Design for Protection of Structures against the Effects of Derailment

Notwithstanding the particular rolling stock to be used, the design live loading from MRT railway vehicles shall be not less than that as determined in accordance with BS 5400 Part 2 for RL loading, or such other loading as specified in the Particular Specification. Dynamic effects shall be allowed for in accordance with BS 5400 Part 2 unless indicated otherwise in the Particular Specification.

3.2.1.2 LRT

The design live loading from LRT vehicles, unless indicated otherwise in the Particular Specification, shall be not less than the larger of the actual system requirement or one half of RL loading determined in accordance with BS 5400 Part 2. Dynamic effects shall be allowed for in accordance with BS 5400 Part 2 unless indicated otherwise in the Particular Specification.

3.2.2 Design for Protection of Structures against the Effects of Derailment

3.2.2.1 General Considerations

The following design requirements apply to the supporting structures for new bridges or new buildings and any new structure carrying hazardous materials (e.g. gas) constructed over or alongside railway tracks. They do not apply to lineside railway infrastructure such as overhead line masts or signal gantries.

Wherever possible, supports carrying any structure over or alongside railway tracks should be placed outside the “danger zone” (see below for definition).

Where supports must be placed inside the danger zone they should preferably be monolithic piers rather than individual columns.

Columns and piers located within embankments, or at the bottom of embankments, may require special consideration even if outside the danger zone because of the possibility of derailed vehicles rolling down the embankment (See Figure 3.2.2.1-A below). If it is not possible to arrange the design to avoid the situation then special measures will be necessary to safeguard such columns and piers. Consideration shall be given to the following:

(a) the use of guard rails

(b) a retaining structure to widen the embankment (c) the use of massive piers.

Figure 3.2.2.1-A

Where isolated columns are used within the danger zone a solid

‘deflector’ plinth shall be provided to a minimum height of 900mm above the rail level or 1200mm above ground level whichever is the higher. The height of the plinth shall be constant and the ends of the plinth shall be suitably shaped in plan to deflect derailed vehicles away from the columns (See Figure 3.2.2.1-B below for typical plinth detail).

For individual columns within station areas a solid platform construction shall be used to provide similar protection from derailed vehicles.

Track Danger Zone

5250mm 5250mm

Embankment

Bottom of Embankment Columns Located

Outside Danger Zone

Figure 3.2.2.1-B

Where, exceptionally, the use of ground anchors are accepted as part of the Permanent Works by the Engineer and where they are situated within the danger zone, special measures shall be taken to protect the anchorages from potential damage by derailed vehicles.

3.2.2.2 Definition of “danger zone”

Within tunnels the danger zone is considered to be bounded by the tunnel walls. At stations, it is bounded on the platform side(s) by the platform structure below platform slab level, and above platform slab level by a zone up to 2500mm from track centre-line; at non-platform locations it is bounded by the nearest continuous wall or 5250mm from track centre-line whichever is less. See Figure 3.2.2.2-A below.

Figure 3.2.2.2-A “danger zone” within stations

5250mm ( If there is no continuous wall within 5250mm from track centreline )

Platform Structure Platform Slab Level 2500mm

Nearest Continuous Wall (where applicable) Track Centreline

“danger zone”

Platform Side

“danger zone”

Non-Platform Side

Within the Depot and outside of any tunnels or stations the danger zone is to be taken as 5250mm from track centre-line. See Figure 3.2.2.2-B below.

Figure 3.2.2.2-B “danger zone” within depot and outside of tunnels

3.2.2.3 Design for Train Impacts

When the face of a loadbearing element lies outside or does not define the boundary of the danger zone, no special provisions apply.

To provide robustness against the effects of light train impacts, all piers, columns or walls, whose nearest face defines the boundary of, or lies within, the danger zone, shall be designed to withstand two point loads without collapse. A single horizontal ultimate design load of P1 kN acting at a height of up to H1 mm above trackbed (or ground) level, and a single horizontal ultimate design load of P2 kN acting at a height of between H1 mm and H2 mm above trackbed (or ground) level. The two point loads need not be considered to act simultaneously. For designs to BS 5400, γf3 shall be applied in accordance with the code requirements.

Within tunnels and underground stations, the two point loads can act in a direction parallel to or up to D1 degrees from the direction of the adjacent track. At crossovers within tunnels, the direction of the load within 1 metre of the ends of dividing walls is parallel to or up to D2 degrees from the direction of the adjacent main-line track. Within the Depot and outside of the tunnels, the two point loads can act in any direction, and the design shall cater for the most adverse direction(s).

Refer to Appendix 1 of this Chapter for the values of P1, P2, H1, H2, D1 and D2.

5250mm

Track

5250mm

5250mm 5250mm Rails

Extent of Danger Zone

PLAN VIEW

The above impact loads shall be considered in combination with permanent loads together with appropriate live loads (where inclusion of live load is more critical) as defined below:

(a) Structures Designed to SS CP 65 or BS 5950

Irrespective of the number of storeys, structures designed to SS CP 65 or BS 5950 shall be checked in accordance with the requirements of those codes for the effects of exceptional loads or localised damage (refer SS CP 65 Clauses 2.4.3.2 and 2.4.4.2, or BS 5950 Clause 2.4.5.4 etc)

(b) Structures Designed to BS 5400

Structures designed to BS 5400 shall be checked for this purpose in accordance with United Kingdom Highways Agency Departmental Standard BD 60/94 using the ultimate loads (equivalent to the partial load factor (γfL) multiplied by the nominal impact load) given in Appendix 1 of this Chapter. γf3 shall be applied in accordance with the code requirements.

3.2.2.4 Disproportionate Collapse

For all buildings irrespective of the number of storeys, all loadbearing elements, whose nearest face defines the boundary of, or lies within the danger zone, shall be detailed in accordance with SS CP 65 Clause 2.2.2.2 including the provision of vertical ties, or BS 5950 Clause 2.4.5.3, as appropriate. For the purposes of this clause each level of a station shall count as one storey.

Structures whose nearest face defines the boundary of, or lies within, the danger zone shall be designed as follows:

(a) Where individual columns are used within the danger zone, the design of the structure above them shall incorporate such continuity that the removal of any one column will not lead to the collapse of more than a limited portion of the structure close to the element in question under permanent loads, together with the appropriate live loads.

(b) Where however the load bearing element is required to act as a key element defined for the purposes of this clause as one whose removal would cause the collapse of more than a limited portion of the structure close to the element in question, the following shall apply:

(i) Tunnels and underground stations

Sept 2002 Civil Design Criteria – Revision A4