Archbridge,thebasicprincipleisthroughahorizontalthrustoriginallyproducedbytheloadofthebendingstresstocompressivestressormostintocompressivestress.Andthearchisupwardconvexsurface,surfaceeffect,themaximumprincipalstressarchbridgeverticaldirectionalongthearchbridge,theminimumprincipalstressiszero.Archesofthedifferencebetweenthelargestpartsofthebeamishorizontalthrust,ifthehorizontalthrustandbearingreactionforceandresultantforcewiththeloadactingonthepointanddirectionjustrightthroughtheaxisofthearch,archisreasonablearch,thatarchisacompressivestress.Iftheyarenotoverlap,thenthereisabendingstress.