Abstract
Tests to determine the structural capacity, failure modes and the economy of the eaves region
of double-bay portal frames made from cold-formed lipped channels connected back to back
at the eaves joint are presented. Two double-bay portal frame eaves joint configurations,
namely; Eaves Connection Type 1 (ECT-1) and Eaves Connection Type 2 (ECT-2) are
investigated. In ECT-1, two rafters are connected to the column back-to-back with one rafter
connected to the column at a lower level than the other while, in ECT-2, two rafters are
connected to the column at the same level through a hot-rolled steel gusset plate.
Variables in the frames include the width of the channel flanges, strength of the channels,
number of bolts, and thickness of the hot-rolled gusset plate. The joints are subjected to equal
loads applied through pins at points of contraflexure until failure. Failure modes and
experimental results are observed, recorded and analysed. A comparison between theoretical
and experimental results is drawn up and analysed.
In all the tested structures (ECT-1 and ECT-2), the cold-formed channels failed but the joints
did not fail. Local buckling in the compression zone of the web and flange of the channels,
bolt-bearing deformations and lateral deflection of gusset plates (in ECT-2 only) are the three
modes of failure which were observed. Local buckling in the compression zone of the web
and flange of the channels was the initial and ultimate failure mode in all structures.
The moment-curvature graphs show that plasticity could not be achieved in both connections
(ECT-1 and ECT-2). The unfactored resistances of the channels are not achieved by all the
joints because of local buckling and bolt-bearing deformation failure. Both theoretical and
experimental results show that the two investigated joints are semi-rigid and partial-strength
joints since they possess some degree of rotational stiffness and moment capacity, but are
insufficiently stiff to develop full continuity and unable to achieve full moment capacity of
the connected members at the eaves joint.
Furthermore, the investigation shows that ECT-1 is the most economic joint from a structural
and material cost point of view, compared to ECT-2 joints. However, ECT-2 joints are...
M.Phil. (Civil Engineering)