valley gutters modification

huangyhg

valley gutters modification
we have a project in the facility-part scope of work is to correct/repair of old leaky 25 year old 2-9"x14" valley gutter attached side by side separated by 8" expansion joint between gutters of the building bays.  the option is to eliminate the existing valley gutter and infill with polyurethane so the water will flow at the surface of newly formed gutter valley over the existing valleys in-filled with poly materials towards the downspout on both ends.  the building is 110' height, both bays are equipped with overhead cranes attached to the building frames down below the roof of the 200' bays span and total length of building is 460' long (total length of gutter on one bay).  another scope of work is to demo existing 8" expansion joint covering the 8" space between 2-bldg-bays covered with board on each side of the bay to narrow 8" gap to 1.5" and sealed with 4"diameter backer rod secure with silicone then sprayed with polyurethane roofing system (the backer rod will serve as expansion joint).
my 1'st concern is the rigid gap between bays if less that 2" gap is enough for building contraction due to combined building movement for wind load induced, seismic due to vibration of moving overhead crane attached to the building structure and possible foundation settlement?  another is the backer rod material on expansion joint.  do you think it will hold and last for more that 10 years without ripping, and changing the physical properties?
i will appreciate all feedbacks as soon as possible. thanks.