Structural Behaviour Of Moment Conections Between Cold Formed Steel Beam-columns

In this paper, a combination of laboratory tests and finite element analyses was used to investigate the seismic performance of bolted moment connections between cold-formed steel sections. The configuration of bolted moment connections is:(1) All structural members such as beams and columns are formed with two lipped C-sections back-to-back; (2) Moment connections between beams and columns are formed with hot-rolled steel gusset plates; (3) Only the webs of lipped C-sections are bolted onto gusset plates with high strength bolts; (4) Four high strength bolts per member are used as a minimum configuration.Five cold-formed steel external joints were tested under cyclic loading to measure the strain distribution of the connection members as well as M -Φand P -Δhysteresis curves. The structural performance of those specimens with different configurations such as thickness of the gusset plate, the bolt pitch and pre-tension load was analysed. Also, the failure mechanics, stiffness regression, hysteresis property, ductility and dissipative characters were discussed. Among the tests, only one mode of failure was identified: flexural failure of connected sections. Five joints can be divided into two groups according to the rule whether the bolts slip or not--GroupⅠand GroupⅡ. High moment capacity, stable capacity degradation, high initial stiffness, severe degradation of stiffness, good energy dissipation capability and ductility were summarized on the basis of test data of GroupⅠwhile GroupⅡcan achieve bad ductility .A simple method employing shell elements and spring elements was explored in finite element analyses to simulate the bolted connections. This method possessed advantages such as modeling easily, calculating quickly, and higher accuracy compared with test results. 3-D parameter finite element models were established to investigate performance of bolted moment connections between cold-formed steel sections. Eighteen specimens was designed with orthogonal design method and calculated, the results were analysed with mathematical statistical methods. It is found that sliding load P_slip depends on bolt diameter and pitch while the maximum load P_max is determined by yield strength, section thickness and height of cold formed steel. Once the section of cold formed steel is chosen, the diameter of the bolt has remarkable influence on the structural performance while the initial stiffness of connections depends largely on thickness of gusset plate.Finally, the rules were proposed for engineers concerned to design this sort of connections.