CE 4560 Structural Steel Design Lecture 06 PDF

CE4560 STRUCTURAL STEEL DESIGN 06. Lateral Loads – Seismic Sunai Kim, Ph.D., S.E. 1  Lecture Outline  Seismic Loads  Relevant code chapters  Lateral Force Resisting System (LFRS) – analysis methods  Win...

CE4560 STRUCTURAL STEEL DESIGN 06. Lateral Loads – Seismic Sunai Kim, Ph.D., S.E. 1  Lecture Outline  Seismic Loads  Relevant code chapters  Lateral Force Resisting System (LFRS) – analysis methods  Wind Loads - not covered in this class  Risk Category & Importance Factors  Response Spectrum  Base Shear  Calculations  Selection of LRFS  Story forces 2  Seismic Loads  Account for building response to earthquake ground motion.  Expected behavior  Yielding and inelastic demands at intended locations (lateral force resisting system) Seismic acceleration M  Prescribed design per code  Requires both CBC 2022 and 1T I sec  ASCE7-16 taller building longer period 3  ASCE7-16 Lateral Load Chapters  ASCE7-16:  Chapter 1 – General (for risk category & importance factors)  Chapter 11 – Seismic Design Criteria  Chapter 12 – Seismic Design Requirements for Building Structures  Chapter 22 – Seismic Ground Motion Long-Period Transition and Risk Coefficient Maps  Chapters 26 – 31: Wind Loads 4  Analysis Procedures  Analysis Procedures:  Structural behavior: Linear / nonlinear  Loading conditions: Static / dynamic ASCE 7-16 base shear Linear Nonlinear (ELF)( hand-calc Static Equivalent Lateral Force Push-over Analysis startnere Analysis Dynamic Response Spectrum Y ~ Nonlinear Response Analysis History Analysis  In general, most low-rise buildings without irregularities: linear dynamic procedure  Complicated (irregular) or high-rise buildings: nonlinear dynamic procedure 5  Analysis Procedures  Analysis Procedures, ASCE7-16 Table 12.6-1: ASCE 7-16 Ch. = lateral Tall building 100' h 6  Risk Category & Importance Factor 7  Seismic Loads – Risk Category  Risk Category  Based on occupancy 8  Seismic Loads – Importance Factor  Importance Factor  Based on Risk Category  Ie – for seismic importance factor 9 Response Spectrum 10  Seismic Loads – Response Spectrum USGS 1. Choose a project site: find out Ss, S1  Ss – MCER spectral response acceleration parameter at short periods  S1 – MCER spectral response acceleration parameter at 1 second  Ss, S1 are for site class B (ASCE7-16 Chapter 22, or USGS website)  Site Classification: ASCE7-16 Ch. 20, Table 20.3-1  Based on soil profile & shear wave velocity  Default for CA: Site Class D SS. S. (site class B) ↓ Assume Sus Sm , ladj For , · project 3 ground is Site) made of M =) max considered rock EQ RTE 2475 yrs 2% chance of exceedence in SDS SD SOXVS , D design basis 11 EQ RT = 475yrs 10 % Chance  Seismic Loads – Response Spectrum 2. Modify responses per site class effects  SMS = Fa·Ss  SM1 =Fv·S1  Look up Fa, Fv in ASCE7-16 Tables 11.4-1 and 11.4-2 12  Seismic Loads – Response Spectrum 3. Convert to Design Acceleration Parameters, plot design response spectrum  SDS = 2/3·SMS DBE Response Spectrum  SD1 = 2/3·SM1 y23DBE FR Y F4 Y F3 & > F2 - T T T 13  Seismic Loads – Response Spectrum  Other Variables:  Spectral Acceleration:  T < T0: Sa = SDS ( 0.4 + 0.6·T / T0)  TS < T < TL: Sa = SD1 / T  T > TL: Sa = (SD1·TL / T2)  Period:  T = fundamental period of the structure  T0 = 0.2·SD1 / SDS  TS = SD1 / SDS  TL = long period, shown in ASCE7-16 Figures 22-12 through 22-16 14  Seismic Loads – Response Spectrum 4. Determine Seismic Design Category:  A, B, C, or D  Mostly D in California (high seismic zone) 15  Seismic Loads – Hazard Maps  Using ASCE7-16 Chapter 22 (approximate):  S1  SS  Can you spot San Andreas fault? 16  Seismic Loads – Hazard Maps  Using ASCE7-16 Chapter 22:  TL 17  Seismic Loads – Hazard Maps  Using U.S. Seismic Design Maps from ASCE7:  https://asce7hazardtool.online/  Try: 3801 W. Temple Ave, Pomona CA 91768 18  Seismic Loads – Hazard Maps  Using U.S. Seismic Design Maps from ASCE7:  You’ll be able to draw the MCE/DBE level response spectra using the spectral acceleration values (ex: excel) 19 Base Shear 20  Seismic Loads – Base Shear  ASCE7-16 Chapter 12.8: Equivalent Lateral Force Procedure ↑ W = &V &R = V ,  Seismic Base Shear:  V = CS·W F = mam = w , a = Cs  𝐶 = - seismic response coefficient V R = ductility. Ie = importance factor  W – effective seismic weight, includes: dead load above the base, and other loads as listed below:  In areas used for storage, a minimum of 25% of the floor live load shall be included.  Refer to Exceptions in 12.7.2. W D([psf) A 7H2] + "Avertical = 16 Decladding = + - · -- 21 vertical  Seismic Loads – Base Shear  Seismic Response Coefficient  Check for max:  Check for min: 22  Seismic Loads – Period  Approximate Fundamental Period  Ta = Ct·hnx  hn – structural height (ft)  Ct, x – look up ASCE7-16, Table 12.8-2  Alternatively, for buildings < 12 stories and where seismic force-resisting system consists entirely of concrete or steel moment frames, and the average story height is min 10ft: Ta = 0.1·N N – number of stories 23  Seismic Loads – R  Response Modification Coefficient, R 24  Seismic Loads – R EBF : eccentrically Braced frame Response Modification Coefficient, R -   Some of more commonly used LFRS: l  Higher R = more ductile CBF Concentrically Braced :  Compare R between special vs. ordinary systems ame & A. Bearing Wall Systems Special reinforced concrete shear walls R = 5 B. Building Frame Systems table Steel eccentrically braced frames R = 8 12 2-1. Steel special concentrically braced frames R = 6 C. Moment-Resisting Frame Systems Steel special moment frames R = 8 Special reinforced concrete moment frames R = 8 D. Dual Systems with Special Moment Frames Capable of Resisting at least 25% of Prescribed Seismic Forces 25  Seismic Loads – Story Forces  ASCE7-16, Chapter 12.8.3: Vertical Distribution of Seismic Forces  Lateral force (Fx), at any level 𝐹 =𝐶 𝑉 𝑤 ℎ 𝐶 = ∑ 𝑤ℎ  Cvx = vertical distribution factor  V = total design lateral force or base shear  wi and wx = portion of the total effective seismic weight of the structure (W) located to level i or x  hi and hx = height from base to level i or x  k = exponent related to period of structure  T < 0.5s: k = 1  T > 2.5s: k = 2 26  Seismic Loads – In summary  Summary of R, Cd, Ω0  E (elastic design base shear)  S (design seismic force level)  S to M (increase in total resistance of system) Reference: SEAOC Blue Book (2007) 27 Lecture 06 Questions? 28  CAL POLY POMONA COLLEGE OF ENGINEERING CE4560: Professor Kim STRUCTURAL STEEL DESIGN Lecture 06 1. Calculate base shear in the N-S direction using Equivalent Lateral Force procedure of ASCE7-16 for the example building. Determine the seismic force acting on each floor. 4 I 13’ 3 13.5’ V I 56’-6” 2 E-W 13.5’ 1 V 16’ N- S 195’-6” Elevation View Plan View Location: 10250 Santa Monica Blvd, Los Angeles, CA 90067 Given:  4 stories  Seismic Force Resisting System (SFRS): o Special Steel Concentric Braced Frame – N/S direction o Special Steel Concentric Braced Frame in the upper 3 floors & bearing shear walls at lower level – E/W direction Structural Behavior  Occupancy: office  Site Class: C loading linear nonlinear  Office DL = 80psf, LL = 50 psf Static ElF Push over analysis  Roof DL = 31psf, LL = 20 psf dynamic response non linear I. Seismic parameters spectrum response history Risk Category : It analysis analysis ASCET-In ChI Table 1 5. - 1 (SAP ETABS) , (Perform 3D) Importance factor : Ie = 1 0. Table 1 5-2 Horizontal force. seismic weight > : typical floor 80psfx(199 51 3 =. x 56. 5)/1000k/# = 884k + 342k 2 = 884k x3 floors = 2994k roof = 31pSf x (199. 51 x 96. 5')/10004# = 342k w = 2994k cladding : roof = [Opsf (195 5' +. x 2 + 56 3 '. x 2) (6. 32]/10004/# = 65. 32k vertical force 3rd = (20ps+ + (99. 5. x 2 + 36 3. x 2)(12. 79177/1000 = 128 32k. Approximate Period : Ta = 0 IN = 0. 1(47 = 0 4 sec.. 1. Ct 75 3 * 0 02 ASCE Ch12 Ta = Xh 10 02) (5670 = or =. Steel =>. = 0 41 sec. Table 12 8 2. 0 75 CBF.. X =. 16 + 13 31 2 + 131 96. = nn =. x Seismic Force Resistance System : R 6 Table 12 2 1 =... 2 Seismic Acceleration Parameters :2009 si comes from location Us a use Stable 11 4. - 12 SMS = FaSs = (1 2) (2009). = 2 496. SM1 = FrS , = (1 4) (0 7439).. = 1 041. => SDs (Short period) 23(2 496) 2/3SMs = *. = 1 664. SD , (1 Sec period) 2/3 2/3(1 041) SM = -. = 0 694. ↳ D DCE = M = MCE Sa 1 SDS 1 664. Sa = SDI/ + L ·. L Sa = SDITz/+ 2 - + Isec) To Ts 1 0. Th SD/ 0 2(0 694) To = 0 2.. 0 083 Sec. = = SDS 1. 604. T :SD - Oba : O.Hs. Base shear 3 V = Cs. W SDS 1 064. (e) (10) O = = 0 27. ASCET-16 Sec 12 8.. table 12 2-1. max = 10 is /1) Rite) * = 0 282. & = 0 044SDsFe = 0 044(1 064)(1 0 = 0 0732 min.....  S 10 If ,. 69 0 5151) 0 310 743) as min. =.. = = 0 062 governs Osmin R/Ie. , 01 [0. 062 , 0. 282] our calculated is between max & min = can use Cs = 0. 27 (smin , max] * If CaIC · is not within Cs range = select the closer boundary as Cs v= 0. 27(2994k) = 808 4k. 4. Distribution of Story Forces #x = Cux - V ASCE 7-16 Sec. 12 8 3.. , whxk ↑ (0 9 = k = 1 crx. = T)2 5 = k = 2 Ewhy. Ta 0 4) = k =. = 1 (wi)(hyk) Floor ni(H) Wi(k) (Willhi) 2/Wil(i) Ex ↓ 10 884 14 , 144. 145 0 10 145) (808.. 41) = 111 2k. 2 29 S. 884 26 , 078 0 208. 10 268)(808 4) 216 7k.. =. 3 43 884 38 , 012 0. 39 10 39) 1808 4).. : 315. 31 R G6 342 19 , 162 0 197. 10 1977(808 4) : 199 3 k... E 299497386 1 00. Fr = 117 2k Y * roof is less bla ↑. it weighs less Fz 319 31 Y =. F = 216 71. F = 117 2k. + Y 1 & V = 808 4k.