Structural terms :) 1

[user277418]

Hi

Just in the sake of curiosity. My head goes round a bit from number of terms in English for practically identical structures.

As I see it:
Truss - assembly of members (commonly triangulated) where the members are organized so that the assemblage as a whole behaves as a single object
Beam - horizontal structural member that primarily resists loads applied laterally to the beam's axis
Girder - main horizontal structural element (truss or beam) that transfers loads from other structures directly to columns
Purlin - secondary horizontal structural member that transfers load from elements that form roof surface (trapezoidal steel sheeting, reinforced concrete slab etc.) to girders
Rafter - the same as purlin only inclined. Forming slope of the roof unlike purlins that follows the slope. May be girder (connected directly to columns/walls)
Joist - the same as purlin only supports structural elements that form floors (RC slabs etc.)
Stringer - sometimes referenced as joist, but currently the term is used as inclined structural elements that support steps of stairs

Am I right?

Best regards

 

[rb1957]

a truss is usually axial loaded members (no transverse loads, no bending).

another day in paradise, or is paradise one day closer ?

 

[phamENG]

Truss - a structural system made up of members experiencing tension/compression only. The exception is a Vierendeel Truss, which isn't really a truss.
Beam - any member that resists loads primarily through bending.
Girder - your definition is spot on. I'd ad that a girder is a more specific definition of a beam.
Purlin - Doesn't typically transfer to girders. usually transfers back to rafters (allows for sheathing to span along the slope, which is good where the roofing surface and structural roof deck are the same, like in barns with a metal roof). I have done some historic restorations where the rafters are supported by purlins which are then supported by roof trusses spaced 15' or so apart. I find that purlins aren't used much in the US modern structures outside of agricultural or industrial applications.
Rafter - I agree with your definition
Joist - secondary beam spanning between girders and/or bearing walls to support a floor or flat roof.
Stringer - stairs as you mentioned, but also used frequently in docks/piers over the water where it's equivalent to a joist.

 

[JoshPlumSE]

I like phamENG's definitions a little better.

Though I would say that a purlin is often an 3 order beam. Meaning it transfers it's load into a beam or rafter or joist, which then transfers the load into a girder.

Granted, non of these definitions are "absolute" in that we tend to be a little loose with our terminology. And, it can vary somewhat between types of structures / industries, regions or countries.

 

[BAretired]

Its easier to see by way of a picture. Word definitions do not assist me to picture what these building elements really do.

If I had no idea what a truss was, the following definition would not help:

Truss - a structural system made up of members experiencing tension/compression only. The exception is a Vierendeel Truss, which isn't really a truss.

I would believe that a cable, rod or column is a truss. And I would have no idea why a Vierendeel Truss is not really a truss. Why call it a truss if it is not a truss? (I would say to myself)

BA

 

[dik]

What is it a 'perforated beam'?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoshPlumSE]

How about the following:

Truss: An assembly of members (commonly triangulated) where the members are organized so that they primarily resist axial forces (i.e. tension and compression).

That's not 100$ true because of King's post and Vierendeel trusses. But, those are special / odd cases. But, it's a good general definition.

 

[dhengr]

User277418:
A Vierendeel Truss is actually some sort of a ridged frame in its analysis and design, although it usually shows itself as some sort of a truss, without diag. web members, in the framing system. I suspect that the biggest problem is not the naming of major structural elements if we stick to our basic textbook learning of structural systems; there are beams, columns, beam-columns, trusses, plate structures, shells, bearing walls, etc. etc., and then variations on those. But, we have a bunch of Uni. Profs., local vernacular, and local builder terminology, each wanting to get their name in the history books for a newly invented term for a long historied item or structural component. Footers (footings) and Hertzian Stresses (Hertz bearing stresses) are two of my favorites, many years old, but they needed a new name for confusions sake. As Structural Engineers, above all else, we should be wanting to communicate our thoughts and our designs in very concise and complete terminology. I want a reasonably technically qualified person (and others) to understand my problem description and my structure, I am not trying/wanting to impress people with all the acronyms I can spout, and all the newest terminology which shows how smart I think I am.

E-Tips OP’s and posts are a prime example of what’s gone hay-wire, almost nobody proof reads their posts for spelling or mis-hit key stokes, so we waste our time determining that ‘ben’ actually means beam, after six readings; they don’t read previous posts for some continuity in the whole thread; they don’t bother give dimensions, thicknesses, sizes, loads, etc. for some representation of magnitudes of the problem, no simple explanation of the intended use, after all, a 16” masonry corbel, a C 8”, 12 long canti…, and a 80’ flag pole are all cantilevers, what’s the diff?, except for their own ignorance? And then, they have hurt feeling when someone calls them on their laziness, or ineptitude. It is a wonder that anything actually ever gets built. If we want to be recognized as professionals, we ought to start acting/performing/communicating like professionals. If Doctors communicated like we do here on E-Tips, they’d be cutting off hands and feet, when the real problem was a heart problem. E-Tips has become too convenient a means of avoiding showing your boss how little you really know, despite how you sold yourself to him. He/she should be guiding you and know what you know and what you don’t know, to keep you and the company out of trouble. Although, today, it appears that many bosses aren’t smart enough to do this, either.

 

[Ron247]

Truss is always a problem because a wood truss for example may not have any loads applied at the joints and does have transverse load thus creating bending. Even bar joists perform in a similar manner.

Girder should be transfers loads from other structures OR structural components, rather than other structures only.

Joists are not limited to floors. Ceiling joist.

Beam is not only horizontal in the engineer world but is in the architect world. Beam is just loaded transverse.

 

[user277418]

didn't expect so much attention to the post

How about... Truss - assembly of members (commonly triangulated) where the members are organized so that the assemblage as a whole behaves as a single member in bending. But each member of the assemblage intended to behave as strut or tie, thus in compression or tension respectively, in exceptional cases in bending as well. Joints between the members of the assemblage are not intended to transfer bending, but in exceptional cases may, like in Vierendeel truss.

Actually when I posted the post, it became clear for me that we have equivalent of almost all of those terms in my language too and I used them daily even without realize it. Only joist doesn't have an equivalent term. For us it is just beam/truss or secondary beam/truss. And the secondary beam/truss sits on main beam/truss or beam/truss sits on girder.

 

[Ng2020]

Dhengr... You might need to proof read your diatribe.
"if we stick to our User277418:
basic textbook learning of"

 

[dhengr]

Ng2020:
Thanks for proof reading my diatribe.

 

[Ng2020]

No problems. I generally agree with what you're saying. I couldn't resist the irony

 

[robyengIT]

Dik "What is it a 'perforated beam'?"

I think that in Europe are the so called "castellated or cellular beams".

 

[jimstructures]

Without a picture to determine what the original user of the term meant, I would add the United States to the list provided by robyengIT for assumed alternate names/definitions of perforated beams.

Jim