3 NAEIM 2009 Code Review

7/29/2019 3 NAEIM 2009 Code Review

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Farzad Naeim Structural Dynamics for Practicing Engineers 1of 51

(Last Revision Date: 5-26-2009)

Part III:Review of Selected

Provisions of

ASCE 7 and CBC

Farzad Naeim, Ph.D., S.E., Esq.Farzad Naeim, Ph.D., S.E., Esq.Vice President and General CounselVice President and General Counsel

John A. Martin & Associates, Inc.John A. Martin & Associates, Inc.



ASCE 7-05: Bring Your Copy to the Lecture

We will review and highlight someWe will review and highlight someimportant provisions of the followingimportant provisions of the followingchapters:chapters: Chapter 11: Section 11.4.7 and stateChapter 11: Section 11.4.7 and state

amendments to it in CBC 1614A.1.2amendments to it in CBC 1614A.1.2

Chapter 12: Sections 12.7 and 12.9Chapter 12: Sections 12.7 and 12.9

Chapter 21: SiteChapter 21: Site--Specific Ground MotionSpecific Ground MotionProceduresProcedures

Chapter 16: Seismic Response HistoryChapter 16: Seismic Response HistoryProceduresProcedures

Chapter 17: Seismic Design RequirementsChapter 17: Seismic Design Requirementsfor Seismically Isolated Structuresfor Seismically Isolated Structures

Chapter 18: Seismic Design RequirementsChapter 18: Seismic Design Requirementsfor Structures with Damping Systemsfor Structures with Damping Systems


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Elastic vs. Inelastic Response

TheThe red linered line showsshows

the force andthe force anddisplacement thatdisplacement thatwould be reached ifwould be reached ifthe structurethe structurerespondedrespondedelastically.elastically.

TheThe green linegreen lineshows the actualshows the actualforce vs.force vs.displacementdisplacementresponse of theresponse of thestructurestructure

TheThe pink linepink lineindicates theindicates theminimum strengthminimum strengthrequired to holdrequired to holdeverything togethereverything togetherduring inelasticduring inelasticbehaviorbehavior

TheThe blue lineblue line is theis theforce level that weforce level that wedesign for.design for.

We rely on theWe rely on theductility of theductility of thesystem to preventsystem to preventcollapse.collapse. from Dr. T. Bart Quimby Lecture Notes



IBC, CBC ASCE-7 Analysis Procedure

1. 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 factor

8. Select structural system and system parameters

(R, Cd, o)


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IBC, CBC ASCE-7 Analysis Procedure

9. Examine system for configuration irregularities10. Determine diaphragm flexibility (flexible, semi-rigid, rigid)

11. Determine redundancy factor ()

12. Determine lateral force analysis procedure

13. Compute lateral loads

14. Add torsional loads, as applicable

15. Add orthogonal loads, as applicable

16. Perform analysis

17. Combine results

18. Check strength, deflection, stability



IBC / CBC-2007/ ASCE 7 / ASCE-41 DESIGN SPECTRUM


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Methods of Analysis

The equivalent lateral force method (ELF) is allowed

for all buildings in SDC B and C. It is allowed in allSDC D, E, and F buildings EXCEPT:

Any structure with T > 3.5 Ts

Structures with T < 3.5 Ts and with Plan

Irregularity 1a or 1b or Vertical Irregularity 1,

2 or 3.

When the ELF procedure is not allowed, analysis

must be performed by the response spectrum

analysis procedure or by the linear (or nonlinear)response history analysis procedure.

Source: FEMA 451B



Equivalent Lateral Force Procedure

Source: FEMA 451B


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Transition Periods for Conterminous United States

Source: FEMA 451B



Approaches to Seismic Hazard Analysis

Deterministic

The earthquake hazard for the site is a peak ground

acceleration of 0.35g resulting from an earthquake

of magnitude 6.0 on the Whittier Fault at a distance of

12 miles from the site.

Probabilistic

The earthquake hazard for the site is a peak ground

acceleration of 0.28g with a 2 percent probability of

being exceeded in a 50-year period.

Source: FEMA 451B


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Steps in Deterministic Seismic Hazard Analysis

Source: FEMA 451B



Ground Motion Attenuation

Source: FEMA 451B


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Attenuation with Distance

Source: FEMA 451B



Example Deterministic Analysis (Kramer)

Source: FEMA 451B


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Steps in Probabilistic Seismic Hazard Analysis

Source: FEMA 451B



Example Probabilistic Analysis (Kramer)

Source: FEMA 451B


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Result of Probabilistic Hazard Analysis

Source: FEMA 451B



Relationship Between Return Period, Period of Interest,

and Probability of Exceedance

Source: FEMA 451B


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Use of PGA Seismic Hazard Curve

Source: FEMA 451B



Use of 0.2 Sec. Seismic Hazard Curve

Source: FEMA 451B


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10% in 50 Year Elastic Response Spectrum

Source: FEMA 451B



Uniform Hazard Spectrum

Source: FEMA 451B


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Uniform Hazard Spectrum

Developed from probabilistic analysisDeveloped from probabilistic analysis

All ordinates have equal probability ofAll ordinates have equal probability of

exceedanceexceedance

Represents contributions from small local,Represents contributions from small local,

large distant earthquakeslarge distant earthquakes

May be overly conservative for modalMay be overly conservative for modal

response spectrum analysisresponse spectrum analysis

May not be appropriate for artificial groundMay not be appropriate for artificial ground

motion generationmotion generation

Source: FEMA 451B



Probabilistic vs Deterministic Seismic Hazard Analysis

The probabilistic approach is capable

of integrating a wide range of

information and uncertainties into a

flexible framework.

Unfortunately, its highly integrated

framework can obscure those elements

which drive the results, and its highly

quantitative nature can lead to falseimpressions of accuracy.

Source: FEMA 451B


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Maximum Considered Earthquake (MCE)

The MCE ground motions are definedas the maximum level of earthquake

shaking that is considered as

reasonable to design normal structures

to resist.

Source: FEMA 451B



ASCE 7 (USGS) Seismic Hazard for Design Maps

5% damped, 2% in 50 years, Site Class B(firm rock)

0.2 second and 1.0 second spectral ordinatesprovided

On certain faults in California, Alaska, Hawaii,and CUS Provisions values are deterministiccap times 1.5. Outside deterministic areas,Provisions maps are the same as the USGSmaps.

USGS longitude/latitude and zip code valuesare probabilistic MCE. To avoid confusion,

ALWAYS use Provisions (adopted by ASCEand IBC) maps for design purposes.

Source: FEMA 451B


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Location of Deterministic Areas

Source: FEMA 451B



Deterministic Cap

Applies only where probabilistic values

exceed highest design values from old maps.

The deterministic procedure for mapping

applies:

For known active faults

Uses characteristic largest earthquake on fault

Uses 150% of value from median attenuation

Use deterministic value if lower than 2% in 50

year value

Source: FEMA 451B


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ASCE 7-05 Maps: 0.2 Second Spectral Response (SS)



ASCE 7-05 Maps: 1.0 Second Spectral Response (S1)


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2% in 50 Year 5% Damped MCE Elastic Spectra

Site Class B (Firm Rock)

Source: FEMA 451B



Site Amplification Effects

Source: FEMA 451B


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Site Amplification Effects

Amplification of ground motion Longer duration of motion

Change in frequency content of motion

Not the same as soil-structure interaction

Source: FEMA 451B



ASCE 7-05 Section 11.4.7

11.4.7 Site-Specific Ground Motion Procedures.The

site-specific ground motion procedures set forth in

Chapter 21 are permitted to be used to determine ground

motions for any structure. A site response analysis shall

be performed in accordance withSection 21.1for

structures on Site Class F sites, unless the exception to

Section 20.3.1is applicable. For seismically isolated

structures and for structures with damping systems on

sites withS1 greater than or equal to 0.6, a ground

motion hazard analysis shall be performed in accordance

withSection 21.2.


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Section 20.3.1 Exception

20.3.1 Site Class F. Where any of the following conditions is

satisfied, the site shall be classified as Site Class F and a siteresponse analysis in accordance withSection 21.1shall beperformed.

1. Soils vulnerable to potential failure or collapse under seismicloading, such as liquefiable soils, quick and highly sensitiveclays, and collapsible weakly cemented soils.

EXCEPTION: For structures having fundamental periods ofvibration equal to or less than 0.5 s, site-response analysis is

not requiredto determine spectral accelerations for liquefiablesoils. Rather, a site class is permitted to be determined inaccordance with Section 20.3 and the corresponding values ofFa andFvdetermined from Tables 11.4-1 and 11.4-2.



Chapter 21 of ASCE 7-05

This Chapter describes requirements for siteThis Chapter describes requirements for site--specific ground motionspecific ground motion

proceduresprocedures

Section 21.1 describes the requirements for Site Response AnalysSection 21.1 describes the requirements for Site Response Analyseses

Section 21.2 describes the requirements for constructionSection 21.2 describes the requirements for construction

of MCE design Spectrum using:of MCE design Spectrum using:

The probabilistic method andThe probabilistic method and

Application of the deterministic cap as described in previous slApplication of the deterministic cap as described in previous slides. Theides. The

deterministic cap is 1.5 times mean deterministic valuesdeterministic cap is 1.5 times mean deterministic values

The deterministic cap is subjected to minimum values specified iThe deterministic cap is subjected to minimum values specified in Sectionn Section

21.2.321.2.3

Section 21.3 simply states that design values shall be taken asSection 21.3 simply states that design values shall be taken as 2/3 of2/3 of

MCE valuesMCE values Section 21.4 places lowerSection 21.4 places lower--bound limits obtained from sitebound limits obtained from site--specificspecific

analysis in comparison with values established in Chapter 11.analysis in comparison with values established in Chapter 11.


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CBC Amendments to Site Response Analysis

Requirements of ASCE-7-05 (Section 11.4.7)

Section 16.14A.1.2 of 2007 CBC amends SectionSection 16.14A.1.2 of 2007 CBC amends Section

11.4.7 of ASCE 711.4.7 of ASCE 7--05 as follows:05 as follows:

Site Response AnalysisSite Response Analysis

1.1. Site response analysis shall be performed per ASCE 7Site response analysis shall be performed per ASCE 7

Section 21.1 and site specific ground motion developedSection 21.1 and site specific ground motion developed

per ASCE 7 Section 21.2 ifper ASCE 7 Section 21.2 if

a)a) Site soil isSite soil is Type EType E and mapped MCEand mapped MCE SSss > 2.0g> 2.0g

b)b) Site soil isSite soil is Type FType F..

EXCEPTIONS:EXCEPTIONS:

1.1. IfIfSSss < 2.0g soil< 2.0g soil Type EType E may be usedmay be used

2.2. If Exception to ASCE 7 Section 20.3.1 is applicable andIf Exception to ASCE 7 Section 20.3.1 is applicable and

building is not base isolated.building is not base isolated.



CBC Amendments to Site Response Analysis

Requirements of ASCE-7-05 (Section 11.4.7)

Section 16.14A.1.2 of 2007 CBC amends SectionSection 16.14A.1.2 of 2007 CBC amends Section

11.4.7 of ASCE 711.4.7 of ASCE 7--05 as follows:05 as follows:

Ground Motion Hazard Analysis (SiteGround Motion Hazard Analysis (Site--Specific HazardSpecific Hazard

Analysis)Analysis)

2.2. Site specific ground motion developed per ASCE 7Site specific ground motion developed per ASCE 7

Section 21.2 whenSection 21.2 when

a)a) TimeTime--history response analysis is being performed as part ofhistory response analysis is being performed as part of

the designthe design

b)b) The building is located within 10 kilometers of an active faultThe building is located within 10 kilometers of an active fault

c)c) For seismically isolated structures and for structures withFor seismically isolated structures and for structures with

damping systems.damping systems.


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ASCE 7-05 Modeling Criteria (Section 12.7)

12.7 MODELING CRITERIA

12.7.1 Foundation Modeling.For purposes of determining seismic loads, it is permittedto consider the structure to be fixed at the base. Alternatively, where foundationflexibility is considered, it shall be in accordance with Section 12.13.3 or Chapter 19.

12.7.2 Effective SeismicWeight.The effective seismic weight,W, of a structure shallinclude the total dead load and other loads listed below:

1. In areas used for storage, a minimum of 25 percent of the floor live load (floor

live load in public garages and open parking structures need notbe included).

2. Where provision for partitions is required by Section 4.2.2 in the floor load

design, the actual partition weight or a minimum weight of 10 psf (0.48 kN/m2)

of floor area, whichever is greater.

3. Total operating weight of permanent equipment.

4. Where the flat roof snow load,Pf, exceeds 30 psf (1.44 kN/m2), 20 percent of

the uniform design snow load, regardless of actual roof slope.





12.7.3 Structural Modeling.A mathematical model of the structure shall be constructed forthe purpose of determining member forces and structure displacements resulting fromapplied loads and any imposed displacements or P-Delta effects.

The model shall include the stiffness and strength of elements that are significant to thedistribution of forces and deformations in the structure and represent the spatialdistribution of mass and stiffness throughout the structure.

Structures that have horizontal structural irregularity Type 1a,1b, 4, or 5 of Table 12.3-1 shallbe analyzed using a 3-D representation.

Where a 3-D model is used, a minimum of three dynamic degrees of freedom consisting of

translation in two orthogonal plan directions and torsional rotation about the vertical axisshall be included at each level of the structure.

Where the diaphragms have not been classified as rigid or flexible in accordance with Section12.3.1, the model shall include representation of the diaphragms stiffness characteristicsand such additional dynamic degrees of freedom as are required to account for theparticipation of the diaphragm in the structures dynamic response.


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12.7.3 Structural Modeling (continued).

In addition, the model shall comply with the following:

a. Stiffness properties of concrete and masonryelements shall consider the effects of crackedsections.

b. For steel moment frame systems, the contribution ofpanel zone deformations to overall story drift shall beincluded.



ASCE 7-05 Modal Response Analysis (Section 12.9)

1.1. Compute modal properties for each modeCompute modal properties for each mode

a)a) PeriodsPeriods

b)b) Mode shapesMode shapes

c)c) Modal participation factorsModal participation factors

d)d) Effective modal massesEffective modal masses

2.2. Determine number of modes to use in analysis.Determine number of modes to use in analysis.

Use a sufficient number of modes to capture atUse a sufficient number of modes to capture at

least 90% of total mass in each directionleast 90% of total mass in each direction

3.3. Using the spectrum curve or table compute spectralUsing the spectrum curve or table compute spectral

accelerations for each contributing modeaccelerations for each contributing mode4.4. Multiply spectral accelerations by modalMultiply spectral accelerations by modal

participation factor and by (participation factor and by (I/RI/R))

5.5. Compute modal displacements for each modeCompute modal displacements for each mode

Source: FEMA 451B


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ASCE 7-05 Modal Response Analysis (Section 12.9)

6.6. Compute element forces in each modeCompute element forces in each mode

7.7. Statistically combine (SRSS or CQC) modal displacements toStatistically combine (SRSS or CQC) modal displacements to

determine system displacementsdetermine system displacements

8.8. Statistically combine (SRSS or CQC) component forces toStatistically combine (SRSS or CQC) component forces to

determine design forcesdetermine design forces

9.9. If the design base shear based on modal analysis is less thanIf the design base shear based on modal analysis is less than

85% of the base shear computed using ELF (and85% of the base shear computed using ELF (and T =T = TTaaCCuu), the), the

member forces resulting from the modal analysis andmember forces resulting from the modal analysis and

combination of modes must be scaled such that the base shearcombination of modes must be scaled such that the base shear

equals 0.85 times the ELF base shear.equals 0.85 times the ELF base shear.

10.10. Add accidental torsion as a static loading and amplify ifAdd accidental torsion as a static loading and amplify if

necessarynecessary

11.11. For determining drift, multiply the results of the modal analysiFor determining drift, multiply the results of the modal analysiss

(including the(including the I/RI/R scaling but not the 85% scaling) byscaling but not the 85% scaling) by CCdd/ I/ I..

Source: FEMA 451B



Chapter 16: Seismic Response

History Procedures


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Use a minimum of 3 earthquake ground motionsUse a minimum of 3 earthquake ground motions

(pairs)(pairs)

If you use 3 you need to use the maximum responseIf you use 3 you need to use the maximum response

parameters obtained.parameters obtained.

If you use 7 or more you can use the average valuesIf you use 7 or more you can use the average values

of response parameters obtained.of response parameters obtained.

Ground motions must be scaled such that theGround motions must be scaled such that the

average value of the 5% damped response spectra ofaverage value of the 5% damped response spectra of

the suite of motions is not less than the designthe suite of motions is not less than the design

response spectrum in the period rangeresponse spectrum in the period range 0.2T0.2T toto 1.5T1.5T,,

wherewhere TT is the fundamental period of the structure.is the fundamental period of the structure.



Scaling for 2-D Analysis

Source: FEMA 451B


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Source: FEMA 451B




The square root of the sum of the squares of the 5%The square root of the sum of the squares of the 5%

damped spectra of each motion pair (Ndamped spectra of each motion pair (N--S and ES and E--WW

components) is constructedcomponents) is constructed

Each pair of motions should be scaled such that theEach pair of motions should be scaled such that the

average of the SRSS spectra of all component pairsaverage of the SRSS spectra of all component pairs

is not less than 1.3 times theis not less than 1.3 times the thethe 5% damped design5% damped design

spectrum in the period range 0.2 to 1.5 T.spectrum in the period range 0.2 to 1.5 T.


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Chapter 17: Seismic Design

Requirements for Seismically

Isolated Structures



Chapter 18: Seismic Design

Requirements for Structures

with Damping Systems


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