Structural Drafting Connection Details and Gages

Beam Gages Steel fabrication is based on standard measurements called gages to reduce possible errors in matching connections. Horizontal hole spacing is generally 3" apart (center to center) with the first hole located 3" below the top of the beam. Edge distances from centers of holes to edges of angles and beams are found in Table J3.4. Using Table J3.4 for minimum edge distances and the standard hole spacing gages, dimensions can be applied to the connection of the angle and beam to begin developing the connection detail drawing. Angle sizes can be determined from the standard hole spacing and the minimum edge

Minimum Edge Distances

Angle Gages The size of one leg of a connection angle can be found using the minimum edge distances in Table J3.4. Leg of angle = 1/2" + 1-1/4" + 1-1/4" = 3“ Note: The nominal setback clearance dimension between the back of the connection angle and the edge of the beam is generally 1/2.

Center to Center Calculations The center to center distance must be calculated based on the assembly clearances for the assembly of the connection. One method of calculation utilizes the Entering and Tightening Clearance, in. Conventional ASTM A325 and A490 bolts found in Table 7-16.

Entering and Tightening Clearance

Center to Center Calculations For example, given a connection using a 1/4" thick angle and 3/4 diameter A325 High Strength bolts calculate the center to center distance. C2 = 3/4" H2 = 1-3/8" Angle (t) = 1/4" tw of beam = 5/16" C to C distance = ((C2 + H2 + Angle (t)) x 2) + tw C to C distance = ((3/4" + 1-3/8" + 1/4") x 2) + 5/16" C to C distance = 5-1/16"

Center to Center Calculations Gage Outstanding Leg (G.O.L.) G.O.L. = (C to C)/2 - (tw)/2 G.O.L. = (5 1/16)/2 - (5/16)/2 G.O.L. = 2 3/8