1. Pure bending moments
2. Axial tension forces
3. Torsional shear
4. Axial compression forces

Explanation

Explanation: Arches resist loads primarily through axial compression, converting vertical loads into horizontal thrust at the abutments. This compression-dominated behavior allows for thinner, more material-efficient designs compared to beam structures, which rely on bending resistance. The elimination of tensile stresses makes arches ideal for materials like stone and concrete that are weak in tension.

Learning Resources:
• "Bridge Engineering Handbook," Chapter 9 – Arch Bridges
• Case Study: Pont du Gard (Roman aqueduct) - 2000 years of compression
• Mola Visualization: See model of the Sydney Harbour Bridge using the Mola Structural Kit by forming a thrust arch with curved top chords and vertical hangers supporting a deck below. Create a similar but simplified model and apply vertical loads to the deck to visualize how the arch carries compressive forces, and how the horizontal thrust is resisted at the abutment blocks.