How best to model uniformly loaded fixed ends members

[Tabaluga]

Hi,

I wanted to get a quick second opinion on the following. I am specifying uniformly loaded beams and plates bolted on both ends to rigid supports and have used the conservative simply supported scenario to get the midspan bending moments (and reactions at supports) as per sketch. Now, for checking the bolts, a co-worker included in calculation bolt tension a force equal to the support reaction. Is there any possibility that that is a correct and valid rule when designing connections? I have tried to get an explanation, but it's not making sense - am I missing something? From basic mechanics all of the reaction force will be transferred to the supporting members, so the bolts should not be taking any tension (and are not even needed as far as resisting that load).

The only other possibility, although I am sure that's not what's they had in mind: If you consider that the connection is bolted at the ends, in reality there will be some prying tension (and shear) induced due to rotation of ends under midspan deflection - which I thought can be ignored if we stayed within the allowable deflection limits.

If anyone has come across something similar any suggestions how best to model this would be appreciated. I don't want a complex analysis lecture, but rather a practical and accepted approach to this or similar scenario. Thanks.

"Reality is merely an illusion, albeit a very persistent one." (A. Einstein)

 

[mike20793]

Is this a steel beam being bolted to a wall or steel beam to steel beam? The tension force equal to the reaction seems odd to me. When it's rigid like a wall or similar, you are going to get some moment caused by the eccentricity of the connection to the support and that gets resolved into a tension force on some of the bolts. I always include the shear and the moment caused by the eccentricity and design for that.

 

[BAretired]

What you have drawn is not a fixed end member. It is a considered to be a simple span. Each bolt carries one quarter of the end reaction in shear. The bolt holes are normally large enough to accommodate beam rotation.

BA

 

[RPMG]

The term fixed end implies that there is a moment connection at the end, which does not apply to pin-pin or pin-roller boundary conditions.


I interpret this few ways:

1. Bolts can be snug-tight or pretensioned. This is specified by chapter J, not the shear force applied to the beam.

2. A beam can develop internal axial load for pin-roller due to diaphragm or other lateral loads. I don't believe that this is the case here.

3. A beam may be subject to internal axial forces for a pin-pin due movement, such as thermal contraction. It is usually an error in computer models, but tension forces can develop due to sag.

Long story short, this is probably just a shear connection.

 

[Tabaluga]

Thank you for your comments. Yes, it is a shear connection to me also, sorry for the misleading title.

Correct, the loading is that for a simply supported member, and the connection is not being designed for moment, yet member is bolted at both ends (hence no movement there). The members are not long, 3' to 9'. I understand that another option would be to use GRP material for members and supports instead of steel, but at this stage they are fine with designing as for steel.

Conservatively, could we say no movement is allowed by the bolt holes, hence shear in bolts proportional to reaction force (BAretired)?

How would we allow for tension in the bolts due to the design loading (RPMG)-do you mean the prying out tension that I believe mike20793 suggested?



"Reality is merely an illusion, albeit a very persistent one." (A. Einstein)

 

[mike20793]

I was referring to designing anchors or an embed plate within a concrete or masonry wall. I may have misunderstood your original question. As mentioned above, a simple shear connection has enough rotation at the joints to be designed for shear only. If it were an embed plate within a concrete wall, you would get some tension on the headed studs caused by the eccentricity of the connection, but not on the bolts for the shear connection to the plate.