Timber Bridge Testing
New cost-effective method proven
National CEO, Institute of Public Works Engineering Australia
Member, APWA International Affairs Committee
The APWA International Affairs Committee presents this series of articles to assist in the exchange of ideas between our international partners. This article is presented as part of the partnering agreement in place between APWA and its Australian counterpart, the Institute of Public Works Engineering Australia (IPWEA).
Local government in Australia is responsible for the management and maintenance of over 20,000 bridges. More than 70 percent of these bridges are aging timber bridges. A major issue is that their condition is largely unquantified to a significant extent. Load capacity and structural adequacy of many have been impaired over time. Damage to the strength and stiffness of these bridges is not readily identifiable from visual inspection, even by staff experienced in bridge maintenance.
In 1999/2000, the IPWEA and the University of Technology, Sydney (UTS) undertook research which has proven that an innovative low-cost procedure to test timber bridges is possible. The procedure measures the "free vibration response generated by an instrumented impact hammer."
In more simple terms, accelerometers placed on the bridge measure the frequency response when a calibrated high-tech sledgehammer is used to hit the bridge deck! This impact is done with and without a load of about two tonnes. The measured difference in frequencies generated provides valuable information on the condition of the bridge superstructure. It can detect a weak timber beam from amongst the remaining beams, e.g., one affected by termites.
A major advantage of this simplified procedure is that it doesn't require full loading of the bridge to simulate design loads, which can itself damage the bridge. It also doesn't require precise measurements of deformations under full load, as is the case for static load tests.
Field tests of the new procedure were carried out on a timber log bridge constructed in 1962 over Cattai Creek in Western Sydney. This demonstration project confirmed the laboratory research and required significantly less time and resources than is the case for conventional load testing. An additional benefit was that this dynamic testing procedure only required minimal interruption to traffic.
Load carrying capacity to be determined
Further work is now taking place to extend the project into an applied research phase. The first stage has proven a low-cost and simple procedure that provides reliable information on load-deflection or stiffness characteristics. The next stage will provide answers on strength characteristics of timber bridges. It will address the question of "what is the load-carrying capacity of the bridge."
The aim is to offer a turnkey solution in determining the state of health of timber bridge stock, their rate of deterioration over time, and their load-carrying capacity. The more cost-effective procedure will make it possible to test bridges over a period of time, monitor their deterioration, and estimate intervention levels.
Expressions of interest were invited from Councils to participate in the next stage. This group of Councils is assisting in overseeing the project to ensure it meets their needs. Forty spans in total across 15 local authority areas are currently being tested to provide a range of test conditions. A range of span sizes, single and multi-span bridges are included in the test program.
Representative computer models for timber bridges are being constructed based on the results of the testing program. The models will also use statistical data available on old timber log properties available from another research program. The computer models will be calibrated against the test results, and with known timber properties including flexural strength, load-carrying capacity can be determined.
It is envisaged that the computer modeling and analysis (and the resultant determination of carrying capacity) will be developed as a user-friendly package for use by bridge managers and their technical staff. A national central database of test results will also be investigated. This could be the beginnings of a national picture of the condition of the nation's bridge stock and also provide valuable data on deterioration trends.
The project is scheduled to be completed by the end of 2002. It is a rare opportunity for local government to directly undertake applied research and one that addresses a critical need. The National Office of IPWEA is pleased to work in partnership with the University of Technology, Sydney to develop this innovative testing method to determine the load capacity and condition of timber bridges.
For more information, please contact Chris Champion, IPWEA National CEO, at firstname.lastname@example.org.
Cultural Quiz: The Czech Republic
1. What was the "Velvet Revolution"?
2. When did Czechoslovakia separate into the Czech Republic and the Slovak Republic?
3. How many flowers would you buy if you were to give them to a woman?
4. When do Czechs celebrate Christmas?
5. When talking about sports with Czechs, which sports would be the best to bring up?
6. What should you be aware of when you make a toast with Czechs?
7. How would you address the wife of Mr. Kovac?
8. What beverage is the pride and joy of the Czech people?
9. What is a typical Christmas meal?
Answers to Czech Republic Quiz
1. In November 1989 people in Czechoslovakia went into the streets with candles and flowers to protest against the communist regime. The "Velvet Revolution" brought the collapse of communism without violence and weapons.
2. In January 1993. The separation was peaceful and that is why it is called the "Velvet Divorce."
3. Odd number but never 13. Even number of flowers is used for funerals and number 13 means bad luck.
4. In the evening of 24 December. The Christmas Eve dinner starts with the rise of a first star.
5. Hockey or soccer.
6. You should look directly into the eyes of the person you make a toast with. Otherwise you would be perceived as impolite.
7. Add a suffixâ€”ova: Kovacova.
9. Wafers with honey, apple, and garlic followed by cabbage soup and fried carp with potato salad. After the meal, the family gathers around the Christmas tree to open the presents.
Except from "Culture Shock" (Issue #7), a publication of Malkam Cross-Cultural Training, Ottawa, Ontario. Used with permission from Laraine Kaminsky, President, Malkam Cross-Cultural Training. Ms. Kaminsky will be a speaker at the 2002 APWA Congress in Kansas City.