Tuesday, 30 June 2015

Expansion Joint Repairs

Hammersmith Flyover is over 600m long and built in two halves with a thermal joint in the middle - actually 6/15th's of the way along from West to East. The expansion joint allows the concrete bridge to "grow" and "shrink" as the bridge temperature changes. During a 24 hour period, the gap at the centre can be 10 to 20mm smaller at night than during the day and over 100mm different between Summer and Winter.

Anyone who has driven over the flyover recently, and especially anyone living nearby, will know that there is a temporary plate covering the joint. This causes cars to have to slow down and makes a loud noise each time a car or lorry passes over it.

Covering over the old expansion joint
Temporary cover and ramp
The temporary covers, which are on hinges, allow works to progress underneath by enabling the plates to be lifted at night, the old concrete to be removed and then being lowered again for normal daytime traffic.

Old and broken out concrete
Surveying the expansion gap
The remedial works are now almost complete and the new expansion joint (a large steel plate with interlocking teeth) to ready to be set into position in the next two weeks.

Once the "steel combs" have been concreted into position, the old covers and temporary Tarmac ramps will be removed and some fresh Tarmac can be laid at the final road level. Job done.

Thursday, 11 June 2015

Awards and UAVs

Another award for Hammersmith

My current project, the Hammersmith Flyover in West London was awarded the CIHT (Chartered Institution for Highways and Transportation Innovation Award on Tuesday. The award was in recognition of the enterprise, ingenuity, design, performance and quality of the project.

Award presented by Robert Llewellyn
Not least were factors such as best-value and cost-benefit.

The re-strengthening of the flyover, working around the existing structure and keeping traffic disruption to a minimum has been a challenge.  Bespoke machinery and techniques have been used to install kilometers of new internal cabling into the bridge to replace the original tendons that have become corroded through use of winter salt and poor maintenance.

Installation of the external "blisters"

French sub-contractor "Freyssinet" was commended for its technological expertise.

UAV Aerial Modelling

As an exercise to determine the method, procedure and results of 3D modelling by use of an unmanned aerial vehicle (UAV), I flew my trusty DJI F550 hexacopter around an old stone building near Thetford, a rabbit Warreners Lodge dating back to about 1400.

DJI F550 with GoPro 4

Approximately 80 photographs were taken from all angles around the lodge and stitched together using Agisoft Photoscan.

Some of the aerial photographs
The photographs are automatically aligned to its neighbour using common points and although there was no positional information, such as GPS data, the software was able to produce a photo-realistic model of the building.

3D model created in Agisoft Photoscan
Once created the program could then export the results in 3DS format (3DS max), Wavefront OBJ (3D data modelling transfer format) or even generate a point-cloud which can be imported into AutoCAD via Autodesks ReCap software.

Point cloud in AutoCAD 2014
The finished model is not orientated or scaled.  This must be done from ground dimensions taken independantly.

The quality of the final product reflects the quality of the screen captured stills taken from the original GoPro video.  My next project will use high resolution photographs taken at 3 to 4 second intervals...