AN interesting development in bridge-work is described in the Engineer of July 27, in which is an account of the reconditioning of the Smithfield Street Bridge which crosses the Monongahela River at Pittsburgh. This bridge forms an important link in communication between Pittsburgh proper and the south side, and is used by trolley-cars, motor vehicles and pedestrians. Built partly of wrought iron and partly of steel and erected in 1882, it has at various times been widened, and strengthened, but an examination made in 1926 showed that it was being subjected to excessive stresses. The main features of the bridge include two ‘fish belly’ trusses of 360-ft. span supporting a floor system which included timber decking 11 in. thick. At first it was considered a new bridge would have to be buil, but financial reasons led to the matter being recon sidered, and it was finally decided to replace the whole of the girders, stringers and decking of the floor by aluminium, thus reducing the dead weight On the trusses. The heat-treated aluminium alloy used has an ultimate strength of about 26 tons, a yield point of about 16 tons and an elongation on 2 in. of 20 per cent, and the total saving in weight is more than 1 ton per lineal foot or 7514 tons in all. The cost of reconditioning has been 276,436 dollars, whereas the cost of a new bridge would have been about two million dollars. The bridge as it now stands is estimated to have a life of twenty-five years.