After completing the design of a spring-damper system for a bridge, you are assigned your next task. The company you work for has been commissioned to design a new two-storey building on-campus at the university. The building in Figure 1 can be modelled as a two-DOF system, with point masses for the first floor and the roof. The mass of the columns can be assumed negligible compared to the mass of the floor/roof.

Structural Analysis
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Chapter2: Loads On Structures
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  1. ω1 = 7.114053 rad/sec with eigenvector α1[1, 7.62988]T                                                                                    and ω2 = 20.34097 rad/sec with eigenvector α2[1, -0.16383]T
After completing the design of a spring-damper system for a bridge, you are assigned your next
task. The company you work for has been commissioned to design a new two-storey building
on-campus at the university.
The building in Figure 1 can be modelled as a two-DOF system, with point masses for the first
floor and the roof. The mass of the columns can be assumed negligible compared to the mass of
the floor/roof.
m2
m₁
(a) Evaluate the remaining natural frequency.
(b) Evaluate the two eigenvectors.
Figure 1: Schematic diagram of the proposed building design
The first floor is supported by four, cylindrical concrete columns of diameter d₁ = 0.5m. The
roof is also supported by four cylindrical columns but these were required to be of diameter d₂ =
0.3m as a consequence of weight considerations. The Young's Modulus of concrete can be taken
as E = 25 GPa and the height of every column is 4 m. The masses of the first floor and the roof are
m₁ = 40000kg and m₂ = 32000 kg, respectively. The bending stiffness of one column modelled
3EI
as a beam of circular cross-seciton can be expressed as k=13, where E is the Young's modulus,
I is the second moment of area of beam's cross-section and I is the beam's length.
1. The company already knows the first natural frequency occurs at ¹7.114rads-¹.
2. The site for the building is between two existing buildings. As a result of CFD modelling
and experimental data, a nodal force vector of
6000 sin (2)
2500 sin (1.4zt)
x(0) =
X2
f(t)=
has been estimated due to the higher frequency eddies as a result of turbulence near ground
level.
8]
x1
Using direct matrix inversion (no modal analysis), calculate the particular solution of each
mass in the absence of damping.
C=aK+BM
3. Your boss contacts you to share data they have recently obtained. It has become clear that
the effect of damping, arising from the joints between columns and the floor/roof is not
negligible. The damping factor can be assumed to take the form of Rayleigh damping
=
with a = 0.15 and ß = 2.0.
(a) Perform a modal analysis to calculate the steady state motion of each mass.
(b) Using the steady-state solution, evaluate the transient solution to obtain the total solu-
tion.
Initial conditions can be taken as
m and *(0) =
8₁
ms-¹.
(c) Is the effect of damping helpful to this design?
(d) Describe whether the transient solution is important for the design of this building when
only wind loading is considered.
Transcribed Image Text:After completing the design of a spring-damper system for a bridge, you are assigned your next task. The company you work for has been commissioned to design a new two-storey building on-campus at the university. The building in Figure 1 can be modelled as a two-DOF system, with point masses for the first floor and the roof. The mass of the columns can be assumed negligible compared to the mass of the floor/roof. m2 m₁ (a) Evaluate the remaining natural frequency. (b) Evaluate the two eigenvectors. Figure 1: Schematic diagram of the proposed building design The first floor is supported by four, cylindrical concrete columns of diameter d₁ = 0.5m. The roof is also supported by four cylindrical columns but these were required to be of diameter d₂ = 0.3m as a consequence of weight considerations. The Young's Modulus of concrete can be taken as E = 25 GPa and the height of every column is 4 m. The masses of the first floor and the roof are m₁ = 40000kg and m₂ = 32000 kg, respectively. The bending stiffness of one column modelled 3EI as a beam of circular cross-seciton can be expressed as k=13, where E is the Young's modulus, I is the second moment of area of beam's cross-section and I is the beam's length. 1. The company already knows the first natural frequency occurs at ¹7.114rads-¹. 2. The site for the building is between two existing buildings. As a result of CFD modelling and experimental data, a nodal force vector of 6000 sin (2) 2500 sin (1.4zt) x(0) = X2 f(t)= has been estimated due to the higher frequency eddies as a result of turbulence near ground level. 8] x1 Using direct matrix inversion (no modal analysis), calculate the particular solution of each mass in the absence of damping. C=aK+BM 3. Your boss contacts you to share data they have recently obtained. It has become clear that the effect of damping, arising from the joints between columns and the floor/roof is not negligible. The damping factor can be assumed to take the form of Rayleigh damping = with a = 0.15 and ß = 2.0. (a) Perform a modal analysis to calculate the steady state motion of each mass. (b) Using the steady-state solution, evaluate the transient solution to obtain the total solu- tion. Initial conditions can be taken as m and *(0) = 8₁ ms-¹. (c) Is the effect of damping helpful to this design? (d) Describe whether the transient solution is important for the design of this building when only wind loading is considered.
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