Safety factors for simultaneous wave, tidal, dead and imposed loads 3

[damo74]

Hi all,

I'm designing an r.c column that is supporting precast concrete pedestrian bridge beams. The bridge spans over the mouth of a river and is supported from piles in the seabed. I have determined the wave, current, dead and imposed loads on the structure. Could anyone give me some guidance on what safety factors I should be using? I was unable to find anything in the British standards.

 

[Lutfi]

My first advise is to use at least four piles under the column. I would not use two piles even if they mathematically will work especially placing them in rivers where they are subjected to tidal currents, scour, and wave action.

I recommend that you try to read FEMA-55 guidelines (Coastal Construction Manual: Principles And Practices Of Planning, Siting, Designing, Constructing, And Maintaining Residential Buildings In Coastal Areas) for piling to support structures built on coastlines. They have excellent guidelines and formulas. You can order them hard and soft copies free of charge directly from FEMA. Here is the link to do that”

http://www.fema.gov/pdf/hazards/nhp_fema55.pdf#search='FEMA55'

You also need to make sure that the piles will extend sufficient depth below scour depth. Your Geotechnical engineers should help you with this elevation.

Regards,



Lutfi

 

[JAE]

Since damo74 is apparently coming from Britain, the FEMA stuff is available - but not free.

Also, I would think that there is some British standard out there regarding this....its not like there are no bridges over water on that particular island!

 

[Lutfi]

Good point JAE. However, he may be able to fine it on the net in the PDF format and then he can view or download it.

Regards,


Lutfi

 

[hamlet104]

First, you need to figure out which are the dependent and which are the independent variables. For instance, there will be a relationship between tidal stage (extreme high, exreme low, or somewhere in the middle), and current velocity and direction. Likewise, the height of the tide governs the area available to resist the flow. Extreme high storm tides will probably be expected to happen only at certain times of the year; do these occur at the same time as,or a different part of the year from flooding of the river? And are the currents in the same or opposite directions?

When you've got those answers, use a 1.7 factor on wave loads and current loads per foot, probably use a 1.4 factor on the variable loads due to increase of height of the water surface, and 1.3 on dead loads. Use a beta of 0.83 on the combinaton to compute the loads.

 

[damo74]

Thanks guys. That info has put me on the correct path.