Question

If using a wooden Crossarm can it be made of Cedar?

Answer 1

Yes, wooden arm can be made up of Cedar or Western Red Cedar but after calculations we come to know that it's factor of safety is 2.67 which is comparatively very less than other trees like Pine has  5.26 and Eucalyptus has 6.34

14 Wood Type No. Density (kg/m^3) 570 570 650 655 510 Chapter 4 4.1 Mechanical properties of wood Type of wood Young's Modulus in the Hardwood/Softwood longitudinal direction (Gpa) Softwood 123 Softwood 121 Softwood 13.7 Softwood 12.7 Softwood 13.4 Softwood 126 Softwood 123 Softwood 103 Softwood 7.66 Softwood 9.24 Softwood 9.31 Softwood 10.08 Softwood 10.06 Hardwood 139 Softwood 97 Hardwood 26.14 Hardwood 21.08 Hardwood 12.14 Hardwood 12.15 Hardwood 10.9 Hardwood 12.62 Grass 18 Table 4.1.1 4|5|16] 1 Southern Pineloblolly 2 Southern Pine. Shortleaf 3 Southern Pine - Longleat 4 Southern Pine-Slash 5 Douglas-FIR . Coast 6 Douglas -FIR - Interior west 7 Douglas-FIR . Interior north 8 Douglas-FIR - Interior South 9 Western red cedar 10 Lodgepolepine 11 Jackpine 12 Scots Pine 13 Radiata Pine 14 Birch, yellow 15 Norway Spruce 16 Eucalyptus . Spotted Gum 17 Eucalyptus - Tallwood 18 Oak - Red 19 Oak-White 20 Yellow poplar 21 Maple 22 Bamboo 15 370 465 500 550 515 690 405 1080 1090 700 755 Modulus of Rupture(Mpa) 88.3 90.3 100 112.4 86.2 85 87 90 51.7 64.8 68.3 83.3 79.2 114.5 63 141.8 121.8 992 1023 60.7 109 168.6 705 850 Mechanical Properties Southern Pine - Longleat Western red cedar Eucalyptus - Spotted Gum Density (g/ m3) 650 370 1060 Modulus of rupture/Mpa) 100 51.7 141.8 EL(GPa) 13.7 7.66 26.15 ET(GPa) 0.75 0.42 1.50 ER(Gpa) 1.40 0.62 2.41 GLRIGpa) 0.97 0.67 1.74 GLTIGpa) 0.82 0.66 1.53 GRTIGpa) 0.16 0.04 0.84 Vrt 0.38 0.48 0.66 VIE 0.37 0.30 0.55 Vir 0.33 0.38 0.49 Table 4.1.2[5][6] Table 4.1.1 shows the different types of wood that has been used around the world and its important mechanical properties Table 4.12 shows the properties of wood that has been used for analysis in this research. The moisture content for all the three types of wood was considered to be 12%. Eucalyptus (Spotted Gum) has the highest mechanical properties in forms of Young's modulus, density and modulus of rupture while Westem red cedar has the least. This was the reason for their selection Southern pine wood was chosen as their properties lies in between Eucalyptus and Western red cedar and also, most of the crossars present currently are made from it.

It will be weak in nature due to shear stress