How does one consider the moment capacity of a combined pipe plus H-section if the infill material is:

  • Sand, friction angle 30 degree
  • Grout, C20
  • Concrete, C45

Pipe with H-section

Eurocode has a section on composite design, which requires use of shear connectors. Where shear connectors are not feasible due to lack of space, can bearing of infill material be relied on for moment transfer? For example, what would be the moment capacities of a 600mm outer diameter pipe section with 10mm thick wall containing a 300x300mm H-section with 25mm thick flange and 16mm thick web, both grade S355 steel, based on each of the three infill materials?

  • $\begingroup$ This looks like a "homework question" (notice the quotation marks). In order for such questions to be answered in this site, we need you to add details describing the precise problem you're having. What have you tried to solve this yourself? Please edit your question to include this information. $\endgroup$
    – Wasabi
    Aug 25, 2017 at 4:01
  • $\begingroup$ @Wasabi, please see edit. The precise problem is to derive the moment capacity of such a section, using the materials mentioned above. These are common construction materials, and they are used in projects involving temporary works for retaining structure of a braced excavation. $\endgroup$
    – Jennifer
    Aug 25, 2017 at 5:48
  • $\begingroup$ @Jennifer: You forgot to include the second piece(s) of information requested by Wasabi: "What have you tried to solve this yourself?" $\endgroup$
    – Transistor
    Aug 25, 2017 at 10:21

1 Answer 1


I'll take your fill options one at a time:

  • Sand - This isn't going to do anything. You could argue that filling the space between the tube and the H-pile would add bracing between one and the other. This could help if you were having issues with the unbraced length part of axial capacity. The sand will not transfer shear though, so it isn't a composite section.
  • Concrete - Concrete will bond to (or at least have greater friction with) the steel elements. This is the same as reinforcing in concrete. Also, just like reinforced concrete this will cause a composite section to be produced. But just like reinforcing, there will be some concept of development length. Data on this has been hard to find in my experience. AISC has a publication specifically about this: Design Guide 6: Load and Resistance Factor Design of W-Shapes Encased in Concrete
  • Grout - This is generally the same as concrete.
  • $\begingroup$ concrete inside a steel box section is very effective, and yes some testing was carried out... :) It was used to fill chassis box sections on banger racers so they did not crumple so much... $\endgroup$
    – Solar Mike
    Aug 24, 2018 at 19:59

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