Applied Loads and Stability of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 216

combination of actions according to BS EN 1990 [ 3.4 ] . Sliding elements
should be designed and manufactured in accordance with EN 1337-2
[ 3.18 ]. The recommended material partial safety factor g m ¼ 1. Roller bear-
ings provide for translation in one direction only. Single rollers permit rota-
tion about the line of contact but multiple rollers require additional elements
to accommodate rotation. Roller bearings for use in curved parts of struc-
tures shall have additional sliding elements and/or rotation elements to
ensure uniform distribution of load across the roller. The axis of rotation
shall be perpendicular to the direction of movement. The curved surfaces
shall be of cylindrical shape. Surfaces in contact shall have the same nominal
strength and hardness. The length of a roller shall not be less than twice its
diameter nor greater than six times its diameter. Guidance shall be provided
to ensure that the axis of rolling is maintained correctly. Location shall be
such that true rolling occurs during movement. Where gearing is used as
security, the pitch circle diameter of the gear teeth shall be the same as
the diameter of the rollers. The design axial force per unit length of roller
contact N 0 Sd specified in BS EN 1337-1 [ 3.11 ] shall meet the following con-
dition under the fundamental combination of actions:
N Sd N 0 Rd 131 Þ

where N 0 Rd is the design value of resistance per unit length of roller contact,
which is calculated as

ð 3 :

N 0 Rk
g 2 m

N 0 Rd ¼ ð 3 : 132 Þ

where N 0 Rk is the characteristic value of resistance of the contact surface per
unit length calculated as

f u
E d

N 0 Rk ¼ 23 R ð 3 : 133 Þ

where R is the radius of contact surface (mm), f u is the ultimate strength of
material (N/mm 2 ), and E d is the design modulus of elasticity (N/mm 2 ). In
determining the values of N 0 Sd , the effects of asymmetrical loading due to
transverse eccentricities and applied moments shall be considered. Roller
plates shall be dimensioned in the direction of displacement to allow for
movement calculated for the fundamental combination of actions plus an
additional roller design movement of 2 t p , the thickness of the roller bear-
ing plate, or 20 mm whichever is greater. The length of the plates parallel to
the roller axis shall not be less than the length of the roller. In determining