Nothing in this chapter shall be construed to limit or repeal any existing powers of cities with reference to the construction or reconstruction of sidewalks or the improvement or maintenance of streets, but the power and authority herein granted is to be exercised concurrent with or in extension of powers and authority now existing. The legislative authority of any city before exercising the powers and authority herein granted shall, by proper ordinance, provide for the application and enforcement of the same within the limitations herein specified.