3D Strut and Tie

[smjohns78]

I am currently working on the design of a pile cap that is supporting a wall pier. I have been given the reactions at the top of the piles and am working to design the reinforcement in the cap. The reactions include forces and moments in all degrees of freedom. Per AASHTO, the design for shear and torsion should be based on a strut-and-tie model.

I am having a hard time visualizing how to model this. I have had experience with 2D problems and simple 3D problems, but feel I am a little lost on this one. Any input would be greatly appreciated. I have attached a file showing geometry in case my description was lacking.

Thanks.

 

[rscassar]

I believe that the pile should only be modelled with translational restraint and therefore no moment is transferred into the pile. If this were the case then the pile cap design becomes a 2d strut-tie design. 3d strut tie design is the same as 2d strut-tie design except there is an extra dimension to deal with. The designer needs to make an assessment of the node zone design and whether to assign CCC/CCT/CTT fields because generally there can be more than 3 strut/ties coming into the one node.

 

[smjohns78]

Thanks for taking the time to respond. I'm not sure I can justify the assumption that there is no moment transfer as the piles will be built integrally with the cap and there is only a single line of piles. At the moment I am just considering modeling the cap using a space truss that matches the perimeter of the cap and applying moments/torsion using equivalent force couples.