Unexpected brittle failure in steel rigid frameconnectionsby concentrated tensions on the welded area and connectionvulnerability in high ductility demands as occurred during the Northridge (1994) and Kobe (1995)has challenged ductility properties and ability to absorbs More
Unexpected brittle failure in steel rigid frameconnectionsby concentrated tensions on the welded area and connectionvulnerability in high ductility demands as occurred during the Northridge (1994) and Kobe (1995)has challenged ductility properties and ability to absorbseismic energy in this type of structural system. So in design of this type of structural system, creating ductility and ability to withstand cyclic large deformations is important. On this basis, in present study two new beam-to-column moment connections with reduced beam section by double orreverse arc-shaped fuseare studied in capacity design approach. The arc-shaped fuse, by removing flange and a part of web and replacing double orreverse arc-shapedin the section bending of the beam, resulted in a ductile fuse away from beam-to-column connections components, which prevents connection vulnerability in high ductility demands. The purpose has been numerically studied byfournumericalmodelsunder cyclic load using ABAQUS 6.10 finite element software. Obtained numerical results were compared with those of other studies. The numerical results show that arc-shapedfuse creates ductile fuses faraway from beam-to-column connectioncomponents and can satisfy acceptance conditions of special moment resistance connection based on AISC and FEMA. The arc-shaped fusecan increase drift story capacity up to 8% without any significant strength loss through increasing the out-of-plane stiffness of the beam longitudinal axis against lateral-torsional buckling.According toelasticflexural strengthandstiffnessof beam criteria,the reversearc-shaped fuseisabetter choicethan double arc-shaped fuse.
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ABSTRACT
One of the forces occurring during an earthquake is the tensile force that arise in the columns. This phenomenon is called ‘uplift’. It causes damage in column, base plate and anchor bolts. In the absence of app More
ABSTRACT
One of the forces occurring during an earthquake is the tensile force that arise in the columns. This phenomenon is called ‘uplift’. It causes damage in column, base plate and anchor bolts. In the absence of appropriate control it may cause the building to collaps. Knowing the reasons which lead to such phonomenon will clarify the point that such phonmenon needs to be controlled. The present study has tried to offer solutions by which the uplift in columns can bereduced. This study has tried to by offering solutions the uplift in columns is reduced. To do so, the numerical models for two buildings were applied in which the location of the braced were changed and the number of brace columns were increased hoping to reduce the uplift strength. For each building, a separate model was built. In the models the proposed ways to reduce uplift were applied. Both EBF and CBF types of the braces were assessed. The numerical results obtained from the study indicate that using the single brace at the corners of the building, aiming to neutralize the uplift does not seem to be appropriate and that even the existence of an additional intermediate frame braced for further support might be needed. The present study showed that the increase in the number of span bracing in different places (situations) are effective in reducing the uplift more than 50%. Also, CBF in lateral columns and EBF for intermediate columns are better ways to reduce uplift, and that different numerical results according to the location of the column in plane.
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The basic strategy of reduce the ductility demand and related concentrated tensions at moment resistance connections is reduce the section of the beam at connected region to column. By this method plastic hinge done at the reduced cross section and this local reduction More
The basic strategy of reduce the ductility demand and related concentrated tensions at moment resistance connections is reduce the section of the beam at connected region to column. By this method plastic hinge done at the reduced cross section and this local reduction decreases the demand of the components of connection. On this basis, in present study a new beam-to-column moment connection with reduced beam section using Tubular Accordion Web that called TAW-RBS is studied analytically. The results show that TAW-RBS create a ductile fuse away from beam-to-column connection components, through removing web from beam flexural capacity. Reduction of beam flexural capacity in the plastic hinge is calculated based on the dimensions of beam and tube. So bending strength of the remaining tubular web would be proportional with square of the thickness of tube and inversely related with the thickness of flat web and the diameter of tube. The optimal location of the tubular web is determined due to the length of beam and the plastic modulus ratio at the plastic hinge to the total cross section. Also shear control at tubular web according to local and global shear buckling are other points of this study. The results show that TAW-RBS reduces flexural stiffness about 14 to 19% in the plastic hinge locations that is equal with the RBS20%. Also the proposed connection, depending on the size of the beam, reduces bending strength between 22 to 28% in the plastic hinge location that is intermediate between RBS20% and RBS50%.
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