Show strength of mine timbers BY LUTSON LETSON the ordinary handbooks that are available for the use of miners and tim bermen seem to contain very little information on the strength of timbers that are commonly used in and around mines in fact there is less known about the strength of wood than any other structural material wood is used in such tremendous quantities around the mines that it would seem SAFE LOAD IN TONS sate safe load in tons for timbers when used as posts center pieces in shaft timbers in head frames trestles and sup ports for and buildings the figures are for first grade pine timbers allowance to be made for poorer grades length of post or stull in feet 1 61 6 81 8 10 12 1 16 1 20 24 28 32 40 50 60 ax 4 1 91 9 81 S 71 7 5 2 I 1 1 I 1 1 I 1 1 I 1 1 I 1 1 ax 6 1 30 22 20 IS 18 1 14 1 5 ax 8 1 53 51 37 ah 1 32 1 26 21 16 10 1 I 1 1 82 82 sa sa 1 55 1 50 42 35 30 17 1 1 1201 1201 1151 1 90 1 sa 70 62 55 38 20 1 1601 1601 1601 1 1 1201 1051 95 85 68 45 23 the weight on oil long posts may be increased it if they are braced to prevent buckling or bending table by letson balliet E al C E table by letson balliet E al C E 14 LOADS ON PLANKS 7 table le of safe loads that can be placed and tunnels the loads are figured tor for yle lie on planks over shafts and dinzes and upon center of the span and may pe be doubled staging or when used as lagging in shafts when load is distributed sizes of length ol of spans in teet feet planks and 1 4 1 6 8 i 1 10 1 12 1 14 1 16 1 is 18 lagging safe load in pounds 1 1 1 1 1 1 1 1 1100 1 1 SO 1 1 1 1 1800 1 1200 1 1 1 1 1 1 2500 1 1800 1 1300 1 1000 1 SOO 1 table by letson balliet E M C E SAFE LOAD FOR TIMBERS safe loads for timbers of first grade figured in pounds for safe loads not breaking pine when used for for beams girders wall loads plates and plates caps and bents load is 1 length of span in feet 1 41 61 81 is 21 ax 4 I 1 soo 2751 2251 1601 1 1 X 1 70 0 i 0 1 4 5 01 1 1 ax G ta 0 0 1 1300 1100 soo ax 6 01 2000 f 6 0 0 j 1 21 CO 1800 1 1250 ax S 1 2 1700 1 8 X 8 1 72 01 1 01 i 1 2 1 1 01 6 63 0 0 1 00 0 1 9 0 0 01 75 01 1 1 4 1 1 L b U U I 1 ta 00 01 1 01 3 f 4 1 70 01 17 1 6 9 6 0 1 burul be doubled for loads that are and may loads are figured at the center of the span PROVIDED D that doubling does not equally distributed throughout the length of the span of tour four feet the bearings at the exceed the figures given in the first fir s t column for spans beam section of t the he end of the spans must have an area equal to a ta table le by letson balliet Ball let E al C E that the state mine aline inspectors accident commissions and even the bureau of mines should furnish ready tables for miners many times I 1 have been asked to prepare tables for operators who wished them for their own reference generally from desire to increase the safety factor that the industrial insurance rate might be lowered the increasing number of requests makes it advisable that they be put in print in the most convenient and simplest form in the hope that the greatest number may benefit by them in squeezing ground when the thrust or load is applied horizontally these figures may be used for horizontal and braces provided the center of the stull is properly supported to hold its weight and prevent buckling or bending in tunnel timbers where the posts are set at an angle with the bottom or floor of the tunnel wider than the cap the weight that the post will carry is reduced by the pitch of the timber two timbers set like a letter A will not carry as much weight as the same two timbers standing like a post under the load the load varies with the angle of the incline safe loads for timbers at an incline per cent of hor vert angle vertical load dist dist from vert Veit allowable if 11 in it I 1 45 7 70 0 V 1 in 2 27 8 80 0 if 1 in V 3 19 9 94 4 clo it I 1 in af V 14 9 96 6 ello if f in 7 so 8 9 98 s co if f in 10 go 6 99 9 9 co long spans may be braced to prevent buckling example an A frame of two 6 in timbers 6 feet long at 45 degrees will support 42 tons whereas the two ain set as posts under the load will support 60 tons 30 tons for each post if spans are braced loads may be increased A common error is in using timbers too big and all out of proportion to the load they are called upon to sustain this is undue extravagance and they are no safer than timbers of the right size and often last no longer under ground though to the mine inspector oversized timbers do not offer the objection that undersized timbers oner offer however with the s price of lumber and timbers this ii ele s waste is IS not only reducing the alvide dividers us by increasing the expense but it is wasteful of the lumber and causing the price to still further increase the other extreme of undersized or overloaded timbers is not only dangerous in too frequent but causes enormous expense replacements which is also wasteful of lumber and frequently fre increase the maintenance expense in cleaning up the re riffi clency Elig engineer ineer 1508 hobart build ing san francisco calif sult suit of caves and broken timbers if not indeed the loss of some part of the mine for the benefit of all concerned I 1 have not copyrighted these tables that publishers of handbooks and magazines mine inspectors spec tors accident commissions and insurance companies may reprint as they see fit |