Expansion joints must accommodate movements produced by concrete shrinkage
and creep, post-tensioning shortening, thermal variations, dead and live loads,
wind and seismic loads, and structure settlements. Concrete shrinkage,
post-tensioning shortening, and thermal variations are generally taken into
account explicitly in design calculations. Because of uncertainties in
predicting, and the increased costs associated with accommodating large
displacements, seismic movements are usually not explicitly included in
calculations.
****Expansion joints should be designed to accommodate all shrinkage
occurring after their installation. For unrestrained concrete, ultimate
shrinkage strain after installation,?, may be estimated as 0.0002. More-detailed
estimations can be used which include the effect of ambient relative humidity
and volume-to-surface ratios. Shrinkage shortening of the bridge deck,? shrink,
in mm,is calculated as

**?shrink = (?) · (µ) · (Ltrib) · (1000 mm/m)where
Ltrib  =  tributary length of structure subject to shrinkage; m
? = ultimate  shrinkage  strain  after  expansion  joint  installation; 
estimated  as  0.0002  in  lieu  of more-re?ned calculations
µ =  factor accounting for restraining effect imposed by structural elements
installed before slab is cast
= 0.0 for steel girders, 0.5 for precast pre-stressed concrete girders, 0.8 for
concrete box girders and T-beams, 1.0 for ?at slabs Thermal displacements are
calculated using the maximum and minimum anticipated bridge deck temperatures.
These extreme values are functions of the geographic location of the structure
and the bridge type. Thermal movement, in mm, is calculated as
?temp = (?) ·
(Ltrib) · (?T) · (1000 mm/m) (25.2)**where
? = coef?cient of thermal expansion; 0.000011 m/m/°C for concrete and 0.000012
m/m/°C for steel
Ltrib = tributary length of structure subject to thermal variation; m
?T = temperature variation; °CAny  other  predictable  movements  following 
expansion  joint  installation,  such  as  concrete  post-tensioning shortening
and creep, should also be included in the design calculations.