Poll
| Evaluate the work of the engine |
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Radial Stresses and Curvature Factor
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The radial stress induced by a bending moment in a member of constant cross section may be computed from
fr=3M/2Rbd
Where:
- M= bending moment, in lb (N m)
- R = radius of curvature at centerline of member, in (mm)
- b =width of cross section, in (mm)
- d =depth of cross section, in (mm) |
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Bending and Axial Tension
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Members subjected to combined bending and axial tension should be proportioned to satisfy the interaction equations
[ft/Fc'+ f b/Fb*]<=1
And
[(fb-ft)/Fb**]<=1
Where:
- ft =tensile stress due to axial tension acting alone
- fb =bending stress due to bending moment alone
- Ft‘=design value for tension multiplied by applica- ble adjustment factors
- Fb*=design value for bending multiplied by appli- cable adjustment factors except CL
- Fb**=design value for bending multiplied by applica- ble adjustment factors except Cv |
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Adjustment Factors
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Design values obtained by the methods described earlier should be multiplied by adjustment factors based on conditions of use, geometry, and stability. The adjustments are cumulative, unless specifically indicated in the following:
ADJUSTMENT FACTORS FOR DESIGN VALUES
The adjusted design value Fb‘ for extreme-fiber bending is given by
Fb‘=FbCDCMCtCLCFCVCfuCrCcCf
Where:
- Fb= design value for extreme-fiber bending
- CD= load-duration factor
- 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 to glued- laminated beams
- 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 |
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Compression on oblique plane
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Consider that a timber member sustains a compressive force with an action line that makes an oblique angle with the grain.
Let :
- P=allowable compressive stress parallel to grain
- Q= allowable compressive stress normal to grain
- N =allowable compressive stress inclined to grain
- x=angle between direction of stress N and direction of grain
By Hankinson’s equation,
N=PQ/(Psin2x+Qcos2x)
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Size and Volume Factors
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For visually graded dimension lumber, design values Fb, Ft, and Fc for all species and species combinations, except southern pine, should be multiplied by the appropriate size factor Cf, given in reference data to account for the effects of member size.
This factor and the factors used to develop size-specific values for southern pine are based on the adjustment equation given in American Society for Testing and Materials (ASTM) D1990. This equation, based on in- grade test data, accounts for differences in Fb, Ft, and Fc related to width and in Fb, Ft, related to length (test span). For visually graded timbers [5*5 in (127*127 mm) or larger], when the depth d of a stringer beam, post, or timber exceeds 12 in (304.8 mm), the design value for bending should be adjusted by the size factor
CF= (12 /d)1/9
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Combined bending and axial load
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Members under combined bending and axial load should be so proportioned that the quantity
Pa/P +Ma /M < 1
Where:
- Pa total axial load on member, lb (N)
- P= total allowable axial load, lb (N)
- Ma= total bending moment on member, lb in (Nm)
- M =total allowable bending moment, lb in (Nm) |
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Invitation to tender When all the preliminaries are completed and the owner has decided to proceed with the work, tenders are invited. Legally this is an attempt to check if there would be interested contractors to carry out the work within the estimated limit of time and finance. The invitation to Tender is not binding to the owner to proceed with the work and does not cause any liability for any expenses to which contractors would spend in preparing and submitting their construction bids.