Elastometric Bearings

Review of Laminated Elastometric Bearing Pad (AASHTO M251 & BS 5400: Part 9)
Steel-Reinforced Elastometric Bearings – Method B
A. Allowable Delamination compressive Stress:
1. Shear Modulus (G) = 130 ~ 199 psi (Say Use 150 psi = 1.03 MPa)

2. Hardness -- Use 50 Durometer (Between 50 ~ 60 on Shore A scale)

3. Compressive Stress (AASHTO 14.7.5.3.2)
In any elastometric bearing layer, the average allowable compressive stress at the service limit state shall satisfy:
• For bearing subject to shear deformation:





S: Shape factor (8.5 < S < 11) For total (all layers) thickness
Service DL per bearing: DL = 300 kN (67.443 kips)
Service LL per bearing: LL = 500 kN (112.404 kips)
Existing L= 600mm W= 200 mm
c= (DL+LL) / LW = 800*1000N/ (600x200)mm2 =6.67 MPa = 1 ksi <1.6 ksi
hri: 6.4mm hrc: 6.3mm
so, S=600*200/(2*6.4*(600+200))=11.7
(actual) c=6.67 MPa < (allowable) s=0.66x1.03x11.7 =7.95 MPa (1.2ksi) ……. OK

B. Determine Bearing Pad size:
4. n: number of interior layers = 6
Reinforcing steel shims : hs= 2.7mm

8. Bearing pad Thickness check:
Total bearing pad thickness t = 2 x hrc + n x hri + (n+1) x hs = 2*6.3+6*6.4+7*2.7=70mm
t < L/3, t=70 < L/3=600/3=200 …… OK
t < W/3, t=70 < W/3=200/3=66.66 ….. OK (Accepted)

Bearing pad size 600 x 200 x 70 meet all the design requirement.

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