Parallel Beam Bracing Another Beam

[axle]

Hi there. I have got a question regarding the bracing of a beam through the use of an identical beam running parallel to it. The beams are tied together through the use of horizontal members running from the top flange to top flange of each beam at approximately 2m centres (the top flange is the critical flange). I know that when the beam is bent about the major x-axis that the horizontal members at the top flange level can be classed as lateral restraints provided that the beam parallel to the beam being loaded is stiff enough about its minor axis to take the restraining loads. My question arises when the beam that is being loaded is bent about the minor y-axis at the top flange level. How does the beam parallel to the beam being loaded help out as such? When a lateral load is applied to the top flange of the beam being loaded, to calculate the moment that is produced in the beam, is the length of the beam taken as the distance between the ties at the top flange? How is this load then transferred to the parallel beam that is bracing the beam that is being loaded? I am just unsure how these two beam interact when one beam is loaded about the minor y-axis at the top flange level. Any help/advise would be greatly appreciated.

 

[apetr26542]

I would recommend modeling this in a structural software program. I think the two would almost form a truss or act in unison.

 

[miecz]

Ignoring any truss action, the two beams will share the load according to thier relative stiffness in the weak direction. The horizontal members transfer the load by tension or compression so that the lateral displacement is identical in both beams. It calls for a stiffness analysis, but I suppose you could analyze the loaded beam as a continous beam on rigid supports, and then superimpose the effect of the "support displacement".

 

[111213]

hi,

i had that case several times.
top flange beam no.1 is supported by the top flange
of beam no.2. you calculate the moment by using the
formulas of an beam with discrete elastic foundations.
these foundations are the ties.
the reaction forces are the loads for beam no.2.

the moments are not the same in both beams !

 

[mrMikee]

If the lateral load is at a crosstie the moments would be very nearly the same in both beams. If not at a crosstie then the loaded beam would need to be evaluated for the addional moments due to bending between crossties.

-Mike