University of Massachusetts - AmherstDepartment of Civil & Environmental Engineering

CEE 331: Structural Analysis

Homework #4 Due October 7

Problem 1: Hibbeler 7-6. Calculate only the force in elements GF BC BF GC.

Problem 2: Construct a MASTAN model of the truss you solved in problem 1. As-sume that all members have cross sectional areaA = 0.5sq. in. andE = 10000ksi

Be very careful of units when building your MASTAN model. Attach a printout of theaxial force diagram.

Problem 3: Increase by a factor of 6 the cross sectional area of the top chord of thetruss in your MASTAN model. Rerun the analysis. Attach a printout of the axial forcediagram.

Problem 4: Summarize the results of Problems 1-3 in the table below. Indicate units.

Element Prob. 1 Force Prob. 2 Force Prob. 3 Force

GF

BC

BF

GC

Problem 5: Comment on your results. How close are the approximate results? Howmuch difference does the change in area to the top chord make?...

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Problem 6: NOTE: This problem is intentionally vague. Think hard about each step.All but equations must be typed. Figures can be hand drawn butmust be very clear andneat. Explain in words each step of your analysis and the thought process underlyingyour work. Clear presentation will count for 1/3 of the points in this problem.

Perform an approximate analysis of the main wind resisting truss of the Chicago Han-cock Tower. Use the idealization shown below.(a) Comment on the idealization. What simplifications to theactual structure have Imade. Evaluate the overall quality of the idealization.(b) Calculate using an approximate method the forces in elements 1-2, 1-3, 2-4, and3-4. State whether you are assumption 1 or 2 and your justification. To perform thisanalysis you will need to find or estimate dimensions of the building and then calculatethe numerical value ofP from the building dimensions and an assumed wind pressureof 20 psf.(c) Construct a MASTAN model of the Hancock idealization. AssumeA = 1750sq.in.

for all members andE = 29000ksi. Compare the results of the MASTAN analysis tothe results of the approximate analysis. What are the percentage differences? Judgethe quality of the approximate results.(d) Include two MASTAN axial force diagrams, one showing theaxial force in thevertical members only and one showing the axial force in the diagonal members only.Comment on the analogy between these axial force diagrams and the shear and momentdiagrams of a vertical cantilever beam with the same loads asapplied to the Hancocktower.

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