.
1.8 The procedures address the determination of thickness and construction type to resist a specified design wind load at a selected probability of breakage. The final glass thickness and construction determined also depends upon a variety of other factors (see ).
1.9 These procedures do not address blast loading on glass.
1.10 These procedures do not apply to triple-glazed insulating glass units.
1.11 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.
1.12 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and to determine the applicability of regulatory limitations prior to use.
1.13 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.