Final answer:
An arch bridge withstands the force of compression by distributing the force as compression throughout the arch and eliminating tensile stresses. The outward thrust at the base of the arch needs to be restrained to prevent collapse, which can be done with internal ties or external bracing.
Step-by-step explanation:
An arch bridge is designed to withstand the force of compression. This means that the arch carries the weight of the bridge and any loads on it by pushing down on the supports, which are usually the ground or piers. By distributing the force as compression throughout the arch, tensile stresses (forces pushing outward) are eliminated.
In order to prevent the arch from collapsing, the outward thrust at the base of the arch needs to be restrained. This can be done with internal ties or external bracing, such as abutments. By providing support to counteract the outward thrust, the bridge can maintain its arch action and remain stable.