| 摘要 |
<p>The prestressed frame may be used on window shutters. It is fabricated from hollow extruded metal sections, and uses screws fixed 'L' shaped double spigot pieces to fix the corners. The spigot pieces subtend an angle (a) of nominally greater or less than 90 deg. The posts of a rectangular frame are thus assembled with an initial prechamber. The camber is obtained by fixing the posts in a state of flexure, the posts both deflecting in towards the centre of the frame or both deflecting outward. At least one intermediate rail is fixed between the posts acting in tension or compression, and acting to correct the precamber. The spigot pieces may subtend an angle of between 90 and 95 deg., pref. 92 deg., and is fixed by self-tapping screws through bores and split sleeve formations in the respective members.</p> |
