Load Indicator Washers

The Load Indicator Washer is a hardened round washer which has a group of protrusions pressed out of the flat surface. In use, the Load Indicator is placed on a bolt with the protrusions bearing against the hardened surface of the bolt-nut-washer assembly, usually the underside of the bolt head. As the bolt is tightened, the bolt clamping force causes the protrusions to partially flatten, closing the gap between the Load Indicator Washer and the bolt head as shown in Figure 1. When the gap is reduced to a prescribed measurement, the bolt has been properly tightened.

Load Indicator Washers are produced tor both A325 and A490 high-strength structural bolts, and are identified appropriately to avoid any possibility of mixing the two different strength levels.

Load capacity of the Load Indicator Washer is varied for each bolt diameter and grade by changing the number and size of the protrusions.

We Will Supply
Specifications
And
Installation
Procedures On Request

Versatility – The load indicator can be used under the bolt head or at the nut end with a hardened washer, and it will take up to a 1 :20 bevel.

The most common method for load transfer is “shearbearing.” The load is transferred from one steel ply into the bolt by bearing against the shank of the bolt, carried through the bolt by shear, then into the next ply of steel by bearing of the bolt against the side of the bolt hole.

Shear-bearing load transfer may be designed as “threads included” (N) or “threads excluded” (X). With the N-type, the threads may be included in the shear plane, located between the plies of steel. In the X-type, the threads cannot be in the shear plane.

Shear – Bearing (N-type)
threads included in shear plane

Shear – Bearing (X-type)
threads excluded from shear plane

Most shear joints using shear/bearing load transfer to be tightened only to the “snug-tight” condition, defined as “the tightness that is attained with impacts of an impact wrench or the full effort ironworker using an ordinary spud wrench to bring connected plies into firm contact.”

Some shear joints are required to be pretensioned AISC, RCSC or AASHTO specification provisions. Joints include certain column splices, certain connections in crane buildings, certain beam-to-column connect taller buildings, connections of members supplied running machinery or loads that produce impact or reversal, or any other connections so designated.

When joints transfer load through shear-bearing an Engineer should designate the joints as “snug-fit” or “pretensioned” and identify the joint design as “N”

When load transfer through friction is required, the joint is designated as a “slip-critical” {SC) joint. In this joint, the bolts must be completely pretensioned. Snug tightened is not enough. The tightening of the bolts develops a clamping force between the plies of steel, and it is assumed that the load is transferred by friction between the steel plies, rather than the shear-bearing action described above. In these joints, the “faying surface”, or contact area between the steel plies, must receive special consideration in design and coating application.

Slip-Critical Joint
bolt tension creates clamping force

The bolts receive direct applied loading from the structure. Such bolts are typically found in T-hangar and similar details. End-plate moment  connection bolts, because of the, rigidity of the end plates, are also considered to be in direct tension. The snug-tight condition is permitted when using A325 or F1852 bolts in direct tension applications not subjected to significant cyclic load. When A490 or F2280 bolts are used in direct tension, they must be pretensioned.