Before any type of public improvements shall be commenced, the money to pay for the same must be available in the city treasury as provided by law; or provision may be made for the issuance of internal improvement bonds to pay for any such improvement as provided by law; provided, that this ordinance shall not be construed to include any repair or maintenance work not amounting to substantial alteration, addition or change in any structure, street or facility; and “public improvement” as used herein shall not include the making of repairs or the maintenance of any building, street, sidewalk or other public facility in this city by employees of this city or the making of any expenditures from the city budget for such purposes. (C.O. 17 § 15, 1-30-71.)