How to Design Capping Beam ?
How to Design Capping Beam ?
(OP)
Dear All,
I need to design cap beam connecting secant piles, can you please guide me about the procedure?
Thanks
I need to design cap beam connecting secant piles, can you please guide me about the procedure?
Thanks





RE: How to Design Capping Beam ?
The restraint provided by the ground against the walls if very true is of difficult evaluation and is normally (and conservatively) left out of the model.
It is not too uncommon to feign fixity conditions on that beam (so passed to the model of the superstructure above, if separate) to reduce the amount of torsional forces applied. In any case a mechanism needs to be provided to ensure proper transmission of loads to the foundation.
RE: How to Design Capping Beam ?
I really appreciate your extensive answer. Is there any "simplified" design methods or procedure that solves the capping beam design issue knowing that the shoring is for temporary purpose.
Regards
RE: How to Design Capping Beam ?
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RE: How to Design Capping Beam ?
So I would say that very rigid cap beams come mainly from lack of confidence of a regular behaviour of the foundation. Exception made of cases where the piles end in layers of vast different rigidities, and surmised one has reasonable investigation of the soil, what uses to be common for this kind of works, most engineers won't go for the top rigid cap beam, but neither are them providing very weak ones, just in case.
RE: How to Design Capping Beam ?
Secant piles wall is required to support excavation. This wall shall be 'water cut-off wall' also. This wall will be located within airport premises so the owner and consultant requires capping beam connecting the secant piles wall (male & female). I need to submit simple approach like if the horizontal component of the active pressure equals (x) for example then i will use a reasonable ecom=nomical safe percentage of it on the cap beam of length say 1.0m and furnish the structural design (section, steel bars, concrete strength ...etc). Does this simple approach seems reasonable and acceptable by the consultant? Does this way of thinking had been used earlier according to your knowledge?
Ishvaaag,
I would like to thank you very much for your interest but as explained above, do you have simple "used before" design approach for temporary shoring works?
RE: How to Design Capping Beam ?
RE: How to Design Capping Beam ?
When I have seen design of others as a general rule the effects of long term settlement (maybe a device of the cases I saw) is usually neglected, and inwards (towards the excavation) movement corresponding to the push is restrained by ties to the ground for temporary situations or the built slabs for the definitive. I really do not remember any quoting a guide book on the matter, they just deal with what think relevant at the moment.
RE: How to Design Capping Beam ?
For example, a sheet pile wall is designed on a per linear foot basis. Each sheet pile supports the same load as long as the wall height, soil properties, and surchargre loads remain the same. Therefore, if you add a cap beam to the sheet piles, it will not perform any useful, structural function. As hokie66 said, the cap beam will just go along for the ride when the sheet piles (or secant piles) deflect. If someone of authority wants a cap beam, you can give them one. I'm just not sure what load you would need to design it for.
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RE: How to Design Capping Beam ?
Kieran
RE: How to Design Capping Beam ?
Good article! I must have missed that edition. Hopefully that answers MHJ35
RE: How to Design Capping Beam ?
RE: How to Design Capping Beam ?
RE: How to Design Capping Beam ?
We are doing a secant walled pile rectangular basement. We are not able to install anchors and the wall needs to be designed as a cantilever wall. Horizontal deflection of the wall governs the design of this specific wall and I'm trying to provide restraint to the top of the wall using a stiff capping beam and am wondering what the best way is to calculate the equivalent spring stiffness that the capping beam will provide to the top of the wall.
My current approach is modeling a rectangular capping beam in isolation, applying a unit load to all four the sides of the basement and extracting the deflections this induces and relating back by k=1/deflection*width to give me a kN/m stiffness that the geotech boys can apply to their frew model.
Sound right?
Thanks
RE: How to Design Capping Beam ?
www.PeirceEngineering.com
RE: How to Design Capping Beam ?
RE: How to Design Capping Beam ?
www.PeirceEngineering.com
RE: How to Design Capping Beam ?
The spring coefficient at top of piles will vary along the wall, minimum at midspan of capping beam and very rigid at the corners. To evaluate springs run a single span beam model of capping beam loaded with uniform load w=1 k/ft. Spring coefficient will be K = (di/w)S, where di - deflection at the pile, S - spacing between piles. Vary capping beam stiffness and beam support conditions to envelope the results. I attached a graphical illustration to this idea.
Hope it helps!
Yakpol
RE: How to Design Capping Beam ?
firstly, it is more polite to start a new thread even if it is closely related to someone elses like this. But since we have started then we may as well continue.
It looks to me like you are overanalysing this. Just model it as a rigid support in order to get a slightly conservative reaction and the design the capping beam for the u.d.l.
If we were to analyse every item in a project in detail without simplifying it I would still be designing my first house (from 13 years ago).
RE: How to Design Capping Beam ?
Simplification will be justified only if you have a small in plan excavation. With longer sides (say over 60-80ft) the forces on capping beam are very substantial, and flexibility of it is important too, you may exceed allowable displacements at midspan.
RE: How to Design Capping Beam ?