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‘Immediate remedial work to rectify a damaged Kent County Council CCTV column located on a busy junction in Maidstone.’

A vital CCTV column situated on a traffic island was damaged following an impact by a heavy vehicle on the 12th October 2010.

Kent County Council commissioned Secure Engineering to immediately evaluate and rectify the damaged column and the CCTV and restore all to a secure safe state.

Secure Engineering originally installed the CCTV column along with 7 other identical columns in February 2010.  The impact on the 15 Metre, 925Kg column could have had a disastrous outcome if it had fallen onto the traffic junction.  Fortunately the special column and base fixings were installed by Secure Engineering, to a specific design able to absorb and withstand an even greater impact assuring the safety of everyone and everything around.

Surveying the site after the impact showed that the column itself was in good condition, most of the impact energy was absorbed by deformation of the studs holding the column in place. This is exactly as the designer had proposed.

Preparations;

A comprehensive work plan was produced with precise Risk Assessments and Method Statements.

The job was planned to take place at first light on the next available Sunday in October 2010.  Comprehensive traffic management was organised to enable safe working at this complex and busy road junction. A contingency plan was prepared to safely halt the operation if needed to allow the passage of emergency vehicles if necessary.

The following plant and equipment was organised:

A very powerful HIAB lorry capable of lifting 3 Tonne at 14.4 Metres
A 14 Metre high reach platform
An extra long articulated lorry to transport the CCTV column to a storage area if required
Standby generator,
Metal cutting equipment
Jacking devices for separation of column from base

Objectives

• Remove the column safely
• Assess, on site, the serviceability of the column
• Assess the serviceability of the column foundation
• Remove damaged fixing stud assemblies
• Assess the serviceability of the stud anchor points
• Fit new fixing stud assemblies
• Re-install the column

How we did it
All traffic management, plant, equipment and personnel were ready to start at 0700 on the Sunday morning.  All personnel were finally and comprehensively briefed on the work plan and method statement before commencing.

A lay down plan and space was prepared for the column in case it was necessary. A strong retaining rope was attached to the base of the column and down through the ducting to a suitable anchor point to control the column swing when separation from the base occurred.

Two 3 tonne rated lifting strops were attached to the column at the 10 Metre level using the high reach platform. Anchor straps were attached to the column base to prevent upward slippage of the strops under load.  It was very important that the HIAB lifting vehicle was only used to support and lift the column but not to apply force to separate the column from the base.  This was to be achieved by jacking the column off the distorted studs. If the column could not be separated from the distorted studs then the plan was to support the column on wooden blocks and cut through the M27 stainless steel studs.

A final check was made and then the traffic was stopped in all directions at a safe distance from the column works. The go ahead was given for the HIAB operator to apply a measured amount of lift to the column to hold it in position.  The holding down nuts and washers were then carefully removed from the studs.  A little more lift was applied and the column began to move up the studs. Some slack was given to the anchor rope to allow more upward movement. A quick check was made and it looked like the studs were not causing an obstruction so a small increase in lift was applied and the column came clear of the studs. 
 
The column was rested vertically on the ground adjacent to the base, inspected and found to be ok for re-installation. Traffic was allowed to flow again. We had a plan to transport the column to Secure Engineering’s office if we were unable to re-install it for any reason.

The base fixing studs were removed and the stud anchors were cleaned and checked for serviceability. These were found to be ok so a new set of four studs were installed with the associated ‘top hat’ nylon washers, stainless steel washers and fixing nuts.

With the traffic stopped the column was then carefully lifted back into position onto the new studs, adjusted for level and all nuts were accurately tightened to a torque of 400nM in stages.

The whole operation took a little more than two hours.  

If you would like to know more information please do not hesitate to contact

Secure Engineering on 01622 844 244.