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Questions and Answers
What is the importance factor denoted as in the context provided?
Which software is mentioned for performing 3D analysis?
Which of the following options indicates seismic weight in the context provided?
What does the acronym ASCET likely refer to in this context?
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Which category is referenced in relation to seismic parameters?
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What is the purpose of seismic loads in structural design?
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Which code chapters are specifically mentioned for seismic design?
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What kind of analysis procedures are mentioned for seismic design?
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Which analysis method is typically used for low-rise buildings without irregularities?
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Which chapter in ASCE7-16 outlines seismic design criteria?
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What kind of procedure is preferred for complicated or high-rise buildings?
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Which type of analysis is associated with equivalent lateral force method?
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Base shear calculations are relevant for which aspect of structural design?
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What is the formula for calculating the Design Accelerations Parameters SDS?
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What condition does the spectral acceleration $Sa$ follow when $T$ is less than $T0$?
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Which seismic design category is most commonly assigned in California?
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Which of the following letters signifies the long period in seismic design parameters?
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What is typically used to determine site class effects in seismic design?
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What does SD1 represent in seismic load calculations?
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When does the formula $Sa = (SD1·TL / T^2)$ apply?
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Where can the U.S. Seismic Design Maps be accessed?
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What is the formula for calculating the approximate fundamental period, Ta, for buildings with specific characteristics?
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What does a higher Response Modification Coefficient, R, indicate about a structural system?
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Which structural system has a Response Modification Coefficient of R = 5?
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For buildings with less than 12 stories and an average story height of at least 10 feet, what is the formula for Ta?
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Which type of braced frame system has the highest Response Modification Coefficient?
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In which scenario is it essential to check for both maximum and minimum seismic response coefficients?
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What does the variable hn represent in the formula for Ta?
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Which of the following reflects the least effective lateral force-resisting system?
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What is the total number of stories in the building located at 10250 Santa Monica Blvd?
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What type of Seismic Force Resisting System is used in the N/S direction?
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What is the live load (LL) for the office space in pounds per square foot?
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What is the dead load (DL) on the roof of the building?
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Which direction does the bearing shear walls primarily contribute to?
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Which occupancy type is classified for the building?
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What is the overall height of the building indicated in feet?
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What is the site class designated for the building?
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In which analysis methods are dynamic and non-linear responses mentioned?
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What type of SFRS system is utilized on the upper three floors?
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Study Notes
Seismic Loads
- Account for a building's response to earthquake ground motion
- Expected behavior: yielding and inelastic demands at intended locations (lateral force resisting system)
- Design is prescribed per code: both CBC 2022 and ASCE7-16 are required
ASCE7-16 Lateral Load Chapters
- Chapter 1: General (includes information for risk category and 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
Analysis Procedures
- Structural behavior can be linear or nonlinear
- Loading conditions can be static or dynamic
- In general, most low-rise buildings without irregularities use a linear dynamic procedure
- Complicated or high-rise buildings use a nonlinear dynamic procedure
- ASCE 7-16 provides a table (Table 12.6-1) for analysis procedures
Seismic Loads - Response Spectrum
- Convert to design acceleration parameters, plot design response spectrum
- SDS (design spectral acceleration for short periods) = 2/3 * SMS (spectral acceleration at short periods)
- SD1 (design spectral acceleration for long periods) = 2/3 * SM1 (spectral acceleration at long periods)
Seismic Loads - Response Spectrum
- Other variables:
- Spectral Acceleration:
- Sa < T0: Sa = SDS (0.4 + 0.6 * T / T0)
- TS < T < TL: Sa = SD1 / T
- T > TL: Sa = (SD1 * TL / T^2)
- 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)
- Spectral Acceleration:
Seismic Loads - Seismic Design Category
- Determined based on response spectrum
- Categories: A, B, C, or D
- California is mostly in category D (high seismic zone)
Seismic Loads - Hazard Maps
- ASCE 7-16 Chapter 22 provides approximate values for:
- S1 (spectral acceleration at 1 second)
- SS (spectral acceleration at short periods)
- TL (long period)
- The San Andreas Fault is a significant contributor to seismic risk
- To find more specific values, use hazard maps like ASCE7-16 or use the ASCH7 Hazard Tool available online
Seismic Loads - Base Shear
- Seismic Response Coefficient (C_s)
- Calculate the maximum C_s using the equation provided in the text
- Calculate the minimum C_s using the equation provided in the text
- Use whichever value is greater
Seismic Loads - Period
- Approximate Fundamental Period (T_a)
- Calculate using the equation: T_a = C_t * h^(x) - where h is the structural height (in ft) and C_t and x are values found in ASCE7-16 Table 12.8-2
- For buildings < 12 stories where the seismic force-resisting system consists of concrete or steel moment frames and the average story height is at least 10 feet (min): T_a = 0.1 * N, where N is the number of stories
Seismic Loads - Response Modification Coefficient (R)
- Response Modification Coefficient (R): accounts for the ductility of the structure
- Higher R indicates a more ductile structure
- Examples of commonly used LFRS:
- Eccentrically Braced Frame (EBF)
- Concentrically Braced Frame (CBF)
- Special systems have higher R compared to ordinary systems
Example Building
- Location: 10250 Santa Monica Blvd, Los Angeles, CA 90067
- 4-story office building
- Seismic Force Resisting System (SFRS):
- Special Steel Concentric Braced Frame (N/S direction)
- Special Steel Concentric Braced Frame in the upper 3 floors and bearing shear walls at the lower level (E/W direction)
- Site Class: C
- Office Dead Load = 80 psf, Live Load = 50 psf
- Roof Dead Load = 31 psf, Live Load = 20 psf
- Structural Behavior: linear
- Loading Conditions: Static
- Analysis Method: Equivalent Lateral Force
- Software: ETABS
- 3D Analysis is recommended
- Importance Factor: Ie (check ASCE7-16 Table 15-2 for the appropriate value)
- Risk Category: It (check ASCE7-16 Chapter 1)
- Horizontal Force: calculated considering typical floor loads, areas, and the importance factor
- Seismic parameters: S1, SS, TL (using ASCE7-16 Chapter 22 or the ASCH7 Hazard Tool)
- Period (T): calculated using the formulas from the text
- Response Modification Coefficient (R): checked based on the SFRS
- Design Response Spectrum: plotted using the calculated parameters
- Base Shear: calculated using the formulas from the text
- Seismic Forces: distributed throughout the building
- The building can either be analyzed using the Equivalent Lateral Force method or performed as a nonlinear response analysis
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Description
This quiz covers the key concepts of seismic loads relevant to building design, including the response to earthquake ground motion as prescribed by the CBC 2022 and ASCE7-16 codes. You'll explore topics such as lateral load resisting systems, seismic design criteria, and analysis procedures for structural behavior. Test your understanding of how these factors come into play when designing for seismic safety.
