secondary arch

rear arch

1. An inner arch of an opening which is smaller in size than the external arch of the opening and may be different in shape.
References in periodicals archive ?
C[pounds sterling]Most recently we successfully completed a complex 2,000-tonne Secondary Arch structure, a major component of the 845-meter-long Sheikh Zayed crossing connecting Abu Dhabi Island with the mainland,C[yen] he pointed out.
This assembly would support a secondary arch structure made of steel tubing that holds the polyester shells.