PROPOSAL OF TRUSS FOR SIGN BOARD

Muhammad Haq�Tareq Alkhateeb�Maxim Mikhaylov

MTM Inc.

Design Requirement

To sustain a 14 foot billboard, our client have asked as to provide a design concept of planer truss of 9 ft width supported over a 10 ft support and 14 ft height is required.

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Design Requirement

• It was required that all the connected must be 1 ft from edges.
• The truss should be statically determinate.
• The internal force between the members should not exceed 2500 lbs.

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Determinate Structure

• A truss is said to be statically determinate if all of its support responses and member forces can be computed using solely static equilibrium equations. To be statically determinate, a planar truss number of members plus the number of support reactions must not be greater than the number of joints multiplied by two.
• 2j = m + 3 where j is the number of joints and m is the number of members
• 2j < m + 3, Statically determinate truss.

Expected Loading

• The truss designed is capable to support the weight of 14 ft high and 3 ft wide billboard which expected loading is 2800 lbs.
• The truss designed is made sure to resist the Uniformly Distributed load of 150 lb/ft due to wind from the right to left of truss.

Truss analysis method

• Analysis of Plane Trusses Using the Sections Method
• Choose a portion that goes through as many members with desired forces as feasible, but no more than three members with unknown forces. The segment should divide the truss into two sections.
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• Any of the two trusses may be used to compute the member forces
• We should choose the one that will take the least amount of computational effort in finding the unknown forces.

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Truss analysis method

• Analysis of Plane Trusses Using the Sections Method

2.(cont.)

• If one of the two sections of the truss does not have any reactions acting on it, then pick this component for the analysis of member forces and proceed to the next stage to eliminate the need for reaction computation.
• If both ends of the truss are connected to external supports, compute responses by applying the equations of equilibrium and condition (if any) to the free body of the entire truss. Next, pick the area of the truss for member force analysis that has the fewest external loads and reactions applied to it.

Truss analysis method

3. Draw a free-body diagram of the selected piece of the truss, including all external loads and reactions, as well as the forces in the members cut by the section. The unknown member forces are often believed to be tensile and are shown on the free-body diagram as arrows pulling away from the joints.

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Truss analysis method

4. Using the three equilibrium equations, calculate the unknown forces. To avoid solving simultaneous equations, attempt to apply the equilibrium equations such that each equation has just one unknown. This is occasionally possible by utilising the alternate systems of equilibrium equations (Fq = 0, MA = 0, MB = 0 or MA = 0, MB 14 0, MC = 0) mentioned in Section 3.1 instead of the standard two-force summations and a moment summation (Fx = 0, Fy = 0, PM = 0).

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Truss analysis method

5. Check the results using an alternate equilibrium equation that was not utilised to compute member forces. This alternate equation should ideally include all three of the member forces obtained by the study. If the analysis was done correctly, this alternate equilibrium equation must be met.

Or

You can use software like SAP2000 or Etabs which can analyse your truss very effectively and it’ll be easier for you to incorporate your desired changes to finalize the final design concept.

SAP2000 is able to do the hand calculation in a very little time with greater efficiency and similar method.

Proposed Design Concepts

Truss -1

Truss - 2

Truss - 3

Analysis Result

Truss -1

�The maximum force within the members is 1966 lb which satisfy the requirement of client that internal force within member does not exceed 2500 lb. Cost : $21388.48

Analysis Result

Truss - 2

�The maximum force within the members is 2624 lb which does not satisfy the requirement of client that internal force within member does not exceed 2500 lb. Cost : $28916.44

Analysis Result

Truss - 3

�The maximum force within the members is 2391.67 lb which does satisfy the requirement of client that internal force within member does not exceed 2500 lb. Cost: $26981.2

Finalized Design

• Final Design selected is truss one, as it require less beam length per foot which save a lot of cost. Doing a comparative cost analysis, truss 1 saves a lot of cost in comparison with truss 3 and truss 2 which is lesser than the cost of truss 2nd and lesser than truss 1. All the trusses are determinate but truss 2 doesn’t satisfy the load requirement. After all the analysis Truss no 1 is most favourable for the use of billboard representation.

Conform to the Requirement

• After application of 2800 lbs of gravity load expected from billboard and uniformly distributed wind load of 150 lb/ft from let face, analysis have shown maximum internal force in the member is -1966 lbs which conforms to the requirement that none of internal force of the truss member is greater than 2500 lbs or 2500 lbs. All of the connections of the truss are 1 ft away from edges.

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