There are several charts available that specify beam sizes based on span, spacing and types of materials used. A beam 20 foot long would be difficult to create with dimensional lumber, but not impossible. You will be more likely to find that a LAM or steel beam will be required.
16. Given a girder loaded as follows: Effective span 28 feet; center load 4,000 lbs.; and a load, 7 feet each side of cen ter, of 3,000 lbs. Required the size of beam such that the deflection will not exceed plaster limits. 17. Given a warehouse 180 feet by 80 feet inside of walls. Columns spaced 18 feet longitudinally and 16 feet transversely.
I wanted to double check the size of a beam recommended by an online structural engineer. I am going to span 18' length with an LVL beam. The beam is going to be flush to the ceiling joist and recessed into the attic. One end will sit on a post that will go to the block foundation, the other will attach to a 3' beam on each side of a hallway.
You can put the days of cold wet feet behind you.
For a clear space of less than 70 feet wide, a straight wall column & beam structure can be built. You will still have open space, but are limited to that maximum size. For a space from 70 to 150 feet in width void of beams or posts, a pre-engineered steel structure is the way to go.
Do not space vertical stirrups closer than 100mm. Therefore, the size of stirrups should be chosen to prevent closer spacing. Distribute stirrups uniformly over short span beams. However, over long spans, it is more economical to compute the spacing required at several sections. And, place stirrups accordingly in groups of varying spacing.
Assume that the beam is a W27x84 made of ASTM A992 steel. The concrete has a 28-day compressive strength, f' c, of 3,000 psi. Use the same thickness for the two plates. Neglecting its own weight, the beam supports two concentrically loaded columns. The leftmost column supports 50 k dead load, 75 k live load, and 20 k snow load.
Span of Beam (inches) Tributary width (inches) Uniform Load(pounds/square foot) e.g. 40/10=50psf: Yield Strength of Steel (KSI) e.g. 36 or 50: Select Beam
Beam: A horizontal structural member that supports the structure above it Column: A vertical upright used to support a structure Girder: A large beam that frames into a column on each end and supports the beams framing into it Wide-Flange: A steel beam or girder shaped like the letter I Please reference Figure 1. Figure 1: Wide-Flange Shapes