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Building Design and Construction Handbook - Merritt - Ventech!

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7.104 SECTION SEVEN<br />

not a factor. Sometimes, the shear capacity of the field fasteners in bearing-type<br />

connections may be limited by bearing on thin webs, particularly where beams<br />

frame into opposite sides of a web. This could occur where beams frame into<br />

column or girder webs.<br />

One side of a framed connection usually is shop connected, the other side field<br />

connected. The capacity of the connection is the smaller of the capacities of the<br />

shop or field group of fasteners.<br />

In the absence of specific instructions in the bidding information, the fabricator<br />

should select the most economical connection. Deeper <strong>and</strong> stiffer connections, if<br />

desired by the designer, should be clearly specified.<br />

7.35.2 Bolted Seated Connections<br />

Sizes, capacities, <strong>and</strong> other data for seated connections for beams, shown in Fig.<br />

7.47, are tabulated in the AISC Manual. Two types are available, stiffened seats<br />

(Fig. 7.47a) <strong>and</strong> unstiffened seats (Fig. 7.47b).<br />

Unstiffened Seats. Capacity is limited by the bending strength of the outst<strong>and</strong>ing<br />

horizontal leg of the seat angle. A 4-in leg 1 in thick generally is the practical limit.<br />

In ASD, an angle of A36 steel with these dimensions has a top capacity of 60.5<br />

kips for beams of A36 steel, <strong>and</strong> 78.4 kips when F y � 50 ksi for the beam steel.<br />

Therefore, for larger end reactions, stiffened seats are recommended.<br />

The actual capacity of an unstiffened connection will be the lesser of the bending<br />

strength of the seat angle, the shear resistance of the fasteners in the vertical leg,<br />

or the bearing strength of the beam web. (See also Art. 7.22 for web crippling<br />

stresses.) Data in the AISC Manual make unnecessary the tedious computations of<br />

balancing the seat-angle bending strength <strong>and</strong> beam-web bearing.<br />

The nominal setback from the support of the beam to be seated is 1 ⁄2 in. But<br />

tables for seated connections assume 3 ⁄4 in to allow for mill underrun of beam<br />

length.<br />

FIGURE 7.47 Typical bolted seated connections: (a) stiffened seat; (b)<br />

unstiffened seat.

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