Construction of New Building for Mechanical Laundry at DH Neyyattinkara Trivandrum

Amount

Civil works

2.6.1 : Earth work in excavation by mechanical means (Hydraulic excavator)/manual means over areas (exceeding 30 cm in depth, 1.5 m in width as well as 10 sqm on plan) including disposal of excavated earth, lead up to 50 m and lift up to 1.5 m, disposed earth to be levelled and neatly dressed.All kinds of soil

2.25 : Filling available excavated earth (excluding rock) in trenches, plinth, sides of foundations etc. in layers not exceeding 20 cm in depth, consolidating each deposited layer by ramming and watering, lead up to 50 m and lift up to 1.5 m.Filling available excavated earth (excluding rock) in trenches, plinth, sides of foundation etc. in layers not exceeding 20 cm in depth, consolidating each deposited layer by ramming and watering, lead up to 50 m and lift up to 1.5 m.

4.1.6 : Providing and laying in position cement concrete of specified grade excluding the cost of centering and shuttering - All work up to plinth level:1:3:6 ( 1 cement : 3 coarse sand : 6 graded stone aggregate 40 mm nominal size)

5.9.1 : Centering and shuttering including strutting, etc. and removal of form for:Foundations, footings, bases of columns, etc for mass concrete

5.9.5 : Centering and shuttering including strutting, etc. and removal of form for:Lintels, beams, plinth beams, girders bressumers and cantilevers

5.9.6 : Centering and shuttering including strutting, etc. and removal of form for:Columns, Pillars, Piers, Abutments, Posts and Struts

5.33.2 : Providing and laying in position machine batched and machine mixed design mix M-25 grade cement concrete for reinforced cement concrete work, using cement content as per approved design mix, including pumping of concrete to site of laying but excluding the cost of centering, shuttering, finishing and reinforcement, including admixtures in recommended proportions as per IS: 9103 to accelerate, retard setting of concrete, improve workability without impairing strength and durability as per direction of Engineer - in-charge. Note:- Cement content considered in this item is @ 330 kg/ cum. Excess or less cement used as per design mix is payable or recoverable separately.All work above plinth level upto floor V level

5.22A.6 : Steel reinforcement for R.C.C work including straightening, cutting, bending, placing in position and binding all complete above plinth level.Thermo - Mechanically Treated bars of grade Fe-500D or more

9.48.2 : Providing and fixing M.S. Grills of required pattern in frames of windows etc. with M.S. flats, square or round bars etc. including priming coat with approved steel primer all complete.Fixed to openings/ wooden frames with rawl plugs screws etc

50.6.1.5 : Solid block masonry using pre cast solid blocks ( Factory made) of size 30x20x20cm or nearest available size confirming to IS 2185 Part I of 1979 for super structure up to floor two level thickness 20cm and above in: CM 1:6 ( 1 cement : 6 coarse sand) etc complete

13.1.1 : 12 mm cement plaster of mix:1:4 ( 1 cement : 4 fine sand)

10.16.1 : Steel work in built up tubular (round, square or rectangular hollow tubes etc.) trusses etc., including cutting, hoisting, fixing position and applying a priming coat of approved steel primer, including welding and bolted with special shaped washers etc. complete.Hot finished welded type tubes

26.19.1 : Providing at all heights, levels and locations Aluminium profile industrial troughed sheet of Alloy 31500/31000/40800, conforming to IS 1254, IS 737, IS 2676. The sheet shall be fixed using self drilling/self tapping SS screws of size 5.5x65 mm with EPDM seal complete upto required pitch in horizontal, vertical or curved surfaces i/c cutting to size and shape where required as per specifications, detail drawings and direction of Engineer-in-Charge. The rate shall be inclusive of all screws, seal, ridge, labour, scaffolding, machinery for fixing and approved sealent where required etc. but excluding the cost of purlins, rafters and trusses.0.71 mm thick, the profile detail width 1044/920 mm, cover width 1000/875 mm.

12.41.2 : Providing and fixing on wall face unplasticised Rigid PVC rain water pipes conforming to IS : 13592 Type A, including jointing with seal ring conforming to IS : 5382, leaving 10 mm gap for thermal expansion, (i) Single socketed pipes.110 mm diameter

od59069/2022_2023 : Providing & fixing PVC Square profile rain water gutter 150mm wide including MS support brackets

10.6.1 : Supplying and fixing rolling shutters of approved make, made of required size M.S. laths, interlocked together through their entire length and jointed together at the end by end locks, mounted on specially designed pipe shaft with brackets, side guides and arrangements for inside and outside locking with push and pull operation complete, including the cost of providing and fixing necessary 27.5 cm long wire springs manufactured from high tensile steel wire of adequate strength conforming to IS: 4454 - part 1 and M.S. top cover of required thickness for rolling shutters.80x1.25 mm M.S. laths with 1.25 mm thick top cover

10.7 : Providing and fixing ball bearing for rolling shutters.

21.1.1.2 : Providing and fixing aluminium work for doors, windows, ventilators and partitions with extruded built up standard tubular sections/ appropriate Z sections and other sections of approved make conforming to IS : 733 and IS: 1285, fixing with dash fasteners of required dia and size, including necessary filling up the gaps at junctions, i.e. at top, bottom and sides with required EPDM rubber/ neoprene gasket etc. Aluminium sections shall be smooth, rust free, straight, mitred and jointed mechanically wherever required including cleat angle, Aluminnium snap beading for glazing /paneling, C.P. brass/ stainless steel screws, all complete as per architectural drawings and the directions of Engineer-in-charge.(Glazing, paneling and dash fasteners to be paid for separately):For fixed portionPowder coated aluminium (minimum thickness of powder coating 50 micron)

21.3.2 : Providing and fixing glazing in aluminium door, window, ventilator shutters and partitions etc. with EPDM rubber / neoprene gasket etc. complete as per the architectural drawings and the directions of Engineer - in -Charge. ( Cost of aluminium snap beading shall be paid in basic item):With float glass panes of 5.50 mm thickness

11.41.2 : Providing and laying vitrified floor tiles in different sizes (thickness to be specified by the manufacturer) with water absorption less than 0.08% and conforming to IS : 15622, of approved make, in all colours and shades, laid on 20 mm thick cement mortar 1:4(1 cement : 4 coarse sand), including grouting the joints with white cement and matching pigments etc., complete.Size of Tile 600 x 600 mm.

13.47.1 : Finishing walls with Premium Acrylic Smooth exterior paint with Silicone additives of required shade:New work (Two or more coats applied @ 1.43 ltr/ 10 sqm over and including priming coat of exterior primer applied @ 2.20 kg/ 10 sqm)

13.60.1 : Wall painting with acrylic emulsion paint of approved brand and manufacture to give an even shade:Two or more coats on new work

13.61.1 : Painting with synthetic enamel paint of approved brand and manufacture to give an even shade:Two or more coats on new work

10.28 : Providing and fixing stainless steel (Grade 304) railing made of Hollow tubes, channels, plates etc., including welding, grinding, buffing, polishing and making curvature (wherever required) and fitting the same with necessary stainless steel nuts and bolts complete, i/c fixing the railing with necessary accessories & stainless steel dash fasteners, stainless steel bolts etc., of required size on the top of the floor or the side of waist slab with suitable arrangement as per approval of Engineer-in-charge, (for payment purpose only weight of stainless steel members shall be considered excluding fixing accessories such as nuts, bolts, fasteners etc.)

19.21.1 : Making connection of drain or sewer line with existing manhole including breaking into and making good the walls, floors with cement concrete 1:2:4 mix( 1 cement:2 coarse sand: 4 graded stone aggregate 20 mm nominal size) cement plastered on both sides with cement mortar 1:3 ( 1 cement: 3 coarse sand) finished with a floating coat of neat cement and making necessary channels for the drain etc. complete.For pipes 100 to 250 mm diameter

18.7.2 : Providing and fixing Chlorinated Polyvinyl Chloride (CPVC) pipes, having thermal stability for hot & cold water supply, including all CPVC plain & brass threaded fittings including fixing the pipe with clamps at 1.00 m spacing. This includes jointing of pipes & fittings with one step CPVC solvent cement and testing of joints complete as per direction of Engineer -in-Charge. Internal work - Exposed on wall20 mm nominal outer dia pipes

18.8.2 : Providing and fixing Chlorinated Polyvinyl Chloride (CPVC) pipes, having thermal stability for hot & cold water supply, including all CPVC plain & brass threaded fittings i/c fixing the pipe with clamps at 1.00 m spacing. This includes jointing of pipes& fittings, with one step CPVC solvent cement and the cost of cutting chases and making good the same including testing of joints complete as per direction of Engineer-in-Charge. Concealed work, including cutting chases and making good the wall etc.20 mm nominal outer dia pipes

18.9.2 : Providing and fixing Chlorinated Polyvinyl Chloride (CPVC) pipes, having thermal stability for hot & cold water supply including all CPVC plain & brass threaded fittings. This includes jointing of pipes & fittings with one step CPVC solvent cement, trenching , refilling & testing of joints complete as per direction of Engineer- in-Charge. External work20 mm nominal outer dia pipes

50.18.8.2.2 : Providing and fixing PVC pipes, fittings including fixing the pipe with clamps at 1.00 m spacing. This includes jointing of pipes & fittings with one step PVC solvent cement and testing of joints complete as per direction of Engineer-in-Charge. Concealed work, including cutting chases and making good the wall etc. 20 mm pipe 10 Kgf/ cm2

50.18.9.2.2 : Providing and fixing PVC pipes includings of pipes with one step PVC solvent cement, trenching, refilling & testing of joints complete as per direction of Engineer in Charge. 20 mm dia 10 Kgf/cm2

50.18.7.4.2 : Providing and fixing PVC, pipes fittings including fixing the pipe with clamps at 1.00 m spacing. this includes jointing of pipes & fittings with one step PVC solvent cement and testing of joints complete as per direction of Engineer-in-Charge 32 mm dia 6 Kgf/cm2 - internal work- Exposed on wall

50.18.8.4.1 : Providing and fixing PVC pipes, fittings including fixing the pipe with clamps at 1.00 m spacing. This includes jointing of pipes & fittings with one step PVC solvent cement and testing of joints complete as per direction of Engineer-in-Charge. Concealed work, including cutting chases and making good the wall etc. 32 mm pipe 10Kgf/cm2

50.18.9.4.1 : Providing and fixing PVC pipes includings jointing of pipes with one step PVC solvent cement, trenching, refilling & testing of joints complete as per direction of Engineer in Charge.32 mm dia 10.Kgf/cm2

50.18.8.8.1 : Providing and fixing PVC pipes, fittings including fixing the pipe with clamps at 1.00 m spacing. This includes jointing of pipes with one step PVC solvent cement and testing of joints complete as per direction of Engineer-in-Charge. Concealed work, including cutting chases and making good the wall etc. 75 mm pipe 6 Kgf/cm2

50.18.9.8.1 : Providing and fixing PVC pipes includings jointing of pipes with one step PVC solvent cement, trenching, refilling & testing of joints complete as per direction of Engineer in Charge. 75 mm dia 6 Kgf/ cm2

18.17.4 : Providing and fixing gun metal gate valve with C.I. wheel of approved quality (screwed end) :50 mm nominal bore

18.18.3 : Providing and fixing ball valve (brass) of approved quality, High or low pressure, with plastic floats complete:25 mm nominal bore

18.19.4.1 : Providing and fixing gun metal non-return valve of approved quality (screwed end):50 mm nominal boreHorizontal

50.18.8.6.1 : Providing and fixing PVC pipes, fittings including fixing the pipe with clamps at 1.00 m spacing. This includes jointing of pipes & fittings with one step PVC solvent cement and testing of joints complete as per direction of Engineer-in-Charge. Concealed work, including cutting chases and making good the wall etc. 50 mm pipe 10 kgf/cm2

50.18.9.6.2 : Providing and fixing PVC pipes includings jointing of pipes with one step PVC solvent cement, trenching, refilling & testing of joints complete as per direction of Engineer in Charge. 50 mm dia 6 Kgf/cm2

50.18.9.16.2 : Providing and fixing PVC pipes, fittings including fixing the pipe with clamps at 1.00 m spacing. This includes jointing of pipes & fittings with one step PVC solvent cement and testing of joints complete as per direction of Engineer-in-Charge 50 mm dia 6Kgf/cm2 - External work - Exposed on wall

18.48 : Providing and placing on terrace (at all floor levels) polyethylene water storage tank :ISI 12701 marked, with cover and suitable locking arrangement and making necessary holes for inlet, outlet and overflow pipes but without fittings and the base support for tank.

$Electrical Works

1.10.3 : Wiring for light point/ fan point/ exhaust fan point/ call bell point with 1.5 sq.mm FRLS PVC insulated copper conductor single core cable in surface / recessed medium class PVC conduit, with modular switch, modular plate, suitable GI box and earthing the point with 1.5 sq.mm. FRLS PVC insulated copper conductor single core cable etc as required.Group C

1.14.1 : Wiring for circuit/ submain wiring alongwith earth wire with the following sizes of FRLS PVC insulated copper conductor, single core cable in surface / recessed medium class PVC conduit as required2x1.5 sq.mm + 1x1.5 sq.mm earth wire

1.14.2 : Wiring for circuit/ submain wiring alongwith earth wire with the following sizes of FRLS PVC insulated copper conductor, single core cable in surface / recessed medium class PVC conduit as required2X 2.5 sq. mm + 1 X 2.5 sq. mm earth wire

1.14.4 : Wiring for circuit/ submain wiring alongwith earth wire with the following sizes of FRLS PVC insulated copper conductor, single core cable in surface / recessed medium class PVC conduit as required2 X 6 Sq.mm + 1 x 6 sq.mm earth wire

1.21.2 : Supplying and fixing of following sizes of medium class PVC conduit along with accessories in surface/ recess including cutting the wall and making good the same in case of recessed conduit as required.25 mm

1.24.1 : Supplying and fixing following modular switch/ socket on the existing modular plate & switch box including connections but excluding modular plate etc. as required.5/6 amps switch

1.24.3 : Supplying and fixing following modular switch/ socket on the existing modular plate & switch box including connections but excluding modular plate etc. as required.15/16 amp switch

1.24.4 : Supplying and fixing following modular switch/ socket on the existing modular plate & switch box including connections but excluding modular plate etc. as required.3 pin 5/6 amp socket outlet

1.24.5 : Supplying and fixing following modular switch/ socket on the existing modular plate & switch box including connections but excluding modular plate etc. as required.6 pin 15/16 amp socket outlet

1.26 : Supplying and fixing modular blanking plate on the existing modular plate & switch box excluding modular plate as required.

1.27.1 : Supplying and fixing following size/ modules, GI box alongwith modular base & cover plate for modular switches in recess etc as required.1 or 2 Module (75mmX75mm)

1.27.2 : Supplying and fixing following size/ modules, GI box alongwith modular base & cover plate for modular switches in recess etc as required.3 Module (100mmX75mm)

1.27.4 : Supplying and fixing following size/ modules, GI box alongwith modular base & cover plate for modular switches in recess etc as required.6 Module (200mmX75mm)

1.27.6 : Supplying and fixing following size/ modules, GI box alongwith modular base & cover plate for modular switches in recess etc as required.12 Module (200mmX150mm)

1.33 : Supplying and fixing 3 pin, 5 amp ceiling rose on the existing junction box/ wooden block including connection etc as required.

1.50.1 : Installation of exhaust fan in the existing opening, including making good the damage connection testing, commissioning etc. as required.Upto 450 mm sweep

1.51 : Extra for fixing the louvers/ shutters complete with frame for a exhaust fan of all sizes

od65890/2022_2023 : Supply of 1200mm, 20W LED Tube fittings prewired complete with all necessary accessories as required

od67458/2022_2023 : Supply of 380 mm sweep Heavy Duty Exhaust fan in metal frame with self opening suitable for operation on 220/240V,50 Hz, single phase AC supply etc. as required.

od68416/2022_2023 : Supply, installation, testing and commissioning of AC 230/250 volts, 50 HZ Wall fan including providing nuts, bolts, mounting frame and other accessories etc. complete <br>400 mm sweep 1350 rpm (Similar Orient Heavy duty/ Havells Turbo force / Usha Turbo Heavy duty / Crompton)<br>

2.4.1 : Supplying and fixing following way, horizontal type three pole and neutral, sheet steel, MCB distribution board, 415 volts, on surface / recess, complete with tinned copper bus bar, neutral bus bar, earth bar, din bar, interconnections, powder painted including earthing etc. as required. (But without MCB/RCCB/Isolator)4 way (4 + 12), Double door

2.5.1 : Supplying and fixing of following ways surface/ recess mounting, vertical type, 415 volts, TPN MCB distribution board of sheet steel, dust protected, duly powder painted, inclusive of 200 amps tinned copper bus bar, common neutral link, earth bar, din bar for mounting MCB's (but without MCB's and incomer ) as required .(Note : Vertical type MCB TPDB is normally used where 3 phase outlets are required.)4 way (4 + 12), Double door

2.10.1 : Supplying and fixing 5 amps to 32 amps rating, 240/415 volts, "C" curve, miniature circuit breaker suitable for inductive load of following poles in the existing MCB DB complete with connections, testing and commissioning etc. as required.Single pole

od64573/2022_2023 : MCB<br>Supply, installation, testing and commisioning of following rating TP C curve MCB, 10kA as per IS/IEC 60898-12002 in the existing MCB VDB including all connections and iterconnections as required and as instructed by engineer in charge/consultant. <br>63A TP MCB<br>

2.13.1 : Supplying and fixing following rating, four pole, 415 volts, isolator in the existing MCB DB complete with connections, testing and commissioning etc. as required.40 amps

2.13.3 : Supplying and fixing following rating, four pole, 415 volts, isolator in the existing MCB DB complete with connections, testing and commissioning etc. as required.100 amps

2.15.2 : Supplying and fixing following rating, four pole, (three phase and neutral), 415 volts, residual current circuit breaker (RCCB), having a sensitivity current 30 mA in the existing MCB DB complete with connections, testing and commissioning etc. as required.40 amps

5.6 : Earthing with copper earth plate 600 mm X 600 mm X 3 mm thick including accessories, and providing masonry enclosure with cover plate having locking arrangement and watering pipe of 2.7 metre long etc. with charcoal/ coke and salt as required.

5.8 : Supplying and laying 25 mm X 5 mm copper strip at 0.50 metre below ground as strip earth electrode, including connection/ terminating with nut, bolt, spring, washer etc. as required. (Jointing shall be done by overlapping and with 2 sets of brass nut bolt & spring washer spaced at 50mm)

5.19 : Providing and fixing 4.00 mm dia copper wire on surface or in recess for loop earthing along with existing surface/ recessed conduit/ submain wiring/ cable as required.

od71021/2022_2023 : Supply of ISI marked aluminium conductor FR XLPE insulated cable as per IS 7098, & cable, armoured, served, sheathed 1100 volts grade.<br>4Cx16 sqmm<br>

od71022/2022_2023 : Supply of ISI marked aluminium conductor FR XLPE insulated cable as per IS 7098, & cable, armoured, served, sheathed 1100 volts grade.<br>4Cx10 sqmm<br>

od71023/2022_2023 : Supply of ISI marked aluminium conductor FR XLPE insulated cable as per IS 7098, & cable, armoured, served, sheathed 1100 volts grade.<br>4Cx6 sqmm<br>

od65390/2022_2023 : Supply of 1.1kV grade aluminium conductor XLPE insulated PVC sheathed armoured power cable of the following size etc. as required3.5Core 70 sq.mm

od67370/2022_2023 : Supply of ISI marked aluminium conductor FR XLPE insulated cable as per IS 7098, & cable, armoured, served, sheathed 1100 volts grade.<br>50 sqmm 3 1/2 core<br>

7.7.1 : Laying and fixing of one number PVC insulated and PVC sheathed / XLPE power cable of 1.1 KV grade of following size on wall surface as required.Upto 35 sq. mm (clamped with 1mm thick saddle)

7.7.2 : Laying and fixing of one number PVC insulated and PVC sheathed / XLPE power cable of 1.1 KV grade of following size on wall surface as required.Above 35 sq. mm and upto 95 sq. mm (clamped with 25x3mm MS flat clamp)

9.1.22 : Supplying and making end termination with brass compression gland and aluminium lugs for following size of PVC insulated and PVC sheathed / XLPE aluminium conductor cable of 1.1 KV grade as required.3 1/2 X 50 sq. mm (35mm)

9.1.23 : Supplying and making end termination with brass compression gland and aluminium lugs for following size of PVC insulated and PVC sheathed / XLPE aluminium conductor cable of 1.1 KV grade as required.3 1/2X 70 sq. mm (38mm)

od68263/2022_2023 : Supply and laying/fixing of earthing conductor of copper strips/wires including necessary earthing trenches, jointing as per IS 3043/87 in trenches, walls, pulling through pipes etc<br>Copper Wire No. 10 SWG

od68380/2022_2023 : Supplying and fixing 4 way metal enclosure on surface / recess along complete with earth bar and din bar detached gland plate, interconnection, phosphetized and powder painted including earthing etc. as required. (But without MCB/ RCCB/ Isolator)

Power Laundry Machines

od63824/2022_2023 : SITC of Vacuum Ironing Table 30"x 48" Top size heavy duty vacuum motor imported padding and top cover with imported steam iron and Jumbo Boiler (Warranty should not be less than 3 years)Make -IFB

od63826/2022_2023 : Industrial washer cum extractor 60 Kgs capacity):S1TC of Industrial washer cum extractor, front loading and unloading, open pocket, soft mount , heavy duty high spin. High speed spinning capability for quick drying of linen, extraction cycle G- force should be more than 340. Machine should be PLC based controlled. It should have at least 22 standard wash programs with minimum 8 variable steps in each program to customized according to the type of the fabric to be processed. It should have a pause & continue feature in case of power loss. LCD displays to visualize the step-by-step advancement of the cycle and user-friendly parameter setting provision for various washing methods. Machine should be single motor with variable frequency inverter drive (VFD) for various speed for wash, distribution and extraction at low, normal and high spin. The machine should be electric heated with the electric controlled water inlet & drain outlet. The parts of machine those are in contact with water and chemical (inner drum and outer drum) shall be of stainless steel 304 grade. Auto electric door lock should be provided for operational safety. This makes the door not to open at the time of operation. Machine should be provided with warning sign alarm for completion of cycle. (Warranty should not be less than 3 years)<br>Technical Specification: <br>Capacity - 55 - 60 Kgs<br>lnner Drum Material (Basket) - SS 304, Minimum 2.0 mm thickness<br>Outer Drum material - SS 304, minimum 3.0 mm thickness<br>Chemical compartment - SS 316, minimum 1.2 mm thickness<br>lnner drum (basket) volume - Minimum 600 Ltrs<br>Basket Diameter - Approx. 1110 mm<br>Basket Depth - Approx. 650 mm<br>Drive Motor - At least 15 HP AC motor HEM I equivalent make<br>Electric Heater - At least 24 kw<br>Extraction Speed - Minimum 780 rpm<br>G - Force - Minimum 340<br>Drain outlet size - Minimum 75mm dia<br>Water Inlet size - Minimum 40 mm dia x 2 nos. & Minimum 25 mm dia water inlet for chemical<br>Bearing housing - GG25 cast iron of SKF Heavy duty makeMake- IFB

od63827/2022_2023 : od191438/2021_2022 Industrial Tumble Drier (60 Kg capacity) :SITC of Industrial tumbler dryer, front loading & unloading, open pocket, forward & reverse cylinder movement with PLC controlled. It should have at least 5 program storage capacity with automatic cool down features. Inner basket to be of stainless steel and outer body powder coated. Safety features should include manual heavy duty latch lock with door limit switch, which stops machine drum rotation when the door is opened at the time of operation. Machine should have two motors, drive motor & blower motor. The machine should be electric heated with high efficiency radiator of at least 27 kw capacity, using the radiator air entered gets heated quickly. Should be provided with a self-collecting lint mesh prior to hot air exit. (Warranty should not be less than 3 years)<br>Technical Specification:<br>Capacity - 55 - 60 Kg<br>lnner Drum- SS minimum 1.2 mm thickness<br>Lint Screen - SS grade filter mesh<br>Outer body - Powder coated<br>Cool down feature - Automatic with cool down feature<br>lnner drum volume - Minimum 1200 ltrs<br>Basket Diameter - Minimum 121 Omm<br>Basket Depth - Minimum 1045mm<br>Drive motor - At least 2HP AC motor HEM I equivalent make<br>Blower Motor - At least 2Hp AC motor HEM I equivalent make<br>Electric Heater - At least 27kw<br>Power supply - 3-Phase. 415V 50Hz<br>Hot air exhaust sizeMinimum 200x200mm<br>Supply, installation, testing, commissioning and labourMake-IFB

Classic Builders

JBR INDUSTRIES

Bidder Name

JBR INDUSTRIES

Rohas Ventures Pvt Ltd

Classic Builders