OCT 1997

TECHNICAL REQUIREMENTS FOR

STOREY SHELTERS CDSB

Contents

CHAPTER 1: PLANNING REQUIREMENTS

1.1 General

A storey shelter (SS) is constructed for the protection of people against weapon effects during emergency. It is not designed for and should not be used as protection during other emergency situations such as fire. The SS is located in a common property area of a storey and serves the residents of the dwelling units of the same storey.

The SS may be constructed to permit it to be used as a common facility for the residents of the storey or building - for example as a store - as well as provide the required protection economically. This is achieved by the efficient usage of space and shape as well as by the optimal location of the SS. The more internally positioned and shielded the SS is, the more protected it will be.

Economy and strength are achieved by exploiting the protective potential of the building elements surrounding the SS. Shielding and covering structural elements may be used to advantage in reducing weapons effects on the SS.

1.2 SS Position

The SS is to be positioned such that the distance from the SS walls to the external periphery of the building is as great as possible.

Wherever possible, the SS should be positioned adjacent to the building staircase core or internal reinforced concrete walls.

Each of the dwelling units served by the SS shall have at least one exit door at the same storey as the SS. The travel distance between the SS door and the exit door (at the same storey as the SS) of any dwelling unit served by the SS shall not exceed 40 metres. (Fig. 1.1)

1.3 SS Size

The SS size should be calculated on the basis of at least 0.80m2 per person. The nominal occupancy of various sizes of dwelling units used to calculate the minimum SS size is given in Table 1.

Table 1: Nominal Occupancy of Dwelling Unit

Gross Floor Area (GFA) of Dwelling Unit Nominal Occupancy of Dwelling Unit (No. of persons)

GFA =< 45m2 2

75m2 => GFA > 45m2 3

140m2 => GFA > 75m2 4

GFA > 140m2 5

Its internal clear floor area shall be the product of 0.8m2 and the sum of the nominal SS occupancy loads of all the dwelling units served by the SS. For example, if the SS is to serve 2 dwelling units, one of GFA 44 m2 and the other of GFA 46 m2, then the minimum SS clear floor area to be provided shall be:

0.8 m2 x (2 + 3) = 4.0 m2

The maximum net area (excluding the walls) of the SS shall be 32m2.

1.4 Applicability of SS Requirements

For SS equal to or less than 4.8m2 (clear internal floor area), it shall be designed, constructed and commissioned in accordance with Chapters 2 to 7 of the Technical Requirements for Household Shelter 1997 except for the following:

a.) Net opening dimension of SS door shall be: Door width - the minimum clear opening of the door way shall be 900mm measured

between the face of the door and the face of the door stop with the door open at 90o. Door height - 1900mm

For SS exceeding 4.8m2 (clear internal floor area), this Technical Requirements for Storey Shelter 1997 as stated herein shall apply.

1.5 SS Tower

The SS on every storey shall be located one on top of the other, to form a vertical SS tower with continuous walls as shown in Fig. 1.2.

1.6 SS In Single Storey Building

The Technical Requirements for SS are also applicable for SS in a single storey building (Case E of Fig. 1.2).

1.7 Staircase

(applicable in a situation where there is only one staircase or scissor-staircase serving the storey where the SS is located)

The staircase shall include strengthened reinforced concrete elements, designed so that the stability of the staircase shall be maintained in the event of damage to the surrounding structure.

1.8 Peacetime Use

Every SS should be designed to a specific peacetime usage. The other statutory requirements (such as building control requirements, environmental health requirements, fire safety requirements, etc.) for that specific peacetime use shall also be complied with.

FIG. 1.1 SS POSITION (not to scale)

FIG. 1.2 SS TOWER (not to scale)

CHAPTER 2: ARCHITECTURAL DESIGN

2.1 SS Form

2.1.1 SS Plan Shape

The plan of a SS should be as close to square as possible as shown in Fig. 2.1a. Rectangular shapes can be designed, in which case the longer SS walls shall not face the building closest elevation wherever possible, and the length to width ratio of the SS floor area shall always be less than 3 : 1 (see Fig. 2.1b).

2.1.2 SS Width

The minimum width (clear space excluding walls) of a SS shall be 1200mm.

2.1.3 SS Height

The minimum clear height of the SS (measured from the finished floor level to the soffit of the concrete slab above) shall be 2500mm. The clear height of the SS may be up to 4000mm but subject to the requirements as given in section 2.2.1 and 2.2.2 below.

2.1.4 Span Limitation

The span of any floor and/or roof slabs of the SS shall not exceed 8000mm in the direction or directions of span of the main reinforcement, measured from the centres of support.

2.2 SS Walls

2.2.1 Requirements on Setback Distance of SS Walls

For SS with clear height not exceeding 4000mm, the following minimum requirements shall be met: (Fig. 2.2)

a.) One SS wall (not for wall with the SS door) shall be located at setback distance as specified in Table 2.1.

Table 2.1: SS Clear Height and Required Setback Distance

SS Clear Height (Ht) Minimum Setback Distance

2500mm =< Ht =< 2650mm 2200mm

2650mm < Ht =< 3000mm 2400mm

3000mm < Ht =< 3500mm 2600mm

3500mm < Ht =< 4000mm 2800mm

b.) The remaining SS walls are to be at least 6000mm from the external building line.

In general, external building line refers to the edge line of the ceiling slab above the SS under consideration. For SS in single storey building, the external building line refers to the edge line of the roof above the SS under consideration.

2.2.2 SS Wall Thickness

The SS wall thickness for various SS clear height and setback distance of walls shall be in accordance to Table 2.2.

Table 2.2: SS Clear Height and Required Wall Thickness

SS Clear Height (Ht) Setback Distance of SS Wall from External

Building Line

Wall Thickness Required

Less than 6000mm but more than 2200mm

300mm 2500mm =< Ht =< 2650mm

6000mm or more 250mm

Less than 6000mm but more than 2400mm

300mm 2650mm < Ht =< 3000mm

6000mm or more 250mm

Less than 6000mm but more than 2600mm

300mm 3000mm < Ht =< 3500mm

6000mm or more 250mm

Less than 6000mm but more than 2800mm

325mm 3500mm < Ht =< 4000mm

6000mm or more 275mm

The thickness for the common wall between two SSs shall be of minimum 150mm.

2.3 SS Door and Rescue Hatch

2.3.1 Door Type

The door of the SS shall be an airtight light steel protective door, opening outwards away from the SS.

2.3.2 Door Dimensions

The SS door net opening dimensions shall be:

a.) Door width - the minimum clear opening of the door way shall be 900mm measured between the face of the door and the face of the door stop with the door open at 90º (Fig. 2.3).

b.) Door height - 1900mm.

2.3.3 Door Location

The SS door shall be located on a wall having a setback distance of at least 6000mm from the external building line and shall be shielded by a 200mm thick reinforced concrete wall (as shown in Fig. 2.4).

At both sides of the door, at least 150mm concrete wall segments shall be provided (see Fig. 2.5).

2.3.4 Protection of Accessibility to the SS Door

For SS located at a storey where only one staircase (or scissor-staircase arrangement) serves that storey, the accessway from the staircase to the SS shall have a minimum width of 2000mm and its floor and ceiling shall be at least 150mm reinforced concrete elements and shall be cast-in-situ with the SS. In addition, the staircase shall meet the structural requirements as specified under section 3.7.

For SS located at a storey where there is more than one staircase serving that storey, only the portion of the ceiling immediately outside the SS door shall be designed as a strengthened element of minimum 150 mm thickness and be cast in situ with the SS. The dimensions of this strengthened portion shall be as shown in Fig. 2.6.

2.3.5 Rescue Hatch

2.3.5.1 General

A rescue hatch shall be provided on the floor and ceiling on every SS in a SS tower, except that the bottom-most SS shall not have a hatch on its floor and the top-most SS shall not have a hatch on its ceiling. The hatch shall be made of airtight sealed galvanised steel construction and be fire rated.

2.3.5.2 Rescue Hatch Dimensions

The net clear opening of the rescue hatch shall be 700mm x 700mm. The dimensions of the rescue hatch are as shown in Fig. 2.7.

2.3.5.3 Rescue Hatch Position

The rescue hatches in an SS shall be positioned adjacent to the SS walls with minimum dimensions as shown in Fig. 2.8a. The vertical centreline of the hatch in the ceiling shall be offset from the centreline of the hatch in the floor of the same SS by at least 1400mm (Fig. 2.8b).

2.3.5.4 Access to the Rescue Hatch

The access to the rescue hatch shall be by a ladder made of either stainless steel or aluminum and shock-mounted to the SS wall with details and dimensions as shown in Fig. 2.9.

2.4 Building Materials and Finishes

2.4.1 Permitted Materials

a.) Construction materials used for the SS shall have the following properties: flexibility, ductility, air tightness, non-combustibility, non-fragility, fire resistance as specified in the Code of Practice for Fire Precautions in Buildings. Materials which release toxic gases shall not be used under any circumstances.

b.) Building materials complying with the above are: reinforced concrete, sheet steel and steel sections.

c.) Selection of the building finishing materials should take into consideration the climatic conditions existing in the SS, e.g. high humidity.

2.4.2 Prohibited Materials

a.) Materials having any of the following properties are generally prohibited in the construction of the SS: brittleness, fragility, materials which explode into fragments when broken, materials which are flammable and/or emit toxic gases during a fire.

b.) Examples of such prohibited materials are: wood, or any wood by-products, asbestos-cement, gypsum, all types of plaster, wall tiles, glass, etc.

2.4.3 Internal Finishes in SS

a.) The internal finish of the SS walls and ceiling shall be smooth with a cast concrete finish.

b.) The surface finish of the walls and ceiling of the SS may be made using a finish skim coat not thicker than 2 mm. Other finishes to be used shall be approved by the Authority.

c.) No tiles or plaster shall be laid on walls and ceiling inside the SS.

d.) All floor tiles/finishes are allowed if these are founded on a cement mortar screed base.

e.) Skirting material on cement mortar wall base are allowed up to a maximum of 100mm height above floor level.

2.5 Internal Fixtures in SS

2.5.1 General

Specified fixtures shall be provided inside the SS to ensure adequate communication and enhance survivability (Fig. 2.10).

The electrical installation and communication system in the SS shall be designed and installed in accordance with the relevant Codes of Practice and statutory requirements.

For peacetime use, only fixtures that are easily dismantled and removed are allowed.

Fixtures to be provided are lighting, power and telephone points and radio/TV outlets.

2.5.2 Power Points

One power point shall be provided in the vicinity of the TV and radio outlets. Two additional power points for other appliances such as fan, etc. shall be provided.

2.5.3 Lighting

The provision of the lighting shall comply with the following:

a.) Luminaries shall be mounted only on the SS ceiling. Wall mountings are prohibited. b.) The luminaries shall be mounted with bolts/screws with plastic sleeves inserted in drilled

holes.

2.5.4 Cables

All cables used in the SS shall be of the fire-retardant type.

2.5.5 Cable Entries and Openings

ll cable entries shall be sealed for air-tightness as required under section 3.10.

2.5.6 Earthing of Electrical Installation

The earthing of the electrical installation in the SS shall be in accordance with CP:5.

2.5.7 Protection against Lightning

Every SS shall be protected against lightning in accordance with CP:33.

2.6 SS Tower Design

2.6.1 General

At least 70% of the SS wall perimeter shall continue into the foundations, as shown in Fig. 2.11.The minimum plan projection of a wall at the corner of the SS shall be 250mm.

2.6.2 Allowable Openings in SS Tower Walls

Openings in the walls of the SS tower shall be permitted only at storeys with no SS and such openings shall comply with the following:

a.) The aggregate horizontal length of the openings shall not be more than 30% of the SS wall perimeter,

b.) The openings shall either be all located in one wall, or in two opposite walls only.

2.6.3 SS Tower with non-SS Units at Various Storey(s)

Where there are no SS on the lower storey(s) of the SS tower, the walls of the tower at those storeys shall be connected structurally by floors at every storey level, as shown in Cases B, C and D of Fig

1.2. The clear height of the non-SS units, except for the non-SS units at the 1st storey and basement level(s) (if any), in the tower for case B shall be of the same clear height as the SS units. For the non-SS units at the 1st storey and basement level(s) (if any), its clear height shall not exceed 4000mm (Cases C and D of Fig. 1.2).

2.6.4 Ceiling Slab of the Top-most SS unit in the SS Tower

The ceiling slab of the top-most SS unit shall extend out from the SS wall by at least a distance (measured on plan) as specified in Table 2.3 and it shall be of reinforced concrete construction of at least 125mm thick (Fig. 2.12).

Table 2.3: Extension of Ceiling Slab of the Top-most SS unit in SS Tower

SS Clear Height (Ht) Minimum Distance of 125mm thick RC ceiling slab extending out from the SS wall

2500mm =< Ht =< 2650mm 2200mm

2650mm < Ht =< 3000mm 2400mm

3000mm < Ht =< 3500mm 2600mm

3500mm < Ht =< 4000mm 2800mm

The above requirements are also applicable for SS in Single Storey Buildings.

2.7 Hacking and Drilling

No hacking or indiscriminate drilling into floor, ceiling and walls of the SS tower is permitted. Refer to chapter 7 for guidelines on permitted and not permitted works in SS.

2.8 Fixtures

For peacetime use, only fixtures that are easily dismantled and removed are allowed. Refer to chapter 7 for guidelines on permitted and not permitted works in SS.

FIG. 2.1 SS LAYOUTS (a) Preferred SS square form(not to scale)

FIG. 2.1 SS LAYOUTS (b) Allowed SS rectangular form(not to scale)

FIG. 2.2 REQUIREMENT ON SETBACK DISTANCE OF SS WALL (not to scale)

FIG. 2.3 CLEAR OPENING OF SS DOOR (not to scale)

FIG. 2.4 SHIELDING FOR SS DOOR (not to scale)

FIG. 2.5 MINIMUM DISTANCE OF SS DOOR FROM SS WALL (not to scale)

FIG. 2.6 REQUIREMENTS FOR STRENGTHENED CEILING IN THE ACCESS WAY TO THE SS (not to scale)

FIG. 2.7 MINIMUM DIMENSIONS OF RESCUE HATCH (not to scale)

FIG. 2.8a MINIMUM DIMENSIONS OF RESCUE HATCH FROM SS WALL (not to scale)

FIG. 2.8b MINIMUM DISTANCE BETWEEN CENTRE LINES OF RESCUE HATCHES (not to scale)

FIG. 2.9 DETAILS OF LADDER TO RESCUE HATCH (not to scale)

FIG. 2.10 TYPICAL SS FIXTURES (not to scale)

FIG. 2.11 SS WALL EXTENDING TO FOUNDATION (not to scale)

FIG. 2.12 CEILING SLAB OF THE TOP - MOST SS UNIT / SINGLE STOREY SS (not to scale)

CHAPTER 3: STRUCTURAL DESIGN

3.1 General

3.1.1 Design Approach

In the structural design of the SS, a static approach is adopted. The SS shall be designed in accordance with BS 8110 taking into consideration additional requirements as specified in this chapter.

3.1.2 Scope

The requirements here are applicable only to the design of a SS constructed from cast-in-situ reinforced concrete.

The use of pre-stressed concrete in the construction of a SS is prohibited.

3.2 Structural Design

Design Method

The design of a SS shall be done according to the limit state method whereby the SS so designed will have acceptable probabilities that it will not reach either ultimate limit states and/or serviceability limit states and that the SS will be durable.

All relevant limit states shall be considered. The SS may be designed for the most critical limit state and a check shall be made to verify that the remaining limit states will not be reached.

3.3 Materials

3.3.1 Materials Requirements

Materials used in the construction of the SS shall comply with the requirements of BS 8110 and the relevant specifications dealing with these materials as well as with the additional requirements specified in this chapter.

3.3.2 Concrete

The minimum grade of concrete in all reinforced concrete elements of a SS shall be Grade C30. The maximum shall be Grade C40. Only normal weight concrete shall be used.

3.3.3 Steel Reinforcement

Reinforcement shall comply with BS 4449, or BS 4483. Other reinforcing steels may be used provided their minimum elongation at rupture is 12%.

3.3.4 Partial Safety Factors for Strength of Material

For the analysis of sections, the design strength for a given material and limit state is derived from the characteristic strength divided by the appropriate partial safety factor for strength of the material. The partial safety factors corresponding to the ultimate limit states are as given in BS 8110 section 2.4.4.

3.3.5 Stress-Strain Relationships

The stress strain relationships for concrete and reinforcement for the analysis of cross-sections shall be as given in BS 8110 section 2.5.3.

3.4 Analysis

3.4.1 General

In choosing a suitable structural system for the SS, the following shall be considered:

a.) The transfer of all the loads to the foundation shall be simple and straightforward. b.) Vertical load bearing elements such as walls shall be located along straight grid lines.

The methods of analysis used shall be based on as accurate a representation of the behaviour of the structure as is reasonably practicable. The analysis of the structure, or part of the structure and the analysis of the sections shall be carried out in accordance with the provisions of BS 8110 subject to the additional requirements in this chapter.

3.4.2 Structural System

The SS at each storey of the block is to be designed one on top of another, forming a continuous tower. At least 70% of the SS wall perimeter in the SS tower shall continue into the foundations.

It is the aim of design to achieve the maximum possible degrees of redundancy for a given structural system. Joints of structural members shall be designed as rigid and hinges shall not be incorporated.

3.4.3 SS Tower Stability

The following should be ensured in the design of the SS tower:

Each SS floor/ceiling slab should be connected to the surrounding building slabs, including appropriate reinforcement.

The SS tower is to be stable under the following conditions:

a.) Removal of any one wall out of the four walls on any storey of the SS tower; b.) Removal of any slab adjacent to a wall on any storey of the SS tower; c.) Removal of piles along periphery of a pile cap and located with a certain damage zone (on a

length of 1.4 metres for piles on a straight line and 2.0 metres for piles on corner, as shown in Fig. 3.1); and

d.) Removal of three consecutive floor slabs (i.e. on top of one another) at interface between the SS tower and external building frame for external prefabricated building, as shown in Fig. 3.2.

3.4.4 Staircases

Each staircase serving the dwelling units of a storey shall be designed for a shock load equal to its characteristic dead weight multiplied by a partial safety load factor of 1.25 and acting in any direction. The staircase supports shall also be designed for this shock load.

3.5 Design of Structural Members

Generally, the design of structural members shall be done in accordance with BS 8110 taking into consideration the requirements specified here.

3.5.1 Solid Slabs

The design of solid slabs shall take into consideration the following:

a.) Two-way design of solid slabs is preferred over one way slabs. b.) Solid slabs shall be designed as fixed or partially restrained at the supports.

3.5.2 Walls

Walls shall be designed in accordance with the provisions of BS 8110. However, all connections transmitting load to a wall shall be designed as fixed or partially restrained.

3.5.3 Bases

Bases shall be designed in accordance with the provision of BS 8110 subject to the following:

a.) Footing is the preferred form of foundation for SS towers. b.) A base or a pile cap is to be designed for the maximum load transferred to it. c.) The service load on a base for the purposes of establishing soil bearing capacity or pile

capacity is obtained by considering the effects of all relevant peacetime loads. Peacetime loads are considered in accordance with relevant codes.

3.5.4 Ceiling in Front of SS Door

The ceiling (section 2.3.4) shall be at least 150mm thick.

3.6 Dimension and Reinforcement Amounts

3.6.1 Minimum Dimensions of Members

3.6.1.1 SS Tower

The minimum dimensions of members forming part of the SS tower shall be as follows (Fig. 3.3):

a.) SS wall - see Table 2.2. b.) Wall common to two SSs - 150mm. c.) Intermediate slabs - 150mm. d.) Ceiling of top-most SS - 300mm e.) Floor of bottom-most SS - 200mm (if located at ground level) (Case A of Fig. 3.3) or 300 mm if

located above ground level) (Case B of Fig. 3.3) f.) Walls beneath a SS or non-SS unit - thickness shall be at least that of the SS or non-SS unit

under consideration.

3.6.1.2 Structure Above, Beneath and Adjacent to the SS Tower

The minimum dimensions of members above, beneath and adjacent to the SS tower shall be as follows:

a. Walls beneath the SS tower - at least same thickness as the SS tower walls above. b. Shielding wall in front of the SS door - 200mm c. Ceiling in front of the SS door - 150mm. d. Ceiling of top-most SS unit in SS tower - refer to section 2.6.4.

3.6.2 Minimum Reinforcement Amounts

The minimum reinforcement amounts, using steel with yield strength of 460N/mm2 in the various members, shall be as follows:

a.) SS wall: See Table 3.1

Table 3.1: Minimum Reinforcement Amounts

SS Clear Height (Ht) Wall Thickness Wall Reinforcement amount at inner

face, top and bottom 1/3 effective span of

the outer face of wall (both ways)

Wall Reinforcement amount at middle

1/3 effective span of the outer face of wall (both ways)

2500mm =< Ht =< 2650mm

250mm or 300mm

T13-100 T13-200

2650mm < Ht =< 3000mm

250mm or 300mm

T13-100 T13-200

3000mm < Ht =< 3500mm

250mm or 300mm

T13-100 T13-200

3500mm < Ht =< 4000mm

275mm or 325mm

T16-100 T16-200

The effective span of the wall is defined as the distance between the centres of its lateral supports.

b.) Intermediate slabs: Two reinforcement (top and bottom) of 10mm bars at 200mm spacing in both directions.

c.) Ceiling of top-most SS: (1) Top slab reinforcement amount at middle 1/3 effective span of the ceiling - T13-200. (2) Slab reinforcement amounts at bottom of slab, top edge 1/3 effective spans of the

ceiling - T13-100. d.) Floor of bottom-most SS:

(1) Bottom slab reinforcement amount at middle 1/3 effective span of the slab - T13-200. (2) Slab reinforcement amounts at top of slab, bottom edge 1/3 effective spans of the slab

- T13-100. e.) Walls beneath the SS perimeter walls:

Same requirements as detailed in sections 3.6.2 (a) and 3.6.2 (b) above. f.) Shielding wall in front of SS door:

Two reinforcement (one on each side of the wall) of 10mm bars at 200mm spacing in both directions.

g.) Ceiling in front of the SS door: Same requirements as detailed in section 3.6.2(c) above.

For steel with yield strength different than 460 N/mm² and at the above specified distances the minimum reinforcement area shall be obtained by multiplying the reinforcement area of the above 10mm bars by a factor of fy/460.

In all structural members, 50% of the reinforcement amount in the tension zone should be provided in the compression zone in the same cross-section.

3.7 Staircase leading to SS

(applicable for SS located at storey where there is only one staircase or scissor-staircase serving that storey)

3.7.1 Staircase Strengthened Elements

The staircase shall include the following strengthened elements:

a.) Waist of staircase and landings - minimum 150mm reinforced concrete. b.) Any walls adjacent to the staircase shall be of reinforced concrete construction.

The minimum reinforcement in the above elements shall consist of 2 reinforcement (top and bottom) of T10mm bars at 200mm distance both ways. Shear links connecting the 2 layers of reinforcement shall be of R6mm at 600mm both ways.

3.7.2 Scissor-Staircase Arrangement

For the scissor-staircase arrangement, the requirements in section 3.7.1 shall apply to both staircases.

3.8 Rescue Hatch and Access to Rescue Hatch

3.8.1 Rescue Hatch

The rescue hatch and its supports shall be designed to withstand a shock load of at least 10g in all directions.

3.8.2 Access to Rescue Hatch

The ladder and its supports shall be designed to withstand a shock load of at least 10g in all directions.

3.9 Structural Detailing

3.9.1 General

Members shall be detailed in accordance with the requirements of BS 8110. In addition, the following recommendations apply.

3.9.2 Laps, Joints and Anchorage of Bars

Requirements for laps, joints and anchorage of reinforcement bars are as follows:

a.) For slabs and walls, tension laps shall be provided at all laps. The design tension lap length shall be calculated in accordance with BS 8110.

b.) Laps shall be made at location of low moments (at points of inflection). Laps of adjacent bars shall be staggered by at least the lap length of the bars.

c.) For bars extending into the end supports, an effective anchorage length equal to a full tension anchorage length shall be provided. Mechanical devices may be used for end anchorage and laps in reinforcements. Test certificate showing the strength and ductility of such devices shall be submitted for approval before the use of such devices.

d.) Welding of reinforcement shall be avoided. Where welding is absolutely essential, test certificate of the combination of weld and reinforcing steel shall be submitted for approval before the use of welded joints.

e.) The use of bundled bars shall be avoided. A three bar bundle is the maximum bundle permissible. Laps of individual bars within a bundle shall be staggered. Only one bar of the bundle shall be lapped at a given location.

3.9.3 Spacing, Cover, Bar Sizes

Requirements for spacing, cover and bar sizes are as follows:

a.) The maximum spacing between bars on inner faces of members susceptible to the effects of blast shall be 100mm. The same shall apply to the edge 1/3 spans of the outer faces of members susceptible to blast. The maximum spacing between bars on middle 1/3 spans of the outer faces of members susceptible to blast shall be 200mm.

b.) The maximum spacing between bars for all other members not stated in section 3.9.3 (a) shall be 200mm.

c.) The nominal cover of reinforcement shall comply with the requirements of BS 8110 subject to a maximum of 40mm.

d.) The minimum diameter of individual reinforcing bars shall be 10mm except for links which shall have a minimum diameter of 6mm.

3.9.4 Slabs and Walls

For solid slabs and walls (see Fig. 3.4, Fig. 3.5, Fig. 3.6 and Fig. 3.7) the following shall apply:

a.) Two layers of reinforcement, one at each facet shall be provided. Each layer shall consist of bars spanning in two perpendicular directions The minimum amount of each set of reinforcement shall be as detailed in section 3.6.2.

b.) 100% of the main tension reinforcement at mid-span shall be extended to the supports and properly anchored.

c.) The minimum amount of compressive reinforcement at a given section shall be at least 50% of the main tension reinforcement at the section.

d.) Links of minimum diameter 6mm at a maximum spacing of 600/600mm properly anchored around the bars of the two meshes shall be provided.

3.9.5 Construction Joints

Joints in a SS tower shall be properly executed to ensure that the strength of the SS is not impaired. The type and location of joints shall be specified in the design taking into consideration the following:

a.) Expansion joints or contraction joints shall not be permitted. b.) Horizontal joints shall be permitted only in connection between floors and walls and between

walls and roofs. The form of the joints shall be as approved by the Authority. A maximum of 100mm concrete kicker is allowed at the slab/wall interface for the construction of the walls.

c.) The full height of a wall shall be cast in one lift.

Fig. 3.8 shows the typical reinforcement around the SS door.

3.10 Penetration of Services

Service cables which do not serve the SS are not allowed to penetrate the walls and slabs of the SS, nor are they allowed to be embedded in the SS walls and slabs.

Where service cables and sockets serving the SS are externally mounted on walls, removable non-metallic inserts are to be used. For embedded service cables and sockets serving the SS, the details as shown in Fig. 3.9 and Fig. 3.10 shall be followed. The socket for power, TV and telephone outlets shall be stainless steel encasement with minimum thickness of 2mm.

At most three numbers of maximum 25mm diameter hole to accommodate the service conduits of electrical cables of the SS are allowed to penetrate the walls. One end of the service conduit located on the external or internal face of the shelter shall be pressure grouted with high strength non-shrink grout to a minimum depth of 100mm into the conduit or shall be sealed with approved Sealing Devices to ensure air-tightness. The non-shrink grout shall be of minimum Grade 30 concrete strength. Approved tests shall be conducted to ensure air-tightness of the service conduit.

Where approved sealing devices are provided, test reports shall be produced to validate the adequacy of the sealing devices with respect to the following:

a.) Protection degree of 3 bars incident pressure b.) Air-tightness

Seals used in sealing devices shall be closed cell expanded rubber with skin coating all around complying with the requirements of ASTM D1056. The material shall be of neoprene or EPDM rubber and shall meet the requirements of Type 2, closed cell expanded rubber, Grade 2 B3 or higher, as specified in Table 2 ASTM D1056.

FIG. 3.1 INCAPACITATION OF PILE FOUNDATION UNDER THE SS TOWER (not to scale)

FIG. 3.2 INCAPACITATION OF PREFABRICATED SLABS ADJACENT TO THE SS TOWER (not to scale)

FIG. 3.3 STRUCTURAL REQUIREMENTS OF SS TOWER (not to scale)

FIG. 3.4 TYPICAL DETAIL OF SLABS / WALLS [Bars Perpendicular To Section Not Shown] (not to scale)

FIG. 3.5 CORNER DETAILS BETWEEN SS WALLS (not to scale)

FIG. 3.6 TYPICAL DETAILS OF WALL COMMON TO TWO SSs (not to scale)

FIG. 3.7 TYPICAL DETAILS OF WALL COMMON TO TWO SSs (not to scale)

FIG. 3.8 TYPICAL DETAILS OF REINFORCEMENT AROUND THE SS DOOR (not to scale)

FIG. 3.9a PART PLAN OF SS WALL At socket location

FIG. 3.9b PART PLAN OF SS WALL At conduit location only (not to scale)

FIG.3.10 DETAILS FOR EMBEDDMENT SOCKET / SWITCH (not to scale)

CHAPTER 4: VENTILATION SLEEVES (OPENINGS)

4.1

In each SS, two 150mm diameter ventilation sleeves shall be cast into the walls. The sleeves shall be located on opposite walls. If this is not possible, they can be located on adjacent walls.

4.2

The centrelines of the sleeves shall be more than 1900mm above the finished floor level and not less than 350mm from the ceiling and the edge of the walls. If the ventilation opening is to be located above the SS door, the minimum distance from the lower edge of the opening to the edge of the door frame shall be at least 150mm.

4.3

An external stainless steel plate of minimum thickness 10mm shall be mounted 75mm away from the exterior face of the SS at each sleeve (Fig. 4.1).

4.4

The ventilation sleeves shall be located in SS walls as far away from the external building line as possible.

4.5

Ventilation sleeves located in adjacent walls of the SS shall be as far apart as possible and in any case not less than 1000mm apart.

FIG. 4.1 FRAGMENTATION PLATE AT VENTILATION OPENING (not to scale)

CHAPTER 5: SS PROTECTIVE DOOR

5.1 General

The SS door shall be airtight and this shall be achieved by adequate sealing.

The various components of the SS door such as hinges, locking mechanisms, leaf and frame shall be designed appropriately to withstand the blast effects of weapons. The SS door and its mechanisms must be simple to operate and functional even under adverse circumstances such as poor maintenance and partial deformation under blast loading.

The SS door shall be designed for easy daily use and with appropriate finishes.

5.2 Approved SS Door Designs

Only SS doors whose designs have successfully passed a type test to the test criteria set by the Authority are approved for installation. All SS doors to be used for installation shall be taken from the list of approved SS doors maintained by the Authority.

5.3 SS Door Notice

All SS doors shall have a notice as specified by the Authority affixed on the interior face within the SS (see Fig. 5.1). A sample door notice is at Fig. 5.2.

FIG. 5.1 LOCATION FOR DOOR NOTICE (not to scale)

FIG. 5.2 SAMPLE DOOR NOTICE

CHAPTER 6: CONSTRUCTION AND COMMISSIONING

6.1 General

The SS shall be constructed according to the SS design specifications and approved detailed design drawings.

6.2 Architectural

In addition the following shall be complied with:

a.) All the fixtures in the SS shall be located as detailed in the drawings. Changes in fixture locations shall only be made after the approval of the Authority.

b.) Any alternative items to those specified in the drawings, and in the design and construction specifications, shall be implemented only after the approval of the Authority.

6.3 Structural

The following shall be implemented:

a.) Special attention shall be given to the correct and proper location and emplacement of the links between the reinforcement meshes in all the SS structural elements.

b.) Any detail of the reinforcement bars which differs from that specified in the design specifications and in the drawings shall only be executed after the approval by the Authority.

c.) No horizontal joints in the SS walls shall be executed other than at the interfaces between the floor slabs and walls. SS walls shall be cast in one lift to their full floor height.

d.) No openings in the SS walls, ceilings and floors shall be permitted after the casting of the concrete. All embedded items, including the SS door, the rescue hatch and the access steel ladder, shall be emplaced in their location before the casting of the concrete and shall be properly connected to the adjacent reinforcement bars to ensure their stability during the casting.

e.) Special care shall be taken while casting the concrete near the SS door frame - bending or displacement of the door frame shall be prevented and the concrete shall fill all voids adjacent to the door frame.

f.) The SS walls and ceiling inner faces shall be executed with smooth concrete finish, as specified for exposed concrete elements. A maximum thickness of 2mm is allowed as a skim coat on the internal face of the walls.

g.) The concrete elements shall be executed with maximum concrete density to provide air-tightness. No concrete areas with segregation or air voids shall be accepted.

h.) No hacking or indiscriminate drilling into floor, ceiling and walls are permitted. Irregularities of wall surface shall not be hacked and plastered back. The method of any remedial work on the concrete shall be approved by the Authority before execution.

i.) For peacetime use, only fixtures that are easily dismantled and removed are permitted.

6.4 Mechanical/Electrical

The following shall be implemented:

a.) All electrical conduits, power sockets - outlets and switches and any mechanical pipes in the SS shall be affixed on the surface of the concrete elements. No embedment of these items in the concrete elements shall be allowed except for approved penetrations perpendicular to the concrete elements.

b.) All sleeves and embedded items shall be emplaced in their final position and adequately anchored to the adjacent reinforcement bars before casting of the concrete. Adequate steps shall be taken during casting to ensure air-tightness around all penetrations.

6.5 SS Protective Door

The following shall be implemented:

a.) Each SS door shall be checked at the manufacturer’s plant and shall only be brought to the site after being approved as conforming to all the design specifications.

b.) Water tightness test shall be carried out at the manufacturer’s plant on the door leaf and frame to a minimum depth of 25mm water for a period of 2 hours. Any seepage of water through the gasket after 2 hours will be considered a failure. After erection of the SS door on site, the door shall pass a chalk mark and light penetration test as specified by the Authority.

c.) The SS door shall be emplaced in its final position before the casting of the concrete, including adequate connections to the adjacent reinforcement bars, to ensure that no bending or displacement of the door frame will occur during the casting of concrete. The SS door frame as well as the SS door leaf shall be emplaced as detailed above.

d.) Leaving an opening in the SS concrete wall and later emplacing the SS door frame and door leaf followed by concrete casting around it is prohibited.

e.) Emplacing the SS door frame only, casting the concrete around it and only at a later stage emplacing the SS door leaf shall not be allowed, except with the approval of the Authority to use specially designed dummy strengthening measures, which have been previously tested and have proved adequate in ensuring the stability and non-deformability of the SS door frame during the casting of concrete.

f.) The SS door shall be brought to the site in its final state, including all finishes, and shall be adequately protected on site throughout the construction period, after being emplaced in its position.

g.) Before and after casting of concrete, the proper functioning of the SS door shall be checked on site and approved by the supervising Architect and the Engineer.

h.) The interior face of the SS door within the SS shall have a notice as specified by the Authority affixed to it.

6.6 Commissioning Requirements

The following shall be checked during commissioning:

a.) Proper functioning of the SS door, rescue hatch, TV, radio and electrical outlets; b.) Satisfactory workmanship relating to structural works, SS door, rescue hatch, airtightness,

ventilation openings, etc.

CHAPTER 7: GUIDELINES FOR PERMITTED & NOT PERMITTED WORKS

7.1 General

The owner or occupier of the building having SS shall not carry out or permit another person to carry out any repair or alteration or renovation works which are likely to damage or impair the efficient use of the SS.

For the peacetime use of the SS, the guidelines for works in the SS in the following sections shall apply

7.2 Architectural and Building Works

7.2.1 Permitted Works

a.) Laying of floor tiles with cement mortar.

b.) Laying of vinyl or linoleum flooring.

c.) Laying of maximum 100mm floor skirting tiles with cement mortar.

d.) Painting of walls, ceiling or door. In the painting of the door, owners shall not cover up or paint over the notice pertaining to the SS which is glued on the door.

e.) Fixing of maximum 50mm long removable screws with non-metallic inserts for fixtures eg. pictures, posters, etc.

f.) Installation of cabinet or shelves using maximum 50mm long removable screws. Such installations have to be removed by the owners within 48 hours’ notice by the Authority in times of emergency, so as to make space for the shelter occupants and to ensure safety of the occupants.

7.2.2 Not Permitted Works

a.) Laying of wall tiles or using of rock tone finish, cement sand finish and gypsum plastering for walls.

b.) Laying of adhesive tiles.

c.) Installation of cornices.

d.) Installation using ramsetting.

e.) Tampering with, removing or covering up of the notice on the door pertaining to the SS. The notice provides important information to the occupants for ensuring their safety in the use of the SS both during the daily routine and in times of emergency.

f.) Modifying, changing, removing, hacking, boring hole or drilling of the SS structure viz walls, floor, ceiling and door. Such works will affect the structural integrity of the SS and endanger the shelter occupants in times of emergency.

7.3 Mechanical and Electrical Works

7.3.1 Permitted Works

a.) Installation of wall/ceiling fan, wall/ceiling lighting or fan coil (air conditioning system) using maximum 50mm long removable screws with non-metallic inserts. Such installations which the owners have put in have to be removed by the owners within 48 hours’ notice by the Authority in times of emergency, so as to make space for the shelter occupants and to ensure the safety of the occupants.

7.3.2 Not Permitted Works

a.) Dismantling, modifying, altering or tampering with any part of the ventilation openings including the mounting devices such as bolts and nuts. Closing up or removal of the steel plates for the ventilation openings. Such works will affect the provision of ventilation in the SS and may pose hazards to the occupants in their daily use and in times of emergency.