Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008. / The Southern African Institute of Steel Construction expressed concern with regard to the unit
definition of the effective length factor, K, stipulated for compressive elements of parallel chord
trusses in Clause 15 of SANS 10162-1:2005 - Limit state design of hot-rolled steelwork. The
simplified method for truss design specified in the code assumes all compression members are
pin-connected, which allows for greater design simplicity and reduces the amount of code
interpretation required by the designer. In addition to this, Clause 15 requires the additional
reduction in resistance of the first web compression members by a factor of 0.85. However, this
approach may be considered overly conservative and in current design practice the effective
length factor is often reduced to less than 1.0.
This research investigates the effective length factor of web compression members in parallel
chord trusses, by means of investigative structural analyses of representative trusses using
ANGELINE and Prokon analytical programs, and by designing, constructing and testing six
representative trusses, using current design practices. A comparative study of a number of
different countries’ codified approaches to truss design is also included.
The structural analyses revealed that in-plane buckling of the web compression members was
the consistent mode of failure, however at a much greater applied load than the design load
determined according to SANS 10162-1:2005. Contrary to the expected mode of failure, all six
tests performed on the representative trusses exhibited elastic out-of-plane buckling, or strongaxis
buckling, of the web compression members, but still at a much greater applied load than
the design load. The unexpected out-of-plane buckling of the web members is due to the inplane
stiffness of the end connections used. In order to stay true to current design practice,
gusset plates and longitudinal welds were used to join the web members to the chords. The
stiffness of the gusset plates therefore significantly reduced the effective length of the web
compression members in-plane, but did not reduce the effective length out-of-plane.
Despite the unanticipated behaviour of the tests performed, certain conclusions can still be
drawn from the results. The unit definition of the effective length factor for in-plane buckling of
web compression members is too conservative and a K factor of 0.8 is recommended. In
addition to this an effective length factor for out-plane-buckling of web compression members of
1.1 is recommended for trusses with welded connections. The necessity of the reduction in
resistance of 0.85 of the first web compression members requires further investigation. The
most important conclusion to be drawn is that out-of-plane buckling of web compression
members can be the dominant failure mode, which is not taken into consideration in current
design practice.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2410 |
| Date | 12 1900 |
| Creators | Dunaiski, Wibke |
| Contributors | Dunaiski, P. E., Pahl, P. J., Van Zijl, G. P. A. G., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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