All persons are hereby forbidden to obstruct the sidewalks, crosswalks or streets of the city, or to permit any gate or other obstruction to swing across any sidewalk of the city to the annoyance of another person; provided, however, that special permission may be granted by the city to place obstructions on sidewalks or streets when necessary for improving the same or to provide protection when buildings are in the course of construction. (1966 Code § 8-2-3)