Bondek Design & Construct Manual

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USING BONDEK

Design & Construction Guide

2003 Edition

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Using

BONDEK

:

Design & Construction

2003

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Published by BlueScope Steel Ltd © BlueScope Steel Ltd 2003

Produced at BLUESCOPE LYSAGHTResearch and Development

Using Bondek: Design & Construction

Supersedes eight previously-published manuals of various titles.

Disclaimer, warranties and limitation of liability

This publication is intended to be a design aid for professional engineers and is not a substitute for professional judgement.

Except to the extent to which liability may not lawfully be excluded or limited, BLUESCOPE LYSAGHTwill not be under or incur any liability to you for any direct or indirect loss or damage (including, without limitation, consequential loss or damage, such as loss of profit or anticipated profit, loss of data, loss of use, damage to goodwill and loss due to delay) however caused (including, without limitation, breach of contract, negligence and/or breach of statute), which you may suffer or incur in connection

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1. Introduction

1.1 Preface . . . .1

1.2 Scope . . . .1

1.3 Design methods for Bondek . . . .1

1.4 General design parameters . . . .2

1.5 Materials: Sheeting . . . .2

1.6 Materials: Concrete . . . .3

1.7 Materials: Reinforcement . . . .3

1.8 Dimensions and properties . . . .3

1.9 Available length . . . .3 1.10 Corrosion protection . . . .4 1.11 Further information . . . .4 1.12 Your suggestions . . . .4 1.13 Design flowchart . . . .5 2. Formwork design 2.1 General . . . .6 2.2 Application . . . .6 2.3 Deflection limits . . . .7

2.4 Formwork design loads . . . .7

3. Composite slab design 3.1 General . . . .10

3.2 Crack control options . . . .10

3.3 Application . . . .10

3.4 Durability . . . .11

3.5 Design loads . . . .12

3.6 Linear elastic analysis . . . .13

3.7 Design for strength in negative-moment regions . . . .14

3.8 Design for strength in positive-moment regions . . . .16

3.9 Design for strength in multiple spans . . . .17

3.10 Design of reinforcement other than class D500N . . . .17

3.11 Design for serviceability . . . .17

3.12 Design for concrete-frame buildings . . . .20

4. Fire design 4.1 General . . . .21

4.2 Application . . . .22

4.3 Fire resistance periods . . . .22

4.4 Design for insulation and integrity . . . .22

4.5 Design for structural adequacy . . . .22

4.6 Reinforcement for fire design . . . .27

4.7 Location of longitudinal reinforcement for fire design . . . .28

1 INTRODUCTION

1.1 PREFACE

BLUESCOPE LYSAGHTproudly presents this new publication on LYSAGHT

BONDEK®_{. We have simplified the work of engineers with this single}

book which replaces eight previous publications. Further, it tabluates the propping, composite slab data and fire design for varioius situations, all at one view. Additionally, the book includes

BONDEK2003, our easy-to-use interactive computer software, which

enables you to bypass the tables altogether and get quick and more economical solutions with more options.

BONDEKis the centre of a formwork and reinforcement system for

concrete slab construction. It is a profiled steel sheeting widely accepted by the building construction industry to be highly

economical, versatile and robust. It has been used to great effect on many major building projects, as well as countless small ones. This new work now embodies limit state design philosophy, and is based on our extensive research conducted on bondek, so the information is not applicable to other sheeting profiles.

We now consider concrete-frame buildings, and several major new technical developments:

• linear elastic analysis of continuous composite slabs;

• saving of up to 30% in negative reinforcement due to

moment redistribution;

• partial shear connection strength theory for designing

positive-moment regions;

• increased unsupported spans of BONDEKsheeting at the

formwork stage (due to the inclusion of negative moment region capacities);

• design for reliable control of flexural cracking in support regions;

• New reinforcement grades D500N and D500L; and

• Enhanced fire design

These developments allow you to make significant improvements compared with the design methods we previously published for

slabs using BONDEK.

1.2 SCOPE

This manual and computer software provide engineers with a

convenient aid to design BONDEKcomposite slabs used in masonry

wall, concrete and steel-frame construction. The book also contains practical construction methods.

1.3 DESIGN METHODS FOR BONDEK

There are three ways you can design concrete slabs using BONDEK.

1. The easiest way of designing for bondek is to run our BONDEK

2003 software included with this manual on the inside back cover (see Chapter 9).

2. Use the design tables in this book.

3. Calculate from first principles using the data in Chapters 2, 3 and 4.

Section 1.13 gives a flowchart outlining the process assumed for design.

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1.4 GENERAL DESIGN PARAMETERS

The design solutions are provided for the following broad range of design parameters:

• design loads are essentially uniformly-distributed;

• spans are either simply-supported, or are end and interior spans

of continuous slabs;

• BONDEKsheeting has three base metal thicknesses (BMT or tbm)

of 1.00, 0.75 or 0.6 mm;

• concrete is either normal density or lightweight;

• vertical deflection limits for a composite slab are L/250 total,

or L/250 total and L/500 incremental;

• vertical deflection limits for formwork are L/150 or L/240;

• exposure classifications are A1, A2, B1 and B2

(as defined in AS 3600—2001);

• reinforcement may be normal or low ductility grades 400Y,

D500N, D500L or 450F;

• ƒ’_c= 25, 32 and 40 MPa

• maximum live load is 15 kPa;

• ratio of the longer slab span (Ll) to the shorter slab span (Ls),

of any two adjacent spans, does not exceed 1.2;

• fire resistance periods of 60, 90, 120 and 180 minutes; and

• Masonry-wall, steel or concrete-frame construction.

1.5 MATERIALS: SHEETING

BONDEKis roll-formed from hot dipped, zinc-coated, high tensile zinc

HI-TEN™ steel, in base metal thicknesses (BMT or tbm) of 1.00, 0.75

and 0.6 mm.

The steel conforms to AS1397 grade G550 (550 MPa minimum yield strength); and

• Z350 and Z450 coatings

In special circumstances bondek may be obtained:

• in other base metal thickness;

• with a non-standard zinc coating mass;

• with a pre-painted finish to the underside.

The mass of BONDEKsheeting is:

• 13.54 kg/m2_{for 1.00 BMT}

• 10.25 kg/m2_{for 0.75 BMT}

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1.6 MATERIALS: CONCRETE

ρ

c= 2000 kg/m3(lightweight) and

ρ

c= 2400 kg/m3(normal density)

See Table 1.1 for strengths.

1.7 MATERIALS: REINFORCEMENT

• For negative, shrinkage and fire reinforcement use D500N, or

400Y, or 450F grades.

• For negative and shrinkage reinforcement use D500N, or D500L,

or 400Y, or 450F grades.

Our design tables assume the use of D500N 10 mm maximum diameter bars for negative reinforcement. If you want to use other grades, refer to Section 3.10. If you want to use diameters other

than 10 mm, run BONDEK2003. The diameter of reinforcing bars must

not exceed 20 mm.

1.8 DIMENSIONS AND PROPERTIES

The dimensions and properties of BONDEKare presented in Figure 1.1

and Table 1.2.

1.9 AVAILABLE LENGTH

BONDEKsheets are readily available, custom-cut, in any length from

600 mm up to 19,500 mm (length tolerance +0, –10 mm). Ask us about longer lengths up to a maximum of 25,000 mm.

To maximise speed of installation, use lengths of BONDEKthat cover

multiple spans.

1 Intr

oduction

Table 1.2

Section properties of Bondek s s e n k c i h T _mSe_oc_dt_uio_l_un_s C_a_rr_eo_ass_o-s_fectional K E D N O B t n e m o m d n o c e S a e r a f o m m T M B Z_x103_m_m3_/_m _A h s mm 2_/_m _I x10 4_m_m4_/_m T M B 0 0 . 1 BONDEK 1.00 16.69 1678 64.08 T M B 5 7 . 0 BONDEK 0.75 12.50 1259 47.98 T M B 0 6 . 0 BONDEK 0.60 9.99 1007 38.37 Figure 1.1

Bondek dimensions (2 sheets shown)

(Fire reinforcement is not shown, see Chapter 4)

b dct c D 32 52 SHEETING ELASTIC CENTROID dcb tbm (BMT) 29 51 13 200 200 190 Cover width 590 h_r= 54 32 CENTROID OF ALL

NEGATIVE REINFORCEMENT Embossments on ribs

Sheet width 620 Concrete Bondek Pan Flute Negative reinforcement for flexure and

crack control Shrinkage and temperature reinforcement • Top location (continuous spans) • Bottom location (single spans)

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1.10 CORROSION PROTECTION

Zinc-coated BONDEKwill provide long and trouble free life without

additional corrosion protection for Exposure classifications A1, A2 and B1 as defined in AS 3600—2001, Clause 4.3.

Where the exposed underside of BONDEKis subjected to a more

severe corrosive environment use a suitable corrosion protection system.

In any exposed application, you need to treat the edges of BONDEK

to prevent moisture entering between the concrete and the sheeting (Figure 1.2).

1.11 FURTHER INFORMATION

• BLUESCOPE LYSAGHTService Centres

• BLUESCOPE LYSAGHTInformation Service on 1800 641 417

• www. lysaght.com

1.12 YOUR SUGGESTIONS

Please send your suggestions for improvements to this manual to: the Technical Writer,

BLUESCOPE LYSAGHT, Research and Development,

PO Box 504, Chester Hill, 2162.

Figure 1.2

Examples of edge treatment to prevent moisture entry at edge of slabs

Bondek Concrete Edge Form Bondek Concrete Required cover

Drip strip cast into concrete (plastic or Alcor) Bondek Concrete Required cover Drip lip SQUARE Drip lip ANGLED Bondek Concrete Required cover Drip groove

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1 Intr

oduction

1.13 DESIGN FLOWCHART

This chart outlines the process assumed in this book for the design of

BONDEKslabs. Steel-frame or masonry-wall building? Normal weight concrete ? Superimposed dead load Gsup≤1kPa ? Simply supported slab ? YES NO Concrete-frame building

Allow for restrictions for concrete-frame buildings Section 3.12 or use BONDEK 2003

Lightweight concrete

Refer to

Section 3.5.4 or use BONDEK 2003

Allow for additional superimposed dead load

Section 3.5.5 or use BONDEK 2003 Continuous slab with L1 / Ls < 1.2 Contact our Information Service

Design slab thickness Tables or alternatives† NO YES NO YES NO NO Flexural cracking control required ? YES NO YES Class D500N reinforcement dia. = 10 mm ? NO

Design negative reinforcement Tables

Multiple span: Section 3.9 or alternatives†

YES

Design negative reinforcement region Section 3.10 or

use BONDEK 2003

Design supports for a formwork stage Tables or alternatives†

Design fire reinforcement Tables or alternatives†

Design transverse reinforcement for shrinkage and temperature

Section 3.11.2

STOP

Design complete Exposure classifications A1, A2, B1 or B2

Concrete grade f'c = 25 MPa, 32 MPa or 40 MPa

Spans Single or continuous (end & interior) Reinforcement grades 400Y, D500N, D500L and 450F

Building constructions Steel frame, masonry-wall or concrete frame Composite-slab

deflection limits (∆tot< L/250) or (∆tot < L/250 and ∆inc < L/500)

YES Is simply-supported design more economical ? YES NO To

_*

*

Detail reinforcement Sections 3.7.3; 3.8.3; 3.11.2; 3.12; 4.6; 4.7 Figures 1.1; 3.1; 3.2; 3.3: 4.2; 4.3; 4.5; 4.6 Fire ratings up to 3 hours

Formwork deflection limits ∆tot < L/240 or ∆tot < L/150

Slab geometry D > 90mm; L1/Ls < 1.2

Bondek sheeting thickness 1.0 mm, 0.75 mm or 0.6 mm Loading parameters ρ = 25 kN/m3_{or 21 kN/m}3

ψs = 0.7, ψ1 = 0.4

Gsup= 1 kPa or more

START: INPUT DATA

Design slab thickness Tables or alternatives†

† Alternatives are: • design from first principles;

• Chapters 2, 3 & 4; or • BONDEK 2003

Consider design as series of simply supported slabs,

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2 FORMWORK DESIGN

2.1 GENERAL

New design rules have been developed for the design of LYSAGHT

BONDEKacting as structural formwork for the construction of

composite and non-composite slabs (where BONDEKis used as lost

formwork). The rules for calculating moment capacities are based on

testing performed at BLUESCOPE LYSAGHTResearch and Development

facility at Chester Hill, AS/NZS 4600:1996, and a finite element strip buckling analysis.

The data obtained allowed us to include moment capacities in negative regions of the design model. As a consequence, the span

limits that previously applied to BONDEKhave been increased by up

to 8%.

Formwork design calculations are covered in this section—geometric layout considerations are generally covered in Chapter 5

(Construction).

2.2 APPLICATION

Our design tables may be used to detail BONDEKacting as structural

formwork, provided the following conditions are satisfied. 1. The support lines extend across the full width of the sheeting

and have a minimum bearing of 50 mm at the ends of the sheets, and 100 mm at intermediate supports over which the sheeting is continuous.

2. The sheets continue over each slab span length without any intermediate splicing or jointing.

3. The ratio of the longer slab span (L1) to the shorter slab span (Ls)

of any two adjacent spans does not exceed 1.2,

that is L₁/L_s

≤

1.2.

4. Prop lines are positioned at equal spacings (L´) within a span (L) in the case of propped construction.

5. The slab has a uniform cross section.

6. The supports are effectively rigid such that their vertical deflection during the construction phase can be ignored in design.

7. BONDEKformwork is not normally cantilevered, though you can

seek advice from our information service for special situations. 8. Separate consideration is given to sides of the sheeting where edges are restrained or where the side of the sheeting is cut longitudinally. End support Interior support Interior support

Slab span L Slab span L

Bondek Outline of

concrete

Equal sheeting spans L’

Temporary props

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2 Formwork design

2.3 DEFLECTION LIMITS

AS 3610—1995 Formwork for concrete, defines five classes of surface finish (numbered 1 to 5) covering a broad range of applications.

We recommend a deflection limit of span/240 for the design of composite slabs in which good general alignment is required, so that the soffit has a good visual quality when viewed as a whole. We consider span/240 to be suitable for a Class 3 and 4 surface finish and, in many situations, Class 2. Where alignment affects the thickness of applied finishes (for example vermiculite), you may consider a smaller limit of span/270 to be more suitable.

We consider span/150 to be a reasonable maximum deflection limit appropriate for profile steel sheeting in situations where visual quality is not significant (Class 5).

The design rules presented may be used for deflection limits other than those stated above however, for deflection greater than span/150, you may contact our information service.

2.4 FORMWORK DESIGN LOADS

bondek must be designed as formwork for two stages of

construction. Stage I—prior to the placement of the concrete, which includes the time:

• during handling and erection of the formwork; and

• once the formwork is erected but prior to the placement of the

concrete, (Stage I as defined in AS 3610—1995.)

When a live load due to stacked materials can be adequately

controlled on the site at less than 4 kPa, the reduced design live load must be clearly indicated on the formwork documentation.

Stage II—during placement of the concrete up until the concrete has set (until fcm reaches 15 MPa and concrete is able to act flexurally to support additional loads such as stacked materials). No loads from stacked materials are allowed until the concrete has set.

Stage III—as defined in AS 3610—1995 must not be considered in the rules presented here.

2.4.1 DEAD LOAD OF BONDEK SHEETING

The dead load of the BONDEKsheeting (G_sh) is:

(AS 3610—1995, Clause 4.4.2.1)

(Gshis in kPa, when tbmis in mm)

2.4.2 DEAD LOAD OF CONCRETE

The dead load of the concrete (Gc) must include an allowance for the

weight of reinforcement as well as the effect of ponding, and is calculated as:

(AS 3610—1995, Clause 4.4.2.2)

The effect of ponding must be taken as 0.7 times the maximum

deflection (

∆

) of the sheeting when supporting the wet concrete.

Gc=ρ

(

D+0 7. ∆

)

Gsh=0 13. tbm

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2.4.3 UNIFORM VERTICAL LIVE LOAD

The uniform vertical live load (Q_uv), for the appropriate stage of

construction, is:

For Stage I construction For Stage II construction

(AS 3610—1995, Clause 4.4.2.3)

2.4.4 CONCENTRATED VERTICAL LIVE

LOAD

A concentrated vertical live load (Qc) is:

(over an area 1.6 m2_{placed at any location)}

(AS 3610—1995, Clause 4.4.2.3)

Provided the formwork design conforms to this manual, you need not consider concentrated loads as specified in AS 2327.1—1996,

Appendix F2.

2.4.5 VERTICAL LIVE LOAD DUE

TO STACKED MATERIALS

A vertical live load (QM) due to stacked materials is:

For Stage I construction maximum

(AS 2327.1—1996 does not allow less than 4 kPa for composite beam construction.)

For Stage II construction

(AS 3610—1995, Clause 4.4.2.4)

2.4.6 LOAD COMBINATIONS

FOR STRENGTH

The design loads for strength are taken from the following load combinations:

For Stage I construction For Stage II construction

(AS 3610—1995, Clause 4.5.4.1)

2.4.7 LOAD COMBINATIONS

FOR SERVICEABILITY

The design service load for vertical deflection is:

(AS 3610—1995, Clause 4.5.4.4) Fdef=Gsh+Gc F_dIIb=1 25. G_sh+1 5. G_c+Q_c FdIIa=1 25. Gsh+1 5. Gc+1 5. QuvII FdI=1 25. Gsh+1 5. QuvI+1 5. QmI QMII=0kPa QMI=4kPa Q_c=3 0. kPa QuvII=1 0. kPa QuvI=1 0. kPa

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2 Formwork design

2.4.8 DESIGN FOR STRENGTH

Design moments

The design positive bending moment (M*+_{) must be calculated from}

statics —treating each span as continuous with design negative moments over supports —and not exceed the values shown in Table 2.1.

Design negative capacities are significantly less than maximum negative and positive capacities, because negative regions begin to ‘soften’ well before the design positive capacity is reached.

Design shear

The design vertical shear force (V*) must be calculated from statics, treating each span as continuous with design negative moments over supports as shown in Table 2.1. Each load combination for strength must be considered and the concentrated vertical live load

(Qc) must be placed in a position which maximises the vertical

reaction.

Design support reaction

The design support reaction (R*_u) must be calculated from statics,

treating each span as continuous with design negative moments over supports as shown in Table 2.1. Each load combination for strength must be considered and the concentrated vertical live load

(Q_c) must be placed in a position which maximises the vertical

reaction.

Strength of positive moment regions

The design positive moment capacity (

φ

Mu.sh+) is given in Table 2.1.

The capacity is applicable when the loading is applied to the pans, or the tops of the ribs provided the distribution width on the ribs is a minimum of 50 mm.

Strength of support regions

The design shear capacity (ØVu.sh) for bearing length of 50 mm or

more, is:

2.4.9 DESIGN FOR SERVICEABILITY

The maximum vertical deflection (

∆

), at completion of the concrete

placement in all spans, is: Where:

• the values of the coefficient kdare given in Table 2.2; and

• the value of the effective second moment of area I_efis calculated

as follows: Single span sheets

(for the range of )

Multiple span sheets

(for the range of )

To keep the amount of ponded concrete to a manageable level,

the maximum vertical deflection (

∆

) within any span must not exceed

(L or L´ )/150. 169750≤Ief/tbm≤508000 Ief /tbm=240 (L or L ')−70250 301025≤I_ef/tbm≤508000 Ief /tbm=205L=96025 φV_{u sh}. =33 99. tbm +8 17. tbm 2 Table 2.1

Bondek moment capacities e v i t i s o p n g i s e D y t i c a p a c e v i t a g e n n g i s e D y t i c a p a c t m b φMu.sh +₍_k_N_m₎ _M h s . u -₍_k_N_m₎ 0 . 1 7.99 2.34 5 7 . 0 4.89 1.75 6 . 0 3.32 1.40 Table 2.2

Values of coefficient kd for calculation of

∆

(The maximum vertical deflection always occurs in the end span for these conditions.)

n a p s -i u q E r e g n o L n a s i n a p s n a p s d n e r e g n o L n a s i n a p s n a p s r o i r e t n i r e b m u N s n a p s f o L1/Ls≤1.2 L1/Ls≤1.2 1 5/384 2 1/185 0.00643 3 0.00687 0.00761 0.00687 e r o m r o 4 0.00646 0.00725 0.00725 ∆ =

_{( )}

(

)

≤

(

)

(

)

k F L or L E I L or L or d def s ef ' 4 ' 150 240

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3 COMPOSITE SLAB DESIGN

3.1 GENERAL

This chapter discusses the parameters upon which our design tables are based. Solutions to your design problems may be obtained by

direct reference to either our BONDEK2003 software, or our design

tables.

The design solutions are based on partial shear connection theory.

Data about the shear connection performance of LYSAGHT BONDEK

have been obtained from slip-block tests and full-scale slab tests. Mechanical and frictional resistance have now been identified as the major contributors to the bond, and a composite slab no longer depends on adhesion bond for anchorage. A method of design for vertical shear is also presented.

Major savings are achieved by allowing moment redistribution from negative to positive moment regions in continuous composite slabs, and this leads to a significant reduction in the amount of top-face reinforcing. Our design tables assume the use of 500 N-class fire and negative reinforcement. In our composite slab design tables, slab thickness has been developed for FRL60. The tables for continuous slabs have been developed for end spans and can be used for

interior spans also. Our BONDEK2003 software often gives more

economical designs.

3.2 CRACK CONTROL OPTIONS

An advanced method of crack control for flexure limits the crack width to 0.3 mm. Our design tables assume continuous slabs with flexural cracking control. However, if aesthetics (wide cracks over supports) is not important, it may be economical to design a continuous slab as a series of one-way slabs—no negative

reinforcement is necessary in such case (refer to Worked example 1, Chapter 6).

Slab design calculations are covered in this section—geometric layout considerations are generally covered in Section 5 (Construction).

3.3 APPLICATION

The rules presented can be used to design BONDEKcomposite slabs

provided the following conditions are satisfied.

1. The specified concrete strength grade ƒ´cis in the range 25 MPa

to 40 MPa (as specified in AS 3600—2001). The concrete density

ρ

cmay be either lightweight (1800

≤ ρ

c

≤

2100 kg/m3) or normal

density (2100

≤ ρ

c

≤

2800 kg/m3) (as specified in AS 3600—

1994).

2. The concrete manufacture and materials satisfy the requirements of AS 3600—2001, Section 19.

3. The lines of support extend across the full width of the sheeting and have a minimum bearing of 50 mm at the ends of the sheets, and 100 min at intermediate supports over which sheeting is continuous.

4. The ratio of the longer slab span ( L1) to the shorter slab span (

L_s) of any two adjacent spans does not exceed 1.2, that is L₁/L_s

≤

1.2.

5. The slab has a uniform cross-section.

6. The design loads for serviceability and strength design must be uniformly-distributed and static in nature.

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3 Composite slab design 7. The bending moments at the supports are only caused by the

action of vertical loads applied to the slab. 8. The exposure classification is A1, A2, B1, or B2.

9. The geometry of the steel sheeting profile must conform to the dimensions and tolerances shown on our production drawings. Sheeting with embossments less than the specified lower characteristic value must not be used compositely unless the

value of H_ris revised.

10. Material and construction requirements for conventional reinforcing steel must be in accordance with AS 3600—2001, Clause 19.2, and the design yield stress, ( ƒsy ), must be taken

from AS 3600—2001, Table 6.2.1, for the appropriate type and grade of reinforcement, and manufacturers’ data.

11. Material and construction requirements for concrete must be in accordance with AS 3600—2001, Clause 19.1.

12. BONDEKmust not be spliced, lapped or joined longitudinally in

any way.

13. The permanent support lines must extend across the full width of the slab.

14. Similar to the requirement in AS 2327.1, Clause 4.2.3, composite action must be assumed to exist between the steel sheeting and the concrete once the concrete in the slab has

attained a compressive strength of 15 MPa, that is ƒ´cj≥15 MPa.

Prior to the development of composite action during

construction (Stage 4 defined in AS 2327.1), potential damage to the shear connection must be avoided; and no loads from stacked materials are allowed.

15. The first interior span must have the same thickness as the end span.

3.4 DURABILITY

The exposure classification relevant to the design of BONDEKslabs are

A1, A2, B1 and B2 as defined in AS 3600—2001, Clause 4.3. The minimum concrete cover (c) to reinforcing steel, measured from the slab top face, must comply with AS 3600—2001, Table 4.10.3.2.

These requirements relevant to the design of BONDEKslabs are in

Table 3.1.

The minimum overall depth (D) of BONDEKslabs must at least comply

with the requirements given in Table 3.2. The values take into account the appropriate exposure classification and concrete

strength grade ƒ´c. They have been derived assuming that the

minimum distance from the top face of the top bar to the soffit of the slab is 70 mm, and that the cover is equal to the appropriate minimum value specified in Table 3.1.

Crack control is important for durability where cracks could provide pathways for ingress of corrosive substances such as water, and also for aesthetic reasons. The maximum crack width under long-term serviceability loads must not exceed 0.3 mm.

Table 3.2

Minimum overall depth (D) in BONDEKslabs

Table 3.1

Minimum concrete cover (c) in BONDEKslabs e r u s o p x E n o i t a c i f i s s a l c s e d a r g h t g n e r t s e t e r c n o C f'c a P M 5 2 32MPa 40MPa 1 A 20mm 20mm 20mm 2 A 30mm 25mm 20mm 1 B 40mm 30mm 2 B 45mm e r u s o p x E n o i t a c i f i s s a l c s e d a r g h t g n e r t s e t e r c n o C f'c a P M 5 2 32MPa 40MPa 1 A 90mm 90mm 90mm 2 A 100mm 95mm 90mm 1 B 110mm 100mm 2 B 115mm

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3.5 DESIGN LOADS

3.5.1 STRENGTH LOAD COMBINATIONS

For strength calculations, design loads for both propped and unpropped construction must be based on the following load combination.

Or simplified:

Composite slabs are designed assuming one-way action, and therefore reduction of uniformly-distributed live load is not appropriate.

3.5.2 SERVICEABILITY LOAD COMBINATIONS

For serviceability calculations other than deflection, design loads are based on the relevant load combination from Table 3.3. Appropriate

values of

ψ

sand

ψ

lgiven in AS 1170.1 are used, depending on the

type of building occupancy.

3.5.3 DEFLECTION

For deflection calculations, design loads must be based on the relevant load combination from Table 3.4, provided that the live load (Q) is applied after the removal of any temporary props and after the addition of any deflection-sensitive finishes. For other cases, appropriate design loads must be derived from the principles of mechanics.

The multiplier for creep and shrinkage ( kcs ) is determined in

accordance with AS 3600—2001, Clause 8.5.3.3. The ratio Asc/Ast, is

obtained by dividing the area of conventional reinforcement in compression by the area of all reinforcement in tension, including sheeting and conventional reinforcement, making no allowance for the different design yield stresses of the steels involved.

Where:

(AS 3600—2001, Clause 8.5.3.3) For this equation:

• Asc/Astis to be taken at the midspan cross-section for a

simply-supported

or continuous span and at the support for a cantilever span; and

• BONDEKsheeting must be included in A_st

For deflections in concrete-frame buildings, refer to Section 3.12.

k A A cs sc st = −2 1 2. ≥0 8. 1 25. G+1 5. Q 1 25.

(

Gc+Gsh+Gsup

)

+1 5. Q Table 3.3

Load combinations for serviceability, excluding deflection s n a p s d e p o r P Unpropedspans m r e t -t r o h S G +ψ_sQ G_s_u_p+ψ_sQ m r e t -g n o L G +ψ₁Q G_s_u_p+ψ₁Q Table 3.4

Load combinations for deflection s n a p s d e p o r P Unpropedspans l a t o T ( + k1 _c_s)G+(ψ_s+ k_c_sψ₁) Q (1+k_c_s)G_s_u_p+(ψ_s+ k_c_sψ₁) Q l a t n e m e r c n I k_c_sG+(ψ_s+ k_c_sψ₁) Q k_c_sG_s_u_p+(ψ_s+ k_c_sψ₁) Q e t a i d e m m I G +ψ_sQ G_s_u_p+ψ_sQ

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3 Composite slab design

3.5.4 LIGHTWEIGHT CONCRETE LOAD

Our design tables assume the use of normal density concrete

(2100 <

ρ

c≤2800 kg/m3) as specified in AS 3600—2001. They may

also be conservatively used for lightweight concrete (1800 <

ρ

c ≤

2100 kg/m3_{). Use}

BONDEK2003 for more economical solutions.

3.5.5 SUPERIMPOSED DEAD LOAD

The maximum superimposed dead load assumed in our design tables is 1 kPa. However bigger loads might be considered in some design situations. It is possible to treat additional superimposed dead loads as factored live load:

Qadditional= 2 Ginexcess of 1 kPa (see Worked example 3)

Use BONDEK2003 for more economical solutions.

3.6 LINEAR ELASTIC ANALYSIS

For strength and serviceability calculations, the linear elastic analysis method of AS 3600—2001, Clause 7.6, must be used to determine design bending moments and vertical shear forces. In calculating action effects in slabs which are continuous over beams, the vertical flexibility of the supporting beams must be small enough to be ignored. For strength calculations, redistrib-ution of moments are permissible up to the limit defined in AS 3600—2001, Clause 7.6.8, with the following exceptions:

• The redistribution limit in each negative moment region

is based on the value of kuin that particular negative-moment

region only.

• Redistribution of moments is permitted from negative-moment

regions to moment regions but not from positive-moment regions to negative-positive-moment regions.

• No redistribution of moments are permissible where the

contribution of class 450F and D500L reinforcement (low ductility) has been included in the calculation of the design negative moment capacity.

The ductility requirements of AS 3600—2001, Clause 7.6.8, need

not be applied to the positive-moment regions of BONDEKslabs.

For strength calculations, the inclusion of pattern variations of live load results in a bending moment envelope in which some regions are both negative-moment regions and positive-moment regions. These regions must comply with the requirements for both types of region. For serviceability calculations, pattern live loads must be included for short-term live loads but excluded for long-term live loads.

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3.7 DESIGN FOR STRENGTH

IN NEGATIVE-MOMENT REGIONS

For strength calculations in negative-moment regions use the detailed procedure in Design of composite slabs for strength (Design booklet DB3.1, BHP, 1998).

3.7.1 MINIMUM BENDING STRENGTH

The minimum bending strength requirement of AS 3600—2001 must be satisfied at all potential hinge locations in negative-moment regions—thus, conventional tensile reinforcement must be provided to ensure that:

Where:

• The negative moment region is part of a cantilever; and

• Class 450F or D500L reinforcement is used to provide negative

moment capacity.

3.7.2 SHEAR STRENGTH

Negative-moment regions must be designed for shear strength, to satisfy AS 3600—2001, Section 9. The negative-moment regions of a composite slab can be treated as solid reinforced-concrete sections.

3.7.3 DETAILING OF CONVENTIONAL

TENSILE REINFORCEMENT

Conventional tensile reinforcement in negative-moment regions must be detailed in accordance with the relevant requirements for one-way slabs in AS 3600—2001, Clause 9.1.3.

Pattern 1

Negative-moment regions must be designed to satisfy the requirements of AS 3600—2001, Section 9. The composite slab negative-moment regions can be treated as solid reinforced-concrete sections.

Muo Mcr

−_≥ −

1 2.

Figure 3.1

Pattern 1 for conventional (standard) reinforcement

Little or no restraint at end support 0.3Ln Negative reinforcement Bondek Ln Ln Restraint at end support by mass of wall Continuous over interior support 0.3Ln 0.3Ln L(span) Concrete slab W all W all Cover W all W all L(span)

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3 Composite slab design Pattern 2

When live loads exceed twice the dead load (red, bold figures in our design tables), at least one third of negative reinforcement must continue over a whole span.

Shrinkage and fire reinforcement, laid on the top, can be assumed to contribute to that additional one third of negative reinforcement.

3.7.4 BENDING STRENGTH

For the strength design of negative-moment regions, the presence of the sheeting in the slab is ignored and the slab designed as an equivalent solid reinforced-concrete member. For this purpose, use the provisions of AS 3600—2001 as they relate to the design of one-way slabs. For a slab which is continuous over any support, but treated as simply-supported for strength at that support, the design

negative bending moment at the support ( M*– _{) must be taken equal}

to zero.

In calculating the design negative bending moment ( M*– _{) an}

allowance may be made for negative-to-positive moment redistribution up to the limit specified in AS 3600—2001, Clause 7.6.8. Thus, the elastic design bending moment before redistribution

( M*–

e) may be reduced in magnitude to obtain the design negative

bending moment after redistribution ( M*– _).

The nominal negative moment capacity ( M_uo– _{) is calculated based on}

the principles of rectangular stress block theory as defined in AS 3600—2001, Clause 8.1.2.

For potential hinge locations at which the neutral axis parameter

( ku– ), as defined in AS 3600—2001, exceeds 0.4, the requirements

of AS 3600—2001, Clause 8.1.3 must be satisfied. In the application of this clause, it may be assumed that the minimum compressive reinforcement requirement is satisfied by the presence of the steel sheeting in the negative moment region.

When applying AS 3600—2001, Clause 7.6.8, be sure that:

• redistribution is normally only allowed if Class N or Class Y

(as opposed to Classes L or F) reinforcement is used over the supports;

• the elastic bending moment distribution before redistribution is

determined assuming uncracked cross-sections; and

• the amount of redistribution is measured by the percentage of

the moment before redistribution.

Figure 3.2

Pattern 2 for conventional reinforcement

Little or no restraint at end support 0.3Ln Bondek Ln Ln Restraint at end support by mass of wall Continuous over interior support 0.3Ln 0.3Ln L(span) Concrete slab W all W all Cover W all W all L(span) 1/3 of negative reinforcement

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3.8 DESIGN FOR STRENGTH

IN POSITIVE-MOMENT REGIONS

For strength calculations in positive-moment regions use the detailed procedure in Design of composite slabs for strength (Design booklet DB3.1, BHP, 1998).

3.8.1 MINIMUM BENDING STRENGTH

The minimum bending strength requirement of AS 3600—2001, Clause 8.1.4.1 must be satisfied at all potential hinge locations in

positive-moment regions, that is, . The steel proportion

for rectangular cross-sections deemed to satisfy this requirement under Clause 8.1.4.1 must not be used. The contribution of both the sheeting and the conventional reinforcement must be included in

the calculation of Muo+.

3.8.2 SHEAR STRENGTH

Positive-moment regions must be designed for vertical shear strength, such that at every cross-section located at distance of at least D from the face of a support, the design positive vertical shear

capacity (

φ

Vuc+ ), is not less than the design positive vertical shear

force ( V*+ _{). The design positive vertical shear capacity (}

φ

_V

uc+ ) may

be calculated in accordance with Design of composite slabs for strength (Design booklet DB3.1, BHP, 1998).

3.8.3 DETAILING OF CONVENTIONAL

TENSILE REINFORCEMENT

The termination locations of any conventional tensile reinforcement in positive-moment regions must be determined by extending the

reinforcement a distance D + L_sy.tpast the point at which it is no

longer required for strength. The requirements of AS 3600—2001, Clause 9.1.3 do not apply.

To allow the concrete to flow into place, the minimum clear distance between parallel bars should be restricted to the larger of either 1.5 times the maximum nominal size of aggregate (normally the

maximum aggregate size is 20 mm), or the diameter of the largest reinforcing bar.

3.8.4 BENDING STRENGTH

Positive-moment regions are designed for bending strength such that at every cross-section the design positive moment capacity (

φ

Muo+ ) is not less than the design positive bending moment ( M*+ ).

For slabs analysed using linear elastic analysis, the design positive

bending moment ( M*+ _{) is calculated such that equilibrium is}

maintained after accounting for any redistribution of moments.

φ

Muo+ ) within the slab at each

cross-section may then be calculated on the basis of either a complete or partial shear connection, as appropriate.

In calculating the design positive moment capacity (

φ

M_uo+ _{) at any}

slab cross-section, the entire cross-sectional area of the sheeting is assumed to be available to act as longitudinal reinforcement, with its effectiveness at any particular cross-section being dependent on the degree of shear connection. Conventional longitudinal tensile and compressive reinforcement may be considered to contribute to the positive moment capacity at a cross-section, provided due allowance is made for the required development length for anchorage of the reinforcement in accordance with AS 3600—2001, Section 13.

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3 Composite slab design

φ

M_uo+ _{) may be calculated in}

accordance with Design of composite slabs for strength (Design booklet DB3.1, BHP, 1998).

3.9 DESIGN FOR STRENGTH

IN MULTIPLE SPANS

Our design tables have been worked out for end spans of continuous slabs. The data in the tables can be used for interior spans also, assuming uniform thickness for end an interior spans.

BONDEK2003 will give more economical solutions for interior spans,

and also offers the opportunity to design interior spans with reduced thickness as compared with end spans.

3.10 DESIGN OF REINFORCEMENT

OTHER THAN CLASS D500N

Our design tables have been worked out for 10 mm diameter D500N reinforcement bars for negative reinforcement.

It is possible to replace D500N negative reinforcement with D500L, 400Y or 450F grades, increasing the area of reinforcement by the factors shown in Table 3.5. The area of reinforcement required is a function of:

• yield stress;

• moment redistribution (not allowed for 450F and D500L); and

• crack control (small diameter bars are more effective).

BONDEK2003 will give more economical solutions and allow more

design flexibility using other diameters and grades.

3.11 DESIGN FOR SERVICEABILITY

3.11.1 VERTICAL DEFLECTIONS

Deflection limits must be selected appropriate to the intended use of the slab. These limits must not exceed those listed in AS 3600— 2001, Table 2.4.2. In that table the reference to members supporting masonry partitions is taken to refer to slabs supporting any

deflection-sensitive finishes. (Incremental deflection is the deflection which occurs after the addition or attachment of supporting masonry partitions.)

Immediate deflections are calculated in accordance with the simplified method. Incremental and total deflections must be calculated as for immediate deflections, using the appropriate corresponding load combinations from Clause 3.6.3 of this manual. Contributions of sheeting and conventional reinforcement must be

included in the calculation of I_ef.

Table 3.5

Factors to increase area of negative reinforcement when not using D500N

t n e m e c r o f n i e R Note e d a r G Factor L 0 0 5 D 1.43 n a h t s s e l e b t s u m r e t e m a i D fi d e s u e b t o n t s u M . m m 0 1 . d e r i u q e r s i e r if r o f n g i s e d Y 0 0 4 1.44 12mmdiameteronly F 0 5 4 1.59 D_l_eia_sm_se_t_hte_ar_nm₁₀u_mst_mbe

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As a guide for calculation of Iefyou may use:

• Crack control of beams (Design booklet RCB-1.1(1), BHP, 2000); • Rules for limit-state design to Australian Standards of

simply-supported and continuous BONDEKcomposite slabs in steel-frame

or masonry wall buildings (BHPR/SM/R/005, 1996); and • Rules for design to Australian Standards of BONDEKcomposite

slabs in concrete-frame buildings (Report No. BHPR/R/1998/066).

3.11.2 CRACK CONTROL FOR SHRINKAGE

AND TEMPERATURE EFFECTS

For bondek slabs with an overall depth (D) not exceeding 250 mm, the one layer of transverse reinforcement is required at any height within the cover slab provided the appropriate concrete cover is maintained.

However, our design tables, and BONDEK2003, have been developed

assuming shrinkage reinforcement is placed at the top for continuous slabs, and at the bottom for single spans. For single spans, longitudinal reinforcement must be located as specified for Fire Detail 2 (Chapter 4). This may result in reduced slab thickness, and less negative and fire reinforcement.

Major bars of shrinkage reinforcement mesh must run across

BONDEKribs.

Using D500N as shrinkage reinforcement (say N10 at 200 mm x N10 at 200 mm) will always reduce both negative and fire

reinforcement—for short spans, it may even eliminate it. This is due to the normal ductility of D500N which can be treated as fire reinforcement and negative reinforcement with moment

redistribution. You will have to run BONDEK2003 for this option.

Table 3.6

Minimum area of D500L reinforcement for crack control in BONDEKslabs s n o i t a c i f i s s a l c e r u s o p x E 2 A & 1 A B1&B2 l o r t n o c k c a r c f o e e r g e D r o n i M Moderate Strong ) m m ( D mm2_/_m _m_m2_/_m _m_m2_/_m _m_m2_/_m 0 9 SL62 SL62 SL72 SL72 0 0 1 SL62 SL62 SL82 SL82 0 1 1 SL62 SL72 SL92 SL92 0 2 1 SL62 SL82 SL102 SL102 0 3 1 SL62 SL82 RL818 RL818 0 4 1 SL62 SL92 RL818 RL818 0 5 1 SL62 SL92 RL1018 RL1018 0 6 1 SL72 SL102 RL1018 RL1018 0 7 1 SL72 SL102 RL1018 RL1018 0 8 1 SL72 SL102 RL1018 RL1018 0 9 1 SL82 RL818 RL1018 RL1018 0 0 2 SL82 RL818 RL1218 RL1218 0 1 2 SL82 RL818 RL1218 RL1218 0 2 2 SL92 RL1018 RL1218 RL1218 0 3 2 SL92 RL1018 RL1218 RL1218 0 4 2 SL92 RL1018 RL1218 RL1218 0 5 2 SL92 RL1018 2RL1218 RL1218 Table 3.7

Cross-reference of OneSteel’s mesh specifications with Grade 450 fabrics

o t s e h s e M L 0 0 5 D n o i t a c i f i c e p s t n e l a v i u q E 0 5 4 F e d a r G s c i r b a f 2 6 L S 2 7 L S 2 8 L S 2 6 F 2 7 F 2 8 F 2 9 L S 2 0 1 L S 8 1 8 L R 2 9 F 2 0 1 F 8 1 8 F 8 1 0 1 L R 8 1 2 1 L R 8 1 0 1 F 8 1 2 1 F

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3 Composite slab design Determine the cross-sectional area of transverse reinforcement

required to control cracking of the cover slab, due to shrinkage and temperature effects, by:

• using AS 3600—2001, Clause 9.4.3.4 (Reinforcement in the

secondary direction in restrained slabs); and

• substituting the overall slab depth (D) with the cover slab depth

(D – h_r) in the equations for the minimum cross-sectional area of

transverse reinforcement.

Cross-references of OneSteel’s mesh specifications with Grade 450 fabrics are shown in Table 3.7.

3.11.3 CRACK CONTROL FOR FLEXURE

For crack control of slabs in flexure, we recommend that you follow OneSteel’s specifications: Crack control of slabs, Part 1: AS 3600 Design (Design Booklet RCB-2.1(1).

Since maximum steel stress in cracked sections is a function of a bar diameter, the bar diameter in our tables is 10 mm (the minimum possible for D500N reinforcement).

The crack control for flexure may not always be required, which is often the case for A1 exposure classification, and when aesthetics are not important. A continuous slab in such conditions may be designed as a series of simply-supported slabs without any negative reinforcement, or as a continuous slab with negative reinforcement designed without crack control, depending on which option is more economical.

3.11.4 END SLIP CONTROL

Check each span to ensure that no sheeting end-slip occurs under the loading for short-term serviceability, as follows:

• Under the loading for strength, determine the critical cross

section in the positive-moment region, which is the cross-section

at which M* / (

φ

Muo ) is the greatest. (The critical cross-section is

where a major crack is assumed to open, thus causing the test block to slip towards the end.)

• At the critical cross section in the positive-moment region,

determine the distance to the nearer end of the sheeting, x_end.

• Calculate the limiting force in the sheeting to produce end slip

from the equation:

Where:

Tslip is expressed in kN and x_endin metres.

(Value of 200 is obtained from tests as an ‘average’ value.)

• Under the loading for short-term serviceability, determine the

moment at the critical cross section in the positive-moment

region ( M_ss) and calculate the force in the sheeting ( T_ss) from

cracked elastic analysis of the cross-section. For this purpose, the properties of the sheeting may be considered to be acting in a plane 15 mm above the soffit of the slab.

• Ensure that there is no end slip between the sheeting and

concrete under service loads. To do this check that Tss

≤

Tslipand,

if necessary, alter the design for strength of the span (for

example: increase Dcand maybe tbm).

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3.12 DESIGN FOR CONCRETE-FRAME

BUILDINGS

This section covers design of slabs spanning between wide reinforced-concrete beams (beams) or prestressed band-beams of concrete-frame buildings.

Other forms of concrete-frame constructions, such as slabs spanning between ‘narrow’ reinforced concrete beams, or reinforced concrete walls, may be designed using the rules for steel-frame and masonry wall buildings.

Use Rules for design to Australian Standards of Bondek composite slabs in concrete-frame buildings (BHP R/R/1998/006).

Our design tables assume the use of steel-frame or masonry wall buildings. However, they may be used for concrete-frame buildings, with the following restrictions:

• The sheeting end must penetrate at least 25 mm into the

concrete cover on the side of a concrete beam formed up with temporary formwork (Figure 3.3).

• Where BONDEKterminates, bending moments must be zero or

negative for all loading combinations. If the moments are

positive (BONDEKis in tension), additional bottom anchorage

reinforcement must be designed (Figure 3.3 and Table 3.8). Bottom fire reinforcement Detail 2 can be treated as anchorage reinforcement. Development lengths must be designed

according to AS 3600—2001, Section 13.

• Vertical flexibility of the support beams must be small enough

to be ignored.

Our tables don’t allow for any beneficial effect on deflections and

propping requirements by band-beams. Run BONDEK2003 for more

economical solutions yielding thinner slabs and fewer props. For the design of concrete-frame buildings, use the following rules in addition to those of steel-frame or masonry wall buildings:

• Calculate the immediate deflections in accordance with the

simplified method as defined in AS 3600—2001, Clause 8.5.3.1, but don’t use the method of averaging Ief over several

cross-sections. Determine the values of I_efat an appropriate number

of selected cross-sections referring to the shape of the moment-curvature diagram for the member to enable deflections to be calculated by integration of curvatures along the length. The curvature at each cross-section is obtained by dividing the

bending moment by E_cI_ef.

• Calculate the nominal positive moment capacity ( Muo+ ) at

cross-sections within the band-beam using conventional reinforced-concrete design methods in accordance with AS 3600—2001.

Figure 3.3 Concrete Bondek 25 mm minimum Negative reinforcement Anchorage reinforcement

(or continuous fire reinforcement to Fire detail 2)

Span L

W

Table 3.8

Area of anchorage reinforcement as a percentage of negative reinforcement

t n e m e c r o f n i e r e v i t a g e n f o e g a t n e c r e P L / w _sI_un_pte_pr_oio_r_tr_s End_b_asu_np_dp_bo_er_ats_mw_sith % % ≤0.1 Notrequired 12 2 . 0 16 23 3 . 0 29 32 4 . 0 40 41 5 . 0 49 49

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4 Fir

e design

• Ignore the contribution of frictional resistance force µR*uin

developing the shear connection force.

• Shear capacity must be calculated according to Rules for design

to Australian Standards of BONDEKcomposite slabs in

concrete-frame buildings (Report No. BHPR/R/1998/066).

4 FIRE DESIGN

4.1 GENERAL

This chapter discusses the parameters relating to the exposure of the soffit to fire, upon which our design tables are based. Solutions to your design problems may be obtained by direct reference to

either our design tables, or our BONDEK2003 software.

The software has enhanced fire design module which allows BONDEK

sheeting to be partially effective during fire for up to 2 hours. Software will give more economical results. Guide tables in this manual have not been modified for enhanced fire design.

Reduction factors are applied to allow for the effect of temperature on the slab materials and slab cross-section. Values of these

reduction factors have been derived from extensive analysis of

BONDEKslab cross-sections. These reduction factors account for the

adverse effect of elevated temperatures on the mechanical properties of concrete and steel, and also include the effect of thermally induced stresses caused from the temperature gradient across the section, resulting in differential thermal expansion. Extensive testing has been conducted to validate the analysis and determine the fire-resistance periods for insulation and integrity. The distribution of temperature through a cross-section of a composite slab subject to fire, is affected by the geometry of the sheeting profile (Figure 4.1). The features important in the sheeting profile are: the rib geometry (shape, height and spacing of

intermediate ribs and lapping ribs), and the pan geometry (such as stiffening flutes).

Fire design calculations are covered in this section—geometric layout considerations are generally covered in Section 5 (Construction).

Figure 4.1

Diagrammatic distribution of thermally induced stress and strain Temperature contours x y _A A B B Section + strain y Thermal strain Total strain Stress-inducing strain (tensile) Stress-inducing strain (compressive) Strain distribution along A-A + stress y Steel stress Concrete stress Stress distribution along A-A

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4.2 APPLICATION

Our fire design tables may be used to detail BONDEKcomposite slabs

when the soffit is exposed to fire provided the following conditions are satisfied.

1. The composite slab acts as a one-way element spanning in the direction of the sheeting ribs for both room temperature and fire conditions.

2. The composite slab has been initially designed and detailed for room temperature conditions in accordance with this manual. 3. The fire design load is essentially uniformly distributed and static

in nature.

4. Transverse reinforcement for the control of cracking due to shrinkage and temperature effects is provided.

5. Adequate detailing of slab jointing, edges, slab holes and cavities (for penetrating, embedded or encased services) to provide the appropriate fire resistance period. Alternatively the local provision of suitable protection (such as fire spray material) will be necessary.

6. The fire cases are for periods of 60, 90, 120 or 180 minutes. 7. Reinforcement conforms to Section 4.6 of this manual.

4.3 FIRE RESISTANCE PERIODS

Four fire cases are considered. In each fire case the fire resistance periods for structural adequacy, integrity and insulation are taken to be of equal duration. The fire cases considered are:

• Fire case F60 = FRL 60/60/60

• Fire case F90 = FRL 90/90/90

• Fire case F120 = FRL 120/120/120

• Fire case F180 = FRL 180/180/180

4.4 DESIGN FOR INSULATION

AND INTEGRITY

Details are in Table 4.1.

4.5 DESIGN FOR STRUCTURAL

ADEQUACY

4.5.1 DESIGN LOADS

Use AS 1170.1, Clause 2.5, together with:

Design load for fire ωf=1 1. G+ΨcQ

Table 4.1

Minimum overall depth D of Bondek slabs for insulation and integrity

e r i F e c n a t s i s e r d o i r e p l a m r o N y t i s n e d e t e r c n o c t h g i e w t h g i L e t e r c n o c s e t u n i M D(mm) D(mm) 0 6 90 90 0 9 100 100 0 2 1 120 115 0 8 1 140 125 0 4 2 170 150

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4 Fir

e design

Figure 4.2

Critical cross sections

Assumed critial

cross-sections PCC = Other potentially critical cross-sections zj zk L z Bondek Concrete Max. positive moment PCC PCC PCC Interior span Assumed critial

cross-section PCC = Other potentiallycritical cross-sections

zj L z Bondek Concrete Max. positive moment PCC PCC End span L z Bondek Concrete Critial cross-section Max. positive moment

Single span xb yb Bondek Concrete Bottom reinforcement d+ D

Nomenclature for location of reinforcing bars

4.5.2 POTENTIALLY CRITICAL

CROSS-SECTIONS

All potentially critical cross sections at which hinges may form must be identified (Figure 4.2) and checked for strength. All negative moment hinges may be assumed to be plastic under fire conditions. These cross sections correspond to where:

• negative moments are a maximum over supports;

• negative tensile reinforcement is curtailed;

• positive bending moment is a maximum; or

• at any changes in cross section (for example changes in depth or

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4.5.3 STRENGTH OF POSITIVE

MOMENT REGIONS

At the potentially critical cross section where the positive moment

is a maximum, the design strength in bending (

φ

MuoT+ ) is

determined

for the given period of fire exposure as follows:

Where:

The reduction factor Rstis given in Table 4.2.

The form of this equation is identical with that used to calculate the design strength in bending of under-reinforced concrete cross-sections at room temperature conditions, but makes allowance for the influence of temperature on the strength of the reinforcing steel. Similar procedure shall be used to calculate additional capacity

due to BONDEKbeing particularly effective against fire. Reinforcement

used to control shrinkage and temperature effects often provides adequate fire resistance.

It is normal to ignore the small design strength in positive bending associated with any continuous top face reinforcement, however on some projects this may be sufficient to provide an equilibrium state without the need to provide any additional reinforcement.

At the end of the fire period the value of kuT+where the positive

moment is a maximum:

Where:

The reduction factor ( R_st) is given in Table 4.2; and γ= [0.85 - 0.007

(f´c– 28)] within the limits of 0.65 to 0.85, and f´cmust be in MPa

(AS 3600—2001, Clause 8.1.2.2). k R A f f sy ut st st,f + c 0.85 bd + ₌ + _≤ γ ' 0 4. φ uoT,i φ st st sy st st sy M R A f d R A f bd f c + + + =  −     1 0 6. ' Table 4.2

Yield stress reduction factor for Bondek ( R_st) e c n a t s i D b i r m o r f ) s e t u n i m ( d o i r e p e c n a t s i s e r e r i F e t e r c n o C e p y t 0 6 90 120 180 240 xb yb Rst yb Rst yb Rst yb Rst yb Rst l a m r o N y t i s n e d m m 0 3 10 0 15 0 25 0 40 0 50 0 0 3 0.65 40 0.57 60 0.79 85 0.88 90 0.75 5 5 1.0 75 1.0 90 1.0 120 1.0 140 1.0 m m 5 8 10 0 15 0 20 0 30 0 40 0 5 2 0.69 40 0.67 45 0.55 75 0.7 80 0.55 0 5 1.0 65 1.0 85 1.0 115 1.0 135 1.0 -t h g i L t h g i e w m m 0 3 10 0 20 0 25 0 40 0 55 0 0 3 0.6 35 0.35 70 0.75 90 0.75 90 0.55 5 5 1.0 75 1.0 90 1.0 115 1.0 130 1.0 m m 5 8 10 0 15 0 20 0 35 0 40 0 5 2 0.55 40 0.55 45 0.55 60 0.5 85 0.6 0 5 1.0 65 1.0 80 1.0 100 1.0 130 1.0 . 1 : s e t o N LinearinterpolationmaybeusedtodeterminevaluesofR_s_tforintermediatevaluesofy_b. . 2Positionoflongitudinalbottomfacereinforcementwithrespecttotheribcentreand . 2 . 4 e r u g i F n i n w o h s s i b a l s e h t f o t i f f o s e h t . 3Forafire-resistanceperiodof30minutes,thebendingstrengthofthecompositeslab . y l t n a c i f i n g i s d e t c e f f a e b o t y l e k il n u s i , g n i t a e h f o s t c e f f e e h t o t e u d , n o i t c e s -s s o r c . s e t u n i m 0 6 f o d o i r e p e c n a t s i s e r e r i f a e s u y a m u o y , n g i s e d r o f , r e v e w o H

(30)

4.5.4 STRENGTH OF NEGATIVE

MOMENT REGIONS

At the potentially critical cross sections associated with negative moments over supports, or where the negative steel is curtailed, the

design strength in bending (

φ

M_uoT+ _{) for the given period of fire}

exposure is:

Where:

The reduction factor Rstis given in Table 4.2; and dxis given in

Table 4.3.

This equation takes into account the adverse effect of elevated temperatures on the compressive strength of the concrete in the slab soffit, and also includes the effect of thermally induced stresses.

4.5.5 CHECK FOR STRUCTURAL

ADEQUACY

The structural adequacy of the end, interior or simple spans must be checked for the assumed period of fire exposure. Do this by finding

an equilibrium state whereby—under the applied loads (

ω

_f) — the

bending moments ( Mz ) at the potentially critical cross sections, do

not exceed the relevant values of positive and negative design

bending strength

φ

MuoT+and

φ

MuoT–respectively.

Interior spans (Figure 4.2)

The bending moment distribution along an interior span for an assumed pair of plastic hinges at potentially critical cross sections in negative bending can be expressed as:

The minimum bending moment (Mmin) corresponds to the maximum

positive value and is located between the ends of the member. The

location of M_mincan be found from:

End spans (Figure 4.2)

The bending moment distribution along an end span for an assumed plastic hinge at the potentially critical cross section in negative bending can be expressed as:

The minimum bending moment (M_min) corresponds to the maximum

positive moment and it is located between the ends of the member.

The location of Mmincan be found from:

Simple spans (Figure 4.2)

The bending moment distribution along a simple span can be expressed as: M L z z L z f =  −   ω 2 1 z z M L z L z min j uoT, j f j j 2 = + −

(

)

+

(

−

)

        − φ ω M z z z z M L z L z M z j f j uoT, j j f j uoT, j 2 =

( )

− +

( )

− − + −

(

)

       + − − 2 2 ω φ ω φ z z M M z z z z min j uoT, j uoT,k f k j k j 2 = + − −

(

)

+

(

−

)

        − − φ φ ω M z z z z M M z z z z M z j f j uoT, j uoT,k k j f k j uoT, j 2 2 =

( )

− +

( )

− − −

(

)

+

(

−

)

       + − − − 2ω φ φ ω φ φMuoT,i φR Ast st f d dx −₌ −

(

−₋

)

sy

(31)

wf 0 — + A—st Muo— MuoT— Envelope Bending moment due to wf wf 0 — + Ast— Muo— MuoT— Envelope Bending moment due to wf

End spans Interior spans

Initial trial

From both these configurations we see that additional moment capacity is required. Two options are below.

wf 0 — + Ast— Muo— MuoT— Envelope wf 0 — + Ast— Muo— MuoT— Envelope

Option 2: Add bottom-face reinforcement

Additional bottom-face reinforcement (Ast+) provides the required positive moment capacity (MuoT+). This is the simplest method, however it may not be the

Ast+ Ast+ wf 0 — + Ast— Muo—new MuoT—original Envelope wf 0 — + Ast— Envelope

Option 1: Increase top-face reinforcement

The additional top-face reincorcement will give an increased negative moment capacity and some positive moment capacity (MuoT+), which is often

Additional Ast— Original bending moment New bending moment MuoT+ Additional Ast— Muo—new MuoT—original MuoT+ Original bending moment New bending moment

optimal solution. Fabric placed in the bottom face for temperature and shrinkage reinforcement may be used in this option. ignored. For end spans this option is usually not an economical alternative. This option effectively produces a series of cantilevers.

Figure 4.4

(32)

4 Fir

e design

The maximum positive moment is located at midspan of the member:

4.6 REINFORCEMENT FOR FIRE DESIGN

The arrangement of reinforcement for fire design is shown in Figure 4.5.

Fire reinforcement is essential, in addition to any negative reinforcement required by our tables for composite slab design. The temperature and shrinkage reinforcement of grades D500N, 400Y or 450F can be treated as fire reinforcement if located and detailed in accordance with Figure 4.5—it may significantly reduce fire reinforcement, or even eliminate it.

The location of reinforcement Ast.f–for Fire detail 1 is in a single

top layer at a depth of dctbelow the slab top face (Figure 4.5).

This detail is applicable to end and interior spans only.

The location of reinforcement Ast.f+for Fire detail 2 is in a single

bottom layer at a distance of yb above the slab soffit (Figure 4.5). This detail is applicable to end spans, interior spans and simple

spans. The fire reinforcement Ast.f+must be continuous over

interior supports. zmin= L

2

Figure 4.5

Details of reinforcement for fire design

0.3 Ln L Bondek Concrete Fire detail 1 Bondek Concrete d— D x_b x_b dct Ast — Ast.f — Ast, transverse L_n Ast — Ast.f — 0.3 Ln L Bondek Concrete Fire detail 2 Bondek Concrete d+ D xb xb yb Ast, transverse Ln Ast — _A st.f + Ast — _A st.f +

Bondek Design & Construct Manual

USING BONDEK

Design & Construction Guide

2003 Edition

Using

BONDEK

:

Design & Construction

2003

CONTENTS

CONTENTS

1

INTRODUCTION

1.1

PREFACE

1.2

SCOPE

1.3

DESIGN METHODS FOR BONDEK

1.4

GENERAL DESIGN PARAMETERS

1.5

MATERIALS: SHEETING

1.6

MATERIALS: CONCRETE

ρ

ρ

1.7

MATERIALS: REINFORCEMENT

1.8

DIMENSIONS AND PROPERTIES

1.9

AVAILABLE LENGTH

1.10

CORROSION PROTECTION

1.11

FURTHER INFORMATION

1.12

YOUR SUGGESTIONS

1.13

DESIGN FLOWCHART

*

*

2

FORMWORK DESIGN

2.1

GENERAL

2.2

APPLICATION

≤

2.3

DEFLECTION LIMITS

2.4

FORMWORK DESIGN LOADS

2.4.1

DEAD LOAD OF BONDEK SHEETING

2.4.2

DEAD LOAD OF CONCRETE

∆

(

)

2.4.3

UNIFORM VERTICAL LIVE LOAD

2.4.4

CONCENTRATED VERTICAL LIVE

LOAD

2.4.5

VERTICAL LIVE LOAD DUE

TO STACKED MATERIALS

2.4.6

LOAD COMBINATIONS

FOR STRENGTH

2.4.7

LOAD COMBINATIONS

FOR SERVICEABILITY

2.4.8

DESIGN FOR STRENGTH

φ

2.4.9

DESIGN FOR SERVICEABILITY

_*

_{( )}