Numerical Simulation Analysis Of Semi-rigid Beam-to-column Connections With Less-tightened Or Super-tightened Bolts In Portal Steel Building

Recent several years,high-strength bolts widely are used in steel connections. Generally high—strength bolts are random checked.So the parts of high-strength bolts maybe escaped examination in strict-requirement connections bolted. Even according to the requirement of standrad construction,high-strength bolts possibily are super-tightened.It is easy to meet with the less-tightened or super-tightened bolts in pratical projects.The so-called less-tightened bolts mean that hige-strength bolts pretension is less than the standard bolts pretension.The super-tightened bolts is opposite to less-tightened bolts. The less-tightened bolts cause anti-shear capacity loss,and super-tightened bolts cause screws delayed fracture.That will bring the connects with hidden danger.Based on experiment datas and reference documents connected less-tightened or super-tightended, the typical extened vertical end-plate connection is studied in this paper.In this connection, eight high-strength bolts are used to connect beam with coloum.The connection is simulated by FLM, when two bolts are less-tightened or super-tightended in upper half part of four bolts in end-plate. The magnitude of less-tightened is divided into three groups:15%,25%,35%.The magnitude of super-tightened is divided into two groups:15%,.25%.Based on the analysised result of datas from FLM, this paper studies the stress distribution in end-plate, the joint elastic rotational stiffness changes and the flexural and shear capacity.Some conclusion are concluded.as follows:1 Less-tightened or super-tightened high-strength bolts will cause much stress in the beam web and end-plate contect zone.So when we design connections,we should adopt some preventive measures to decrease these much stress.2.less-tightened or super-tightened strength bolts both affect the joint rotational stiffness.The joint rotational stiffness decrease as strength bolt is less-tightened. The joint rotational stiffness increase as strength bolt is super-tightened. Less-tightened or super-tightened strength bolts don't change the ultimate flexural capacity,only elastic flexural capacity. 3.When high-strength bolts are installed, the rotational stiffness loss is much big.So how to early prevent the rotational stiffness loss is important for project danger.4.Compared normal conditions to super-tihhtened conditions,the materials is more full used.5. It is necessary to prevent super-tightened bolts in seismic areas and vibration environment connections.