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Building Design and Construction Handbook - Merritt - Ventech!

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5.108 SECTION FIVE<br />

TABLE 5.8 Maximum Span-Width or Span-Depth Ratios for diaphragms—Roofs or<br />

Floors*<br />

Diaphragm construction<br />

Masonry <strong>and</strong><br />

concrete<br />

walls<br />

Wood<br />

<strong>and</strong> light<br />

steel<br />

walls<br />

Concrete Limited by deflection<br />

Steel deck (continuous sheet in a single<br />

plane)<br />

4:1 5:1<br />

Steel deck (without continuous sheet) 2:1 21 ⁄2:1<br />

Cast-in-place reinforced gypsum roofs 3:1 4:1<br />

Plywood (nailed all edges) 3:1 4:1<br />

Plywood (nailed to supports only—blocking<br />

may be omitted between joists)<br />

21 ⁄2:1 31 ⁄2:1<br />

Diagonal sheating (special) 3:1† 31 ⁄2:1<br />

Diagonal sheating (conventional<br />

construction)<br />

2:1† 21 ⁄2:1<br />

* From California Administrative code, Title 21, Public Works.<br />

† Use of diagonal sheathed or unblocked plywood diaphragms for buildings having masonry or reinforced<br />

concrete walls shall be limited to one-story buildings or to the roof of a top story.<br />

FIGURE 5.86 Distribution of horizontal load to parallel<br />

shear walls: (a) walls with the same length <strong>and</strong> rigidity share<br />

the load equally; (b) wall half the length of another carries<br />

less than one-eighth of the load.<br />

obtained from Eq. (5.149), with H/L � 4 ⁄4 � 1. For any one of the piers, the<br />

deflection is<br />

3 10<br />

��v � (1 � 3) � 0.208 in<br />

3 2.4 � 10 � 8<br />

The rigidity of a single pier is 1/0.208 � 4.81, <strong>and</strong> of the three piers, 3 � 4.81 �<br />

14.43. Therefore, the deflection of the three piers when coupled is

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