WHY ARE ARCHES SO STRONG?

Arches are very strong because they transfer the weight upon them horizontally, and each section of the structure diverts a portion of the load into its neighbouring section. This means that the load placed upon the bridge is evenly spread throughout, with the downward-acting force distributed into the abutments – the arch’s supports, which are commonly placed either side – and into the ground, or into the ground directly and absorbed. As stone and brick are strong in compression, any arch constructed out of them is constantly under compression due to the force of a bridge’s load emanating constantly out from its central keystone. In essence, this means that within the tolerance of the material, the more load put onto an arched structure, the stronger it becomes.