Class Exercise-1 Truss Structure & Stability

Transcription

1 Class Exercise-1 Truss Structure & Stability 1) How many bars do you need to make a simplest stable truss? a) 4 b) 3 c) 5 d) 0 2) The figure below shows three frame structure A, B, C respectively. The figure A is a square frame without any bracing. The figure B is a square frame with one bracing and the figure C is a square frame with double bracing. All the three frames have the same size. F F F A B C Questions: #Which frame is the most stable frame amongst A, B and C for the same given load? #Which frame is the least stable frame amongst A, B and C for the same given load?

2 Class Exercise-2 Truss Analysis 1) The figure below shows two bars A and B with loads acting in the opposite directions. A B Questions: #Which bar is under compression? #Which bar is under tension? 2) The figure below shows a simple truss. A point load is applied on the joint in the vertical direction. The upward forces acting on the truss are R A and R B. 30 lb C A B R A =15 lb R B Questions: #What is the value of R B? #Determine which member is in compression or in tension?

3 3) The figure below shows a simple truss. A point load is applied on the joint in the horizontal direction. 30 lb Questions: #What is the value of R C? R C 4) The figure below shows a truss formed by the combination of three simple triangles. A point load is applied on each of the joints respectively. The point loads on the joints are 35 lb and 45 lb respectively. The upward forces acting on the truss are R A and R B. The horizontal force applied to the truss is R C. 35 lb 45 lb R C R A =40 lb R B Questions: #What is the value of R B? #What is the value of R C?

4 Class Exercise-3 Structural Load 1) The figure below has three beams A, B and C with same cross-section but different length. The beam A is 20 feet length. The beam B is 15 feet length and the beam C is 25 feet length. Equal point load P is applied to all the three beams at the mid point. P P P A B C Questions: #Which beam is going to deflect the most under the same load P? #Which beam is going to have the least deflection under the same load P?

5 2) The upward force acting under the base of the ship is a 3) The given figure shows a beam AB with a force acting upward at the mid point. A B Questions: Is the beam AB hogging or sagging? Force 4) The given figure shows a beam AB with a load acting downward at the mid point. Force A B Questions: Is the beam AB hogging or sagging?

6 Hands-on Activity 1 Square Beam Objective: Understand different types of load and measure deflection in square beam. Activity-1: Bending and Twisting- 1) Hold square beam horizontally, keeping surface A on top and try to bend it as shown in picture I Now observe the grid lines near surface A and surface B. Note that the surface, where grid line are going away from each other, is in TENSION and the surface, where grid lines are coming closer to each other, is in COMPRESSION. 2) Try to twist the Square beam as shown in picture II to the effect of TORSION Observation: 1) Which surface of the beam is in TENSION? 2) Which surface of the beam is in COMPRESSION? I (Bending) II (Twisting)

7 Activity- 2: Calculations of square beam deflection- In this activity, we are analyzing the deflection of a beam for different loads. 1) Hold the beam as shown in above figure; hanging from the mark on surface B with yard ruler on the top of it. The yard ruler represents original position of the beam. 2) Now hand weights 20 grams to 140 grams (20, 50, 80, 100 and 140 grams) one by one to the thread attached at one end of the beam. 3) Measure the deflection of the beam from its original position using small ruler for each weight. Wright deflections in following table. 4) Mark points on the following graph by plotting weights on X-axis and deflection on Y-axis. Sr. No. Weight Deflection

8 Y 40 Deflection Weights X

9 Hands-on activity 2 Frame Stability Objective: To check the stability of frames under different loads. Frame-1: A simple square frame Frame-2: A simple square frame with a single bracing Frame-3: A simple square frame with double bracing Frame-1 Frame-2 Frame-3 Procedure: Frame-1: Make a simple square frame with the given parts listed below. Quantity: 90 degrees support-4 85 mm bar conector-4 Frame-2: Make a simple square frame with the given parts listed below. Quantity: 90 degrees support-4 85 mm bar conector-4 54 mm bar conector-4 Straight connector -1

10 Frame-3: Make a simple square frame with the given parts listed below. Quantity: 90 degrees support-4 85 mm bar conector-4 54 mm bar conector degrees support-1 Instruction: After completing above procedure of frame making, try to apply tension, compression and twisting load, which we have learned in our previous Hands on activity, by hand.

11 Hands-on activity 3 Deflection in Structure Objective: Comparison of deflections in Square and triangular truss frames. Bridge-1: Bridge of Truss frame. Bridge-2: Bridge of Square frame. Students must keep the length of both bridges equal. K nex parts provided are: # Part Name Quantity Picture 1 85 mm grey bar mm blue bar gray joint 44 4 Wooden Block 2 Frame-1: Triangular Frame Bridge Procedure: Make a bridge of triangular frames using given parts listed above and referring pictures shown below.

12 I II III IV

13 V Now, apply a standard mass of 500g and 1000g from the center of the truss frame. Then observe the vertical deflection from the original position of the truss frame. Frame-2: Square Frame Bridge Procedure: Make a bridge of square frames using given parts listed above and referring a picture shown below. Repeat the same procedure as above with the same weight. Then measure the vertical deflection from the original position of the frame to the deflected frame. VI VII

14 Hands-on Activity 4 Offshore Structure Building Objective: Construction of floating oil rig with given parts such that it floats 60 mm above the water level. This simulation activity deals with construction of an offshore structure- Semi-submersible Oil Rig. This oil rig consists of two main parts: Platform base and Platform. Instructions: 1) Students will be divided into groups of five and each group will work on their simulation no more than 30 minutes. 2) A simulation kit, which contains two bags; one is for the construction of platform base and other is for platform, will be provided to each group. 3) In simulation model, the main deck of the platform should be at least 60 mm above the water level. 4) Minimum size the platform should be 120mm X 120 mm. Kit contents: Ruler Parts for Platform Base- # Part Name Quantity Picture 1 85 mm grey bar mm blue bar Support - Yellow 8 4 Straw 1 5 Full circled white joint 2

15 Gray joint mm gray bar 4 8 Float 4 Parts for Platform- Legos of different sizes. Students should use all the materials assigned for platform building.