Valid inequalities for problems with additive variable upper bounds

We study the facial structure of a po[polyhedron associated with the single node relaxation of network flow problems with additive variable upper boun ds. This type of structure arises. for example. in production planning prob lems with setup times and in network certain expansion problems. We derive several classes of valid inequalities for this polyhedron and give conditio ns under which they are facet-defining. Our computational experience with l arge network expansion problems indicates that these inequalities are very effective in improving the quality of the linear programming relaxations.