Laterally unrestrained bearing strength of hot-wet conditioned pultruded FRP material

Presented in this paper are test results of a study pertaining to the reduction in bearing strength due to the effect of hot-wet conditioning on specimens cut from a polyester matrix based pultruded FRP structural shape. A total of 100 coupons (for 20 batches of five) were immersed in distilled water for three and six months at a constant temperature of 40°C. Subsequently, they were load tested using stainless steel ‘pins’ of M10 and M20 sizes with material orientations of 0o, 45o and 90o to the direction of pultrusion. Furthermore, this test series considered the effect of loading with and without bolt thread in the bearing zone. Testing employed a non-standard set-up that accommodates smaller test coupons, allowing material to be sourced from the web and flange of a 254×254×9.53 mm wide flange shape. An evaluation of the salient results provides characteristic bearing strength values (in accordance with Annex D of EN1990) and comparisons are drawn between equivalent strengths for non-aged (zero months) material from a previous test series. The degree of strength reduction is found to be influenced by both the ‘pin’ size and type, and observations are drawn towards the safe and reliable design of bolted connections

Virtual characterization of delamination failures in pultruded GFRP angles

This paper deals with the application of cohesive zone models to study delamination failures in leg-angles of pultruded glass fibre reinforced polymer material using the general-purpose finite element software Abaqus. The objective of the study is present a finite element modelling methodology that can, for example, help to fill-in knowledge gaps in the available experimental data pertaining to the tying force resistance of angle-cleated jointing in frame construction. It may be used to optimize cleat shape and laminate lay-up (dependent on composite processing method) for the strongest cleat against a minimum cost requirement. A benchmark example taken from literature is used to show that the numerical predictions from the authors’ simulations are reliable. The approach is next used to analyse an equal leg-angle component where one leg is fixed and the other orthogonal leg is being deformed by a tensile force applied over the free end surface. Numerical results from Abaqus are used to show that a lamination produced by the pultrusion processing method fails unstably by delamination cracks radiating around the curved region and extending into the leg panels. As a preliminary study to show the potential of the new modelling methodology it is used to show the influence of the radius of curvature at the junction between the legs on the tying force resistance; based on the load at delamination onset a smaller radius reduces the cleat’s strength

Plain and threaded bearing strength for the design of bolted connections with pultruded FRP material

Presented are results from testing 28 batches of 5 or 10 nominally identical specimens to characterise the laterally unrestrained pin-bearing strength when bolting is with and without thread. For the test series flange material is taken from a 254x254x9.53 mm Pultex® SuperStructural 1525 series shape. Strengths are measured with the Fibre Reinforced Polymer (FRP) material oriented at either 0° or 90° to the direction of pultrusion. Four steel bolt sizes of M10, M12, M16 and M20 are used, and when threaded there are different standard teeth (pitch) geometries. To remove this variable in a comparison with plain pin strengths a unique test series of 12 batches was carried out with three non-standard thread profiles. The effect on pin-bearing strength of having a threaded bolt is evaluated using mean and characteristic strengths, the latter determined in accordance with EN 1990. A key finding is that the proposed reduction factor of 0.6 in a forthcoming American LRFD standard to calculate a thread characteristic strength from the plain value is acceptable. Other findings are important to the determination of pin-bearing strength, and to us having knowledge and understanding to prepare a universal design procedure for resistances in bolted connections when the mode of failure is bearing

Aspects of bolted connections in pultruded fibre reinforced polymer structures.

This thesis presents an extensive test programme for bolted connections using SuperStructural Pultruded Fibre Reinforced Polymer (PFRP) materials with an emphasis on characterising strengths for the pin-bearing failure mode and linking coupon results to bearing failure in lapshear bolted connections. The motivation for the research is to address key gaps in knowledge that are known to be hindering the preparation of recognised design guidelines for PFRP (frame) structures, which upon becoming available shall broaden exploitation in civil engineering works. Prominent among these knowledge gaps has been the need to have statistically verified pinbearing and bolted connections strengths that are with connection configurations complying with current design practice. Thread in bearing, as found in practice, is investigated together, for the first time, with the plain shaft situation. Both as-received and environmental (hot-wet aging) conditioned PFRP materials are characterized to study long-term behaviour. A nonstandard pin-bearing strength test methodology, developed at The University of Warwick, is used to provide targeted test results for a comprehensive test matrix of 150 batches having 5 or 10 nominally identical specimens per batch. A key contribution from the pin-bearing strength characterisation is that the in-house test method (WUTS) is shown to be suitable for the determination of pin-bearing strengths for flange and web materials, for bolting with or without thread and sizes from M10 to M20, and with a PFRP material orientated at 0o, 45o or 90o to the direction of pultrusion. Thread in bearing does not always have an adverse effect, and it is found that both thread pitch and material orientation have a significant contribution on the measured pin-bearing strength. It is recommended, for the situation when thread is in bearing, a reduction factor of 0.7 is applied to the characteristic plain pin-bearing strength value in the bearing strength equations. Accelerated aging regimes and long-term strength prediction modelling has shown a mean pinbearing strength reduction of up to 25% over 7.8 years, at UK service temperature of 10.5 °C. This value is found to lie within the bounds set by an American Load and Resistance Factor Design (LRFD) Pre-standard and gives confidence to the mandatory design requirements. The thesis also reports on a series of strength tests following the methodology for pin-bearing characterization with single and double lap-shear bolted connections having configurations for single and two-rows, and for single and multi-bolts. Reported are a series of open-hole tension tests carried out to characterise the by-pass load situation in multi-rowed connections. A reduction factor of 0.6 between single and double lap configuration is found, with the possibility of multiple mixed failure modes, including block shear. The SuperStructural material has a tri-axial stitched fabric mat reinforcement (usually in pultrudates the mat is a continuous filament mat) which is influencing the strength of bolted connections. Using the procedure in Eurocode 1990, a partial factor of 1.3 for pin-bearing resistance has been calibrated by combining the WUTS and lap-shear bolted connection tests results. Results from an open-hole tension study have shown that the correlation coefficient proposed in the 1970s by Hart-Smith does not satisfactorily relate the isotropic stress concentration factor to the orthotropic stress concentration factor. The findings and recommendations from the 1500 individual and 230 batch strength test results presented in this thesis have been successful in addressing or partially addressing a number of the key gaps in knowledge