- Why does a smaller wedge angle produce a larger outward force?
- A smaller half-angle θ (between the wedge bisector and each face) makes sin θ smaller, so N = W/(2 sin θ) grows: the same vertical load W demands larger contact normals on the sides. The FAQ uses the same θ as the simulator slider. Geometrically, wedge length/thickness scales like cot θ, which is a different number from N/W.
- What does it mean if the 'line of thrust' leaves the middle of the arch in the simulator?
- If the line of thrust moves outside the middle third of the arch's thickness, it indicates that tension would develop on one side of the joints. Since stone and masonry have very low tensile strength, this can cause the joints to open, creating hinges and leading to potential collapse. In a real arch, stability requires the thrust line to remain within the material, which is why arches are often thick relative to their span.
- Does this model account for friction between the blocks?
- No, this is a key simplification. The simulator assumes frictionless contacts to focus purely on the geometry of force resolution and compressive thrust. In real stone arches and wedges, friction provides additional shear resistance, increasing stability and allowing for more slender designs. The principles shown here are the foundational, first-order analysis.
- How is the force in the arch related to the force from the wedge?
- They are directly connected. The outward thrust generated at the base of an arch (the horizontal force the abutments must resist) is essentially the same force produced by a wedge. The arch voussoirs act like a series of inverted wedges, converting the downward weight into inclined compressive forces that push outward. Understanding the wedge helps explain why arches need strong side supports (abutments) to contain this thrust.