Hysteretic Behavior And Design Criterion Of Beam-To-Column Web Connections In Steel Moment Frames Under Cyclic Load

During the Northridge Earthquake and Hyogoken-Nanbu Earthquake, beam-to-column connections of steel frames experienced a great deal destruction.Then analyses of response and damage mechanism of beam-to-column connections under seismic load was widely studied in the world, but few people conduct the research on seismic-resistant behavior of beam-to-column web connections. Due to moment resisting connections are made in both directions in steel frames, so beam-to-column web connections are generally as flange connection. The construction and performance under load of web connections are different from flange connections, and there are more difficulties for theory analysis and design. Studies on mechanism of beam-to-column web connections under cyclical load are not only significant to the theoretical research, but also important in practice.A nonlinear finite element model is constructed, considering the large deformation, large strain, bolts pretension, bolt contact-slide, as well as material harden and soften, and Miese yield criterions and double nonlinear 3-D element are adopted, so it can predict performance of beam-to-column web connections under cyclic loads. After the verifications of triple nonlinear FEM involving geometry, material and status by test results, study on response under monotonous load and hysteretic behavior under cyclical load of 18 classifications include 59 specimens. The research is the first in the world. Plastic rotations of most specimens are between 0.024 and 0.028 rad. According to computation results, study on stress distribution of beam-to-column web connection and damage mechanism of connection weld under cyclical load show, the primary reason that causes beam flange connection weld brittle fracture is that stress connection exists at both beam end under seismic load and three directions stress have same sign; beam section near shear tab edge suffers biggest force; because configuration of weld access hole is not continuous and other reasons, so they cause stress distribution of beam section near connection is very different from classic theory; shearing stress curve of shear tab and beam web section near connection along beam height is reverse parabola, and the complex stress concentration exits at both end. A systematic parametric computation on the behavior of web connection is carried out, the parameters such as: column flange thickness, column flange width, beam depth, beam flangethickness, axial pressure on column, pretension of high -strength bolts, beam span, steel and welding strength, continuity plate width and stretch length, column reinforcing ribs on the far sicte of beam, configurations of weld access hole, weld backing bar and so on; Study and compute on reduced beam section connection and middle joints. Then draw lots of useful conclusions, shear tab strength formulation, equation between axial pressure ratio of column and bearing capacity of beam-to-column connection, and so on. According to results, the article gives out design recommendations on computation and construction of steel frame web connection to improve seismic-resistant behavior.In conclusion, the FEM Model can well simulate the behavior of beam-to-column web connections under cyclical load. The study is rather comprehensive and systematic. The conclusion and design recommendations are very useful for revising design specifications and guiding design of engineering. This article will play a basic role in the further study on beam-to-column connections and analyzing the seismic- resistant behavior of whole strucure.