Multi-Load Performence Based Design (PDF)/Double-Acting PFD
Double-acting PFD is an interesting device. The challenge was how to provide two slip loads (SL1 and SL2) in the same unit, where SL1 = DBE slip load and SL2 + SL1 = MCE
slip load. This became possible with the making of a gap in one set of friction plates. The opposing set of friction plates are continuous without any gap. During cyclic loading,
if the first half cycle is in compression mode, the next half cycle is in tension mode or vice-versa.
During compression mode, first the gap closes and then SL1 starts pushing SL2. During tension mode, first the gap opens then SL1 starts pulling SL2. It is seen that when the gap is
closing or opening, only SL1 is slipping (DBE) and then at MCE slip load both SL1 and SL2 are slipping.
Performance-Based Design is economically feasible with Double Acting Dampers become economically feasible to adopt Performance.
Multi-load dampers are particularly beneficial for structures located in regions with varying seismic demands or for buildings requiring both vibration control and high seismic resilience. Their customizable design allows engineers to fine-tune activation thresholds and energy dissipation capacity, making them a versatile and efficient solution for modern performance-based structural design.
Some engineers have tendency to use higher slip load to make the structure stronger. On the contrary, if the slip load is high, the dampers will not slip and the advantage of
gaining supplemental damping is lost. The new Hi-Performance PFD incorporates features that detect such mistakes and rectifies by adopting default value. The default value is usually MCE / DBE = 1.4 - 1.5. SL1 starts dissipating energy earlier at lower level, therefore, 20–30% more energy is dissipated. This leads to saving in quantity of PFD or use of lower capacity PFDs and higher
seismic performance. Overall savings 10–15%.
Hysteresis Loop
Hysteresis Loop of Double-Acting PFD is shown. This stepped loop has lower slip loads at the beginning and end of a cycle. Lower slip load at the extremities help reducing or eliminating permanent offset.