Bus Depot Electrification Harrow

Bus Depot Electrification – TFL Harrow Bus Depot Civil and Structural Design Services

Transport for London TFL is embarking on a programme to install electric charging infrastructure to the bus network. This is rolled out to chosen bus depots and Harrow bus depot (Harrow Weald) is one of them. The main depot, built in 1900 and the depot extension built in 1960 as well as the ex-Hearn Coaches depot built in 1947, were all going to be adapted to receive this infrastructure of charges, electrical equipment and containment cables.

The large span trussed roof was deemed not to have sufficient margin to receive new loading

The main-depot extension had a steel frame with adequate reserve capacity to receive containment

Containment spanning the depot extension supported on main steel rafters using unistrut hangers

Works were installed while the depot was in use

brick wide solid masonry walls were used to support containment using mechanical fixings

The old Herne Coaches depot also adapted to support electric charging of buses

Beta Design Consultants were commissioned by the Client, an electrification contractor working for RATP/TFL, to carry out the following services:

- Inspection of existing TFL bus depot structures built at different stages from 1900 to 1980 and assessing the roof, walls and foundations ability to accommodate new loads.

- Design of supports for new cable containment racks/ladders needed to electrify the bus network.

- Design of new equipment foundations, including transformer, feeder pillar and other electrical equipment (e.g. RMU, GPR enclosures).

- Arranging trial pits and assessment of impact of new equipment foundations on existing depot foundations.

- Assessment of cracking in existing masonry depots.

Beta Solution

We carried out a measured survey to establish the layout and sections sizes of the depot structure. This allowed us to establish its load carrying capacity following a structural analysis. The impact of adding new cable containment supports to the roof truss, super structure beams and super structure columns was then established. Supports for the containment, using a mix of unistructs and bespoke structural supports then followed. Spacing of supports varied from at 3m spacing horizontally and vertically to supports at and before/after every bend/radius.

One of the challenges was to introduce new masonry supports in walls that had some historic cracking. The solution was to divert the containment cables away from locations of worst cracking to avoid loading an already stressed wall.

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