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PAF - Technical Note 113012
2010 Steel eNotes: Techical
CFSEI Tech Note X Bracing L2001-09
The Cold-Formed Steel Engineers Institute (CFSEI) has recently published Tech Note L001-09 entitled Design of Diagonal Strap Bracing Lateral Force Resisting Systems for the 2006 IBC. As the title implies, the publication relates to the use of diagonal strap bracing as the stabilizing element for a building or structure.
The intent of the Technical Note is to discuss some of the design requirements, detailing and practical limitations of diagonal strap bracing. Although the publication is intended to aid engineers, the topics that are covered will be useful to designers and fabricators alike.
The following is a summary of the items discussed in the publication:
1) Fabrication Considerations:
- The strap can be applied to one side of the wall or both sides of the wall.
- The strap can be connected directly to the stud and track or a gusset plate can be used to make the connection.
- Pros and cons associated with each option are discussed.
- Safe-guarding against loose straps through pre-tensioning.
2) Design Considerations:
- Determining the width of the strap and the connection to the stud and track
- Design of anchor bolts
- Response Modification Factor (R-Factor) selection and background information.
- Ensuring ductile behavior during a seismic event, in which the capacity is controlled by the strap.
- Codes and standards that can aide in the design of diagonal strap bracing.
The Technical Note also includes a design example that illustrates the procedure used to design a diagonal strap bracing system that resists wind loads.
Unfortunately this Technical Note does not address how to determine the quantity and loading for each diagonal brace. This is a complicated procedure that is unique to each structure. While this Technical Note does not address all issues associated with diagonal strap bracing, it does shed some light on common fabrication options and design procedures that can be used to optimize the system.
Diagonal strap bracing is common solution for lateral stability of cold-formed steel structures. The connections associated with this system can be very labor intensive and thus costly to construct. Understanding how the system works and how to correctly design the members and connections will ensure that you are providing the most economical solution for the project and your fabrication shop.
This Technical Note along with many others is available for purchase on the Steel Framing Alliance website:
CFSEI Tech Note L200-09
The Cold-Formed Steel Engineers Institute (CFSEI) has published a Tech Note, L200-09, which is the organization’s interpretation of the wind load requirements for truss design and truss to structure connection design with regard to the wind pressure calculation method: Main Wind Force Resisting System (MWFRS) or Components and Cladding (C&C). The primary author of the Tech Note is Sam Hensen, P.E. of Simpson Strong-Tie Co., Inc. In the Tech Note multiple sources are referenced which include the 2006 IBC, 2006 IRC, 1999 SBCCI Standard for Hurricane Resistance Construction (SSTD 10-99), Standard for Residential Construction in High Wind Regions (ICC-600) and others, of whose contents resulted in the conclusions in the Tech Note.
In summary the Tech Note provides these conclusions and recommendations.
1. Truss assemblies should be designed for MWFRS wind pressure because they receive wind load from more than one surface.
2. Individual truss members should be designed for C&C wind pressure because they receive wind load directly or from sheathing.
3. MWFRS wind pressures are applicable when designing truss to support uplift connections for wind applied to the truss system. MWFRS wind pressures are also applicable when calculating the horizontal load at the truss to support connection from wind applied to a bearing wall.
4. The final decision on the method on which the wind load pressures are calculated shall be made by the project Engineer of Record.
Although the CFSEI is not a code writing organization it is recognized within the CFS engineering community as a premier provider of technical information and design guidelines.
This Tech Note is clearly written and understandable and includes design examples. The suggested procedure of C&C wind pressure for individual truss member design and MWFRS uplift connection design is handled by the Apogee Design program by selecting the “Combined” option under Wind Design Method on the Wind Load Dialog box. This Tech Note along with many others is available for purchase on the Steel Framing Alliance website:
Updates to Aegis Connectors
Recently Aegis Metal Framing has made enhancements to two of our connectors to improve both utility and ease of installation.
In a previous letter to customers we introduced the updated 423/426HD truss hold downs. These connectors now incorporate a larger, pre-punched hole for typical truss-to- concrete bolted connections. The 423HD has a 7/16" diameter bolt hole while the 426HD has a 9/16" diameter hole. The addition of these bolt holes does not affect the capacity of the HD in any way, nor does it reduce the allowable area for other types of fasteners. It simply facilitates the use of this part with concrete bolted connections.
The USKW truss-to-truss connector has been updated with the addition of two “locator notches” that facilitate proper in-plant placement of the part for attachment of the tie-in truss with a USD bottom chord to the girder bottom chord. The USKW has also been lengthened from 6" to 7" to better accommodate 45 degree connections of corner girders and jacks.
Below are links to the detailed drawings of the new parts: