Dead Load Deformation for a Tall Building
Dead Load Deformation for a Tall Building
(OP)
Dear all
I'm working in a high rise building (about 70 stories Residential Building)
The system is post tensioned flat slab with RC shear walls & Columns.
We got a high lateral deformation in the suspended slabs due to dead load besides the lateral forces drift.
The lateral drift satisfied H/650
The problems are:
-these deformations (from dead load only) making a high sagging and hogging moment near the slabs supports ( higher than deformations due to lateral forces)
-each story deform in a different shape which cases a different moment for each floor which is very difficult to study for each floor.
- the post tensioning design will be done by another firm so what we have to do is estimate the differences between the moment due to gravity and from the deformation shape, because the other firm well design tendons for gravity loads only(the ultimate one).
I argued with my senior about the load combination which we have to consider in this case, he provide ultimate one but I suggest to take the service one because the deformation should be a serviceability issue but he think we can't compare between ultimate case and service case.
Does any body familiar with this issue? Is it common to get the high deformation due to dead load? And how u investigates it?
Best Regards
Ahmed
I'm working in a high rise building (about 70 stories Residential Building)
The system is post tensioned flat slab with RC shear walls & Columns.
We got a high lateral deformation in the suspended slabs due to dead load besides the lateral forces drift.
The lateral drift satisfied H/650
The problems are:
-these deformations (from dead load only) making a high sagging and hogging moment near the slabs supports ( higher than deformations due to lateral forces)
-each story deform in a different shape which cases a different moment for each floor which is very difficult to study for each floor.
- the post tensioning design will be done by another firm so what we have to do is estimate the differences between the moment due to gravity and from the deformation shape, because the other firm well design tendons for gravity loads only(the ultimate one).
I argued with my senior about the load combination which we have to consider in this case, he provide ultimate one but I suggest to take the service one because the deformation should be a serviceability issue but he think we can't compare between ultimate case and service case.
Does any body familiar with this issue? Is it common to get the high deformation due to dead load? And how u investigates it?
Best Regards
Ahmed






RE: Dead Load Deformation for a Tall Building
RE: Dead Load Deformation for a Tall Building
RE: Dead Load Deformation for a Tall Building
RE: Dead Load Deformation for a Tall Building
RE: Dead Load Deformation for a Tall Building
Yes u understood right the problem, More lateral deformation from dead load
actually what happened that the building has about 15 different levels and there are some changes in the columns lay out like floated columns on a beam girder that duo to the architectural shape.
but about 70 % of the stiffness in the core which is definitely in his place in all the floors.
the building has been modeled by ETABS with not by me cuz i joined there recently
stiffness of all members has been reduced (70% for walls & 35% for Slabs & beams)
, and all the column ,Walls , building members and stability check already done. only some parts unfinished like the slabs action .
now I'm exporting the floors from etabs to safe and i getting a very high sagging moment (about 350 KN.m for 260mm slab!) in the moment near the supports and the moment diagram be very difference than the case with out deformation.
the deformation due to seismic also significant but it's less than the dead load and it's increasing gradually when u go up in contrast with dead load Deform which irregularly varying between floors.
ETABS model has been done by Experts and a bout 4 Engineers
so i don't think there is problem in the model.
RE: Dead Load Deformation for a Tall Building
Etabs Results should be combinations of axial shortening and the distortion of supports.
also axial shortening cases deformation in x,y & z direction due to irregularity of building.
may be I have to ask a new questions
are the etabs results due to this matter should be taken as it?
what about the effects of creep and construction sequences ? is it going to give different results?
and with which case we have to investigate this ultimate or service ?
RE: Dead Load Deformation for a Tall Building
RE: Dead Load Deformation for a Tall Building
AhmedR, how about check the lateral deflection diagram (due to DL) along a maijor column and a shear wall and check the base reactions to see the reasons. Or the shear walls are very eccentrically located, then the shortening may cause the problem.
I don't know how can you design member strength without post-tension info and how can the other company design the post-tensioning for gravity load only.
RE: Dead Load Deformation for a Tall Building
Regards,
AUCE98