Engineering Structures Group

Mechanical Property Characterisation of Pultruded GRP Material

[EPSRC Funded] Dr Y Zhang, Dr P Wang, D Dawson, Prof M J Joyce, Dr G J Turvey

A pultruded GRP I-profile with its web-flange junction tested in flexure

The research has been focused on the characterization of the mechanical properties of pultruded GRP structural sections, including flat plate and I, channel and angle profiles. An extensive investigation of the open-hole strength of flat plate has been completed [3]. It has been shown that two failure criteria, both of which are frequently used to predict the failure of laminated aerospace composites, are not applicable to pultruded GRP plate.

An important mode of flexural failure, which often arises in pultruded GRP I-profiles and box-sections, is separation of the flanges from the web(s). The fibre architecture of the web-flange junction is significantly different from that of the flanges and web(s). Consequently, its strength characteristics are also different. In order to be able to predict the collapse of pultruded GRP profiles, it is essential to evaluate the stiffness and strength properties of the junctions. A variety of test fixtures have been developed and used to determine the stiffnesses and strengths of web-flange junctions subjected to tension, shear and bending .
A preliminary investigation has also been completed on the strength of webs of pultruded GRP profiles.

Further Information

See publications[8, 10 - 12, 27, 30, 36, 38, 41 & 42]

Flexural, Buckling and Vibrational Response of Pultruded GRP Plates

F Rangognio, F Bourdet, J Alamatian, Prof M Khadkodayan, N Mulcahy, Dr G J Turvey

The use of composite materials in engineering structures of various kinds is continuing to increase as designers become more competent at exploiting their inherent advantages, eg. low mass, high stiffness, ease of fabrication etc. However, current understanding of the flexural behaviour of pultruded GRP plates remains limited. This project was concerned with using the ANSYS FE software to model the elastic large deflection response observed in lateral pressure tests on circular unstiffened/stiffened GRP plates. Reasonable correlations between theory and experiment were achieved. Further analytical studies of the small and large deflection of pressure loaded unstiffened orthotropic clamped circular plates have been completed recently and are in the process of being reported.

Likewise, the vibration response of pultruded GRP structures is not yet well understood. An investigation of the free vibration response of clamped circular plates with central circular cut-outs was completed recently. The NASTRAN FE software was used to predict the natural frequencies and mode shapes observed in small scale plate vibration tests and reasonably good correlation was achieved.

Further Information

See publication [33]

Flexural Behaviour and Design of Pultruded GRP Beams with Semi-Rigid End Conditions

R J Brooks, Dr G J Turvey

Pultruded GRP beams have several advantageous characteristics compared to steel and aluminium structural profiles, eg. low self-weight, high corrosion resistance etc. However, these are offset to a large extent by their low flexural stiffness (nearly and order of magnitude lower than their metallic counterparts). Moreover, for pultruded GRP profiles the range of profile sizes is relatively small and the size increments are relatively large, compared to steel profiles. The consequence of these negative attributes is that, GRP profiles have difficulty in competing with metallic profiles for beam applications. This is exacerbated when the simple design method is used, because the beams are assumed to have simply supported ends, irrespective of their actual end conditions.

Three-point flexure test on a simply supported CFRP stiffened pultruded GRP beam.

One approach to achieving greater flexural efficiency with the current range of pultruded GRP profiles is to replace the simple design method with the semi-rigid design method, which takes account of the rotational stiffness of the beam’s real end conditions. New equations have been developed for the semi-rigid design of pultruded GRP beams. The equations also take into account the shear flexibility of the profiles. Beams with bolted GRP and stainless steel end connections have been tested and the deformation data have been used to check the accuracy of the design equations.

Investigations of other approaches to enhancing the flexural stiffness of pultruded GRP beams have been undertaken. One approach which has found widespread use in concrete beams is to bond high modulus CFRP strip to the soffit. This technique has been investigated for pultruded GRP beams. Simple design equations have been developed for practical load cases. The equations have been verified by using them to predict deflections, curvatures and strains observed in tests on CFRP stiffened GRP beams with a variety of bolted end connections.

Further Information

See publications [2, 13,17 & 32]

Elastic Buckling and Failure of Pultruded GRP Plates Beams and Columns

[EPSRC Funded] F Lippens, G Tzokas, Prof W Wei, Dr A Afifi, Dr Y Zhang, Dr K Zied, D Dawson, Prof M J Joyce, Dr G J Turvey

Extensive investigations of the initial buckling, postbuckling and collapse behaviour of unstiffened and CFRP stiffened I-section pultruded GRP columns and short GRP angle and channel section columns have been undertaken. Supporting investigations have been undertaken on the elastic buckling and postbuckling of unstiffened/stiffened pultruded GRP plates and beams. The ANSYS FE software has been used to simulate the elastic initial buckling, postbuckling and initial failure responses of a large number of failure tests on unstiffened/stiffened GRP columns. In general, the correlations between the experimental and predicted responses have been good. A high speed video camera has also been used to capture the brittle failure modes of several columns.

Bolted and Bonded Tension Joints in Pultruded GRP Materials

[EPSRC Funded] Dr Cooper, D Skitskas, Dr J T Mottram, Dr P Wang, C Friloux, Dr G J Turvey

Three-point flexure test on a simply supported CFRP stiffened pultruded GRP beam.

The behaviour of double-lap single bolt tension joints in pultruded material has been investigated both theoretically and experimentally. More than seven hundred joint tests have been carried out in order to gain an understanding of the factors, which dominate joint strength and determine failure modes . Much of the recent joint testing has been directed towards evaluating the effects of hot-wet conditioning on joint strengths and failure modes . In parallel with experimental investigations, FE analyses have been undertaken to evaluate stresses in joints and this information has been used to evaluate the accuracy of current design procedures for bolted tension joints .

Recently, the research on bolted joints has been extended to bonded tension joints. An investigation in which more than 150 bonded edge and side-lap joints fabricated from plate material has been completed. Stiffnesses, strengths and failure modes have been quantified.

Further Information

See publications [4, 15, 16, 18, 22, 23, 26, 29, 39, 40 & 44].

Bolted Joints in Pultruded GRP Beam and Frame Structures

[EPSRC Funded] Dr C Cooper, Dr G J Turvey

Beam to column bolted web cleat connections tested in combined in-plane bending and shear.

Mechanical fastening is the preferred mode of connection for pultruded GRP beam and frame structures. Knowledge of the rotational stiffness and strength characteristics of bolted joints is essential for the efficient design of such structures. Unsurprisingly, over the past decade and a half a large number of bolted joint tests have been reported. Recently, a critical review of fifty or so of the most comprehensively reported joint tests was completed [5]. In addition, a critique of pultruded GRP frame design has also been completed [25].

Even though many tests to determine the moment – rotation response of bolted joints in beam structures have been reported, knowledge of some aspects of connection behaviour remains scant. For example, the effect of end connections on torsional response of beams has not been adequately explored. A preliminary investigation of the torsional response of pultruded beams with bolted cleat end connections has been completed recently [35].

Pultruded GRP Beam and Structural Systems

[NWCC Funded] I Tsafos, M Hulland, Dr G J Turvey

A system of pultruded GRP profiles has been developed for the assembly of a wide range of lightweight sub-structures and/or complete structures. The system embodies a number of novel features, which exploit the availability of low cost mechanical fasteners for their rapid assembly. Initial research has focused on proof-of-concept testing, some of which is reported in [24].

A novel hybrid approach, which utilizes the UK’s only Quickstep manufacturing facility, is being developed as part of a North West Composites Centre (NWCC) investigation into the rapid manufacture of enhanced stiffness pultruded GRP beam profiles.