Seismic Behaviour of RC Knee Joints in Closing and Opening Actions

Authors: S. Mogili, J. S. Kuang, N. Zhang

Abstract:

Knee joints, the beam column connections found at the roof level of a moment resisting frame buildings, are inherently different from conventional interior and exterior beam column connections in the way that forces from adjoining members are transferred into joint and then resisted by the joint. A knee connection has two distinct load resisting mechanisms, each for closing and opening actions acting simultaneously under reversed cyclic loading. In spite of many distinct differences in the behaviour of shear resistance in knee joints, there are no special design provisions in the major design codes available across the world due to lack of in-depth research on the knee connections. To understand the relative importance of opening and closing actions in design, it is imperative to study knee joints under varying shear stresses, especially at higher opening-to-closing shear stress ratios. Three knee joint specimens, under different input shear stresses, were designed to produce a varying ratio of input opening to closing shear stresses. The design was carried out in such a way that the ratio of flexural strength of beams with consideration of axial forces in opening to closing actions are maintained at 0.5, 0.7, and 1.0, thereby resulting in the required variation of opening to closing joint shear stress ratios among the specimens. The behaviour of these specimens was then carefully studied in terms of closing and opening capacities, hysteretic behaviour, and envelope curves to understand the differences in joint performance based on which an attempt to suggest design guidelines for knee joints is made emphasizing the relative importance of opening and closing actions. Specimens with relatively higher opening stresses were observed to be more vulnerable under the action of seismic loading.

Keywords: Knee-joints, large-scale testing, opening and closing shear stresses, seismic performance.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1129786

References:

[1] L. M. Megget, “Reinforced concrete beam-column knee joints,” Bulletin of the New Zealand National Society for Earthquake Engineering, vol. 31, pp. 215-245, 1998.
[2] S. Mazzoni, J. P. Moehle and C. R. Thewalt, Cyclic Response of RC Beam-Column Knee Joints: Test and Retrofit, Earthquake Engineering Research Center, College of Engineering, University of California, 1991.
[3] P. A. Cote and J. W. Wallace, "A study of reinforced concrete knee-joints subjected to cyclic lateral loading," Report no.CU/CEE, vol. 94, 1994.
[4] S. W. McConnell and J. W. Wallace, Behavior of Reinforced Concrete Beam-Column Knee-Joints Subjected to Reversed Cyclic Loading, Department of Civil Engineering, Clarkson University, 1995.
[5] NZS 3101:2006, Concrete Structures Standard, NZS 3101: Part 1, Commentary NZS 3101: Part 2 (2006), Wellington: Standards Council of New Zealand, 2006.
[6] Eurocode 8, Design of Structures for Earthquake Resistance - Part 1: Genral Rules, Seismic Actions and Rules for Buildings, Brussels: European Committee for Standardization, 2004.
[7] ACI 318M-14, Building Code Requirements for Structural Concrete (ACI 318M-14) and Commentary (ACI318RM-14), Farmington Hills, Michigan, USA: American Concrete Institute, 2014.
[8] ACI 352R-02, Recommendations for Design of Beam-Column Connections in Monolithic Reinforced Concrete Structures, Farmington Hills, Michigan, USA: Americal Concrete Institute, 2010.
[9] B. Angelakos, The Behavior of Reinforced Concrete Knee Joints Under Earthquake Loads, 1999.
[10] L. M. Megget, “The seismic design and performance of reinforced concrete beam-column knee joints in buildings,” Earthquake Spectra, vol. 19, pp. 863-895, 2003.
[11] M. N. Priestley, F. Seible and G. M. Calvi, Seismic Design and Retrofit of Bridges, John Wiley & Sons, 1996, pp 352-362.
[12] N. Zhang, J. S. Kuang and S. Mogili, “Cyclic behaviour of reinforced concrete beam-column knee connections,” Sixteenth World Conference on Earthquake Engineering, Santiago, Chile, 2017.
[13] BS EN 206-1: 2000 Concrete, Specification, Performance, Production and Conformity BSI, 2001.