Regulations and Methods for Considering Accidental Eccentricity Effects in Seismic Design in China, the United States and Europe
1. Regulatory Basis
● China
The Code for Seismic Design of Buildings (GB 50011-2010) stipulates that accidental eccentricity must account for uncertainties in structural mass distribution, stiffness distribution, and spatial variations in seismic motion. Torsional effects shall be calculated using either static or dynamic methods.
● United States
ASCE 7-22 (American Society of Civil Engineers Standard) requires consideration of accidental torsional effects, typically calculated using static methods, with verification through dynamic analysis results.
● Europe
Eurocode 8 (EN 1998-1:2004) simulates the misalignment between mass centres and stiffness centres by introducing accidental eccentricity, and mandates consideration of the effects of bidirectional seismic actions.
2. Definition and Values of Random Eccentricity
● China
Eccentricity: ±5% of the edge length perpendicular to the direction of seismic action.
Calculation method: Shift the mass centres of each storey in the same direction and calculate the resulting additional torque.
Scope of application: All regular and irregular structures must be considered, though appropriate simplifications may be applied to regular planar structures.
● United States
Eccentricity: Take the greater of ±5% of the structure's maximum planar dimension or ±10% of the mass centre displacement.
Calculation method: Verify by applying additional static torque through mass centre displacement; high-rise buildings require dynamic analysis (e.g., response spectrum method).
Dynamic amplification effect: For torsionally sensitive flexible structures (e.g., high-rises), additionally consider dynamic amplification factors (e.g., Accidental Torsional Amplification Factor in ASCE 7).
● Europe
Eccentricity: ±5% of the structural plane dimension, or calculated via formula eai=±0.05Li (where Li is the plane dimension of the i-th storey).
Partial factor: When combined with seismic action, multiply by partial factor γRd (typically 1.0–1.5).
Bidirectional seismic action: Simultaneous consideration of seismic forces in two orthogonal directions is mandatory, superimposed with accidental eccentricity.
3. Future Trends
● Convergence: National codes are progressively incorporating dynamic amplification factors (e.g., China's revised code proposes adding a dynamic adjustment factor).
● Refinement: Performance-based design methodologies (PBSD) are driving more precise modelling of accidental eccentricity and true torsional effects.
● Through this comparison, designers can rationally select calculation methods and optimise seismic design according to the code requirements of the project location.
评论
发表评论