If the owner of any property upon which the sidewalk is in a bad state of repair and unsafe and dangerous for travel shall fail, neglect or refuse to repair the same and place such sidewalk in a condition safe and convenient for travel within the time in the notice herein provided for specified, the city shall cause said sidewalk to be repaired and placed in a condition safe and convenient for travel, and the expense thereof shall be assessed against the lot upon which such sidewalk is located; such assessment shall be made, returned and collected in the manner as provided by law. (Ch. 141)