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4.2.4.2 Effective bridge temperaturesV.4.2.4.2Amendment No. V-l/92 (Jan.)Values of basic effective bridge temperaturesshould be obtained from Table 4.2.5 for superstructureGroups 1 to 4. Basic effective temperatures appropriateto a return period of 120 years should be used except forthe cases given below.Basic effective bridge temperatures appropriateto a return period of 50 years may be used for :(i) foot/cycle track bridges,(ii) carriageway joints and similar equipmentlikely to be replaced during the life of thestructure,(iii) erection loading.4.2.4.2.1 Adjustment for thickness of surfacingThe effective bridge temperatures are dependenton the depth of surfacing on the bridge deck, and thevalues given in Table 4.2.5 assume surfacing depths of 40mm for Groups 1 and 2 and 100 mm for Groups 3 and 4.Where the depth of surfacing differs from these values,the minimum and maximum effective bridge temperaturesshould be adjusted by the amounts given in Table 4.2.64.2.4.2.2 Adjustment for height above mean sea levelThe values of effective temperature given inTable 4.2.5 shall be adjusted for height above mean sealevel by subtracting 0.5°C per 100 m height for minimumeffective temperatures and 1.0°C per 100 m height formaximum effective temperatures.4.2.4.2.3 Range of effective bridge temperatureIn determining load effects due to temperaturerestraint, the effective bridge temperature at the timethe structure is effectively restrained shall be taken asdatum in calculating expansion up to the maximumeffective bridge temperature and contraction down to theminimum effective bridge temperature.4.2.4.3 Temperature differenceEffects of temperature differences within thesuperstructure should be derived from the data given inFigure 4.2.2.Positive temperature differences occur whenconditions are such that solar radiation and othereffects cause a gain in heat through the top surface ofthe superstructure. Conversely, reverse temperaturedifferences occur when conditions are such that heat islost from the top surface of the bridge deck as a resultof re-radiation and other effects.