The Variable Stiffness Bracing System
Dr. Farzad Hejazi, Amir Fateh, Prof. Dato' Ir. Dr. Mohd Saleh Jaafar, Prof.
Azlan Adnan
Department of Civil, Faculty of Engineering, UPM
Email: farzad@eng.upm.edu.my
Summary
Severe vibration events due to ground motion, wind load, vehicle, machinery,
tsunami and earthquake have underscored the necessity of dynamic excitations
protecting techniques for the existing moment resistance frames. These design
techniques are supposed to include detailed considerations of the effect of
supplementary controller device on the original frames response
The variable stiffness bracing (VSB) scheme is one of the innovative passive
structural controller technique which increase overall lateral stiffness of structure
under dynamic loads. The variable stiffness bracing component or intelligent
structural control system does not operate for small and medium vibration
amplitudes by aid of nonlinear variable stiffness that depends on structural
displacement specification therefore; in this case most part of dynamic load is
dissipated through small vibration of structure in acceptable range. For large
vibration amplitudes, the VSB system acting and restrain unacceptably large story
drift and protect the structure against risky vibration.
Mathematical and constitutive model of VSB is formulated base on flexible bar
theory and variable stiffness characteristic of system is developed. The Newmarks
method with considering variable stiffness system is performed to evaluate the
seismic response of structure equipped with VSB system. Then, the effect of
proposed system is evaluated by application of variable stiffness bracing component
in numerical modeling by aid of time history analysis. The seismic response of
modeled structures furnished with VSB system revealed the efficiency of VSB
system in decreasing seismic effects on structure.
Market potential
Local market:
This product is appropriate for high rise building which are located in seismic
regions in Malaysia such as Sarawak to diminish the structural damage and ensure
structure stability during the vibration load such as wind and earthquake.
Global Market:
Considering the seismic effects on the structures which are located in seismic area is
compulsory. So, Variable stiffness bracing system has shown enough capability to
put into practice as cheap and useful supplementary product to install in new and
existing structure to mitigate and eliminate the structural damage.
Keywords: dynamic load, variable stiffness bracing system, seismic rehabilitation
system, structural dynamic, finite element simulation
Product profit
 Prevent devastating toll of human life & properties
 Alleviate seismic damage to structural elements.
 ·Diminish the structure response
 Enhance seismic energy dissipation tendency
Industrial Application
Construction and housing company
Industries deal with fabrication of seismic Supplementary controller systems
Consultant, housing industry, governmental sectors, private organizations, risk
management divisions and whom related to design and rehabilitation of building
Seismic engineering
Bridge construction companies
Mechanical engineering
Aerospace engineering
Short Description about Research Output:
Figure 1 shows schematic perspective of VSB system. Four leaf springs acting in
bending situations under large displacement are tagged as label 1. Label 2 refers to
circle core that can move fro and back in longitudinal direction through steel rail as
shown in label 3. Rods ( label 4) are passed thru side’s plates ( label 5) and fixed to
the cubic core ( label 6) .When the force is applied to the cable, the steel core moves
and contacts with the C shape member (label 2), where the spring are clamped. The
C-shape elements help to keep the initial spring shape and changing it during
performance of system. By other words, global stiffness of nonlinear spring should
be protected from curvature extension, therefore, four quarter solid cylinders (label
7) and two C-shape elements are essential to act as supports. In addition to, the
spring protection systems (label 2 & 7) guarantee that, the leaf springs are not
yielded when they reach the maximum curvature.
As mentioned, this system increases the lateral stiffness of story without any
reduction effect of moment’s frame ductility characteristic. It means that the VSB
bracing system does not operate too much for small or medium vibration’s
amplitudes but in the case of large one controls unacceptably large story drift.VSB
system can easily be installed on the bottom beam /foundation by aid of horizontal
VSB plate (label 8). Figure 2, depicts the one side and double sides on VSB
prototype. Furthermore overall mechanism algorithm of VSB system in structure is
shown in Figure 3.the application of VSB system in structure is shown in figure 4.
2
5
4
3
8
7
1
1. Leaf Spring
2. Circle Core
3. Square Rail
4. Steel Rod
5. Vertical Side Plate
6. Cubic Core
7. Quarter Solid Cylinders
8. Horizontal VSB Plate
Figure 1: Schematic body of VSB System
5
(a) VSB Prototype with both sides leaf spring
(a) VSB Prototype with one side leaf spring
Figure 2: VSB Prototype
Input
M: Mass of structure; Ɛ: Damping coefficient; K Stiffness of
frame; KC : Stiffness of cable, El-Centro Time history
K total=K+KC+KVSB
Find KVSB by use of
obtained displacement
Solve equation of motion by
Newark method
M x¨ + c x˙ + f k (x) = f (t )
KVSB=Maximum value
Obtained displacement <
Maximum displacement
value of VSB
END
Figure 3. General computation algorithm of variable stiffness system adopted in Matlab code
Figure 4.VSB Installation layout in frame