M 251 SPECIFICATIONS FOR MATERIALS

Standard Specification for

Plain and Laminated Elastomeric Bridge Bearings

AASHTO DESIGNATION: M 251-92

1. SCOPE D 4014 Specification for Plain and only virgin crystallization resistant poly-
Steel-Laminated Elastomeric chloroprene (neoprene) or virgin natural
Bearings for Bridges polyisoprene (natural rubber) as the raw
1.1 This specification covers the material polymer. All materials shall be new with
requirements for plain and laminated 2.4 Rubber Manufacturer's Association,
Inc.: RMA F 3 no reclaimed material incorporated in the
elastomeric bridge bearings. Elastomeric finished bearing. The elastomer com-
bearings furnished under this specifica- RMA T.063
RMA F 2 pound shall meet the minimum require-
tion shall adequately provide for thermal ments of Table 1.
expansion and contraction, rotation, 2.5 Steel Structures Painting Council
camber changes, and creep and shrink- Specifications: 4.2 The physical properties of the cured
age, where applicable, of structural SSPC-SP6, Surface Preparation elastomeric compound shall be deter-
members. Elastomeric bearings as herein Specification Nº 6, Commercial mined by using samples taken from
defined shall include unreinforced pads Blast Cleaning actual bearings. Testing for the physical
(consisting of elastomer only) and rein- properties of the elastomer may require
SSPC, Vis 1, Pictorial Surface Prepa- the destruction of one or more bearings
forced bearings with steel or fabric lami- ration Standards for Painting
nates. from a lot. Therefore provisions should
Steel Surface be made to provide additional bearings
1.2 The values stated in SI units are to be for testing purposes.
regarded as the standard.
3. GENERAL REQUIREMENTS 4.3 All material tests shall be carried out
at 23 ± 2°C (73 ± 4°F) unless otherwise
2. REFERENCED DOCUMENTS noted.
3.1 Bearings shall be furnished with the
design dimensions within the tolerances 4.4 For the purpose of determining con-
2.1 AASHTO Standards: shown in Section 6.1. They shall be formance with this specification, an
composed of the specified elastomer type observed or calculated value shall be
M 183 Specification for Structural
and hardness (or shear modulus); shall be rounded off to the nearest 70 kPa (10 psi)
Steel
adequate for the specified design load; for tensile strength, to the nearest 10
R 11 Recommended Practice for percent of elongation, and to the nearest 1
shall be tested at the appropriate level
Indicating Which Places of percent for change in aged tensile and
and shall satisfy any special requirements
Figures are to be Considered aged elongation. Hardness and aged
of the designer. In the absence of more
Significant in Specified Lim- hardness shall be rounded off to nearest
specific information, bearings shall be
iting Values point, in accordance with AASHTO R11.
50-durometer elastomer, adequate for
T 67 Practices for Load Verifica- 690 kPa (100 psi) design compressive 4.5 Steel Laminates-Steel laminates used
tion of Testing Machines stress, with the compressive strain not to for reinforcement shall be made from
2.2 ANSI Standards: exceed 10.0 percent of the design effec- rolled mild steel conforming to AASHTO
ANSI B46.1 Surfaces and Surfac- tive rubber thickness at a compressive M 183, ASTM A 570, or equivalent,
ing load equal to the actual design load (± 2 unless otherwise specified by the pur-
percent), and tested to all the require- chaser. The laminates shall be of the
2.3 ASTM Standards: ments of Level I. thickness specified by the purchaser or, if
A 570 Hot-Rolled Carbon Steel 3.2 All bearings shall be designed in left unspecified, have a minimum nomi-
Sheet and Strip, Structural accordance with specifications contained nal thickness of 1.52 mm (0.060 in.).
Quality in the latest edition of the AASHTO Holes in plates for manufacturing pur-
D 395 Rubber Property- Standard Specifications for Highway poses shall not be permitted unless con-
Compression Set Bridges. sidered in the design of the bearing.
D 412 Rubber Properties in Tension 3.3 The contractor shall provide the 4.6 External load bearing plates shall
purchaser with written notification 30 conform to the requirements of AASHTO
D 573 Rubber-Deterioration in Air
days prior to the start of bearing produc- M 183, unless otherwise provided upon
Oven
tion. This notification shall include the the plans or in the contract. Except as
D 624 Rubber Property-Tear Resis- noted, all bearings surfaces of external
contract number, quantity, and size bear-
tance, Test for load plates shall be finished or machined
ings being produced, manufacturer's
D 1149 Rubber Deterioration-Surface name, location, and the representative flat within 0.25 mm (0.010 in.). The
Ozone Cracking in a Cham- who will coordinate production, inspec- bottom surfaces of external load plates
ber (Flat Specimens) tion, sampling, and testing with the pur- (masonry plates) designed to rest on
D 2137 Rubber Property-Brittleness chaser. bearing pads shall not exceed an outof-
Point of Flexible Polymers flatness value of 1.59 mm (0.0625 in.).
and Coated Fabrics, Test for The external load bearing plates shall be
4. MATERIALS protected from rust until all exposed
D 2240 Rubber Property-Durometer surfaces can be field painted. Any rust
Hardness inhibitor utilized must be removed from
4.1 Properties of the Elastomer-The
D 3183 Rubber-Preparation of Pieces all surfaces to be welded prior to weld-
elastomer compound used in the con-
for Test from Products ing.
struction of these bearings shall contain
386
M 251 SPECIFICATIONS FOR MATERIALS

4.7 Fabric Reinforcement-Fabric rein- external steel plates are required, a cold results. Each reinforced bearing shall be
forcement shall be woven from 100 bonding process which will yield the marked in indelible ink or flexible paint.
percent glass fibers of "E" type yam with strengths required in Section 8.2.4 may The marking shall consist of the order
continuous fibers. The minimum thread be used in lieu of hot bonding. When number, lot number, bearing identifica-
count in either direction shall be 1 thread fabric pads are combined for greater tion number, and elastomer type. Unless
per mm. (25 threads per in.). The fabric thickness, one cold bond will be allowed. otherwise specified in the contract docu-
shall have either a crowfoot or an 8- 5.3 Plain pads may be molded or ex- ments, the marking shall be on a face
Harness Satin weave. Each ply of fabric truded, and vulcanized in large sheets and which is visible after erection of the
shall have a minimum breaking strength cut to size. Cutting shall not heat the bridge.
of 140 kN/m (800 lbs/in.) of width in materials, and shall produce a smooth 7.2 A lot of pads shall be considered to
each thread direction. finish to ANSI B46.1 6µm (250 micro be a group of 100 or less pads which are
inches). Plain pads shall be molded or manufactured from the same batch of
5. FABRICATION extruded to the finished thickness. Fabri- elastomer, cured under the same condi-
cators will not be allowed to make pads tions, and are all the same size and type
of finished thickness by plying pads of (plain, fabric reinforced, metal rein-
5.1 Bearings with steel laminates shall be lesser thickness together. External load forced). A lot may include 100 or less
cast as a unit in a mold and bonded and plates, when used, shall be protected fabric-reinforced bearings of different
vulcanized under heat and pressure. The from rusting by the manufacturer, and plan size if cut from a large sheet or
molds shall have standard shop practice shall be hot bonded by vulcanization sheets meeting these requirements.
mold finish. The internal steel laminates during the primary molding process.
shall be blast cleaned to a condition 5.4 Flash tolerance, finish, and appear-
matching that of SSPC-Vis 1, Pictorial 8. BEARING TESTS AND ACCEP-
ance of bearings shall meet the require- TANCE CRITERIA
Standard CSa2 and additionally cleaned ments of the latest edition of the Rubber
of any oil or grease before bonding. Handbook as published by the Rubber
Plates shall be free of sharp edges and Manufacturers Association, Inc., RMA 8.1 The acceptance criteria shall be at
burrs, and shall have a minimum edge F3 and T.063 for molded bearings and two levels. Level I acceptance shall be
cover of 3 mm (⅛ in.). External load RMA F2 for extruded bearings. applied to all bearings. Level II accep-
plates (sole plates) shall be protected tance criteria shall, at the discretion of the
from rusting by the manufacturer, and purchaser, be applied to more critical or
shall be hot bonded to the bearing during 6. TOLERANCES unusual bearings. It shall also be used to
vulcanization. Bearings with steel lami- resolve differences over the acceptance
nates which are designed to act as a of bearings to which only Level 1 tests
single unit with a given shape factor must 6.1 Plain pads and laminated bearings
shall be manufactured to the design shall have been applied. Level 1 and
be manufactured as a single unit. Level II tests may be performed by the
dimensions and these specifications with
5.2 Fabric-reinforced bearings may be the tolerances listed in Table 2, unless manufacturer, by the purchasing agency
molded and vulcanized in large sheets other tolerances are shown on the design or by an outside independent laboratory
and cut to size. Cutting shall be per- drawings. subject to the approval of the purchaser.
formed so as to avoid heating the materi- Regardless of the agency designated to
als and produce a smooth finish with no test the pads, the purchaser will reserve
separation of the fabric from the elas- 7. MARKING AND CERTIFICA- the right to obtain test samples from the
tomer. Fabric reinforcement shall be TION job site for confirming test results.
single ply at the top and bottom of the 8.2 Level I criteria shall include the
reinforced bearings and double ply for following requirements:
7.1 The manufacturer shall certify that
internal reinforcement layers. Fabric shall
each bearing satisfies the design specifi-
be free of folds and ripples and shall be
cation, and supply a certified copy of test
parallel to the top and bottom surfaces. If

TABLE 1 Elastometer Proneries

Material Natural Rubber Polychloroprene
ASTM Standard Test Requirements Units
Property 50 Duro 60 Duro 70 Duro 50 Duro 60 Duro 70 Duro
Physical D 2240 Hardness 50 ± 5 60 ± 5 70 ± 5 50 ± 5 60 ± 5 70 ± 5 Shore points
properties D 412 Min tensile strength 15.5 15.5 15.5 15.5 15.5 15.5 MPa
(2250) (2250) 2250) (2250) (2250) (2250) psi
Min ultimate elongation 450 400 300 400 350 300 %
Heat resis- D 573 at speci- Specified temp. of the rest 70 70 70 100 100 100 °C
tance fied temp. (158) (158) (158) (212) (212) (212) ºF
Aging time 168 168 168 70 70 70 Hours
Max change in durometer hardness + 10 + 10 - 10 - 15 + 15 + 15 Shore points
Max change in tensile strength - 25 - 25 - 25 - 15 - 15 - 15.
Max change in ultimate elongation - 25 - 25 - 25 - 40 - 40 - 40
Compression D 395 Specified temp. of test 70 70 70 100 100 100 ºC
set (158) (158) (158) (212) (212) (212) °F
Method B at Max permissible (after 22 hrs.) 25 25 25 35 35 35 percent
specified temp.
Tear resis- D 624 Min kN/m (Die C) 31.5 31.5 31.5 31.5 31.5 31.5 kN/m
tance (180) (180) (180) (180) (180) (180) lb/in.
Brittleness D 2137 Low temp. britdeness at =40°C (-40°F) Pass Pass Pass Pass Pass Pass
Ozone D 1149 Partial pressure of ozone during test 25 25 25 100 100 100 MPa
Resistance Duration of test 48 48 48 100 100 100 Hours
Tested at 20-percent strain 37.7 ± 1°C No No No No No No
(100 ± 2°F) mounting procedure D 518, Cracks Cracks Cracks Cracks Cracks Cracks
procedure A
387
M 251 SPECIFICATIONS FOR MATERIALS

8.2.1 All bearings shall be manufac- TABLE 2 Tolerances

tured according to the requirements set mm (in.)
forth in this specification and any addi- 1. Overall vertical dimensions:
tional requirements specified by the Design thickness 32 mm (1 ¼ in.) or less -0, +3 (-0, +⅛)
Design thickness over 32 mm (1 ¼ in.) -0, +6 (-0, +¼)
purchaser. The elastomer will meet the
2. Overall horizontal dimensions:
specific requirements of Table 1. In 914 mm (36 in.) and less -0, +6 (-0, +¼)
addition all components shall meet the Over 914 mm (36 in.) -0, +12 (-0, +½)
requirements of their designated specifi- 3. Thickness of individual layers of elastomer (lami- ± 20 percent of design value but no more
cation and the finished bearing shall be nated bearings only) at any point within the bearing than ± 3 mm (⅛ in.)
assembled within the tolerances given in 4. Variation from a plane parallel to the theoretical
Table 2. surface: (as determined by measurements at the
edge of the bearings):
8.2.2 The elastomer shall be tested for Top Slope relative to the bottom of no more
conformance with the minimum re- than 0.005 radians
quirements of Table 1. Sides 6 (¼)
8.2.3 The manufacturer shall proof 5. Position of exposed connection members 3 (⅛)
6. Edge cover of embedded laminates of connection
load each steel reinforced bearing with a members
-0, +3 (-0, +⅛)
compressive load 1.5 times the maximum 7. Size of holes, slots, or inserts ±3 (± ⅛)
design load. If bulging patterns imply 8. Position of holes, slots, or inserts ±3 (± ⅛)
laminate placement which does not
satisfy design criteria and manufacturing
tolerances or if bulging suggests poor
laminate bond, the bearing shall be re-
jected. If there are three separate surface
cracks which are greater than 2.0 mm
(0.08 in.) wide and 2.0 mm (0.08 in.)
deep, the bearings shall be rejected.
8.2.4 A minimum of one pad per lot
shall be tested for bond strength in ac-
cordance with Section 9.2. Fabric rein-
forced pads shall have a minimum bond
strength of 5.2 kN/m (30 lb/in.) and steel
reinforced pads a strength of 7.0 kN/m
(40 lb/in.).
8.2.5 Optional Cold Weather Require-
ment:
A minimum of two pads per lot shall be
tested for cold temperature shear in
accordance with Section 9.1.
8.3 Level II criteria shall include the
following requirements:
8.3.1 The pads must meet all Level I
criteria.
8.3.2 The shear modulus of the elas-
tomer shall be determined in accordance
with ASTM D 4014. The shear modulus
shall be within ± 15 percent of the value
specified in the design document or
within the limits listed below if no shear
modulus is specified and the nominal
hardness is specified.
Note the shear modulus determined by
Level II criteria is not a true material
property, but is adequate for practical
purposes. A minimum specimen- size of
75 by 75 by 6 mm (3 by 3 by ¼ in.) is
recommended for the shear test.
8.3.3 The purchaser may require more After conditioning the bearings at -29 ± 15 minutes after the ultimate shear
severe testing of pads such as fatigue or 0.5°C (-20 ± 1°F) for 96 ± 1 hour, the strength is reached. The shear stress,
test to failure under Level II criteria. bearings shall be loaded in compression measured 15 minutes after the ultimate
to a stress of 3447 kPa (500 psi) based on shear strain has been met, shall not ex-
the net internal reinforcement area of the ceed 345 kPa (50 psi) for bearings con-
9. TESTING bearing. The bearings shall then be structed with neoprene nor 207 kPa (30
sheared to a total strain equivalent to 25 psi) for bearings constructed with natural
9.1 Optional cold temperature shear percent of the effective rubber thickness. rubber. The total time lapse between
testing shall be performed as follows: Shear stresses, based on the net plan area removal from the -29°C (-20°F) envi-
of the rubber, shall be recorded at 0 and
388
M 251 SPECIFICATIONS FOR MATERIALS

ronment and completion of the test shall 9.2.2 The samples shall be cut from a uniform manner far enough to place in
not exceed 30 minutes. finished bearings using a saw capable of the grips.
9.2 Determination of Bond Strength: cutting smoothly through either fabric or 9.2.4 Install the specimen in the grips
metal reinforced pads. so symmetrical tension is applied.
9.2.1 The testing apparatus shall in-
clude a testing machine capable of meas- 9.2.3 A 25-mm (1-in.) wide (full thick- 9.2.5 Apply the load by separating the
uring loads up to 450 N (100 lb) with an ness) sample shall be taken from the platens at a uniform speed of 50 ± 5 mm
accuracy of plus or minus one percent. center ⅓ of the pad as shown in Figure 1. per minute (2 ± 0.2 in. per minute).
The platen speed shall be 50 ± 5 mm per The minimum length shall be 150 mm (6
in.). Cut this section into test specimens 9.2.6 Record the strength in Newtons
minute (2 ± 0.2 in. per minute). The per mm of width (pounds of load per inch
machine shall be equipped with grips as shown in Figure 2, and initiate peeling
by neatly cutting the neoprene back to of width).
designed for holding rubber without
cutting or slipping. The grips shall have neoprene-reinforcement interface as
faces at least 25 mm (1 in.) wide. shown in Figure 2. Initiate the peeling in

389