Calc. No.    
Project Title:   Calc. By Date Rev.    
Steel beam capacity calculation in accordance with the "Manual of Steel Construction" Load and Resistance Factor Design" (LRFD)  
Beam Design for Flexure and Lateral-Tortional Buckling.  
Section properties           Braced length        
Section           Lb = 150 in      
A = in2 beam cross-sectional area Lb - distance between points braced against lateral    
Iy = in4 moment of inertia about Y axis displacementof the compression flange or between  
Sx = in3 elastic section modulus - major axis points braced to prevent twist of the cross section.  
ry = in radius of gyration about minor axis (This parameter can not be mdoified in the Demo Version)  
J = in4 tortional constant            
Cw = in6 warping constant            
Zx = in3                    
Steel properties                      
E = ksi modulus of elasticity of steel   per Manual of Steel Construcion (LRFD)  
G = ksi shear modulus of elasticity of steel   Chapter F Section 2.a  
Fy = ksi minimum yield stress of the type of steel being used          
Fyf = ksi yield stress of flange          
Fyw = ksi yield stress of web          
Fr = ksi compressive residual stress in flange for rolled shapes Fr = 10 ksi, for welded shapes Fr = 16.5 ksi  
Cb =   bending coefficient dependent upon moment gradient Cb is permitted to be conservatively taken as 1.0  
fb =   resistance factor for flexure          
Yielding flexural design strength             per Manual of Steel Construcion (LRFD)  
Mp = Fy * Zx = kip-ft plastic section moment < 1.5 My Chapter F Section 1.  
    1.5*My = Fy * Sx = kip-ft              
Mn = Mp = kip-ft                    
fb * Mn = kip-ft Yielding flexural design bending moment      
Lateral - torsional Buckling         per Manual of Steel Construcion (LRFD)  
Lr - limiting laterally unbraced length Chapter F  
Lp = 1.76*ry*sqrt(E/Fyf) = in       Eq. F1-4 for I shaped members and channels  
FL = smaller of (Fyf - Fr) or Fyw                  
FL = ksi                    
Mr = FL * Sx = kip-ft         Eq. F1-7        
X1 = (p/Sx)*sqrt(EGJA/2) = ksi       Eq. F1-8        
X2 = 4*(Cw/Iy)*(Sx/GJ)2 = ksi-2       Eq. F1-9        
Lr = (ry*X1/FL)*sqrt(1+sqrt(1+X2*FL2)) = in     Eq. F1-6        
for Lb < Lr         Chapter F Section 2.a applies  
Mn = Cb*[Mp-(Mp-Mr)*(Lb-Lp)/(Lr-Lp)] = Eq. F1-2        
fb * Mn =              
for Lb > Lr         Chapter F Section 2.b applies  
Mn = Mcr                      
Mcr = Cb*Sx*X1*sqrt(2)/(Lb/ry)*sqrt(1+X12*X2/(2*(Lb/ry)2)              
Mcr =          
fb * Mn =                      
Manual of Steel Construction - American Institute of Steel Construction Inc., 2005