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What are the Adjustment Factors to be done in Design Values?

Posted in Timber Engineering | Email This Post |

Their is always some variation in the design values calculated in timber. Therefore we need to apply the required adjustment to them.

Case- Extreme Fiber Bending
Fb‘=FbCDCMCtCLCFCVCfuCrCcCf

where
Fb= design value for extreme fiber bending
CM =wet service factor
CCt =temperature factor
CL =beam stability factor
CF =size factor applicable only to visually graded, sawn lumber and round timber flexural members
Cv =volume factor applicable only when beams are glued or laminated
Cfu= flat use factor applicable only to dimension- lumber beams 2 to 4 in (50.8 to 101.6 mm) thick and glued-laminated beams
Cr= repetitive-member factor—applicable only to dimension-lumber beams 2 to 4 in (50.8 to101.6 mm) thick
Cc =curvature factor—applicable only to curved portions of glued-laminated beams
Cf =form factor
When the beams are glued, laminated we have to use the smallest of the two CL or Cc

Design value for Tension
Ft‘= FtCDCMCtCF

where
Ft – Design value for tension.

Fv‘=FvCDCMCtCH

where
Fv– design value for shear and CH is the shear stress factor >=1 permitted for Fvparallel to the grain for sawn lumber members.

Adjustment for compression perpendicular to the grain
design value Fc1‘is obtained from
Fc1‘=Fc1CDCtCb

where
Fc1is the design value for compression perpendicular to the grain
Cb is the bearing area factor.

Adjusted design value for compression parallel to the grain
Fc‘=FcCDCMCtCFCp
where
Fc is the design value for compression parallel to grain
Cp is the column stability factor.

Adjusted design value for end grain in bearing parallel to the grain
Fg‘= FgCDCt
where
Fg is the design value for end grain in bearing parallel to the grain.

The adjusted design value for modulus of elasticity, E’
E’= ECMCTC
where E= design value for modulus of elasticity
CT= buckling stiffness factor