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' No. <br />1 <br /> TABLE N0. 2 <br />Theoretical Bending Stresses by Layer, Span Condition, and Support Condition <br /> <br />Roof Thick- <br />Span Hess ~nfs ~f ~f ~s ifs ifs <br />(f t.) (in.) (psi) (psi) (psi) (psi) (psi) (psi) <br />15 9.6 1688 1264 1421 240 179 201 <br />18 2430 1873 2080 345 266 295 <br />20 3000 2349 2589 426 334 368 <br />15 31.2 519 389 437 354 265 298 <br />18 748 576 640 510 393 436 <br />20 923 723 797 629 493 544 <br />15 45.6 355 266 299 483 362 407 <br />18 512 395 438 696 538 596 <br />20 631 494 545 859 672 741 <br />Cnfs - stress from unsupported roof condition (no friction or suspension) <br />~f - stress from friction supported condition <br />Cs - stress from suspension supported condition <br />ifs -stress from combined friction and suspension supported condition <br />*Rock bolts post tensioned to 13,600 psi <br />**Rock bolts post tensioned to 3400 psi <br />