continuous beam

mronlinetutor · Dec 8, 2019

Is this correct?

A continuous beam is equivalent to a beam segmented which is momently joined.

How do we prove that? This has to do with finite element modeling. When we model a building in which a girder is divided into several girders where there are beams sitting in the perpendicular direction, can we assume that the girder is equivalent to a girder segmented with spacings of the beams without putting support below the segmented girder? In reverse, can we model a segmented girder without modeling it with a continuous girder without placing support below the segmented girder?

This is very basic but I just want to make sure. Thank you.

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

msquared48 · Dec 8, 2019

Yes, but there also has to be a support allowing rotation at the support present to equate the systems.

Mike McCann, PE, SE (WA, HI)

mronlinetutor · Dec 8, 2019

Thank you for your answer.

But do you mean there must be a support at the continuous girder or support at each of the segmented girder in building modeling? The segmented girder is actually a continuous beam but in building modeling, it is shown as segmented but momently connected.

I am afraid some steel detailing guys might interpret the segmented girders as segmented girders but not a continuous girder because, in modeling, I use segmented girders to replace a continuous girder were actually in steel detailing, the segmented girders are meant to be a continuous girder. How should it be drawn out on the modeling plan, construction plan, and steel detailing plan? I am using Midas Gen 2013. In Midas Gen, all the nodes are considered as momently connected. But there are beam-ends releases. You cannot place support in Midas Gen under the beam because the beam can only be simply supported through the means of beam ends release. I cannot put a boundary condition support there. Is this okay?

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

msquared48 · Dec 8, 2019

For a two span continuous girder there needs to be three supports.

Mike McCann, PE, SE (WA, HI)

Ron247 · Dec 8, 2019

I think what you are calling a continuous beam may be 2 different definitions. A classical "continuous beam" has 3 or more supports.

On the other hand, if I had 2 supports with a 30' simple span steel beam spanning between them, it would be the same as three 10' beams that were connected to transfer all forces between their joints. Is that what you are calling a continuous beam, mronlinetutor?

The 2nd one I describe would be analyze the same for forces, reactions and deflections but may not analyze the same for allowable loads if you do not correctly modify the lengths of the members for purposes of the steel checks. For example calling the length of the member as 10' would not yield the same allowables as 30'.

mronlinetutor · Dec 8, 2019

Attached is my floor plan for 7 stories mid-rise. The blue lines are girders and the red lines are beams. The columns are placed in a 40'x40'grid. The total plan is 200'x200'. Therefore the girders are 40' long and the beams are 40' long too. The beams are placed 10' apart simply supported to the girders.

So is it okay to place a note on the girder and beam on the overall building modeling? The building is momently connected.

How else would you place the girders and beams with a 40'x40' grid columns?

Thank you.

disclaimer: all calculations and comments must be checked by senior engineers before they are taken to be acceptable.

msquared48 · Dec 9, 2019

Well, to lower the overall depth of your floor structure, you could alternate the joist directions 40 foot bay by 40 foot bay, i.e., a checkerboard pattern. More girders, fewer joists. Has worked for me in the past, particularly in large warehouses.

Looks like each girder has three point loads from the joists, with two more joists going directly to the columns, hence reducing the load to the girders.

Mike McCann, PE, SE (WA, HI)

r13 · Dec 9, 2019

A continuous beam is equivalent to a beam segmented which is momently joined.

A segmented beam/girder in FE program is a integral piece (continuously joined), provides that the internal forces and moments are passed through the interfaces (or joints) without discontinuity. I don't know whether "momently joined" is the correct description or not. If you have any doubt on the modeling technics prescribed by the program, why not go through an example problem in the user's manual, or try to model two beams in orthogonal directions, and verify the result by hand.

I am afraid some steel detailing guys might interpret the segmented girders as segmented girders but not a continuous girder......

How should it be drawn out on the modeling plan.....

Label the beam and girder on plan, then cut an elevation view on beam-girder joint to show the details.

BAretired · Dec 9, 2019

I may be color blind, but to me, the members on the perimeter are blue; the typical members running on column lines both N/S and E/W are olive green; most of the members running N/S on the page are red and there are a few that are yellow. In the central bay, there are orange members running in both directions, making a two way grid.

The columns are shown as round, but this may be merely a convenience to show column locations.

mronlinetutor said:
Is this correct?

A continuous beam is equivalent to a beam segmented which is momently joined.

How do we prove that?

A continuous beam is a beam running continuously from end to end. It is not practical to provide beams 200' long, so full continuity is not possible. "Momently joined" is undefined. Beam segments joined together by full strength welds would tend to render the girder fully continuous, but the reality is that full continuity is unlikely to be achieved in practice. This means that the deformation of the joint must be considered.

BA

BAretired · Dec 9, 2019

On second thought, the perimeter members may be cyan.

BA

r13 · Dec 9, 2019

I believe the beams are pink colored, running continuously over the blue girders. Beams and girders are in touch with each other (thru bolting, or clamps, I guess), they act (displace) together, but do not interact as rigidly joined members. BA's comment highlights the importance of show legend on the drawing, and member labelling. So, there is less chance for misunderstanding.

rb1957 · Dec 9, 2019

so blue are continuous beams, and the crossing ones are piecewise continuous (ie gussets and splices around the continuous beams) ?

does "The building is momently connected." have some special meaning to yous guys ?

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

IRstuff · Dec 9, 2019

According to

https://www.color-blindness.com/color-name-hue/

the peripheral members are "seagull" inte blue family

The interior vertical members are "puce" in the red family while the interior horizontal members are "Air Force Blue."

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r13 · Dec 9, 2019

IRstuff,

An old friend of mine, a mechanical engineer, used to kid me with "A wall is a concrete slab turns 90°, what difficult about it?" Yah, sort of

r13 · Dec 9, 2019

rb1957,

Similar, to an extent, to the plate on plate problem you have commented on.

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continuous beam

mronlinetutor

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msquared48

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mronlinetutor

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msquared48

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Ron247

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mronlinetutor

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msquared48

Structural

r13

Civil/Environmental

BAretired

Structural

BAretired

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r13

Civil/Environmental

rb1957

Aerospace

IRstuff

Aerospace

r13

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r13

Civil/Environmental

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