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N S B A E L A S T O M E R I C B E A R I N G D E S I G N ( E N G L I S H U N I T S )
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A A S H T O L R F D , 3 R D E D . , 2 0 0 4 W I T H 2 0 0 5 I N T E R I M S
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M E T H O D A - E L A S T O M E R I C P A D S AND S T E E L - R E I N F O R C E D E L A S T O M E R I C B E A R I N G S - S E C T I O N 1 4 . 7 . 6
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The following design program was developed based upon the above-referenced AASHTO LRFD code. The program is applicable to the design of
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elastomeric pads and steel-reinforced elastomeric bearings, both rectangular and circular in shape. For steel-reinforced elastomeric bearings and fiber-
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reinforced pads, the program assumes that interior elastomeric layers are of equal thickness, as are the two exterior elastomeric layers. For fiber-
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reinforced pads, the fiberglass reinforcement comprising hs shall be assumed to consist of a double fiberglass layer separated by a 0.125 in. bonding
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layer per article 14.7.6.3.1. Compressive deflections and anchorage requirements for bearings are to be verified by the user in accordance with provisions
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outlined in articles 14.7.6.3.3 and 14.7.6.4 respectively.
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I. INITIAL DESIGN INPUTS
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Bearing Type:Steel-Reinforced Bearing
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Dead Load = PD =102kips
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Live Load = PLL =122kips
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Horizontal Movement of Bridge Superstructure = Δ0 =1.0in.
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Calculated Rotation =0.004
Radians
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Rotation Construction Tolerance =0.005
Radians
(14.4.2.1)
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Design Rotation = θs =0.009
Radians
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Bearing Shape:Rectangular
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Bearing Subject to Shear Deformation?yes
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II. BEARING GEOMETRY
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Flange Width =18in.
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Bearing Width = W =17in.
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Flange Width>W
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18>17in.OK
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Total Unfactored Compressive Load = PT =224kips
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Minimum Required Area of Bearing (shear deformation permitted) = Amin =224.00in.2Based on service limit (14.7.6.3.2)
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Minimum Required Area of Bearing (shear deformation prevented) = Amin =N/Ain.2 *
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Minimum Bearing Length = Lmin =13.18in.
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Bearing Length = L =19in.
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L>Lmin
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19.0>13.18OK
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N/A>N/A
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N/A>N/AN/AN/A
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Bearing Area = A =323.0in.2
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*Note - Stress limit increased 10 percent due to prevention of shear deformation per Section 14.7.6.3.2.
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III. SHEAR DEFORMATION (AASHTO LRFD 14.7.6.3.4 )
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Maximum Total Shear Deformation of Elastomer at Service Limit = Δs = Δ0 =1.000in.
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2Δs =2.000in.
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10Δs =10.000in.
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Elastomeric Layer Thickness=hri =0.625in.
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Thickness of Top and Bottom Cover Layers (each) = hcover =0.250in.
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hcover<
0.7hri
(14.7.6.1)
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0.250<0.438in.OK
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Number of Interior Elastomeric Layers (Excluding Exterior Layer Allowance) = nint =5(nint = 0 for PEP and CDP)
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Total Elastomer Thickness = hrt = 2hcover + ninthri = 3.625in. *
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Total Elastomer Thickness of PEP = hrt =2.000in.
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Total Elastomer Thickness of CDP = hrt = tp =12.00in.
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For PEP, FGP, and Steel-Reinforced Elastomeric Bearings:
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hrt>
2Δs
(14.7.6.3.4-1)
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3.625>2.00in.OK
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For CDP Elastomeric Bearings:
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hrt>
10Δs
(14.7.6.3.4-2)
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N/A>N/AN/A
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*Note - Applies to FGP and steel-reinforced elastomeric bearings only.
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IV. COMPRESSIVE STRESS (AASHTO LRFD 14.7.6.3.2)
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Shear Modulus of Elastomer = G =0.100ksi
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For PEP, FGP, and CDP Elastomeric Bearings:
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0.08 <G
< 0.250
ksi(14.7.6.2)
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0.08 <N/A
< 0.250
ksiN/A
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For Steel-Reinforced Elastomeric Bearings:
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0.08 <G
< 0.175
ksi (14.7.6.2) and (14.7.5.2)
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0.08 <0.100
< 0.175
ksiOK
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 Service Average Compressive Stress (Total Load) =0.69ksi
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 Service Average Compressive Stress (Live Load) =0.38ksi
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 Rectangular Shape Factor = Sl 7.18(14.7.5.1-1)
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 Circular Shape Factor = Sl N/A(14.7.5.1-2)
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Bearings Subject to Shear Deformation:
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 PEP:
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 σs<0.80ksi(14.7.6.3.2-1)
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N/A<N/AksiN/A
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 FGP:
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σs<
1.00GS
ksi(14.7.6.3.2-2)
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N/A<N/AksiN/A
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σs<0.80ksi(14.7.6.3.2-2)
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N/A<N/AksiN/A
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 CDP:
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 σs<1.50ksi(14.7.6.3.2-3)
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N/A<N/AksiN/A
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 Steel Reinforced:
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σs<1.00ksi(14.7.6.3.2-4)
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0.69<1.00ksiOK
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σs<
1.00GS
ksi(14.7.6.3.2-4)
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0.69<0.72ksiOK
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Bearings Fixed Against Shear Deformation*:
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*Note - Stress limit increased 10 percent due to prevention of shear deformation per Section 14.7.6.3.2.
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 PEP:
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 σs<0.88ksi(14.7.6.3.2-1)
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N/A<N/AksiN/A
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 FGP:
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σs<
1.10GS
ksi(14.7.6.3.2-2)
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N/A<N/AksiN/A
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σs<0.88ksi(14.7.6.3.2-2)
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N/A<N/AksiN/A
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 CDP:
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 σs<1.65ksi(14.7.6.3.2-3)
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N/A<N/AksiN/A
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 Steel Reinforced:
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σs<1.10ksi(14.7.6.3.2-4)
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N/A<N/AksiN/A
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σs<
1.10GS
ksi(14.7.6.3.2-4)