It is common practice in the fabrication of welded plate girders to stagger the butt splices of webs and flanges and to avoid placing cross frame connector plates within six to twelve inches of one another. I don't recall exactly where this is specified nor do I recall if the value is six or twelve inches. Check the bridge welding code, D1.5, for more information. I once heard this is necessary to accommodate the inspection of the welds. I can not say if this is correct though.