Building Structures

Introduction The aim of this project is to successfully design an effective truss bridge, through the analysis conducted on case studies, as well as the points discussed throughout various lectures. The main material that is to be utilized in the construction of the bridge is fettuccini; though the application of glue for minor connection and layering of the fettuccini is permitted.

The truss is a structural component of a bridge that is made up of three or more members. These components are then arranged along the span of a bridge in patterns that best enable them to support the whole structural load. In this particular support system, the load applied to the truss is transmitted to the joints so that each individual members are in either pure tension or compression.

Throughout the duration of the project, a good understanding of the way forces are distributed in a truss system is required so that any initial failures can be rectify.

Initial failures are expected to happen during the testing phase of the project so that we are able to further improve upon the design and mechanics of the bridge structure.

Some of the requirements stated in the project brief are the aesthetical value and efficiency rating of the bridge as a whole. It is imperative to remember that the amount of material used to increase the bridge’s aesthetical value must not take priority over the amount of materials used to construct the main component of the bridge as this factor is essential in determining the efficiency rate of the structure; as can be seen through this formula:

The efficiency rate of the bridge largely depend on factors such as the strength of the materials and the structural analysis of the truss being employed in the bridge’s design. the former, is significant due to the fact that by knowing the strength of the different types of fettuccini available, we would gain a better idea of which members needed to be strengthen. The latter, is important due to the fact that throughout the analysis we will be able to identify which part of the bridge is categorized as being critical members if needs be, the critical members can also be strengthen in addition to the materials.

The image above shows the different truss systems that are available for us to incorporate into our design, though the way in which these are being employed depends wholly on how the structural frame is intended to channel the forces through the various members.

Truss bridge are usually constructed for a shorted span compared to suspension bridges. The resulting lack of suspension wires holding up the bridge means that most of the supporting elements come from the distribution of the forces through the adjoining members of the trusses. Thus, it is imperative to note that a truss bridge should have a major supporting component that runs along the bottom of the load platform (roads, railways etc).

How strong can a pasta stick be?

Fettuccine That little stick of 4mm wide and 1mm thick can withstand a load close to building materials when it comes to efficiency wise once installed properly in a structure form such as a truss bridge.

CHARACTERISTICS Brittle Bio-degradable Strong in tension Weak in compression Sensitive to humidity Note: Not to forget that the fettuccine stick is potential of high elastic limit.

STRENGTH Through a series of test to failure point, we arrived to the very conclusion that this piece of flour-based material is as strong as steel or timber.

Inspiration We inspired ourselves from the traditional truss-bridge type, PENNYSYLVANIA in order to proceed and exert the allocated material’s strength.

PENNYSYLVANIA TRUSS BRIDGE This nominated truss bridge is specially designed to resist compression forces better than tension, as well-known that the enemy of most tough materials is compression as exerts better at tension.

Ameliorations In order to achieve maximum efficiency some changes were to be made to the traditional configuration of the nominated bridge as it has been revealed through a series of test that some of the parts were actually redundant to be the force distribution.

Arriving to conclusion, instead of using the conventional tangential arch of the Pennysylvania Bridge, we replaced the top part by an arch- shaped one piece unit. Making the arch as a one piece unit compared to the tangential segments made it easier for the bridge to direct the reaction forces back to the action spots.

PROPERTIES OF ARCH High resistance to compression forces Subject to high elastic tolerance Force transferring is smoother and direct from the loading spot to the action spots.

Note: the arch is at the same time tough and flexible which exposes the material to a high elastic limit.

Hint: In most of the tests, the bridge’s arch stayed still, the only parts failing were either the base of the bridge or the spot where the load was located.

DURING THE TESTS Knowing the potential of the material, some of the parts, which were making the bridge’s performance redundant were removed believing in achieving better efficiency.

TEST RESULTS TEST 1 BRIDGE WEIGHT : 150g LOAD: 5kg TEST 2 BRIDGE WEIGHT : 113g LOAD: 3.5kg TEST 3 BRIDGE WEIGHT : 140g LOAD: 3.35kg TEST 4 BRIDGE WEIGHT : 131g LOAD: 4.5kg TEST 5

BRIDGE WEIGHT: 133g LOAD: 5kg

BRIDGE ANALYSIS (STEP BY STEP) TEST 1

At test 1, the bridge weigh 150g net. It was exposed to a loading session until failure which resulted into a maximum load of 5kg.

The structure failed at the arch part and the arch was composed of only 3 layers of fettuccine which compared to the based was composed of 5 layers.

TEST 2 Coming onwards with new solutions, the redundant bracings which were causing readily compression segments within the structure were removed. Once removed, the bridge was composed of loose neutral members not subject to any readily forces. At the same time, the bridge weigh a lighter value of 113g but was unfortunately weaker than the bridge in Test 1.

The bridge was exposed to a clear span of 600mm from which started the loading test to failure.

The bridge started failing at the center part where the load spot was located as the bridge was designed to support point loads. The failure was due to the cause that the bracings were not strong enough as they were connected by butt joints.

The second fact that it failed was because of the weak vertical pillar connection.

As predicted the bridge failed at the center part which was an improvement to the previous one. It was subject to a maximum loading of 3.5 kg weighing 113g which allowed us to determine the weak spots of the bridge.

TEST 3

At test 3, the bracings were connected in a followed-up v shape pattern in order to distribute the reaction forces equally to both action spots. The bridge was weighing 140kg and was subject to a maximum loading of 3.35kg which was a failure in terms of efficiency.

But it seemed that the test was a success and a step forward to the design of the final bridge as it failed only of its loading spot. The bridge stayed as a whole and no additional failure was located else than the center part.

Note: The bridge failed at the center part where the load was located during all the tests.

TEST 4

Before the final test, the last mock test revealed that by laminating the base, better strength could be achieved. But as u can see on the picture, the bridge reached its optimum point and started cupping at the loading spot.

The bridge was subjected to test to failure and resulted into a maximum load of 4.5kg weighing 131g.

TEST 5 Finally, the bridge at its optimum potential ready to be tested on the Official testing day.

The bridge weigh 133g and was subject to a maximum load of 5kg net which through the efficiency calculation gave out a value of 18‌

But this time the bridge failed at the joint between the arch and the diagonal edge due to high compressive strength exerted by the live load.

The weakness of the bridge was still spotted at the center part and revealed that even with a better connection which means 2 sticks in for the slotting joint, it was still showing sign of failure at the same spot.

This time the bridge rotated at the failing point showing that moment due to human error when loading affected the process. The minor oscillations of the load made the load to spin the bridge at its optimum point. But still the failure was at the center point.

AMELIORATIONS TO BE CONSIDERED: -

strengthen the middle joint increase the height of the bridge add more bracings sharing the load all along the bridge during load testing

Conclusion To determine the structural feasibility of the different bridges, an efficiency formula has to be applied to the results obtained from our conducted analyses. The efficiency ratio of the bridge is calculated through this formula:

The efficiency ratio of each preceding bridge test enables us to improve the structural design of the next one, thus allowing us to create a design which strives for a higher score.

Bridge Test 1

The efficiency score for our very first bridge is 166.7. Though it is a design in which the score ranks second in our series of tests, the weight of the actual bridge is at the maximum material allowed. This is noted down as we approach the design of our second bridge. The aim in the second design is to significantly reduce the amount of material utilized in the construction; in the hopes that a higher efficiency ratio can be attained. This is done by removing bracings which are considered redundant and act more as dead weights.

Bridge Test 2

The second bridge did not achieve a high efficiency score, in fact much lower, with a score of only 108.4. The reduction in material used for the construction of this particular bridge was so disproportionate that it was only able to carry a maximum load of 3.5kg. The removal of several bracings meant that parts of the bridge are strictly composed of loose neutral members. Though they are not subjected to any readily forces, this also meant that less structural supports are able to assist in resisting forces acting on other parts of the bridge.

Bridge Test 3

The design of third bridge is an extension to the previous one, where follow-up bracings are connected in “v� patterns in the hopes of distributing the reaction forces equally along the supporting members. Though the bridge receive the lowest score of a mere 80.16, some design elements are kept and used in the design of the final bridge as the only failure occurred in the loading spot, whilst the rest of the bridge remains intact.

Bridge Test 4

With the failure from test 3 in mind, we designed this particular bridge with a laminated base, so that the base at which the point load is located at is significantly enhanced. The bridge reached an efficiency score of 154.5 which makes it the third most efficient bridge in our series of tests.

Bridge Test 5

The final bridge is designed for optimum efficiency score, which meant that key elements found in the previous test are integrated with one another to create a structurally sound hybridization of architectural and engineering feat. The last test revealed that the bridge’s main weakness lies at the location at which point load is exerted. Thus this in this bridge, two layers of fettuccini is utilized for the slotting joint.

Though it has been structurally enhanced, the bridge’s failure is due to minor oscillations that are created when more loads are added to the point. This sway creates moment throughout the bridge which causes the structure to rotate out of place once it reaches optimal load. However, with an efficiency score of 188, the final bridge proved to be the most efficient one out of the batch.

Several factors can be considered in terms of further improvement to the bridge. First and foremost the failure at the point load has to be addressed and one of the ways in which to rectify this is to strengthen the middle joints. This can be achieved by

perhaps applying a horizontal truss system along the base of the bridge, in addition to the existing horizontal elements that connects the two side of the bridge together. This particular amelioration will also enable the bridge to share loads along its span during load testing.

Another way in which the bridge can be improved upon is by way of increasing its height. The overall height of the bridge would allow the structure to distribute its own weight evenly along its membrane. The increase in height would also allow for more bracings, perhaps even more intricate ones, to be applied, which in turn would provide the bridge with a more suitable equilibrium to support heavier loads.