The dome beams are extruded 6061-T6 or 6005A-T6 aluminum alloy. 6061-T6 and 6005A-T6 have the same minimum strength properties. 6005A-T6 is a relatively new alloy that has some advantages over 6061-T6. The main advantages are a better finish, less sensitive timeframe to quench after extruding, and its ability to be air quenched instead of water quenched for most extrusion sizes. Finally, it costs a little less, mainly due to the easier quenching process for the extruder. The protrusion on the top of the beam must be milled or cut back to allow the beam to bolt to the connection hub.
This aluminum dome beam extrusion is typical. Note the protrusions on the top. The protrusions are the attachments for the dome panels and batten bar. The batten bar holds the dome panels in place and is attached by a ¼" tri-lobe screw in the slot at the center of the beam. The flange stiffeners at the end of each flange are typical for a thin-wall beam extrusion. The flange stiffeners increase the allowable compression and bending in a thin-wall shape by about 20-25%. They also increase the weak-axis moment of inertia, section modulus and radius of gyration without increasing the width of the beam. They are not needed on thicker shapes.
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