Why modifiers are used in Etabs?
During earthquake or dynamic load event the section of the concrete cracks and the concrete below the neutral axis or the One in tension region would be ineffective. This leads to decreased stiffness of the section. In order to account for this effect we would use property modifiers in etabs .
What is stiffness modifiers?
stiffness modifiers in ETABS are the factors to increase or decrease some properties of the cross. section for example area, inertia, torsional constant etc. Generally they are used to reduce stiffness of concrete sections to model for cracked behavior of. +4.
How do I check the safe beam deflection?
In SAFE, the following principle may apply on the modeling; LONG TERM DEFLECTION– is the sum of immediate deflection for 75\% Live load, (DL+SDL+LL) – (DL+SDL+0.25LL) and Long-Term Deflection for DL+SDL+25\% Sustained Live Load.
How is deflection limit calculated?
Maximum deflection limits are set by building codes. They are expressed as a fraction; clear span in inches (L) over a given number. For example: a floor joist appropriately selected to span 10 feet with an L/360 limit will deflect no more than 120″/360 = 1/3 inches under maximum design loads.
What is permissible deflection of beam and slab?
As per IS 456 permissible deflection for beam or slab from all loads is span/250 or 20 mm which ever is lower.
What is f11 in Etabs?
In ETABS, shell or area element has two types of stiffnesses i.e. inplane stiffness refers as f11, f22 and f12 and out-of-plane stiffness refers as m11, m22 and m12.
What is S11 S22 and S33 in Abaqus?
The components of normal stress in the three directions are called the principal stresses and are denoted as S11, S22 and S33. In the STRAUS output, s11 is the largest value of stress in the algebraic sense and the principal stress S33 is the smallest value of stress.
What is the use of property modifiers in Etab design?
Property modifiers in etabs are used to model cracked behaviour of concrete sections. They are only applied to concrete members because of cracking. Gross moment of inertia is bd^3/12 for a rectangular section, but when you make this member of concrete, it will experience cracking when loaded after some time.
What is the flexural modifier for EI in ETABS?
When drawing in ETABS the default is to have the 1 axis horizontal and the 2 axis vertical. This means that the flexural modifier for EI should be applied to f22 for wall piers and to f11 for spandrels.
What modifiers are required to model cracking behavior of a slab?
If you apply the modifier to both f11 and f22 it hardly affects the results. For slabs where bending is always in the out-of-plane direction, modifiers m11, m22 and m12 are required to model cracking behavior. Assuming beams and columns are modeled as frame then the stiffness modifier table is as follows:
Should I use modifiers for F12 shear walls?
You should, however, note that some of our users use modifiers for f12 also, where they expect deterioration of shear stiffness and want to be realistic in their modeling. The above discussion applies assuming the local axes 1 and 2 of the shear wall area object are either vertical or horizontal.