FRANKFURT (AFX) - German construction union IG Bau said about 8,000 workers on 400 construction sites in Berlin, Magdeburg, Bremen, Hamburg and the industrial Ruhr area have gone on strike as they demand pay increases of 4.5 pct. The strikes started today after some 98.6 pct of union members last week voted in favour of all-out strike action. The head of IG Bau, Klaus Wiesehuegel, said strikes will continue to expand throughout the country until the employers meet the demands.