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Structural Design Requirements for Commercial Structures

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Get information about structural engineering and design requirements for new and existing commercial buildings and projects in the City of Portland. Find information about phased seismic agreements, updated seismic cost triggers for URM buildings and seismic evaluations.
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The current state building code governing commercial and engineered residential construction is the 2019 Oregon Structural Specialty Code (OSSC), which is based upon the 2018 International Building Code (IBC) as amended by the State of Oregon. 

Soils and Foundations 

Foundation and retaining wall design parameters may be based upon the default soil properties of the building code or as justified by submission of a Geotechnical Report. 

  • Default allowable foundation bearing capacity within the City of Portland is 1,500 psf (minimum 12” wide footing). 

  • Default lateral soil load for the design of basement and retaining walls supporting level backfill shall be 40 psf/ft for laterally unrestrained retaining walls and 60 psf/ft for laterally restrained retaining walls. Lateral pressures for walls supporting sloping backfill or surcharge loads must be determined by a Geotechnical Report. 

  • Design of basement and retaining walls shall include lateral soil loads due to earthquake motions. 

  • Soil frost depth is 18-inches. 

Snow 

  • The minimum design roof snow load is 20 psf + 5 psf rain on snow surcharge where applicable per the Oregon Structural Specialty Code. 

  • Ground snow load used for determining drift requirements is based on Snow Load Analysis for Oregon as published by the Structural Engineer Association of Oregon. 

  • Ground snow loads at a specific site can be determined online using the Structural Engineer Association of Oregon website

Wind 

Design wind pressures are to be determined using the 3-second gust wind speed and the procedures of the 2016 edition of Minimum Design Loads for Buildings and Other Structures (ASCE 7-16) or in accordance with the alternate method contained in the OSSC (if applicable). The design wind speeds 3-second gust for the City of Portland are: 

Risk CategoryVult (mph)
I92
II98
III105
IV110

Wind exposure category is site dependent and must be determined by the Engineer of Record based upon site conditions.

Seismic 

Existing Buildings- Information on Chapter 24.85 - Seismic Design Standards for Existing Buildings - including Phased Seismic Upgrades

Portland City Code Chapter 24.85 governs the seismic design requirements for existing buildings. A seismic upgrade may be required for existing buildings undergoing a change of use or occupancy, addition, renovation, alteration, or URM building re-roof. Please refer to Portland City Code Chapter 24.85 for further information. 

  • Cost triggers:

    Chapter 24.85, of the Portland City code requires certain cost triggers for seismic evaluation or seismic upgrades be adjusted annually by the construction cost index. The costs are updated annually in the first quarter of the calendar year when the construction cost index is available.   

    The following are the current updated cost triggers:  

    (a) Seismic Evaluation, ection 24.85.060: An ASCE 41 evaluation report is required when the cost of construction exceeds a cost threshold. The current cost threshold is $290,977. 

    (b) Unreinforced Masonry Building (URM), Section 24.85.065 (B) :  A seismic upgrade may be required for URM building undergoing a repair or alteration when the cost of alteration or repair exceed certain thresholds. The following are the updated cost thresholds for Table 24.85-C 

    Table 24.85-C

    Building DescriptionCost of Alteration or Repair in 2-year period
    Single story Unreinforced Masonry (URM) building $66.51
    Unreinforced Masonry (URM) building two or more stories, or URM building with special hazards (see Title 24.85.065B)$49.88

    Please refer to PCC Chapter 24.85 for additional triggers for seismic upgrades and other information. 

  • Find answers to commonly asked questions on Chapter 24.85 
  • Find information on phased seismic upgrades 

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