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Arch Thrust Line 2D — Rise, Load & Middle-Third Stability

Interactive 2D thrust-line diagram for a stone arch: dial in the rise/span ratio, arch thickness, a point load's position and magnitude, and watch whether the compression thrust line stays inside the arch's middle third or pushes the structure toward cracking and collapse.

Engineering & Materials2DModerate60 FPS📱 Mobile-adapted⇄ 3D version

This 2D side-view diagram computes and draws the true thrust line of a compression-only stone arch — the same physics as the paired 3D voussoir arch, reduced to the graphic-statics calculation an engineer actually checks. The arch centerline is a parabola set by the rise/span ratio; a point load and a distributed self-weight bend the thrust line away from that centerline exactly as a three-hinged arch's bending-moment diagram predicts, scaled by the horizontal thrust needed to close the line at the crown hinge. A shaded band marks the middle third of the arch's own thickness: keep the thrust line inside it and every joint stays in pure compression; push it out and the diagram turns from green to amber to red as cracking gives way to a full hinge and collapse risk, just as it does in a real masonry arch under an eccentric load.

⚙ Under the hood

Adjust an arch's rise/span ratio, thickness, and a point load's position and magnitude to see whether the resulting thrust line stays within the arch's middle third or pushes it toward cracking and collapse.

archthrust linecompressionmasonrystructural engineeringmiddle thirdstatics

2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install