Shuriken HSS connections by Atlas Tube and their applications in structural design

The problem with conventional HSS connections

Hollow Structural Sections offer clear advantages over wide-flange columns in many building configurations: equal compression efficiency about both axes, smaller footprint, and cleaner aesthetics in exposed applications. In Japan, Ted noted, approximately 99 percent of building columns are HSS or built-up box sections. In North America adoption has been lower, partly because one genuine impediment has constrained their use in multi-story construction: the difficulty of splicing and connecting to a closed tube.

Conventional approaches to this problem carry real fabrication and inspection cost. Welded HSS column splices require end preparation, backing bars, and full-penetration welds followed by ultrasonic inspection. Beam connections to an HSS column typically require a field weld or complex shop-welded extended shear plates. Any connection to an inaccessible interior face has historically forced a choice between field welding or elaborate plate extensions. Shuriken was invented to eliminate this constraint.

How the Shuriken system works

Shuriken is a disposable wrench. It holds a standard nut on the inside of a tube or other inaccessible location, so that standard A325 or A490 bolts can be installed and tightened from the outside using standard tooling. The nut is not a proprietary fastener; it is a standard heavy hex nut. The engineering of the connection is therefore entirely standard AISC bolt design.

Installation begins in the shop: a nut is hand-tightened onto an alignment bolt to centre the nut over the hole in the splice plate. The Shuriken is then dropped over the nut and tack-welded at its corners. The alignment bolt is removed, leaving the nut encapsulated. Flexible tabs in the Shuriken's steel ring allow the nut to shift slightly to accommodate minor positional variation, ensuring the field bolt can always be engaged. When a pretensioned or slip-critical installation is specified, DTI washers are placed under the bolt head on the accessible side, providing torque verification without requiring interior access.

The name comes from the star-like appearance of the fitting. The Shuriken itself is fully consumed in the connection: it is tack-welded into place and left permanently within the assembly.

Applications in structural frames

The primary application is the HSS column splice. Splice plates are laid flat in the shop, Shurikens are tack-welded to the plate surface, and the plates are then slid into the lower column section and shop-bolted. In the field, the upper column section slides over the protruding splice plates and is field-bolted from outside. No full-penetration welds are required, and no ultrasonic inspection. Lead times for the connectors within North America are generally under a week from Atlas Tube's distribution centre.

Beam-to-HSS column connections use the same principle. For simple shear connections, the beam is coped at the bottom and lowered onto a pair of shop-welded shear plates with Shurikens already in position, then field-bolted. For moment connections, Shurikens are mounted to thin non-structural mounting plates, which are bolted to the interior of the tube in the shop, allowing the moment plate to be brought in from the side and field-bolted.

Connections to inaccessible faces are another strong use case. For moment connections at inaccessible faces, Shurikens can be mounted to both the column shear tab and the beam flange on the blind side, allowing the full moment connection to be bolted without any field welding. Ted showed a real project example from Schuff Steel: a large pyramid-shaped structure retrofitted onto an existing building several hundred feet in the air, where the fourth wall panel was connected entirely by field bolting using Shurikens pre-installed in the shop. Without Shuriken, that panel would have required exterior field welding at height.

Worked connection example: 200-kip tension splice

Ted demonstrated a complete connection design for a 12-inch square HSS with a three-eighths-inch wall (ASTM A500 Grade C, Fy = 50 ksi) under 200 kips tension. The connection uses half-inch splice plates, nine inches wide, with three Shurikens per face using seven-eighths-inch A325 slip-critical bolts at three-inch spacing.

Bolt shear capacity: 24 bolts in single shear at 8.81 kips per bolt yields 211 kips, exceeding the 200-kip demand. Gross section yielding of the HSS: gross area times 50 ksi, divided by omega of 1.67, gives 479 kips. Net section rupture: the effective area equals the gross area minus 12 bolt holes, each calculated using the hole width times the wall thickness multiplied by the 0.93 ASTM A500 thickness tolerance factor. The resulting effective area gives 366 kips. Block shear gives 329 kips. Splice plates: gross section yielding 539 kips; net section rupture 390 kips. All limit states clear the 200-kip demand.

Ted noted that net section rupture and block shear are the limit states most likely to govern for HSS connections, and that the 0.93 ASTM A500 thickness factor applies in all net section and weld calculations for this material and should be included as a matter of course.