Aluminium Angle Profile Bracket 80x80x9 mm 45 Degree Corner Gusset for Angled Bracing

OEM / ODM Available Free Sample Available ISO 9001:2015 RoHS REACH

45 degree corner gusset 80 x 80 x 9 mm machined from 6061-T6 plate, for fixing a diagonal brace to a profile frame corner. Raises racking stiffness far more than a larger profile would.

Wholesale Price $1.90 - $6.20 / piece per piece

Material	Aluminium
Alloy Grade	6061-T6
Temper	T6
Section Size	80 x 80 mm legs
Slot	Round holes to drawing, M8 typical
Length	80 x 80 x 9 mm
Tolerance	ISO 2768 medium for machined parts
Surface	Mill finish / anodised
MOQ	500
Lead Time	18-28 days after deposit
Loading Port	Shanghai / Ningbo
Supply Ability	200,000 pieces per month
Payment Terms	T/T 30% deposit + 70% before shipment \| L/C at sight
Trade Terms	FOB \| CIF \| EXW
Certifications	ISO 9001:2015 \| RoHS \| REACH

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Connecting · 45 degree gusset

This is an 80 x 80 mm corner gusset, 9 mm thick, with one face set at 45 degrees to take a diagonal brace. It is used at the corner of a frame where a brace runs from one corner to the opposite corner, and it gives the brace a solid, drilled landing instead of relying on a bracket bolted through at an angle.

The reason to add a brace at all is that a rectangular frame is much weaker against racking than it looks. The four members are stiff in bending, but the frame is a four-bar linkage held square only by its corners. Push the top sideways and the frame does not bend its members much, it rotates about the corners. A diagonal brace turns that into an axial load in a single member, and axial stiffness for the same member is hundreds of times the bending stiffness. It is by a wide margin the cheapest stiffness available on a profile frame.

45 degree gusset: the flat leg lands on the frame member and the angled face takes the brace, so the brace loads the corner axially rather than through a bolt in shear.

A right-angle frame is a linkage, not a beam

When a frame racks, most people picture the members bending. They do not, at least not at first. Four members joined at four corners form a four-bar linkage, and a linkage with pinned corners is free to rotate into a parallelogram. What stops it is the rotational stiffness of the corners, not the bending stiffness of the members.

That is why adding profile size to a racking problem helps so little. Making the members deeper makes them harder to bend, but bending is not what is happening. The frame is rotating about its corners, and the only thing resisting that is the bracket at each corner.

How much a brace is worth

A diagonal brace changes the mechanism into a triangulated structure. The lateral load no longer has to be carried by the corners rotating; it goes down the brace as an axial force. That is the whole benefit, and it is enormous because axial stiffness and bending stiffness are not comparable quantities.

Take a 40 x 40 profile with a second moment of area of about 13 cm4 and a cross section of about 5.6 cm2, so a radius of gyration of about 15 mm. Over a 500 mm span, the axial stiffness of that member is about 360 times its bending stiffness. Over a longer span it gets worse for bending, because the ratio rises with the square of the length: at 1,000 mm it is about 1,400 times.

Span	Axial stiffness divided by bending stiffness	Comment
300 mm	About 130 times	Short brace, still a large gain
500 mm	About 360 times	Typical panel brace
1,000 mm	About 1,400 times	Tall frame, huge gain
2,000 mm	About 5,700 times	Very tall frame, brace is essential

Why no profile upgrade can match it

The natural response to a frame that racks is to specify a bigger profile. It is worth working out what that would actually take. Stiffness in bending scales with the fourth power of the section depth, so to multiply the bending stiffness by 360 you need a section about 4.4 times as deep, because the fourth root of 360 is about 4.4.

On a 40 mm member that means going to a 175 mm section. That is not a bigger profile in the same family, it is a different order of structure, and it will weigh more, cost more and take up more space than the frame was designed for. One brace and two gussets do the same job in the plane that matters.

Approach	Stiffness gain	Effect on the frame
Go from 40 x 40 to 45 x 45 profile	About 1.6 times	Slightly heavier, slightly dearer
Go from 40 x 40 to 60 x 60 profile	About 5 times	Noticeably heavier and dearer
Go from 40 x 40 to 80 x 80 profile	About 16 times	Much heavier, changes the design
Add one 45 degree brace with two gussets	Up to about 360 times	One extra member, two gussets

Where the brace has to go

A brace works only in the plane of the frame it braces. A single brace on the front of a frame does nothing for racking in the side plane, so a frame that can be pushed in two directions needs a brace in each, or a braced panel that acts as a diaphragm.

The brace also has to be continuous. Two short braces meeting at a node in the middle of a member is not the same as one brace running corner to corner, because the node has to transfer the load through the member it lands on. Where a brace has to be split, put the node at a corner rather than mid-span.

Brace in the plane that racksA frame open on the front and braced on the back still racks on the front. Brace each plane that sees the load, or close the panel and let it act as a diaphragm.

Brace from corner to cornerA brace that runs to the corners loads them axially and needs no mid-span node. A brace that stops short puts a bending load into a member that was not sized for it.

Size the corner brackets for the braceThe corner now carries an axial force from the brace as well as the frame load. The gusset at each end of the brace has to be sized for that force, not for the frame alone.

Check the brace member itselfA brace in compression can buckle. Over a long span the brace needs to be sized for buckling rather than for yield, which usually means going up a section size for the brace alone.

Bolt layout for a 9 mm gusset

At 9 mm thick the gusset is stiff enough to spread load into the member, but it is not thick enough to ignore the bolt pattern. Three things decide whether it works.

First, the bolts on the flat leg should straddle the point where the brace force enters. If both bolts are on one side of that point the gusset rotates about them. Second, the bolt nearest the corner carries most of the load and should be as close to the corner as the profile allows. Third, the brace should land on the angled face square, so the brace end is cut at the matching angle rather than butted against a corner.

Cut the brace end to match the angled face The brace should land flat on the 45 degree face. A brace end cut square and butted against the gusset transfers load through a line contact, which crushes the gusset edge and loosens the joint.
Straddle the brace force with the leg bolts Place the two bolts on the flat leg so the line of the brace force passes between them. Both bolts on one side of that line leaves the gusset free to rotate.
Use the corner bolt as the primary fixing The bolt nearest the corner takes the largest share of the load. Put it as close to the corner as the profile face allows, and do not move it out to make room for something else.
Tighten the brace fixing before the leg fixings Set the brace on the angled face and tighten it first, then tighten the leg bolts. The other order pulls the gusset out of position before the brace is seated.
Check the frame is square before final tightening A brace fixes the frame’s shape. Check the diagonals before the brace is tightened, because once it is tight the frame cannot be adjusted without slackening the brace.

Brace or bigger profile? If the problem is the frame racking, add a brace. If the problem is a member sagging under a load in the middle of its span, a bigger profile is the right answer, because that is bending. The two problems look similar on a drawing and are fixed in completely different ways, so identify which one you have before changing anything.

Frequently asked questions

What is a 45 degree gusset for?

Fixing a diagonal brace to the corner of a profile frame. It gives the brace a flat drilled landing at 45 degrees, so the brace loads the corner axially instead of transferring its force through a bolt in shear.

How much stiffer does a brace make a frame?

A great deal, because it changes the load path from bending to axial. Over a 500 mm span the axial stiffness of the same member is about 360 times its bending stiffness, and the ratio rises with the square of the span.

Can I just use a bigger profile instead?

In practice no. Bending stiffness scales with the fourth power of section depth, so matching a braced frame would take a section about 4.4 times as deep. On a 40 mm member that is a 175 mm section, which is a different structure altogether.

Do I need a brace in every direction?

Yes. A brace works only in the plane of the frame it is in, so a frame that racks in two directions needs a brace in each, or a closed panel acting as a diaphragm. One brace does not protect both planes.

How should the bolts be arranged on the gusset?

The two bolts on the flat leg should straddle the point where the brace force enters, and the bolt nearest the corner should be as close to it as the profile allows, because that bolt carries most of the load.

Tell us the frame and where it racks

Send the frame drawing and describe the load that makes it rack. We will confirm the brace size and the gusset angle, quote the bulk price and supply samples for a trial frame.

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