CE311 Lesson 1: Structural Engineering (brief intro) Fall 2018

“You’re a long time dead. Why not enjoy every day” – Johnny UnitasLESSON 1: STRUCTURAL ENGINEERING (BRIEF INTRO)

Monday, August 27, 2018LESSON OBJECTIVES

1. Define strength and serviceability limit states.2. Distinguish between strength limit states of material failure and instability.3. Distinguish between member instability (member buckling) and overall structural instability (e.g., “a pin-connected

rectangle”)4. Define Structural Analysis and Steel Design.

READING: Refer to the 2019 Steel Bridge Competition Rules for the reading assignment, due in Lab

HOMEWORK:Checklist – The following items must be completed

By the beginning of the first lab (Tomorrow!!):1. Complete the LAB ASSIGNMENT (attached)2. Read the Lafayette Structural Engineering Lab General Safety Rules (online) and sign the last page

(handout).3. Remember the dress code for the Structural Engineering Lab: long pants, short sleeve shirt,

construction boots, long hair tied back, no dangling jewelryREFERENCE:

Formulae below are needed for the homework assignment that is due in lab. Note: denotes the deflection. x provides deflection as a function of x position, while max provides the maximum deflection.

CE311 Lesson 1: Structural Engineering (brief intro) Fall 2018

Name: ________________________________________________LAB ASSIGNMENT

Due by the beginning of Lab One (tomorrow!!!)Presentation does not count. Simply hand this sheet in. Show no work on this page – report final answers, only.

BEFORE HANDING IN, WRITE YOUR ANSWERS DOWN ON A PIECE OF PAPER (OR SCAN OR TAKE PICTURES), SO THAT YOU CAN DISCUSS YOUR ANSWERS, IN LAB, AFTER HANDING THIS IN.

Background: you are expected to know Strength of Materials. This assignment is partially a Strength of Materials review. You may need to refer back to your Strength of Materials course.

1. Compute the moment of inertia I (also called the 2nd moment of area) for the 1/8”x2” beam cross-sectional area shown, with respect to the x-axis.

2. A steel beam (E=29000 ksi), made of the previous cross-section, spans 16 inches, simply-supported. If it is subjected to a centerpoint load of 50 lbs, causing bending about the x-axis, use the appropriate deflection formula from the previous page to compute the maximum (midspan) deflection of this beam.

3. Compute the moment of inertia I (also called the 2nd moment of area) for the 1”x1” hollow square tube shown, with respect to the x-axis. The wall thickness of the tube is 1/16”.

4. A steel beam, (E=29000 ksi) made of the previous cross-section, spans 16 inches, simply-supported. If it is subjected to a centerpoint load of 50 lbs, causing bending about the x-axis, use the appropriate deflection formula from the previous page to compute the maximum (midspan) deflection of this beam.

x

y

y

50 lbs

16 in.

x

1/8” x 2” Beam Cross-Section

I = in4

Answer

= inchesAnswer

x

y

y

x

Beam Cross-Section1” Square Hollow Tube with 1/16”

Wall Thickness

I = in4

Answer

50 lbs

16 in.= inches

Answer

CE311 Lesson 1: Structural Engineering (brief intro) Fall 2018

5. Compute the moment of inertia I for the cross-section shown, with respect to the x-axis. The cross-section consists of two ¾” square hollow tubes, each a wall thickness of 1/16”.

6. Compute the moment of inertia I for the cross-section shown, with respect to the x-axis. The cross-section consists of two 1” square hollow tubes, and two 2” square hollow tubes, all with all thickness of 1/16”.

x

y

y

x

Cross-Section(2) ¾” Square Hollow Tubes, each

with 1/16” Wall Thickness. (not to scale)

6”I = in4

Answer

x

y

y

x

Cross-Section(2) 1” Sq.Tubes & (2) 2” Sq. Tubes,

all with 1/16” Wall Thickness. (not to scale)

5”I = in4

Answer8”

CE311 Lesson 1: Structural Engineering (brief intro) Fall 2018

7. Skim/Read the 2019 Steel Bridge Rules as follows:Sections 1, 2, 3, and 4. There is no need to read theseSection 5: ReadSection 6: Important. Read

6.2.2 to 6.2.7 are Extremely Important. Read CarefullySection 7: Skim this

Read 7.1, particularly Table 7.1. Use Table 7.1 with the drawing on the last page.Section 8: Important. ReadSection 9: Skim, for now (important, later)Section 10: Skim, for now (important, later)Section 11: Skim, but read 11.5 very carefullySections 12 to 16: There is no need to read thesePage 33, 34, 35: These drawings are the most important pages in the rules. Study Carefully.

a. A team builds its bridge in 6 minutes, using 4 builders. During construction, the builders drop 3 bolts in the Construction Zone. There are no other penalties. What is the Construction Economy (cost)?

b. What is the maximum size that a bridge member can be? i.e., a legal member must fit into a prismatic box of what dimensions?

c. Given: A steel bridge enters the competition. The bridge, itself, weighs 200 lbs. During timed construction, it is assembled by 6 people in 10 minutes, with no penalties. It passes the lateral load test. During the vertical load test, it has vertical deflection measurements of D1=0.6” and D2=0.4”. What is the total cost of this bridge?

Total Cost: $Answer

Max. Size:Answer

Construction Economy:Answer