Assessment of Arch Bridges is most of my life and has been a pivotal issue for over 20 years. I am endlessly challenged by the difficulty of declaring a capacity for a structure where we know so little about the geometry and understand so little about real behaviour. Arch 04 seems a good opportunity to meet with people with similar concerns, and with those who have solved the problems to their own satisfaction. I have promoted a workshop session intended to be largely discussion. The principle topics I would like to see covered are listed below. You may have others. If so, please add them as a comment, or email them to email@example.com if you wish to be less public.
1) Why assess: Current capacity, Condition, Damage, New loading regimes
In the UK assessment means certifying a capacity. The levels of judgement required are beginning to be reflected in the rate for the job, but I am sure some engineers have sleepless nights. While the loading regime remained largely unchanged, people were comfortable with low grade tools and relatively light inspections, but that doesn't apply any more. On both roads and railways, vehicle loads and particularly frequencies, have risen inexorably and the effect on bridges is beginning to be visible. In earlier times most structural damage was caused by the environment. Now we are not so sure.
2) What levels of assessment are recognised
Let's begin by suggesting four:
Empirical models the prime one being MEXE
Simple models based on Equilibrium in 2 dimensions
More complex models including material properties
3D models using FE
My own concern about working down that list is that the input data available becomes progressively less reliable. The element of judgement is then transferred from relatively simple issues like: Can I treat spandrel walls as a secondary load path which provide me with an additional safety (= confidence) factor, to what adjustments do I make to the measured material properties in order to get reasonable answers.
3) What models are used for analysis at the various levels
There are a number of models in use in the UK and others currently dormant. It is obvious tat there are many more in other countries and more people should know about them. If you have a model you would like to bring to our notice, perhaps a response to this would be a good place.
4) How do we assess the significance of defects with regard to capacity and serviceability
Most of the analytical models provide very limited ability to deal with deterioration of the structure. For example, it is simple to deal with general loss of mortar from the intrados, but less easy to consider patch lossess, especially if they are very deep. Comments would be welcome.
5) How do owners prioritise action in assessment, maintenance and repair
Bridge owners in the UK have largely outsourced the assessment process. They still have to steer the work and prioritise it. Are there tools availabel to help?
6) Assessment of values material properties and their implications.
This is perhaps the most difficult issue. Measuring properties without invsion of the structure is almost impossible. Are the methods used for assessment particularly sensitive to certain parameters? If so how do we progress with methods for obtaining the parameters economically. Failing that, can we really be sure we are making conservative assumptions?
The more comment we can get to te discussion here, the easier it will be to channel efforts when we meet. Please click the button and add your notes.
Sorry it has taken so long to get this up.