Messages and Online Forum Q&A

Re: Sonotube Framing Details

From: info@builderswebsource.com
Category: Structural
Remote Name: 63.198.181.43
Date: 18 Jun 2001
Time: 10:35 PM

Comments

Thank you for the additional information. We have a better vision of your project now. Given the scope of this project and the significant live and dead loads and potential safety concerns, we unfortunately cannot provide structural guidance in this case.

However, we do have some pointers and things to make sure you consider, including:

1) You must know first what the soil bearing capacity is in order to engineer a proper footing. If it is unknown, generally most codes use 1,000 PSF as a worst-case figure (typical of many soft clay soils). Higher PSF ratings apply to sandy or sandy-gravel soils or stiff clays.

2) Next, you need to understand any seismic or wind risks, which could impart lateral forces on the structure, causing it to topple.

3) As to your question about a monolithic pour, this is not required for strictly structural reasons. In fact, in most cases, the foundation or footings are poured first (with rebar well in place). Sometimes as many as four or more heavy-duty rebars (#5 or higher) are bent at 90-degree angles to form the columnar shaft rising out of the slab or footing. This rebar anchors the column to the footing and prevents lateral movement, even if it's done in two pours.

Continuous helical or individual round column ties wrap around the rebar all the way to the top, providing strength against buckling. Sometimes, for added shear strength, the number of ties increases at the top and bottom of the column.

We strongly recommend you consult a licensed structural engineer who understands you soil conditions as well as other environmental conditions to properly engineer the structure, including anchoring details, reinforcement schedule, concrete strength, pad size and lateral reinforcement. Furthermore, if the ground is subject to freezing, you may need to recess your foundation pad several feet below grade, or use drilled piers based on the friction bearing capacity of your soil.

As a result of all the variables, there is no one source of engineering details that will show how your specific job should be built. A good structural engineer can bang this one out for you pretty quickly given a complete set of information about your site conditions.

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