Tables to Summarize Your Calculations
The table below summarizes the truss calculations. These calculations are for a single truss subjected to 1,000 lbs. Please use the full 1,000 lb. load in your truss calculations. Do not divide the 1,000 lb. load by the number of parallel trusses used for your design (that is, don't base your calculations on 500 lbs. if your design has two parallel trusses).
Members |
Member Length (in) |
Member Area (in^2) |
Member I (in^4) |
Type of |
Total
Member Force (lbs) |
T or C |
Axial Stress (psi)** |
Predicted Buckling Load (lbs) |
AB, DE | ||||||||
AG, EF | ||||||||
BC, CD | ||||||||
BG, DF | ||||||||
CG, CF | ||||||||
GF |
* Member Type Designations
** Taken at point of peak stress (which could be at the joint hole)
Symbol | Member Description |
S | single flat member |
B | single thickness bent member (such as "L" shaped) |
Mx | multiple stacked flat members where "x" is the number of stacked members |
C | composite members: multiple members fastened together to form a 3D shape such as a "T" or "I". |
The next table summarizes the calculations used to predict the failure load. This table should also be based on 1,000 lbs. being applied to a single truss. Be sure to supply the tensile strength of the truss member material as well as the shear strength of the screws used to connect the members at the joints ABOVE the table.
Tensile Strength of Member Material = _______________
Shearing Strength of Joint Screw Material = ______________
Members |
T or C |
Total
Member Force (lbs) |
Member Axial Stress (lbs)* |
Tensile FS |
Member Predicted Buckling Load (lbs) |
Buckling
Load FS |
Shear Stress in Joint Screw (psi) |
Screw FS |
AB, DE | ||||||||
AG, EF | ||||||||
BC, CD | ||||||||
BG, DF | ||||||||
CG, CF | ||||||||
GF |
* This is based on information from the in-class tensile testing.
Tensile FS = Tensile Strength of Member Material / Member Axial Stress due to 1000 lb Load
Buckling Load FS = Load to Buckle Member /
Total Force in Member due to a 1000 lb. Load
Screw FS = Shearing Strength of Joint Screw Material / Shearing Stress in Joint Screw due to a 1000 lb Load
Note that some joint screws will be in single shear, and some will be in double shear. From the table above, the member with the lowest factor of safety is the critical member. The predicted failure load can be obtained as follows:
Predicted Failure Load = 1000 lbs * FS * Number of Parallel Trusses