Mahin and Bertero (1975, 1976) noted a minor deficiency in the Clough model. They noted that when unloading from a part of the curve with reduced stiffness (branches 7-8-9 and 9-10-11-12 in Figure 27), the reloading branch is still directed towards the largest point which is not always realistic. They proposed a modification whereby upon reloading, the response is directed toward the last unloading point, after which the response is directed back to the maximum prior displacement in that direction (branches 7-8-9 and 10-11-12-13-14 in Figure 28).

Figure 28 illustrates the hysteresis rules of the modified Clough model.

References:

1. Mahin S.A., and V.V. Bertero. An Evaluation of Some Methods for Predicting Seismic Behavior of Reinforced Concrete Buildings. Report No. UCB/EERC-75/5; Earthquake Engineering Research Center, University of California at Berkeley, CA, 1975.
2. Mahin, S.A., and V.V. Bertero, "Nonlinear Seismic Response of a Coupled Wall System," Journal, Structural Division, ASCE, Vol. 102, No. ST9, 1976, pp. 1759-1780.
3. Mahin SA, Lin J. Construction of inelastic response spectra for single degree of freedom systems. Report No. UCB/EERC-83/17; Earthquake Engineering Research Center, University of California at Berkeley, CA, 1983.

Figure 28: Hysteresis Behavior for the Modified Clough Bilinear Stiffness Degrading Model