Load tracing - UMass...
Transcript of Load tracing - UMass...
Load tracing
Loads travel along load paths Load path analysis is known as load tracing
How a Light-Frame Building Resists Loads (Building Construction by Mehta et al., 2008)
Ground Reaction
Why do load tracing?
Load tracing determines how much load is apportioned to individual members When we know how much load each member carries, we can analyze the member by using:
______ ______ diagrams and equations of _____________
Tributary dimensions tributary width: the distance between midway of adjacent similar members
tributary area: the area that is assumed to load any given member tributary area = tributary width x span
Tributary width of joist A = _____
Tributary width of joist C = _____
Tributary area of joist D =______
Tributary dimensions of a beam or column
Tributary width for Beam A = ______________
Tributary area for Column C = ______________
Column C
Load paths
Load (plf)
Reactions (lb)
Loads (lb)
Ground
reactions (lb)
joist
column
Area loads from roof and floor become line loads on trusses and joists Truss and joist reactions become point loads on studs below
Units!
• Area loads:
• Line loads:
• Point loads:
Calculating line loads from area loads
Line load (plf) = area load (psf) x trib. width (ft)
**Find FBD of G1 given
area load = 100psf
Calculating point loads (reactions) from line loads (statics review)
Example: simply supported beam with uniform load
10 ft
Beam
Column
below
1000 plf
Column
below
Calculating reactions from line loads
For a general case, solve for reactions using equations of equilibrium. (statics review)
15 ft
Beam
Column
below
1000 plf
3 ft
Column
below
Classwork to hand-in – load tracing practice BCT 540 Design of Wood Structures
1. Given the joists are 2ft o/c, area load is 30psf and the RTU weighs 400lb, find the
line and point loads on joist A.
2. Draw the Free Body Diagram.
3. Find the reactions on the girders.
Girder
Girder
Double joist A
Roof top unit (RTU) at
midspan on sleepers 20’
Homework – load tracing practice BCT 540 Design of Wood Structures
Given the area load is 50psf, find the line loads and point load on joist A above.
That is, put the magnitudes on the free body diagram shown.
Joist A
Open
to
below
2’ o/c
Similar framing in 3D