Carport/Pergola footings

[Builder]

Hello all, I am new to this forum.

I am seeking advise on footing specifications. I am designing an 8' x 12' four post (detached) open structure with a 14 degree monoslope roof with a mean height of 7.5" over an existing slab. It will be a bicycle shelter for a charitable non-profit organization.

I will be using prescriptive building design determined by IRC 2021 for framing and roof requirements. However, I cannot find prescriptive design criteria for footings.

I recall using prescriptive design criteria for pier footings for similar detached carports many, many years ago. However, I am having difficulty locating any current resources.

Am I overlooking something or is this information unavailable. I can easily calculate tributary point loads for the footings but am uncertain about wind uplift loads and moment resistance.

From what I recall one prescriptive approach was to embed posts 48" deep in a 24" pier. This seems excessive for a four post structure with an 8" x 12" roof however I would consider this approach if I could find a prescriptive reference to this. I would prefer not to embed my post however and would rather use a steel post base such as a Simpson MPBZ. I can use Simpson's load tables but are there tables I can reference for wind i.e. uplift, lateral and moment given my design criteria.

Wind
Risk occupancy 2, v = 97, exposure B, seismic category D

Can anybody suggest a reference I am overlooking to assist me in completing my plan designs? I am accustomed to basic engineering calculations and hope to curtail the expense of engineering given the shoestring budget I am working with.

Thanks,

 

[Joe.B]

It will be a bicycle shelter for a charitable non-profit organization.

I will be using prescriptive building design determined by IRC 2021

Review the scope is Chapter 1 of the IRC and confirm that it is applicable to your project. Check with the AHJ and see what the local codes in effect are.

 

[mtlogcabin]

Footing Design Calculator

Several footing design calculators are available to assist engineers in designing foundations for various structures. Here are some options: SkyCiv Concrete Footing Calculator: This online tool helps in designing foundations for footings, combined footings, concrete piles, and concrete pads...

search.brave.com

or

FOOTINGS - Rectangular Spread Footing Analysis Spreadsheet

FOOTINGS is a spreadsheet program written in MS-Excel for the purpose of analysis of rigid rectangular spread footings with up to 8 total piers, and for either uniaxial or biaxial resultant eccentricities. Download structural analysis software FOOTINGS 3.7 developed by Alex Tomanovich.

www.cesdb.com

 

[Yankee Chronicler]

Hello all, I am new to this forum.

I am seeking advise on footing specifications. I am designing an 8' x 12' four post (detached) open structure with a 14 degree monoslope roof with a mean height of 7.5" over an existing slab. It will be a bicycle shelter for a charitable non-profit organization.

Why are you using the IRC? What type of facility will this bicycle shelter serve?

I can use Simpson's load tables but are there tables I can reference for wind i.e. uplift, lateral and moment given my design criteria.

No.

 

[Builder]

Review the scope is Chapter 1 of the IRC and confirm that it is applicable to your project. Check with the AHJ and see what the local codes in effect are.

Good point. I did mean the 2021 IBC however. I don't work much outside the IRC. Anyhow, the small size exempts it from a commercial building permit but is triggering an SPR through Land Use and zoning.

Thanks for the reply, Joe.

 

[Builder]

Why are you using the IRC? What type of facility will this bicycle shelter serve?



No.

Thanks.

 

[Yankee Chronicler]

Good point. I did mean the 2021 IBC however. I don't work much outside the IRC. Anyhow, the small size exempts it from a commercial building permit but is triggering an SPR through Land Use and zoning.

Thanks for the reply, Joe.

The size exemption under the IBC for permits is 120 square feet.

One-story detached accessory structures used as
tool and storage sheds, playhouses and similar uses,
provided that the floor area is not greater than 120
square feet (11 m2).

However, the fact that the size exempts it from requiring a building permit doesn't exempt it from having to be constructed in accordance with the code. It just means you don't need a building permit. In general, unlike things such as rafter span tables in the IRC, the IBC does not include prescriptive designs. It provides the criteria that a structure has to be constructed to withstand, such as wind load, snow load, and seismic load. The biggest issue I see is that an open "carport" for bicycles can be suject to significant upload in some wind conditions, and someone has to first calculate the uplift, and then design the connections between the roof and the posts, and the posts to the foundations to resist those uplift forces.

 

[Joe.B]

I think this might be the best resource for you:

2018 NDS

awc.org

 

[Builder]

The size exemption under the IBC for permits is 120 square feet.



However, the fact that the size exempts it from requiring a building permit doesn't exempt it from having to be constructed in accordance with the code. It just means you don't need a building permit. In general, unlike things such as rafter span tables in the IRC, the IBC does not include prescriptive designs. It provides the criteria that a structure has to be constructed to withstand, such as wind load, snow load, and seismic load. The biggest issue I see is that an open "carport" for bicycles can be suject to significant upload in some wind conditions, and someone has to first calculate the uplift, and then design the connections between the roof and the posts, and the posts to the foundations to resist those uplift forces.

Yes, I am aware. thank you for your reply.

 

[redeyedfly]

Yes, I am aware. thank you for your reply.

To be fair, it doesn't seem like you are aware. You're asking for prescriptive guidance on what is definitely the easiest part of your proposed structure to design. What are you using for prescriptive lateral? Shear walls somewhere? Do your post bases have moment capacity or are you designing moment connections at the top of the posts to the roof structure (prescriptively)?
Your comments lead me to believe you think this is pretty easy but you're missing most of the important aspects of the design. You can easily have 4000# of wind force on this or a lot more depending on where it is.

Hire someone who knows what they're doing, you don't. People could get hurt.

 

[redeyedfly]

In general, unlike things such as rafter span tables in the IRC, the IBC does not include prescriptive designs.

Sections 2308 & 2309 disagree.

 

[Inspector Gift]

Have you spoken to plans examiners or Building Official at your jurisdiction in SW Washington? There are some who are open to alternative methods - Like the Ready Build Plans that were created for use in Oregon. The design criteria is the same for your area. Do a google search and you can find links to the plans for garages, patio covers, and porches. The plans have more than one type of prescriptive footings. Or you can email me at the City of Sandy Oregon Building Division. I can send you a "PERMIT-READY PLAN" in PDF format.

 

[ICE]

3’x3’x3’ concrete footing with cantilevered 4” sq. 1/4” tube steel. That’s an engineered solution. If you need a stamp, I have Venmo. Buckets by others.

 

[jar546]

The size exemption under the IBC for permits is 120 square feet.

This is a local issue as most jurisdictions modify Chapter 1, so I don't think you can point to this exemption with certainty.