Modeling Concrete Cracked Section Properties for Building Analysis P 3

Petronas Towers - Kuala Lumpur, Malaysia

Horizontal Supporting Elements

Second we will discuss the horizontal supporting elements (beams and slabs) in the structure under our consideration.

Concrete Beams

For concrete beams which are often modeled as frame element,  the flexural stiffness (EI) and the axial stiffness (EA) govern according to ACI 318-14 Recommendations  and there is no recommendation about modifying the shear stiffness (GA) or torsional stiffness (GJ).

From table table 6.6.3.1.1(a), to model cracking behavior of the beams the frame property modifiers  should be as follows:

aN	1.00  Axial modifier
aS2 , aS3	1.00  Shear modifier
jO	1.00  Torsion modifier
i22 , i33	0.35  Bending modifier

Concrete Slabs

For concrete slabs which are often modeled as Shell element, based on  the default orientation of the local axis:

• The axial behavior is controlled by either f11 , f22 and f12 modifiers.
• The flexural behavior is controlled by either m11 , m22 and m12  modifiers.
• The shear behavior is controlled by v13 and v23 modifier.

To model cracking behavior of the slabs and apply to the ACI 318-14 code Recommendations Section 6.6.3.1.1 table 6.6.3.1.1(a) and the best practices the shell stiffness modifiers  should be as follows:

f11 , f22 , f12	1.00  Membrane modifiers
m11 , m22 , m12	0.25  Bending modifiers
v13 , v23	1.00  Shear modifiers