Minimum Reinforcing in Masonry Fence Columns

[marinaman]

I've got a client who wants to build a fence around his property.

He's asked a landscape architect and civil engineer to design his fence. His fence has 8' tall masonry columns (4' square in plan size) composed of 8" CMU faced in brick veneer, spaced at 26' o.c.

A tall metal fence runs between the big masonry columns. The metal fence sits on a low masonry "knee wall" that runs continuously beneath the metal fence. The metal fence is connected to the low knee wall at the fence 1/3rd pts via a vertical steel member in the fence being attached to the continuous knee wall below (acting as a cantilever support to the fence).

Columns:

I'm saying, regardless of forces, ACI 530 has minimum reinforcing requirements that must be met in the columns. There are minimum seismic requirements and minimum column/pier requirements. I placed (1) #5 bar in each corner and had them grout those corners. The owner's rep, who is mostly a residential contractor, is saying he doesn't want to vertically reinforce and grout these columns. I'm saying it has to be done to meet the code requirements of ACI 530. Am I missing something?

Knee Wall:

In the knee wall, I've got a minimum amount of reinforcing called. (1) #4 at 10' o.c., except at these fence column locations, where I've placed two dowels in side by side cells. I also call for a continuous open bottom bond beam to the reinforced and pour integrally with the knee wall, as the knee wall provides overturning support to the fence. Again, I'm met with resistance.

Its my understanding that ACI 530 is going to require at least some minimum amount of vertical reinforcing in order to provide ductility to any structure in these parts. I'm normally looking at a Seismic Design Category of C.

Am I wrong?

 

[DaveAtkins]

I would not consider these to be columns, since they are not supporting vertical load. I would say they are pilasters.

I am not sure if unreinforced CMU is permitted in SDC C. But I think for the small amount of lateral load these pilasters will see, they might work unreinforced.

DaveAtkins

 

[JAE]

Your columns aren't really columns (i.e. vertical members primarily taking vertical loads). The intent of the minimum reinforcement provisions are based on the idea that columns are generally non-redundant members that if failing would produce catastrophic collapse.

They are really vertical beams primarily taking lateral wind forces correct? Therefore, in my view, the "columns" should be designed under the ACI 530 flexural requirements.
That may still require (4) #5 bars in each corner, however. But you can check it to see if there are flexural issues with non-reinforced column under code wind.

I would almost expect your knee walls to require more reinforcement than the columns since the columns have some additional dead load helping to prevent tensile/failure stresses.

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[jike]

Four foot square are pretty large columns.

 

[marinaman]

As I understand ACI 530, there are flexural requirements for minimum reinforcing as well as minimum seismic reinforcing requirements.

Just considering seismic, as i understand the code, I need a bar in each corner, at each cell to each side of a joint, at 10' oc, etc etc. These are minimums. The columns act as cantilevered beams. Their lateral stability is provided by their ability to resist lateral forces by their own structural flexural capacity.

The ACI commentary states this minimum reinforcing, for seismic, is required in order to provide at least some minimum level of ductility to structures that would not be ductile otherwise during a seismic event.

This is how I understand it.

 

[JAE]

I think you are correct.

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