FEA Final Report

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A Finite Element Analysis on Hanalei Bridge

By Cassie A. Kuwahara

Department of Mechanical Engineering

University of Portland

ME 304

Dr. Deborah Schenberger

December 14, 2011


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Abstract:

A finite element analysis was performed on the Hanalei Bridge located in Kauai to determine

where the main points of stress, strain, and displacements were located. The frame had only

gravity acting in the downward direction on it. The purpose of this analysis is to help determine

points on the bridge that should be closely focused on for fatigue. The bridge was analyzed inALGOR as a 3D simply supported beam type model with gravity acting in the downward

direction. The stress and strain analysis showed that the bigger stresses were located on the

bottom wall beams, with the largest stress present in the middle of the bridge. The displacementanalysis showed the middle of the bridge to have the highest displacement. These results are

important to inspectors of the bridge because the areas with highest stress and displacements are

most likely to show the most fatigue over a period of time. This analysis does not mean onlythese areas should be inspected. The entire bridge should be inspected for fatigue, although

based on this analysis, the areas that will show the most fatigue will be the beams in the middle

of the bridge.

I. INTRODUCTIONThe Hanalei Bridge is located on Kauai in the Hanalei Valley. It was originally built in 1895 asan iron-truss bridge and was reconstructed in 1912 using steel, making it the oldest American

made steel truss bridge in Hawaii [1]. The structural type of the bridge is a Pratt-truss steel

bridge, constructed on reinforced concrete abutments with a timber deck [2]. The bridge spans

113 feet over the Hanalei River with a vertical clearance of 15 feet and a horizontal clearance of17 feet [1]. It is a one-lane bridge with a weight limit of 15 tons [2].

A finite element analysis was performed on the steel truss bridge to determine the stresses,strains, and displacements displayed on the bridge. This analysis will help determine areas of the

bridge that should be closely focused on when inspecting the bridge.

II. METHODSThe Hanalei Bridge was analyzed using the Autodesk ALGOR Simulation Professional 2011

educational version program on the computers in Shiley Hall 208 and 249. Most of theinformation used in the finite element analysis was researched on Google or other Internet search

engines and the remaining information was assumed based on previous knowledge. A diagram

of the bridge is shown in Appendix B, Figure 5.

The 3D simply supported bridge was analyzed as a static stress with linear material model. The

beam type bridge had only the force of gravity in the downward direction acting upon it. Thetype and dimensions of the steel used on the Hanalei Bridge were not available, so ASTM A-36and W10X39 were assumed. A screen shot of the frame constructed in ALGOR is shown in

Appendix B, Figure 6.

III. RESULTS


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The Hanalei Bridge was analyzed in ALGOR to show the stress distribution. The axial stress is

shown in figure 1 below.

Figure 1: Axial stress analysis with only gravity acting on the bridge.

The bridge was also analyzed in ALGOR to show the strain distribution. The axial strain isshown in figure 2 below.

Figure 2: Axial strain analysis with only gravity acting on the bridge

A final analysis on the bridge was done in ALGOR to show the displacement distribution. Thedisplacement distribution is shown in figure 3 below.

Figure 3: Displacement analysis with only gravity acting on the bridge.


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IV. DISCUSSIONBased on figures 1, 2, and 3 above the beams located in the middle of the bridge is under the

most stress, strain, and displacement. During inspection of the bridge these beams should be

focused on closely for fatigue and failure. The analysis was performed with only gravity acting

on the bridge, so the stress, strain, and displacement shown above are acting on the bridge

constantly.

This finite element analysis was meant to determine areas on the bridge that should be closely

focused on when inspecting the bridge. However, it should be understood that since assumptions

were made, this analysis might not be exact to the Hanalei Bridge. The areas of high stress,

strain, and displacements should not drastically change based on material type and dimensions

but the values of stress and displacements may change. The first assumption made in this

analysis was the type of steel used. ASTM A-36 steel was chosen based off of information

found on common steels used in bridges. A-36 steel is the cheapest steel available for structuralusers where stiffness is more important than the strength [3]. The second assumption made was

the beam dimensions. Based on the picture of Hanalei Bridge shown in Appendix A, Figure 4,

W10X39 was chosen.

If more time and information was available, a better and more accurate finite element analysis

could have been performed. In this analysis the timber decking was not accounted for as a

distributed force on the steel frame. This was due to the lack of information found on the type of

timber decking used on the Hanalei Bridge. The next step in this analysis would be to actually

inspect the bridge to determine whether this analysis proved accurate. If the analysis proved to

be correct, this analysis could be adjusted to add the load of a car, truck, or van onto the bridge.This analysis would show values of stress, strain, and displacements acting on the bridge with

the weight of a vehicle. The bridge could also be analyzed with the 15 ton weight limit to

understand what might happen if the bridge was to fail.


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V. APPENDIX A

Figure 4: Hanalei Bridge on Kauai, Hawaii.


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VI. APPENDIX B

Figure 5: A sketch of Hanalei Bridge with dimensions.

Figure 6: The Hanalei Bridge constructed in ALGOR


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VII. WORK CITED1. Schmidt, Michael R. "The Historic Hanalei Bridge | Kauai, Hi." Kauai Real Estate &

Hanalei Vacation Rentals - Coldwell Banker. Coldwell Banker, 7 Sept. 2011. Web. 09 Dec.

2011. .

2. Harrington, Daniel. "Hanalei Bridge."Hawaiian Encyclopedia. Web. 09 Dec. 2011..

3. "Steel Bridges." INSDAG. Web. 09 Dec. 2011. .

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