Experimental Investigation on the Effects of Temperature on the Bearing Capacity of High Strength Bolt Connections

High strength bolt connection is one of major method used in steel structure construction on site. Taking the form of slotted hole in bolt connection, it will be more convenient and efficient in construction since this form shows better tolerance in installation deviation. At present, there is less research focused on high strength slotted bolt connection while it is blank in the research field of high strength slotted bolt connection under high temperature. 14 tests were conducted according to different experiment schemes including standard or slotted hole high strength bolt connection and different test temperatures of room temperature, 130 ℃ and 200 ℃. Among these 14 tests, slippage in bolt connection was studied and variables including temperature, bolt hole style, bolt diameter and so on were considered. The high temperature strain gauge was adopted to observe the change of bolt pretension force throughout the tests.
The results indicated that: 1) From 20 ℃ to 130 ℃, effects of temperature on slipping load and displacement were measured. Reductions were observed while temperature rising to 130 ℃ and it showed 0.9%~4.3% reduction in anti-slip load, 7.5%~7.8% reduction in mean slip coefficient and 22.4% reduction in bolt pretension.2) From 130 ℃ to 200 ℃, effects of temperature were significant. Comparing to room temperature, reduction about anti-slip load of M30 bolt was 9% and 34% respectively for 130 ℃ and 200 ℃ while reduction about mean slip coefficient was 11% and 7% respectively. Irregular change of bolt pretension was observed under this temperature situation.3) Under room temperature, anti-slip load and mean slip coefficient were decreased in slotted hole bolt connection comparing to standard hole style. Such reduction weakened with the increasing of bolt diameter in slotted hole bolt connection. The anti-slip load dropped 11.0% and 4.0% while the mean slip coefficient decreased 12.0% and 10.0% respectively for M20 and M30 slotted hole bolt connection compared with standard hole style under room temperature.4) At 130 ℃, reductions of slotted hole bolt connection for anti-slip load and mean slip coefficient were 9.0% and 13.0% respectively compared with standard hole style. The reduction was greater at 130 ℃ than room temperature.5) Slotted hole bolt connection would aggravate the relaxation of bolt pretension. Reduction of M30 bolt-pretension was 16.3% for standard hole connection and 30.7% for slotted hole bolt connection. Difference of 14.4% was observed.6) From 20 ℃ to 130 ℃, mean slip coefficient of M20 bolt was about 30.0% greater than that of M30 bolt, indicating that the mean slip coefficient improves with the increase of bolt connection stiffness. However, mean slip coefficient of M30 bolt connection was 12.4% smaller than that of M20 bolt connection at 200 ℃ and there was error in the measurement of mean slip coefficient for M20 bolt connection.7) At 130 ℃, reduction of bolt pretension for M20 and M30 bolt connection was 28.4% and 16.3% respectively, indicating that the bolt pretension relaxation weakens with the increase of bolt connection stiffness. With the temperature increasing to 200 ℃, reduction of mean slip coefficient for M20 bolt connection became obvious and greater with higher discreteness than that of 130 ℃. However, pretension of M30 bolt connection showed up and down changes without obvious pattern for temperature rising to 200 ℃.