- 1 Engineering metal work
- 1.1 Scope
- 1.2 Welding and Heat Treatment
- 1.3 Flooring
- 1.4 Laddering and Stairways
- 1.5 Miscellaneous
1 Engineering metal work
This section sets out the general requirements for the engineering metalwork required in the works.
The permissible design stresses for materials, bolts, rivets, etc., are given in DIN 18800, for welds in DIN 4100. Rolled structural steel sections shall be mild steel, conforming to DIN 17100. The dimensions, tolerances and properties of the structural sections shall conform to DIN 18201 up to 18203 and to DIN 18800. Where the use of prefabricated proprietary designs is proposed, the standards to which they are manufactures shall be no less rigorous than specified herein. For structural steel work assemblies, steel bolts, nuts and washers shall be high strength friction grip bolts conforming to DIN 6914 up to DIN 6916 or black bolts including nuts and washers conforming to DIN 7989 and DIN 7990. All welding consumables (electrodes, wire, filler rods, flux, shielding gas and the like) shall comply with the requirements of the appropriate DIN standard and with the requirements of the appropriate welding procedure.
1.1.2 Design and Detailing
Structures and components, such as required for the laddering, hoppers, etc., shall be shop fabricated so as to form sub-assemblies of the largest practical size suitable for transportation, handling and erection. Detailing should be in accordance with DIN 18800.
All erection processes shall be carried out in accordance to DIN 18800.
1.2 Welding and Heat Treatment
All welding carried out during fabrication in the factory and erection on the site shall be carried out in accordance with the requirements of DIN 4100 and as shown on the approved detail drawings. Before welding is commenced either in the fabrication shop or on site, weld procedure tests shall be carried out where directed by the Engineer. All welders employed either in the fabrication shop or on site shall pass qualification tests relevant to the weld procedures in use in accordance with the appropriate DIN standard. Welders shall have satisfactory evidence of having been engaged in welding for at least 9 months in the preceding period. If the work of any welders employed on the Contract is unsatisfactory, the Contractor shall carry out such further welder qualification tests as are necessary to demonstrate that the welders are proficient. When not otherwise specified, welds shall be subject to non-destructive testing by processes which may include but not necessarily be limited to radiographic, ultrasonic, magnetic particle, or dye penetrant methods, depending on the type of weld and its position in the structure. About 50 % of all welding shall be tested.
1.2.2 Preparation for Welding
No welding over zinc primers or paint will be allowed.
Flooring shall be fabricated from chequer plate or open mesh panels. Flooring and supports thereto shall be designed and manufactured to resist a uniform applied live loading of 7.5 KN/m2unless otherwise specified or stipulated in the applicable DIN standards. Flooring panels shall generally be removable by one man and the maximum weight of each panel shall not exceed 25 kg. Removable sections of flooring shall be provided with holes for lifting keys, keys to suit for each location, and be arranged to permit removal without disturbance to support brackets, spindles, pipework, etc. Intermediate support members shall be provided as required and attached to the supporting structure. Flooring shall be detailed and fabricated so that no cutting is required on site. Supporting steelwork shall comply with the requirements of clauses for structural steelwork. Bolt holes in brackets and mountings shall be slotted to allow for adjustment of line and level. Mild steel continuous kerbing shall be provided for seating the flooring in concrete. Kerbing and other supporting structures for building into concrete shall have lugs welded on a maximum spacing of 600 mm. Flooring shall be secured to the kerbing or supports by stainless steel flush screws. The width of any access walkway shall be not less than 750 mm.
1.3.2 Floor Plating
Floor plating over openings in concrete or brickwork shall be set flush in mild steel framed kerbing provided with adequate integral lugs for building in. Plating and frames shall be heavily galvanized or aluminium alloy. Floor plating shall have a raised pattern Open mesh flooring panels shall be fabricated from mild steel load bearing bars of flat section backed with round, square, or twisted bars perpendicular to and welded to each load bearing bar. Panels shall be trimmed across the ends of load bearing bars by flats of the same cross section welded to each load bearing bar. Cut-outs for plant items shall be trimmed with curved or straight edge trimming as appropriate. Panels shall be fixed to the kerbing or supporting steelwork with adequate flush stainless steel screws or clips so that movement is prevented.Open mesh flooring shall be heavily galvanized.Internal access covers shall generally be designed and fabricated as specified for flooring. In situations which warrant special measures to prevent pollution of filtered water the covers shall be air tight. If not anywhere otherwise required, external access covers over such as raw water or sludge channels shall be steel open mesh.
1.3.3 Cast Iron Access Covers
Access covers and frames for use with manholes, chambers, draw pits and other structures shall be lockable and shall comply the relevant quality requirements of DIN 1239. Where covers and frames are supplied from manufacturers to standards other than those specified, the alternatives shall be designed and tested for loadings equal to or greater than the covers specified, and the clear openings of the frames of the alternatives shall be equal to or greater than the covers specified.
1.3.4 Permissible Differences
For metalwork at floor level joints differences between flooring sections and between steel flooring and adjacent concrete shall be:
- difference in level at joints: 3 mm
- joint gap: 3 mm
Handrailing shall be provided along every edge of all metalwork and concrete walkways, stairs or accessible open areas where the drop beyond the edge exceeds 700 mm. Handrailing shall consist of standards at regular intervals not exceeding 1.5 m, and two rails. The upper rail shall be 1.0 m above the adjacent finished floor level, and 900 mm above the nosing line on stairways. The lowest rail shall be midway between floor and upper rail. The handrailing fixing and anchorages shall be designed to withstand a continuous horizontal load at the top rail of 750 N/m. Unless otherwise required in the particular specification standards for handrailing inside buildings, all rails shall be fabricated from 32 mm bore galvanized medium weight steel tube. Handrailing shall be flush jointed. Handrailing terminating against a wall shall either have a suitable wall fixing flange, or shall terminate at a standard with a gap between the standard and the wall not exceeding 100 mm. Where the shape of the concrete structure does not incorporate an upstand at the edge of walkways, toe plates 5 mm thick and 100 mm high shall be fixed to handrail standards. The bottom edge of such toe plates shall be 10 mm above the surface of the concrete walkway. The handrail standards for stairways and for landings and walkways of width less than 1.2 m shall have palm fittings for bolting to the side of the structure. Elsewhere the standards shall be designed for fixing 100 mm inside the edge of concrete structures, or at the supporting edge girder of steel flooring, or have palm fittings. Horizontal mounting palms shall be drilled for not less than three bolts with two bolts on a line parallel to and on the walkway side of the line of the handrailing. Vertical mounting palms shall be drilled for not less than two bolts the line through the bolts being vertical. Where required ladders, stairways or other openings shall be guarded on three sides by handrailing conforming to the requirements stated above. Access to the ladders or openings shall be guarded by two removable galvanized hanging chains secured to eyes at top and middle levels. Handrailing shall be of uniform appearance and manufacture. Aluminium alloy handrails and standards shall consist of tubular polished aluminium alloy. Standards shall be fitted with approved bases.
1.4 Laddering and Stairways
Stairs shall have an inclination of approximately 300 and ladders of 750 where practicable. Stairs shall be complete with handrails, mm. 100 cm vertical height. Vertical ladders shall be installed alternating left hand/right hand side to horizontal platforms placed approximately every 6 m of vertical height. Vertical ladders of more than 3 m height shall be provided with safety hoops at intervals not exceeding 900 mm, with the lowest hoop 2.5 m above the ladder foot. Load assumptions for ordinary platforms shall be: - for platforms used by personnel and for support of light equipment with single weights of less than 50 kg 2.5 kN/m2 - for all other platforms 7.5 kN/m2 unless otherwise specified or stipulated in the applicable standards.
With exception of internal access ladders to water tanks, reservoirs and wet sumps, laddering shall be in steel. Ladders for internal access shall be in aluminium alloy or stainless steel. Generally all ladders shall be in accordance with DIN 3620. The stringers shall be sized to suit the height of the ladder and the interval of the stringer supports. Stringer shall be radiused over the top and drilled to receive the rungs which shall be welded to the stringers on each side of each stringer. The bottom ends of the stringers shall not be designed for floor fixing, but shall terminate at wall fixing supports at least 150 mm above the floor. All edges of stringers shall be ground smooth to remove burrs and sharp edges. Where the installation of hoops is not possible or inappropriate, as agreed with the Engineer, anchorage points shall be provided for attaching safety harnesses.
1.4.3 Steel Stairways
Stairways shall be designed for a loading of 7.5 kN/m2 of plan area of the stairway. Steel stairways shall be provided with tubular handrailing, stringers of cross section suitable for the span and loading, and treads of open mesh flooring or chequer plating. Except where specified otherwise, the rise between treads shall be uniform and between 150 mm and 175 mm. Stairways in the same area of the works and in similar locations shall have the same angle and height of rise between treads. The width of the treads shall be between 250 mm and 300 mm. The width of the stairways shall not be less than 750 mm. The stringer shall be mounted by means of angle brackets with slotted holes for adjustment of line and level.
1.5.1 Dissimilar Metals
The use of dissimilar metals in contact, liable to lead to galvanic action, shall be avoided. Mild steel surfaces to be in contact with aluminium or aluminium alloy shall be deemed to satisfy this requirement if they are galvanized. For fixing aluminium to steel structures, bolts, nuts, washers and screws shall be cadmium plated.
1.5.2 Opening Tools
Lifting keys and devices for unfastening screws shall be galvanized mild steel and supplied at the rate of one set for each five similar covers, with a minimum of two sets of each particular type.
1.5.3 Step Irons
Step irons for buildings into precast concrete and step irons and handholds for building into the wall of in-situ concrete manholes and chambers shall be of round pattern. All step irons shall be galvanized or stainless steel. Step irons shall only be used where ladders would not be an appropriate alternative.
1.5.4 Surface Boxes
Surface boxes for key operation of valves shall be cast grey iron or ductile iron and shall comply with the relevant requirements of DIN 405. The lid shall be chained to the frame.
1.5.5 Road Gully Gratings
Gully gratings and frames for road drainage shall be cast iron or ductile iron and shall comply with the relevant requirements.
The engineering metal work shall be protected in accordance with the general specification for "Painting and Protective Coating".
Where metalwork is to be founded on and fastened to concrete, the Contractor shall use one of the following methods as subsequently detailed:
1. Bolting or screwing the metalwork to plates or angle sections with anchors set into the concrete structure or set into pockets left in the concrete structure.
2. Setting the metalwork into pockets or recesses formed in the concrete structure.
3. Bolting the metalwork to bolts set into the concrete structure or set in pockets or holes in the concrete structure.
4. Bolting the metalwork to self-anchoring epoxy resin fixed bolts placed in drilled holes.
5. Bedding the metalwork on cement-mortar placed on the concrete surface.
Cement-mortar of 1 part of cement to 3 parts of sand shall be used for bedding access covers and the like and for filling around metalwork or bolts set into pockets or holes smaller than 100 mm2. For larger holes, concrete of the same grade as the structure shall be used instead of mortar. The installation methods permitted for each type of metalwork are specified in the table below:
Metalwork item Permissible methods of installation Stairs, ladders, flooring 1, 3 and 4 Step irons 2 Handrailing 3 Access covers, surface boxes and gully gratings 2 and 3
During installation, each item of metalwork shall be temporarily braced as necessary to resist all forces which are likely to be applied to it during installation, fixing and building in. Any bolted connections required as part of the installation operation shall be fitted and tightened before fixing bolts are tightened or pockets are grouted. The nuts of grouted or resin fixed bolts shall not be tightened until the grout has fully cured. Small or lightly loaded items may be fixed using screws and approved plugs set in drilled holes.
1.5.8 Inspection and Testing
The Engineer may require to inspect engineering metalwork during fabrication and to witness testing at the fabrication shop in addition to inspections and tests undertaken on site. The Contractor shall give the Engineer 20 working day's notice of any operations which the Engineer has named to the Contractor in order that the Engineer may arrange to undertake such inspections.