New Millennium Building Systems

Flex-Joist™ tension-controlled open web steel joists

Steel Joist Institute, ANSI, Steel Deck Institute Steel Joist Institute ANSI Steel Deck Institute


A new approach for today's high-performance, safety-optimized building environment

Flex-Joist™ tension-controlled open web steel joist design gives building owners and specifiers the option of consistently higher steel joist performance at an affordable cost.


Increased steel joist performance metrics — when and where you need them

Laboratory testing has consistently demonstrated the Flex-Joist™ design to exceed standard steel joist design for strength, reliability and ductility.

Steel joist performance metrics

31% higher reliability index

Standard SJI joists are designed based on procedures derived from the American Institute of Steel Construction (AISC) design specifications. AISC states that their design specifications result in an average member reliability index of β = 2.6, where β is the ratio of the standard deviation to the mean. Flex-Joist™ has been demonstrated to have a system reliability index of β = 3.4, or 31% higher than the industry standard.

29% stronger

By selectively increasing the size of the weakest components without decreasing the size of the strongest components, the strength of a Flex-Joist™ is substantially increased at an affordable cost.

129% higher ductility

The Flex-Joist™ design is based on limit states control, so it has a much higher probability of achieving a ductile tensile yielding limit state that is characterized by slow collapse, with large inelastic deformations and inelastic reserve capacity. This very ductile behavior gives sensory warning of impending collapse, allowing more time for evacuation and response.

Optimized safety sensoring

The Flex-Joist™ is ideally suited for the optional, post-erection installation of electronic sensoring and alarms to establish an early, roof overload warning system. The bottom chord and end webs of a Flex-Joist™ will be highly stressed prior to collapse and the location of sensors along these components can readily be installed by a third party provider.

Disclaimer: No joist will withstand sudden and catastrophic impact forces that exceed system capability. Flex-Joist™ design offers probability of high ductility and time delay under static gravity overload conditions.

Downward force on structural components


  • Increased strength
  • Higher reliability index
  • Improved ductility & safety
  • Optimal overload sensoring
  • Engineered overload yielding
  • Timeframe for emergency management
  • Enhances building safety


Find out more…

Download Flex-Joist™ overview (pdf)

AISC Engineering Journal Article

Contact us for more information

Steel Dynamics, Inc

New Millennium Building Systems is a wholly owned subsidiary of Steel Dynamics Inc.