Archie_M_notes

SV loads, a little more

The SV vehicles are very wide and have widely spaced wheels on the axle. This means that, with shallow fill depth, the action of the two wheels do not overlap. The distribution within Archie was built on the assumption (reasonable for all other loads) that the distributions do overlap. The distribution width is worked out as Axle track +1.5m + depth from wheel to extrados.

There is a further complication in this because the rules in BD21 sa that the load can be treated as a UDL across the full width once the loads are combined. Load transfer due to centrifugal action is thus cancelled. If that assumption is invalid, the effect must be taken into account. As with railway loading, the simplest way to deal with this is to treat wheel loads rather than axle loads. I will therefore build a set of SV load files based on wheels instead of axles, but users must then be sure to restrict the "bridge width" used appropriately for half a vehicle.

SV Loads

It has been pointed out to me that the rules for SVloads are different from HB loads and therefore the load files need modifying.

New files can be downloaded here, but please note that they are only valid (for the time being) if there is enough fill at the critical poisition to ensure that the two wheels on an axle act together. That means 1.15m of fill at about 1/4 span. If this isn't the case it may be necessary to use a resticted bridge width to make sure the load is sufficient.

A seriously skew bridge

I have seen some skew bridges in my time but this one almost defies photography. The two views below might show what I mean.

 

This is looking more or less axially through the bridge and shows the semi-circular arch with a 20ft span (this WAS the canal era).

Looking square to the spandrel shows the enormous elliptical stretch.

The end view of the acute corner of the abutment below gives another emphatic illustration of the skew. Ballard had considerable trouble geting the centring out and transferring stress. There are bulges evident that probably date from that time, though the cracks he describes seem to have been repaired effectively.

Reinforced concrete arches

A common question in a slightly different form:

Hi Bill,

I am currently undertaking some arch bridges assessments for which I am using Archie-M (version 2.4.1). One of these bridges has a multi-span masonry arches widened with reinforced concrete arches. My query was – can we use Archie to assess a multi-span RC arches as well using appropriate RC material properties? If not suitable for reinforced concrete arch, can we use it assess plain concrete arches?

 

I will be grateful for your response.

 

Best Regards,

**********************

Many bridges were extended in this way. They were designed assuming arching behaviour and assuming very low bending effects but modern requirements suggest elastic analysis. If you do that, the result is almost certain to be an indication of substantial overstress.

I have, in the past, somewhat facetiously, suggested cutting the reinforcement to turn it into an "arch". That is clearly unnecessary but I am sure the case can be made that if it would work as an un-reinforced arch, the reinforcement will not reduce the capacity.

When does an arch need a detailed survey?

Here is a lovely example of an arch that has distorted enough to need a detailed survey. It was almost certainly originally three centred. An ellipse certainly doesn't come near to fitting. I suspect that the pier to the left has settled and rotated a little to the right. The arch has then fleattened to the left, but there is some evidence in the bed joints in the spandrel at the right of the arch having been compressed and so forced up at the right hand haunch.

However, it is certain that nothing short of a proper survey, with perhaps 20 or 30 points in the span, will give any hope of modelling the arch effectively. Even then one should note that the joints in the left half of the span are nearly all open at the bottom giving a very much reduced ability to carry live load.

So here we have a bridge that should not be assessed except as a guide to how it might perform once properly repaired.

The changes to Archie-M from 2.2.1 to 2.4.1

Over the past years, we have struggled with a range of problems. Some engineering and some software. As we developed Archie-M so the goalposts mived. Some movements (such as our developng understanding) we could set aside for later, but the changes to Windows and the programming environment could not be ignored.

The new version (2.4.1, download from the post below) comes with a manual that was updated nearly a year ago. We are now working on a fresh edition of that and a complete revamp of the web site. In the mean time, here is Zoltan's list of the changes since the last released versin 2.2.1. The intervening ones each fell foul of windows problems.

For those who still use the 2.2.x versions, the main changes are (starting
with v2.3.0):

- control panel in the graphical bridge window to speed up operation and
give visual feedback about current values
- the indroduction of effective lane width and the use of bridge/lane width
in the load files
- Obvis web page access and email sending functionality under the Help menu

From version 2.3.1:

- removal of the load editor (to be replaced with an improved one in the
future)

From version 2.4.1:

- support for Vista
- change of thrust calculation to clip thrusts at span boundaries
- change of software protection scheme (end of HASP HW protection, software
only protection requiring product activation)

I think these are the main changes. I assume everyone will upgrade to 2.4.1
and skip 2.3.x if using and earlier version than that.

A New Release

These links were refreshed on 18-04-10. I believe it should now work properly as  demo or be activated as a full running program. Bill

Many users are aware that we have had a lot of difficulty with VISTA. We believe that we now have a stable version of 2.4.1 which works under vista. There are a lot of changes. Too many to detail here, though none should raise any difficulty for users.

Click the LINK to DOWNLOAD

This should work as a demo for 30 days but will then need activating. The Demo is fully functional.

There is an updated manual at this LINK, though it is not yet completely up to date.

Lane width and bridge width

Let's get one thing straight first. Archie-M works out the distribution for each load using the appropriate distribution rule. The lane width you should put in (Bridge Width from version 2.4) should be the maximum width available for a load to distribute to. This might be bounded by the edge of the bridge, an adjacent lane or a crack in the arch ring.

The sketch below might help.

New version screenshot

This is here mainly as a trial for the new OBVIS web. Seems useful, though, to let you see where Archie is heading.

 

Some History

2010 is a significant year for ARCHIE. in 1984, Arnold Hendry and his Edinburgh team tested the arch at Bridgemill for TRL. On site, Bill was able to run continuous checks on analysis using Jacques Heyman's model and an HP41CV pocket calculator. No graphics, but the essence of ARCHIE was there. The program output was a series of 12 offsets of the thrust line from the intrados exactly like the thrust in, thrust out columns in the Archie-M output.

In 1985 (I can't remember when but probably about November) there was a meeting at New St Andrew's House in Edinburgh to show the results. Two weeks before that. Bill took delivery of an NCR Decision Mate V (approximately) PC compatible computer. It had a colour screen (7 colours and black) and came with GW Basic which had graphics functions to draw on the screen.

In the two weeks available, Bill managed to produce CIRAR, a program to analyse circular segmental arches using the full zone of thrust model that became ARCHIE.

SO ARCHIE IS 25 YEARS OLD THIS YEAR

We will have to think of a way to celebrate.

Of course. Archie-M 2.4 is a long way from CIRAR, but it also reflects just under thirty years of active research and consultancy on arch bridges. Bill's first arch assessment was of Dairsie Bridge in Fife and it was done using the HP41CV and some plotter routines programmed into a Commodor Pet.