(a) Every public agency shall require that every contract document for the construction, reconstruction, alteration, repair, improvement, or maintenance of public works contain a provision that if any steel products are to be used or supplied in the performance of the contract only steel products as herein defined shall be used or supplied in the performance of the contract or any subcontracts thereunder.
(b) This section shall not apply in any case where the head of the public agency, in writing, determines that steel products as herein defined are not produced in or readily available in the United States or that the steel products shall not exceed fifteen percent (15%) of the costs of any other steel products obtainable nationally or internationally.