20150404-Scabbling and Levelling shims

Preparing the Foundation for Steel Erection Data Date 07/04/2015

File and path of 25 Allan S Phillips QAQC Coordinator

Scabbling piers, setting Levelling shims, preparing the Foundation for Steel Erection

Between the concrete foundation and the steel baseplate there is a minefield of technology that this

paper attempts to explain. HD Bolt types and treatment, scabbling why when and where, levelling

shims why when and where, grout types why when and where plus grout testing. Read this paper

before you prepare for steel erection, it will help you to forward plan the work plus assist you to

comply with the Engineers requirements.

Index

Item Description Page

1 Typical Pier - after scabbling in preparation for steel erection

2 What’s involved in preparing a pier for steel erection?

3 Engineers Instructions

4 HD Bolt Treatment

5 Levelling shims

6 Where to find the correct RL (relative level) to Underside of Baseplate

7 Correct setup and use of the Dumpy Level

8 Grout Types

9 So What have we learned so far

10 Inspection - what to look for

11 Formwork for grouting

12 Preparation and pouring of the grout

13 Curing and forming the grout profile

14 Inspection – what to look for – what documentation is required for sign off

15 What takes the column load, the levelling shims or the grout

16 An alternative to Cast in HD Bolts

17 Preparation for installation of heavy rotating equipment

18 Test the grout properties before you need to use them

19 Further reading



Photo shows a typical Pier being made ready to accept the column. Top of Pier has been scabbled to take the grout; four levelling pads are glued on, the HD Bolts Have been cleaned, with a nut run down to check thread fit and clearances (lubricant used on the bolt) note that the bolts are galvanised. The 4 washer plates sit on top of the baseplate that comes with oversize holes for ease of erection. The remaining work involves taking levels and installing the levelling shims on the glued levelling pads so as to provide four surfaces at the correct RL (Relative Level) to the underside of the baseplate.

2 What’s involved in preparing a pier for steel erection?

Let’s start by dealing with the all too familiar instruction; prepare the foundations were erecting the

steel tomorrow. So what do we need to do and look out for in order to comply with the Engineers

requirements, the codes and specs etc.?

The photo above shows the finished product, the following illustrated sections commencing with the Engineers Instructions will show you how to prepare the foundation, the tools and equipment needed, and when to call for the inspection of your work and what the Inspector will be looking for. 3 Engineers Instructions The structural concrete foundations are covered by AS 3600 whereas the erection of the structural steel is covered by AS4100 and we are dealing with the gap in between. So let’s start by looking at both specs to see if they contain any guiding advice.

AS 4100 Section 15 Grouting at Supports Grouting or packing shall not be carried out until a sufficient portion of the structure has been aligned, levelled and plumbed and adequately braced by other structural members that have been levelled and are securely held by their permanent fastenings. Steel packing or levelling nuts on the anchor bolts shall be under the base plate to support the steelwork. The space under the steel shall be thoroughly cleaned and be free from moisture immediately before grouting.



Grout shall completely fill the space to be grouted and shall either be placed under pressure or placed by ramming against fixed supports. AS3600 details grout requirements for the pre cast industry but does specify that:- The Grout materials shall comply with AS3600

4 HD Bolt Treatments

Take care and do not recut the threads. Do not take a die and recut the thread at any cost. If the threads are damaged and the nut does not run down the bolt thread, talk to the structural superintendent who will advise you not to touch the bolt thread, leave it for the fitters.

The column reaction can be upwards and sideways. That’s correct, the structure is subject

to wind forces that can see the structure try to lift off the HD Bolts, and at the same time move

sideways. If the nut is loose on the bolt thread there is little or no resistance to the upward force,

that’s why you should not, recut the bolt threads.

As to wind forces lifting columns, take a four legged chair push sideways and notice that two closest

legs lift up, so the two far legs now take the entire load. It works the same way with structures,

especially so when you leave a large sliding door open, up she comes unless the nut stays on the HD

Bolt.



Polystyrene pockets. Used to provide a small amount of side springing of the bolt when the

baseplate is dropped over, the grout pocket needs to be clean so the polystyrene needs to be

removed, any acetone will do the job quickly, but you may not be allowed to use it. So be prepared

to cut it all out using a knife.

Plumbers tape used to protect the galvanised surface and keep the surfaces clean during concreting; all the tape is to be removed prior to grouting. There’s no reason why you cannot use some yourself to protect the bolts when scabbling and trial fitting the sole plates, but all the tape must come off just before the final inspection.



The air driven scabbling tool shown here with a red handle consists of a series of vibrating pins that

impact and roughen the concrete surface to provide clean exposed aggregate free of laitance and

possible bleed water.



For projects where a large area must be prepared high pressure water blast unit (green cut) can be

used. Best done immediately after removal of formwork.

Summary for Scabbling

Remove all laitance to relieve any bleed water

Prepare a sound rough surface for adhesion of the grout

Yes we do need to scabble all the surfaces in the shear key pockets

How rough – expose the aggregate

Inspection- have the work inspected before erecting the steel



5 Levelling shims

Four levelling shim pads glued to the scabbled area, note the survey Bench Mark in the upper LH

Corner of the photo.

6 Where to find the correct RL (relative level) to Underside of Baseplate

Usually found on the Structural General Arrangement Drawing look for RL U’s ide Baseplate RL

XXXXX

For mechanical Equipment Look for the RL of the underside of base frame as well as the RL of the

Inlet and outlet if the unit is a pump say, or the RL of the Main Drive shaft if a turbine for example

Next look for a survey drawing that has Bench Marks – quite often this is a drawing kept by the

Engineering Surveyors, or the Area Project Engineer. In any case make sure that you have the RL

reference point checked by an Engineering Surveyor before starting your levelling work.

If there is a BM close by with numbers – have the information checked before proceeding- don’t just

assume that the numbers are automatically the RL they can easily be the BM identity number.

Always check first with the Eng Surveyor and the Project Engineer- 10 minutes here can save you

hours of explanation later on.



7 Correct setup and use of the Dumpy Level

The dumpy level is a survey instrument used for transferring levels from one point to another.

Always check that the dumpy has a current calibration certificate if it has proceed to check that it is

working properly by applying the ¼ distance method. Now why would we do this when we can see

the calibration certificate is still valid? The reason is this; dumpy levels are used by everybody and

that’s a good thing, unfortunately they do get knocked around a fair bit, then put back in the case

and back in to the stores. So always check the instrument before you use it.

Please refer to the Application of a Dumpy Level paper for more details on checking the instrument.

On setting up for your job you need to site the dumpy where you can see the BM and the job (base

where you will attach the packers or set the levelling nuts) secondly make sure that the dumpy

tripod is not in everyone’s way. You would not like to have the setup disturbed with a vibrating roller

one meter away, or knocked by people walking by, so position the tripod in an out of the way place

say no more that 15-20 meters from the Job.

Be sure to tramp down the three legs by standing on the lugs provided.

Now establish the Dumpy level RL relative to the BM (Bench Mark) and write down the BM details as

your backsight and the level of the Instrument. Make a sketch just so you do not confuse yourself

with numbers.



Now shoot the scabbled area that should read a RL equal to the design grout thickness below the

Design Baseplate RL E.G, if the baseplate is to end up at RL 4765 and the design grout thickness has



been called up as 50mm you should be reading RL 4715 few mm either way say between RL 4710 to

4720 is just fine. (Refer to the correct use of a dumpy level for more detail if you need to)



Now glue the first of the levelling pads to the scabbled area at the locations agreed to with the

Project Engineer. Some structures have two pads, others 4,6,8 and so on.

So using a 20mm pad make sure that the pad is flat and level. You do not need to have all pads at

the same level, but they must be flat, use an engineer’s level if you have one, a standard spirit level



is second best. Once the pads are glued down, and cured say overnight, set up the dumpy again and

shoot the tops of the pads and record the individual levels on a sketch. Now make up the difference

Between the top of Pads and the design RL u’side Baseplate and tape them as individual packs.

Set them on the pads and tape them off so that they will not move for a day or two. Now check the

RL of the Top of Pad that should read equal to the u’side of Baseplate RL - make any necessary

adjustments. Now have an Engineering Surveyor check your work, he will make the As Constructed

record and pass same to the Project Engineer.

8 Grout Types

Of the two types of grout commonly used in construction, the Cementitous grout is the one we will

deal with the most, as it is a load bearing grout, taking static loads, whereas Epoxy grout is

specifically used under rotating equipment where shock loads need to be resisted.

As the name cementitous suggests there is a component of cement, sand and bonding agents that

when mixed look like a flowable smooth cement paste. There are several brand name products that

produce similar products; you should refer to the specification to be sure you are using the

nominated brand for your particular job. Be careful not to just take a bag or two from the stores as

you could easily end up with a product meant for another job. If not done already (with the test

results in the work pack) you will need to prepare and pour a sample for testing. More about this in

Section 18

Masterflow Combextra Sika

Are all manufacturers whose products are commonly used in the Industry-this paper recognises many other similar products and does not make any recommendation or preference towards any particular product.

9 So What have we learned so far The very first lesson to take with you is to be sure that all the checks are complete and signed off before proceeding with the actual grouting. Take another look at the Australian Code to see what it requires. I have copied the extract here so that you can follow the logic easier

AS 4100 Section 15 Grouting at Supports Grouting or packing shall not be carried out until a sufficient portion of the structure has been aligned, levelled and plumbed and adequately braced by other structural members that have been levelled and are securely held by their permanent fastenings. Steel packing or levelling nuts on the anchor bolts shall be under the base plate to support the steelwork. The space under the steel shall be thoroughly cleaned and be free from moisture immediately before grouting. Make sure that the grouting check sheet carries a signature that clears you to proceed with the grouting. Keep in mind that when you are instructed to proceed with the grouting, you are required to check the paper wok first. Don’t just go ahead expecting someone else to have looked at the check sheets. Check it yourself. So why is it so important to carry out all these checks, before grouting. Let me explain.



The grouting of the baseplate indicates a milestone in the erection of the structure, as no further work will be done other than to pre tension the bolts where required. As structural technicians, and that’s what we are, the completion of the grouting is a handover point, hence the importance of the completed check sheets, and the grout work itself of course. 10 Inspection

Check the documentation (ITP and Check Sheets) has been signed off for

a) Structural Alignment – is the structure aligned within the tolerances set down in the code?

b) Is the structure adequately braced ( i.e, will it move after grouting )

c) Are the packers under the baseplate.

d) Can the grout be poured from one side / or if there is a shear key- will the pour take place

from two or four sides.

e) Have all the bolts been snug tightened only

f) Has the concrete scabbled area been wetted overnight ( 24 hours)

g) Has all the water been removed ,( vacuumed out)



11 Formwork for grouting

Usually made up of 10mm ply stripped to a depth equal to the distance from the u’side of the baseplate to the scabbled surface plus at least 10mm. At one end, the end we are going to pour from, the formwork should be higher to allow for a head when we pour, and to provide a no spill Lip. Unless directed otherwise the size of the formwork (width and length) should be the size of the baseplate plus twice the depth of the grout. The reasoning behind this is that the grout when firm will be stuck level with the underside of the baseplate then at 45 deg back down to the scabbled surface. The formwork should be lightly braced to keep the box in position throughout the pour. Also run a bead of sealant around the outside edge to prevent leaks. Do not apply oil to the inside surface as the oil could easily drip on to the scabbled surface and prevent bonding of the grout.

12 Preparation and pouring of the grout

Prior to pouring The area is soaked with fresh clean water for 24 hours prior to the pour. This is done to be sure that the concrete surface does not rob the grout mix of any moisture (water content) on pouring. The area must be free of any excess water and kept clean and free of any extraneous matter prior to the pour Again we follow the specification and manufacturer’s instructions. When we are directed to use Specific equipment, stirrers, specific quantities of water measured out, temperature controllers etc. If in doubt refer to the equipment used when the test cubes were prepared. In general terms, for cementitous grouts we take a drum with a measured quantity of fresh drinkable water and add a measured quantity of grout powder to the water, stirring as we go. It’s normal and often recommended to commence with say 80-90% of the water and dry mix and see how the product is reacting on the day, before adding the remaining 10% - just follow the manufacturer’s instructions to be sure



We continue stirring until all the powder has turned to custard like paste, flowable but not runny, no lumps or dry parts.

Let the paste settle for a few minutes to allow time for any trapped air to rise to the surface. Keep a record of the temperature just before you pour the paste.



No vibration during grouting, and for next 24 hours

Inspection

Check the grout manufacturers batch number – match with the test batch number

Check the water temperature against the Engineers specification or manufacturers spec.

Check the volume of water used plus the volume of grout powder used

Check to see that the mix is stirred for the required amount of time

Check to see that the air has had time to rise to the surface and escape.

Check that all this data is recorded on the inspection check sheet

Check the area for cleanliness- no loose items – old flaky concrete etc

Check the temperature of the concrete before the pour

Check the temperature of the pour at the time of pouring

Check to see that adequate protection of the poured grout is available ( hessian bags

Or clean rags)

13 Curing and forming the grout profile,

Baseplate to be covered with wet hessian bags keep steel to ambient temp



When grout has sufficient strength to support cut a 45 deg profile commencing with the underside

of the baseplate back down to the scabbled pier.

Over scabbled areas to be treated with Emaco Nanocrete or approved equivalent

14 Inspection - What to look for-what documentation is required for sign off.

The grout should be left for 4-7 days depending on the grout and the job. Make regular checks

during this period to see that the grout is not damaged in any way and that no cracks have

appeared.



If not done already gather together all the check sheets and Inspection and Test Plan

Obtain all the signatures that are set down on these documents. Hand the signed documents over

to the MDR clerk.

Check that no cracks are evident or laminations away from the baseplate



15 What takes the column load, the levelling shims or the grout?

Before we tackle this discussion, let’s look at what we did to erect the steel before we used

levelling shims.

In this case there is insufficient room for levelling shims, so we revert to the old method of taking the

load directly on the HD bolts by providing a nut and washer-note also that the load bearing nut has a

lock nut under, so that we can lock off after we have set the correct RL for the underside of the

baseplate.

When grouted and the full load applied, the thread will “give” hence the load is evenly distributed

via the baseplate to the full area of the grout on to the pier and onward down to the pad and

supporting engineered foundation and ultimately the underlying soils.

The system of loading the HD Bolt works when we stick build, that is when erecting an industrial

building for example we erect the column and rafter complete with bracing align the columns then

grout the baseplate. So the load on the HD bolt is not significant when compared to the total load

when the structure is complete, including the effect of wind loads, earthquake loads etc.

Now let’s look at how we go about installing a heavy module that arrives on site with all components

in place, that is with a full dead load. It could easily buckle the HD Bolt especially as there is no

restraint on the HD Bolt until it meets the concrete. So for full loads we use steel packers. We still



assume that there will be a degree of flexure at the packer /load interface and that the concrete

directly under the packer will fail and hence the grout will take the full load.

There are structures however where this cannot occur, the packer will take full load throughout the

life of the structure- The following is an example where there is nil flexure of the steel base and due

to the number of steel pads the load on the concrete directly under the pads is insignificant to the

stress.



Photo of a stack foundation, note the levelling shims are taking the load; the HD Bolt is threaded

in to a socket attached to the lower half of the bolt cast in to the concrete.



16 An alternative to Cast in HD Bolts

Corrugated Sleeves cast in to the concrete pier. After the column has been positioned, the HD Bolt

(in this case a threaded rod) is dropped through the holes in the baseplate, with the bolts “glued” in

by pouring an approved high strength grout around the bolts.

Note the speed of construction, survey times greatly reduced, plus there are no bolts sticking up to

hinder erection equipment.

Gone are the days of trying to vibrate concrete around a set of HD Bolts, usually at the end of the

pour when the concrete becomes firm.

Gone are the days of spending countless hours ( and dollars) trying to position HD Bolts to plus or

minus 3mm, made all the more difficult when the steel fixers are completing their work also.

Gone are the days of having to take pre pour surveys at 7am before the sun comes up.

17 Preparation for installation of heavy rotating equipment

Although the subject of a more detailed paper, the scabbling work is carried out as above for

structural work, the sole plates are grouted in to precision levels, and then the mechanical

equipment is lifted on to the sole plates.



The Glued pads and dumpy are replaced with a jacking mechanism (four corner bolts through

tapped holes in the sole plates, plus not the laser driven Hammer levelling system



Engineers level used to keep the plate level and horizontal, the laser level is used to set precision RL

Photo shows special purpose levelling feet before being grouted in, that take an equal load by

torqueing the protruding bolt that adjusts a steel wedge to raise the pad and cylinder. The units are

grouted in for life, the adjusting bolt is open for adjustment at any time. This type of support is

common where say a turbine is to be aligned with a gear box ( reduction unit) and a generator.



The couplings require aligning after installing the equipment, they are re-aligned say 1 year after

installation and re-aligned every 5 years thereafter.

18 Test the grout properties before you need to use them.

All grouts are to be tested by identifying each batch and testing each batch independently.

Prepare the mixture precisely as per the specification and manufacturer’s instructions, and then

pour the grout in to the test cylinders. Cure on site as directed, and then send off for compression

testing.

Refer to the spec for any specific way to carry out the tests and follow the advice therein. Especially

important is ambient temperature, the condition of the grout itself, the condition and temperature

of the water used, and the curing temperature of the grout in the test mould.

Once poured and cured according to the spec, that usually requires curing at the job site Under site conditions, the test cubes are taken to the NATA accredited laboratory and placed in a compression test M/C that applies a load up to the point where the test cube fails. The result Is the ultimate carrying capacity of the grout that is factored back to the acceptable load for the particular job. The actual load can be calculated by knowing the force of the equipment that is distributed over the area of the baseplate. 19 Further reading

20150404-Scabbling and Levelling shims

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