Application of GIS to Bridge Health Monitoring

Presented in partial fulfillment of the requirements for CVEN 689

Presented by : Mohammed Safi Uddin Adil

Overview of Today’s Presentation

• Bridge Health Monitoring –Present practice and Issues

• How to improve bridge health monitoring

• Proposed GIS based Model details for bridge health

monitoring.

• Limitations of the proposed model

• Future work

• Acknowledgements

Bridge Health Monitoring• What is structural health – The health of a structure

determines its capacity and ability to function under

present load conditions.

• Why should we worry – The bridges are important from

transportation point of view and need to be intact for the

safety of the vehicular traffic.

• Also it is necessary to determine in advance the conditions

of bridge so as to enable the authorities to provide alternate

routes to traffic in case of any repair work to be carried on.

• Bridge health monitoring is now a multi-million dollar industry and still a growing field.

Why Monitor Bridges• Everything gets old and older things need care and repair.

Most of the bridges in USA were built in 1960’s and are in

need of some repair or replacement.

• According to NBI survey out of 500,000 bridges in the

nation 200,000 are structurally deficient.

• Also the increase in the vehicular traffic poses a great

danger to already deficient bridges.

• The record of all the bridges in the nation is kept and

updated by FHWA and is accessible at National bridge

Inventory.

• The present condition of the bridges in Texas as of 2000

from National bridge Inventory is as follows

Texas

NHS HIGHWAY BRIDGES

YearTotal # of Bridges

Structurally Deficient Functionally Obsolete Total of Both

# % # % # %

1992 15,073 403 2.67% 2,152 14.28% 2,555 16.95%

1993 15,259 395 2.59% 2,108 13.81% 2,503 16.40%

1994 15,323 412 2.69% 2,074 13.54% 2,486 16.22%

1995 14,695 462 3.14% 2,073 14.11% 2,535 17.25%

1996 14,967 481 3.21% 2,065 13.80% 2,546 17.01%

1997 15,167 372 2.45% 1,972 13.00% 2,344 15.45%

1998 15,295 314 2.05% 1,998 13.06% 2,312 15.12%

1999 15,543 311 2.00% 2,072 13.33% 2,383 15.33%

2000 14,986 242 1.61% 1,845 12.31% 2,087 13.93%

TEXAS NHS Highway Bridges

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

Structurally Deficient Functionally Obsolete Total of Both

Texas

NON-NHS HIGHWAY BRIDGES

YearTotal # of Bridges

Structurally Deficient Functionally Obsolete Total of Both

# % # % # %

1992 34,006 5,516 16.22% 4,640 13.64% 10,156 29.87%

1993 34,270 5,168 15.08% 4,755 13.88% 9,923 28.96%

1994 34,393 5,057 14.70% 4,815 14.00% 9,872 28.70%

1995 35,158 4,324 12.30% 5,169 14.70% 9,493 27.00%

1996 34,892 4,208 12.06% 5,362 15.37% 9,570 27.43%

1997 35,164 3,815 10.85% 5,512 15.68% 9,327 26.52%

1998 34,607 3,579 10.34% 5,310 15.34% 8,889 25.69%

1999 34,804 3,407 9.79% 5,452 15.66% 8,859 25.45%

2000 32,782 3,066 9.35% 5,217 15.91% 8,283 25.27%

TEXAS NON-NHS Highway Bridges

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

Structurally Deficient Functionally Obsolete Total of Both

Present State of Practice• Presently state DOT’s monitor all the bridges under their

territories.

• The bridges are visually inspected every two years and if anything wrong is noticed then detailed testing is done.

• The detailed testing is generally carried on by implanting strain gauges on the bridge girders and taking data for 48 to 100 hours.

• Then the strain is plotted versus time and the strains under different loading are identified.

• If the allowable moment capacity lies under the limits then the bridge is kept open to traffic otherwise repair work is

carried on.

How the strain gauges work• The strain gauges are implanted on the bottom flange of

the girders underneath the bridge.

• Whenever a vehicle passes the bridge there are some deformations which results in a change of voltage in the strain gauge setup.

• This results in an analog signal which is received by a computer and changed into a digital signal.

• The strains are then plotted versus time.

Issues in current practice

• Every time the bridge is to be tested whole equipment is to be setup near the bridge and the data is recorded.

• The data received is huge and there are issues related to its storage and processing

• There are problems relating the data received to the correct strain gauge and mismatching may result in wrong results.

• No visual link exists between the data collected and the strain gauges which may not be good for later use of the data.

• Other issues are related to accessibility to the bridge girders every time the bridge is to be tested as illustrated by the following image.

• Continuous monitoring is not possible under present conditions.

How this can be Improved?

• With the evolving technology the bridge health monitoring can be improved in many ways.

• Bridge health monitoring can be made totally online.

• The strain gauges can be implanted in all the deficient bridges and the data is received by some main supercomputer then it is filtered and send to a GIS based model where one can visually perceive the present situation of each bridge

A step towards improvement• As a first step towards this improvement a GIS based

model is proposed which can receive the data from the

super computer and assign it to the corresponding bridges.

• The model has a very simple flow diagram which is

illustrated stepwise in the following slides

How the Model runs

• The model presented is based on the bridges in Harris county of Texas.

• First the data of the highways is downloaded from the TNRIS website which have data in .dgn and .e00 format

• The data was then filtered to get the bridges in the Harris county.

• A tool that links the county bridge map and the plan of each individual bridge is being developed in VB.

• This tool will enable the user to open the Arc map file containing the plan of the bridge in a new window by double clicking on the bridge in the county.

• The plans of all the bridges in the county are to be uploaded in the directory, however due to inaccessibility to the data a couple of plans will be uploaded and the tool will be tested.

• The Arc map file also contains a point shape file which can be edited to correctly identify the positions of the strain gauges on the bridge.

• This can be done by first adding the image of the bridge in arc map using add data tool. Then using Arc Catalog a point feature class is created which is also added to Arc map file

• The point feature class can be edited using editor toolbar to correctly specify the positions of the strain gauges

McKee Street Bridge

• The attribute table of this point feature class contains the name of the strain gauge, its position on the bridge etc.

• This table is then linked to the super computer to receive the reading at every specified period and the table gets updated automatically.

• The present readings column shows the reading of the strain gauges associated with the bridge. The strain gauges can be selected on the view and then the attribute table can be opened to get their readings

Additional Features

• Some additional features can also be added to this model.

• If the present readings for a strain gauge surpasses a given

limit then the strain gauge having that reading will go red

and in turn the bridge in the county map goes red.

• This feature will help the personnel monitoring the bridge

to take appropriate action

Conclusions

• Bridge monitoring issues has been addressed

• A model has been proposed to enhance the bridge

monitoring program.

• The present model can be applied to make online bridge

monitoring possible.

Limitations of the Model

• Need for a sophisticated technology to transfer data from

the field to supercomputers and then filter the data and

then import into GIS model.

• The application can prove to be costly initially, but will be

cost effective in long run.

• The present tools in GIS cannot be used readily. Needs

more specific tools for the model.

Future Work

• The future work can be focused on programming all the

tools discussed in the present model as it is not a part of

present project to actually develop all the tools.

• The future work can be to enhance the database by

obtaining all the plans of the bridges in counties and

linking them to the model.

Possible Funding

• Texas Department of Transportation (TxDOT)

• Federal Highway Association (FHWA)

Acknowledgements

• Dr. Francisco Olivera – CVEN 689 course instructor

• TNRIS – Database source

• TxDOT – Data source

• NBI – Data source