about buckling restrained braces

What is a Buckling Restrained Brace Frame, and How Does it Work?

BRBF's are characterized by the ability of bracing elements to yield inelastically in compression as well in tension. This behavior is achieved through limiting the buckling of the steel core within the bracing elements.

Axial stress is de-coupled from flexural buckling resistance; axial load is confined to the steel core while the buckling restraining mechanism (typically a casing) resists overall brace buckling and restrains high-mode steel core buckling (rippling).

BRBF can provide elastic stiffness that is comparable to that of EBF or SCBF.

The ductility and energy dissipation capability of BRBF is expected to be comparable to that of SMF and greater than that of SCBF. This high ductility is attained by limiting buckling of the steel core.

The Axial yield strength of the core "Pysc" can be defined without dependence on other variables.

This ability to control "Pysc " significantly reduces the adverse effects of relying on normal yield strength values.

Careful proportioning of Star Seismic braces throughout the building height can result in specification of required "Pysc" values that meet all the strength and drift requirements of the Applicable Building Code.

Star Seismic's brace design utilizes additional features to isolate the core from external shear and moment.


What is unique about Star Seismic's design?

Unique Pin and Collar Design (Patent US 6837010, 7065927, and 7188452).

The unique design of Star Seismic's PowerCat™ brace creates a system that will not transmit shear and moment created by frame drift to the yielding core. The use of the pin connection reduces the overall connection length. This allows a longer yield length and reduces the strain in the brace. The unique design of the collar of the Star Seismic brace forces all external moments to the outside of the tube and away from the hard-working energy-absorbing core. Ask us about our eccentric pin, allowing up to 1/2" tolerance on overall length of each end and still giving a full bearing connection.

Engineering Expertise.
The principals of Star Seismic have extensive knowledge of brace and connection designs. Call us to help you with your seismic building designs.

Reduced Fabrication and Erection Costs.
Due to the simplicity of the pin connection, fabrication and erection costs are significantly reduced. Cost studies have shown that the pin connection reduces fabrication cost by 15-25% when compared with a bolted connection. Cost studies have also shown that the pin connection reduces erection time and therefore cost by 15-25% compared to a bolted connection.

Faster Erection Schedule.
Overall system costs are about the same as an EBF but the erection schedule is reduced.

Dimensional Flexibility.
We have a variety of tubes sizes to offer, and use of technique of combining tubes for higher loads, giving more dimensional flexibility.

Architecturally Attractive.
The aesthetically-pleasing design of Star Seismic's brace makes it ideal for architecturally exposed frames.

Accessibility.
Our braces are made in the USA, resulting in shorter lead times for delivery.

Easy to Build

Managing risk in the construction of a building is essential. At Star Seismic, we reduce your risk by providing a system that is significantly easier to fabricate and erect:

Fabrication:

The Star Seismic PowerCat™ and WildCat™ BRB systems use considerably less weld and smaller gusset plates than other seismic systems. The plates used in the system are easy-to-fabricate rectangular plates that are simple to lay out, use less material, and produce less waste than other systems. The PowerCat™ system connection requires only the location of one large pin hole, and the WildCat™ system requires only an erection aid hole.

Erection:

The extensive experience and expertise from the team at Star Seismic emphasizes erection friendly design. As our braces were conceived and designed, our objective was to ensure we had the most erection-friendly brace possible. Our efforts have paid off and construction teams who have used the braces can attest to the erect ability of the system. The simplicity of both the pinned and the welded connections reduces risk for the erection team.

Aesthetics

Simply Said, We Just Have A Better Looking Brace

Designing for seismic loads has taken a toll on building aesthetics. Gusset plates have greatly increased in size on braced frames. Moment frame beams and columns have also become very large, decreasing window sizes and ceiling heights.

Not so with Star Seismic's PowerCat™ and WildCat™ Buckling Restrained Brace Frame systems. These systems incorporate smaller connections, smaller beams, and smaller columns.

And with Star Seismic Buckling Restrained Brace Systems, it is possible to express the bracing as an architectural feature. Our pinned connections, coupled with our collar, give the structure a sleek, finished appearance.

 

 

 

Easy to Design

Although in the past designing with a superior seismic system has been complicated, this is not the case with the PowerCat™ and WildCat™ Buckling Restrained Brace Frame systems. These systems are straightforward to design and simple to detail. The basic procedure is as follows:

  • Calculate the base shear of your structure, the same way you always have. Since BRB's are a codified system in the AISC Seismic Provisions and ASCE7-2005, simply use the code values for R, Ωo, Cd, and the coefficients for the approximation of the period found in the code.
  • Analyze your structure to determine the required brace strength.
  • Determine the required brace stiffness.
  • Check drift.
  • Determine brace displacements at Δm.
  • Contact Star Seismic to obtain the overstrength factors for our braces.
  • Design beams, columns, and connections for brace capacity.
  • Specify brace strength and strand area (or stiffness) to Star Seismic.

 

Of course, there are questions that you may have along the way. Star Seismic is here to assist you in any way that we can. Feel free to call us with your questions, or arrange for a free presentation to your staff. If desired, we can even provide you with the gusset connections to the beams and columns. We are here to make your job easier!

 

Cost Benefits

You Could Save $2.40 Per Square Foot On Your Building

That is what a recent study presented at the North American Steel Construction Conference found. Not only do you get a superior seismic performance with the PowerCat™ and WildCat™ systems, but you also save money.

Savings on the Building Frame:

The system shares the highest seismic response factor, which allows the structure to be designed for lower force levels, saving money on columns, foundations, beams, drag struts and collectors. You also could have fewer seismic frames.

Savings on the Connections:

• The Star Seismic BRB systems require significantly smaller gusset plates with easy-to-fabricate, material-saving orthogonal shapes. • Our system requires no stiffeners in the gusset due to our patented collar system. The stability of the brace is built into the brace! • Our fast and easy-to-erect pinned or welded connection saves money on erection, and time savings on the erection... which equates to savings in crane time, general conditions, and potential early generation of revenue for the project owner. • Savings through reduction in the amount of weld required and the use of only simple fillet welds.

Savings after the Earthquake:

With these systems, beams and columns will not deform because the seismic energy is dissipated in the braces, which are much easier to replace, if necessary, than beams and columns. That means potentially less damage to floors, walls, partitions, mechanical systems, and other non-structural elements. Additionally, unlike any other system, our braces can be analyzed after an earthquake to verify additional capacity to withstand additional earthquakes.

But that's not all!

Give us a call today for a copy of the cost study or to discuss other ways to save on your project. Or, better yet, include our steel and seismic experts early on in your next project to help increase your competitive advantage.

Superior Performance

Many Experts Concur:

The buckling restrained brace frame system (BRB) is one of the premier seismic systems available. At Star Seismic, close attention to detail has gone into our robust PowerCat™ and WildCat™ Buckling Restrained Braces to produce superior performance:

Extreme Ductility – Yielding Strand Technology:

Because the central strand is the major load-carrying and energy-absorbing element, this is where ductility is most critical. At Star Seismic, we take this element very seriously. We start with steel specifically ordered for its ductility and material properties. We employ only radiused transitions, discouraging crack propagation. There are never any sharp corners in our strands. And, with our braces, you will not see any structural welding in the yielding region, with the accompanying shrinkage stresses and deformation incompatibility.

Patented Pin/Welded and Collar Design:

(Patent US 6837010, 7065927, and 7188452)
Our PowerCat™ system utilizes a pin connection; our WildCat™ system utilizes a welded connection. These connections, used in conjunction with our collar, isolate our central area from bending and shear forces, keeping these loads away from the hard-working energy-absorbing strands. Because both our PowerCat™ and WildCat™ braces employ our patented collar system, stiffeners are not required on the gusset plates to achieve stability in the system.

Proprietary Ganging System:

Because we employ a proprietary ganging system through component testing, we can provide braces to a much higher capacity than testing requires by connecting them such that they act in conjunction with one another. Need more capacity? We simply add another element to our brace.

At Star Seismic, our close attention to detail has paid off. We have achieved 23 Δ Y in our testing, where only 10 Δ Y is required by code, and have exemplary test results on braces up to 1200 K.

THAT'S PERFORMANCE.