Lateral Restrain At MidSpan
Lateral Restrain At MidSpan
(OP)
I'm confused with condition of lateral restrain.
Can the following cases be considered a lateral restrain?
1. Secondary beam connected at midspan between 2 parallel Primary beams via web-side plate. (See Diagram 1 below)
(Would it be regarded as Unrestrain?)
2. Secondary beam connected at midspan between 2 parallel Primary beams via full depth web-side plate (acting as stiffener) (See Diagram 1 below)
(Would it be regarded as Partial restrain?)
| |
| |
|----|
| |
| |
(Verticals are Primary beams, horizontal is secondary beam)
Diagram 1
==========
3. Equal Angle bracing connected to Primary beam via Flexible Cleat Connection at 150mm below top of flange to Primary beam (See Diagram 2 below)
(Would this be considered restrained at top flange only? and unrestrained at bottom flange)
-------- <<(Primary beam - Top flange)
|
|--l=========== <<(Bracing)
|
|
|
|
--------
Diagram 2
==========
Thanks guys!
Aston
Can the following cases be considered a lateral restrain?
1. Secondary beam connected at midspan between 2 parallel Primary beams via web-side plate. (See Diagram 1 below)
(Would it be regarded as Unrestrain?)
2. Secondary beam connected at midspan between 2 parallel Primary beams via full depth web-side plate (acting as stiffener) (See Diagram 1 below)
(Would it be regarded as Partial restrain?)
| |
| |
|----|
| |
| |
(Verticals are Primary beams, horizontal is secondary beam)
Diagram 1
==========
3. Equal Angle bracing connected to Primary beam via Flexible Cleat Connection at 150mm below top of flange to Primary beam (See Diagram 2 below)
(Would this be considered restrained at top flange only? and unrestrained at bottom flange)
-------- <<(Primary beam - Top flange)
|
|--l=========== <<(Bracing)
|
|
|
|
--------
Diagram 2
==========
Thanks guys!
Aston





RE: Lateral Restrain At MidSpan
1. Unrestrained (beams will deflect laterally together)
2. Unrestrained (only "partially restrained if the restraint ... effectively prevents lateral deflection..."
3. Possibly restrains top flange in some situations eg. for deep beams (obviously top flange not restrained for 200mm deep beam for flexible connection). A stiff connection between brace and beam will help of course.
RE: Lateral Restrain At MidSpan
BTW, there are two excellent AISC (now SIA) journal papers that address the restraint afforded to beams and cantilevers by various connections:
- Trahair NS, et al (1993), Design of Unbraced Beams, Steel Construction, Vol 27, No 1
- Trahair NS (1993), Design of Unbraced Cantilevers, Steel Construction, Vol 27, No 3
(www.steel.org.au)
They should be in every structural engineer's bookshelf. Unfortunately my copies are in storage!
RE: Lateral Restrain At MidSpan
csd
RE: Lateral Restrain At MidSpan
Thanks!
Aston
RE: Lateral Restrain At MidSpan
Marco
RE: Lateral Restrain At MidSpan
If only one beam was loaded then, yes, I would probably agree. But with both beams loaded you would need to condider the restraint stiffness and non-linear effects.
AS4100 does not stipulate a restraint stiffness but its American counterpart AISC 360-05 does. In this case I would say stiffness of the restraint is obviously very important.
Another thing, if the beam has the required minor axis capacity then LT buckling might not be much of an issue, even without the midspan 'restraint'.
RE: Lateral Restrain At MidSpan
I think it's best to take the conservative case and assume that 'Case 2' is unrestrained.