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What is a shear key in steel structures?

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 In steel structure engineering , the column base connection serves as the pivotal interface linking the superstructure to the concrete foundation below. It must safely and reliably transmit various loads from the upper structure: vertical pressure , uplift forces , bending moments , and horizontal shear forces . When horizontal shear forces become substantial, the friction alone between the column base plate and the concrete foundation surface proves insufficient to resist them. At this juncture, a critical small component becomes indispensable—the shear key . Shear keys, as the name suggests, are structural steel connection components specifically designed to resist and transmit horizontal shear forces. Essentially, they are short steel members. Installation location: Typically welded or anchored to the base plate of a steel column (or other load-bearing components such as equipment supports ), with its lower end embedded in the concrete foundation or concrete structure cast ...
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How do China, the United States and Europe account for accidental eccentricity in seismic design?

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 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.



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