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flat beam question

flat beam question

flat beam question

I need a software or somebody or a research centre for a structural calculation.
I want to calculate the difference in deformation (bending and torsion) of a reinforced concrete flat beam (cm.80x25cm. or cm.100x25cm.) on pillars (cm.30x30cm.) placed at intervals of m.3,50 or more
In the first case the pillars are well-aimed while in the second case on the edge of the beam.


     X               X

on the edge
   X             X


This is very important for me because I am examining a  supporting structure with the latter feature.
and engineering software generally  does not take in consideration this question.
   thanks for your help        

RE: flat beam question

Its difficult to explain adequately as u have not indicated the load pattern! However,
Case 1:
U can analyse your continuous beams using any software. This will give u both Moments and shear forces.
Case 2:
Torsion exists only with the case where your beams are off centre. I have assumed 80 or 100cm to be beam width. Both beams &  columns will be subjected to torsion. Beams will have moments and shear in the other axis too. This should be carried out manually.

I can email to u a spreadsheet based on hardy cross method for analysis of forces in a cont. beam of atleast 5 spans if it helps.


RE: flat beam question

Thanks Riz
My question is not unmotivated.
You can see the supporting structure:               


In this building there are cracks in the outside and inside (see image 5 and 6).
Some little beam at the first and second ceiling (are these the english words?) are broken (in particular, see image “carpentery 2” where is an asterisk ) and there are little cracks everywhere in the building.   
In your opinion, the structure, with flat beam an columns in those positions, can be the cause?
Besides, the ground has risen and so the floor of the basement too. Can be this the sole cause of all damages?

An engineer tells in the first way (the structure) and another engineer tells in the latter way (sole the ground).
I’m not an engineer (but talking about I'm becoming)
How can I decide? There is a software for an exact prove of THIS supporting structure?

RE: flat beam question

Dear Riz ,

Please send me the spreadsheet as it will be of great help to me also.


RE: flat beam question

The photos have certainly helped but at the same time raised Q's.
How old is the building!
Is it residential?
Is the Geo report available?

Soil-Structure interaction:
Quoting " The basement floor and ground have risen" implies that u have an expansive soil which is creeping too.
From the fact that the ground is sloping and an existing non uniform semi-basement, such problems do occur after elapse of many years.
Do u have trees in the vicinity. Check if they are bowing towards the slope. This will be indicative of your creep problem.
Do the buildings in your immediate neighbourhood face the same problem.
Is the basement having damp rising problem, find out the water table and its seasonal variation.
What are  the piling depths. Find out more about the piles!

The building centroid and centre of gravity loads do not coincide! This eccentricity creates torsional stresses in your structure if subjected to lateral forces or movement associated with sub-soil conditions.

Divide your cracks into superficial, moderate and severe cracks. Locate serious cracks.
Beam having diagonally inclined cracks at or near support implies shear and possibly inadequate depth.
Helical cracks in beam face and extending to the outside implies torsional shear stresses.
Excessive deflection may be due to inadequate design or overloading.

External Walls
If walls are out of plumb than foundation movement must have occured. Do u have a ground beam tying all the pile caps?
Cracks in masonry also occurs if there is movement or inadequate lateral restraint.

Hope this is useful. Look for an experienced engineer to assist in your assessment too.

RE: flat beam question

Other informations from GGi

The building is ten yers old, but the damages are eight (or more) years old.
Yes, it’s residential

Soil- Structure interaction
Yes the Geo report is avilable: I shall write about… in the next days.
Yes the soil is an expansive soil (blue clay). Under the building there is a little of water that flows down from the hill, so it has been built on special foundations (the piling depth is 12 meters, see image)
I have not trees in the vicinity neither there is a building in my immediate neighbourhood with the same problem.

I’m worried for eccentricity and I would somebody could calculate (or tell me if a software exists) the deformation of the flat beams. The most worrying cracks are in the walls (inside and outside) on (or near) the flat beams.

The most worrying cracks are red marked on the building plants (see photos):
n.1 : it’s the effect of the risen or (also) of the pressure of the first floor?
n.2 : in this point there are two little beams broken (like photo n.2). It’s the effect of the risen or of an inadequate supporting structure? Two little beams are broken also at the ceiling of the  second floor (where is 8).
n.3:this is the dividing wall on the same point of the broken little beams (see plants). Note: the crack (at the point 6) on the third floor  is like this.  
n.4 (without photo): there is a detached column. It’s caused by the lack of a pile? (see asterisk and arrow in “foundations”). But, perhaps, this pile was important only for the balcony.
n.5: It’s the most worrying external (and internal) crack.  From the other side of the building there is another like this (but smaller, near the window, n.7)  
Besides there are over 150 smaller crack  or superficial crevices in all the building.

I shall continue (perhaps) with other informations.

RE: flat beam question


Your presentation, I admit is very good.

I have understood that you have buildings in your neighbourhood that are sound. Were these buildings founded on piles too!

In plain English, u have a big problem and due to the reason that failure started just 2 years after construction was complete implies that sub-soil condition is not favourable.

I will need to go thru your GI report before expounding further.


RE: flat beam question

I pubblished an extract of Geo report, but it's not in english. I hope..... somebody will translate for me.
I can say the Geo report excludes subsidence of foundations because the rising of the floor is very much: if subsidence the cause, the building would be already collapsed.
See others photos and see better the supporting structure, please. It's a real skeleton?

RE: flat beam question

I have pubblished in http://digilander/iol.it/Gi9 what (I think) is important for talking about this problem.
But now I explain myself better……

Two engineers studied this question.

Both agree the cracks seem not caused by a movement of the foundations (as is said also in the Geo report).

But, the first engineer said:

- The sole cause of cracks is the rising of the clay soil - and  he invokes the Geo report

The second instead:
it’s odd that the rising of the ground causes the cracks of the little beams at the first and second floor  so it’s impossible to consider well-made the design.  
He maintains that:
1)    the class of ground is negligible.  In the immediate neighbourhood there are not other buildings with the same problems.    
2)    the excessive structural deformation is the cause of all the cracks: the cracks of the little beams and even the rising of the floor (in the basement) is caused by the pressing of the ceilings on the dividing walls.
This all goes to prove it:
-    the rising is more at the center of every  room (in the basement); in other terms,  the ground (and the floor of the basement) rises like a “spring mattress” pressed around.  
-    in the other parts (B and C, see image of prospect) of the building there are few and smaller cracks, and the ground has not risen because the flat beams are fixed at both ends to tall beams (1-31, 4-34, 7-37)  

In short, the design is not a skeleton but only a combination of rigid elements because neither the axises of the beams and those of the columns are on the same plane nor any device provides for such a lack: the effect is the deformation of  the floors also where the beams have small spans.
The eccentricity increases the twist.
The eccentricity of the beams and the columns has not been calculated and the usual model of calculation, in this case, is useless.
At last, but not the least…..the building is in a deformation period, not yet collapsing.
3) the lack of a pile is the cause of the breakaway of the column (point n.4)

I’m worried because, as it’s said “while the doctors are talking, the patient dies”.

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