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Building Design and Construction Handbook - Merritt - Ventech!

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7.86 SECTION SEVEN<br />

prevent overstressing the bottom flange of the steel beam when temporary shoring<br />

is omitted, a limitation is placed on the value of S t used in computation of ƒ b with<br />

Eq. (7.65):<br />

ML t � � s<br />

MD S � 1.35 � 0.35 S (7.66)<br />

where M D � moment, kip-in, due to loads applied prior to concrete hardening (75%<br />

cured)<br />

M L � moment, kip-in, due to remaining dead <strong>and</strong> live loads<br />

S s � section modulus, in 3 , of steel beam alone relative to bottom flange<br />

Shear on Connectors. Shear connectors usually are studs or channels. The total<br />

horizontal shear to be taken by the connectors between the point of maximum<br />

positive moment <strong>and</strong> each end of a simple beam, or the point of counterflexure in<br />

a continuous beam, is the smaller of the values obtained from Eqs. (7.67) <strong>and</strong> (7.68).<br />

where ƒ� c<br />

0.85ƒ�A<br />

c c<br />

Vh � (7.67)<br />

2<br />

AF<br />

s y<br />

Vh � (7.68)<br />

2<br />

� specified strength of concrete, ksi<br />

Ac � actual area of effective concrete flange, as indicated in Fig. 7.36a <strong>and</strong><br />

b, in2 As � area of steel beam, in2 In continuous composite beams, where shear connectors are installed in negativemoment<br />

regions, the longitudinal reinforcing steel in the concrete slab may be<br />

considered to act compositely with the steel beam in those regions. In such cases,<br />

the total horizontal shear to be resisted by the shear connectors between an interior<br />

support <strong>and</strong> each adjacent infection point is<br />

AsrFyr Vh � (7.69)<br />

2<br />

where A sr � total area, in 2 , of longitudinal reinforcing steel within the effective<br />

width of the concrete slab at the interior support<br />

F yr � specified yield stress of the reinforcing steel, ksi<br />

These formulas represent the horizontal shear at ultimate load divided by 2 to<br />

approximate conditions at working load.<br />

Number of Connectors. The minimum number of connectors N 1, spaced uniformly<br />

between the point of maximum moment <strong>and</strong> adjacent points of zero moment,<br />

is V h/q, where q is the allowable shear load on a single connector, as given in<br />

Table 7.22. Values in this table, however, are applicable only to concrete made with<br />

aggregates conforming to ASTM C33. For concrete made with rotary-kiln-produced<br />

aggregates conforming to ASTM C330 <strong>and</strong> with concrete weight of 90 pcf or more,<br />

the allowable shear load for one connector is obtained by multiplying the values<br />

in Table 7.22 by the factors in Table 7.23.

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