How Does a Strap Footing Fix an Eccentric Column Load Case?

A strap footing uses a rigid beam to connect an eccentric exterior footing to an interior footing, transferring the exterior column's overturning moment to the interior footing. The strap is designed as a spanning beam kept clear of soil contact so its lever action works as intended. It's an elegant, economical solution to the property-line column problem — two modest footings and a beam doing the work of one big pad.

The exterior column load acts eccentrically on its pad, creating a moment that wants to rotate the pad outward. The strap beam, rigidly connected to both footings, carries that moment to the interior footing, where the interior column's gravity load and the footing's bearing resistance absorb it. Equilibrium is checked across the whole assembly: bearing pressures under both pads stay within allowable limits, and neither pad uplifts. The strap's rigidity is the linchpin. A flexible strap would bend instead of transferring moment, leaving the exterior pad to rotate. That's why strap beams are deep, heavily reinforced, and detailed with full moment connections into both footings — the beam-column joints at each end have to develop the transferred forces.

Strap footings fail when the mechanism is drawn but not truly designed — the beam drawn too shallow, the soil contact ignored, the interior footing unchecked. My review is mechanical. Every strap footing detail should answer these questions.

• The exterior eccentricity and resulting moment are calculated explicitly, not eyeballed
• The strap beam is sized and reinforced as a rigid moment-transfer element with full end connections
• The strap is detailed clear of soil contact — void forms or compressible fill beneath it
• The interior footing is checked for the combined gravity plus transferred moment, including uplift
• Bearing pressures under both pads stay within allowable limits under all load combinations