Each year the ICC Evaluation Service performs an analysis of blind bolts to assure that everyone is on the same page involving material used in the bolts, how the bolts are used, a general description on how the bolts should be constructed, and explanation of installation procedures. This is a review of the January 2021 evaluation.
How Are Blind Bolts Manufactured?
Blind bolts are made of five steel components including a slotted bolt, toggle, and a flange nut with an integrated washer. There is a partially threaded shank with a smooth slotted cylindrical section and toggle incorporated into the bolt. They are available in carbon steel with zinc flake finish or stainless steel. Sizes include 5/16-inch,M8: 3/8-inch,M10: ½-inch,M12: 9/16-inch,M14: 5/8-inch,M16: ¾-inch,M18: 1-inch,M24: and 1-3/16 inche,M30.
The bolt is manufactured to comply with Class 10.9 carbon steel and stainless steel regulations. The toggle is made to comply with the BS EN ISO 4014 regulations. The flange nut complies with BS ISO EN4032 Grade 8 and Grad 10 regulations for carbon steel blind bolts and A4-70 regulation for stainless steel blind bolts. The carbon steel finish coating includes non-electrolytic zinc flake covered with Geomet® 500.
How Are Blind Bolts Used?
Blind bolts are engineered to connect structural steel to hollow structural sections of steel members and other structural steel elements where access is restricted to only one side of the element. The bearing-type connection of the blind bolt is often assessed for its tension resistance and shear load. Blind bolts are used as an alternative to bolts described in section J3 of the AISC 360 regulation that is referenced in section 2205.1 of the IBC regulations for bearing-type connections.
These bolts are used to resist static, wind, and seismic loads in structures that are assigned to Seismic Design Categories.
Design Of Blind Bolts
The connection design of blind bolts is required to conform to the ESR-3617 report, Section J3 of the AISC 360 rules, and the strength design information for blind bolts. The load-carrying capacity of the connection depends on the blind bolt itself, the type of steel elements connected with the bolt, and their thickness. The weakest component in the bolted assembly, which includes the steel elements of the connection and the blind bolt, limits the strength of the entire bolt. All limit conditions must be checked to ascertain the load-carrying capacity of the connection within the bolt. The combined tension of the bolt as well as its shear load must comply with:
Tension Demand 2 Shear Demand 2
____________________ + ________________ _< 1.0
Tension Capacity Shear Capacity
In order to comply with regulations, the blind bolt must be installed within a specific procedure that includes:
- The driller of the hole into the steel section, which is to be connected, must be sure that the hole has the proper diameter and spacing in accordance to the ICC ES Evaluation Report and the proper design requirements for the connection.
- The steel elements to be connected to each other must be positioned to ensure that:
- The two sections are lined up and rest one against the other without any gap. Clamps must be used as necessary to hold the two steel elements together and to prevent formation of any gaps.
- That the holes are aligned, using a mandrel if necessary.
- The supplied flange nut is attached to the threaded end of the blind bolt and the bolt is inserted into the hole noting the position of the indicator mark on the bolt head. The orientation of the toggle and the slot must be parallel to the applied shear force. The shear plane must be within the slot length.
- Rotate the blind bolt 180 degrees to release the toggle or, for M16 size or larger bolts, a supplied wire tool may be used to release the toggle.
- Use a flat head screwdriver to brace the blind bolt to keep it from rotating.
- Tighten the flange nut with a wrench to the specified torque.
The staff at Abrafast is knowledgeable with all rules and regulations involving fasteners and is available to assist you in answering any questions you may have pertaining to the ESR-3617 rules of the ICC ES Evaluation Service. Call us at (630) 882-9010 for more information.