Effects of Changing Double Angles Configuration Used as Braces in Seismic Resisting Systems

Abstract:

Seismic resisting systems consisting of double angles are used in many parts of the world. Generally, these double angles are arranged in the shape of a T, with a very small distance between them. However, sometimes these angles are distanced and faced in order to improve their mechanical characteristics about the axis of symmetry. In the past, their design was made in the same way as the double angles arranged in a T shape, that is, considering the limit states of flexural buckling and buckling by flexural-torsional, but ignoring the properties of the connectors and their effect on the modified slenderness ratio, as well as the fact that in this case the warping constant is not negligible. These parameters are taken into account in this research in order to study the effects of increasing the distance between the connectors and their possible use as braces in seismic resisting systems. The theoretical results were compared with the experimental results of fifty-seven specimens tested in the laboratory of structures of the Universidad Nacional de Colombia – Sede Manizales. The models were classified according to the main angles, the connectors, the total lengths, and the width of separation. All of them were subjected to axial compressive stress, with free rotation at both ends. Three identical specimens of each model were constructed. The flexural buckling length about x-axis was limited to two meters in all specimens tested whereas the flexural bucking length about y-axis and flexural-torsional buckling length were not limited, i.e. these lengths are equivalent to the total length of each specimen tested. This in order that the critical limit state was to be the flexural-torsional buckling as a function of the torsional buckling term in Z, except in the models of class 2 in which this induced condition was not reached. This was proposed to better evaluate the torsional buckling term in Z. The experimental results show that the nominal compressive strength for the flexural-torsional buckling limit state, when it is governed by torsion, is undervalued. A new methodology is proposed for the calculation of the nominal compressive strength for the flexural-torsional buckling limit state, when it is governed by torsion.

• Periodical: Key Engineering Materials (Volume 763)
• Pages: 279-286
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.763.279
• Online since: February 2018
• Authors: Carlos Bermudez*, Oscar Gutierrez
• Keywords: Double Angles, Flexural-Torsional Buckling, Limit States

References

[1] AIS, Reglamento Colombiano de Construcción Sismo Resistente NSR-10 (Colombian Standards for Design and Earthquake Resistant Construction NSR-10), Asociación Colombiana de Ingeniería Sísmica Bogotá, D. C., Colombia, (2010).

DOI: 10.16924/revinge.32.3

[2] W Garza, L., Lara, L., Posada, Resistencia a la Compresión de Angulos Dobles Separados (Strength for compression of distanced double angles), Universidad Nacional de Colombia, Sede Medellin, (2005).

[3] Morales, J. D., Ospina, T. A., Criterios de Diseño de Angulos Dobles Enfrentados (Design criteria for double facing angles), Universidad Nacional de Colombia, Sede Medellin, (2004).

[4] Bermudez, C. A., Paredes, J. A. Díaz , Ávila J. C., Brigss, N. J., García, A. F., Loaiza, C. M. Romero, E., Verificación de las fórmulas de la NSR-10 de diseño a compresión para ángulos enfrentados (Verification of the formulas of the NSR-10 of compression design for facing angles), Universidad Nacional de Colombia, Sede Manizales, Manizales, Colombia, (2013).

DOI: 10.17230/ad-minister.29.8