Within six months after this charter takes effect every public utility, and every owner of a public utility franchise, shall file with the city certified copies of all such franchises owned or claimed, or under which any such utility is operated within the city. Certified copies of all public utility franchises, and of all amendments, renewals and extensions thereof, made subsequent to the taking effect of this charter shall be filed with the city by the grantee within ten days after acceptance thereof. No franchise to construct or operate a public utility shall be transferable except with the approval of the commission expressed by ordinance; and certified copies of all transfers, mortgages and other documents affecting the title or use of public utilities shall be filed with the city within ten days after their execution. The certified copies of franchises and other documents required by this section to be filed with the city shall be filed and preserved as a public record in such office thereof as the commission may by ordinance designate.