Che cos'è una connessione momentanea?
A moment connection is a joint that transfers momento flettente between a column and a beam, o tra due membri qualsiasi. If a beam carries internal moment at its end, the connection has to carry that moment across the joint rather than letting the end rotate freely.
Extended end plate connection, one example of a moment connection. The bolts outside the tension flange give the couple a longer lever arm.
The aim of a momento di connessione is to hold the end rotation, which in analysis terms is the codice di fissità FFFFFF: restrained in all three translations and all three rotations. That is why moment connections are also called rigid connections.
AISC 360-16 Section B3.4 is more precise about it, and the distinction matters when you model the frame. A moment connection is either fully restrained (FR), which holds the angle between the members and justifies the FFFFFF assumption, o partially restrained (PR), which transfers moment but rotates enough that the analysis has to account for the joint’s real stiffness. Treating a PR joint as fully rigid overstates the frame’s stiffness and understates its drift.
Where a connessione a taglio works mostly through the beam web, a moment connection has to engage the flanges, because that is where the bending stress is. Piastre flangiate, welded flanges or an end plate all do the same job: they turn the beam’s moment into a tension force in one flange and a compression force in the other, and carry that couple into the column.
Tipi di connessione del momento
Moment connections carry far more moment than a shear connection, and they cost more to make: more material, more welding, more fit-up and more inspection. Most frames use them only where the structure relies on frame action for lateral stability, and use shear connections everywhere else.
Which configurations are available depends on the design code and on what the beam frames into.
Beam to I-section column (AISC 360-16)
Four configurations, framing to the column flange or to the column web.
Flangia Piastra
Plates run across the top and bottom flanges of the beam, bolted or welded to the beam and to the column. Mentre la trave si piega, one plate goes into tension and the other into compression, and that couple carries the moment. The beam web is usually carried by a separate shear plate, so the connection splits the job: flanges take the moment, web takes the shear.
Vedi il flange plate connection calculator.
Flange saldate
The beam flanges are welded straight to the column flange, with no intermediate plate, and the web is bolted to a shear tab. This gives the stiffest joint of the group and the cleanest load path, but it is field welding on a member that has to fit within tolerance, so it carries preheat, access and inspection costs that a bolted detail does not.
Piastra terminale a filo
A plate welded to the end of the beam and bolted to the column, with the plate finishing flush with the beam flanges and all bolts sitting between them. It suits lower moments, because the bolt group’s lever arm is limited by the beam depth.
Piastra terminale estesa
The same idea, with the plate extended past the tension flange so bolts can sit outside it. Those outer bolts have a longer lever arm about the compression flange, which is what buys the extra moment capacity. Prying action on the extended part becomes a governing check. It is the configuration shown at the top of this page.
Both end plate configurations are covered by the moment connection calculator.
Beam to HSS column (AISC 360-16)
Framing a moment connection into a hollow section is harder, because there is no flange to bolt through and no access to the far side. One configuration is available: un carico piastra flangiata welded to the face of the HSS, without stiffeners.
AS 4100:2020
AS 4100 coverage in SkyCiv Connection Design is shear connections only, framing beam to I-section column or beam to beam. Moment connections to AS 4100 are not available. For moment design, use AISC 360-16.
What does the software check?
Detailing runs first: distanze dal bordo dei bulloni, distanza tra i bulloni (passo e calibro), tool clearances, minimum and maximum plate dimensions, and clash detection between plates, rinforzi, bolts and welds. A connection that cannot be built does not reach the solve.
The strength checks then follow the couple through the joint. On the flange side that means the plate in tension and in compression, taglio dei bulloni, bolt bearing and tear-out, rottura per taglio del blocco, prying action on the bolts, and weld throat stress. On the supporting member it means local flange bending, web local yielding and web crippling, which are the limit states that decide whether the column needs stiffeners or a doubler plate.
Ogni formula, design check and code reference is shown in full, with clause numbers from AISC 360-16, so you can follow the calculation rather than take it on trust.
Connessione Moment vs Connessione Shear: la differenza
The difference is what happens to the angle between the two members. In a moment connection that angle is held, so bending in one member carries into the other. In a shear connection the joint is free to rotate, so the beam end turns and no meaningful moment crosses the joint.
| Connessione momentanea | Connessione a taglio | |
|---|---|---|
| Forze trasferite | Taglio e momento | Solo taglio |
| Nomi alternativi | Rigido, Fisso, Moment-resisting | Appuntato, Cerniera, Semplice |
| AISC 360-16 termine | FR or PR moment connection | Simple connection |
| Rotazione | Restrains rotation | Free to rotate |
| Codice di fissità del software | FFFFFF | FFFFFR |
Software di progettazione della connessione SkyCiv
The models and checks above are from Progettazione di connessioni SkyCiv. It covers over 80+ pre-configured connection types, designs to AISC 360-16 in LRFD and ASD and to AS 4100:2020, and shows every formula, design check and code reference in full.
You can model the connection in 3D, swap bolts, welds or plates without losing your load data, produce 2D detail drawing sheets in CloudCAD, and export the 3D geometry to IFC for coordination in Revit, Tekla o Navisworks.
It runs entirely in the browser, senza download, updates or IT setup.
