LAU EE TIAN0309596

CH’NG XING YUE0310425

Project 1: Understanding Forces in Skeletal Structure

FAM LI KIAN0310639

WESLEY HEW XIN HAN0307585

GOH CHIN ZHI03145623

ELAINE BONG POH HUI0310432

• • • • •

3. Transfer of ForcesThere are several type of forces has been applied into a popsicle sticks tower. The internal forces included tension force, torsion force, shear strength, bending force and compression force.

DESIGN TOWER CRITERIAS

1. Types of bases

Triangular Square

• Lessen the amount of sticks used by an estimation of 25% but

reduces the stability of the tower as the base surface area is lower.

• Remain in shape well when force is applied.

• Higher stability and more vertical columns to support the tower but

will increase the mass of tower.

• Easily deformed when force is exerted to the shape.

2. Bracing method

4. Placement of sticks

Double Layer Single Layer

Strength• Able to withstand higher pressure by increasing

the contact surface area of the popsicle sticks.

• Able to tolerate stronger compression force.

• Lighten the weight of the tower and the amount of popsicle sticks used to increase the efficiency of the tower.

• Time span on construction is shorten.

Weakness• Increase the weight of the tower and amount of

popsicle sticks used reducing the efficiency of the tower

• Work labor is increased

• Increases the stress received as the force does not distribute to other popsicle sticks.

• Hard to combine the sticks together without using slot in

• The horizontal sticks acting as the beam for the tower are placed upwards to reduce the possibility of the bending of the sticks as easily as horizontally positioned stick due to the rigidness and inflexibility of popsicle sticks.

• Upward placed stick will receive more pressure than horizontally positioned stick due to its smaller surface area, so double layer pinned together strengthen the joint making it acting as a three layer unit channeling the force from the top to bottom.

a) Slot in

Slot-in with groove• Will reduce the structural strength of the sticks as it will break more easily when force is

exerted

• It might cause the sticks to split into half when force is applied

• It is easier to combine the sticks together using slot in compared to other methods

• Transfer of load is more efficient and direct

b) Use of pins

• The use of pin might causes the stick to split according to the direction of wood rays

• Able to fix all sticks together firmly

5. Joints

Slot-in with double layer• Requires more sticks and very strong bond joining all three sticks to ensure the load force

transfer down all three sticks as one unit

• Might break easily at the joint if the load doesn’t transfer vertically down as the slot-ins are at the end of the sticks

c) Type of knots

Square Lashing Diagonal Lashing

Square Lashing Diagonal Lashing

Strength - More aesthetic and neat

- Use lesser string

- Lesser contact area with the vertical popsicle stick, hence lesser pressure applying to the popsicle stick and causes it to break

- Distribute more force among threads

- Able to hold the popsicle stick in position more firmly

Weakness - Higher tension force in thread compared to diagonal lashing

- Requires more effort and more time consuming in comparison to square lashing

Bracing 1

Strength • Able to withstand greater pressure and weight due to the spreading of force.

Weakness • The center point between two bracing become the weak point due to the intersection of force hence easier to break.

Extension

Strength • To avoid the popsicle sticks intersection with the popsicle sticks of other floors

Weakness • Increases the height of the tower hence the center of gravity is higher, weaker the stability of tower

Single layer

Strength • Avoid unnecessary extra weight to increase the efficiency of tower

Weakness • Increases the chance of breaking due to less spreading of force at vertical columns

Joint

Strength

Weakness Joint is extended beyond boundaries causing tower to be unstable on smaller points.

Small area of force creates higher pressure even with low force being applied.

Single layer

Extension

Strength Ensuring force from shorter brace can be transferred to horizontal bracing.

Weakness Exertion of force is not efficient. Joints might break when pressure is applied.

Bracing 2

Strength Reduces force applied on horizontal bracing by transferring it to the vertical and diagonal brace.

Weakness Single diagonal bracing may cause tower to twist in a spiral motion .

Joint

Strength Larger surface reduces amount for pressure and force being transferred to the ground.

Weakness Spiral direction of force abruptly ends as diagonal bracing isn’t directly in contact with ground surface.

Bracing 3

Strength • Withstand the greatest pressure among all bracings due to it’s triangular design

Weakness • Horizontal sticks become the weak point due to uneven distribution of forces/ sudden pressure.

• Might break at the top part when large force is exerted due to weak bonding strength of slot in bracing

Single layer

Extension

Strength Ensuring force from shorter brace can be transferred to horizontal bracing.

Weakness Extension has fewer proper connection that may result in rigid stance.

Joint

Strength Larger surface reduces amount for pressure and force being transferred to the ground.

Weakness Horizontal brace absorbs less pressure as force from 3 directions are transferred to end points instead.

Mass of tower: 137g

Total of sticks used: 96 sticks

Time span: 2 minutes 10 seconds

Efficiency of tower =

=

= 9.27

Load Held (g)

Mass of Tower (g) X Height of Tower (cm)

FINAL MODELObjective:

To construct a popsicle stick tower exceeding 30cm that is able to support the most load with the least amount of sticks without the use of adhesive.

40000g

137g X 31.5cm

Bracing used: Bracing 2

Double layer vertical columns

Joint used:

TIME LAPSE FOR MODEL TESTING

ANALYSIS OF FINAL MODEL

Tower before model testing

• The force of the tower supposedly to move in torsion and downwards vertically.

• The vertical supports were strengthen with double layer

• Additional horizontal sticks were added at the extension gap to allow the load from the top to transfer to the horizontal beams below and not just rely solely on the vertical supports.

• Alternating gaps of horizontal beams were used(without changing the degree or length of the slanted bracing).

• This reduces the length of the columns in between the horizontal beams and increases the load capacity.

gap

Added horizontal sticks

ConclusionPrecision of the tower is very important as inaccurate measurements lead to uneven distribution of forces and contribute to the racking of the

structure. Tower built using double layer slot -ins requires higher level of accuracy due to its more complicated structure than single layer tower with

slot-ins that have grooves. This makes single layer tower easier to construct and have lighter mass but double layer structure could withstand more

load if it is built well.

Besides, internal bracings could be added to the tower to prevent the deformation of the vertical and horizontal structures.

• The tower was not structurally straight in the first place. Hence torsion in opposite direction of the bracing happened once weight are applied. This was the main reason of the structure failure since the bracings and columns could not perform their function well as supposed to transfer the load.

• Since the force was wrongly transferred, it falls on one side at the end and causes the horizontal element at one of the corners breaks.

• Lack of internal bracing allowed the deformation of the tower to happen.

• Besides, joining the popsicle sticks by using pin made them crack. It might weaken the ability of the sticks to transfer load as it will split with strong shear force.

• The bottom part of the tower is still in good condition proves that the force are not going downwards efficiently.

Tower after model testing