As used in this act, the words “maintenance and support” shall include the general and usual cost and expense of operating such free public library but shall not include the cost of erecting or equipping a public building therefor or the cost of a site for such building, except in any city having a population of more than 35,000 and not more than 150,000 where such free public library occupies a public building upon a site acquired therefor and which public building and site are free from any bonded indebtedness, then not to exceed 20% of any annual budget prepared, published and approved by the board of directors may be allocated to a special accruing fund for the cost of erecting and equipping any addition to, or branch of, such free public library and for the acquisition of any additional site required for the erection of any such addition, branch or parking facility for use by the patrons of such library. Expenses for major capital improvements or major equipment purchases to cover such matters as, but not limited to, major roof repair, new computerized circulation or security systems and bookmobile replacement may also be paid with funds from the special accruing fund.