Tension‐shear interaction of high‐strength bolts during and after fire

Abstract

Connections in steel structures play an essential role in the structural stability of the entire construction. This is also true in the event of a fire. The difficulty in designing connections for fire lies in the fact that not only material properties, but also loads applied to the connections change depending on temperature. In addition, the temperature‐dependent decrease in the tensile strength of high‐strength bolts does not coincide with the decrease in shear strength. So far, the influence of combined tension and shear loading on high‐strength bolts has not been studied in detail. This project included carrying out interaction tests on high‐strength bolts of property class 10.9 (fu = 1000 N/mm2). Post‐fire performance was examined in addition to observing the loadbearing behaviour during fire. The examinations were completed with additional material tests. The results were compared with earlier research on the temperature‐dependent loadbearing capacity of high‐strength bolts during and after temperature loading as well as on the loadbearing behaviour of bolts in steel structures under combined tension and shear loads. This investigation contributes to a better understanding of the loadbearing capacity of high‐strength bolts under combined loading during and after a fire.

Behaviour of stainless and high strength steel bolt assemblies at elevated temperatures — A review

“…Relative strength between mating threads [7,10] Friction between mating threads Implicitly included in the reported studies but there is no clear conclusion Galvanization [7,13,18] Lubrication No studies reported Pretension Fan et al [8] Effect of washers No studies reported Applied load (static or dynamic) All reported studies adopted low strain rate except [7] exploited high strain rate of 0.02min −1 .…”

“…Combined stress Only one study [18] Temper temperature level Implicitly included in the reported studies but there is no clear conclusion Chemical compositions Implicitly included in the reported studies but there is no clear conclusion [22], British [27] and Japan [28] standards…”

“…Liquid metal embrittlement (LME) failure, as observed in a limited number of tests on high strength bolts by [7,13,18], is due to the instability of platings and coatings at high temperatures. LME of galvanized steel bolts occurs when there is a simultaneous application of stress and high temperature.…”

“…A very limited number of tests have been conducted on bolts subject to combined tension and shear at elevated temperatures, with only one dataset currently available [18]. In the work by [18], the resulting combined stress reduction values lie between the test results for pure tension and pure shear. Notwithstanding these results, the number of the tests conducted is not enough to drive a reliable conclusion about the effect of combined stress on the bolt reduction factor during a fire.…”

“…European designations will be used hereafter, however, when a specific reference is being discussed, the designation of the reference will be adopted. Table Tested parameter at ambient temperature during the last century Re-evaluation at elevated temperature during the last two decades Bolt grade 10.9 [8,[12][13][14][17][18][19] Bolt grade 8.8 [7, 10-12, 14, 17, 20] Bolt grade 5.6…”