## The calculation

This my design with all the truss name

This picture shows the calculation of the tension sticks .in the tension sticks I’ve got three damnation sticks (60mm ,104mm ,120mm )the calculation shows , how much the one  or two or three sticks can hold ,as required  .and I’ve mention the name of each truss in the calculation paper .

The calculation was done , Depends on the tensile test

This picture shows the 104 mm tension sticks calculation

This picture shows the 120 mm tension sticks calculation

This picture shows the calculation of the compression  sticks .in the compression  sticks I’ve got three damnation sticks (60mm ,104mm ,120mm )the calculation shows , how much the one  or two or three sticks can hold ,as required  .and I’ve mention the name of each truss in the calculation paper .

The calculation was done , Depends on the tensile test

This picture shows the 104 & 120 mm compression  sticks calculation

The reason of doing the calculation to make a load prediction of how much the bridge can carry and where exactly will break

## Method of Joints

In this method you need a Free Body Diagram of each joint and solve for the unknown member forces at that joint. Once this joint is completed, move joint to joint through the truss to solve for the force in all members.

Procedure

1. Draw a Free Body Diagram of the whole truss and find the external reactions if required (using Moments).
2. Choose a joint with only 2 unknowns (probably starting at the roller joint).
3. Draw a Free Body Diagram of that joint and find internal forces (by a force polygon).
4. Transfer these forces to adjacent joints (compression = pushing both ends, tension = pulling both ends).

Notes

• If you can’t guess, assume tension (pulling on joint). If you get a negative answer it must be in compression.
• Give your answer for the force in each member as a positive number (with a T for tension) OR a negative number (with a C for compression).
• Once a force is known on one end of the member, the same force is then OPPOSITE on the other end. (rotated by 180 ).

The Method of Joints will solve any truss, but sometimes is might be doing it the long way – especially if you want to know what is happening in the middle of a complex truss. However, if you are designing the thing, you probably want to know the forces in every member anyway, so this method is usually suitable. Also, this method is self-checking. By the time you work all the way through the truss you should have forces that match the reactions at the other end.

I’ve tried the method of joint to make sure that I am using the bridge software in right way, so the applied weight in the software was around 100 but I don’t know if it’s in pound or KG OR gram.

And then I decide to practice more on the method of joints, so I’ve converted the 100 was the applied weight in the software form pound to kg. it was 45.3 kg ,after that the applied weight was substitute it into the method of joins ,and later on after finishing from method of joints .it was the same value of the truss force I’ve got in the software .which means everything in the software in pound .

This is The bridge designer (bridge software )

http://www.jhu.edu/virtlab/bridge/bridge.htm

## my reference

This is the required book to the mechanics subject

## The equipment where used

The drilling apparatus

This machine was used to make the surface very soft after the drilling and cutting the sticks

This the hacksaw where used to cut the sticks

## The problem

So these are the heights level of the load acting on the truss, so I decide to double them to make them stronger after making the tensile test. In fact I have double must of them and trouble some of them, and I left the other sticks .that is my mistake and later on I figure out ,while I am increasing the Strength of some of the stick .that is mean I am increasing the load on the other truss .I was thinking about where I am going to stick the load .therefore the adjacent or nearby truss will represents  the highest load truss .which is right but also the other truss will be loaded .

This picture shows the highest loaded truss

## The reason of the collapse and the breaking point

The bridge after the collapse

There are two sides of the bridge, were built to make the bridge balanced. And I have to connect these two sides together .so I need some sticks to connect each sides of the bridge together. After building the two sides of the bridge, I have just 12 sticks left .so I distribute the 12 sticks along to the bridge .and it is not enough to the 660 mm long. So the joints in my bridge was weak .that is why the bridge before the collapse the bridge was bended.

The problem is I have made the top and the bottom of the bridge very strong, and I missed the joints between the bridges.

On that day, we took another assumptions because we believed that the calculations have some factors could make them inaccurate enough. So, our assumptions was, the bridge will break at 38 Kg and at LM member. Fortunately, the bridge broke at the exact member which was LM, but it broke at 26 KG which was not really far from the prediction value ,And I have mentioned the reason above in (the problem section).

## Project overview

Project overview:

The bridge was build to study and understand the mechanics staff .such as the tensile test, strain member force and lots of mechanics staff. And then build it based on the calculation and the design was chosen .I was bound by building the bridge by use 130 sticks only ,It will run in to 600mm long, but I have made it 660 mm ,so 30 mm right ,30mm left so the bridge sat on the table . It was made based on my calculation, and I am going to test the bridge by adding some weights on it, in front of my teacher, by the following rules: I have to made a production based on my calculation in other word, I have to mention the breaking point of the bridge, where the bridge will break and how many weights can carry

The bridge cast (130 sticks, 24 L joints, 92washers ,92 nuts and bolts ).all the angles in the Bridge was 60  ,I chose that angle, because its suitable to my design based on my calculation, which is strong enough  to the sticks bridg

this is the nuts , washers and bolts were used .

this is the( L) joints were used

This is the Bridge design

After building it

After the Collapse

## Essential points

This stick, I will use it for the tension truss member. So it is 150 mm long ,and i am going to drill two hole to be 60 mm in the middle .so it will be strong in tension .because imagine that the bolt bull out ,if it small distance to the end of the stick ,so it will be easy to brake .

In this stick, i will use it for the compression truss member, so it is 75 mm long, and I am going to drill two holes to be 60 mm in the middle. imagine that the bolts pushes in , on 150 mm ,it will be very weak .so if I cut the half of the 150 it will be 75 , which will going to be stronger than the 150 long stick ,by the way ,I going to save some of the sticks and use them to make the bridge very strong ,by double them in one truss member   ,so it will not be easy to brake.

This is my bridge design, as you can see the blue color, is a compression .and the red color is a tension.

Which the blue color represents the small stick and the red color represent the big stick.