Isolated Footing Design for Column Load per ACI 318-25

Summary: Design a square isolated footing for axial column load per ACI 318-25 Chapter 13 for flexure, shear, and development length. Free structural design…

Overview

Building / scenario

• Site / exposure: ACI 318-25

Problem statement

A concrete column supports a two-story wood-frame building. Given: column dead load D = 80 kips; column live load L = 40 kips; allowable soil bearing pressure q_a = 3 ksf (from geotechnical report; IBC Table 1806.2 presumptive values if no report). Design a square isolated footing per ACI 318-25. Footing dimensions: 8 ft × 8 ft (Lx × Ly); footing thickness 12 in. Verify bearing pressure q = P/A ≤ q_a; check one-way shear, two-way (punching) shear, and flexure per ACI Chapter 13. Load combinations per ASCE 7-22 §2.2 ASD.

Workflow in StructSuite

StructSuite's free structural design software applies ACI 318-25 Chapter 13 (footings), flexure (§7.3), one-way shear (§7.4.3), two-way shear (§7.4.4), development length (§25.4). In Geometry: select Isolated footing (column); enter Dimension Lx = 8 ft, Ly = 8 ft; Thickness = 12 in. In Loads: add D = 80 kips, L = 40 kips. In Materials: enter allowable bearing 3 ksf (3000 psf), f'c, fy. StructSuite computes bearing, shear, and flexural checks.

Design considerations (excerpt)

Bearing area A = P/q_a. 120 kip / 3 ksf = 40 ft² → 6.3 ft square min. Larger footing reduces bearing and punching shear stress. Thickness drives shear: one-way and two-way (punching) often govern before flexure. 12 in. typical for 8×8 under 120 kip; 14–18 in. for heavier. IBC 1500 psf presumptive when no geotechnical report—limits apply. Geotechnical 2–4 ksf common; 6+ ksf for rock.

Related terms

• StructSuite
• structural engineering
• design example
• foundation
• ACI 318
• square isolated column

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