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CivilComp Proceedings
ISSN 17593433 CCP: 73
PROCEEDINGS OF THE EIGHTH INTERNATIONAL CONFERENCE ON CIVIL AND STRUCTURAL ENGINEERING COMPUTING Edited by: B.H.V. Topping
Paper 25
The Influence of Column Base Connectivity on the Carrying Capacity of Columns H.H. Lau, M.H.R. Godley and R.G. Beale
Centre for Civil Engineering, Oxford Brookes University, United Kingdom
H.H. Lau, M.H.R. Godley, R.G. Beale, "The Influence of Column Base Connectivity on the Carrying Capacity of Columns", in B.H.V. Topping, (Editor), "Proceedings of the Eighth International Conference on Civil and Structural Engineering Computing", CivilComp Press, Stirlingshire, UK, Paper 25, 2001. doi:10.4203/ccp.73.25
Keywords: baseplates, column, connectivity, pallet racks, buckling, stability.
Summary
Storage racks fabricated from coldformed sections are often installed on flat
floors without any substantial connection between the floor and the column.
Previous research into storage racks has primarily been concerned with
investigations into the behaviour of the beamtocolumn joints and the overall
stability of frames with semirigid joints[1,2,3,4].
The effects of base connectivity on
the overall stability of storage rack frames has received little attention.
This paper investigates the failure mechanisms of columns with slenderness
ratios varying from 50 to 200 both theoretically and experimentally. The model
comprises a single column with one end pinned and the other end flat and which is
subjected to a combined axial load and a side load applied at the middle of the
column. The flat end is treated as being fixed, when it is in contact with the ground,
or as an eccentrically loaded, pinned connection rotating about one edge. The model
is representative of a member in the middle of a storage rack where the baseplate
connecting the column to the ground is often only lightly bolted and is normally
considered as pinned. A previous paper by the authors[5] investigated a slender
column, using elastic stability functions[6], and concluded that such a column,
resting on a flat base, was able to achieve failure loads in excess of the Euler pinned
buckling failure load. Storage rack columns typically have slenderness ratios
between 100 and 150 and plasticity occurs at the columnbase and beamcolumn
intersections. This paper extends the earlier work to consider the influence of plastic
hinge formation on the failure mechanism of the column.
The paper investigates the different failure mechanisms that can occur for a
column on a flat base. The mechanisms are: failure by buckling as a column on a
fixed base; failure by buckling as a column on a pinned base, including
complementary paths; failures by buckling with plastic hinges at base and at the
centre. In the analyses it was assumed that as the axial load increased the side load
was increased in proportion. The theory shows that for a small side load that a
column on a flat base behaves as if it were a column on a fixed base. The load
deflection curve follows that of a fixed base. This path then intersects with a
complementary descending pinnedend path producing a bifurcation. (See Figure 25.1(a).)
This bifurcation load is in excess of the Euler pinned buckling load. If the side load
is large then the column immediately rotates about one edge of the base and cannot
carry a load in excess of the Euler load. Similar phenomena occur for stockier
columns where intersections with elastic rising load paths and plastic descending
paths produce bifurcations.
In order to verify the analysis a series of experiments was carried out. Mild
steel square hollow sections of different lengths had a flat plate welded on one end
and a pinned connection made at the other. Each specimen was placed in a
Losenhausen column testing machine and a small axial load applied to hold the
specimen into the rig. A side load was then applied at the centre of each specimen.
Each specimen was then loaded to failure under displacement control. Although the
theory described above was for proportional loading, a modified theory with a fixed
side load was also produced. Good correlation was achieved between experiment
and theory as can be seen in Figure 25.1(b). Formulae for the side loads below which
loads in excess of the Euler failure load can be achieved, are derived in the paper.
References
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