P-Delta effect refers to

• A. The panel deflection under its own weight and roof/floor loads
• B. The ratio of unsupported height of the panel to its thickness
• C. The chemical process that causes concrete to harden
• D. The tilt-up construction loading pattern during seismic events

Answer: (A)

P-Delta is a second-order structural effect where vertical loads acting on a displaced element create additional bending moments. When a tilt-up panel deflects under its own weight and roof/floor loads, the weight no longer acts exactly through the original vertical line, so the lateral deflection generates an extra moment proportional to the load times the deflection (M ≈ P × δ). This can increase bending demands and overall sway, especially in taller or more flexible panels, so designers include it in analysis to avoid overstress or instability.

The option describing panel deflection under its own weight and roof/floor loads captures this mechanism. It’s not about concrete curing, the height-to-thickness ratio, or a seismic loading pattern.