Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 06: Concrete and Steel Works  1 of 18   type, quality and quantities to be ordered from available (local or non-local) stocks.  Test certificates from the steel manufacturers shall be required to be submitted to the Engineer for the  materials ordered. Material obtained from stocks shall be checked by the Engineer for the exterior de- fects either in the workshop or at the site.  Manhole and access covers and frames shall have minimum openings of 625 mm diameter or 600 mm  x 600 mm or 750 mm x 750 mm and shall be capable of taking a load of 40 tonne (400 kN) in accord- ance with TS 1478 EN 124 Traffic Class D400.  6.4.4 Manhole and access covers and frames  Manhole covers and frame material shall be spheroid graphite cast iron in accordance with TS 526 EN  1563.  Employer's name, logo and the collector type (rainwater or wastewater) shall be designated on the  manhole covers.  A heavy grease seal is to be formed between the cover and frame to prevent the ingress of sand.  Keyways in manhole covers shall be closed.  6.4.5 Surface boxes  6.4.6 Ladders and step irons  6.4.7 Steel stairways in buildings  Cast iron surface boxes shall comply with the relevant requirements of TS 1478 EN 124. The lid shall  be chained to the frame.  With the exception of internal access ladders to water tanks, reservoirs and wet sumps, ladders shall be  in steel (fully hot-dip galvanized). Ladders for internal access shall be in stainless steel.  The stringers shall be sized to suit the height of the ladder and the interval of the stringer supports.  Stringers 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 string- ers shall be ground smooth to remove burrs and sharp edges.  Where the installation of hoops is not possible or appropriate, as agreed with the Engineer, anchorage  points shall be provided for attaching safety harnesses.  Stairways shall be designed for a loading of 5.0 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 be- tween 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.  6_Vol3_d4.3_Section 6 Concrete and steel works_en_GIR_rev6.docx 