2695 Flexible or Dynamically Sensitive Buildings or Other Structures For

# 2695 flexible or dynamically sensitive buildings or

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26.9.5 Flexible or Dynamically Sensitive Buildings or Other Structures For flexible or dynamically sensitive buildings or other structures as defined in Section 26.2, the gust-effect factor shall be calculated by G I g Q g R g I f z Q R v z = + + + 0 925 1 1 7 1 1 7 2 2 2 2 . . . (26.9-10) g Q and g v shall be taken as 3.4 and g R is given by g n n R = ( ) + ( ) 2 3 600 0 577 2 3 600 1 1 ln , . ln , (26.9-11) R , the resonant response factor, is given by R R R R R n h B L = + ( ) 1 0 53 0 47 β . . (26.9-12) R N N n = + ( ) 7 47 1 10 3 1 1 5 3 . . / (26.9-13) N n L V z z 1 1 = (26.9-14) R e = ( ) 1 1 2 1 2 2 η η η for η > 0 (26.9-15a) R = 1 for η = 0 (26.9-15b) where the subscript in Eqs. 26.9-15 shall be taken as h , B , and L , respectively, where h , B , and L are defined in Section 26.3. n 1 = fundamental natural frequency R = R h setting η = 4.6 n 1 h / V _ z _ R = R B setting η = 4.6 n 1 B / V _ z _ R = R L setting η = 15.4 n 1 L / V _ z _ β = damping ratio, percent of critical (i.e. for 2% use 0.02 in the equation) V _ z _ = mean hourly wind speed (ft/s) at height z _ determined from Eq. 26.9-16: V b z V z = 33 88 60 α (26.9-16) In SI: V b z V z = 10 α where b _ and α _ are constants listed in Table 26.9-1 and V is the basic wind speed in mi/h. 26.9.6 Rational Analysis In lieu of the procedure defined in Sections 26.9.3 and 26.9.4, determination of the gust-effect factor by any rational analysis defined in the recognized literature is permitted. 26.9.7 Limitations Where combined gust-effect factors and pressure coefficients ( GC p ), ( GC pi ), and ( GC pf ) are given in figures and tables, the gust-effect factor shall not be determined separately. 26.10 ENCLOSURE CLASSIFICATION 26.10.1 General For the purpose of determining internal pressure coefficients, all buildings shall be classified as enclosed, partially enclosed, or open as defined in Section 26.2. 26.10.2 Openings A determination shall be made of the amount of openings in the building envelope for use in determin- ing the enclosure classification. 26.10.3 Protection of Glazed Openings Glazed openings in Risk Category II, III or IV buildings located in hurricane-prone regions shall be protected as specified in this Section. 26.10.3.1 Wind-borne Debris Regions Glazed openings shall be protected in accordance with Section 26.10.3.2 in the following locations:
CHAPTER 26 WIND LOADS: GENERAL REQUIREMENTS 256
MINIMUM DESIGN LOADS 257 1. Within 1 mi of the coastal mean high water line where the basic wind speed is equal to or greater than 130 mi/h (58 m/s), or 2. In areas where the basic wind speed is equal to or greater than 140 mi/h (63 m/s). For Risk Category II buildings and other structures and Risk Category III buildings and other structures, except health care facilities, the wind-borne debris region shall be based on Fig. 26.5-1A. For Risk Category III health care facilities and Risk Category IV buildings and other structures, the wind-borne debris region shall be based on Fig. 26.5-1B. Risk Categories shall be determined in accordance with Section 1.5.

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