Introduction
The fixed panels of interior glass partitions, mounted or restrained on only two sides (top and bottom), require special design considerations:

Glass held only on two sides is much more flexible than glass supported on all four sides. If the glass is too thin, small fluctuations of interior air pressure can cause the glass to tremble or shimmer. People pushing or leaning on glass that is too thin will noticeably deflect the glass. As the unsupported span or height of the glass panels increases, the glass thickness must also increase to maintain a reasonable stiffness.

Table 1 below shows the recommended minimum thickness of fully tempered glass for various glass heights used in interior butt-glazed, fixed-glass panels.

Recommended Minimum Thickness for Fully Tempered Glass Used in Butt-Glazed, Fixed Interior Panels mounted or restrained at Top and Bottom only.

Cautions
The following cautions are not addressed in any way by Table 1 above. BOCA's model National Building Code, Section 2402.3, states, regarding interior glazed areas: "Where interior glazing is installed adjacent to a walking surface, the differential deflection of two adjacent unsupported sides will not be greater than the thickness of the panels when a force of 50 pounds per linear foot is applied horizontally to one panel at a point up to 42 inches above the walking surface." Thicknesses shown in Table 1 above WILL NOT MEET the BOCA code for adjacent panels not linked together by adequate silicone or permanent clips. Table 2, on the following page, shows the recommended minimum thickness of fully tempered glass required to meet the BOCA code for panels that are not linked together to prevent differential deflection greater than the panel thickness.

Silicone joints or permanently clipping adjacent panels do not add to the structural strength or rigidity of the assembly and do not permit the reduction of the recommended thickness shown in Table 1 above.

Open narrow joints between butt glazed glass panels may catch or pinch fingers. The best preventative is to avoid open joints by filling them with silicone. An alternative is to install permanent clamps approximately every four feet to couple the adjoining panels together to prevent relative movement between panels. The gap between panels with unfilled joints should be such that fingers cannot be inserted and trapped.

Table 2
Recommended Minimum Thickness for Fully Tempered Glass to Meet BOCA Requirements (Section 2402.3) for Interior Partitions

Interior Applications
Heavy glass doors are becoming increasingly popular for interior applications. Although wind load is not a consideration, other types of structural loading may limit the size of interior doors. Interior, fully tempered glass sidelite panels are not always sealed. See Appendix I of the GANA Tempered Glass Engineering Standards Manual for additional information regarding height and thickness recommendations for fully tempered interior, butt-glazed glass panels. Traffic volume for interior applications needs to be considered, as with exterior applications. Interior doors are often locked in both the open and closed position, eliminating the need for closers. Structural design of fully tempered all-glass interior entrance systems is discussed in detail in the GANA 1999 Fully Tempered Heavy Glass Door and Entrance Systems Design Guide.

Door Size Limitations
Door sizes need to be limited due to glass flexibility and hardware limitations. Closers and pivots have weight limitations. Doors that are too wide are difficult to control in windy conditions and may exceed hardware limits. Larger doors may be used when locked open or infrequently used. Full rails, top and bottom, are recommended for larger door sizes. (See Table 3.)

Types of Glass
Glass in fully tempered heavy glass doors and entrances is clear or tinted monolithic, fully tempered float glass complying with standards defined in ASTM C1036 and C1048. Typical heavy clear float glass thicknesses used include 3/8" (10 mm); 1/2" (12 mm); and 3/4" (19 mm). Tinted (gray and bronze) heavy float glass thicknesses used include 3/8" (10 mm) and 1/2" (12 mm).

The exposed vertical edges of the glass are ground and polished prior to tempering the glass. Holes for handles and patch fittings must be drilled in the glass prior to tempering. The diameter of these holes is usually slightly larger than the thickness of the glass. See ASTM C1048 for glass fabrication guidelines.

Table 3: Recommended Maximum Interior or Exterior Swinging Door Sizes

Fully Tempered Glass Transoms

Fully tempered glass transoms are those fixed glass panels immediately above the door opening, and often span between the top of the doors and the finished ceiling. These fully tempered glass transoms can be incorporated into the glass entrance using patch fittings or other transom support methods. Large-size glass transoms using patch fittings may require mechanical fastening to the ceiling structure, based on weight, size and other design considerations. (See pages 23-26.)

Fully Tempered Glass Stabilizer Fins

With all glass transoms and sidelites, perpendicular, fully tempered heavy glass mullions, sometimes called fins, may be mounted from the ceiling to the bottom of the transom to reduce the amount of deflection of the glass entrance. The fin must be mechanically fastened and anchored to the overhead load-carrying structure. Suspended ceilings do not provide an adequate structure for the attachment of stabilizer fins. Typically these glass fins are made using 1/2" (12 mm) or 3/4" (19 mm) thick fully tempered glass. See pages 23-26 for structural design criteria for the design and use of glass stabilizer fins.

Structural Design of Interior Glass Entrance Systems

One of the primary purposes of this design guide is to ensure that the designer has considered the structural limitations of the glass and metal fittings, so that the fully tempered entrance system will function satisfactorily and safely. Fully tempered all-glass entrance systems using patch fittings were originally designed in Europe and were used in both interior and exterior installations. Interior glass is not subject to uniform wind loading, other loading criteria had to be developed.

Many interior entrances are designed with the glass panels supported at the head and sill only and without additional mullions or other lateral support. Because the glass panels of interior glass entrances and partitions are mounted or restrained on only two sides (top and bottom), they require special design considerations. Glass held only on two sides is much more flexible than glass supported on all four sides. If the glass is too thin, small fluctuations of interior air pressure, or the operation of a door can cause the glass to tremble or shimmer. Persons pushing or leaning on glass that is too thin will noticeably deflect the glass. As the unsupported span of height of the glass panels increases, the glass thickness must also be increased to maintain a reasonable stiffness. In this design guide we have separated the design considerations into two-sided support and three-sided support. Uniform horizontal pressures or other interior loading criteria are not clearly defined in most building codes. The National Building Code (BOCA) limits the differential deflection of two adjacent unsupported sides of the interior glass panels. The recommended minimum thickness of fully tempered glass required to meet the National Building Code (BOCA) for adjacent panels that are NOT linked together to prevent differential deflection is shown in Table 2 of Section 11 of the GANA Tempered Glass Engineering Standards Manual. By permanently clipping adjacent panels or siliconing the joints of adjacent panels, the thickness limits shown in Table 1 (Section 11 of the GANA Tempered Glass Engineering Standards Manual) can be used.

Two-Sided Support

Based upon the recommendations shown in Table 1 of the GANA Tempered Glass Engineering Standards Manual, the maximum height of heavy glass sidelite panels is as shown below in Figure 20.

Most fully tempered all-glass interior entrance systems are designed using 1/2" (12 mm) thick fully tempered glass; the following design examples are for 1/2" (12 mm) thick fully tempered glass. The structural loading criteria used for two-sided supported panels in this design guide were developed using the force developed by the weight of the glass doors being opened 90� to the plane of the entrance as the primary design load for these interior applications. This load is often greater than the 0.25-0.5 kPa (5 to 10 PSF) interior design load often stated in building codes. When a sidelite is located adjacent to a door, this sidelite is often required to support the weight of an operating glass door. If this sidelite is too narrow, it doesn't have sufficient strength to support the weight of the door without deflecting (flexing) to the point where the toe of the door will drag on the floor as it is opened. The chart in Figure 21 is furnished using common door sizes. This chart is constructed so that if the glass door toe deflects downward more than 1/4" (6 mm) due to the weight of the door, the sidelite is too flexible. If this occurs, the design must be changed either by securing the jamb of the sidelite to provide three-sided support or by adding fully tempered stabilizer fins.

In order to determine if fins are (or are not) required for an interior glass entrance system with two-sided support, the door width and transom height must be known. See "T" (transom height) and "W" (sidelite width) in Figure 20. The maximum height for 1/2" (12 mm) glass is 120" (3 m), as shown in Figure 20, and must not be exceeded. As can be seen in the chart, the minimum width for a sidelite that must support the weight of the door is 12" (305 mm). Use "T" and "W" in the chart below (Figure 21) to establish a reference point. If this reference point is below the door width line in the chart, fins are not required. If this point is above the line, fins are required to provide additional lateral stability for the entrance.

Three-Sided Support

Often an interior glass entrance can be supported structurally at the jambs, as well as at the head and sill, as shown in Figure 22. Three-sided support is obtained with the addition of structural members on the vertical edges of the sidelites adjacent to the doors. If the glass sidelite is structurally supported on three sides, it will deflect much less than when it is supported only at the top and bottom. Narrower sidelites are stiffer because they are also supported at the jambs. It is also possible to provide a structurally supported edge for a sidelite by making a 90� corner so that the perpendicular sidelite becomes a full-height structural stabilizer for the adjacent sidelite. Structural silicone is often used to connect the glass corner to provide structural adequacy, but 90� patch fittings and clamps can also be used to stabilize the corners.

If the sum of the height of the transom "A" plus the width of the sidelite "B" is 72" (1,830 mm) or less, the stabilizer fins are not required. (A + B < 72" [1,830 mm], fins are not required). The traditional method of analyzing the requirement for structural glass stabilizer fins was developed in Europe more than 20 years ago. The European method of determining fin requirements is more conservative than this formula, because it was used for both interior and exterior openings with low-wind-load design. The European formula that has been used is that if A + B < 48" (1,200 mm), fins are not required.

If the entrance is to be used heavily or additional stability is desired, a more conservative formula could be used, so that fins would be required for smaller openings. Conversely, in applications (such as interior malls) when the doors are locked, open all-day stabilizers may not be needed because of the limited use of the doors. The design professional must consider glass strength and deflection for both two- and three-sided glass support using this analysis to determine glass fin requirements.

Stabilizer Fins

In most interior applications a 12" (305 mm)- deep 1/2" (12 mm) glass mullion is adequate for transom/fin heights of up to 24" (610 mm). If the transom/fin height is greater than 24" (610 mm), the fin width at the top will need to increase, as shown on Figure 23. The top of the stabilizer fin must be securely fastened to a rigid structure at the top of the assembly, usually by means of back-to-back metal angles clamped to the fin using gaskets and through bolts. Two bolts are sufficient for fins up to 36" (1 m) high, but three or more bolts will be required for higher and deeper stabilizer fins.

Even with glass stabilizer fins, the recommended maximum height limit for 1/2" (12 mm) fully tempered glass is 168" (4.2 m) for three-sided, supported interior applications, and even less for exterior applications depending on the wind load. Fully tempered glass transoms using patch fittings may also require a mechanical fastening to the ceiling structure due to the weight of the glass transom.