The beam stability factor, C L, accounts for the possibility of lateral-torsional buckling when the compression edge of a beam isnot adequately braced. Wood beams acting individually must be designed accordingto the most conservative assumptions regarding their actual strength whereas closely-spaced joistsor rafters enjoy an additional margin of safety - particularly heavy concentrated loads (or unusuallyweak joists or rafters) are "helped out" by the adjacent members. The repetitive member factor, C r, accounts for the increased safety of joists and rafters made from dimension lumber when they are joined by floor or roof decks and spaced not more than 24 in. The flat use factor, C fu, accounts for the apparent increase in bending strength when beams are stressed about their weak axes. In addition to factors for load duration, wet service conditions, and size, three new adjustment factors are introduced for bending: a flat use factor, a repetitive member factor, and a beam stability factor ( Appendix Table A-3.6). This adjusted value is found by multiplying the tabular value, F b ( Appendix Table A-3.5), by various adjustment factors. Wood beams are generally designed for bending stress and then checked for shear and deflection.Using allowable stress design, the required section modulus is found by dividing the maximum bendingmoment by the adjusted allowable bending stress, F b', as shown in Equation 1.24. Introduction to wood | Material properties | Sectional properties | Design approaches | Construction systems | Tension elements | Columns | Beams | Connections | Ch.
0 kommentar(er)
