# Seismic and Wind Force Calculator

Jonathan Ochshorn

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Directions: Enter general data (city, importance factor), seismic data (site class, seismic force resisting system), and wind data (exposure category, plan and parapet dimensions, and coefficients for directionality and topography). Then, enter values for story heights above grade and seismic weight (approximately equal to the dead load) for each story. Start at the highest floor (i.e., the roof), and work down to the lowest above-grade floor level. Press "update" button.

Story forces for wind and seismic loading will be displayed to the right of the values entered for seismic weight. In this way, the magnitude of wind and seismic forces may be compared for a given building on a given site. Note that there are some limitations for the use of this calculator: the building is assumed to be rectangular, and is limited to 20 stories (for buildings with more stories, an approximate calculation can be obtained by combining the seismic weight of two adjacent stories and entering the average height above grade). Calculations are based on analytic procedures for rigid buildings, neglecting internal pressures (wind), and equivalent lateral force procedures (seismic) as described in ASCE/SEI 7-05, Minimum Design Loads for Buildings and Other Structures. Plan dimensions for wind loading calculations are shown in Fig. 1. To obtain wind story forces from calculated wind pressures, windward and leeward pressures are combined into a single set of forces, as shown in Fig. 2. Account is taken of higher wind pressure on parapets. Story forces for seismic loading are shown in Fig. 3.

More detailed explanations and examples can be found in my text.

Fig. 1. Wind direction and plan dimensions.

Fig. 2. Building sections comparing windward and leeward pressures with wind story forces and base shear.

Fig. 3. Building section with seismic story forces and base shear.

 floor/roof height above grade (ft) seismic weight per floor (lb) seismic story force (lb) wind story force (lb) windward pressure (psf) leeward pressure (psf) general data city wind speed (mph) seismic Ss seismic S1 seismic TL Boston, MA Chicago, IL Little Rock, AR Houston, TX Ithaca, NY Los Angeles, CA Miami, FL New York, NY Philadelphia, PA Phoenix, AZ Portland, ME Other importance factor plan dimensions (ft) L B I - low hazard II - normal III - high hazard IV - essential wind data parapet height above roof (ft) exposure Kd Kt B C D 1 0.85 0 1 2 3 4 5 6 7 8 9 10 seismic data lat-force-resist system: main category bearing wall systems building frame systems moment-resisting frame systems dual systems, special moment frames dual systems, interm. moment frames cantilevered col systems conforming with: miscellaneous other systems sub-category 01. Special reinforced concrete shear walls 02. Ordinary reinforced concrete shear walls 03. Detailed plain concrete shear walls 04. Ordinary plain concrete shear walls 05. Intermediate precast shear walls 06. Ordinary precast shear walls 07. Special reinforced masonry shear walls 08. Intermediate reinforced masonry shear walls 09. Ordinary reinforced masonry shear walls 10. Detailed plain masonry shear walls 11. Ordinary plain masonry shear walls 12. Prestressed masonry shear walls 13. Light framed walls, wood-struct/sheet-steel shear panels 14. Light framed walls with shear panels—all other materials 15. Light-framed wall systems using flat strap bracing 01. Steel ecc-br frames, mom-res, conn at cols away from links 02. Steel ecc-br frames, non-mom-res, conn at cols away from links 03. Special steel concentrically-braced frames 04. Ordinary steel concentrically braced frames 05. Special reinforced concrete shear walls 06. Ordinary reinforced concrete shear walls 07. Detailed plain concrete shear walls 08. Ordinary plain concrete shear walls 09. Intermediate precast shear walls 10. Ordinary precast shear walls 11. Composite steel and concrete ecc-braced frames 12. Composite steel and concrete concentrically braced frames 13. Ordinary composite steel and concrete braced frames 14. Composite steel plate shear walls 15. Special comp. reinf. conc. shear walls with steel elements 16. Ordinary comp. reinf. conc. shear walls with steel elements 17. Special reinforced masonry shear walls 18. Intermediate reinforced masonry shear walls 19. Ordinary reinforced masonry shear walls 20. Detailed plain masonry shear walls 21. Ordinary plain masonry shear walls 22. Prestressed masonry shear walls 23. Light frame walls w/ wd-struct/sheet-steel shear panels 24. Light framed walls with shear panels—all other materials 25. Buckling-restr braced frames, non-mom-resist beam-col conn 26. Buckling-restr braced frames, mom-resist beam-col conn 27. Special steel plate shear wall 01. Special steel moment frames (no limits) 02. Special steel truss moment frames 03. Intermediate steel moment frames 04. Ordinary steel moment frames 05. Special reinforced concrete moment frames (no limits) 06. Intermediate reinforced concrete moment frames 07. Ordinary reinforced concrete moment frames 08. Special composite steel and concrete moment frames (no limits) 09. Intermediate composite moment frames 10. Composite partially restrained moment frames 11. Ordinary composite moment frames 01. Steel eccentrically braced frames (no limits) 02. Special steel concentrically braced frames (no limits) 03. Special reinforced concrete shear walls (no limits) 04. Ordinary reinforced concrete shear walls 05. Comp steel and concrete ecc-braced frames (no limits) 06. Comp steel and concrete conc-braced frames (no limits) 07. Composite steel plate shear walls (no limits) 08. Spec comp reinf conc shear walls with steel elements (no limits) 09. Ordinary comp reinf concrete shear walls with steel elements 10. Special reinforced masonry shear walls (no limits) 11. Intermediate reinforced masonry shear walls 12. Buckling-restrained braced frame (no limits) 13. Special steel plate shear walls (no limits) 01. Special steel concentrically braced frames 02. Special reinforced concrete shear walls 03. Ordinary reinforced masonry shear walls 04. Intermediate reinforced masonry shear walls 05. Composite steel and concrete concentrically braced frames 06. Ordinary composite braced frames 07. Ordinary comp reinf concrete shear walls with steel elements 08. Ordinary reinforced concrete shear walls 01. Special steel moment frames 02. Intermediate steel moment frames 03. Ordinary steel moment frames 04. Special reinforced concrete moment frames 05. Intermediate concrete moment frames 06. Ordinary concrete moment frames 07. Timber frames Steel systems not specifically detailed for seismic resistance Shear wall-frame interactive system site class (soil) A = hard rock B = rock C = dense soil or soft rock D = stiff soil E = soft soil paramenters for calculation of period CT x T (sec) Steel moment-resisting frame Concrete moment-resisting frame Steel eccentrically-braced frame All other structural types Use default values shown: Checks: errors: sub not permitted exceeds height floor heights are not in descending order wind speed must be > 0 seismic Ss out of range seismic S1 out of range seismic TL out of range plan dimension L must be > 0 plan dimension B must be > 0 heights must be > 0 weights must be > 0 Kt out of range (should be between 1 and 3)