Metal Building Basics

Secondary Framing

Secondary Framing Members are those members that join the primary framing members together to form building bays and provide the means of supporting and attaching the walls and roof. Secondary framing members are:

Purlins
Girts
Eave Struts
Bracing

Purlins

A purlin is a secondary framing member that serves to support roof panels and transfer the roof load to the rafter or main frame. The purlin is zee shaped and are available in 6",8",10", and 12" depth and also available in different gauges of steel to meet various loading conditions.

Girts

Girts are secondary framing members and run horizontally between main frame columns and between endwall columns. They are zee shaped members like pulins and available in depths of 8', 10", or 12" and gauges of 16,14,13,or 12. The standard girt spacing to the first girt above finish floor is 7' 3-1/2" and a maximum of 6' there after. This spacing fits door and window header heights. Other spacing is available to satisfy any design criteria.
Girts and purlins are pre-painted, factory baked red oxide finish for a smooth, attractive appearance and to improve durability. A&S welds all girt clips to the frames for easier and quicker erection. A BYPASS girt attaches to the outside flange of the columns to take advantage of continuous beams spanning from bay to bay. They also allows for an open wall condition for the use of masonry or other wall material below it.

Bypass Girt

The FLUSH girt attaches to the web of the columns, with the girt face in the same plane as the column face. This provides greater interior clearance and an easier interior finish.

Eave Struts

The eave strut provides an attachment and bearing points for the end of the roof sheets and wall sheets. The eave strut is a cee shaped cold-formed member and are available in nominal depths of 8", 10", or 12" to match the purlin depth.

Bracing

The building system must have adequate bracing to make the system stable in a lengthwise direction. Bearing frame endwalls also require longitudinal bracing. Bracing systems transfer wind loads from endwalls and sidewalls to the foundation. They must include two types:

Longitudinal bracing, for wind on the endwall.
Transverse bracing, for wind on the building sidewall.

A variety of methods are available for providing wind bracing: diaphragm action, X-bracing (cable or rod), fixed base columns and portal frames.

Diaphragm Action

Diaphragm action utilizes the undisturbed sheeting panels, floor to roof line and assumes all wall panels are attached correctly.

X-Bracing

This alternative provides cables or rods connected in a X between columns that transfers the forces to the foundation. Diaphragm and X-bracing are the most widely used methods of bracing used.

Fixed Base Columns

A fixed base column is a column with special base plate condition which is designed to resist rotation as well as horizontal and vertical movement. This allows wind load to be transferred to the foundation.

Portal Frame

A portal frame is an I shaped section of built up material consisting of two columns and a rafter, running parallel to the sidewall and attached to the web of the sidewall columns.

Portal Frame Bracing

The portal frame is a good alternative in a braced bay when your requirements call for a large opening in a sidewall such as an overhead door or several windows.

(To continue on to the next section, Covering Systems click here.)

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Last updated 7/16/01 by Don