What is "portal bracing"

Portal \Por"tal\, n. [OF. portal, F. portail, LL. portale, fr. L. porta a gate. See Port a gate.]

1. A door or gate; hence, a way of entrance or exit, especially one that is grand and imposing.

   Thick with sparkling orient gems The portal shone.
   --Milton.

   From out the fiery portal of the east.
   --Shak.

2. (Arch.)

   1. The lesser gate, where there are two of different dimensions.

   2. Formerly, a small square corner in a room separated from the rest of the apartment by wainscoting, forming a short passage to another apartment.

   3. By analogy with the French portail, used by recent writers for the whole architectural composition which surrounds and includes the doorways and porches of a church.

3. (Bridge Building) The space, at one end, between opposite trusses when these are terminated by inclined braces.

4. A prayer book or breviary; a portass. [Obs.]

   Portal bracing (Bridge Building), a combination of struts and ties which lie in the plane of the inclined braces at a portal, serving to transfer wind pressure from the upper parts of the trusses to an abutment or pier of the bridge.