You won't need any flanges unless the system will have an underground portion.

Rolled groove galvanized steel piping, with grooved fittings, per NFPA 14 requirements.   Use multiple flexible couplings where necessary for thermal expansion or seismic.  Contractor to submit complete material specifications prior to design or construction activities.   

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.  

my understanding is that grooved fittings would not work because they would pull out and seperate due to the large amount of bridge movement and expansion.  I was under the impression that restrained joints were a must to prevent joint seperation???

I agree with pipesnpumps

Flexible couplings is the option. Any motion and vibration from the bridge itself will be absorbed by the hanging components of the bridge and the flexibility of the structure itself. Bridge standpipes are self contained and dry. Never connected to any underground. At least I have never seen one and I travel the country a lot. 600 psi flanges would be an overkilled.  

No offense swoosh, but you are advising the advisor?   It's ok I do the same thing, it's part of being a good engineer to question why.

Restraint is needed to counteract the axial aka longitudinal forces due to the water pressure.   Think of the end cap on your 6" standpipe.   It will have a force of 175 psig * pi/4 * ID^2.  Where ID is the inner diameter.

This force is held back by the wall of the pipe.  As it goes across a flexible coupling the axial force is still transmitted but the pipe is allowed to rotate (a small amount but enough to account for wind, thermal expansion, structural deflection, and seismic deflection of the supporting structures).  If you put two or more flexible couplings together it allows upstream and downstream piping to move relative to each other.   The way the flexible couplings should be arranged depends on the movements that would apply.

The rest of the couplings would be rigid couplings, which do NOt rotate.   The engineer you hire will know this, so basically if you specify to follow NFPA 14 you should be fine..,

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.  

Thanks for the responses guys.  My standpipe will be dry and have a FDC at grade on opposite ends of the bridge, 6,000 feet apart, so no underground portion.  I am just doing performance specs and drawings for a client to bid out to a FPE firm, so this is really for my own knowledge.  I do sprinkler design for buildings all the time, but this is a new beast.  I was wondering about the 600lb flanges due to the 100psi required at the highest/furthest hose connection which is 300 feet above grade, plus the 6,000 feet of pipe friction loss to get there.  I'm looking at like 400 psi at the ground.  The connections close to the fire department connection would be seeing a lot of pressure.  Also, what type or brand of expansion joint/flex connection?  Thanks again.

Centrifigual pumps installed on U.S. fire apparatus are not rated to deliver a flow at 400 PSIG. Typical fire apparatus pumps are rated for 1,500 GPM at 200-250 PSIG. Expecting the fire department apparatus being capable of supporting the hydraulic demand is an incorrect design basis.

I assumed the FDC was on the same level as the bridge.   You never mentioned that and it is key info..  Now I get why you mentioned 600 lb flanges.  

Just a side bar if you want to learn something else; from my days as a pipe stress engineer; I believe you will find that 300 lb flanges are good for up to about 400+ psig or so at water temps..  The 300 designation is roughly the pressure rating when the metal is at a temp of 300 psig saturated steam.   Eg 150 lb flange good for ~150 psig at a temp of 366 F.   At room temps, the allowable design pressure goes up.   It is easy to google up the actual allowables.

But to stay on subject, the solution here is to change the FDC location to be on the same level as the bridge.

There is no brand of flexible coupling required.  Every company that makes grooved fittings makes a flexible coupling.   Victaulic is one example.

BTW If you are a "hatched plan mechanical engineer" as I call them, and really want to learn about fire protection buy the SFPE Study Guide for the Fire Protection Professional Engineering Exam.   It would help you fill in knowledge gaps regarding standpipes, sprinklers, passive features, life safety plans, fire dynamics.    I have a strong hunch you don't know everything you should know about sprinklers, water supply, or pumps to keep yourself out of trouble in the work you already do regularly.   I am a reformed mechanical engineer myself (BSME) and it takes one to know one.

Best of luck on your project. I'll bow out of this thread now.  

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.  

The basic standpipe dimensions were mentioned in the original post. I became concerned when the standpipe had a height of 300 feet and never mentioned water supply data. I envisioned someone trying to use a fire apparatus pump pulling suction from a river and trying to use a dry standpipe to meet a certain hydraulic demand, which was also not presented in the original question.

This is why internet based engineering is dangerous.

The bridge is over a waterway into a city so it has to be 300 feet at its highest so container ships can get under it.  The approach ramps begin several thousand feet away and essentially begin at grade, i.e sea level.  I would have an FDC at the start of each approach ramp.  This is preliminary design right now and I have not contacted the authority having jurisdiction yet about their pumper truck capabilities.  Perhaps a deluge valve with stationary fire pump would be more appropriate.  I am scheduling a flow test to be done at the nearest hydrant.