Martin, Deierlein, and Ma 2019
This paper introduces the Modified Modal Superposition method of testing scale structural models and compares it to recently developed capacity design procedures featured in past papers. The methods are compared among seven structural models of different heights, width: height ratios, and strength properties, including location of a post- tensioning system and an energy dissipating system.
System Concept
The rocking braced frame system is tested using different modes of testing on seven different structural models featuring different height, width: height ratios, and strength properties. The newest of which, the Modified Modal Superposition method, features a similar procedure to both the Equivalent Lateral Force and Modified Response Spectrum Analysis methods featured in Steele and Wiebe 2016, by reducing first mode forces that are placed upon the structure to the base overturning moment, though a key difference in the methods is that the Modified Modal Superposition method features a hinged base rather than a fixed base.
Experimental Study, Results, and Discussion
The Modified Modal Superposition analysis yielded similar results to the Equivalent Lateral Force and Modified Response Spectrum Analysis methods featured in Steele and Wiebe 2016. Both had a maximum percent error at 17%, though the Modified Modal Superposition method was slightly more accurate because it better represents the rocking behavior of structures. Higher mode effects and an inverted S shaped profile of story shear forces are better represented due to the reduction of first-mode forces by the R1 force reduction factor, as to mimic the maximum considered earthquake, and the values for brace forces more closely match the response history analysis values.
Reference
Martin, A., Deierlein, G. G., and Ma, X. (2019). “Capacity Design Procedure for Rocking Braced Frames Using Modified Modal Superposition Method,” Journal of Structural Engineering, 145. 6, pp. 5.