Impact loads - Navigation Piles
Impact loads - Navigation Piles
(OP)
Hi I’m designing some navigation piles (free ended, single laterally loaded piles) to protect a water inlet structure for a water treatment works. The inlet is constructed on the River Thames (UK). The design impact load from a vessel on the river is 100 tonnes at 2.5 meters/second. However I’m not quite sure to convert that force into kN. Any ideas please!






RE: Impact loads - Navigation Piles
momentum = P=mv mass = 1000kN * 2.5 = 2500kN
hope this helps!
RE: Impact loads - Navigation Piles
Coming up with the spring stiffnes of your piles will require geotech input. If the soil strata are uniform it becomes a fairly straight forward problem. It may be worth looking at ductility of the system as well, depending on frewuency of occurence and the replacement cost of the piles versus the cost of piles large and deep enough to survive the impact.
Also, 100 tonnes only equals ~1000kN when accelerated due to gravity. The acceleration due to a vessel hitting a pile will be at a much different rate.
RE: Impact loads - Navigation Piles
The guy was asking to convert the force into kN.
RE: Impact loads - Navigation Piles
RE: Impact loads - Navigation Piles
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Impact loads - Navigation Piles
To get the KE equation you simply intergate the momentum equ.
RE: Impact loads - Navigation Piles
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Impact loads - Navigation Piles
yeah it didn't come out right! I meaning to write mass = 1000kN and V = 2.5m/sec, then apply the momentum equ.
sorry for poor description.
RE: Impact loads - Navigation Piles
Trust me, the complexities are immense.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Impact loads - Navigation Piles
You can calculate KE, deflection, stresses etc but I think the guy wanted to know how to convert one unit into another.
RE: Impact loads - Navigation Piles
RE: Impact loads - Navigation Piles
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Impact loads - Navigation Piles
RE: Impact loads - Navigation Piles
Use Force * distance = 1/2 * mass * velocity ^ 2
where distance = tip displacement of pile
You know all variables except Force.
HTH
RE: Impact loads - Navigation Piles
Nam Myoho Renge Kyo.
RE: Impact loads - Navigation Piles
RE: Impact loads - Navigation Piles
The correct form of the impulse equation is F*dt=m*dv
for constant mass
If you can assume constant F, then this becomes F=ma, but constant F is hard to achieve with a structure. So that still is not much help.
Rather more usefully if we can assume that the system can be represented by a 1 dof spring damper system, then the instantaneous work for a small period of time is
d(1/2m*v^2)/dt+d(1/2k*x^2+c*v*x)/dt =0
where dx/dt=v
But in order to get a solution you need to make some assumptions about k and c, the latter in particular is quite problematical, for your system. If you set it to zero then in theory the boat will just bounce off, at -2.5 m/s, but this will at least give you a force that is easy to calculate for a known k
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Impact loads - Navigation Piles
http://www.jhmenge.com/fentek/fentek_catalog.pdf
However, they only provide a factor for compliance of the structure. In designing monopile fenders, you can certainly benefit from using the flexibility of the pile itself - it reduces the resultant maximum load. Take note of the load/deflection curves for the fenders in the catalog. If you don't put a fender on your pile, your "curve" will be a straight line. I do recommend the fenders on page 36 for this application, though.
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: Impact loads - Navigation Piles
RE: Impact loads - Navigation Piles