Whenever the county engineer deems any bridge or culvert unsafe for traffic, he shall condemn the same and shall cause to be put up at each end of such structure in a substantial manner a notice, which shall be printed in conspicuous letters with the following words, “condemned by the county engineer,” with his signature to same, and shall, if necessary, erect structures sufficient to prevent travel upon such condemned bridge. The county engineer or township trustee shall immediately report the condition of said bridge or culvert to the county or township board, as the case may be, with his recommendations as to what improvements are necessary, and such board shall commence at once the proceedings necessary to repair or reconstruct the same.