MFE FORMWORK TECHNOLOGY SDN. BHD.
SURVEY PROCEDURES. Setting Out, Alignment & Verticality. Dec 2008
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1.0
Setting Out, Alignment and Verticality
1.1
Introduction
1.2
Base or Primary Setting Out 1.2.1 1.2.2 1.2.3 1.2.4
1.3
Base Control Points Transferred Setting Out Point Bench Mark Temporary Bench Mark (TBM)
Day to Day Detail Survey 1.3.1 1.3.2 1.3.3 1.3.4 1.3.5 1.3.6 1.3.7 1.3.8
300mm Offset Line Concrete Level Survey Kicker Level Survey Deviation Survey Analysis of Survey Results Method of Adjustment Deviation Survey Not Making Sense Plumb and Alignment of Walls
1.4
Keeping of Survey Records
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Miscellaneous: -
Simplified Plan of Marking Out Principles Control and Adjustment of Vertical Alignment by Packing Everyday Survey Check Bench Marks Plumbing Buildings and Tall Structures
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1.0
Setting Out, Alignment and Verticality
1.1
Introduction In order to achieve the dimensional and vertical accuracy that is possible with the MFE System Formwork it is absolutely necessary that the survey control for the building is maintained both accurately and systematically. In the first instance the base survey for the building, meaning the primary setting out lines and reduced level bench marks must be established accurately. These survey control points must also be transferred accurately up the building as work progresses. In the second instance the day to day detail survey, meaning marking out of wall alignment and column positions, kicker level survey, concrete level survey and deviation report must also be carried out accurately. Some of the work is usually carried out by the main contractor or by his setting out sub contractor. However, because of the major impact that surveying and particularly survey accuracy has on the formwork positioning and thereby the as cast concrete position you must fully understand survey control and how it affects the formwork.
1.2
Base or Primary Setting Out The base or primary setting out means the reference lines and levels from which all survey work should originate from and which all survey work should close back to. The base survey in terms of our building work means the transferred setting out points and the temporary bench marks (TBM’s). The Transferred Setting Points and TBM’s should themselves originate from Base Control Points for the building. The definition of these terms is listed below and a simplified plan of setting out principles is attached at the back of this section.
1.2.1.
Base Control Points These are established and maintained on the transfer plate level for the duration of the structural frame construction. They are to be carried vertically up through each and every floor slab using a plumb bob or preferably an optical or laser plumb. Refer to the attached typical layout plan and textbook extracts showing suggested methods of setting out and transferring these base control points.
1.2.2.
Transferred Setting Point These are the Base Control Points that have been transferred up to the current working level.
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1.2.3.
Bench Mark This is the reduced level from which all other level measurements on the site are referenced. It is usually established by Government or registered surveyors.
1.2.4.
Temporary Bench Mark (TBM) The TBM is the reduced level mark for the current working level. They should be established on every working floor using steel pins or nails secured into the concrete floor slab. They are transferred each time from the previous TBM. They are the reference level for the given floor, they are used as the bench mark against which the kicker level and concrete level surveys are carried out. Please refer to attached textbook extract for examples of typical TBM’s.
1.3
Day to Day Detail Survey The day to day detail survey means the setting out measuring and leveling carried out on every floor cycle to ensure that the formwork has been set accurately to line, level and verticality. You are reminded that if the MFE Formwork is to achieve the accuracy that it is capable of the Day to Day Detail survey control must be carried out accurately for every concrete pour. The definitions and explanations of typical terms used on a project are given below. Please also refer to the simplified plan of setting out principals attached at the back of this section.
1.3.1
300mm Offset Line This is the setting out line that is “snapped” onto the concrete surface. It is offset normally 300mm from the internal face of the external wall. It is to set and check the formwork alignment and to carry out the deviation survey.
1.3.2
Concrete Level Survey. By this we mean the reduced level of the concrete surface along the entire plan length of the yet to be erected inside face wall formwork again the most critical points being the corners. The level survey is taken from the TBM for the current floor and is carried out immediately after concreting the floor so that analysis of the levels and corrective action, if necessary, can be carried out prior to the next erection of formwork.
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1.3.3
Kicker Level Survey This means the reduced level of the “kicker” along the entire plan length of the yet to be erected outside face of the external walls. The level survey is taken from the TBM for the current floor and is carried out immediately after concreting the floor so that analysis of levels and adjustment of kickers, if necessary, can be carried out prior to the next erection of formwork. Again the most critical points are the corners.
1.3.4
Deviation Survey. This is a measure of the horizontal deviation of the as built plan position of each wall relative to the design position. The survey is also carried out after concreting and immediately after the new plan alignments for the walls have been marked out on the current slab. The most critical points are again at the corners.
1.3.5
Analysis of Survey Results The results of the deviation survey, kicker level and concrete level survey have to be analyzed for each and every floor. Corrective action (concrete chipping) chipping) and or adjustment (by (by packing or sometimes lowering in the case of the kickers) has to be carried out before commencing erecting of the formwork for the current floor.
1.3.6
Method of Adjustment The principal control and adjustment for vertical alignment of the building using MFE formwork is through the kicker and concrete levels. Further adjustment if necessary can be made with props props but this should be kept to a minimum as it can distort the formwork. The principal measure of achieved vertical alignment is the deviation survey. The assumption made is that when fully pinned and wedged the formwork forms a relatively rigid frame. It follows that packing (using plywood shims) or lowering lowering (by chipping concrete or by using using the slotted holes in the kicker) one side of the frame will push in or pull out the plan position of the top edge of the frame, please refer to attached sketch “Control and Adjustment of Vertical Alignment by Packing”. The deviation survey must therefore be analyzed first, any locations that show the wall leaning out, will require the packing of the kicker in the same plan location to bring in the wall on the next cast. As a general rule the maximum of 6mm 6mm to be adjusted over one floor. If the deviation reports, shows a deviation from plumb in two directions then this should be improved over two floors, one for each direction. The kicker level and and concrete level surveys surveys are reviewed together with the deviation deviation report. A comparison of the information from both sources allows cross checking of the results. At the same time the level surveys will tell you if the floor to floor heights are being maintained or are they creeping up, which which sometimes happens with grout build build up between Wall and T panels i.e. 2 3mm per floor over 10no floors can develop a creep of + 25mm.
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Concrete up to (+ 6mm high) is acceptable, above 6mm must be chipped to the correct level. Any low points should be packed to the correct level. Note: in certain cases it is good practice practice to mark ( + ) plus or ( - ) minus as the survey is being being carried out. This eliminates unnecessary circulation of paper paper and the supervisor can identify at a glance the adjustment work that is necessary. Any high points on the kicker level survey will need to be adjusted downward by means of the 26mm slotted hole in the kicker that allows for this kind of adjustment.
1.3.7
Deviation Survey Not Making Sense? If for some reason the deviation survey results do not make sense it is easy to check and confirm the results over a number of floors by hanging a plumb bob down the 2 or 3 floors and checking the deviation of the concrete face between floors. This method of check can confirm if the survey results are correct or incorrect.
1.3.8
Plumb and Alignment of Walls Once wall formwork has been fixed in position every wall must be checked for verticality (deviation correction allowed for) using a plumb bob for trueness of alignment using a string line. See “Everyday Survey Check” sketch attached at back of this section. Optional for this scope of work is the use of a Laser Instrument which is, highly recommended allowing you to check alignment or verticality of the Formwork at any location with one setting of the Instrument. More efficiency and better accuracy is the advantage by using such an instrument.
1.4
Keeping of Survey Records The survey record for the kicker level, concrete level and deviation report must be kept in the job file for every single pour. This is a must and the responsible responsible engineer must ensure the record is kept and maintained.
1.4.1
First Time Setup It is very beneficial to spend additional time with the setup of the first pour. Even if it takes an extra day to get the level and alignment correct this will pay big dividends later on in the project by way of better quality, easier cycle and less remedial works.
Tip:
It is always always easier easier to pack than to chip concrete or lower the kickers so set the first time concrete pour at - 10mm to give yourselves more adjustment to play with.
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1.5
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Miscellaneous
Simplified Plan of Marking Out Principles Control and Adjustment of Vertical Alignment by Packing Everyday Survey Check Bench Marks Plumbing Buildings and Tall Structures
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Bench Marks Each side should have a primary bench mark which may be : A convenient nearby Ordnance Ordnance Bench Mark Referenced to an Ordnance Bench Mark Referenced to a given level on existing works The supervising authority authority should specify which is to apply. If an Ordnance Bench Mark is to be used but which one has not been specified, obtain the current local list of Ordnance Bench Marks (see Appendix C) and agree which to use with the supervising authority. • • •
In addition to the primary bench mark, it will be necessary to set up secondary bench marks unless all leveling can conveniently be referred to the primary bench mark. mark. Secondary bench bench marks are commonly called temporary bench marks (TBMs). To ensure accurate primary and temporary bench marks : Establish primary bench mark * from the agreed Ordnance Bench Mark or from existing works and agree level in writing with the supervising authority. Plan positions of TBMs in good time, taking account of temporary and permanent works (all points of the works should, where possible be within 40 m of a TBM) Verify the levels of previously established TBMs by leveling from the primary bench mark. Establish TBMs not more than than 80 m apart. Closing error to primary bench mark must not exceed 5 mm. Use existing permanent features for es tablishing bench marks whenever possible (see illustrations) Where no permanent feature is available for a bench mark, establish it in firm ground and mark as shown in the illustration. Protect bench marks from site traffic as necessary If assumed datum has been used for schema, as shown on contract drawings, check with the supervising authority that this datum may be used. Record position, reference number, level and date last checked of each TBM and the primary bench mark on the site plan. Display copy of site plan or list of bench marks with details in site offices Check levels of TBMs at regular intervals* Report any apparent disturbance of TBMs Update displayed plan list of TBMs Transfer levels from TBMs to permanent works as soon as practicable Remove redundant TBMs •
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*BRE leveling station can conveniently be used. See Cheney.J.E. in Bibliography *Warning: Earthworks and ground settlement, settlement, heave, heave, expansion or contraction can affect TBMs
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Plumbing Plumbing of modest accuracy can be achieved with a good quality 1-m spirit level, but other methods must be used as the height and or need for precision increases.
Use of plum bob In the example shown, a freshly concreted wall is checked for verticality. The plumb bob is suspended from a piece of timber nailed to the top of the formwork and shielded from the wind or immersed in a pail of oil or water. Offsets from the back of the form are measured at top and bottom with due allowance for any steps or tapers in the wall. Any necessary adjustments are made with a push-pull prop.
Use of theodolite The formwork for a tall column form is being plumbed in the example. A theodolite is set up on a plane parallel but offset to one face and sighted on suitable offset marks at the top. (Observe both edges to check on twist.) Similar observations are made on the bottom of the form. Any discrepancy in verticality (mean of observations on left and right face) is read at the bottom for convenience and the column form adjusted. The whole process is then repeated for the adjacent face. Sighting at a steep angle above the horizontal is facilitated by using a diagonal eyepiece. Note :
The theodolite must be some distance from the column for accuracy this may be impossible on a cramped site.
Use of optical plumbing instrument The operation is relatively simple as follows:Set up and level instrument over ground station Sight down and center over ground station Sight up (through second telescope or by operating prism mechanism) onto target and mark a defined point Turn instrument through 90 0 ,1800 and 270 0 in horizontal plane to define three further points Intersection of diagonals joining four points lies on vertical line through ground point • • •
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Optical plumbing is particularly useful for ensuring the accuracy of lift shafts, slip formed structures and climbing forms. The example shows the use of an optical plumbing instrument in a lift shaft using perspex targets fixed at the top levels. At least three ground stations should be used to check for possible twisting.
Use of lasers Lasers can be used to define a vertical line or plane.
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Buildings: tall structures
Plumbing The primary instruments for plumbing are: Plumb bob Theologize Optical plumbing instrument The principles of use are described under Plumbing. • • •
Verticality and twist Tall structures must be checked for verticality and twist. This is best achieved by plumbing up or down from four points.
Rectangular structures The use of an optical plumbing instrument to control the verticality of a multistorey building is illustrated. Within multi-storey buildings, the plumbing of list shafts is particularly critical operation because the installation tolerances are small. Four setting-out points should be established at the base of the lift shaft such that the vertical lines through them will not be obstructed by formwork or scaffolding. Plumbing can be from top to base using plumb bobs or from base to top using an optical plumbing instrument. The latter is preferable if a plumb bob would be disturbed by winds. See illustration under Plumbing.
Tapered structures To plumb a tapered column or s imilar structure: Set out orthogonal center-lines on the base Plumb from top corners (plumb bob or theodolite) Check equality of offsets on all four sides If the structure narrows toward the top, it will be necessary to cantilever out from the top of the formwork to fix plumb bobs. • • •
Height and level Floor-to-floor dimensions are controlled by a weighted steel tape measuring each time from a datum at the base of the structure. Each floor is then provided with datum marks in key positions from which to transfer levels on each floor. The base datum level should be set in a location which allows unrestricted taping to roof level. If a tower crane is used,`` a tape can conveniently be fixed to the mast (see il lustration) Warning: Errors, apparent or real, can result from differences in thermal movement of the tape relative to that of the building particularly if construction spans a number of seasons.
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