Rigid pile cap VS flexible pile cap

[edward law]

What kind of computer software can modelling the rigid pile cap and flexible pile cap used to compared the different between the both of it? Or any literatures are explaining this problem?

 

[WARose]

Pretty much any FEA software can model it. Using solid elements, you can model pretty much anything at this point. (For caps with a good span between piles, plate elements tend to be more appropriate.)

 

[KootK]

Some commonly used software options in North America include:

CSI SAFE
RISA FOUNDATION
RAM FOUNDATION
IES VISUAL FOUNDATION

used to compared the different between the both of it? Or any literatures are explaining this problem?

The difference is fairly straight forward as is mostly about complexity versus accurate load distribution. A rigid cap assumption is nice and simple but less accurate with regard to load distribution. Non-rigid, finite element analysis is much more complex but, presumably, more accurate.

An important consideration for this kind of problem is the expected accuracy in the parameters defining the things that you wish to model in FEA. Geotechnical parameters are difficult to determine accurately and are often best represented by ranges of values. Unless you're willing to bracket your solutions based on a range of parameter values, the inaccuracy in your input parameters may neuter any perceived accuracy gained from FEA modelling.

For what it's worth, I most often do rigid analysis for simple pile caps having conventional loads and geometries.

 

[ukbridge]

90% of the time we use the rigid pilecap assumption such that the piles are assumed to take all the bending. We typically only really break that out if we find a significant mistake later on. Practically all pseudo-FE packages like REPUTE and PIGLET use this assumption.

You can use whatever software you like as long as its reputable, but realistically you would need to model the pilecap using shell elements and the piles with beam elements. I've done this before with by modelling the ground using winkler springs calibrated from a geotechnical model.

I wouldnt really recommend it unless its worth the economy e.g. larger projects.

 

[edward law]

Actually, the purpose of this comparison is prepared for my final year project. So i need a computer model is possible to analysis the rigid and flexible behaviour in pile cap. I tired to model the pile cap by CSI SAFE, however it seems can not consider the rigid behaviour, so any other computer softwares are suggested to model the rigid pile cap.

 

[ukbridge]

Whats your reasoning for thinking that it can't consider the rigid behaviour?
I haven't used CSI SAFE before admittedly, but from a quick glance it looks capable enough of modelling slabs, footings etc.

I'm basically repeating myself with a bit tacked on but in any case:

1. Model the pilecap using shell/plate elements.
2. Model the piles using beam elements.
3. Model the ground either by springs or using an elastic continuum and apply the appropriate loading. If your supervisor hasnt clarified this/given you a place to start go and see him asap.

Without giving the answer away do a parametric study varying E (or the thickness) for the pilecap e.g. E, 10E, 100E, 1000E while keeping the E for the piles constant. At Epc=1000Epiles its probably "rigid" enough at that point, you'll need to fiddle with your value of E to find the point where the flexural behaviour of the pilecap is no longer sensitive to the value of E).

4. Compare the bending moment distributions for each case and write it all up (i.e. the more flexible the pilecap, the lower the bending moments in the piles.

In fact start even simpler, model a 2D frame and do the same exercise and note how the bending moment distribution changes as the relative stiffness of the beam increases by 10, 100, 1000 etc. I imagine this is the general point of the project.

If you cant work it out/its not in the manual go and chat to your supervisor, although again I'd be surprised if it can't do what I'm suggesting.