The slab is a super structure element in building and the main function of it are to tranfer all the dead load and live load to the beam.Normally 1st floor beam and slab are cast together.The works involved are
- setting out
- using a modern technology of surveying,setting are more easy with this method.all the beam position are follow the column align ment and a new transfer beam alignment also to be set.the engineer layout must read together with architech drawing.
- formwork and scafholding
- the first item to be fixed is a sleeper or soffit beneth the beam between the two column.the wooden sleeper follow the width of the beam and nail to the wooden T strut spacing 600 each other or use a set of metal scaffholding.the inner side of beam formwork must be depth of beam deduct thickness of slab.the outther formwork of the beam size are full height of beam.for slab formwork,scaffholding will erect first then main string spacing 1.2 m from timber and the secondary string spacing 600mm will be fixed on the top of main string.the plywood then fixed on the top.the connection between plywood must cover by tape of piece of small metal stripe.then all the beam are lock and tight up.
- re bar
- rebar for beam will fixed first the the slab bar.the rebar for beam will prefab at the top and then bring down to the ready formwork.all the main bar,top bar,lapping and link must follow the engineer drawing.then the rebar for slab normally BRC will then fixed.the bottom BRC will fixed first the the top bar or BRC will be fixed.the top BRC at the edge must be bend .the S shape of rebar nust be install at the slab drop.dont forget the chairs or xconcrete cover between formwork and BRC and BRC and BRC.
- concrete
- after slab and beam are inpected and approved by the engineer then the slab can be concrete.if the thickness of slab more than 200mm,must be 2 layer of concrete.if below 200mm one layer of concrete.the vibration must be carry out at all time of concreting.after concrete set,the water will jet to the surface of slab for curing at least for one week.
- formwork dismantling
- after 3 or 7 day of cast date,the formwork will dismantle with special tool and equipment especially at the edge of slab.after no formwork,the strut will the be fixed to the beneth of the slab until 14 day.
- curing
- for curing for beneth and side of beam and slab,water jetting used for curing at least one week.
This process will repeat for other storey for highrise building.
2.Column casting
Column is the superstructure element in building.The function of column is to tranfer all the dead load and live load from wall 1st floor slab.There are 2 type of column short column and slender column .Many shape of column such as rectangular,circle ,L shape to the odd like oval and etcs.
How to cast and erect it,?Works involve to make a column is
1.setting out
- Normally they are using a tradisional method,using tape and string and marktaw to the slab.the alignment always to be check whether the grid is out in centre or in
2.rebar
- Rebar installation is very easy.the prefabricated rebar is lifted and fixed to the position.the bottom lapping always to be check.the 25mm concrete cover must be fixed around link and through the height of column.the re bar of column consist of 4 or more main bar and a number of link from bottom to top.
3.formwork
- Formwork erection using plumbob as tradisional method to get the straight verticality or theodalite as modern equipment.then the formwork will strut in 4 or 2 direction to firm or lock it into position.last time the hole at 4 ft interval in height will do for concreting purpose to avoid seggration and then to avoid honey com at the bottom of the column especially for small size of column.
4.concrete
- actually the best way for laying a concrete is using a chute to avoid seggration but not practise for small project.they just pour from the top using bucket and vibrate or hit the formwork to compact it.the site of vibrator also must be small for small size of column.
5.formwork dismantle
- after one day cast,the formwork can dismantle using a right tool and equipment.always check the hney com,if worse,the colum must demolish to make anew one and if less just cover with cement grout.
This process are repeat for 1st floor until the desire storey of the building.
3.Beam Casting
The main fuction of concrete beam inthe building are to carry a live load and dead load from wall,windows,doors and etc and tranfer the load to the column or stump below.How to cat this beam?
In the building there are 3 type of main beam inclufing ground beam,1st to a seriel number of intermediate beam and roof beam.Starting from a ground beam.
Works involve to produce ground beam
1,excavation
- same as stump,using an eccavatot to eccavate the position of ground beam.more easy compare to footing coz the alignment are based on footing centre but always chevk with the drawing.the eccavation width must be wider 2 ft from the size of ground beam.the surface of must be compacted.
2.formwork
- same as footing the formwork must be install at 2 side of beam.vertical and diagonal strit between 450mm must be fixed.the right angle between 2 beam are check and measure.the alignment and level must be always checked.the height of formwork are depend on the type of ground floor slab.if the ground floor slab is suspended the the height of beam must be reduce by the thickness of slab,if tje slab are non suspended then the formwork are full height.to indentify between suspended have a NAZI mark and non suspended are empty at the ground beam layout.
3.rebar
- after lay a lean concrete and set the rebar will be fixed.the main and top bat will tight together with the link at the top of formwork.a concrete cover are placed around the 3 side of link.the top bar at column,lapping are being measured and followed drawing.then ready for engineer inspection.
4.concrete
- if the formwork and re bar passed then ordering the voncrete.the ground beam are also call sub structure and the grade of concrete must be correct.the vibration taken plave after laying the concrete,slump test must be carry out at site.no allowance for add a water at site.consult the engineer first before add a water.if heavy rain,stop all the concreting work.
5.backfill
- after 1 day cast the form work can dismantling with using a right tool and equipment with ver carefully.the water jetting to fresh ground beam as curing ptocess.
- cont for 1st floor beam next
4.Footing casting
Footing or pile cap is a buried structure and socalled substructure element in the buiding construction.The main purpose of these structure is to distribute evenly all the force from the column to the subgrade or to the group of pile to the stronger soil layer.
The contruction of footing or pile cap including:
- setting out
- setting out are the most importanr work.the position of footing are rely on survey based on the architect and engineer drawing.the suveying using whether teodolite or TDM to locate the centre point of footing.a temporary marker inserting to the soil a line to mark a size of footing also did at the same time.
- excavation
- after confirmation the centre point of al the footing,the excavator are using to excavate the footing to the required level and size.the minimum height are 1.5 m from the top of ground beam and the saiz of exczvztion must be extra 2 ft for each side.if the soil condition at the required depth soft ,extra depth will be excavate depending the decision by resident engineer.the excavated sopl must be 1 m from the edge of the hole.check all the utility line,bomb,antique item during the construction.the surface of subgrade must be flat and compacted.
- lean concrete
- a grade of 15 non structure concrete are laid.a 50 mm thick of lean concrete were lain for entire area of excavated.
- formwork
- a four side of formwork will fixing after lean concrete are harden.the formwork is made from timber and plywood,vertical and horizontaal strut or support are made from 2"x 1"timber are fixxing around 4 side and located 500mm centre to centre.the poition of formwork must be centre follow the string above and nail in one line position.
- rebar
- the re bar wil fix after the formwork were lock firmly into position.the top rebar and the second rebar followed.normally rebar for footing are getting prepare by prefabricate at the yard and fixing are more faster.the concrete cover will locate at base and at the four side touching tothe formwork surface.the one layer of tie will fix to tie all the vertical U shape rebar.the rebar for stump also fix after that and suppot with timber or straight rebar to hold the stump in centre position.the rebar size and link must follow the structural drawing and rebar must be BS standard.
- concrete
- after all the rebar check and verify by the engineer,the concrete can be poured.the conrete must be correct grade and must be ready mix quality and no site are allowed.the concrete pump or the crane are using to convey the fresh concrete fro the lorry to the footing.the vibration using suitable vibrator are inserting to the concrete until the shape of O ring appeared at the top surface of the concrete then stop.if heavy rain,the concreting process will stop.
- backfilling
- the formwork for the footing can dismantle after 1 day concreting work.the footing will then backfill with good soil and compact with water for rapid compaction process and can continue with ground beam.
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