2008 shoring engineering

Modular Shoring SystemEngineering Data

used for construction. They are not engineered and are for illustration purposes only.

Special Notes: Always use skilled erectors. Always consult Performance Safety Manual. If one is not available call 905-844-5300 or check www.tablashoring.com.

Illustrations and specifications contained in this and other Tabla Construction Systems publications are based on the latest product information. Tabla Constructions Systemsreserves the right to make changes at any time, without notice.

Illustrations are typical ideas and are not to be

Tabla Construction Systems Inc.1541 Hurontario StreetMississauga, Ontario, Canada L5G 3H7Phone: 905-844-5300 • Fax: 905-844-5303Web: tablashoring.com • Email: [email protected]

Engineering Data

Modular ShoringSystem

Table of contentsTabla Safety

Tabla Code of Safe Practices ......... 1

Tabla Safety Notices ...................... 2

Engineering Bulletins

Field Strategies .............................. 3

Third Floor ..................................... 4

Typical Sections .............................. 6

External Walkway for P.-T. Operation (1003) ......................... 8

K-Clamp (1010) .............................. 9

Tabla Prop Installation Procedure (1001) ........................... 10

Shear Pin Procedure ....................... 11

Tabla Pioneer Components ............ 12

S-Beam (1009) ............................... 13

Information Setup Sheet ................ 14

Tabla Props Load Chart .................. 15

Transition Panels(1014) .................. 17

Beyond 16” Slab (1006) ................. 19

Ramp Procedures (1002) ................ 20

Stripping of Tabla Panels Report .... 22

Reshore Safety Factor .................... 23

Panel Strip Time Report .................. 24

Assessment of Minimum Cube Strength for Striking Tabla Forms . 26

Backshoring and Reshoring Data ... 27

Multistory Procedures (1005) ......... 28

Multystory Step by Step (1007) ...... 30

Tabla Engineering

E. & O.E.For G1 equipment, read this manual in conjunction with previous editions.

1

Tabla Safety

Code of Safe Practices for erecting and dismantling vertical shoring

Reprinted with permission from page 168 of the Scaffold Industry Association Code of Safe Practices.If this notice is not readily available, cut and post on jobsite

It shall be the responsibility of all employers and users to read and comply with the following common sense guidelines, which are designed to promote safety in the erection, dismantling and use of vertical shoring. These guidelines are not all inclusive nor do they supplant or replace other additional safety and precautionary

measures to cover usual or unusual conditions. If these guidelines conflict in any way with any state, local, pro-vincial or federal government statute or regulation, said statute or regulation shall supersede these guidelines and it shall be the responsibility of each user to comply therewith and also to be knowledgeable.

Give a copy of this document to your workers and post it on the job site.

These safety guidelines (Code of Safe Practice) set forth common sense procedures for safely erect-ing, dismantling and using shoring. However, equipment and shoring systems differ, and accordingly, reference must always be made to the instructions and procedures of the supplier and or manufacturer of the equipment. Since field condi-tions vary and are beyond the control of the S.I.A., safe and proper use of shoring is the sole responsibility of the user.

I. General Guidelines A) Post these shoring safety guidelines in

a conspicuous place and be sure that all persons who erect, dismantle or use shor-ing are aware of them and also use them in Tool Box Safety Meetings.

B) Follow all state, local and federal codes, ordinances and regulations pertaining to shoring.

C) Survey the job site. A survey shall be made of the job site by a competent per-son for hazards, such as untamped earth fills, ditches, debris, high tension wires, unguarded openings, and other hazard-ous conditions created by other trades. These conditions should be corrected or avoided as noted in the following sections.

D) Plan shoring erection sequence in advance and provide a safe method state-ment of work which addresses the hazards and risks of item (C) and submit this to the site safety manager for approval. Upon approval or revised amendments, this should be issued to all operatives involved with the work and formerly accepted as confirmation of compliance.

E) Inspect all equipment before using. Never use any equipment that is damaged or defective in any way. Mark it or tag it as defective. Then remove it from the jobsite.

F) A shoring drawing, consistent with the shoring manufacture’s recommended safe working loads, shall be prepared by a qualified person (or professional engineer where required), and used on the jobsite at all times.

G) Erect, dismantle or alter shoring shall be supervised by a competent person with adequate experience of the equip-ment used for shoring and shall be the responsibility of the employer of the “persons Employed” to erect, adapt and dismantle the shoring to ensure that the aforementioned “persons employed” can demonstrate experience and/or qualifica-tion of the type of shoring to be used in the erection, adaptation and dismantling of the shoring.

H) Do not abuse or misuse the shoring equipment.

I) Inspect erected shoring: (a) immediately prior to concrete placement; (b) during concrete placement; (c) while vibrating concrete, and (d) after concrete placement until concrete is set.

J) Never take changes if in doubt regard-ing the safety or use of the shoring, consult your shoring supplier.

K) Use shoring equipment only for the purposed or in ways for which it was intended. Use proper tools when installing equipment.

L) Erecting and dismantling of shoring requires good physical condition. Do not work on shoring if you feel dizzy, unsteady in any way or are impaired in any way by drugs or any other substance. Never lift equipment which requires more than one person to safely lift and remember to keep a straight posture when lifting, ensuring to keep the load close to your body during the lifting operation.

II. Guidelines for Erection and Use of Shoring

A) Provide and maintain a solid footing. The sills or cribbing for shoring shall be sound, rigid and capable of carrying the maximum design load without setting or moving.

B) Always use base plates. When sills or cribbing are used, base plates must be centered on them.

C) Adjusting screws shall be used to adjust to uneven grade conditions. Maintain all screw adjustments within the recommend-ed height for the design load.

D) Plumb and level all shoring frames and single post shores as the erection proceeds. DO NOT force braces on frames. Level the shoring towers until proper fit can be made. Maintain all shoring towers plumb and level.

E) Maintain the shore frame spacings and tower heights as shown on the shoring drawing. Where jobsite conditions require deviations from the shoring drawing, consult a qualified person.

F) Single post shores shall be stabilized in two directions. Bracing shall be installed as the shores are being erected.

G) Single Post Shores More Than One Tier High shall not be used. Where greater shore heights are required, consult the shoring supplier.

H) Adjustment of shoring to raise or lower formwork shall not be made during concrete placement.

I) If motorized concrete equipment is to be used, be sure that the shoring lay-out has been designed for use with this equipment and so noted on the layout, or drawing.

J) Use caution when erecting freestand-ing towers. Prevent tipping by guying or bracing although stability is a concern. For base/height ratio’s of towers please refer to local recommend or local statu-tory requirements. Ensure good ladder access to and from your place of work and adequate access and storage area on plat-forms. Always inspect scaffolding before

work periods and never use scaffolding which is unsafe.

K) Give special consideration to temporary loading. Areas where re-bar, material or equipment is to be stored temporarily may need to be strengthened to meet these loads.

L) Do not climb cross braces.M) Use special precautions when shoring

from or to sloped surfaces.N) Shoring loads are intended to be carried

by vertical legs. Loading of horizontal members may require special consider-ation. Consult your shoring supplier for allowable loads on horizontal members.

O) Avoid eccentric (off center) loads on U-Heads, top places and similar mem-bers by centering stringer loads on those members.

III. Guidelines for Dismantling Shoring

A) Do not commence adaptations, reshor-ing or dismantling of shoring until written authority has been issued by a competent person.

B) Dismantled equipment should be stock-piled in a planned manner and distrib-uted to avoid concentrated loads on the partially cured concrete.

C) Use proper access equipment in the dismantling process.

IV. Guidelines for ReshoringA) Reshoring procedure should be approved

by a qualified engineer.

Tabla Safety

Additional notes from Tabla shoring.Always seek advice before starting erecting and carefully study provided shoring layout drawings and the Tabla Shoring System manual includ-ing safety notices. Users, always consult professional advise when in any doubt whatsoever or however small. This information does not purport to address the many job site conditions that can arise. Always stop work and ask for advice when in doubt. Compare for compatibility, all pro-vided shoring drawings with jobsite conditions and structural & architec-tural drawings and specifications. Report immediately any discrepancies. Do not erect when in doubt.

These guidelines are provided by TABLA Shoring as common sense guideline ONLY, to alert users and workers to (some of) the jobsite condi-tions to be avoided or professionally allowed for. This manual cannot suppose to address every possible jobsite condition which may arise – these conditions must be identified and addressed by site professional management and site safety.

Safety NoticeThis Publication contains instructions concerning the use of Tabla Shoring Systems.

Every effort has been made to provide safe, reliable equipment. It is important that Tabla equipment be erected and used properly and safely and in conformity with government regulatory agencies, local regulations, Tabla recommendations and recognised codes of prac-tice which are applicable to the Tabla Modular Shoring System.

Consult Tabla Construction Systems to assure safe prac-tice and to furnish additional items of equipment where necessary to maintain maxi-mum standards of safety.

In order to assure proper fit, safety and compliance with government regulations & codes in the use of this equipment, do not mix this equipment with components of others.

Tabla Construction Systems Inc.1541 Hurontario SreetMississauga, OntarioCanada L5G 3H7Phone: 905-844-5300Fax: 905-844-5303Web: www.tablashoring.comEmail: [email protected]

Safety RulesIt is unsafe as well as unlawful to use this equip-ment without proper supervision.

Be extra careful around cantilever and edge conditions. Watch out for wind conditions (wind is a powerful force).

Follow all drawings and instructions from the manufacturer and the professional engineer. If you have any doubts, stop and talk immediately with your supervisor.

Make sure that you follow all the informed instructions from your supervisor.

You could get seriously injured from improper erection or use of this equipment.

Erecting workers, make sure you are familiar with, and follow, safe practices, instructions and all safety rules contained herein.

Stop if you are uneasy in any way; consult your supervisor.

The Code of Safe Practices Safety Rules are on the opposite page. Write, email or visit our web site for extra copies are required at your job site.

More injuries occur each year as a result of operatives not wearing and using “Personal Protection equiPment”. Don’t take the risk, your safety at work is paramount to you, your family and your employer.

2

PPE

3

Tabla Engineering

Field strategies

Note:Where telescopic beams span more than 5’, the telescopic beam must be supported at mid span with post shores and aluminum beam. See layout plan.

Side Filler Beam

Telescopic Beam

Section A Section B

Section C

Side FillerBeam

Ledger by Contractor

Telescopic Beam Hanger

Ledgerby Contractor

Telescopic Beam

High PointHigh Point

High PointHigh Point

Typical Drain Field. Section D

Guard Rail Panelc/w Toe Board

Safety Toggle PinSafety Chain

End PanelConnector

Guard Rail Panelc/w Toe Board

Slab Grab Uplift PreventerMounting Shoe

Cantilever Post

Cross Brace

Pour DirectionSteel Button

4

Tabla Engineering

5

For

illus

trat

ion

purp

oses

onl

y, n

ot f

or c

onst

ruct

ion

6

Tabla Engineering

7

For

illus

trat

ion

purp

oses

onl

y, n

ot f

or c

onst

ruct

ion

Tabla Engineering

8

9

28th Nov 2008 ENG-BUL-1010F. Shibli B-1010NTS

Drop Head Panel Support

K-Clamp

K-Clamp

K-Clamp

TABLA Standard Panel

Tabla Engineering

10

11

Shear Pin procedure

Additional “Shear Pin Procedure Decals” for Props are available upon request.

Before any load is placed on Panels above, contractor must confirm that Shear Pin is fully engaged and resting on the hardened washer/cast nut.[Prop must be Perpendicular to slab above on ramps]

Correct Incorrect

Leaving this gap will cause prop rotation under wet concrete loads

Loaded PanelCorner fromadvancingconcrete pour

Base Plate must be firmly resting on slab or suitable sill

Pouring on unstableProps may cause rotation of Prop from under load

Unloaded Panel Corner

Shear Pin

Pour direction Pour direction

Stable Unstable

Cast Adjustment Nut

12

Tabla Engineering

Maximum 16” slab on standard 8’ x 4’ panel.

19th Nov 2008 ENG-BUL-1008F. Shibli B-1008NTS

Extra Height Slabs Using Frame SupportTabla Pioneer

Tabla Prop “Locking” Gate Brace (Typical)

13

12th Nov 2008 ENG-BUL-1009 1

B-1009F. ShibliNTS

S-Beam

S-Beam

Tabla Engineering

14

1541 Hurontario StreetMississauga, Ontario Canada L5G 3H7 Web: tablashoring.com

M i s s i s s a u g a , C a n a d a • P h o n e : 9 0 5 - 8 4 4 - 5 3 0 0 • F a x : 9 0 5 - 8 4 4 - 5 3 0 3

Information Setup Sheet

FlagsHeights shown below are clear height of Tabla Props

Standard Tabla PropsFloor height less than 3353mm (11’-0”)…….. Maximum slab thickness 400mm (16”)

Floor height 3353-3658mm (11’-0”-12’-0”)….Maximum slab thickness 350mm (14”)

Floor height above 3658-4953mm (12’-0”-16’-3”) Using 1475mm (4’-6”) Tabla Prop Extension with 244 kg/M^2 (50 lbs/ft^2) Live Load…..See Below

Standard Prop with Extension tested 19th December 2006 at 3:1 Safety FactorUsing 2400mm x 1200mm (8ft x 4ft) Tabla Panel

4953mm (16’-3”) Allowable Load 2184 kg (4816 lbs) 21.422 kN….200mm (8”) Slab4648mm (15’-3”) Allowable Load 2652 kg (5848 lbs) 26.013 kN….250mm (10”) Slab4343mm (14’-3”) Allowable Load 3120 kg (6880 lbs) 30.603 kN….325mm (13”) Slab4039mm (13’-3”) Allowable Load 3276 kg (7224 lbs) 32.134 kN….350mm (14”) Slab3734mm (12’-3”) Allowable Load 3588 kg (7912 lbs) 35.194 kN….400mm (16”) Slab

Any load exceeding the loads shown above can be achieved provided that additional props are used at mid span of Tabla side rails but backshoring and reshoring design must accommodate those conditions.

Shoring, Backshoring and Reshoring can be used provided that the panel size is reduced to allow all props to remain in contact with freshly poured concrete.

At no time should concrete depth exceed 850mm (34”) on a 1200mm (4ft) wide panel unless prior authorization is given by Corporate Engineering.

In Multilevel construction additional factors can apply depending on Architectural design. The most common of these factors are the use of Mezzanine floors

A mezzanine is a partial floor extending over only part of the floor area leaving an area where the observer can look down upon a lower floor. In residential construction this is most common where part of the upper level is left open so that the resident can look over a balcony to the lower level such as the living area. It also provides high ceilings in parts of the living area adding appeal to the residence.

In commercial construction this can be found in foyers or large areas in the ground levels or podiums and may extend more than one level.

These areas are to be carefully noted since Tabla may require extra equipment to provide the shoring for greater heights. The use of extensions may be insufficient to solve the problem however the Tabla pioneer system can be used which incorporates a frame shoring system to support the Tabla panels. Care has to be taken when designing this system since the supporting shoring is made up of individual towers than can be interlaced in only one direction.

Page 1 of 2

ConstructionSystems Inc.

15



A typical shoreframe layout is shown above.

Note that the towers can be interlaced in one direction using standard cross bracing but in the opposite direction the rows of panels must be an odd number to work properly. This can be achieved using a series of 600 wide and 1200 wide panels.

Supporting a building perimeter when that perimeter is circular in shape is another common occurrence when architectural design is paramount to

the overall appearance of the finished structure.When designing the layout for these conditions do not try to form around the columns. This will lead to excessive use of plywood and telescopic beams in areas that can seem excessive. The objective is to use the accessories to form the more complex areas where rectangular panels cannot be used.

Page 2 of 2 Correct

Incorrect


Tabla Engineering

16

Page 1 of 1

Prop Height 2.4 Metre X 1.2 Metre Panel 1.8 Metre X 1.2 Metre Panel 1.2 Metre X 1.2 Metre Panel

3.36 Metre 400 mm 500 mm 850 mm3.66 Metre 350 mm 575 mm 810 mm

Standard PropsMax Slab Thickness On Panels Supported At Corners Only

Standard Props Max Slab Thickness On Panels Supported At Corners and Centre Of Side Rail


3.36 Metre 850 mm 850 mm n/a3.66 Metre 810 mm 850 mm n/a

Standard Props With Extensions Max Slab Thickness On Panels Supported At Corners Only


4.95 Metre 200 mm 300 mm 510 mm4.65 Metre 250 mm 390 mm 640 mm4.34 Metre 325 mm 480 mm 770 mm4.04 Metre 350 mm 510 mm 810 mm3.73 Metre 400 mm 560 mm 850 mm

Standard Props With Extensions Max Slab Thickness On Panels Supported At Corners and Centre Of Side Rail


4.95 Metre 510 mm 850 mm n/a4.65 Metre 640 mm 850 mm n/a4.34 Metre 770 mm 850 mm n/a4.04 Metre 810 mm 850 mm n/a3.73 Metre 850 mm 850 mm n/a

Charts Are Based On A Safety Factor Of 3:1 On Props and 2:1 On Panels

Tabla Props Load Chart




8x4 Transition Panel 1200x1200 Transition Panel

9th Dec 2008 ENG-BUL-1014F. Shibli B-1014NTS

17

Transition Panels

Tabla Engineering

18

20

Tabla Engineering

Stripping of Tabla Panels Report

22

Tabla Engineering

Ramon J. Cook, P. E.913 Dimrock Drive Schertz, Texas 78154 Phone: 210-659-0022 E-mail: [email protected]

Page 1 of 1

2006 P.E. Licenses: Delaware = 6119; District of Colombia = 7543; Maryland = 12521; Virginia = 13351; Georgia = 17268; Texas = 22830; New Jersey = 28480

Stripping of TABLA Panels from under Green Concrete Reinforced Concrete or Post Tensioned Concrete / Pre-Tension

When it is desirable or required to strip (remove) TABLA Panels from under recently poured concrete, it is acceptable to do so under the following conditions.

1) The ambient temperature under the slab must be no less than 45 F (7 C) – naturally or artificially maintained.2) The tested strength of a slab poured and cured cylinder must be at least 2,000 PSI.3) The grid spacing (size / dimensions) must not exceed 8’ x 4’ panel / prop spacing (2,500mm x 1250mm). 4) The TABLA Prop head must not at this point be disengaged from the curing concrete slab, avoiding stripping shock. 5) Until the concrete cylinder strength exceeds 2,500 PSI, construction loads on the suspended slab must be limited to no more than 20 Ibs per sq ft (9.0 kg) between the TABLA Props (Backprops) supporting this slab. 6) Continue to cure concrete in accordance with jobsite specifications. 7) Leave TABLA props undisturbed until contract specification concrete strength is gained. 8) This bulletin pertains only for use where TABLA System undisturbed BackPropping is employed, and is not intended to be interpreted as applying to the jobsite as a whole.

This bulletin is a synopsis of an overview by engineer Ramon Cook P.Eng. If more information is required contact Art Magee, TABLA Engineering Department (TED) at [email protected] here to arrange consultation with Mr. Cook.

Reshore Safety Factor

23

Ramon J. Cook, P. E.913 Dimrock Drive Schertz, Texas 78154 Phone: 210-659-0022 E-mail: [email protected]

Page 1 of 1


18 April 2006 Mr Paul Gillespie, President Gillespie Practical Technologies, IncToronto, Ontario Canada Re: TABLA Reshore Safety Factor Safety Factors of shoring: supports for concrete forms under unstable wet weights; have long been required to adhere to minimum limits of 2.5/1.0 for framed shoring and 3.0/1.0 for single post shoring. TABLA takes no exception to this rule. TABLA standard post shore rating is 7,200 lbs each, when plumb, under braced panel arrays, and extended to 12’- 0” max height, with 3/1 Factor of Safety on ultimate strength. OSHA, ANSI A10.9, and ACI 347 are all silent on the subject of Safety Factors for RESHORES of dry weights. ACI 347.2R-05, Shoring/Reshoring of Concrete Multi-Story Buildings says ”Where manufactured shores/reshores are used, the manufacturer’s data should be consulted for safe working loads and other safety requirements of the shores/reshores and hardware.” (Section 5.1.5, Adequacy of shoring/reshoring system) GPT has chosen a safety factor for RESHORES of 1.7 based on the structures own design load factors. These are given in SEI/ASCE 37 as 1.2 for dead loads, 1.4 for all loads, and 1.6 for construction live loads. Dead load of TABLA shoring/reshoring sys-tem is so light in comparison to construction slab & superimposed construction forces being carried (which equal to ”live loads”, as far as reshoring is concerned) that the total factor = 1.7 was chosen by GPT as a legitimate load factor for practical design purposes and jobsite safety.

This is tenable because the reshores are standing on a braced surface: a completed slab is braced into its building structure, or it wouldn’t be able to support reshores! In addition, the slab above being propped is stable, also tied into its columns and walls, or it couldn’t have been stripped of forms to be reshored. So, it only remains for the reshores to be stable at ceiling heights per ACI’s spec: ”manufacturers’ data”. TABLA post shores were tested per SSFI methods to obtain that verified strength-to-height data.

Respectfully submitted,

Ramon J. Cook, P. E.

Panel Strip Time Report

24

Tabla Engineering

Page 1 of 2



TABLA Panel Strip Time Report 31 Mar 2006

913 Dimrock Drive Schertz, Texas 78154 Phone: 210-659-0022 E-mail: [email protected]

Gillespie Practical Technology has invented a slab form and shore system which has a firm root in existing and traditional ACI documents.The TABLA system combines 1.) Shoring: support of wet weight and placing loads; with 2.) Reshoring: support of curing or dry weight.

In ACI 347R-04 definition, stripping the panels out separately from their shoreposts equals the ”Backshoring” method of floor construction. ”Backshoring” is defined in 347’s document as stripping out ONLY SMALL AREAS of form, and immediately placing reshores so ”the slab does not deflect and carry its own weight” alone. Backshoring has been found by long practice as satisfying the need for form removal while main-taining immediate green slab support. Thus, structurally, the TABLA panel-removal method does not strip TABLA prop supports, while it does permit the Contractor to get out the panels alone.

With props in place, as-cast, no slab is allowed to deflect and transfer its own weight to beams and columns. Nor, is any beam on TABLA shoring allowed to transfer its own weight to columns and walls. Both are completely supported according to Code. Soffit areas are subject to curing spec’s and top live load limits (20 psf, overall average, max), of course.

TABLA shoring patterns are the same for any slab thickness: 4 ft x 8 ft max. The con-crete green strength needed before panel strip depends on concrete tensile capacity for post punching shear and ”unreinforced bending (per tilt-up standard practice) rather than traditional compression strength. If compression strength is in the range of 2000 psi, and modulus of rupture (beam test) tensile strength in the range of 250 - 300 psi, then panels may be stripped. If these levels can’t be guaranteed, the panels must stay in place until they ere known and guaranteed.

At all times, Owner’s specification minimum concrete compression strength stripping time in contract documents does apply to TABLA prop removal, however. ”Reshoring” is another process, totally separate from TABLA panel removal. TABLA props may be reshores, also, and often are. But, other reshoring methods are available, and are not germane to the subject of ”getting out panels earlier than props”.

Respectfully submitted,


25

Ramon J. Cook, P. E.913 Dimrock Drive Schertz, Texas 78154 Phone: 210-659-0022 E-mail: [email protected] TABLA Panel Strip Time Report 31 Mar 2006

Page 2 of 2

Addendum & References: Panel removal flexure considerations: The distance at which ”full flexure” deflection vs ”shear-block” deflection takes place is in the span/depth range of 32 to 1. This means a ”span” of 32 times thickness. Under an 8” slab, for example 32 x 8” = about 21 feet, or 6.3 m is required before ”flexure” as measured by ”standard” calculation methods can occur. ”Span” is figured from out-side a support half-slab-depth, when supports are not theoretical knife-edges. TABLA max spans are only 11 to 1 span/depth ratio with panels removed, and flexural support widths are over 20% of clear spans. These geometries make TABLA supports far wider in ratio to span than simple ”pin” or ”knife-edge” bearings. The TABLA prop system firmly supports slabs and beams in a direct, fool-proof pattern of exact placement and test-proven strength, during pour, during cure, and during re-shore conditions. No reports of premature green-cracking of slabs after panel removaI have been received from the many jobs this system has supported, when proper curing of that green concrete has been applied. In short, TABLA props hold up green slabs with full-contact support at every shore head before, during, and after panel removal. TABLA props do it without drop-head shock, without delay in reshore placing, without error in reshore location, and without varia-tions in plumb and preload... Many Specifications haven’t quite caught up with this new TABLA system.

Refrences: 1. ACI 347 – 04, Section 3.5.1, Shoring; Section 3.7.2.1, Removal of forms & supports; Section 3.8.3, Other methods (backshoring) 2. ACI SP-4 7th Ed, Section 6, P35, Shoring design, ”Other Patented Shoring Devices” 3. op cit: P35, and ”Multistory Work”, particularly the recommendation for removal of ALL forms & shores at 70% fc specified minimum 28-day concrete ultimate strength. (Note: This does NOT mean removal of panels, leaving props in place, the TABLA Method) 4. op cit: P35, Table 6-9B, ”obtain project-specific age-strength data for the mix and job conditions with which they are working”

5. op cit: Section 6, P37, Table 6-4A

26

Tabla Engineering

E: \MCA Dr a wi n g s 2 0 0 6 \ 0 6 3 2 8 - Gi l l e s p i e I n d u s t r i e s \ C o r r e s p o n d e n c e \ L e t t e r ( St r i k i n g F o rms ) 0 3 - 0 4 - 0 8 . d o c

Pa r t n e r s F e l i x Ma g e e Sy d n e y Cr a n s t o n Pe t e r Sc o t t

Co n s u l t a n t P e t e r F i t z p a t r i c k

Magee Cranston FitzpatrickC o n s u l t i n g Ci v i l a n d S t r u c t u r a l E n g i n e e r s

I n c o r p o r a t i n g F i t z p a t r i c k C o n s u l t i n g ( NI ) L imi t e d

Dear Mr Gillespie

Assessment of Minimum Cube Strength for Striking Tabla Forms

Further to our discussion we have examined limiting factors in the performance of a 200mmthick concrete slab under the following conditions (a) supported on a 2.4m x 1.2m Shore Grid,(b) assumed to contain the minimum area of tensile reinforcement allowable under the designcode and (c) subject to a construction loading of 2.5KN/sq.m (~ 50 lbs/ft2).

Three conditions were checked for lower-bound slab capacity, based on a shore-head platesize nominally 150mm x 80mm on plan and using conservative analysis and design inaccordance with BS8110

1 Capacity based on flexural resistance of steel in tension.2 Capacity based on flexural resistance of concrete in compression.3 Capacity based on shear resistance of concrete.

Of these, punching shear, during the early low-strength phase of the curing concrete, is thelimiting condition and based on our calculations the concrete strength, below which punchingshear failure is critical, is around 5.0N/mm2 (750 psi). Above this strength, punching shearresistance rapidly improves and the slabs lower-bound capacity switches to being governed bythe minimum area of tensile reinforcement, which provides more than sufficient capacity forload transfer the shore heads.

However, in arriving at a suitable minimum strength at which the Tabla panels can be struckwhile leaving the shore prop undisturbed, account needs to be taken of the dynamics at theinstant of load transfer during the striking operation and of uncertainty due to the fact that veryearlystrength is not necessarily consistent throughout in a large area of slab.

As such we would suggest that 13.0N/mm2 (1950 psi) is a safe and satisfactory strength atwhich the Tabla forms can be struck under normal temperate conditions. It could in our view beless, where ambient conditions are conducive and where more certainty with regard to thequality of site and mix design control is qualified and in evidence, but under no circumstancesshould the cube strength be less than 10.0N/mm2 (1500psi).

We trust that this is helpful and should you require any further comment please do not hesitateto contact us.

Yours sincerely

Felix James MageeOn behalf of MCF Consulting

Galwally Lodge

4 Saintfield Road

BELFAST

BT8 6AA

Tel: 028 9064 4655

Fax: 028 9064 4744

Email: [email protected]

[email protected]

3rd April 2008

Paul Gillespie CEOTabla Shoring Systems1541 Hurontario StreetMississauga,Ontario, Canada L5G 3H7

Asessment of Minimum Cube Strength for Striking Tabla Forms

27

Prop loads on Backprop and Reshore Prop for 8’x4’/2400x1200 grid

Shoring

Before Reshore Operation640 lbs/290 kg

After Slab Pour8000 lbs/3629 kg @ 3:1 SF

Backshore

Before Reshore Operation7700lbs/ @ 3.1:1 SF

After Slab Pour8600 lbs/3493 kg @ 2.8:1 SF

Reshore

Before Reshore Operation14000 lbs/6350 kg @ 1.7:1 SF


Pour Slab After Reshore Operation

Standard Prop

12’0”/3658 for 14”/356 SlabsIn Accordance With A.C.I.

Shoring

Before Reshore Operation640 lbs/290 kg

After Slab Pour4800 lbs/2177 kg @ 3:1 SF

Backshore



Reshore



Pour Slab After Reshore Operation

Standard Prop with Extension

Backshoring and reshoring data

E. & O.E.

Tabla Engineering

28

Tabla Engineering

30

2008 shoring engineering

Documents