Ron,
Thanks for that seasoned response and I agree that considering deflection is a greater issue to contend with than with grade beams. However, as the columns will be detailed for fixity with the piles (continuous curve through 10 to 20 feet of soft soil to bedrock) we should be able to create a reasonable model that estimates the deflection, adjusting pile cap/footing size as needed. We do not have liquefaction potential but just soft near-surface soil to contend with, which contains organic material. The conventional MRF option was ruled out for reasons that would take too much space here to elaborate on but I appreciate that thought as well. Your main point regarding the intent of the ASCE 7 SFRS description is sincerely appreciated.
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Edward Tornberg M.ASCE
Creative Building Works, LLC
Medford OR
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Original Message:
Sent: 01-04-2026 02:49 PM
From: Ronald Hamburger
Subject: Cantilevered column system: concrete columns connecting wood-framed building to deep foundation
Ed
The intent of the requirement to detail as per "special reinforced concrete moment frames" is to assure that appropriate confinement through ties and cross ties, and reinforcement splices (if any) are provided. It is not intended to force you to construct grade beams. One concern I might have about not providing grade beams is that the base of the columns will be quite flexible meaning that you may get substantial deflection of the top of the columns under load. Grade beams would be an effective (if costly) way to minimize this effect, as would a beam at the top of the columns, in which case the substrucutre could be designed as an SMF or IMF with appropriate R factors.
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Ronald Hamburger, SE
Consulting Principal
Simpson Gumpertz & Heger
Original Message:
Sent: 01-02-2026 02:42 PM
From: Edward Tornberg
Subject: Cantilevered column system: concrete columns connecting wood-framed building to deep foundation
We are designing a beach house; the complication lies in justifying the lateral force resisting system and transfer to foundation at a difficult coastal location. The essence of the question is this: the SFRS selection from ASCE 7-16 Table 12.2-1 and site and building criteria allow us only one option: "Cantilevered column systems detailed to conform to the requirements for special reinforced concrete moment frames". The problem is that this system, by way of ACI detailing, implies beams. However, the columns terminate at the soil level and soil grade beams have proven to be very costly. Can the cantilever system, without the use of any grade beams, utilize the soil restraint around discrete footings/pile caps and tie directly to steel piles for bearing and moment fixity? I am aware of other projects that used discrete pile caps (one cap per pile and column) but I do not have confidence that ASCE-7 allows it. This is for Seismic SDC E; the question is not derived from wind design criteria although that is part of the design.
Sketches are attached that convey more information. We have already designed Option 1 and as a value-engineering service are evaluating Option 2.
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Edward Tornberg M.ASCE
Creative Building Works, LLC
Medford OR
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