RAM Structural System Help

ACI-318 2014

This section discusses the features that are implemented or changed due the implementation of ACI 318-14 within the RAM Concrete Wall module and the assumptions made by the program when selecting this ACI Code.

Number of Curtains of Reinforcement

This section discusses the requirement given in ACI 318-14 Sec. 18.10.2.2 and the assumptions the program performs in order to check it. In this way, at least two curtains of reinforcement are required in the program when:
Vu>2Acvλfc'
or
hwlw≥2.0 ACI 318-14 (18.10.2.2)
where
Acv
=
Gross area of concrete section (without considering reveals) bounded by web thickness and length of section in the direction of shear force considered.
λ
=
Modification factor to reflect the reduced mechanical properties of lightweight concrete relative to normal-weight concrete of the same compressive strength.
lw
=
Length of entire wall.
hw
=
Height of entire wall.

RAM calculates the parameter Acv as the product of the thickness and the length of the section. For λ, the program considers the value for normal weight concrete.

The parameter lw as the overall horizontal dimension of the wall panel or core as measured in the direction of loading for a specific load combination (see Dimensional assumptions for calculation of limiting c value per ACI 318-11, Eq 21-8).

The parameter hw is taken as the vertical distance from the bottom of the story at which the Section Cut is located to the overall top of the Wall Design Group.

Parent topic: ACI Technical Notes

Special Boundary Element Check

Displacement method

ACI 318-14 18.10.6.2 limits the special boundary requirement based on the displacement method to those walls that meet the following condition:
hw/lw≥2.0 ACI 318-14 (18.10.6.2)

RAM Concrete Wall evaluates the limiting boundary neutral axis calculation only when ACI 318-14 (18.10.6.2) meets.

Stress-based method

According to ACI 318-14 18.10.6.3, when 18.10.6.2 does not apply, the program requires special boundary elements at boundaries and edges around openings of walls when:
E > 0.2 f c ' ACI 318-14 (18.10.6.3)
where
E
=
Maximum compressive stress calculated within the load combinations including earthquake effects.

Limiting Boundary Neutral Axis Calculation

RAM Concrete Wall performs the check of the neutral axis depth according to ACI 318-14, 18.10.6.2. This Section code states that compression zones shall be reinforced with special boundary elements when:

c≥lw6001.5δuhw ACI 318-14 (18.10.6.2)
where
c
=

Largest neutral axis depth calculated for the factored axial force and nominal moment strength consistent with du.

lw, d u, d e, Cd, hw, and c are defined in 7.7.1.

Minimum boundary thickness

RAM Concrete Wall checks the boundary thickness according to ACI 318-14 Sec. 18.10.6.4 (b) and (c). For each section cut, where boundary is required, the program considers the following requirements:

b≥hu/16 ACI 318-14 18.10.6.4 (b)
If hw/lw≥2.0 and c/lw≥3/8:
b≥12 ACI 318-14 18.10.6.4 (c)
where
b
=
the Width of the flexural compression zone. Considered by the program as the boundary thickness.
hu
=
the laterally unsupported height at extreme compression fiber of wall, in.
Note: The value of hu considered by the program to apply ACI 318-14 18.10.6.4 (b) is the Wall Panel height.

hw, lw, and c are defined in Section Limiting Neutral Axis Calculation .