kg m kg kg m =1 slope

Transcription

1 (5) Win loa Wen structure blocks te flow of win, te win's kinetic energy is converte into otential energy of ressure, wic causes a win loaing. ensity an velocity of air te angle of incience of te win 3 te sae an stiffness of te structure 4 te rougness of its surface Analysis: static or ynamic () For static aroac, mean win ressure can be aroximate: V q=, ρ= te ensity of air, V= te win velocity (kinetic energy) kg m kg kg m unit : ressure( N / m ) 3 m sec m.sec m sec - Groun elevation is imortant te velocity of te win increases wit elevation. Te iger te structure, te more severe win loaing becomes. - Once te mean ressure q as been calculate, its magnitue is multilie by various coefficients to obtain esign static ressure tat is alie to te structure. Imortance of te structure Possibility of win gust 3 Te ressure ifference outsie an insie te structure () Dynamic aroac for ig rise builing Win tunnel tests - fining te ressure effects on te builing Static Aroac ASE 7-0 stanar q= V is moifie to account for te imortance of te structure, its eigt, an terrain. (win ressure) q K K K V 0.63 (N/m²) K : velocity ressure exosure coefficient eigt, terrain (0.85~.09) Table.5 K : a factor tat accounts for win see increase ue to ills an escarments. For flat groun level K = sloe K : a factor accounting for te irection of te win. (Only nee subjecte to te combinations of loas). For win acting alone, K = V : velocity in m/sec of a 3 secon gust of win measure at 0m above te groun tat as a 50 year recurrence erio. From a win ma (47 m/sec for agricultural an storage builings, 54m/sec for osital) DESIGN WIND PRESSURE Once te value of q ( q 0.63 K K K V can be etermine from a list of relevant equations liste in ASE 7-0 stanars. ) is obtaine, te esign ressure Te coice te flexibility eigt of te structure 3weter te esign for te main win-force resisting system, or for te builing s comonents an claing. For examle, for a conservative esign win ressure on nonflexible builings of any eigt is etermine using qg q ( G ) (N/m²) i q = q for winwar wall at eigt above te groun q = q for leewar wall, sie walls, an roof were = (: mean eigt of roof)

2 G: a win guest effect factor Exosure. For a rigi structure, G=0.85 : wall or roof ressure coefficient etermine from ( Table (a):wall Table (b):roof G : internal ressure coefficient tyes of oening in te builing. i For fully enclose builings ( G i ) = ±0.8 in Fig -3) EX -3 Given V = 47 m/s (See of 3secon gust win measure at 0m above groun level for 50 year recurrence erio) K = for flat terrain K = only win loaing is consiere win ressure q 0.63K K K V = 0.63* K ***47²=354* K eigt () calculate q (: mean eigt of te roof) [use for leewar later] = tan 0 / = /= 9.48m For, linear interolation for = using able K ( 9.) 0.98 at = (mean eigt). 9. At = 9.48, K Z =K Z= = K =0.987 q q = 354 K = 354x0.997=337 N/m² 3 esign win ressure = qg - q ( G ) i = q(0.85) -337( 0.8) = 0.85q 4 from Table -5 an K ( 9.) (m) K q (N/m ) G = 0.85(gust factor) G = ±0.8 for fully enclose builing i q = 354 K =

3 () Winwar wall for all L/B, = 0.8 (winwar) q=q =0.85q q = or = = 54 N/m² =04 N/m² 6. = = 588 N/m² or 070 N/m² 7.6 =65 N/m² or 07 N/m² ()q= q Leewar wall for L/B = (.5)/45 =, = -0.5 = 0.85 q q + 4 = (-0.5) -4 = -809 N/m² or -37 N/m² (3)q= q sie wall for all L/B = = 0.85 q -4=-037 N/m² or -555 N/m² (4)q= q winwar roof for /L=9.48/(x.5) = 0. < 0.5 =-0.7 = 0.85 q -4= -037 N/m² or -555 N/m² (5)q= q Leewar wall roof =-0.3 = -58 N/m² or -00 N/m² +ressure - suction Te frame structure must resist tese loaings as well as loaings calculate from win blowing on te front or rear of te builing. Design win ressure for signs. F=q G f A s Here, q = te win ressure at te eigt, measure from te groun to te to of te sign G = te win-gust coefficient factor f = a force coefficient wic eens uon te asect ratio (wit B of te sign to te eigt s of te sign), an te clear area ratio (sign eigt s to te elevation, measure from te groun to te to of te sign). A s = te area of te face of te sign rojecte into te win in m TABLE -6 (B/s=4) Force oefficients for Above-Groun Soli Signs, f s/ f

4 (6) Snow & Ice loa ANSI ASE 7-0 Snow / ice treate as static roof loas. Base on a groun snow converte to roof conversion. Use 50 years recurrence interval Geograical mas For flat roof (sloe <5%) P f (kn/m ) = 0.7 e t I s g Here, e exosure factor eening on terrain (0.8: exose roof in an unobstructe area,.: oterwise) t = imensionless termal factor (.: for uneate structure,.0: for eate structure) I s = imortance factor (0.8 for agriculture builings,. for scools an ositals) g = groun snow loa if g 0.96 kn/m P f = max(i g, 0.7 e t I s g ) if g > 0.96 kn/m P f = Iⅹ0.96 kn/m For sloe roof P s = s P f Here, s = sloe factor (0~.0) sloe & termal factors [EXAMPLE -4] Te uneate storage facility sown in Fig -5 is locate on flat oen terrain in central Illinois, were te groun snow loa is 0.7 kn/m. Determine te esign snow loa on te roof (4% sloe). <Solution> Given groun snow loa = 0.7 kn/m, oen terrain e = 0.8, uneate storage t =., I = 0.8 Since g = kn/m, P f = max(i g, 0.7 e t I s g ) P f = 0.7 e t I s g = 0.7ⅹ0.8ⅹ.ⅹ0.8ⅹ0.7 = 0.39 kn/m P f = I g =0.8ⅹ0.7 = 0.58 kn/m P f = max(0.58, 0.39) = 0.58 kn/m (7) Eartquake loas During an Eartquake te groun vibrates bot oriontally an vertically. Te vertical motion is sligt an is usually neglecte in esign. - Eartquake rouce loaings troug its interaction wit te groun & its resonse caracteristics - Teir magnitue eens on amount & tye of groun acceleration, mass & stiffness of structure - To block is te lume mass of te roof - Mile block is te lume stiffness of all te builing s columns - During eartquake, te groun vibrates bot oriontally & vertically S S DS R / I R: resonse moification factor I: imortance factor S : sectral resonse acceleration DS (8) Hyrostatic an Soil ressure Wen a structure is nee to retain water, soil, or granular materials, ressures eveloe by loaings become an imortant criterion for teir esign. (retaining walls) 4

5 (9) Oter natural loas Effect of blast, temerature canges, ifferential settlement. Structural Design Material uncertainties occur ue to - variability in material roerties - resiual stress in materials - intene measurements being ifferent from fabricate sies - material corrosion or ecay Many tyes of loas can occur simultaneously on a structure Allowable stress esign (or working stress esign): comute elastic stress in material must not excee te allowable stress along wit te following tyical loa combinations: (D: ea loa, L: live loa, S: snow loa, L r : roof live loa, W: win loa, E: eartquake loa) D D L 3 D Lr or S or R 4 D 0.75 L 0.75 Lr or S or R 5 D W or 0.7E 6 D 0.75 W or 0.7 E 0.75 L 0.75 Lr or S or R 70.6 D W or 0.7E Strengt Design (or Loa Resistance Factor Design, LRFD): te eman from ultimate loa calculate by te following loa combinations must not excee ultimate strengt of critical sections. In strengt esign, material uncertainty an loa uncertainty are searately etermine. ().4D (). D.6 L 0.5 Lr or S or R (3). D.6 L or S or R 0.5 L or 0.8W r (4). D.6 W 0.5 L 0.5 Lr or S or R (5). D.0 E 0.5 L 0.S (6)0.9 D.6 W or.0e Plastic esign: eveloe for steel frames 5