Here is a code snippet to add a new file location and to set it as the new sheet location using the Sheetset API :
AcSmSheetSetMgr manager = new AcSmSheetSetMgr();
AcSmDatabase sheetDb =
manager.FindOpenDatabase(@"D:\\Temp\\MySheetset.dst" );
sheetDb.LockDb(sheetDb);
// New sheet location
AcSmResources resources
= sheetDb.GetSheetSet().GetResources();
AcSmFileReference fileRef = new AcSmFileReference();
fileRef.InitNew(resources);
fileRef.SetFileName(@"D:\\Temp\\SampleDrawings" );
sheetDb.GetSheetSet().SetNewSheetLocation(fileRef);
// Add New location
AcSmFileReference fileRef1 = new AcSmFileReference();
fileRef1.InitNew(sheetDb);
fileRef1.SetFileName(@"D:\\Temp\\SampleDrawings" );
resources.Add(fileRef1);
sheetDb.UnlockDb(sheetDb);
After you run the code, the model views from all the drawings in the path should get listed under Model Views as shown in this screenshot :