Statics-CIVE1187-Bridge Design Project PDF

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Statics CIVE1187 Group Project: Bridge Design Project

Contents Statics CIVE1187...................................................................................................................................... 1 Group Project: Bridge Design Project ..................................................................................................... 1 1.

Executive Summary..................................................................................................................... 3

2.

Introduction ................................................................................................................................ 4

3.

Part A: Custom Bridge Design ..................................................................................................... 5

4.

3.1

Justification: ........................................................................................................................ 5

3.2

Materials ............................................................................................................................. 6

Part B: Truss Bridge Design ......................................................................................................... 8 4.1.1 4.2

Dead Load: .......................................................................................................................... 9

4.3

Condition 1: T44 Traffic Loading: ...................................................................................... 10

4.3.1

Tension Member Design: .............................................................................................. 14

4.3.2

Compression Member Design....................................................................................... 15

4.3.3

Material Selection: ........................................................................................................ 18

4.3.4

Connection .................................................................................................................... 19

4.4

5.

Introduction: ................................................................................................................... 8

Condition 2: L44 Traffic Loading .......................................................................................24

4.4.1

Tension Member Design ............................................................................................... 28

4.4.2

Compression Member Design....................................................................................... 29

4.4.3

Material Selection ......................................................................................................... 32

4.4.4

Connection .................................................................................................................... 32

Conclusion: ................................................................................................................................ 37 5.1

Part A:................................................................................................................................ 37

5.2

Part B:................................................................................................................................ 37

6.

References: ...............................................................................................................................38

7.

Appendix ABCDEFGHIJKLMNOPQRSTUVWXYZ ......................................................................... 39

1. Executive Summary This report was commissioned to analyse, propose and create a suitable bridge to allow access to a to-be-constructed research laboratory in Benalla, as well as accommodate for specific traffic loading requirements. Our primary objective with this task was constructing a bridge that could efficiently span an 18-metre waterway, and have sufficient structure to sustain T-44 traffic loading. Upon the initial viewing of the first part of this project, we recognised that the design solution we would create for this project would have to be as simple as possible, in order to minimise unnecessary costs, and reduce any environmental impact. We brainstormed a variety of bridges we could possibly utilise for this task, and conducted a feasibility study to determine the best bridge for this project. There is a pre-existing bridge over the waterway, which is incapable of supporting the loads required for day to day operation. However, certain structures within the bridge (i.e. the concrete abutments upon which the bridge rests) are capable of being reused for a new bridge design. Whilst we juggled many ideas for a suitable bridge in this scenario, we ultimately decided that a simple span bridge would do an excellent job, in the simplest manner. We determined this was the most appropriate design, based on historical designs in similar conditions, simplicity of construction, and optimum re-usage of existing components. A truss bridge was designed for the second part of this assessment. We created the dimensions for the truss, calculated the forces acting throughout the bridge, and determined which types of metalbeam constituents to use to create the bridge. We ensured that, through our calculations, the truss bridge will absolutely be able to carry any T44 loads subjected to it.

2. Introduction The School of Civil, Environmental and Chemical Engineering of RMIT University has decided to build a brand-new research laboratory in rural Benalla. Our task is to create a bridge which can effectively and efficiently span an 18-metre waterway, in order to safely accommodate for construction vehicles and civilian traffic. We have been asked to brainstorm an innovative, self-chosen bridge design, and additionally we have also been asked to create a simple truss bridge, presented as two separate design solutions. For our self-chosen bridge design, we had a wide variety of ideas to pursue. We chose not to consider some particular bridge designs, such as cable-stayed, suspension and cantilever. We immediately discounted these designs because we found them to be rather excessive for the given criteria, and they simply would cost too much (relative to our proposed design). Some of the designs we decided to pursue were ideas such as arch, truss and beam. These are more typical bridge designs used in scenarios like this, as they are appropriate for the size of the bridge, and don’t require too much labour (relatively) to create. For the second part of the project (the truss bridge layout), we were required to come up with our own version of a truss bridge. This involved creating all the dimensions, deciding how many steel members we should use, how far apart steel members should be and calculating all the forces acting on the structure. We also needed to keep in mind that this structure would be placed on the existing concrete abutments, thereby needing to modify the truss to fit within these particular dimensions.

3. Part A: Custom Bridge Design 3.1 Justification: For our custom bridge design, we weren’t too particularly worried about creating a bridge with pleasing aesthetics, rather, we were more concerned with creating a bridge which was simple, efficient, and got the job done with minimal resources and labour required. We decided the bridge which fulfilled our criteria was a simple beam/girder bridge. Attached are some basic images of what the bridge should look like.

Side View

Top View

Front View

For this design proposal, we proposed a girder bridge instead of other types of bridges, namely arch and truss bridges. When considering the bridge design, we recognised that the girder bridge is the best choice for simple applications (as it is in this scenario) as the span length of the required bridge is only 18-metres and there are only “normal” traffic loads (as compared to L44 Lane Loading or HLP Loading). Moreover, the girder bridges are incredibly easy to construct, and from a financial perspective, the costs are relatively low. Furthermore, we also decided on using I-beam girders, as they are the most suitable type of girders to use in short spans. I-beams are especially practical in bridge designs where there are no curves, so it makes even more sense to select this variant of building material.

3.2 Materials In terms of material costs, girder bridges are typically built using simple building materials, namely steel and reinforced concrete. Concrete has very high compressive strength, but has a very low tensile stress value. In order to compensate for this, we will use reinforced concrete, which will increase the tensile stress the structure can handle. Steel has excellent compressive strength and tensile strength values, as well as being incredibly cheap to procure in large quantities, making it suitable for any sort of construction. It is important to note that there is a fire hazard present in areas such as Benalla, due to bush fires, so it is vital that infrastructure around this area be fire-proof in the case of an emergency evacuation. Reinforced concrete is fire and weather resistant, so it isn’t a major concern, as long as construction is done correctly. There is still the risk of metal components’ structural integrity degrading due to extreme temperatures, as steel melts at around 1400 °C, whilst bush-fires can reach a maximum temperature of 1100 °C. However, as bushfires are not a common occurrence, we can disregard this risk, especially considering that this bridge is surrounded by a water-way.

Reinforced concrete is weather-proof, so the risk of its’ quality degrading over time is quite minimalised, however, steel is at risk of oxidising and rusting. For this reason, we have decided to expend the additional cost of galvanising the steel to prevent rusting from occurring, as it can seriously undermine the longevity of the bridge. Considering the characteristics of both reinforced concrete and steel, we have decided to use steel for the superstructure, and reinforced concrete as the substructure, as this plays to both materials strengths. Steel has great strength (thereby suitable for the body), and reinforced concrete (to be used for a majority of the bridge’s construction) is an economical efficient material to use. In short, we believe that a beam/girder bridge is the best design solution for the given scenario, as it is incredibly easy to construct, requires very few resources, has very little environmental impact, and is the most efficient design compared to any other type of bridge.

4. Part B: Truss Bridge Design 4.1.1 Introduction: In order to create a truss design that met the performance requirements of the bridge, we had to take many steps to come up with the final design. First thing that had to be decided on was what type of truss bridge we would adopt for the design. Truss bridges consist of a series of triangular components and joints which also known as nodes. The use of triangular components in the truss bridge is to act as bridge superstructure in order to transfer the deck load to the piers. The triangular components are all slim and straight in form. These triangular shapes may appear in many different forms. We decided that the bridge design should be simple and withstand a the T44 traffic loading required of us, leading to our decision to adopt a Warren truss design, which is a type of through truss, with added vertical members. We chose to add the vertical members in the design for stability reasons as we decided to keep the added features to the bridge design to minimum, allowing us the flexibility to focus on the structural integrity of the bridge itself. This type of shape allows for right angled triangles to be formed all around the bridge, with the loading spread across and mainly acting on the larger equilateral triangles.

Figure 1: Design of our truss bridge

The bridge covers a length of 18 meters, with the distance between each node being 1.8 meters. It consists of two-way traffic lanes, each with the width of 3 meters. We decided to not include a pedestrian walk-way as we believed that for the given distance of the bridge there would not be a need for the extra width as the traffic on the bridge isn’t expected to be that busy. Once the design of the truss was constructed, it was time to calculate the types of loading that would be applied to the bridge. We were expected to determine the dead load as well as the loading for two specific traffic loads; T44 and L44 loading. The load path can be summarised in Figure 2 below.

Figure 2: Load path of the bridge

Traffic Load

Deck

Stringer

Cross Girder

Truss member

Bridge Bearing s

Piers

Earth

4.2 Dead Load: In our truss bridge, the load on the deck is transferred to the stringers, which is then transferred to the cross girder before finally being applied to the two joints of the supporting trusses. To determine this dead load at these nodes, the following calculations were carried out (ignoring the stringers): 𝑈𝑛𝑖𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑐𝑜𝑛𝑐𝑟𝑒𝑡𝑒 = 25𝑘𝑁/𝑚 3 𝑇ℎ𝑒 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 𝑜𝑓 𝑑𝑒𝑐𝑘 = 0.25𝑚 𝑇ℎ𝑒 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 𝑜𝑓 𝑒𝑎𝑐ℎ 𝑛𝑜𝑑𝑒 𝑝𝑜𝑖𝑛𝑡 = 1.8𝑚 𝑇ℎ𝑒 𝑤𝑖𝑑𝑡ℎ 𝑜𝑓 𝑏𝑟𝑖𝑑𝑔𝑒 = 6𝑚 𝑈𝑛𝑖𝑓𝑜𝑟𝑚 𝑑𝑖𝑠𝑡𝑟𝑖𝑏𝑢𝑡𝑒𝑑 𝑙𝑜𝑎𝑑 (𝐷𝑒𝑎𝑑 𝑙𝑜𝑎𝑑 𝑜𝑓 𝑑𝑒𝑐𝑘) = 25 ∗ 0.25 = 6.25𝑘𝑃𝑎 =

6.25𝑘𝑁 𝑚2

𝐿𝑖𝑛𝑒 𝑙𝑜𝑎𝑑 𝑎𝑙𝑜𝑛𝑔 𝑡𝑟𝑎𝑛𝑠𝑣𝑒𝑟𝑠𝑒 𝑏𝑒𝑎𝑚 = 6.25 ∗ 1.8 = 11.25𝑘𝑁/𝑚 𝑃𝑜𝑖𝑛𝑡 𝑙𝑜𝑎𝑑 𝑎𝑡 𝑛𝑜𝑑𝑒𝑠 𝑝𝑜𝑖𝑛𝑡𝑠 𝑜𝑓 𝑡𝑟𝑢𝑠𝑠 = 11.25 ∗

6 = 𝟑𝟑. 𝟕𝟓𝒌𝑵 2

𝑃𝑜𝑖𝑛𝑡 𝑙𝑜𝑎𝑑 𝑎𝑡 𝑡ℎ𝑒 𝑒𝑛𝑑 𝑛𝑜𝑑𝑒𝑠 𝑝𝑜𝑖𝑛𝑡𝑠 𝑜𝑓 𝑡𝑟𝑢𝑠𝑠 (𝐴 & 𝐾) = 25 ∗ 0.25 ∗

1.8 6 ∗ 2 2

= 𝟏𝟔. 𝟖𝟕𝟓𝒌𝑵

Each node of the truss design has a load of 33.75kN except the end nodes A and K which have a load of 16.875kN acting on it. So, from here, we needed to calculate the traffic loads for T44 and L44, both with the inclusion of this calculated dead load.

4.3 Condition 1: T44 Traffic Loading: For this first condition, the design criteria states that the bridge design should be able to hold T44 truck loading with axle group spacing as shown in Figure 3. To determine the loading, the five loading forces of truck can be summarised further to make things easier to calculate. When placing the loading on the truss design, we found that if we placed the third wheel on the middle node F, the second wheel would end up 1.2 meters to the left. We decided to move it to the center node and add the two wheels together. This way the force would provide for the most critical loading, allowing for the greatest safety levels to be reached as we take that as the value we work towards in the design and material selection for the worst-case scenario. The same thing was done to the back two wheels. The overall loading of the truck can be summarised in Figure 4 below.

Figure 3: T44 Truck Loading

(AUSTROADS Bridge Design Code, 1992)

Figure 4: Diagram showing the T44 traffic loading on the truss design

(Assume A is a pin support, and K is a roller support)

From the calculations of the T44 Load (see Appendix A), we end up with the T44 loading with the dead load at each node in Table 1. Once all the values are calculated, we can find the reaction forces at the end points A and K. Figure 5: Diagram showing the T44 traffic loading with the dead load on the truss design

Table 1: Calculations of the total load (T44 Load + Dead Load) at each node of the truss design T44 Load + Dead Load Joint

Calculation (kN)

A

1.2*16.875

=20.25

B

1.2*33.75

=40.5

C

1.2*33.75

=40.5

D

1.2*33.75 + (2*48*0.9)

=126.9

E

1.2*33.75

=40.5

F

1.2*33.75 + [2*(96+96)*0.9]

=386.1

G

1.2*33.75 + [2*(96+96)*0.9]

=386.1

H

1.2*33.75

=40.5

I

1.2*33.75

=40.5

J

1.2*33.75

=40.5

K

1.2*16.875

=20.25

Assume it is pin support at A, and roller support at K.

For all sign convention, ∑ 𝐹𝑥 = 0 ∑ 𝐹𝑦 = 0 ∑𝑀 = 0

Take moment about A: ∑ 𝑀 = 0, 𝐾𝑦 − 20.25 ∗ 18 − 40.5 ∗ 16.2 − 40.5 ∗ 14.4 − 40.5 ∗ 12.6 − 386.1 ∗ 10.8 − 386.1 ∗ 9 − 40.5 ∗ 7.2 − 126.9 ∗ 5.4 − 40.5 ∗ 3.6 − 40.5 ∗ 1.8 = 0 ∴ 𝐾𝑦 = 608.58𝑘𝑁

Take all forces in the y-direction: ∑ 𝐹𝑦 = 0 𝐾𝑦 + 𝐴𝑦 − 40.5 ∗ 6 − 386.1 ∗ 2 − 126.9 − 20.25 ∗ 2 = 0 ∴ 𝐴𝑦 = 574.02𝑘𝑁

Take all forces in the x-direction: ∑ 𝐹𝑥 = 0, ∴ 𝐴𝑥 = 0

Once we know all the forces acting on all the joints of the truss bridge, we can find the tension forces in each of the member (see Appendix A). Table 2: Tension and compression forces in horizontal members of the truss design (T44 traffic loading + dead load) Horizontal Member Tension (kN)

Compression (kN)

AB

415.3275

LM

852.12

BC

415.3275

MN

852.12

CD

1154.858

NO

1582.74

DE

1154.858

OP

1582.74

EF

1643.288

PQ

1414.26

FG

1643.288

QR

1414.26

GH

1232.618

RS

800.28

HI

1232.618

ST

800.28

IJ

441.2475

JK

441.2475

Table 3: Tension forces in vertical members of the truss design (T44 traffic loading + dead load) Vertical Member Tension (kN)

Zero Force member (kN)

BT

40.5

CS

DR

126.9

EQ

FP

386.1

GO

HN

40.5

IM

JL

40.5

Table 4: Tension and compression forces in diagonal members of the truss design (T44 traffic loading + dead load) Diagonal Member Compression (kN)

Tension (kN)

AT

692.2125

CT

641.5875

CR

590.9625

ER

432.3375

EP

381.7125

GN

583.5375

GP

100.9125

IL

684.7875

IN

634.1625

KL

735.4125

4.3.1 Tension Member Design: Once we have found all the forces in the members of the truss design for T44 traffic loading with dead load condition, we can determine the maximum tension in the horizontal, vertical and diagonal members. With this we can find the most appropriate material to use for the members. Table 5: Maximum Tension (kN) in members for T44 traffic loading Member

Maximum Tension (kN)

Horizontal

1643.2875

Vertical

386.1

Diagonal

684.7875

In order to select the most appropriate steel member that is able to endure all the tensile strength above, we should take the highest tension as the design capacity by using the formula of strength design of tension member. 𝑁 ∗ ≤ ɸ𝑁𝑡

As we have obtained the design axial tension force 𝑁 ∗, which is the maximum tension of 1643.2875 kN, we can find the minimum cross-sectional area of the design member that would be required to withstand the loading in a safe manner. We use the...