Static and fatigue performance of resin injected bolts for a slip and fatigue resistant connection in FRP bridge engineering

This paper presents test results to evaluate the slip and fatigue performance of Resin Injected Bolted Joints (RIBJs) for pultruded Fibre Reinforced Polymer (FRP) material. The objective of the test series is to provide a robust method of connection for structural engineering that is both fatigue and slip resistant. Forty-six joints (using 23 specimens) were subjected to either static or combined static/cyclic loading at ambient room temperature. Ten specimens (five batches of two) had bolted connections without injected resin and were included to provide baseline static joint strengths. Sikadur®-30 and RenGel®-SW404 were the two cold-curing epoxy based resins used to fabricate the 13 RIBJ specimens. Testing was conducted with double lap-shear joints in accordance with modified guidance from Annex G and Annex K in standard BS EN 1090-2:2008. The specimen’s geometry was established using this British Standard and an American Society of Civil Engineers pre-standard for pultruded thin-walled structures. Rectangular plates for the lap joints were cut from either a wide flange section of size 254×254×9.53 mm or a flat sheet of 6.35 mm thickness. Bolting was with either M16 or M20 steel threaded bolts of Grade 8.8. Sixteen specimens, for eight batches of two specimens were failed in a short duration for static strength. Four RIBJ specimens had static load cycling to an assumed service load level. Three specimens out of 23 were subjected to staged static and cyclic fatigue loadings to determine stiffness changes, life-time ‘slip’ load and residual joint strength. The reported results are evaluated for slip and fatigue performance and the main finding is that resin injection shows much promise as a mechanical method of connection in pultruded FRP structures

Mechanics of Confined Thin-Walled Cylinders Subjected to External Pressure

Motivated by practical engineering applications, the present paper examines the mechanical response of thin-walled cylinders surrounded by a rigid or deformable medium, subjected to uniform external pressure. Emphasis is given to structural stability in terms of buckling, postbuckling, and imperfection sensitivity. The present investigation is computational and employs a two-dimensional model, where the cylinder and the surrounding medium are simulated with nonlinear finite elements. The behavior of cylinders made of elastic material is examined first, and a successful comparison of the numerical results is conducted with available closed-form analytical solutions for rigidly confined cylinders. Subsequently, the response of confined thin-walled steel cylinders is examined. The numerical results show an unstable postbuckling response beyond the point of maximum pressure and indicate severe imperfection sensitivity on the value of the maximum pressure. A good comparison with limited available test data is also shown. Furthermore, the effects of the deformability of the surrounding medium are examined. In particular, soil embedment conditions are examined, with direct reference to the case of buried thin-walled steel pipelines. Finally, based on the numerical results, a comparison is attempted between the present buckling problem and the problem of "shrink buckling." The differences between those two problems of confined cylinder buckling are pinpointed, emphasizing the issue of imperfection sensitivity