Guide to Fixings for GRC Cladding

7/24/2019 Guide to Fixings for GRC Cladding

1/55

GUIDE

TO

FIXINGS

FOR

GLASSFIBRE

REINFORCED

CONCRETE

CLADDING

Administration

cl0 The Concrete Society

Century House, Telford Avenue

Crowthome RG45 6YS

United Kingdom

Tel: +44

0)

1344 466007

Fax

+44 0) 1344 466008

[email protected]

Advisory

Service

26 Gorsey Brow

Billinge, Wigan W N 5 7NX

United Kingdom

Tel: +44

0)

1744 893423

Fax:

+44

0)

1744 892359

[email protected]

GRC

GRC

GRC

GRC

GRC

GRC

GRC

GRC

GRC

GRC

GRC

GRC

GRC

GRC

FIXING GUIDE

so110

October 1998. Revised November 1999

International


2/55

Contents

1. Introduction 1

2

Functions o f Fixings 2

3. Design Principles

3

3.1. Overview 3

3.2. Positioning of Fixings 4

3.3.

Allowing

for

Movements 6

3.3.1. Principles of Fixing 6

3.3.2. Shrinkage and Moisture Movements

of

GRC

3.3.3. Thermal Movements of GRC

9

3.3.4. Movements

of

Support Structure

8

10

3.4. GRC Stud Frame Construction 12

4. T y p e s of Fixings 16

4.1. Fixings into GRC 16

4.2. Fixings to Support Structure 19

5

Tolerances

21

5.1. Introduction 21

5.2. Adjustments 21

5.2.1. Angle Support Brackets 21

5.2.2. Restraint Fixings 29

5.2.3. GRC Stud Frame Cladding

33


3/55

6. Fixings

for

Lifting/Handling 34

7. Materials and Durability 37

7.1. Galvanised Fixings 37

7.2. Stainless Steel Fixings 37

7.3. Other Metals 39

7.4. Galvanic Corrosion 40

7 5 Crevice Corrosion

42

7.6. Stress Corrosion Cracking 42

8.

Typical Examples

43

I.


4/55

1.

Introduction

Glass reinforced cement (GR C) is a compo site material comprising a

mixture of hydraulic ceme nt, silica sand, alkali resistant (AR ) glass

fibres and water. Th e glass fibres effectively reinforce the mortar mix

thereby improving its tensile and flexural characteristics.

GRC is a p articularly attractive and durab le cladding material. I t can

be moulded into a wide variety of comp lex shapes and profiles and is

ideally suited to the pop ular fast-track approach o f using lightweight,

prefabricated cladding pane ls for the exteriors of mo dem buildings.

The main advantage

of

GR C panels over the corresponding precast

concrete alternatives

is

the considerable saving in weight. Th is results

in significant sav ings in the costs of transportation, handling and

erection of the panels. If this weight advan tage is considered at the

design stage, it should be possible to effect substantial econom ies in

the design of foundations and superstructures

for

high rise building

constructions. Other notable advantages of GRC cladding are its

durability, chem ical resistance, non-combustibility and go od sound

heat insulation properties.

This publication

is

intended to explain and illustrate acceptable

methods of fixing GR C panels to a building or other structure and

providing fixings for Iiftinghand ling. The basic principles

of

design are

outlined and related to the p racticabilities of ensuring adequ ate

tolerances to allow for erection and the subsequent, comb ined

move ments of the panels and supporting structure. Illustrations of

several different types o f fixings that are in comm on use are given,

together with informa tion abou t the materials used to manu facture

them. Particular reference is made to the need to isolate materials

which might give rise to galvanic corrosion if they were allowed to be

in direct contact with each other. General details of the widely used

GR C stud frame type of construction are also illustrated, together

with recommendations on how to fix the GR C facing

to

the stud frame

Finally, d etails of several fixing sys tems are presented

to

illustrate

typical examp les of securing GRC cladd ing panels to the supporting

structures. The y are not presented in any particular orde r and are only

intended

to

give general guidance.

1


5/55

2.

Functions

of Fixings

The main functions of fixings for GR C cladding panels are

as

follows:

a.

b.

joints.

C.

d.

e.

f.

CT

b

. .

to secure the cladding panels to the building for the life of the

panels a n d o r building.

to allow translational and rotational movem ents to occur

between individual panels and between the panel(s) and

supporting structure whilst maintaining w aterproofing at the

to provide sufficient adjustment to accomm odate normal

constructional inaccu racies in combina tion with the anticipated

move ments referred to in (b) above.

to maintain integrity of suppo rt and restraint under all

conditions o f exposure (imp act, vibration, wind, fire, etc.) by

minimising local concentrations of stress in the GR C.

to provide lifting points for the cladding during manufacture,

handling and erection.

to ensure that force s transmitted through the fixings are

distributed ov er as wide an area o f GR C a s possible.

Fiuings

for

liyting

should

have F

of S

of at

least

8 to 10

to utilise th e full strength properties of the GR C by providing

supp orts at the base o f the panels and lateral restraints at both

the top and bottom o f the panels.

Th e movem ents in (b) above can be difficult to quantify. H owever. it

should be possible

to

make conserva tive estimates of the magn itudes

and directions of these move ments for the purposes of designing the

fixings and join t sealants.

2


6/55

3.

3.1

Design Principles

Overview

In order to prod uce a safe, efficient and econom ic fixing system, it is

necessary to understand the basic design principles and criteria.

Th e designer sho uld first identify any constraints which might be

imposed by cond itions on site. Such constraints, if any, may have a

significant influence o n the choic e and detailed design of the fixings.

Typical exam ples of these constraints are problems a ssociated with

access, conflict with fixings for other elements, excessive

misalignments of support elements and conformance to a demanding

programme o f works.

GR C panels shou ld not be over-fixed to the structure as this will

inhibit moisture and thermal m ovem ents and is likely to result in

detrimental cracking

of

the panels. Fixings are usually provided at

each of the four corn er points of the panels.

Th e structural behaviour of the G RC panels under load should be

carefully exam ined. It is advisable to avoid long horizontal panels

(with sp d d e p t h ra tio >4) s bending can cause distress of the GRC in

the vicinity of the fixings du e to rotational and/or translational

movements.

Fixings should also be positioned so as

to

minimise any permanent

stresses which m ight be induced into the panels. Forces transmitted

through the fixings should be distributed over as wide an are a of GRC

as possible. Ad equa te bearing areas must also be provided for the

GR C on the su ppo rts at the base of the panels to avoid distress to the

GRC.

BS 5606:

1990

and BRE Digests 199 and 223 contain important

information abou t inaccuracies to be considered in the design of the

fixings. Adeq uate tolerances must be incorporated into the fixing

system if

i t

is to perform func tions (b) and (c) listed in Section 2.

Ideally, all fixing s should be easily accessible for adjustmen t although

this is not alw ays possible.

I t

is important to remem ber that galvanised fixing comp one nts have a

finite life which is directly proportional to the thickness of the zinc

coating. As

a

general rule, stainless steel fixings should be used

whenever possible because of their high resistance to corrosion.

Stainless steel is an obvious ch oice of material for fixings which are

unavoidably inaccessible (positioned out of sight).

3


7/55

Separate

fisings

should be provided for lifting/ handling purposes to

avoid possible damage to the perm anent fixings.

The total costs

of

fixings should be considered in the context

of

the

simple balancing equation

Total Cost

of

Fixings

=

MateriaVFabrication Cost s +

Costs of Installation

An increase in materiay fabrication costs , associated with the use of

more expensive an d sophisticated fixings, can be balanced against the

reduction in costs of installation resulting from s avings in tim e on site.

This point should be borne in mind when choosing the type of fixing(s)

to

be used.

3.2 Positioning

of

Fixings

Fixings can be broadly categorised into those which supp ort the self-

weight load of the panels and those which offer restraint. Som e

fixings may be required

to

hlfil both

of

these functions. Ideally, GR C

panels should have no more than four restraint fixings and no more

than two support fixings, as show n in Fig.

3.1.

4

NO RESTRAINT flXlNCS

-

TOP RESTRAINT flXlNGS

- SOTiOM

RESTRAINT &

lOCATlON FlXlNGS

BASE SUPPORTS -

2

NO 8ASE SUPPOR

JS

E L E V A T @N SECTION

Figure

3.1 -

Positioning

of

Fixings

4


8/55

GR C panels should alway s be supported at their base to ensure that the

permanent direct stresses due to self weight are compressive. This

utilises the full strength properties of the GRC to resist transient

imposed loading. It follows that GRC panels should not be top hung

in service as this would obviously induce permanent, direct tensile

stresses into the panels Th e tensile strength of the panels should be

checked for lifting purpo ses, bearing in mind that

it

is only a tem porary

condition.

In providing support points at the base of the pane ls,

it

is good design

practice to limit the eccentricity (e)

of

the self weight

(W)

from the

support point

(Fig. 3.2

a).

Th is will, in turn, limit the permanent

reactions

in

the top and bottom restraint fixings and hence the ben ding

and shear stresses induced into the panels. Ideally, the eccentricity (e)

should be ze ro, but this

is

rarely achievable. In vertical panels, the

permanent stresses resulting from this eccentricity are usually small.

However, w hen the panel leans at some angle to the vertical, as

illustrated in

Fig.

3.2

b,

the eccentricity (e) increases

and

the induced

stresses may become significant.

H

e (eccentr ic i ty )

W

H

(eccentr ic i ty )

Figure

3.2 -

Eccentricity of Self-Weight

5


9/55

3.3

Allowing for

Movements

Shrinkage, moisture and thermal m ovemen ts of GRC cladding panels

are time dep endent and su bject to wide v ariations due to the

complexity of the variables inv olved.

In

order to avoid distress and

possible damage to the GR C, fixing systems must allow these

movements to take place unhindered. Additional tolerances may also

be required in the fixings to allow for anticipated movements o f the

supporting structure.

3.3.1

Principles

of

Fixing

Fig 3.3 illustrates a recomm ended fixing sy stem for GRC cladding

panels showing the necessary freedo ms of movement

to

avoid restraint

to the GR C.

VERTICAL & HORIZONTAL

MOVEMENTS

TOP flXING

RESTRAINTS

HORIZONTAL

BOTTOM FIXING

ESTRAINT

LOCATION FIXING:

CAN BE FIXED

OR

ALLOW

HORIZONIAL MOVEMENTS

S SHOW

Figure 3.3

-

Degrees

of

Freedom

6


10/55

Th e main features of the system are:

a.

b.

Panels on ly have four fixings providing lateral restraint

Vertical support is provided at two points at the base of each

panel

Both the top restraint fixings allow vertical and horizontal

movements

One bottom restraint fixing allows horizontal move me nts whilst

the other ca n be fixed

or

identical to the other bottom fixing

e.

All fixings offer so me degree of rotational freedom.

Sections 4 and 5 illustrate the types of fixings which can be used

to

provide various degrees of freedom to satisfy the requ irements of this

fixing system .

In addition to providing allowances for move ment at the fixing

positions, the detailing

of

building areas around the GRC pa nels should

ensu re that mov em ent of the GRC is not restrained (Fig

3.4).

c .

d.

GR C t D O lN G

fRff 10 MOM

\

Figure

3.4 -

Avoidance of Restraint to

G R C

7


11/55

3.3.2

Shrin kage and M oisture Movements

of

GRC

As

GR C is wetted and dried it undergoes dimensional changes that are

attributable to shrinkage and.moisture movements. These changes are

more pron ounced than tho se occuring in comparable precast concrete

products. After the GR C panels have been manufactured and cured,

they are allowed to dry ou t and undergo an initial drying shrinkage.

Any subsequent w etting and drying causes reversible m oisture

movements

to

occur.

The se moisture movements are less than the

initial drying shrinkage an d so the GR C suffers an irreversible

shrinka ge during the initial drying process as illustrated in Fig 3.5.

1

EXPANSION

IN WATER

A T E R

S T O R A G E

........ .

....

1

_

~

.

IRREVERSIBLE

...

... ......

I

MOISTURE

MOVEMENT

.

I .. .

D R Y D R Y D R Y

i

i

Figure 3.5 - Shrinkage and

Moisture Movements

of GRC

As a general guide, the irreversible shrinkage amounts to one quarter

to one third of the ultimate drying shrinkage and is largely dependent

on the w aterlcement ratio.

Moisture movements tend to decrease with

age and are mainly governed by the cemen t content. The typical

variation

of

ultimate drying shrinkage

(%)

with the sa d c e m e n t ratio is

indicated in Fig 3.6.

- =

3

W

W

m

cI_

z

Ln

z

w

r

n

c

z

-J


12/55

0.3

0. 2

0.1

0.0

S,AXD : CERlENT R A T I O

Figure 3.6 - Variation

of

Drying Shrinkage with Sand/Cem ent Ratio

Current practice is to use sandjcement ratios of between 0.5

:

1

and

1 : 1.

The se result in a fiee shrinkage or moisture move ment in

the region of

0.15% or 1.5

mm/metre length.

3.3.3

Thermal

Movements

of GRC

The magnitude

of

thermal movements in GR C can be of

a

similar order

to shrinkage and moisture movem ents.

If

these move ments are

restrained, sign ifican t stresses can be induced into the GR C.

Th e coefficient

of

expansion ( )

of

G RC

is

within the ran ge

of 10

to 18

s

10d C. hermal dimensional changes in the GR C can be

calculated

fiom

the well-known formula

AL = a

A T L

where

A L =

change inlength

a = coefficient of linear expansion

L

=

length over which

AL is

being

AT

=

change in temperature

and

measured.


13/55

Example

Assuming a rise in tem perature

(AT)

of

30

C and a value of

coefficient of linear expans ion (a)f 18 x lO /OC a 2.500 metre long

panel will expand by

( 1 8 x 1 0 - 6 x X O x 2 . 5 x 1 0 0 0 ) m m= 1 .35m m

G RC cladding panels o f single skin construction are usually stiffened

with ribs formed aroun d expanded foam. Sandwich panels are doub le

skin construction with a core of expanded foam. In both cases, the

GR C on opposite sid es of the core material

is

likely to exp erience

different condition s

of

temperature, hum idity and moisture content.

These differing conditions have a tendency to produce bowing o f the

panels. This bow ing only occurs to a limited extent in ribbed G RC but

can be very pronou nced in sandw ich construction. Clearly, som e

account o f this bow ing m ust be mad e if it is likely to affect the

performance of the fixings. Care must be taken to place fixings in

positions w hich do no t restrict this bowing, otherwise significant

seconda ry stresses ca n be induced into the GRC panels.

3.3.4 Move me nts

of

Supporting Structure

The movem ents that are com mon to both concrete and steel structures

are:

i

a.

elastic deformation under load

b.

sway of the building under load

C. thermal movem ents

d.

e.

deflections of beam s under load

possible differential settlements of the foundations.

In addition, concrete structures are subject to shrinkage/m oisture

mov emen ts and cree p of the concrete under sustained loading.

Panels of single

skin

constrriction are now

generally used in

preference to sandwich

panels because the

latter are prone to

bowing and

concentrations of

dvferential

temperature

/

siirittkage stresses.

1 0


14/55

It

is generally very d ifficult to quantify these movem ents with any

degree

of

accuracy

so

a

conservative approach should alw ays be used.

Constructions which alleviate the effects of ariy of these movements

should be used whene ver possible. One method of overcom ing

problems associated w ith the deflections of the main beams and floor

slabs of the building is to provide a se parate, adjustable steel

framew ork, wholly sup ported at ground level, for supp orting the GRC

cladding as shown in Fig 3.7 a. This construction allo ws the main

beam s to d eflect indepen dently whilst still giving lateral restraint to the

secondary support steelwork which is supporting the GR C cladding.

Th e construction shown in Fig 3.7 b must not be used as the tops and

bottoms of the

GRC

panels are fixed to different lengths of steelwork

which can m ove relative to one another.

Secoridary steelwork

srrpport system s f o r

GRC cladding patiels

should be adjiistable

in both horizontal

directions to offset

possible out-of-

tolernme(s) of the

main steelwork.

PCE PACXINC

AS REQEED\

m aAoO0pH

HaES I R I

NMI

rO1EfiA CE

Pl ff PACKING

UAN BEAU

-i"

C E U C

LML

mc WMti

EBINC

LEML

Figure 3.7

1 1


15/55

3.4 Stud

Frame Construction

A GR C stud frame cladding panel consists of a single skin of

GRC

attached to a prefabricated fram e, usually metal, by m eans of L-shaped

flexible anchors (termed flex anch ors) and support anchors

known

s

gravity anchors) as indicated in Fig

3.8.

Regu lar spacing of the flex anchors ensures that the effects of wind

loading are even ly distributed over large areas of the panels. Th e

spacing of the flex an chors is governed by the strength of the G RC but

is usually no m ore than 600 mm n each direction. These anch ors offer

lateral support

to

the G RC facing whilst allowing some degree of

rotation and shrinkage/mo isture movem ent of the

GRC.

Th e gravity

anc hors are positioned along the bottom of the panel and support the

self-weight of the GR C.

I t

is important

to

understand certain basic

principles when detailing this form

of

construction. These principles

are illustrated below in Figs

3.9,3.10

and 3.1

1

for easy reference.

See

also GRCA

Pu blicatiori

'GRCit i Use -

Strid Frame

Cladding

POINRNG IOWAROS

ENRf OF

PANEL

ELEVATION ON

BACK

OF PANEL

G C PANE1

\

CRC GONCING

PAD

ROLLfO

lN fO

BAUINC CRC

SECTION 1 -

Figure

3.8

- G R C Stud Frame Cladding Panel

1 2


16/55

INSUFFICIENT MICKNESS

O

ANCHOR

PAD AR XIND

TACK flLOIkG

G

FLEX ANCHOR

IS GENfRALLY

UNRELIABLE AND

SUBJECT TO

F A l l C u E

FAliORE

INCORRECT7

I

7 I N C :

flp v

PAD

TO

BE MAINTAINED

AROUND FLEX ANCHOR

VERTICAL

SECTION

S N D FRAME

ANCHOR

W l l l

IMPEDE

FREE MOVEMENT OF

CRC SKIN

OR

LOCK

NUT CAN

BE USED

Figure

3.9

- Do s an d

Dont s with Flex Anchors

1 3


17/55

i

INSUfFlCJENT THICKNESS

OF

I h

BONDING

PAD AROUND

G R A V ~ T Y

\

(

ONDING

PAD .

\

/

\

GRC PANEL

FULL STRENGTH M L D

-NO T TACK WELDING

I I: :I

PLASTIC TUBE CAN BE

USED TO DE-BONO

GRAVlTY ANCHORS

BONDING PAD SHOULD

NOT EXTEND PAST BEND

IN GRAVTY ANCHOR

GRAWTY ANCHORS POINT r O W A R D s

CENTRE

O

PANEL

SO

A S NOT TO INHIBIT

SHRINKAGE AND MOISTURE MOMMENT

LAN

Figure

3.10 - Do s

and

Dont s with

Gravity A nchors

1 4


18/55

FULL STRENGTH WELD

-NOT TACK WELDING

\

STUD FRAME

(SECURED

TO

MAIN BUILDING)

GRC PANEL

VERTICAL SECTION

\

\

SUFFlClENT CLEARANCES

TO ALLOW SHRINKAGE,

MOISllJRE AND THERMAL

MOVEMENTS

OF

PANELS

PLASTIC SLEEVES CAN "F/

USED TO DE-BOND

GRAVlTY ANCHORS

FRAME

Figure

3.11

-- Alternative, T-B ar G ravity Anchor

Figure

3.1

1 illustrates an alternative T-bar type of gravity anchor which

is sometimes used. Th e recommended details shown in Figs 3.5 to 3. 1

inclusive are intended to give the GRC panels freedom

of

movement.

adequate lateral support and vertical suppo rt at their base.


19/55

4.

Types of Fixings

4.1 Fixings into GRC

Ideally, sockets cast into the GR C should be used as a means

of

securing the GR C panels to the building. How ever, it

is

not always

possible to adopt this method and face fixing of the panels an d o r use

of

dowels are the only alternatives. In all cases, the loads in the fixings

should be spread over as large an area of GR C as possible. Many of

the standard fixings in comm on use for other materials can be used

or

readily adapted for use with G RC . Th e three main types of cast-in

sockets are illustrated in F ig

4.1.

,

4

CONE TYPE

CROSS PIN ANCHOR TYPE

. , ..

/

Figure 4.1 - Cast-In Sock ets

Figure

4.2

-

Encapsulation of

Cast-In Soc ket

I t

is very impo rtant that cast-in soc kets are encapsulated

in

an adequate

volume of G R C with good fibre distribution around them. The ends of

these sockets should be left slightly proud of the GRC as shown in Fig

4.2. This avoid s the possible adv erse effects of overtightening against

the face

of

the GR C during fixing.

6


20/55

The actual performance and minimum edge distance of cast-in so ckets

will be specified by the manufacturer. How ever, as a general rule, the

socket should not

be

placed any nearer to the edge of the

GRC

than the

e.

O/A LENGTH OF

CAST IN SOCKET

=

1

T

3

1.71L

O/A LENGTH OF

CAST IN SOCKET

=

L

,L

T

1.71L

C 2

1.70L

c

T

O/A

LENGTH OF

CAST IN SOCKET

=

L

11

O/A

LENGTH OF

CAST IN SOCKET = L

T

2 1.71L

C

2

1.701

- T

Figure

4.3

1 7 I


21/55

Face fixing

of

the panels is sometimes used, particularly when acc ess

for fixing the panels is restricted

andor

when the panels are very sma ll

(Fig

4.4).

r

MAIN STRUCTURE

OVERSIZED POCKET

WlTH TAPERS

TO ASSIST

MANUFACTURE

AND ERECTION

U-SHAPED PACKS

AS RiOUlRED

ANGLE SUPPORT

DOWEL WELDED TO

SUPPORT ANGLE

CAST-IN WASHER

MAIN

BUILDING

GRC PANEL

/

I I

Figure 4.4

Figure 4.5

1 8


22/55

4.2

Fixings

to Supporting Structure

4.2.1

Concrete Structures

Fixing into concrete

is

usually

by

expansion fixings, resin fising s or

cast-in fixings.

a .

Expan sion Fixings

(

Fig 4.6)

When these are tightened, a sleeve is forced along a cone

or

a pair of

cones into the surrounding concrete. The fixing holds

by

a combination

of keying and friction.

I -

-

Figure 4.6

9


23/55

b.

Resin Fixing s

(Fig

4.7)

Resin fixings rely on the ability of the resin to transmit the force in the

steel rod

by

bond into the surrounding concrete. These fixings can be

used closer together and at closer edge d istances than expansion bolts.

Th e time taken for the resin to set and the fixing to achieve its work ing

strength will vary according to the ambien t temperature.

Figure

4.8

c. Cast-in Fixings (Fig 4.8

These are generally cha nnels with ancIlorsfixed to the back and are

cast into the conc rete. In conjunction with 'T' head bolts, these fixings

allow the fixing position to move along the length of the channel.

Channels can be used at close centres and at closer edge distances than

other fixings.

I t is

recommended that cast-in channels are used wherever possible.

These a llow greater adjustment, can be positioned around the

reinforcement and used closer to the edge of the concrete. Cast-in

fixings are also more effective when used in the tension zone

of

reinforced conc rete beams.

4.2.2 Steelwork Structures

Fixings are usually bolted to structural steelwork, through p re-drilled

holes

or

holes drilled on site, though w elding is som etimes used

to

fasten fixing c om ponen ts to supp ort steelwork.

2 0


24/55

5.

Tolerances

5.1

Introduction

GR C panels cannot be produced to an exact size nor can buildings be

constructed precisely to line and level. Con sequently, a degree of

tolerance sh ould be incorporated into fixing systems for cladding

panels to avoid fixing problems o n site.

I t

is also essential not

to

use

movem ent allowan ces in fixing components as tolerance. When the

panels are finally fitted, the mov emen t allowance s are required to avoid

possible distress to the GRC panels. The designer should refer to BS

56 6:

1990

an d relate the specified tolerances

of

the support structure

to tolerances required

for

the cladding panels. Ho wever, it is not

always possible to allow

for

the combination of building movements,

panel m ovem ents and worst tolerances, as this would result in

acceptably w ide joints between the G RC panels. In such cases, an

accurate site survey w ould enable the designer to address these

problem s, mainly by customising the panels andor fixings.

Notwithstanding this, some reliance must also be placed on the skills of

the erection team to overco me toleran ce difficulties o n site.

5.2 Adjustments

Ad justm ents will be required in all three planes, the degree of

adjustmen t necessary will depend o n the type

of

structure, individual

tolerances (structures and G RC panels), site control and the overall

finished tolerances to be achieved.

5.2.1 Angle Support Brackets

Adju stments in the fixing of angle support brackets may be provided in

several ways as follows:

Figure

5.1

- Packing

Shims

2 1


25/55

In-plan adjustment ca n cause problems o n site.

A

minimum bearing

area

of GRC

on the suppo rt must be m aintained to avoid distress to the

GRC. Packing shim s (plate or horseshoe w ashers) should gen erally be

limited to a maxim um thickness of 12

mm.

Packs should b e positioned

such that their lower ed ge is at or below the start of the bend in the

angle as indicated (Fig 5.1).

/

Figure

5.2

Oversize holes in co njunction with serrated washers provide multi-

directional adjustm ent with a positive

lock.

Packing shims are used to

provide in-plane adjustment as shown in Fig 5.2.

Horizontal slotted holes facilitate lateral adjustment. Vertical

adjustment can be provided by fixing the angle slightly low and seating

the cladding on tw o

or

more PTFE packs as indicated (Fig

5.3).

2 2


26/55

Figure

5.3

Figure 5.4

2 3


27/55

Channel fixings anchored to the backing support can provide considerable

fixing adjustm ent in one direction only (vertical or horizontal).

A

toothed

channel should be used to provide vertical adjustment and a positive lock.

In this case, horizontal slotted holes in the angle provide the necessary

adjustment as show n

in

Fig 5.4.

1

horizontal adjustment. Packing shi ms are used to provide in-plan

. .

I.

AA

C CLADOING

PANEL

CRC CLADDING

8 - J

PANEL

S

APPROMD

RE9LlEN1

FILLER

~~~

Figure 5.5

2 4

..

t

~

r


28/55

Angle support brackets may incorporate dowels or welded flats to

provide horizontal fixture for the GRC panel

as

indicated in Fig 5.5 a,

b

and c.

Incorrect fixing

of

angle supports, as shown in Fig

5.6,

can result in

bearing problems. Angle

supports

with only o ne fixing bolt are to be

preferred as they take le ss time to fix and have the capacity to rotate

and provide the intended bearing area.

P o s s t e L E DISTRESS

TO GRC IN BEARING

SECTION

AND /

OR

GRC CLADDING

PANEL

POSSIBLE

DISTRESS

/TO GRC IN 8EARINC

/

IXING BOLTS

.

ANGLE

SUPPORT

FRONT VIEW

Figure

5.6 -

Incorrect Fixing

of

Seating

Cleats

2 5


29/55

P o s s i e i E

DISTRESS TO

DUE TO HIGH BEARING

PRESSURES.

EOUCEO BEARING

AREA

SECTION .

AND

1 OR

GRC

I

REOUCEO BEARING

AREA

FRONT V l EW

PossieiE

OISTRESS

TO GRC

DUE TO

HIGH

BEARING

/

R E s w x S

Figure

5.7 -

Problems

with

Undersized Packs

Reductions in bearing from using undersize packings can result

in

excessive bearing pressures and possible distress to the

GRC

(Fig

5.7).

2 6


30/55

\

\

F

Figure 5.8

PACKINGS AS

\

TAINLESS STEEl

ANGLE SUPPORT

\

RESILIENT

FILLER

P o n e l s d o n o t hove i n d e p e n d e n t

h o r i zo n t a l adjJstrnent

8 o d p o ck i n g co n re su l t

in

r o t o t i n g s/s onqle s u p p o r t a n d

d i s t r e s s

to

GRC

\

STAINLESS STEEL

DOWEL

IN

HOLE

THROUGH ANGLE

SUPPORT

COMBINED

FIXING

FOR ADJACENT PANELS

The com bined fixing shown in

Fig

5.8

is

some times used

for

lighter

GRC

panels. it does

not,

however,

allow

independent horizontal and

in-plane adjustme nts

of

the upper and lower panels.

2 7


31/55

i

f

- Allows independeni hor iz sntd

SLOTTED HOLE IN

STAINLESS STEEL pone15

FLAT FOR VERTICAL

adjus tment c f upper ond lower

/

DJUSTMENT

@cd

packinq

con

result

in

rolation

of

s/s anyle support

STAINLESS STEEL FLAT

WlTH

PACKINGS AS

REQUIRED

STAINLESS STEEL

FIXING SOCKET

Figure

5.9

An alternative, preferred detail which do es allow separate adjustment

of

the upper and lower panels

is

illustrated in

Fig 5.9.

4

A L T E R N A T I V E

FIXING

D E T A I L

SiAlNLESS STEEL

FLA

1

2 8


32/55

5.2.2 Restraint Fixings

Details of typical restraint f ix in g are s h o w in Fig 5 10 (at the top of

the GRC panel) and

Fig

5.1 1 (at the bottom of the

GRC

panel).

GR

PANEL

PACKING

STAINLESS STEEL

FIXING

SOCKET

CLEARANCE

-

METAL TUBE AND PLASZC

SEPARA TlNC SL EE K

PTFE WASHERS

TYPICAL FIXING DE

TAIL

r

rop

OF

GRC

PANG

Fixinq socket sliqh ly proud of

sur face

10

ensure that

forcei

applied during

liqhteninq cannot pcll aut fixinq.

solation

o f mild

sk l and stcinless steel

ensued b y plaslic i c b c and PTFE washers.

Figure 5.10

-

Restraint Fixing at Top

In the top fixing (Fig

5

IO), the cast-in s ocket should be slightly proud

of the GRC surface

to

ensu re that forces applied durin g tightening

cannot pull

i t

out. Tolerances can be provided by the use of packs and

oversize holes. Isolation of the m ild steel and stainless steel

components, to prevent an y galvanic corrosion, is ensured by the use

of PVC tubes and

PTFE

washers.


33/55

T Y P I C A L SUPPORT D E T A I L

A T BOTTOM C O R N E R

.

Fixings give a measure

of

hor izonld

ond ro la l ional movemenl by

use of

PTFf

washers.

SPANNING HORIzONlALLY)

Toleronces calered

for

by use of

pocks

ond oversize

holes

m

ploles which ore

welded

to

hor izonla l ly spanning sup por l

onqle.

lsololion of

mi ld sleel ond sloinless

sleel ensured by PVC lube ond

PTFf

washers.

SIMILAR

TO

ABOM

Figure

5.1

1

-

Restraint F ixing at Bottom

Th e bottom fixing (Figure 5.1 1 ) provides lateral restraint and supports

the weight

of

the panels. Tolerances are again provided by the use of

packs and oversize holes. Isolating tubes and washers are required to

prevent the possibility

of

galvanic corrosion.

3 0


34/55

4

SOUARE STAINLESS

Preferred detail because

of qoad tderances and

freedom o f

movement

to

1

T

RC CLADDING I

lsdatirm

01

mad steel

and

stainless

sleel

ensured b y PV tube and

P lFE washers

I

I

VIEW

A

Figure 5.12

A combined fixing which provides se at in g, lateral restraint,

good

tolerances and freedom of movement for the

GRC

panels is illustrated

in Fig

5.12.

3 1


35/55

P R O B L E M A R E A S

-

T O L E R A N C E S

OR

PROBLEM EVEN MORE LIKELY

IF

THIS DISTANCE

IS RELATIVELY LARGE

Figure 5.13 - Problems with Cast-In Sockets

Cast-in sock ets being way out

of

tolerance are commo n (Fig

5.13).

Care shou ld be taken during manu facture to ensure that the positioning

and alignment of cast-in sockets is as accurate as possible. In addition,

outsized holes an d/or other adjustments should be provided in the

support comp onents to avoid this becoming a problem on site.

3 2


36/55

5.2.3

GRC Stud

Frame

Cladding

When the stud frame

is

suspended ov er the freshly sprayed

GRC

facing, to facilitate bonding o f the flex and gravity anchors onto the

facing, the frame mu st be placed within tight tolerances to avoid

problems with erection

and

jointing of the panels o n site.

Figure

5.14

highlights the critical dimensions

of

the stud frame panel

with typical tolerances for m anufacture of panels


37/55

i

6.

Fixings

for

Liftingmandling

Separate fixings should be provided

for

lifting purposes to avoid possible

damage to the permanent fixings. Lifting points should be placed a s close

to the centre

of

gravity of the panel to ensure that

it

hangs as near vertical

as possible when being lifted/handled (Fig 6.1).

Guide to Fixings for GRC Cladding

Documents

Transcript of Guide to Fixings for GRC Cladding