Fence mount a top of Precast Concrete Block modules

[jagti]

How deep the fence post should be grouted on 300lb/ft block module the dimensions of precast module is 6ft L X 2ft W X 1 ft H & wt of each module is 1800lbs. Assuming ht of fence is 3.0ft & post spacing not to exceed 6.0ft

When doing overturning force calculation should i compare Overturning moment V/s Wt of the Block & ensure overturning force never exceeds resisiting Block Mass i.e

ht of fence + max embedment in block= 3ft+1ft
Checking for UDL load
50X4=150lb-ft + Soil & Surcharge moment load < 300lb/ft (block mass per ft)

In order to trigger overturning failure driving moment must exceed block wt.

Checking for post load
assuming post spacing must not exceed size of block i.e 6.0ft & fence post is mounted on center of the block

224 X 4 + Soil & Surcharge moment load < 1800lbs total wt of block

Top Course & Second Course have a shear key connection.

or should i compare overturning moment to resisting moment (at point of rotation)

 

[jagti]

Some of these block i have seen weighs about 2000lbs to 3000lbs each

 

[Ron]

jagti...it would help to know where you are located. This is an international forum and it makes a difference where you are located with respect to requirements. For instance, if you are located in the US, this would likely be considered a guardrail not a fence, as I gather from your description that you are locating a fence on top of a retaining wall. If a guardrail, you will have to meet building code requirements that are different than for a fence.

If only a fence, then wind load would likely prevail. If it is not a solid fence, then I wouldn't worry about it...just anchor a reasonable amount and don't overthink it. If a guardrail, it is likely not high enough and will have to meet a lateral load resistance requirement in addition to the wind loads.

 

[jagti]

Thanks Ron,

We are located in Canada. The fence could be chain link fence or Pedestrian guard railing the ht would be 3 to 6 ft max. I am aware the best option would be to plan it behind on a separate footing there is a Sleeve-It fence product from Strata we have looked on it our plan is to bring fence in line with retaining wall for aesthetics point & save some real estate space.

There are some massive machine place blocks Lock -block, Redi Rock almost weighing 1Tonne per module.

i was thinking how high can we mount a non wind bearing fall protection fence on those massive blocks & also meet all the UBC loading requirements for non wind bearing fence.

 

[RFreund]

Normally for gravity wall big block system I will check 'local' overturning and shear for the block that the open fence/hand rail (now called 'gaurds' in the US) is attached to. I apply soil pressure on the block and apply the handrail load (50plf load) x the spacing of the posts. Check shear and overturning as you have indicated. Then I will check 'overall' overturning and sliding. I will assume for this check that a certain tributary length of wall is engaged. Usually for a running bond pattern or staggered vertical joints the block above will engage 2 blocks below. So I find the tributary length at the bottom and the top then take the average length of wall and sum forces and moments about the base. If I feel it is reasonable I will include the vertical component of the soil pressure in this calculation.



EIT

http://www.HowToEngineer.com

 

[bridgebuster]

Keystone Retaining Wall Systems has standard drawings for mounting fence and guiderail.