Computer Aided Engineering ANSYSCivil Engineering

Analysis of an Overcrossing Truss Bridge

1 Outline Pedestrian/Bicycle overcrossings represent one of the most crucial elements of a

community's non-motorised transportation network. They are the critical links joining the areas separated by a variety of “barriers” like rail lines, rivers or highways. A truss bridge is a type of overcrossing where the connected elements of the bridge form triangular units. Trusses are rigid and transfer loads from single point to a wider area.

While designing the elements of a bridge factors like cost, design life, loads, deflections, dynamic behaviour, material etc. have to be analysed to ensure the safety and reliability of the structure.

On a shared bridge, there are three main types of loads to be considered during analysis –

▪ Dead load: Weight of deck, Weight of any railing/supports, self-weight of the structure.

▪ Live Load: Pedestrians, Cyclist, Wind. ▪ Moving Load: Loading of a moving service vehicle

2 Objectives The aim of this project is to conduct a finite element based structural, modal and

harmonic response analysis on a truss bridge. The members of the system must be investigated for multiple cases to ensure the safety and performance of this system.

Each student is assigned a total length and width that you are to use and adjust the beam profiles accordingly

Then, you are to assign appropriate Beam Profiles to the given model in SpaceClaim and conduct a Modal analysis to review the natural frequencies at 20 mode shapes. For the modal and structural analysis, you are to consider –

▪ The vibrational frequency of members at different mode shapes with application of Standard Earth Gravity. (No Frequency is Zero Hz)

▪ Assigning appropriate materials for the deck and Beams.

▪ Based on the results of initial analysis try to modify the beam profiles, material of deck and bridge to reduce the stress concentration with overall weight of the bridge. All the supports and boundary conditions must remain the same.

▪ Meshing strategy to ensure type of and good element quality especially in areas of high stress concentration.

▪ The boundary conditions (loads and supports) are modelled and provide accurate representation of the following loading cases;

1. Dead load where only the weight of the structure from gravitational acceleration is considered.

2. Uniformly Distributed load of 5 kPa as per the design standards below.

During post processing you must analyse the stress and deformation contours of the bridge, comment on the stress development within the structures.

Based on the results of initial analysis, modify the material of deck and bridge to reduce the stress concentration while limiting the increase of the overall weight of the bridge by no more than 15%. All the supports and boundary conditions must remain the same. This may also mean you need to add additional truss elements as shown in Figure 1.

Figure 1

Refer AS 5100 – Design Loads. AS5100- 6.1, 6.2, 8.1, 8.2, 8.3, 8.4 for design load factors.

Having developed the new design (such as with additional supports, braces and profiles)

write a technical report of the design process. (Ignoring – Soil loads)

3 Loading Conditions

Additional truss elements

in total8 Fixed supports

Supports

4 AS5100 Design Loads

before applying the load!plates in SpaceClaim join the individual surface HINT: It is suggested you

kPa of 5Uniformly Distributed load

Pressure load

5 Technical Report Layout The report can be laid out as follows:

• Use size 12 font for the body text, and format section and titles accordingly. • Font can be Timed New Roman, Calibri or similar. • Use spell check and read your assignment before submitting. • Reference figures and other sources of information. Use a referencing tool such as

Zotero https://www.zotero.org/ • Use the numeric IEEE style type. • MAX 2000 words! Be concise!

To ensure your submission fits the page/word count ranges, make certain to count words in the body using your word processor and then add in the equivalent word counts

for your tables and images. References do not count towards the wordcount. Figures and tables are counted by the amount of words they replace. A good rule of thumb is 50 words per image (picture, graph, spectrum, etc.). Figures with two images (e.g. 1A and 1B) are counted as 100 words. Three images amount to 150 words and so on. Brief tables are counted as 100 words each, while longer or wider tables can be up to one full page (200 words). Make sure you include only highly relevant images and remove non-essential images to help your manuscript be more reader-friendly while fitting within the page/word limits.

A Technical Report can contain the following sections: Section Details Title page Title of the report. Student details including name, ID, date and subject, the

main text word count. Summary A summary of the whole report including important features, results and

conclusions Contents Numbers and lists all section and subsection headings with page numbers

Introduction States the objectives of the report and comments on the way the topic of the report is to be treated. Leads straight into the report itself. Must not be a copy of the introduction in this handout.

The sections which make up the body of the report

Divided into numbered and headed sections. These sections separate the different main ideas in a logical order

Conclusions A short, logical summing up of the theme(s) developed in the main text References Details of published sources using the IEEE style. Acknowledgements List of people who helped you research or prepare the report, including your

proof-readers Appendices (if appropriate)

Any further material which is essential for full understanding of your report (e.g. large-scale diagrams, computer code, raw data, specifications) but not required by a casual reader

Systéme International (SI) units are to be used. Non-SI measurements can be included, but they should follow the SI measurement in parentheses. An example is 2.54 cm (1.00 inch).

6 Marking A marking rubric will be provided separately on the LMS.

7 Supporting Documents • https://www.tmr.qld.gov.au/business - industry/Technical - standards publications/

Options - Design - Pedestrian - Cyclist - Bridges

• Pedestrian and Cyclist Paths - VicRoads

• Australian Standard 5100 – Design Loads

• http://web.pdx.edu/~jdill/Files/Renfro_Bike - Ped_Overcrossings_Report.pdf