Cover [PDF]

Standards [PDF]

Foreword [PDF]

Acknowledgements [PDF]

Dedication [PDF]

Contents [PDF]

Chapter 1 General

Chapter 2 Combinations of Loads

Chapter 3 Dead Loads, Soil Loads, and Hydrostatic Pressure

Chapter 4 Live Loads

Chapter 5 Flood Loads

Chapter 6 Reserved for Future Provisions

Chapter 7 Snow Loads

Chapter 8 Rain Loads

Chapter 9 Reserved for Future Provisions

Chapter 10 Ice Loads - Atmospheric Icing

Chapter 11 Seismic Design Criteria

Chapter 12 Seismic Design Requirements for Building Structures

Chapter 13 Seismic Design Requirements for Nonstructural Components

Chapter 14 Material Specific Seismic Design and Detailing Requirements

Chapter 15 Seismic Design Requirements for Nonbuilding Structures

Chapter 16 Seismic Response History Procedures

Chapter 17 Seismic Design Requirements for Seismically Isolated Structures

Chapter 18 Seismic Design Requirements for Structures with Damping Systems

Chapter 19 Soil-Structure Interaction for Seismic Design

Chapter 20 Site Classification Procedure for Seismic Design

Chapter 21 Site-Specific Ground Motion Procedures for Seismic Design

Chapter 22 Seismic Ground Motion Long-Period Transition and Risk Coefficient Maps

Chapter 23 Seismic Design Reference Documents

Chapter 24

Chapter 25

Chapter 26 Wind Loads: General Requirements

Chapter 27 Wind Loads on Buildings‒MWFRS (Directional Procedure)

Chapter 28 Wind Loads on Buildings‒MWFRS (Envelope Procedure)

Chapter 29 Wind Loads on Other Structures and Building Appurtenances‒MWFRS

Chapter 30 Wind Loads ‒ Components and Cladding (C&C)

Chapter 31 Wind Tunnel Procedure

Appendix 11A Quality Assurance Provisions

Appendix 11B Existing Building Provisions

Appendix C Serviceability Considerations

Appendix D Buildings Exempted from Torisional Wind Load Cases

The requirements of Section 21.1 shall be satisfied where site response analysis is performed or required by Section 11.4.7. The analysis shall be documented in a report.
A site response model based on low-strain shear wave velocities, nonlinear or equivalent linear shear stress-strain relationships, and unit weights shall be developed. Low-strain shear wave velocities shall be determined from field measurements at the site or from measurements from similar soils in the site vicinity. Nonlinear or equivalent linear shear stress-strain relationships and unit weights shall be selected on the basis of laboratory tests or published relationships for similar soils. The uncertainties in soil properties shall be estimated. Where very deep soil profiles make the development of a soil model to bedrock impractical, the model is permitted to be terminated where the soil stiffness is at least as great as the values used to define Site Class D in Chapter 20. In such cases, the MCER response spectrum and acceleration time histories of the base motion developed in Section 21.1.1 shall be adjusted upward using site coefficients in Section 11.4.3 consistent with the classification of the soils at the profile base.
A site response model based on low-strain shear wave velocities, nonlinear or equivalent linear shear stress-strain relationships, and unit weights shall be developed. Low-strain shear wave velocities shall be determined from field measurements at the site or from measurements from similar soils in the site vicinity. Nonlinear or equivalent linear shear stress-strain relationships and unit weights shall be selected on the basis of laboratory tests or published relationships for similar soils. The uncertainties in soil properties shall be estimated. Where very deep soil profiles make the development of a soil model to bedrock impractical, the model is permitted to be terminated where the soil stiffness is at least as great as the values used to define Site Class D in Chapter 20. In such cases, the MCER response spectrum and acceleration time histories of the base motion developed in Section 21.1.1 shall be adjusted upward using site coefficients in Section 11.4.3 consistent with the classification of the soils at the profile base.
Base ground motion time histories shall be input to the soil profile as outcropping motions. Using appropriate computational techniques that treat nonlinear soil properties in a nonlinear or equivalent-linear manner, the response of the soil profile shall be determined and surface ground motion time histories shall be calculated. Ratios of 5% damped response spectra of surface ground motions to input base ground motions shall be calculated. The recommended surface MCER ground motion response spectrum shall not be lower than the MCER response spectrum of the base motion multiplied by the average surface-to-base response spectral ratios (calculated period by period) obtained from the site response analyses. The recommended surface ground motions that result from the analysis shall reflect consideration of sensitivity of response to uncertainty in soil properties, depth of soil model, and input motions.
The requirements of Section 21.2 shall be satisfied where a ground motion hazard analysis is performed or required by Section 11.4.7. The ground motion hazard analysis shall account for the regional tectonic setting, geology, and seismicity; the expected recurrence rates and maximum magnitudes of earthquakes on known faults and source zones; the characteristics of ground motion attenuation near source effects, if any, on ground motions; and the effects of subsurface site conditions on ground motions. The characteristics of subsurface site conditions shall be considered either using attenuation relations that represent regional and local geology or in accordance with Section 21.1. The analysis shall incorporate current seismic interpretations, including uncertainties for models and parameter values for seismic sources and ground motions. If the spectral response accelerations predicted by the attenuation relations do not represent the maximum response in the horizontal plane, then the response spectral accelerations computed from the hazard analysis shall be scaled by factors to increase the motions to the maximum response. If the attenuation relations predict the geometric mean or similar metric of the two horizontal components, then the scale factors shall be 1.1 for periods less than or equal to 0.2 sec 1.3 for a period of 1.0 sec., and 1.5 for periods greater than or equal to 5.0 sec., unless it can be shown that other scale factors more closely represent the maximum response, in the horizontal plane, to the geometric mean of the horizontal components. Scale factors between these periods shall be obtained by linear interpolation. The analysis shall be documented in a report.
The probabilistic spectral response accelerations shall be taken as the spectral response accelerations in the direction of maximum horizontal response represented by a 5% damped acceleration response spectrum that is expected to achieve a 1% probability of collapse within a 50-year period. For the purpose of this standard, ordinates of the probabilistic ground motion response spectrum shall be determined by either Method 1 of Section 21.2.1.1 or Method 2 of Section 21.2.1.2.
At each spectral response period for which the acceleration is computed, ordinates of the probabilistic ground motion response spectrum shall be determined as the product of the risk coefficient, CR, and the spectral response acceleration from a 5% damped acceleration response spectrum having a 2% probability of exceedance within a 50-year period. The value of the risk coefficient, CR, shall be determined using values of CRS and CR1 from Figs. 22-17 and 22-18, respectively. At spectral response periods less than or equal to 0.2 s, CR shall be taken as equal to CRS. At spectral response periods greater than or equal to 1.0 s, CR shall be taken as equal to CR1. At response spectral periods greater than 0.2 s and less than 1.0 s, CR shall be based on linear interpolation of CRS and CR1.
At each spectral response period for which the acceleration is computed, ordinates of the probabilistic ground motion response spectrum shall be determined from iterative integration of a site-specific hazard curve with a log-normal probability density function representing the collapse fragility (i.e., probability of collapse as a function of spectral response acceleration). The ordinate of the probabilistic ground motion response spectrum at each period shall achieve a 1% probability of collapse within a 50-year period for a collapse fragility having (1) a 10% probability of collapse at said ordinate of the probabilistic ground motion response spectrum and (2) a logarithmic standard deviation value of 0.6.
The deterministic spectral response acceleration at each period shall be calculated as an 84th-percentile 5% damped spectral response acceleration in the direction of maximum horizontal response computed at that period. The largest such acceleration calculated for the characteristic earthquakes on all known active faults within the region shall be used. For the purposes of this standard, the ordinates of the deterministic ground motion response spectrum shall not be taken as lower than the corresponding ordinates of the response spectrum determined in accordance with Fig. 21.2-1, where Fa and Fv are determined using Tables 11.4-1 and 11.4-2, respectively, with the value of SS taken as 1.5 and the value of S1 taken as 0.6.


Period, T (sec)
FIGURE 21.2-1 Deterministic Lower Limit on MCER Response Spectrum
The site-specific MCER spectral response acceleration at any period, SaM, shall be taken as the lesser of the spectral response accelerations from the probabilistic ground motions of Section 21.2.1 and the deterministic ground motions of Section 21.2.2.
The design spectral response acceleration at any period shall be determined from Eq. 21.3-1:
(21.3-1)
where SaM is the MCER spectral response acceleration obtained from Section 21.1 or 21.2. The design spectral response acceleration at any period shall not be taken as less than 80% of Sa determined in accordance with Section 11.4.5. For sites classified as Site Class F requiring site response analysis in accordance with Section 11.4.7, the design spectral response acceleration at any period shall not be taken as less than 80% of Sa determined for Site Class E in accordance with Section 11.4.2.
Where the site-specific procedure is used to determine the design ground motion in accordance with Section 21.3, the parameter SDS shall be taken as the spectral acceleration, Sa, obtained from the site-specific spectra at a period of 0.2 s, except that it shall not be taken as less than 90% of the peak spectral acceleration, Sa, at any period larger than 0.2 s. The parameter SD1 shall be taken as the greater of the spectral acceleration, Sa, at a period of 1 s or two times the spectral acceleration, Sa, at a period of 2 s. The parameters SMS and SM1 shall be taken as 1.5 times SDS and SD1, respectively. The values so obtained shall not be less than 80% of the values determined in accordance with Section 11.4.3 for SMS and SM1 and Section 11.4.4 for SDS and SD1.
      For use with the equivalent lateral force procedure, the sitespecific spectral acceleration, Sa, at T shall be permitted to replace SD1/T in Eq. 12.8-3 and SD1TL/T2 in Eq. 12.8-4. The parameter SDS calculated per this section shall be permitted to be used in Eqs. 12.8-2, 12.8-5, 15.4-1, and 15.4-3. The mapped value of S1 shall be used in Eqs. 12.8-6, 15.4-2, and 15.4-4.
The probabilistic geometric mean peak ground acceleration shall be taken as the geometric mean peak ground acceleration with a 2% probability of exceedance within a 50-year period.
The deterministic geometric mean peak ground acceleration shall be calculated as the largest 84th-percentile geometric mean peak ground acceleration for characteristic earthquakes on all known active faults within the site region. The deterministic geometric mean peak ground acceleration shall not be taken as lower than 0.5 FPGA, where FPGA is determined using Table 11.8-1 with the value of PGA taken as 0.5 g.
The site-specific MCEG peak ground acceleration, PGAM, shall be taken as the lesser of the probabilistic geometric mean peak ground acceleration of Section 21.5.1 and the deterministic geometric mean peak ground acceleration of Section 21.5.2. The site-specific MCEG peak ground acceleration shall not be taken as less than 80% of PGAM determined from Eq. 11.8-1.
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