Fundamental time period of bridge pier

I want to calculate fundamental time period (eigen value method, using command MODAL CALCULATION REQUESTED) of  bridge pier in staad pro using lumped mass in long & Trans direction as per IRC 6 & IRC SP 114.

I am enclosing the details . I think there are some mistakes in my models. But I am not able to figure it out. Would any one be kind enough to check the models7140.Fundamental Time Period Trans Direction.std4760.Fundamental Time Period Long Direction.std?

Details are:

Span of superstructure: 27 m simply supported

Total DL of one span: 523 T

SIDL (Crash barrier + Wearing Coat) of one span: (54 T + 52 T)

Maximum Live load in the pier: 123 T

Depth of superstructure: 2.420 m

Bearing Type: Elastomeric Bearing

Total No of Bearing per Pier: 8

Shear Modulus of Elastomeric bearing: 1.15 Mpa

Total Beating Stiffness: 25870 kN/m

Pedestal: 0.80 m x 0.80m x 0.14 m

Pier Cap:

Rectangular (upper part):

Length (Transverse direction): 11.70 m

Width (Longitudinal Direction): 3.30 m

Height: 0.60 m

Trapezoidal (lower part):

Length at top (Transverse direction): 11.70 m

Width at top (Longitudinal Direction): 3.30 m

Height: 1.00 m

Length at bottom (Transverse direction): 2.10 m

Width at bottom (Longitudinal Direction): 2.10 m

Pier: Circular

Dia : 1.90m

Height: 5.5 m

Pile Cap:

Length: 4.3 m

Width: 4.3 m

Height: 1.5 m

Pile:

Total no: 4

Dia : 1.00 m

C/C spacing b/w pile: 3.0 m

Length of pile below pile cap: 14.0 m

Depth of Fixity below pile cap: 6.950 m

Type of Soil: Medium Soil

  • I don't know how to advise you on this. This model is of the pier, but a spring at the top is presumably there to simulate the resistance of the bridge deck. The spring is fairly stiff in both lateral directions relative to the applied horizontal force (and mass) which is at the same node location. As such the significance of that point mass will be significantly reduced, and the structure period will be dominated by the self-weight of the remaining parts. The modal results that you get will be very sensitive to the stiffness of that spring.