Palram PALGAR - Manual (Page 17)

PALSUN® PALGARD™
Glazing Guide
17
c. Flat Glazing Requirements according to Size, Support System & Wind/Snow Loads:
1) General Glazing Comments:
a) Shape & Dimensions Ratio:
A glazing pane can come in many shapes but most common is four-sided, generally rectangular. Ratio
between rectangle’s dimensions a (width) and b (length) is crucial in determining the load bearing ability
of a glazing pane (or any flat, load bearing element).
Best case is when a = b (a square) all four glazing supported sides carry the loads equally.
Glazing rigidity & strength are optimal in both directions.
A round glazing is actually even better as it got no distant corners.
As a:b ratio grows smaller, (say 1:1.5) the effect of the further supports on the glazing bearing ability is
reduced, until at a:b = 1:2 the shorter sides have only negligible influence on the glazing load capacity.
From that ratio down a glazing should be considered as supported only on its two long sides and local
supports at the ends reckoned only as added safety bonus.
b) Four, Three & Two Sides Clamped Glazing:
In reality a glazing isn’t just supported, but clamped tightly along its edges (harnessed). Clamping adds
significantly to glazing’s load capacity. A glazing harnessed on all four sides has the largest load capacity.
Each decrease in clamped sides number reduces load capacity of said glazing.
Designs requiring only three or two sides clamping would need to increase glazing thickness or reduce
allowed span.
c) General Load Tables Comments:
(1) Following PALSUN tables are based on a commonly accepted maximal glazing deflection, at the middle
of each span under a depicted load, of 1/20 or 5% of said span. This rate, accepted for plastic glazing,, does
not indicate imminent failure or break of glazing sheet.
(2) Plastics high flexibility and impact properties produce higher deflections than usual rates for glass &
other conventional building materials, however such deflection rate will cause no damage to the glazing
and it will return to its original position when loads are removed.
(3) Plastics high flexibility needs larger rabbet and engagement depth prepared for PALSUN glazing,
assuring positive seat, preventing glazing extraction due to shortening by undue deflection.
(4) Only tables 9 & 10 (flat glazing) suits both PALSUN & PALGARD. Table 11 (curved glazing) suites
PALSUN only as PALGARD should not be curved.
(5) Plastics higher thermal expansion rate requires larger allowance gap for the PALSUN glazing to assure
free thermal expansion, preventing distortion & possible buckling.
(6) Other glazing details (clamping, sealing etc.) are similar to those familiar from glass, with plastics
specific fitting points, as mentioned elsewhere in this guide.
(7) Data in tables is based on professional expertise, accumulated knowledge & experience, actual tests
made on typical glazing panels, similarity to other products’ behavior, interpolations & educated
estimates.
(8) PALSUN tables begin with 4mm (5/32”) thickness as lowest thickness recommended for permanent
quality glazing. 1 to 3mm sheets are suitable for signs, advertising, vacuum-forming, agricultural
structures, exhibitions pavilions etc.
(9) A PALSUN sheet may withstand even larger loads without buckling, but undue shortening by higher
deflection may cause a pullout when the glazing edges slip out of their Supporting frame.
(10) Additional internal supports, perpendicular to main rafters or supporting arches, can add more snow-
load capacity when required, while uplift wind-load remains the same. Such configuration suites heavy
snow-bound areas while uplift wind forces are moderate.
This option should be calculated separately, according to pertinent conditions.