Finite Element Analysis of Sleeve-Wrapped Double Steel Pipe Constraint Buckling Braces

Literature Overview

This study presents a finite element analysis (FEA) of a novel sleeve-wrapped double steel pipe constraint buckling-restrained brace (CBRB) system. Buckling-restrained braces (BRBs) are a widely used seismic energy dissipation device in structural engineering, but conventional designs face challenges related to buckling restraint effectiveness, energy dissipation capacity, and manufacturing complexity. The proposed sleeve-wrapped double steel pipe configuration aims to address these limitations by combining the advantages of dual steel pipe energy dissipation with an external constraint sleeve that prevents both outward and inward buckling of the steel pipe cores.

Technical Background

Conventional BRB Limitations

Traditional buckling-restrained braces typically consist of a steel core pipe (energy dissipation element) encased in a concrete or mortar restraint jacket. While effective, these designs suffer from:

• Inward buckling: Local inward buckling of the steel core can occur if the restraint jacket is not sufficiently rigid or if the interface bond is compromised.
• Concrete cracking: The restraint concrete can crack under cyclic loading, reducing restraint effectiveness over time.
• Corrosion: Steel cores exposed to moisture through cracked concrete are susceptible to corrosion.
• Manufacturing complexity: Precise concrete placement around the steel core is labor-intensive and quality-dependent.
• Limited axial capacity: The axial capacity is often governed by the concrete restraint rather than the steel core strength.

Proposed Sleeve-Wrapped Double Steel Pipe Configuration

The novel design incorporates:

• Inner steel pipe: Primary energy dissipation element (yielding in tension and compression)
• Outer steel pipe: Secondary energy dissipation element providing additional capacity and redundancy
• Constraint sleeve: A rigid external sleeve (typically steel or composite) that prevents buckling of both steel pipes by providing continuous lateral support
• Gap medium: The space between the inner pipe and outer pipe is filled with a controlled medium (mortar, polymer, or left as air gap with friction contact)

Finite Element Model Development

Geometric Configuration

Material Model

The FEA employed the following material models:

Steel pipes (elastic-plastic with kinematic hardening):

Mortar (elastoplastic with damage):

Boundary Conditions and Loading

The FEA model applied displacement-controlled cyclic loading to simulate seismic response. The inner and outer steel pipes were loaded axially through end plates, while the constraint sleeve was fixed at both ends to prevent lateral displacement. The loading protocol followed the FEMA 343 standard cyclic loading procedure with displacement amplitudes ranging from 0.5% to 10% of the brace length.

Analysis Results

Load-Displacement Behavior

Buckling Behavior Comparison