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Design of Wood Beams

Jonathan Ochshorn

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Directions: Enter values for span (ft), spacing, species, grade, live and dead load (psf), duration of load and wet service conditions, allowable deflection criteria (e.g., span/360 for live load only), and select dimensions and properties from either the 2005 or 2012 National Design Specification (NDS). Updated design values for Southern Pine dimension lumber, effective June 1, 2013, are included with the 2012 NDS settings. Choose design criteria by entering "yes" or "no" in the appropriate cells. Press "update" button.

The two lightest sawn lumber sections for the 4 framing plan options shown below will be displayed. More detailed explanations and examples of wood beam design can be found in my text.

Note that the allowable stress method is used; only rectangular sawn lumber sections are tested; beams are assumed to be simply-supported and may be laterally-braced either continuously or only at the supports and point loads (if any).

Four plan types are included for each selection of beam span and spacing, as shown in the framing plans below:

sketch showing building dimensions
Fig. 1. Framing plans and load diagrams: a) uniformly-distributed load; b) single concentrated load at midspan; c) concentrated loads at third-points; and d) concentrated loads at quarter-points
 

span (ft) spacing   load of least duration wet service conditions?
 
species live load (psf) dead load (psf)  
 
 
grade  
 
 
allow. live load deflection = span/  
 
 
allow. total load deflection = span/  
 
 
 
Load type Mmax (ft-lb) Vmax (lb)* Lightest choice Next-lightest
 
Design criteria (these do not apply to alternate method below):  
  reduction coeff: live load (psf) used:  
 
 
 
 
 
 
 
 
   
 
 
 
Checks:  
errors:  
selected grade does not exist  
span must be greater than 0  
spacing must be greater than 0  
live load must be greater or equal to 0  
dead load must be greater or equal to 0  
LL defl. demoninator must be greater than 0  
TL defl. denominator must be greater than 0  
 
 
alternative method errors:  
selected grade does not exist  
Alternative moment must be greater than 0  
Alternative shear must be greater than 0  
 
warnings: