Short introduction

Buckling Restrained Braced Frames (BRBF) offer an alternative to conventional braced frames which surpasses their energy dissipation capacity and thus is cost-effective. Conventional steel bracing element shows unsymmetrical behavior under cyclic loading as it is shown below: on one hand, it is characterized by high ductility in tension due to the ductile yielding material characteristics; on the other hand, its performance is governed by buckling under compression. The stability problem influences the overall cyclic response of the element, reflected by the cyclic degradation. Excluding the buckling phenomenon - that is the basic idea of BRB - leads to a balanced, extremely ductile and dissipative cyclic behavior as illustrated below.

brbf

Comparison of Conventional Braced Frames (CBF) and Buckling Restrained Braced Frames (BRBF)

brbf concept

The concept of BRB

Three major components can be distinguished in the cross-section:

  • steel core
  • bond-preventing layer and
  • casing

Star Seismic’s patented manufactured air gap decouples the casing from the core. Accordingly, the axial load of the brace is transmitted by the steel core only, while the casing - through its flexural rigidity - provides the proper lateral support against flexural buckling of the core.

The steel core is to resist the full axial force designed in the bracing. Its cross-sectional area can be significantly lower than that of regular braces since its performance is not limited by buckling. Along its length the core can be divided into three parts: the middle, so-called yielding length and the rigid, non-yielding parts on both ends. The increased cross-section of the non-yielding part ensures that it remains elastic, and thus plasticity is concentrated in the middle part of the steel core. Such configuration provides high confidence in prediction of the element behavior and failure.

Sections of a BRB steel core

The casing is typically made of concrete filled steel tubes. The design criterion for the casing is to provide adequate lateral restraint (i.e. rigidity) against the steel core buckling.

Our products

Star Seismic Europe's Powercat pinned connections allow the quickest and easiest building erection, with reduced material costs and man-hours associated with welding, crane time and oversight/general conditions.

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Lifting of a Star Seismic Powercat BRB

Because Wildcat BRBs are engineered to achieve smaller force levels in tension and compression, they can be connected to significantly smaller gusset plates using simple fillet welds. Wildcat BRBs have lower product cost and in general, they are connected to the superstructure by field welds. Wildcat products are also available with connection plates, so they can be bolted to the superstructure, therefore field weld can be omitted. In case of very high axial forces, the use of Powercat BRB is recommended due to the secondary moments.

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Redundant Core System is the highest capacity tested brace of Star Seismic. It contains up to 8 independent cores and have 9800kN capacity.

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BRBF in the European Standards

Although Eurocode 8 Part 1 currently does not support the simplified (q-factor based) design of the BRBF system, it enables the verification using e.g. pushover analysis. For such analysis, Star Seismic Europe can provide the necessary test results and performance parameters adopted as needed. Strain hardening and compression modification factors can be obtained from the completed test results and can be used in design in conjunction with European Standards.

Additionally, for preliminary design stage, engineers are encouraged to use the q-factor method, based on supporting guidance of the brace manufacturer.

We would emphasize that in the near future BRB systems are expected to appear in the revision of Eurocode 8 as well as in other European standards. The relatively new European Standard EN 15129, Anti-seismic devices considers BRB as a displacement dependent anti-seismic device.

The new Romanian Seismic Design Code, P100-1/2011, which is expected to be operative in the near future, includes behavior factors and design rules of BRBF system similarly to other conventional dissipative systems.

Certification

certification brbfAustrian Standards plus Gmbh, No. 0988-CPD-0817 certificate attests that all provisions concerning the attestation of conformity and the performances described in the Annex ZA of the standard EN 15129 were applied and that Star Seismic Europe's Buckling Restrained Braces fulfil all the prescribed requirements which entitle the manufacturer to affix the CE marking. CE affirms that a product is in conformity with European standards for safety, public health and consumer protection.
Test results of our Buckling Restrained Braces are in compliance with the standards found in Appendix T of ANSI/AISC 341-05.
Our products are produced in ISO 9001, ISO 14001 and AQAP 2110-certified factory.

certification
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