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For design values, engineering and design assistance please contact us at design@starseismic.eu.

Downloads

downloadCE Certification
downloadWildcat test report according to EN 15129 and ECCS
downloadCost analysis based on Eurocode
downloadWildcat test report, USA
downloadPowercat test report 1, USA
downloadPowercat test report 2, USA
downloadPreliminary design of BRBF system - Use of equivalent force method
downloadDesign check of BRBF system according to Eurocode 8 - Use of pushover analysis
downloadPowercat drawings
downloadWildcat drawings

Test reports

These reports describes the results and analysis of tests performed on 20 Buckling Restrained Braces manufactured by Star Seismic. The tests were performed on the Seismic Response Modification Device (SRMD) shake table facility at the University of California, San Diego, at the University of Utah and at the Budapest University of Technology and Economics.

Wildcat test results according to EN 15129 and ECCS

The paper describes detailed test results of two Star Seismic BRBs. The tests were performed according to EN 15129 (Anti-seismic devices) and ECCS (European Convention for Constructional Steelwork) protocols at the Budapest University of Technology and Economics.

Wildcat test report, USA

This report describes the results and analysis of tests performed on seven Buckling Restrained Braces manufactured by Star Seismic, LLC. The tests were performed and the Structures and Materials Laboratory of the Department of Civil Engineering at the University of Utah during the spring of 2006.

Powercat test report 1, USA

Subassemblage testing of eight full-scale Buckling Restrained Braces for Star Seismic, LLC was conducted using a shake table facility at the University of California, San Diego. Each specimen was pin-connected to a gusset knife plate at each end. The shake table imposed both longitudinal and transverse deformations to one end of the brace. Both modified Standard Loading and Low-cycle Fatigue tests as derived from the proposed SEAOC-AISC Recommended Provisions for Buckling Restrained Braced Frames were conducted; one specimen was also subjected to a simulated Sylmar, Northridge earthquake response in real-time. All specimens performed well under the Standard Loading Protocol. The hysteresis behavior of the braces was very stable prior to fracture, and a significant amount of energy was dissipated by each specimen.

Powercat test report 2, USA

The results of a series of tests performed at the UCSD Caltrans Seismic Response Modification Device (SRMD) testing facility on the Star Seismic Mercy San Juan Hospital Project are presented in this report. Three Buckling Restrained Braces were tested over this time period.

Design and engineering assistance

Star Seismic Europe can assist through the modeling, preliminary and final design and document process including design aids, sample drawings, typical details and sample specifications. Do not worry if you have never designed a BRB project before: we are available every step of the way from project conception through completion. Star Seismic's engineering team works closely with engineers and delivers accurate brace stiffness, behavior characteristics and overstrength factors necessary for design.

Step-by-step design guidance

Step-by-step structural design guidance can be found here:

Design guide to BRBF system according to Eurocode 8 - Use of equivalent force method

Design guide to BRBF system according to Eurocode 8 - Use of pushover analysis

Design of BRBF systems is easy and straightforward. In general, engineers should follow the capacity design rules, ensuring that failure of the dissipative BRB members precedes the failure of the non-dissipative members (connections, beams, columns, foundation, etc.) that shall remain elastic during the seismic event. With such respect, the design steps of BRBF are not distinguished from other dissipative structure types. The design is complicated only by the fact that each Buckling Restrained Brace element is fully designed and manufactured by the brace manufacturer and thus interaction of the structural engineer and the brace manufacturer is necessary at certain design stages. In case seismic provisions support the use of BRBF, the engineering process follows:

  • Calculate the base shear of your structure following the corresponding seismic provisions.
  • Structural analysis: determine required brace strength and stiffness.
  • Check global and interstory drifts, calculate brace displacements.
  • Contact brace manufacturer to obtain brace overstrength factors and/or load-displacement characteristics of the BRB.
  • Design other - non-dissipative - elements, such as beams, columns and connections.
  • Specify brace strength and stiffness to brace manufacturer.
As it can be seen, the concentration of energy dissipation into single BRB elements that are fully designed by the brace manufacturer leads to incomparably simpler design than other dissipative structures where engineers shall follow complicated and strict design rules for overall element as well as for structural details (cf. capacity design rules of moment resisting frames).

In case the relevant seismic codes do not include BRBF, Star Seismic Europe recommends as follows:

  • Following the above steps, do preliminary design using assumed approximate values for the seismic parameters not included in the code.
  • For the final check of your structure, do pushover analysis and capacity design checks: deformation check of the brace and strength check of other elements at the target displacement level.

The beams, columns and their connections to each other and to the braces have to be designed for the maximum possible load level that may occur during an earthquake event. This is represented by the overstrength factor that shall reflect the possible deviations in the material properties (e.g. the actual yield strength is larger than the characteristic value), the strain hardening, system overstrength, etc.

The connection of the braces to the beam-column joints is usually created using gusset plates. Star Seismic basically provides two different joint configurations: Powercat with real pinned connection and Wildcat, the welded type. The former is considered better for eliminating in-plane secondary moments induced by drift and also increasing the yield length of the steel core. However, the assembly of this type of frames is encumbered by the small erection tolerance of the connection. Welded connections on the other hand facilitate the construction, but engineers may have to take the effects of secondary moments in the connection and the brace into account. Wildcat products are also available with connection plates, so they can be bolted to the superstructure, therefore field weld can be omitted.

Compared to the gusset-plate joints of special conventionally braced frames, the lower forces and the elimination of buckling problems result drastically decreased joint size.

Conventional and BRB connection

brb pinned connection

Pinned connection (Powercat)

brb welded connection

Welded end connection of the braces (Wildcat)

Application fields

BRBF systems are currently applied as primary lateral force resisting structures both in new construction and in seismic retrofit projects, it can also be used as supplemental hysteretic dampers in seismic retrofitting.

Compared to conventionally braced frames, rigidity of the bracing is typically lower due to the smaller steel core sections as the force demand is also smaller. This may result larger deformations. To control the deformations as well as to facilitate plastic load re-distribution, BRBF systems are often designed in conjunction with elastic moment resisting frame. The moment resisting frame also increases the re-centering capability of the combined system. Dual system (i.e. both BRBs and the moment resisting frame are to dissipate energy due plastic hinges) can also be developed utilizing all the benefits of the two systems.

As for seismic retrofit applications, BRB can be added not only to steel, but also to reinforced concrete structures. The European research action Prohitech discusses the advantageous use of BRB in historical buildings, too.

Advantage of the BRBF system is that, braces can be applied as single diagonals due to their equivalent behavior in tension and compression, providing more freedom in brace configurations, helping furnish of architectural requirements. brb diagonal

Star Seismic Powercat braces used as single diagonals

Structural software programs

For the design, several finite element method (FEM) structural software programs can be used, therefore it is not necessary to purchase special design program. Numerous international structural softwares already had made the use of BRBs even easier with Star Seismic BRB software tools, e.g.: ETABS, RAM, RISA and REVIT.

Buckling Restrained Brace shapes produced by Star Seismic can be assigned, analyzed and designed in RAM. Please refer to this wiki article for detailed information.

ram brb

Star Seismic buckling restrained braces are available in the RAM Structural System

Engineering videos

ATLSS Engineering Research Center, Lehigh University

See our brace in action in a simulation of the Northridge, CA Earthquake of 1994

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