153) | |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | NOTE .-- The working unit-stresses given in the table are intended for railroad bridges and trestles.

For highway bridges and trestles the unit-stresses may be increased | | twenty-five (25) per cent.

For buildings and similar structures, in which the timber is protected from the weather and practically free from impact, the unit-stresses may be | | increased fifty (50) per cent.

To compute the deflection of a beam under long-continued loading instead of that when the load is first applied, only fifty (50) per cent of the | | corresponding modulus of elasticity given in the table is to be employed.

| |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | | BENDING | SHEARING | COMPRESSION | | | |---------------------------------+-----------------------------------------+-------------------------------------------------------------------------| Ratio | | | Extreme | Modulus of | Parallel to | Longitudinal | Perpendicular | Parallel to | For | Formulae for | of | | | fibre | elasticity | the grain | shear in | to the grain | the grain | columns | working stress in | length | | KIND OF | stress | | | beams | | | under 15 | long columns over | of | | TIMBER |--------------------+------------+--------------------+--------------------+--------------------+--------------------| diameters | 15 diameters | stringer | | | Average | Working | | Average | Working | Elastic | Working | Elastic | Working | Average | Working | working | | to | | | ultimate | stress | Average | ultimate | stress | limit | stress | limit | stress | ultimate | stress | stress | | depth | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Douglas fir | 6100 | 1200 | 1,510,000 | 690 | 170 | 270 | 110 | 630 | 310 | 3600 | 1200 | 900 | 1200( 1-_l_/60_d_) | 10 | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Longleaf pine | 6500 | 1300 | 1,610,000 | 720 | 180 | 300 | 120 | 520 | 260 | 3800 | 1300 | 980 | 1300( 1-_l_/60_d_) | 10 | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Shortleaf pine | 5600 | 1100 | 1,480,000 | 710 | 170 | 330 | 130 | 340 | 170 | 3400 | 1100 | 830 | 1100( 1-_l_/60_d_) | 10 | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | White pine | 4400 | 900 | 1,130,000 | 400 | 100 | 180 | 70 | 290 | 150 | 3000 | 1000 | 750 | 1000( 1-_l_/60_d_) | 10 | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Spruce | 4800 | 1000 | 1,310,000 | 600 | 150 | 170 | 70 | 370 | 180 | 3200 | 1100 | 830 | 1100( 1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Norway pine | 4200 | 800 | 1,190,000 | 590[d] | 130 | 250 | 100 | | 150 | 2600[d] | 800 | 600 | 800( 1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Tamarack | 4600 | 900 | 1,220,000 | 670 | 170 | 260 | 100 | | 220 | 3200[d] | 1000 | 750 | 1000( 1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Western hemlock | 5800 | 1100 | 1,480,000 | 630 | 160 | 270[d] | 100 | 440 | 220 | 3500 | 1200 | 900 | 1200( 1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Redwood | 5000 | 900 | 800,000 | 300 | 80 | | | 400 | 150 | 3300 | 900 | 680 | 900( 1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Bald cypress | 4800 | 900 | 1,150,000 | 500 | 120 | | | 340 | 170 | 3900 | 1100 | 830 | 1100( 1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | Red cedar | 4200 | 800 | 800,000 | | | | | 470 | 230 | 2800 | 900 | 680 | 900( 1-_l_/60_d_) | | |-----------------+----------+---------+------------+----------+---------+----------+---------+----------+---------+----------+---------+-----------+-------------------+----------| | White oak | 5700 | 1100 | 1,150,000 | 840 | 210 | 270 | 110 | 920 | 450 | 3500 | 1300 | 980 | 1300( 1-_l_/60_d_) | 12 | |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | These unit-stresses are for a green condition of timber and are _l_ = Length in inches.