Bolt attachments of composite materials under conditions of climatic ageing

Introduction: the glass-fibre reinforced plastic (GFRP) is a composite material that found wide application in construction due to its unique properties. One of the techniques of joining composite units is a bolt attachment that is distinguished by its stability and manufacturability. Owing to relative novelty of the material, there is no comprehensive experimental database and it is impossible to define the corresponding reliability coefficients. The given problem can be solved by means of accelerated climatic tests, which will replace multi-year observation over the installations and will allow conducting precise calculations during design work right nowadays. Materials and methods: the climatic tests were conducted over samples fabricated from polymeric structural pultrusion profile GFRP for construction purposes produced by Research-and-Production Enterprise ApATeCh (Moscow). The samples were fabricated from a single batch of U-channel 388 × 120 × 10/12 (SPPS-340). The test method consists in sequential cyclic exposure of artificially created system of climatic factors (elevated air temperature and humidity, negative temperature, temperature gradients) to the tested samples and determination of material property variations under the described impacts in the main indicators or the indicator responsible for workability of the material. Results: the obtained data were processed and the strength-time variation dependences were presented in graphic form. Using approximating dependences, the strength reduction coefficients of the bolt attachment were calculated for 100-year thermomoist exposure. Conclusions: any significant influence of ultraviolet exposure to strength of the bolt attachments was not revealed. 100-year thermomoist exposure will reduce the bolt attachment strength by not more than one third. One can recommend to introduce revisions in normative documents including reduction of reliability coefficient K2, allowing for GFRP maintenance ageing, from 1.2 to 1.13 in company standard “Road and construction structures from composite materials”.