Robustness of simple joints in pultruded FRP frames

Structural robustness of simple beam-to-column joints in pultruded frames is assessed through tension pull tests.
The tying capacity and failure modes are determined from static tests on two batches of specimens for six joints.
Tying resistance is an important joint property for maintaining structural integrity in frames in case of accidental
loads. No tests have been previously reported to investigate this key structural property for the design of
Pultruded Fibre Reinforced Polymer (PFRP) structures. The tension pull tests consist of a PFRP Wide Flange
(WF) section bolted to a stiff steel baseplate by a pair of PFRP web cleats, and at the other end the tensile load
is applied. One batch of three specimens has a WF 254 × 254 × 9.53 mm section with 100 × 9.53 mm cleats of
equal leg-angle material and the other has a WF 203 × 203 × 9.53 mm with angles of size 75 × 9.53 mm. Tension
versus displacement curves are plotted to establish linear-elastic response, damage onset, non-linear response
and ultimate tensile strength. Damage initiation is characterised by audible acoustic emissions. The load–
displacement curve remains linear elastic up to 0.35 to 0.4 of the maximum (ultimate) tension force and damage
happens at 0.6 of the ultimate value. Failure is from excessive delamination cracking emanating in the region of
a cleat's fillet radius. A model to predict tying resistance is proposed, and successfully calibrated against experimental
results. The most important finding of this study is that a pair of 9.53 mm thick PFRP leg-angle web cleats
should possess an adequate tying capacity for design against disproportionate collapse.