Safe Punching Shear Problem

[jammer3425]

well i dont believe SAFE gives wrong results as compared with manual calculations.. and here im talking about SAFE 12

But you have to consider following things:-

1) check the load size for perimeter calculation

2) apply the correct parameter for location of column...For example if it is interior column , select the point goto Design>Punhcing Overwrites and make it interior

3) Make correct cover settings. Goto Design> Design Preferences and put the correct cover and bar size

4) Make sure you are familiar with the load combos for which you will design your structure or punching

After analysis, right click on the point of column you will see detailed calculations for punching and the governing combination. Make sure SAFE 12 is calculating the effective depth and the perimeter correct which will surely be correct if you follow above steps. You can also check punching calculations of other non governing combinations.

now in foundation if we have a column that is interioir column of the bldgn and on that particular slab it is exterior so do we have to make that building reference or that slab/footing

[WR1]

it depends upon column location with referene to foundation centroid..NOT THE BUILDING...because these factors are used to caluclate punching area of foundation....

[jammer3425]

if i put a slab beneath a slab and by assigning it soil support means to reduce the soil pressure under that area...you can chk it by simply putting two slabs over each other...and here in some design offices people use 4 in thk lean beneath foundation in SAFE and it reduces the soil pressure but they are keep on doing this i argue this matter with different peoples but they think they are doing it right....

dear member lean beneath is provided to have a uniform lvl surface if you examine the condition of lean after years especially when you demolish any old building you will discover that the lean that you poured is not there it is converted to fine powder and the foundtion poured took the place so there is no role of lean towards adding strength. I practically saw this phenomenon myself. But couldnt conclude then why we use different thicknesses of lean

[asadishaq]

thanks alot all of u people for ur expertise....

[Ayesha]

dear member lean beneath is provided to have a uniform lvl surface if you examine the condition of lean after years especially when you demolish any old building you will discover that the lean that you poured is not there it is converted to fine powder and the foundtion poured took the place so there is no role of lean towards adding strength. I practically saw this phenomenon myself. But couldnt conclude then why we use different thicknesses of lean

Plus, lean is also called mud slab in US. Lean is also provided so that there is no slush formation in the ditches if it rains and there is a time delay between foundation pouring and excavation.

[Waqar Saleem]

dear member lean beneath is provided to have a uniform lvl surface if you examine the condition of lean after years especially when you demolish any old building you will discover that the lean that you poured is not there it is converted to fine powder and the foundtion poured took the place so there is no role of lean towards adding strength. I practically saw this phenomenon myself. But couldnt conclude then why we use different thicknesses of lean

i have doubt here that lean is converted into fine powder and place of lean is taken by foundation, it is right that is doesn't take any part in strength as its purpose is to keep the trenches safe from rain water and protecting foundation from soil, but if after a certain time it totally disappears into fine powder then there must be some reasonable settlement.

[UmarMakhzumi]

It is not converted. There can be cases. Reasons random.

[jammer3425]

i have doubt here that lean is converted into fine powder and place of lean is taken by foundation, it is right that is doesn't take any part in strength as its purpose is to keep the trenches safe from rain water and protecting foundation from soil, but if after a certain time it totally disappears into fine powder then there must be some reasonable settlement.

the case is while designing we also consider factors like permissible settlement and secondly lean is poured after leveling the sfc properly beneth the lean and top sfc of lean is also leveled b4 foundation concrete. so even if it converets to powder it will do so uniformly as the thickness of lean is also kept constant.

[Waqar Saleem]

the case is while designing we also consider factors like permissible settlement and secondly lean is poured after leveling the sfc properly beneth the lean and top sfc of lean is also leveled b4 foundation concrete. so even if it converets to powder it will do so uniformly as the thickness of lean is also kept constant.

@jammer sir what is the permissible settlement for foundations for different cases?why lean converts into powder under load?(if no other cases chemical or non-standard materials)

[WR1]

due to high load on foundation lean is converted into fine powder...(crushing) simple....permissible settlement varies..but generally its 1 inch or 25mm!

[jammer3425]

@jammer sir what is the permissible settlement for foundations for different cases?why lean converts into powder under load?(if no other cases chemical or non-standard materials)

please refer

Settlement in foundation 2009 Handout.pdf

[jammer3425]

Interesting to know

30 m of marine clay sits at a depth of 10 m below the surface of the tower’s foundations known as Leaning Bell Tower at Pisa, Italy

[Firoz Rahuman Shukoor]

Can somebody post a detailed Manuel calculation for punching shear for rectangular column in BS standard. It would be really helpful for me.

[abbaskhan2294]

On 6/23/2012 at 10:14 PM, Rana said:

well i dont believe SAFE gives wrong results as compared with manual calculations.. and here im talking about SAFE 12

But you have to consider following things:-

1) check the load size for perimeter calculation
2) apply the correct parameter for location of column...For example if it is interior column , select the point goto Design>Punhcing Overwrites and make it interior

3) Make correct cover settings. Goto Design> Design Preferences and put the correct cover and bar size
4) Make sure you are familiar with the load combos for which you will design your structure or punching

After analysis, right click on the point of column you will see detailed calculations for punching and the governing combination. Make sure SAFE 12 is calculating the effective depth and the perimeter correct which will surely be correct if you follow above steps. You can also check punching calculations of other non governing combinations.

Rana what if i have 4 columns in a row at corner of mat footing then what should I do for option 2?

[WR1]

On 6/25/2019 at 4:02 AM, abbaskhan2294 said:

Rana what if i have 4 columns in a row at corner of mat footing then what should I do for option 2?

I would be designing them as corner columns with load (or moment) = sum of all column loads and geometric properties of 1 composite section (it also depend of the distances between the columns) so just rationalize it with any appropriate assumption.

[G_Farooq]

Do check, what is the type of column SAFE is using to calculate the punching shear. This can be checked by right clicking at column point or punching shear design output. Its a common problem in safe both v8 and v12 that it treats all columns as corner columns, despite their location, thereby reducing the concrete strength. This can be solved by selecting column point and assigning punching shear modifiers to them (corner, edge or interior).