Numerical and experimental performance evaluation of upgraded knee braces under cyclic load

Document Type : Research Paper


1 Department of Civil Engineering, Faculty of Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran.

2 Department of Civil Engineering, Faculty of Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran. (Corresponding author


In this paper, the seismic performance of the structure is analyzed by introducing a new angular knee element. Cyclic loads are applied to determine the seismic performance. The result is compared with a vertical knee element. The angular knee element showed better seismic performance as compared to the vertical knee element. The new short knee element studied in two positions including 1- a vertical knee element perpendicular to cross-brace is called VSKE 2- An angular knee element that is called ASKE. Using reduced knee section specimens for better performance. Effect of Angular knee element in knee-braced frames (KBFs) under Cyclic Loading was investigated by testing using a half scale specimen mounted on a reaction frame at two positions including horizontally for VSKE and inclined for ASKE. For experimental tests, specimens were loaded by using a hydraulic actuator. Finite element modelling was used for the simulation of detailed behavior using a verified experiment base model. It has been shown that the performance of knee element fuses can improve the ductile behavior of knee braced frames. Based on the results of vertical and angular cases, it has been shown that an increase of angle between main cross brace and short knee element (incline specimen) can reduce maximum equivalent plastic strain (EPEQ) in the web of knee element fuse.


 Knee element, Fuse, Cyclic-Loading, Plastic Deformation, brace, Numerical Modelling.

[1] J.D. Aristizabal-Ochao, Disposable knee bracing: improvement in seismic design of steel frames, J. Struct. Engin. 7(112) (1986) 1544–1552.
[2] A. Atashzaban, I. Hajirasouliha, R. Ahmady Jazany and M. Izadinia, Optimum drilled flange moment resisting connections for seismic regions, J. Constr. Steel Res., 112 (2015) 325–338.
[3] T. Balendra, E.L. Lim and S.L. Lee, Ductile knee braced frames with shear yielding knee for seismic resistant structures, Engin. Struct. 16(4) (1994) 263–269.
[4] T. Balendra, M.T. Sam and C.Y. Liaw, Diagonal brace with ductile knee anchor for aseismic steel frame, Earthquake Engng. Struct. Dyn. 6(19) (1990) 847–858.
[5] E. Junda, S. Leelataviwat and P. Doung, Cyclic testing and performance evaluation of buckling-restrained kneebraced frames, J. Constr. Steel Res. 148 (2018) 154–164.
[6] M. Mofid and P. Khosravi, Non-linear analysis of disposable knee bracing, J. Comput. Struct. 75 (2000) 65–72.
[7] C.W. Roeder and E.P. Popov, Eccentrically braced steel frames for earthquakes, J. Struct. Engin. 104(ST7) (1978) 391–411.
[8] SAC, Protocol for fabrication, Inspection, Testing and Documentation of Beam-Column Connection Test and Other Experimental Specimens, SAC Rep. SAC/BD-97/02, SAC Joint Venture, Sacramento, Calif., USA, 1997.
[9] D. Skeji’c, I. Cudina, I. Garaˇsi’c and F.M. Mazzolani, Behaviour of steel tubular knee joint in aluminium frames with tension-tie element, Appl. Sci. 11(1) (2021) 70.
[10] M.S. Williams, A. Blakeborough, D. Cl´ementand and N. Bourahla, Seismic behavior of knee braced frames, Structs Build. 152(2) (2002) 147–155.
[11] H. Zhen, L. Qing-song and C. Long-zhu, Elasto plastic analysis of knee bracing frame, J. Zhejiang Uni. Sci. 6 (2005) 784–789.
Volume 13, Issue 1
March 2022
Pages 1863-1872
  • Receive Date: 04 August 2021
  • Revise Date: 10 September 2021
  • Accept Date: 15 October 2021