LRFD BEAM DESIGN FULL

That is, a rigid frame with a All three methods summarized by AISC5 assume a lin-ﬁxed base plate will usually attract enough bending mo- ear triangular distribution of the resultant compressivement to require anchor rods to prevent uplift of the base bearing stress. This is a common situation for ﬁxed base platesin structural ofﬁce practice.

Assume independent strain distribution.crete. Assume a linear strain distribution such that the an- chor rod strain is dependent on the bearing area Case D evolves from Case C by the addition of sufﬁ- strain.cient bending moment to require anchor rods to preventseparation between the base plate and the supporting con- 3. Assume that the resultant compressive bearing stresscorresponds to the common elastic limit where any addi- is directly under the column ﬂange.tional moment would initiate separation between the baseplate and the supporting concrete. Case C evolves from Case B by the addition of a spe- ciﬁc bending moment such that the uniform pressure dis- tribution is the smallest possible length without separation ENGINEERING JOURNAL / FIRST QUARTER / 1999 29īetween the base plate and the supporting concrete.

LRFD BEAM DESIGN FULL

The moment changes the full length uniform pressure distribution to a partial length uniform pressure distribution, but is not large enough to cause sepa- ration between the base plate and the supporting concrete. Case B evolves from Case A by the addition of a small bending moment. This case is summarized in the LRFD Manual4 beginning on page 11-54 and is summa- rized herein for completeness. This case results in a full length uniform pressure distribution between the base plate and the supporting concrete. Case A is a load case with axial compression and shear, without bending moment. The progression of beam-column loadings, in order of in- creasing moments, is presented in four load cases. Elkin is Structural Engineer, Fluor Daniel, Irvine,CA. Drake is Principal Structural Engineer, Fluor x ‫ ס‬f Ϫ d ‫ ם‬tf (3)Daniel, Irvine, CA. Base Plate Design Variables moment direction, in.Richard M. A typical beam-column base plate geometry is shown n ‫ ס‬B Ϫ 0.80b f (2)in Figure 1, which is consistent with that shown on page 211-61 of the LRFD Manual.4 x ‫ ס‬base plate tension interface cantilever parallel to Fig. f ‫ ס‬anchor rod distance from column and base plate Typically, these beam-column base plates have beendesigned and/or analyzed by using service loads1 or by centerline parallel to moment direction, in.approximating the stress relationship assuming the com- m ‫ ס‬base plate bearing interface cantilever directionpression bearing location.2 The authors present anotherapproach, using factored loads directly in a method consis- parallel to moment direction, in.tent with the equations of static equilibrium and the LRFDSpeciﬁcation.3 m ‫ ס‬N Ϫ 0.95d (1) 2 The moment-resisting base plate must have designstrengths in excess of the required strengths, ﬂexural (Mu), n ‫ ס‬base plate bearing interface cantilever perpendic-axial (Pu), and shear (Vu) for all load combinations. ELKIN INTRODUCTION where:It is common design practice to design a building or struc- B ‫ ס‬base plate width perpendicular to moment direc- tion, in.ture beam-column with a moment-resisting or ﬁxed base.Therefore the base plate and anchor rods must be capable N ‫ ס‬base plate length parallel to moment direction, in.of transferring shear loads, axial loads, and bending mo- b f ‫ ס‬column ﬂange width, in.ments to the supporting foundation.

> girder plate beam ywywFEthFEth Bending M = bending moment at the cross section under consideration y = perpendicular distance from the neutral plane to the point of interest xI = moment of inertia with respect to the neutral axis xS = elastic section modulus of the cross section For elastic analysis, from the elementary mechanics of materials, the bending stress at any point can be found xbIMyf= The maximum stress xxxSMcIMIMcf=/max This is valid as long as the loads are small and the material remains linearly elastic.Beam-Column Base Plate Design-LRFD MethodRICHARD M. Wang 153:134 structural Design II Shapes that are built up from plate elements are usually called plate girders the difference is the height-thickness ratio wth of the web. Chapter F and Appendix F of the Commentary of the AISC LRFD Specifications ( part 16 of LRFD Manual) Basic Theory If the axial load effects are negligible, it is a beam otherwise it is a beam -column. Chapter F and Appendix F of the AISC LRFD Specifications ( part 16 of LRFD Manual) 3. Example: confidence Search Design of Beams (Flexural Members) (Part 5 of AISC/LRFD)ĥ3:134 structural Design II Design of Beams ( flexural members ) ( part 5 of AISC/LRFD) References 1.

Lrfd beam design