This report presents the
results of structural tests that were performed at the NAHB Research Center
on a prototype slit web stud. Based on this work, and that of the companion
report on Thermal Performance of Slit-Web Steel Wall Studs, it is hoped
that manufacturers may have interest in commercializing the thermal stud.
The reader is cautioned that the
Research Team had the following specific questions and concerns related
to the report:
- From the photos it appears that the flexural
tests failed in a combination of bending and web crippling. No reinforcement
was added to the webs to preclude a web crippling failure at the load
application. This may explain the failure mode being reported as “local
buckling under the point load”. Comparisons should have been made
between the tests of the solid web stud and the AISI Specification calculations.
There is insufficient information in the report to determine the test
failure moment and the mode of failure for the solid web studs.
- There are no photos of the solid web
stud tests and it is unclear whether they had standard perforations.
This would affect the calculated capacities.
- A portion of the difference in strength
is attributed to the higher yield and ultimate strength values of 27%
and 30%. Per Table A1, the difference in yield is only 13%.
- The bracing of the two members in the
axial tests precluded anything but local buckling. The results of the
stub-column tests, essentially the same as the axial tests, confirm
this.
- Table 7 gives the shear test results,
but is not clear whether these are the test loads or the failure shear
values.
- The results of the axial tests of the
solid web studs should be compared with the AISI Specification. Since
these were essentially stub column tests, the results should be able
to be calculated.
- The shear test set-up seems to be unnecessarily
complex. Most shear tests are carried out on short specimens reinforced
to prevent a flexural or web crippling failure. The report concluded
that failure was localized buckling of the flanges under the point load.
This does not sound like a shear failure, but may be combined shear
and bending.
- The shear wall tests are not relevant
to the investigation of the strength of the member by itself. Also,
the shear walls tested experienced premature failures (first due to
the hold-down tearing out of the web and then due to an inadequate number
of chord studs). This precluded any meaningful conclusions to be reached
regarding their
performance.
- Web crippling tests were not conducted.
The report implies that web crippling would not need to be investigated
for fully sheathed walls; however, this statement is not necessarily
correct. Industry experts advise that web crippling would need to be
tested even for sheathed walls, but definitely for unsheathed walls.
- The report concludes that the slit web
stud “performed similar to or better than a solidweb stud”.
While this is true for the tests carried out, there is some question
whether the desired failure mode was achieved. It should be recommended
that addition tests be
carried out to isolate the specific failure modes (shear, web crippling,
distortional buckling, overall buckling) to verify the behavior.
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