SEISMIC LOAD ANALYSIS - University of Memphis

1 SEISMIC load ANALYSIS 9 - 1 Instructional Material Complementing FEMA 451, Design ExamplesSEISMIC load ANALYSISS eismic load ANALYSIS 9 - 2 Instructional Material Complementing FEMA 451, Design ExamplesTopic Objectives Selection of method of ANALYSIS Description of ANALYSIS techniques Modeling considerations System regularity load combinations Other considerations Drift computation and acceptance criteria P-delta effectsSeismic load ANALYSIS 9 - 3 Instructional Material Complementing FEMA 451, Design ExamplesLoad ANALYSIS Procedure(ASCE 7, NEHRP Recommended Provisions)1.

2 Determine building occupancy category (I-IV)2. Determine basic ground motion parameters (SS, S1)3. Determine site classification (A-F)4. Determine site coefficient adjustment factors (Fa, Fv)5. Determine design ground motion parameters (SdS, Sd1)6. Determine SEISMIC design category (A-F)7. Determine importance factor8. Select structural system and system parameters (R, Cd, o) SEISMIC load ANALYSIS 9 - 4 Instructional Material Complementing FEMA 451, Design ExamplesLoad ANALYSIS Procedure(Continued)9. Examine system for configuration irregularities10. Determine diaphragm flexibility (flexible, semi-rigid, rigid)11.

3 Determine redundancy factor ( )12. Determine lateral force ANALYSIS procedure13. Compute lateral loads14. Add torsional loads, as applicable15. Add orthogonal loads, as applicable16. Perform analysis17. Combine results18. Check strength, deflection, stabilitySeismic load ANALYSIS 9 - 5 Instructional Material Complementing FEMA 451, Design ExamplesOccupancy Category (ASCE 7)I) Low risk occupancyAgricultural facilitiesTemporary facilitiesMinor storage facilitiesII) Normal hazard occupancyAny occupancy not described as I, III, IVIII) High hazard occupancyHigh occupancy (more than 300 people in one room)Schools and universities (various occupancy)

4 Health care facilities with < 50 resident patientsPower stationsWater treatment facilitiesTelecommunication load ANALYSIS 9 - 6 Instructional Material Complementing FEMA 451, Design ExamplesOccupancy Category (ASCE 7, continued)IV) Essential facilitiesHospitals or emergency facilities with surgeryFire, rescue, ambulance, police stationsDesignated emergency sheltersAviation control towersCritical national defense : NEHRP Recommended Provisionshas Occupancy Categories I-III;ASCE 7 I+II = NEHRP I, ASCE 7 III = NEHRP II, ASCE 7 IV = NEHRP IIIS eismic load ANALYSIS 9 - 7 Instructional Material Complementing FEMA 451, Design Examples Provide 5% damped firm rock (Site Class B) spectral accelerations Ssand S1 or 2% in 50 year probability or times deterministic peak in areas of western US Modified for other site conditions by coefficients FvandFato determine spectral coefficients SMSand SM1 Divided by to account for expected good performance.

5 This provides the design spectral coordinates SDSand Maps Design Ground MotionsSeismic load ANALYSIS 9 - 8 Instructional Material Complementing FEMA 451, Design ExamplesT = Spectral Accelerations (Ss) for Conterminous US(2% in 50 year, 5% damped, Site Class B) SEISMIC load ANALYSIS 9 - 9 Instructional Material Complementing FEMA 451, Design ExamplesT = 1 Spectral Accelerations(S1) for Conterminous US(2% in 50 year, 5% damped, Site Class B) SEISMIC load ANALYSIS 9 - 10 Instructional Material Complementing FEMA 451, Design ExamplesAHard rock vs> 5000 ft/secBRock: 2500 <vs< 5000 ft/secCVery dense soil or soft rock: 1200 < vs< 2500 ft/secDStiff soil.

6 600 < vs< 1200 ft/secEVs< 600 ft/secFSite-specific requirementsSITE CLASSESS eismic load ANALYSIS 9 - 11 Instructional Material Complementing FEMA 451, Design ExamplesNEHRP Site Amplification for Site Classes A through ESite ClassSite Period Acceleration S1 (g)Response Acceleration ParamaterSite ASite BSite CSite DSite Period Acceleration Ss (g)Response Acceleration ParamaterSite ASite BSite CSite DSite ESeismic load ANALYSIS 9 - 12 Instructional Material Complementing FEMA 451, Design Examples avg max1a) and 1b) Torsional < >No irregularityIrregularityExtreme irregularityHorizontal Structural IrregularitiesIrregularity 1b is NOT PERMITTED in SDC E or load ANALYSIS 9 - 13 Instructional Material Complementing FEMA 451, Design Examples2) Re-entrant Corner > >Irregularity exists ifandHorizontal Structural IrregularitiesSeismic load ANALYSIS 9 - 14 Instructional Material Complementing FEMA 451, Design ExamplesOpen3)

7 Diaphragm Discontinuity IrregularityIrregularity exists if open area > times floor areaOR if effective diaphragm stiffness varies by more than50% from one story to the Structural IrregularitiesSeismic load ANALYSIS 9 - 15 Instructional Material Complementing FEMA 451, Design Examples4) Out of Plane OffsetsHorizontal Structural IrregularitiesSeismic load ANALYSIS 9 - 16 Instructional Material Complementing FEMA 451, Design Examples5) Nonparallel Systems IrregularityNonparallel system Irregularityexists when the verticallateral force resisting elements are not parallel to orsymmetric about the major orthogonal axes of the seismicforce resisting Structural IrregularitiesSeismic load ANALYSIS 9 - 17 Instructional Material Complementing FEMA 451, Design Examples1a, 1b) Stiffness (Soft Story) IrregularityVertical Structural IrregularitiesIrregularity (1a)

8 Exists if stiffnessof any story is less than 70%of the stiffness of the story above or less than 80%of the averagestiffness of the three stories extreme irregularity (1b) exists ifstiffness of any story is less than 60%of the stiffness of the story above or less than 70%of the averagestiffness of the three stories : Irregularity does notexist if no story drift ratio is greaterthan times drift ratio of story 1b is NOT PERMITTED inSDC E or F. 11 K=1/ SEISMIC load ANALYSIS 9 - 18 Instructional Material Complementing FEMA 451, Design Examples2) Weight (Mass) IrregularityVertical Structural IrregularitiesIrregularity exists if the effectivemass of any story is more than 150%of the effective mass of an.

9 Irregularity does notexist if no story drift ratio is greaterthan times drift ratio of story load ANALYSIS 9 - 19 Instructional Material Complementing FEMA 451, Design Examples3) Vertical Geometric IrregularityVertical Structural IrregularitiesIrregularity exists if the dimension ofthe lateral force resisting system atany story is more than 130% of thatfor any adjacent storydidi-1di+1 SEISMIC load ANALYSIS 9 - 20 Instructional Material Complementing FEMA 451, Design Examples4) In-Plane Discontinuity IrregularityVertical Structural IrregularitiesdoffsetIrregularity exists if the offset isgreater than the width (d) or thereexists a reduction in stiffness of thestory load ANALYSIS 9 - 21 Instructional Material Complementing FEMA 451, Design Examples5a, 5b) Strength (Weak Story) IrregularityVertical Structural IrregularitiesIrregularity (5a) exists if the lateralstrength of any story is less than 80%of the strength of the story above.

10 An extreme irregularity (5b) existsIf the lateral strength of any story isless than 65% of the strength of thestory above. Irregularities 5a and 5b are NOTPERMITTED in SDC E or F. Irregularity 5b not permitted in SDC load ANALYSIS 9 - 22 Instructional Material Complementing FEMA 451, Design ExamplesStructural SystemsA. Bearing wall systemsB. Building frame systemsC. Moment resisting frame systemsD. Dual systems with SMRFE. Dual systems with IMRFF. Ordinary shear-wall frame interactive systemsG. Cantilever column systemsH. Steel systems not detailed for seismicSystem Parameters.