Seismic Analysis Simulator
Model the effects of seismic forces on structures to evaluate performance and safety. Professional structural engineering tool with real-time calculations and visualization.
Seismic Analysis Principles
Base shear calculation per ASCE 7:
Where Cs is the seismic response coefficient and W is the effective seismic weight. The response coefficient is calculated as:
Where S_DS is the design spectral acceleration, R is the response modification factor, and I_e is the occupancy importance factor. For period-dependent calculations:
- Base Shear (V): Total lateral seismic force at base
- Seismic Coefficient (Cs): Depends on site class and structure period
- Effective Weight (W): Dead load plus applicable live loads
- Response Factor (R): Reduction factor based on structural system
Seismic Parameters
Seismic Response Analysis
Response Spectrum
Legend
Analysis Results
| Parameter | Value | Unit | Status |
|---|
Analysis & Recommendations
Enter seismic parameters to see analysis results.
- Verify structural system matches selected response factor
- Consider site-specific seismic hazard analysis
- Check local building codes for specific requirements
- Perform detailed analysis if drift exceeds limits
Q&A
Q: What is the difference between R-factor and Cd-factor in seismic design?
A: R-factor and Cd-factor serve different purposes in seismic design:
R-Factor (Response Modification Factor):
- Purpose: Reduces the elastic seismic force to account for energy dissipation
- Application: Used in base shear calculation (V = CsW)
- Values: Higher for ductile systems (R=8 for steel moment frames)
- Concept: Accounts for inelastic behavior and redundancy
Cd-Factor (Deflection Amplification Factor):
- Purpose: Amplifies elastic deflections to estimate inelastic displacements
- Application: Used to calculate design displacements (Δ = CdΔe)
- Values: Typically lower than R-factor (Cd=5.5 for steel moment frames)
- Concept: Accounts for increased deflection due to inelastic behavior
Relationship:
- R-factor reduces forces, Cd-factor amplifies displacements
- Both factors depend on structural system ductility
- They reflect the same physical phenomena from different perspectives
- Design must satisfy both force and displacement requirements
Understanding both factors is essential for proper seismic design.
Q: How do I determine the appropriate seismic design category?
A: Seismic Design Category (SDC) is determined by combining site class with spectral accelerations:
Step 1 - Determine Site Class:
- Class A: Rock (Vs30 > 2500 ft/s)
- Class B: Rock (1500 < Vs30 ≤ 2500 ft/s)
- Class C: Stiff soil (760 < Vs30 ≤ 1500 ft/s)
- Class D: Soft soil (360 < Vs30 ≤ 760 ft/s)
- Class E: Very soft soil (Vs30 ≤ 360 ft/s)
Step 2 - Obtain Spectral Values:
- Sds: Short-period spectral acceleration parameter
- Sd1: 1-second spectral acceleration parameter
- Obtained from ASCE 7 maps or USGS online tools
Step 3 - Apply Site Class Modifications:
- Adjust Sds and Sd1 based on site class amplification factors
- Softer soils increase seismic demands
- Harder rocks generally reduce demands
Step 4 - Assign SDC:
- SDC A: Sds ≤ 0.167g
- SDC B: Sds > 0.167g
- SDC C: Sds > 0.33g OR Sd1 > 0.2g
- SDC D: Sds > 0.5g OR Sd1 > 0.33g
- SDC E: Sds > 0.75g
Always verify SDC with geotechnical engineer for accurate site classification.