Optimization of the test procedure for slip factor tests according to EN 1090‐2

Abstract

Slip‐resistant connections are always used when slip and deformation in a bolted connection must be avoided at all costs, e.g. in radio masts and bridges. For some popular surface treatments, slip factors are given in EN 1090‐2, the execution standard for steel structures. For those surface conditions not considered in EN 1090‐2, the slip factor can be determined experimentally according to Annex G of EN 1090‐2. By reviewing slip factor values obtained with the Annex G test procedure and reported in the literature, it becomes obvious that in most cases the slip factors achieved experimentally are not comparable for identical surface conditions. This is potentially caused by different interpretations of the Annex G slip test procedure. As the slip factor is one of the main parameters influencing the bearing capacity of slip‐resistant connections, its determination should be on the safe side and not dependent on the various interpretation possibilities of the test procedure itself. For this reason, the optimization of the Annex G test procedure was thoroughly investigated in the European RFCS research project SIROCO, with the final objective being to enhance its reliability. The focus was on investigating the various test parameters such as type of preload measurement, ascertaining the possible slip planes, test speed, position of slip measurement, clamping length, preload level, evaluation of critical slip load and the performance of the extended creep test. The results achieved in these investigations have already been partly implemented in the revision of the current draft version of EN 1090‐2.

Behaviour of lockbolts in slip‐resistant connections for steel structures

“…The absolute loss of preload is obtained according to Eq. (14) and is approximately equal to the experimental result (mean ΔF p,C,setting = 11.6 kN).…”

“…Therefore, the preload was measured by strain gauges in the bolt shank. The full description of the measurement and calibration procedure will not be given at this point and instead the reader is referred to [14]. Fig.…”

“…The detailed procedure for carrying out the slip load test is given in Annex G of EN 1090-2 [12]. More detailed information on the test procedure can also be found in [14], [17], [18]. This paper focuses on the presentation and evaluation of the results of the slip load tests.…”

“…The load level for the ECT is based on the mean slip load F Sm , evaluated as the maximum load that occurs during the slip load test to consider the physics of the connection. The load level derived from the step test, which was developed in the research project SIROCO [1] and in [14], is 90 % of F Sm . Using this load level, an ECT was performed for both specimens, HV_Al-SM_289-290_15 (test load F = 461.7 kN) and…”

Comparative numerical investigations into the determination of slip factors according to the EN 1090‐2 and RCSC

“…The results show a noticeable loss of preload at slip when the tests are performed in tension according to EN 1090-2. The same phenomenon has been also observed from experimental investigations, see (7). 3 (a) and (b) show that by increasing the clamping length ratio the loss of preload decreases.…”