Annex A: Numerical Damping Values

In this annex, some numerical values for structural damping are given.

A.  EC 8 - Part 6 (ENV 1998-6:2003 Annex B) suggest the following values for the damping ratio:

Structural material	Damping ratio ξ
Steel elements	1%  -  4%
Concrete elements	2%  -  7%
Ceramic cladding	1.5%  -  5%
Brickwork lining	3%  -  10%

B.  Other values for damping are suggested by EC1 - Part 2-4 (ENV 1991-2-4:1995 Annex C):

The fundamental logarithmic decrement is given by:

Where:

d_s  :  Fundamental structural damping,

d_a  :  Fundamental aero dynamical damping

d_d  :  Fundamental damping due to special devices

The structural damping is given by:

Where:

n₁  :  Fundamental flexural frequency,

:  Parameters given in the following table for different structural types.

 

Structural type		a1	b1	δmin
Reinforced concrete buildings		0.045	0.030	0.080
Steel buildings		0.045	0	0.050
Mixed structures: concrete + steel		0.080	0	0.080
Reinforced concrete towers		0.050	0	0.025
Lattice steel towers		0	0.030	0
Reinforced concrete chimneys		0.075	0	0.030
Prestressed steel cable		0	0.010	0
Unlined welded steel stacks		0	0.015	0
Steel stack with one liner or thermal insulation		0	0.025	0
Steel stack with two or more liners		0	0.030	0
Steel with brick liner		0	0.070	0
Coupled stacks without liner		0	0.015	0
Guyed steel stack without liner		0	0.040	0
Steel bridges	Welded	0	0.020	0
	High resistance bolts	0	0.030	0
	Ordinary bolts	0	0.050	0
Concrete bridges	Prestressed without cracks	0	0.040	0
	With cracks	0	0.100	0
Bridge cables	Parallel cables	0	0.006	0
	Spiral cables	0	0.020	0

E.g.:  for a steel building with first frequency of 3Hz, the logarithmic decrement is:

0.045 x 3  + 0   = 0.135   (> 0.05)

C. Other values for the logarithmic decrement are suggested by:

Structural material	Logarithmic decrement
Steel (welded)	0,025
Reinforced or Prestressed Concrete	0,056
Brickwork	0,25
Wood	0,13

In this reference, preliminary formulas can also be found for aerodynamic damping and damping caused by the foundation.