BRACKETS

1 Stiffened Seat Bracket designThere are two analyses: (A) in which the seat stiffener is at right angles to the web of the beam. (B) in which the seat stiffener is in line with the web of the beam.

1.1 Seat stiffener is at right angles to the web of the beamFor analysis, the stiffener of Type (A) is considered an eccentrically loaded column with the reaction load applied at a fixed point.

The maximum stress is the sum of the direct load and bending effects. The line of action of the compressive load is approximately parallel to the outer edge of the stiffener. The critical cross-section of the stiffener (to be used for the area and section modulus) is at right angles to the line of action of the load.

Area and section modulus are

Minimum thickness:Thus, Min Thickness

The eccentrically loaded column formula ( # 1) is seldom used in this case because it will result in an excessively thick bracket \web or stiffener.

This is because the formula is based upon stress only and does not take into consideration some yielding of the bracketwhich will cause the point of application of the load to shift in toward the support, thus reducing the moment arm and bending stress.

treq can also be determined using nomogramsFIGURE 2-Thickness of Stiffened Seat For A36 Steel - NOMOGRAPH NO. 4

BRACKETS

1.1.1.1 seat stiffener is in line with the web of the beamlf the beam rests in line with the bracket stiffener, Type B, Figure 3, the bearing length ( N) of the beam ( AISC See 1.10.10) is-

The eccentricity ( e") of the reaction load is

Lv = column lengthAISC Manual, page 4-39 recommends for A36 bracket material that the bracket web's thickness be at least equal to 1.33 times the required fillet weld size ( E70 welds).

Also it should not be less than the supported beam web thickness for A7, A373 and A36 beams, and not less than 1.4 times the beam web thickness for A242 and A441 beams.

BRACKETS

For stiffened seats in line on opposite sides of the column web, the fillet weld size should not exceed 3/4 the column web thickness when determining its length(Lv).

2 BS APPROACHThe outside edge of the welded column bracket, shown in Fig. 25.4, is in compression and provided that a reasonably conservative approach is used in calculating the extreme fibre stress, semi-Compact criteria

for the outstand are appropriate (i.e. ).

With relatively light loads, this may require an unnecessarily thick stiffener. To overcome the problem, the simple design approach of substituting fa for Py in the formula for E, so that , where

fa = 1.5 X the extreme fibre compressive stress (at factored loading) can be used.