Street Light Pole Foundation

Something like this, but your local authority having jurisdiction should ok and approve plans beforehand...If you need to pull permits and have inspections you'll need a detailed set of plans that are drawn up according to local codes....The installation may need to be inspected at certain intervals during the installation process...certain licenses and certifications may be required...

https://www.ablegroup.net/Lighting_Poles.Foundations.htm

Your frost line and other soil conditions will be very important here.

Solar Eagles detail is pretty common and usually good, what you need to verify is your soil conditions, and your wind loads and if you will have underground vs overhead power lines . When we have poor disturbed soil we often use a 1 meter x 1 meter x 60 cm foundation with a min. 1 meter coverage on top of the sguare pad, then at least 60 cm above grade with concrete to your bolts. Be sure to use galvanized or stainless bolts!

When installing street light or power poles the rule of thumb used to be inground foundation should be 1/7 of the above ground height. So for your pole the hole should be 1.1m deep.

You have not given enough information to advise you but by making some assumptions I can show the type of calculations and forces that you will need to consider. If you do not feel confident then employ a professional. Dropping a lighting pole onto parked cars is expensive, dropping one onto a pedestrian is a prison sentence. Collect together the following information. The size of your luminary and it's drag coefficient ( that may be difficult to calculate so you can assume a worst case which is a cube face on to the wind (drag coefficient 1.05) the size of the largest cross sectional area, CSA). I have assumed 500 x 500mm in the example. The dimensions and drag coefficient of the pole. For the purposes of the example I have assumed that an 8m high pole would need to be 250mm diameter (a smooth pole has a drag coefficient of 0.82). The maximum wind speed that you need to design for and what safety factor needs to be included. Where I live that is a 100mph wind so that is what I have used in the example. The planning authority covering where to pole is to be erected will provide the maximum wind value and safety factor. The mass of air at sea level 1.25kg/m³ (can be reduced for an elevated location). The formula Pressure = 0.5 x C (drag coefficient) x D (mass per cubic meter of air) x V² (square of wind speed). 1mph = 0.447m/s

Pressure on the luminary = 0.5 x 1.05 x 1.25 x 44.5 x 44.5 = 1300N/m²

Assuming a CSA of 500 x 500m = 1300N/m² x 0.25m² = 325N

Torque applied to base of pole by luminary = 325N x 8m = 2600Nm

Pressure on pole = 0.5 x 0.82 x 1.25 x 44.5 x 44.5 = 1015N/m²

Assuming a pole CSA of 250mm x 8m = 1015N/m² x 2m² = 2030N

Torque applied to base of pole by pole = 2030N x 4m (average) = 8120N

Combined torque applied to base of pole =10720N or approx 1 tonne

Assume a safety factor of 3 then the foundation needs to resist a side loading of 3 tonnes.

It depends on your ground conditions but I doubt that 400 x 400 x ??? reinforced concrete will suffice.

I think you're mixing up forces and torques there.

For the lateral force at the base, only need to add 325N (for the luminaire) to the 2030N for the pole (not 4*2030) = 2355N.

Also to check stress in the pole wall and to size the hold-down bolts, need to find torque at the base, 325*8 + 2030*4 = 10720N.m

A rule of thumb for a pole of "one in the ground for four above" gives a measure of safety above that presented in #4⇑. Were that pole supporting something like a rigid fence then one might be tempted to go deeper to provide greater resistance to wind thrust.

As always, local soil conditions dictate what actually happens.

Just had a look at the requirements for street lighting in the UK (No easy way to rip a copy) but the whole thing is much simpler. From the bottom of the pole, a 2" concrete pad at least 6"all round larger than the pole, lean mix concrete up to the cable entry and also 6" all round followed by sand around the cable entry and another layer or dry mix to ground level. That's it, no concrete pile or bolts. A 6 m pole would be 1 m into the ground. Decades ago they changed the rules on lamp posts to make them more resilient if hit by a vehicle and outlawed concrete posts that could break and fall on the vehicle and it may be these footings were part of the same thing. In spite of the storms over the last few years I have not seen any posts blown down.

Impossible to answer with information provided.

What is your seismic zone?

What is your wind load zone?

What is your soil density?

What is the diameter of the pole?

What is the worst case "face" area of the light fixture?

See where these persnikety design questions are going?

Just bolt it down to one of the dock pilings.

500/600mm will be enough.