Which force pushes inward on an arch, helping to transmit loads to the abutments?

• A. Compression
• B. Gravity
• C. Tension
• D. Torsion

Answer: (A)

The key idea is that arches carry loads mainly through compression. When a vertical load sits on the arch, the materials press against one another along the curved shape, creating compressive forces that run through the arch from one side to the other. This pushing together, or compression, directs the load along the curve toward the abutments and generates a horizontal thrust that the supports must resist. Gravity supplies the load that the arch must transfer, but the internal force that actually pushes inward and keeps the arch stable is compression. Tension would pull pieces apart, which isn’t how a typical arch functions, and torsion would twist the arch rather than transmit its load along the curve.