Out-of-Plane Skew Effects on the Cyclic Performance of Column-Tree Steel Moment Connections

Area of Science:

• Structural Engineering
• Earthquake Engineering
• Steel Structures

Background:

• Column-tree steel moment connections are crucial seismic force-resisting systems.
• Understanding the impact of geometric imperfections like beam skew is vital for seismic resilience.
• Existing research often assumes perfect alignment, necessitating studies on skewed connections.

Purpose of the Study:

• To investigate the influence of out-of-plane beam skew on the cyclic performance of column-tree steel moment connections.
• To evaluate the connection's ability to meet seismic design criteria under skewed conditions.
• To identify potential failure modes and recommend design limitations for skewed connections.

Main Methods:

• Validated finite element (FE) models were used to simulate cyclic responses.
• AISC cyclic loading protocol was applied up to a story drift ratio of 0.05 rad.
• Skew angles (0°, 10°, 20°, 30°) and beam depths were systematically varied.

Main Results:

• All configurations met AISC 341 criteria, retaining 80% of plastic moment capacity up to 0.04 rad drift.
• Energy dissipation decreased with increasing skew (2.9-8.9% at 30° skew).
• Inelastic energy dissipation was more sensitive to skew (up to 15.4% reduction); fracture susceptibility and column twisting remained low.

Conclusions:

• Column-tree connections with out-of-plane skew up to 30° are generally viable for seismic applications.
• A design limit of 20° skew is recommended for deep beam configurations to avoid premature bolted splice failure.
• Beam skew impacts energy dissipation and inelastic behavior, requiring consideration in seismic design.