Seismic Loads Based on IBC 2015/ASCE 7-10

Transcription

1 Seimic Load Baed on IBC 2015/ASCE 7-10 Baed on Section of IBC 2015, Every tructure, and portion thereof, including nontructural component that are permanently attached to tructure and their upport and attachment, hall be deigned and contructed to reit the effect of earthquake motion in accordance with ASCE 7, excluding Chapter 14 and Appendix 11A. The eimic deign category for a tructure i permitted to be determined in accordance with Section 1613 or ASCE 7. Exception: 1. Detached one- and two-family dwelling, aigned to Seimic Deign Category A, B or C, or located where the mapped hort-period pectral repone acceleration, S S, i le than 0.4 g. 2. Agricultural torage tructure intended only for incidental human occupancy. 3. Structure that require pecial conideration of their repone characteritic and environment that are not addreed by thi code or ASCE 7 and for which other regulation provide eimic criteria, uch a vehicular bridge, electrical tranmiion tower, hydraulic tructure, buried utility line and their IBC 2015 Safety Concept IBC 2015 intend to deign tructure for collape prevention in the event of an earthquake with a 2 % probability of being exceeded in 50 year 94

2 Introduction Seimic Repone Spectra: - A repone pectrum provide the maximum repone of a Single Degree Of Freedom (SDOF) ytem, for a given damping ratio and a range of period, for a pecific earthquake. - A deign repone pectrum i a moothed pectrum ued to calculate the expected eimic repone of a tructure Figure (1) how ix inverted, damped pendulum, each of which ha a different fundamental period of vibration. To derive a point on a repone pectrum, one of thee pendulum tructure i analytically ubjected to the vibration recorded during a particular earthquake. The larget acceleration of thi pendulum tructure during the entire record of a particular earthquake can be plotted a hown in Figure 1(b). Repeating thi for each of the other pendulum tructure hown in Figure 1(a) and plotting and connecting the peak value for each of the pendulum tructure produce an acceleration repone pectrum. Generally, the vertical axi of the pectrum i normalized by expreing the computed acceleration in term of the acceleration due to gravity g. In Figure (2), diplacement, velocity, and acceleration pectra for a given earthquake are hown. In thi figure, tructure with hort period of 0.2 to 0.5 econd are almot rigid and are mot affected by ground acceleration. Structure with medium period ranging from 0.5 to 2.5 econd are affected mot by velocitie. Structure with long period greater than 2.5 econd, uch a tall building or long pan bridge, are mot affected by diplacement. 95

3 Reference: Wight, J. and MacGregor, J "Reinforced Concrete Mechanic and Deign" 6 th Edition, Pearon, NJ, Vicou damping (a) Damped pendulum of varying natural frequencie 4 Accele ration Sa % Damping 2% Damping 5% Damping Natural period of vibration, T (ec) (b) Acceleration repone pectrum Figure (1): Earthquake Repone pectrum 96

4 Figure (2): (a) diplacement, (b) velocity and (c) acceleration pectra for a given earthquake 97

5 Analyi Procedure 1- Determination of maximum conidered earthquake and deign pectral repone acceleration: Determine the mapped Maximum Conidered Earthquake MCE pectral repone acceleration, S for hort period (0.2 ec.) and S 1 for long period (1.0 ec.) uing the pectral acceleration map (ee Figure 3 and 4). Where S 1 i le than or equal to 0.04 and S i le than or equal to 0.15, the tructure i permitted to be aigned to Seimic Deign Category A. Determine the ite cla baed on the oil propertie. The ite hall be claified a Site Cla A, B, C, D, E or F in accordance with Chapter 20 of ASCE 7. Where the oil propertie are not known in ufficient detail to determine the ite cla, Site Cla D hall be ued unle the geotechnical data determine Site Cla E or F oil are preent at the ite. Determine the maximum conidered earthquake pectral repone acceleration adjuted for ite cla effect, SMS at hort period and S M1 at long period in accordance with IBC where: S F S MS a F S M1 v S 1 F a = Site coefficient defined in IBC Table (1). F = Site coefficient defined in IBC Table (2). v 98

6 Figure (3): Long period pectral acceleration for Paletine 99

7 Figure (4): Short period pectral acceleration for Paletine 100

8 Determine the 5% damped deign pectral repone acceleration period and S D1 at long period in accordance with IBC SDS at hort S (2 / 3) DS S MS S D1 ( 2/3) SM1 where: S MS = The maximum conidered earthquake pectral repone acceleration for hort period a determined in ection S M1 = The maximum conidered earthquake pectral repone acceleration for long period a determined in ection Determination of eimic deign category and Importance factor: Rik categorie of building and other tructure are hown in IBC Table Importance factor, Ie, are hown in ASCE 7-10 Table Structure claified a Rik Category I, II or III that are located where the mapped pectral repone acceleration parameter at 1-econd period, S 1, i greater than or equal to 0.75 hall be aigned to Seimic Deign Category E. Structure claified a Rik Category IV that are located where the mapped pectral repone acceleration parameter at 1-econd 101

9 period, S 1, i greater than or equal to 0.75 hall be aigned to Seimic Deign Category F. All other tructure hall be aigned to a eimic deign category baed on their rik category and the deign pectral repone acceleration parameter, SDS and S D1, determined in accordance with Section or the ite-pecific procedure of ASCE 7. Each building and tructure hall be aigned to the more evere eimic deign category in accordance with Table (1) or (2), irrepective of the fundamental period of vibration of the tructure. 102

10 3- Determination of the Seimic Bae Shear: The tructural analyi hall conit of one of the type permitted in ASCE 7-10 Table , baed on the tructure eimic deign category, tructural ytem, dynamic propertie, and regularity, or with the approval of the authority having juridiction, an alternative generally accepted procedure i permitted to be ued. The analyi procedure elected hall be completed in accordance with the requirement of the correponding ection referenced in Table Structural Irregularitie are hown in Table , and Table and Figure (5) and (6). 103

11 104

12 Figure (5): Horizontal Structural Irregularitie 105

13 106

14 Figure (6): Vertical Structural Irregularitie 107

15 3.1 Equivalent Lateral Force Analyi: Section 12.8 of ASCE 7-10 hall be ued. The eimic bae hear V in a given direction i determined in accordance with the following equation: V C W where: W = effective eimic weight The effective eimic weight, W, of a tructure hall include the dead load above the bae and other load above the bae a lited below: 1. In area ued for torage, a minimum of 25 percent of the floor live load hall be included. Exception a. Where the incluion of torage load add no more than 5% to the effective eimic weight at that level, it need not be included in the effective eimic weight. b. Floor live load in public garage and open parking tructure need not be included. 2. Where proviion for partition i required in the floor load deign, the actual partition weight or a minimum weight of 50 kg/m 2 of floor area, whichever i greater. 3. Total operating weight of permanent equipment. C = Seimic repone coefficient SDS R / I e R = repone modification factor, given in ASCE 7-10 Table I e = importance factor The value of C hall not exceed the following: C S D1 for T TL T R / I e 108

16 C S T D1 L for 2 T TL T R / I e The value of C hall not be le than: C 0.044S I 0.01 DS e For tructure located where S 1 i equal to or greater than 0.6g, C hall not be le than C S R / I e where: T = fundamental period of the tructure T L = long-period tranition period, which i the tranition period between the velocity and diplacement-controlled portion of the deign pectrum (given in Figure 7 for Paletine). An approximate value of T a may be obtained from: T C a t h x n where: h n = height of the building above the bae in meter C t = building period coefficient given in Table x = contant given in Table The calculated fundamental period, T, cannot exceed the product of the coefficient, u in Table time the approximate fundamental period, T a. C, 109

17 110

18 111

19 112

20 113

21 114

22 Figure (7): Long-period tranition period for Paletine 115

23 Table : Coefficient for upper limit on calculated period Deign Spectral Repone, S D1 Coefficient C u In cae where moment reiting frame do not exceed twelve torie in height and having an average tory height of 3 m, an approximate period T a in econd in the following form can be ued: T a 0. 1 N where: N = number of torie above the bae

24 3.2 Vertical Ditribution of Seimic Force: and F C x C vx w i1 V x vx n w h i k x h k i F F F w n w x w 1 h h h where: F x = Lateral force at level x C vx = Vertical ditribution factor V = total deign lateral force or hear at the bae of the building w x and w i = the portion of W aigned to level x and i h x and h i = the height from bae to level x or i k = an exponent related to the tructure period a follow: k = 1 for building with T le than or equal to 0.5 econd k = 2 for building with T more than or equal to 2.5 econd Interpolate between k = 1 and k = 2 for building with T between 0.5 and Horizontal Ditribution of Force and Torion: Horizontally ditribute the hear V x x V x F i i1 where: F = portion of the eimic bae hear, V, induced at level i i Accidental Torion, M ta M ta = V x B Where B i the building dimenion perpendicular to the direction of eimic force Total Torion, M T M t M ta Where earthquake force are applied concurrently in two orthogonal direction, the required 5 percent diplacement of the center of ma need not applied in both of the orthogonal direction at the ame time, but hall be applied in the direction that produce the greater effect. 117

25 3.4 Story Drift: The deign tory drift,, i defined a the difference between the deflection of the center of ma at the top and bottom of the tory being conidered. Where: Cd x I e xe C d = deflection amplification factor, given in Table = deflection determined by elatic analyi. xe 3.5- P-delta Effect: The P-delta effect can be ignored if the tability coefficient,, from the following expreion i equal to or le than Where: Px Ie V h C max x x d C d P x = Total unfactored vertical deign load at and above level x V = Seimic hear force acting between level x and x 1 x h x = Story height below level x = Deign tory drift occurring imultaneouly with V x = Ratio of hear demand to hear capacity for the tory between level x and x 1. Where the ratio i not calculated, a value of = 1.0 hall be ued. When the tability coefficient,, i greater than 0.10 but le than or equal to max, P- delta effect are to be conidered. To obtain the tory drift for including the P-delta effect, the deign tory drift hall be multiplied by 1.0/(1 ). When i greater than max, the tructure i potentially untable and ha to be redeigned. Where the p-delta effect i included in an automated analyi, the equation for evaluating max hall till be atified, but the value of in the firt equation uing the reult of the p-delta analyi i permitted to be divided by 1 before checking the econd equation. 118

26 3.6 Redundancy: The value of ρ i permitted to equal 1.0 for the following: 1. Structure aigned to Seimic Deign Category B or C. 2. Drift calculation and P-delta effect. 3. Deign of diaphragm collector element. 4. Deign of member or connection where the eimic load effect including overtrength factor are required for deign. 5. Diaphragm load. For tructure aigned to Seimic Deign Category D, E, or F, ρ hall equal 1.3 unle one of the following two condition i met, whereby ρ i permitted to be taken a 1.0: a. Each tory reiting more than 35 percent of the bae hear in the direction of interet hall comply with Table b. Structure that are regular in plan at all level provided that the eimic force-reiting ytem conit of at leat two bay of eimic force-reiting perimeter framing on each ide of the tructure in each orthogonal direction at each tory reiting more than 35 percent of the bae hear. The number of bay for a hear wall hall be calculated a the length of hear wall divided by the tory height or two time the length of hear wall divided by the tory height, hx, for light-frame contruction. 4. Seimic Load Effect and Combination: The eimic load effect, E hall be determined in accordance with the following: For ue in combination that include eimic load, E hall be determined in accordance with E E h E v E E h E v where E E E h Q E v 0. 2 S DS (effect of horizontal eimic force) D (effect of vertical eimic force) mh Q E (effect of horizontal eimic force including over-trength factor) The vertical eimic load effect, 0.2 S DS D, i permitted to be taken a zero when S DS i equal to or le than

27 4.1 Baic combination SDS D QE L 0. 2S S D Q 1. H DS E Baic combination with over-trength factor SDS D QE L 0. 2S S D Q 1. H DS E 6 Note: 1-The load factor on L in combination 5 i permitted to equal 0.5 for all occupancie in which L in Table 4-1 of ASCE 7-10 i le than or equal to 480 kg/m 2, with the exception of garage or area occupied a place of public aembly. 2- The load on H hall be et equal to zero in combination 6 if the tructural action due to H counteract that due to E. Where lateral earth preure provide reitance to tructural action from other force, it hall not be included in H but hall be included in the deign reitance. 4.3 Minimum upward force for horizontal cantilever for eimic deign categorie D through F In tructure aigned to Seimic Deign Category D, E, or F, horizontal cantilever tructural member hall be deigned for a minimum net upward force of 0.2 time the dead load in addition to the applicable load combination. 120

28 Example (3): For the ame building hown in Example (2), evaluate the eimic force at floor level in the direction of hear wall A, B and C, uing IBC 2015/ASCE Note that the oil i dene with an average SPT value of 35 blow/foot. Solution: Baed on IS (2013), S, S (Figure 3 and 4). Baed on Table , ite cla i claified a "D". S Uing Table (1) and (2), for ite cla "D", hort-period ite coefficient F 1. 6 and long-period ite coefficient F a v Maximum conidered earthquake pectral repone acceleration adjuted for ite cla effect are evaluated g g SMS Fa S SM1 Fv S The 5% damped deign pectral repone acceleration S DS at hort period and S D1 at long period in accordance are evaluated. 2 2 SDS SMS SD 1 SM g g0. g g Occupancy importance factor, I e a evaluated from IBC 2015 Table and ASCE 7-10 Table (rik category II). From Table (1), Seimic Deign Category (SDC) i A. From Table (2), SDC i B. Therefore, eimic deign category (SDC) i B. For ordinary hear wall and uing ASCE 7-10 Table , repone modification coefficient R 5.0. The eimic bae hear V in a given direction i determined in accordance with the following equation: V C W 121

29 The value of C hall not exceed the following: From example (2), T 1.293ec From Table , approximate period T ec. C T u a ec i.e., T 0.90 ec. S C C DS R / I e D1, max for L T R / I S e C, max C, min SDS Ie 0.01 T T ( T 13.0ec., Figure 7) Or, C, min i.e., C The eimic bae hear V ton L V W Vertical ditribution of force: F x C vx V a C vx w x n i1 w h i k x h k i and K = 1.20 (from linear interpolation). 122

30 Vertical Ditribution of Force: Level w h 1. 2 w C vx i x h x x F x 123