Bridge Bearings

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Bridge Bearings

2018 Bridge Construction Inspection School

Rex L. Pearce, PE

VDOT Staunton District

Bridge Engineer

Bearing Purpose2

Bearing -Expansion

Bearing -Expansion

Bearing -Fixed

Bearing -Expansion

Abutment Abutment

DeckSuperstructure (Girders)

Pier Pier

Purpose & Function of Bearings• Transfer Superstructure Loads to Substructures• Allow Longitudinal Expansion & Contraction Movement• Allow Rotation Caused by DL & LL Deflection• Section 408 Road & Bridge Specs

Types of Bearings• Fixed• Expansion• Noted on Front Sheet of Bridge Plans• Typically a single-point of fixity – one fixed bearing• Occasionally multiple-points of fixity

- superstructure erection must more carefully follow procedure

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Functions of Bearing

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Summary of Bearing Capabilities

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Bearing Type

Load Translation Rotation Cost

Min.(kips)

Max(kips)

Min.(in.)

Max(in.)

Limit(Rad.)

Initial Maint.

Plain Elastomeric PadPer

Design100 0 0.625 0.01 Low Low

Laminated Elastomeric Bearing (Elastomer, Steel Layered)

Per Design

780 0 4 0.04Low-

ModerateLow

Hybrid Laminated Elastomeric Bearing (Elastomer, Layered,

PTFE/Steel Plate Top)0 780 0 > 4 0.04

Low-Moderate

Moderate

Low Profile Bearing –Fixed (Steel)

0 400 0 0 0 Low Low

Low Profile Bearing – Expansion (Steel, Bronze)

0 400 0 2 0.04 Moderate Moderate

High-Load Multi-Rotational Bearing –Fixed

Spherical, Pot, Disk(PTFE, Bronze, Elastomeric)

0 5000 0 0 0.02 High High

High-Load Multi-Rotational Bearing –Expansion

Spherical, Pot, Disk(PTFE, Bronze, Elastomeric)

270 5000 0 6 0.03 High High

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VDOT Standard DetailsLow Profile Bearings for Steel Beams or Girders

Manual of the Structure and Bridge Division Part 3 Current Details

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VDOT Standard DetailsLaminated Elastomeric Pad for Prestressed Beams


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VDOT Standard DetailsLaminated Elastomeric Pad for Steel Beams/Girders


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VDOT Standard DetailsHigh Load Multi-Rotational Bearings - FixedManual of the Structure and Bridge Division Part 3 Current Details

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VDOT Standard DetailsHigh Load Multi-Rotational Bearings – Expansion - Guided


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VDOT Standard DetailsHigh Load Multi-Rotational Bearings – Expansion – Non-Guided


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Rte 11 over North River – Plan & Elevation

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Rte 11 over North River – Bearing Details

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Rte 624 over Morgans Ford – Plan & Elevation 1/2

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Rte 624 over Morgans Ford – Plan & Elevation 2/214

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Rte 624 over Morgans Ford – Bearing Details

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Plain Elastomeric Bearing Pad• Support modest gravity loads

• Accommodate limited translation & rotation

• Low cost

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Laminated Elastomeric Bearing

• Support relatively large gravity loads

• Accommodate relatively large translation & rotation

• Low – to – Moderate cost

• Sec. 408.03 (g) Placement (Pg. 506)

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Heavy Hex Nut

Washer

Sole Plate

Elastomeric Padw/ 11 ga. Shims

Swedged Anchor Bolt

Bridge Seat

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22

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Anchor Bolts – DO NOT Bend to Set Steel!

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Anchor Bolts – Check Slots for Expansion!

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Anchor Bolts – Check Projection!28

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Hybrid Laminated Elastomeric Bearing

• Support relatively large gravity loads

• Accommodate relatively large rotation

• Accommodate larger translation

• Moderate cost

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Hybrid Laminated Elastomeric Bearing30

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Low Profile Fixed Bearing

Support larger gravity loads

Accommodate rotation only

Moderate cost

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Bridge Seat

Washer

Heavy Hex Nut

Sole Plate

Masonry Plate

3 layers canvas duck or 0.1 in. sheet lead or 1/8” preformed fabric See Sec. 408.03.

Swedged Anchor Bolt

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Low Profile Expansion Bearing

• Support larger gravity loads

• Accommodate translation and rotation

• Moderate cost

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Self – Lubricating

Washer

Self –Lubricating Plate

Sole Plate

Bridge Seat

3 Layer canvas duck or 0.1-in. sheet lead or 1/8” preformed fabric See Sect. 408.03.

Swedged Anchor Bolt

Heavy Hex Nut

Masonry Plate

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High Load Multi-Rotational Bearing

• Support largest gravity loads

• Accommodate rotation about any axis

• Can accommodate translation if add guide bars

• Higher cost than low profile and elastomeric

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Fixed Pot Bearing

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Fixed Pot Bearing

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Fixed Pot Bearing

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Fixed Pot Bearing

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Expansion Pot Bearing

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High Load Multi-Rotational “Pot” Bearing

Sec. 408.03 (a) 11 Installation (Pg. 504):• Bearings shall be lifted by undersides only or by designed lifting lugs.

• Avoid damage to and contamination of bearing surfaces.

• Align guiding mechanism with designated expansion direction of structure.

• Shipping straps shall remain in place as long as possible to ensure that bearing parts are not inadvertently displaced relative to each other.

• Concrete seats shall be prepare at the correct elevation. Confirm bearing heights from shop drawings and compare to Plans. Adjust seat elevations if necessary.

• No load shall be transmitted to the bearings until erection of structural steel for spans contiguous to the bearing is substantially complete. Field welding of bearing plates shall be accomplished under no load condition. Blocking required during erection.

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Pot Bearing Orientation & Location Plan

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Expansion Pot Bearing - Installed Incorrectly!

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Expansion Pot Bearing – Shipping Material Not Removed from Expansion Surface!

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Blocking for Pot Bearing @ Abutment

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Blocking for Pot Bearing @ Pier

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Expansion Pot Bearing – Sole Plate Not Welded

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Setting Expansion BearingsExpansion due to Dead Load

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x = 4 (∆'s) (D/L) for SIMPLE SPANS

x = Dead Load Rotation or Expansion (inches)

∆'s = Concrete Dead Load Deflection at midspan as indicated on the bridge plans (inches)

D = Depth of girder including flanges near the end of the span (feet)

L = Span length between centers of bearings (feet)

Note: This formula cannot be used with continuous spans!

Continuous Steel Rolled Beam: x = 1/8”

Continuous Steel Plate Girder: x = ¼”

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Setting Expansion BearingsExpansion due to Dead Load

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• A steel girder span has 120’-10” between centers of bearings • Concrete Dead Load Deflection at the midspan is 2.5” • The depth of the girder is 6’-3”• How much will the span length elongate when the deck concrete is placed?

x = (4)(2.5”)(6.25/120.83)= 0.518” = ½”

In this example if “x” were not taken into consideration the final position would be 1/2” from proper location.

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Setting Expansion BearingsExpansion due to Dead Load - Example

Setting Expansion BearingsExpansion due to Temperature

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• Last sentence of Sec 408.03 Bearings…12. Shop Dwgs… (g) Placement:• Expansion devices shall be centered … at 60 degrees F.

• Last sentence of Sec. 404.05 …Concrete Operations…Exp. & Fixed Joints…(c) Steel Joints:

• Normal temperature shall be considered as 60 degrees F, and correction to this temperature shall be computed using a coefficient of expansion of 0.0000065 per foot per degree F.

• Paragraph B, Steel Joints, Pg. 185 of Construction Manual, 2005:

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• Coefficient of Expansion for Steel: 0.0000065 per degree F.

∆L = 0.0000065 (L) (∆T)

for a 100’-Span:

∆L = 0.0000065 (100 ft) (15° F) = 0.010 ft = 1/8”

• An excellent rule-of-thumb for the Inspector at the erection site is the following:

• FOR EACH 15°F CHANGE OF TEMPERATURE, A 100 FT SPAN WILL CHANGE IN LENGTH APPROXIMATLEY 1/8”.

• It is typically acceptable to round off actual temperature to nearest 5° and length of span to nearest foot.

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The span length of a simple girder span is 125’-4” and the temperature is 82°.

What is a reasonable temperature correction to apply in setting the bearings (or expansion joints)?

Solution:

Correction = ((80°-60°)/15°) *(125’/100’)*(1/8”) = 0.21”

Therefore a ¼” correction will be adequate.

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Setting Expansion BearingsExpansion due to Temperature - Example

Combined Displacement due to Dead Load & Temperature Effects Example

The following example problem takes both the dead load and temperature into consideration:

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Dead Load Effect Correction

• x = (4) ∆’s(D/L)

• x =(4)*(3.13”)*(5.75’/135.58’)

• x = 0.531” = 1/2” (short)

• When the deck is placed, the bearing will slide to a neutral position – or as offset by temperature conditions if not 60 degrees F.

Considering Only the Dead Load Effects:

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Temperature Effect Correction

• ((95°-60°)/15°)*(136’/100’)*(1/8”)

=0.397” = 3/8” (long)

• When the temperature drops to 60° F,

after the deck is constructed, the bearing will slide to a neutral position.

Considering Only the Temperature Effect:

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Combined Expansion due toDead Load & Temperature Effects

Considering the combination of both effects the difference would be 1/2’’ (short) – 3/8’’ (long) = 1/8’’ (short).

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Questions?

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Documents

Bridge Bearings