火災時の冷却過程における高力ボルト摩擦接合継手の応力変形挙動

<p> To investigate stress and deformation behavior of steel structure in fire, it is important to consider behavior of friction type high strength bolted joints during not only heating phase but also cooling phase. The purpose of this study is to clarify stress and deformation behavior of the joints during cooling phase in fire. Failure of the joints may occur due to tensile forces of the connected beam under cooling phase during decay period in fire. Furthermore, strength degradation of the high strength bolt steel which experienced high temperature cause the bolt in shear failure in fire. However, there was few research with the test which focused on the deformation behavior of the joint during cooling phase.</p><p> This paper reports on results of tensile tests of friction type high strength bolted joints during cooling phase and the numerical analysis on the basis of component based model. Post-fire-heating tensile tests were carried out in order to obtain the maximum strength of the joint after fire. This test was carried out on 6 specimens of the joint. The main test parameters were steel temperature and main plate thickness. Cooling-phase restraint tests, which simulated the development of tensile force during cooling phase, were carried out on 2 specimens of the joint. In addition, finite element analysis on the basis of component based model were carried out to discuss the behavior of the joint during cooling phase. The follow conclusions could be indicated from this research.</p><p> 1) Result of post-fire-heating tensile tests indicated that failure mode of the friction type high strength bolted joint could be changed from plate tear-out failure to bolt in shear failure. This is caused that strength of the bolt decrease considerably after fire heating. Maximum tensile resistance of the tests approximately agreed with the calculated result on the basis of the tensile tests of the employed steel plate and bolt.</p><p> 2) In case of the specimen which designed to investigate the behavior of plate tear-out failure, the sufficient deformation capacity was confirmed because of the ductility of the plates with a bolt hole. To prevent failure of the joint during cooling phase in fire, the tear-out failure of the steel plate is better than the bolt in shear failure.</p><p> 3) In case of the specimen which has much thickness of the main plate, the specimen failed with bolt in shear failure due to development of the tensile force at the joint during cooling phase. Damage of the bolt at high temperature affected maximum strength of the joint during cooling phase.</p><p> 4) The numerical analysis result of the joint with plate tear-out failure approximately agreed with the test result on increasement of the tensile force due to shrinkage of steel and restraint of axial displacement at both ends during cooling phase.</p><p> 5) Influence of shear deformation of the bolt at elevated temperature on the resistance of the joint during cooling phase was indicated by the numerical analysis results of the joint with bolt in shear failure.</p>