NAME CM 3505 Fall 06 Test 2 Part 1 is to be completed without notes, beam tables or a calculator. Part 2 is to be completed after turning in Part 1. DO NOT turn Part 2 over until you have completed and turned in Part 1. DO NOT look at your notes sheet or beam tables until you have turned in Part 1. PART 2 INSTRUCTIONS To be started after turning in Part 1. A calculator, 1 sheet of notes front and back and beam tables are allowed while taking Part 2. Read the questions carefully. Do all that is asked for. Show your answers clearly. Include units wherever appropriate in your final answers for full credit. Part 2 is worth 77 points. There are a total of 14 problems. 7 3 pt. problems and 7 8 pt. problems. Points and an estimate of time needed are shown with each problem in Part 2. Part 1 is estimated to take 10 minutes and is worth a total of 23 points. (Bonus section) (10 pts max.) You will be given points from only one of the two bonus problems in this section. You may work both if you have time. Only the best score will be taken. Points for correct answers only. (10 pt. max)
Part 1 To be completed without notes or beam tables. 1) Short answer: (1 pt. ea. blank) Reinforced concrete is able to resist tensile forces due to the use of. Wood is generally stronger when stressed in a direction to the grain. Following the sign convention used in the text, a simple beam with only gravity loads acting between the supports would have a bending moment. (positive or negative) A simple beam as described in the previous question would be in on the top surface and in on the bottom surface. Following the sign convention used in the text, a cantilever with only gravity loads acting on it would have a bending moment. (positive or negative) Describe the centroid of an area.. 2) True or False: (1 pt. ea.) Creep is caused by short duration overstressing. Steel has a higher yield strength in tension than in compression. The need for fire protection is a major disadvantage of structural steel. The moment of Inertia can be described as a measure of resistance to bending and buckling. 3) Multiple choice: (1 pt. ea.) is the stiffest of the materials listed below. a) Concrete b) Steel c) Wood d) Brick
is much weaker in tension than compression. a) Concrete b) Steel c) Wood d) Plastic If a steel rod is placed between fixed supports then heated. will occur in the rod as the temperature rises. a) An increase in compressive stress b) An increase in tensile stress c) A decrease in shear stress d) No change in stress 4) ESTIMATE the radius of gyration about the x and y axis of the rectangle. Indicate your answers with units in the space provided and sketch the approximate location on the drawing. (2 pts.) y r x = r y = x 40 20 5) Indicate F y and the elastic region on the stress-strain curve of mild steel in tension shown below. (2 pts.) f ε
6) Which is the strong axis of the box beam. overall base = overall height, top and bottom elements have twice the thickness of the right and left elements. (1 pt.) x y Answer 7) Qualitative Shear and Moment Diagrams. Indicate line shapes and relative magnitudes, no values necessary. (4 pts.) P P V V M M
NAME Turn in this part of your test to get part 2 CM 3505 Test 2 a To be started after turning in Part 1. A calculator, 1 sheet of notes front and back and beam tables are allowed. Read the questions carefully. Do all that is asked for. Show your answers clearly. Include units wherever appropriate in your final answers for full credit. Part 2 is worth 77 points. There are a total of 14 problems. 7 3 pt. problems and 7 8 pt. problems. Points and an estimate of time needed are shown with each problem. 1) Determine y for the cross-section shown below. The shaded area is a hole. (8 pts.) y =
2) Determine the moment of inertia about the x-axis, of the built-up cross-section shown below. y is given and shown on the figure. Use the dimensions as shown on the drawing. NOT dimensional lumber sizes. (8 pts.) I xx = 3) Find the moment of inertia around the x-axis and y-axis of a W21x50. (3 pts.) I xx = I yy = 4) Find the radius of gyration about the x-axis of a W14x90. (3 pts.) r x =
5) Determine the Maximum allowable load (P) on the 2 diameter bar, if F a = 24,000 psi. (3 pts.) P = 6) The bolt in the figure below is 1 in diameter. If the load P is 10 kips, determine the average shearing stress in the bolt. (3 pts.) f v = 7) A column 16 long shortens ½ in. under load. Determine its average unit strain. (3 pts.) = 8) A sample of unknown material is being stressed in a tensile testing machine. Stress is found to be linear with strain in the elastic region. When initially loaded f = 5 ksi, =.0005, at a greater load, f = 20 ksi, =.002. Determine the E value for steel. Using information from the appendix, select a material that may have been the one tested. (3 pts.) E = Material selected
9) A 1 diameter mild steel rod, 10 long, supports a load of 10 kips. Determine its total elongation. (8 pts.) = 10) A 40 long roadway section made of concrete is exposed to temperatures within a range from 110 F to -10 F. Determine the total change in length of the roadway section over the full range of temperatures. (8 pts.) = 11) A W21x50 is used as a simple beam spanning 12. It must carry a uniform load of10 k/ft. Determine the maximum bending stress. (8 pts.) f b =
12) Determine the reactions and draw the shear and moment diagram for the beam shown below. (8 pts.) V M 13) Find section modulus, S x, for a C10x30 channel. (3 pts.) S x =
14) Select the lightest adequate W-section with a depth of 14 in or less, given that the maximum bending moment = 56 k-ft and the maximum allowable bending stress is 24 ksi. (8 pts.) Answer
(Bonus section) (10 pts max.) You will be given points from only one of the two bonus problems in this section. You may work both if you have time. Only the best score will be taken. Points for correct answers only. (10 pt. Max) Bonus 1) TRUSS Find the forces in the members AC, AD, BF, BG, BJ, CD, DI, EI, FI, and HI for the truss shown below. Indicate magnitude and sense of the forces in each member. (1 point per member) AC = AD = BF = BG = BJ = CD = DI = EI = FI = HI =
Bonus 2) BEAM DESIGN A simple beam spanning 12 has the loading pattern shown below. Determine the maximum bending stress and required section modulus, select the smallest adequate 2 x lumber section, using an allowable stress of 1150 psi. Then determine the extreme fiber bending stress and the bending stress at a y of 1 in. from the neutral axis. (4 pts.) M max = (2 pts.) S r = (2 pts.) 2 x selected (1 pt.) f b = (1 pt.) f y @ 3in. =