Masonry Anchorage
Masonry Anchorage
(OP)
Regarding ASD and Strength Design for Masonry (ACI 530-02):
For ASD the allowable tension (when masonry controls) is Ba = 0.5 * Ap * f’m^0.5
For Strength Design the nominal axial tensile strength (when masonry controls) is ? Ban = 4 * 0.5 * Ap * f’m^0.5
The difference is a factor of 4.
With trying to compare apples to apples (I realize ASD to LRFD is not apples to apples) a load combination of 0.6DL+WL for ASD and 0.9DL+1.6WL for Strength Design say WL = 1 and DL = 1.
For ASD this results 1.6
For Strength Design this results in 2.5
Now the question/concern why is the Strength Design factor of difference of 4 when computing tensile strength (when masonry controls) allowing so more capacity particularly when the load combination for Strength Design is only ~1.5 times as much as ASD?
For ASD the allowable tension (when masonry controls) is Ba = 0.5 * Ap * f’m^0.5
For Strength Design the nominal axial tensile strength (when masonry controls) is ? Ban = 4 * 0.5 * Ap * f’m^0.5
The difference is a factor of 4.
With trying to compare apples to apples (I realize ASD to LRFD is not apples to apples) a load combination of 0.6DL+WL for ASD and 0.9DL+1.6WL for Strength Design say WL = 1 and DL = 1.
For ASD this results 1.6
For Strength Design this results in 2.5
Now the question/concern why is the Strength Design factor of difference of 4 when computing tensile strength (when masonry controls) allowing so more capacity particularly when the load combination for Strength Design is only ~1.5 times as much as ASD?






RE: Masonry Anchorage
Also - there is a tendency to push engineers toward LRFD.
RE: Masonry Anchorage
The 2002 code (2.1.3.3.2) says the “Nominal Strength” = 2.5 x allowable stress value and that the “Design Strength” = Nominal Strength x “phi” (2.1.3.3.3). For axial load, “phi” = 0.8.
So, for axial loads, the allowable design stress = 2.5 x 0.8 x allowable stress = 2.0 x fa
The 1995 code says allowable stress = fa.
The load combinations (per the masonry code) didn’t change, and the axial compression equations didn’t change.
Am I missing something here?