DESIGN GUIDE AUSTRALIA AND NEW ZEALAND DESIGN...
Transcript of DESIGN GUIDE AUSTRALIA AND NEW ZEALAND DESIGN...
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DESIGN PROCEDURES FOR TIMBER ONLY COMPOSITE
FLOOR SYSTEMS
DESIGN GUIDE AUSTRALIA AND NEW ZEALAND
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Structural Timber Innovation Company (STIC)
Authors:
Prof. Keith CrewsProfessor of Structural Engineering, Faculty of Engineering and Information Technology, University of Technology, Sydney
Dr. Rijun ShresthaResearch Associate, Faculty of Engineering and Information Technology, University of Technology, Sydney.
ImpressumDesign Procedures For Timber Only Composite Floor Systems
Report no: STIC- 2013-44
Version 1-0
UTS Project no: RES 08 - 244
First publication 2013
Copyright © 2013 by Structural Timber Innovation
Company (STIC), Christchurch 2013
All rights reserved.
Disclaimer:
This guide is supplied only to authorised licensees and registered users of the EXPAN® system and may only be used by them during the term of their licence or registered user agreement. If you do not have a current licence or are not a current registered user, you may not use this guide in any way (including making copies of it or supplying it to any other person). The guide will be updated from time to time. Licensees and registered users are responsible for ensuring that the version that they use is current and for obtaining updated versions and related information from EXPAN® website.The authors and STIC have taken all reasonable care to ensure the accuracy of the information supplied in this guide. However, neither the authors nor STIC warrant that the information contained in this guide will be complete or free of errors or inaccuracies.By using this guide you accept all liability arising from your use of it. Neither the authors nor STIC will be liable for any loss or damage suffered by any person arising from the use of this guide, however caused.
Design Guide Australia and New Zealand
Design Procedures For Timber Only Composite Floor SystemsFirst Edition 2013
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The research and development forming the foundation of this Design Guide as well as its preparation
and production was proudly made possible by the shareholders and financial partners
of the Structural Timber Innovation Company Ltd.
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Design Guide Australia and New Zealand
Design Procedures For Timber Only Composite Floor SystemsFirst Edition 2013
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Table of contents
Chapter Page
1. Introduction 5
2. Design requirements 5
3. Notation 6
4. Design procedure 7
5. Manufacturing provisions 8
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1. IntroductionThis design guide has been prepared to complement that
produced for Timber Concrete Composite floor systems, for use
in commercial and multi-residential timber buildings. Timber only
floor systems are well established in Australia and New Zealand, but
mainly for residential floor loads comprised of either sawn timber
or Engineered Wood Products such as I-joists, in conjunction with
sawn and dressed particle board or plywood flooring between 17 and
22mm in thickness.
This Guide presents a design procedure based on AS1720.1 –
2010 for composite timber floor structures, manufactured using
Engineered Wood Products such as Laminated Veneer Lumber
and/or glulam, fabricated into “T” or box beam “cassettes”. The
notations throughout this document are based on AS1720.1 – 2010
and the modification “k” factor subscripts should not be mixed or
confused with those in NZS 3603.
The Australian and New Zealand timber structures design codes
have many similarities, but in some cases use different notation
to describe the same modification factor for modifying the
characteristic property being assessed. The table opposite provides
guidance on “equivalencies” between the two standards.
Description NZS 3603 – 1993 AS 1720.1 - 2010
Capacity factor All current Australia / New Zealand product standards for Engineered Wood products (LVL and glue laminated tim-ber), have properties derived on the basis of the capacity factors in Table 2.1 of AS 1720.1 – 2010, to ensure an appropriate level of reliability.
Table 2.1
Most normal applications for TCC and timber only floors will require:
Φ = 0.90 for LVL
Φ = 0.85 for glue laminated timber
Duration of load – strength k1 k1
Duration of load – stiffness / deflection
k2 j2
Bearing factor k3 k7
Parallel support k4 k9
Grid systems k5 g42
Strength sharing – glue laminated timber
k6 Not applicable
Stability k8 k12
Extensive laboratory testing has been undertaken to validate the
design assumptions within this guide. The results of this testing
program have confirmed that provided the flange to web connections
meet the prescriptive requirements contained within this guide, the
floor can be designed using the existing provisions of AS1720.1 as a
fully composite section, with linear elastic behaviour in resisting load
actions predicted using AS/NZS 1170.1.
2. Design requirementsThe design procedure addresses performance requirements for
the strength (normative) and serviceability (advisory or informative)
limit states. Load type and intensity, load combinations and
modification factors for both the ultimate and the serviceability
limit states have been defined in accordance with the AS/NZS 1170
standards.
The limit states that require checking are:
1. Short-term ultimate limit state; where the response of
the structure to the maximum load is analysed. It generally
corresponds to short-term exertion of the structure.
2. Long-term ultimate limit state; This analysis focuses on the
response of the structure to a quasi permanent loading and to
avoid failure due to creep of the timber member in particular*.
3. Short-term serviceability limit state; This corresponds to the
instantaneous response of the structure to an imposed load.
4. Long-term serviceability limit state; To identify the service life
behaviour, this analysis considers time-dependent variations of
the material properties; in particular creep.
5. 1.0-kN serviceability limit state; The instantaneous response to
and imposed load of 1.0 kN at mid-span provides an indication
of dynamic behaviour. This can be replaced with a dynamic
analysis if available.
*Checking the end-of-life ultimate limit states correspond to
analysis and assessment of the durability/reliability of the structure.
Introduction Design requirements Notation Design procedure Manufacturing provisions
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3. NotationUnless noted otherwise in the figures below, all symbols and letters
used in the design procedure conform to those in AS1720.1 – 2010:
Figure 1: Notation for a typical composite timber only floor system
Figure 1: Notation for a typical composite timber floor system
Figure 2: Notation for an individual “cassette” in a typical composite timber floor system
A Cross-sectional area of the entire section
Afc Cross-sectional area of the top (compressive) flange
Aft Cross-sectional area of the bottom (tension) flange
As Shear area of the web = 2/3 bw hw
Aw Cross-sectional area of the web
bf.c Width of the top (compressive) flange (equals c/c spacing of webs)
bf.t Width of the bottom (tension) flange
bw Width (thickness) of the web
h Overall depth of floor
hc Distance from the centroid to the top of the top flange
ht Distance from the centroid to the bottom of the bottom flange
hf.c Height of the top (compressive) flange
hf.t Height of the bottom (tension) flange
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2.pages
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Figure 2: Notation for an individual “cassette” in a typical composite timber only floor system
Figure 1: Notation for a typical composite timber floor system
Figure 2: Notation for an individual “cassette” in a typical composite timber floor system
A Cross-sectional area of the entire section
Afc Cross-sectional area of the top (compressive) flange
Aft Cross-sectional area of the bottom (tension) flange
As Shear area of the web = 2/3 bw hw
Aw Cross-sectional area of the web
bf.c Width of the top (compressive) flange (equals c/c spacing of webs)
bf.t Width of the bottom (tension) flange
bw Width (thickness) of the web
h Overall depth of floor
hc Distance from the centroid to the top of the top flange
ht Distance from the centroid to the bottom of the bottom flange
hf.c Height of the top (compressive) flange
hf.t Height of the bottom (tension) flange
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2.pages
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A Cross-sectional area of the entire section
Afc Cross-sectional area of the top (compressive) flange
Aft Cross-sectional area of the bottom (tension) flange
As Shear area of the web = 2/3 bw hw
Aw Cross-sectional area of the web
bf.c Width of the top (compressive) flange (equals c/c
spacing of webs)
bf.t Width of the bottom (tension) flange
bw Width (thickness) of the web
h Overall depth of floor
hc Distance from the centroid to the top of the top flange
ht Distance from the centroid to the bottom of the
bottom flange
hf.c Height of the top (compressive) flange
hf.t Height of the bottom (tension) flange
hcentroid Distance from the bottom of the bottom flange to the
centroid = ht
I Second moment of inertia of the composite section
Z top Section modulus above the centroid (top flange)
Z bot Section modulus below the centroid (bottom flange)
E value of the modulus of elasticity of the timber members
hcentroid Distance from the bottom of the bottom flange to the centroid = h f.t
I Second moment of inertia of the composite section
Z top Section modulus above the centroid (top flange)
Z bot Section modulus below the centroid (bottom flange)
E value of the modulus of elasticity of the timber members
characteristic strength in bending
characteristic strength in compression
characteristic strength in shear
characteristic strength in tension
j2 stiffness modification factor – load duration
k1 duration of load (timber)
k4 moisture condition (timber)
k6 temperature (timber)
k7 length and position of bearing (timber)
k9 strength sharing between parallel members (timber)
k11
size factor (timber) – this is normally applied to the characteristic
strength property by the manufacturer
k12 stability factor (timber)
M* Moment action resulting from applied loads
M d_top Design moment capacity – top flange
M d_bot Design moment capacity – bottom flange
N*c Axial force (compression) induced in top flange from bending
N*t Axial force (tension) induced in bottom flange from bending
N d_top Design axial capacity (compression) – top flange
N d_bot Design axial capacity (tension) – bottom flange
Q top First moment of shear area for top flange
Q bot First moment of shear area for bottom flange
q top Shear flow at interface between web and top flange
q bot Shear flow at interface between web and bottom flange
V* Maximum shear effect
Vd Design shear capacity of the web
Capacity factor
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2.pages
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characteristic strength in bending
hcentroid Distance from the bottom of the bottom flange to the centroid = h f.t
I Second moment of inertia of the composite section
Z top Section modulus above the centroid (top flange)
Z bot Section modulus below the centroid (bottom flange)
E value of the modulus of elasticity of the timber members
characteristic strength in bending
characteristic strength in compression
characteristic strength in shear
characteristic strength in tension
j2 stiffness modification factor – load duration
k1 duration of load (timber)
k4 moisture condition (timber)
k6 temperature (timber)
k7 length and position of bearing (timber)
k9 strength sharing between parallel members (timber)
k11
size factor (timber) – this is normally applied to the characteristic
strength property by the manufacturer
k12 stability factor (timber)
M* Moment action resulting from applied loads
M d_top Design moment capacity – top flange
M d_bot Design moment capacity – bottom flange
N*c Axial force (compression) induced in top flange from bending
N*t Axial force (tension) induced in bottom flange from bending
N d_top Design axial capacity (compression) – top flange
N d_bot Design axial capacity (tension) – bottom flange
Q top First moment of shear area for top flange
Q bot First moment of shear area for bottom flange
q top Shear flow at interface between web and top flange
q bot Shear flow at interface between web and bottom flange
V* Maximum shear effect
Vd Design shear capacity of the web
Capacity factor
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2.pages
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characteristic strength in compression
hcentroid Distance from the bottom of the bottom flange to the centroid = h f.t
I Second moment of inertia of the composite section
Z top Section modulus above the centroid (top flange)
Z bot Section modulus below the centroid (bottom flange)
E value of the modulus of elasticity of the timber members
characteristic strength in bending
characteristic strength in compression
characteristic strength in shear
characteristic strength in tension
j2 stiffness modification factor – load duration
k1 duration of load (timber)
k4 moisture condition (timber)
k6 temperature (timber)
k7 length and position of bearing (timber)
k9 strength sharing between parallel members (timber)
k11
size factor (timber) – this is normally applied to the characteristic
strength property by the manufacturer
k12 stability factor (timber)
M* Moment action resulting from applied loads
M d_top Design moment capacity – top flange
M d_bot Design moment capacity – bottom flange
N*c Axial force (compression) induced in top flange from bending
N*t Axial force (tension) induced in bottom flange from bending
N d_top Design axial capacity (compression) – top flange
N d_bot Design axial capacity (tension) – bottom flange
Q top First moment of shear area for top flange
Q bot First moment of shear area for bottom flange
q top Shear flow at interface between web and top flange
q bot Shear flow at interface between web and bottom flange
V* Maximum shear effect
Vd Design shear capacity of the web
Capacity factor
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2.pages
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characteristic strength in shear
hcentroid Distance from the bottom of the bottom flange to the centroid = h f.t
I Second moment of inertia of the composite section
Z top Section modulus above the centroid (top flange)
Z bot Section modulus below the centroid (bottom flange)
E value of the modulus of elasticity of the timber members
characteristic strength in bending
characteristic strength in compression
characteristic strength in shear
characteristic strength in tension
j2 stiffness modification factor – load duration
k1 duration of load (timber)
k4 moisture condition (timber)
k6 temperature (timber)
k7 length and position of bearing (timber)
k9 strength sharing between parallel members (timber)
k11
size factor (timber) – this is normally applied to the characteristic
strength property by the manufacturer
k12 stability factor (timber)
M* Moment action resulting from applied loads
M d_top Design moment capacity – top flange
M d_bot Design moment capacity – bottom flange
N*c Axial force (compression) induced in top flange from bending
N*t Axial force (tension) induced in bottom flange from bending
N d_top Design axial capacity (compression) – top flange
N d_bot Design axial capacity (tension) – bottom flange
Q top First moment of shear area for top flange
Q bot First moment of shear area for bottom flange
q top Shear flow at interface between web and top flange
q bot Shear flow at interface between web and bottom flange
V* Maximum shear effect
Vd Design shear capacity of the web
Capacity factor
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2.pages
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characteristic strength in tension
j2 stiffness modification factor – load duration
k1 duration of load (timber)
k4 moisture condition (timber)
k6 temperature (timber)
k7 length and position of bearing (timber)
k9 strength sharing between parallel members (timber)
k11 size factor (timber) – this is normally applied to the
characteristic strength property by the manufacturer
k12 stability factor (timber)
M* Moment action resulting from applied loads
M d_top Design moment capacity – top flange
M d_bot Design moment capacity – bottom flange
N*c Axial force (compression) induced in top flange from
bending
N*t Axial force (tension) induced in bottom flange from
bending
N d_top Design axial capacity (compression) – top flange
N d_bot Design axial capacity (tension) – bottom flange
Q top First moment of shear area for top flange
Q bot First moment of shear area for bottom flange
q top Shear flow at interface between web and top flange
q bot Shear flow at interface between web and bottom flange
V* Maximum shear effect
Vd Design shear capacity of the web
hcentroid Distance from the bottom of the bottom flange to the centroid = h f.t
I Second moment of inertia of the composite section
Z top Section modulus above the centroid (top flange)
Z bot Section modulus below the centroid (bottom flange)
E value of the modulus of elasticity of the timber members
characteristic strength in bending
characteristic strength in compression
characteristic strength in shear
characteristic strength in tension
j2 stiffness modification factor – load duration
k1 duration of load (timber)
k4 moisture condition (timber)
k6 temperature (timber)
k7 length and position of bearing (timber)
k9 strength sharing between parallel members (timber)
k11
size factor (timber) – this is normally applied to the characteristic
strength property by the manufacturer
k12 stability factor (timber)
M* Moment action resulting from applied loads
M d_top Design moment capacity – top flange
M d_bot Design moment capacity – bottom flange
N*c Axial force (compression) induced in top flange from bending
N*t Axial force (tension) induced in bottom flange from bending
N d_top Design axial capacity (compression) – top flange
N d_bot Design axial capacity (tension) – bottom flange
Q top First moment of shear area for top flange
Q bot First moment of shear area for bottom flange
q top Shear flow at interface between web and top flange
q bot Shear flow at interface between web and bottom flange
V* Maximum shear effect
Vd Design shear capacity of the web
Capacity factor
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2.pages
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Capacity factor
EIeff effective stiffness of timber floor cross-section
G self-weight
Introduction Design requirements Notation Design procedure Manufacturing provisions
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4. Design procedureThe design procedure has three fundamental stages:
1. Identifying the geometric characteristics of the cross-section
of the composite beam.
2. Evaluation of the strength capacity.
3. Assessment of the serviceability limit states.
4.1 Cross-section characteristicsIn cases where the flanges and webs have differing properties (such
as the use of cross laminated timber), it is necessary to determine
the modular ratio and apply this to determine effective widths of
members, prior to determination of the section properties.
For irregular sections (e.g. where the top and bottom flanges are
different) the location of the centroid must be determined, in order
to calculate the relevant section properties.
It is strongly recommended that the c/c web spacing be such that
shear lag effects do not occur in the flanges. This is normally met by
satisfying Equation 1.
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
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4 Design procedureThe design procedure has three fundamental stages:
1. Identifying the geometric characteristics of the cross-section of the composite beam. 2. Evaluation of the strength capacity.3. Assessment of the serviceability limit states.
4.1 Cross-section characteristicsIn cases where the flanges and webs have differing properties (such as the use of cross laminated timber), it is necessary to determine the modular ratio and apply this to determine effective widths of members, prior to determination of the section properties.
For irregular sections (e.g. where the top and bottom flanges are different) the location of the centroid must be determined, in order to calculate the relevant section properties.
It is strongly recommended that the c/c web spacing be such that shear lag effects do not occur in the flanges. This is normally met by satisfying Equation 1.
𝑏𝑏𝑓𝑓.𝑡𝑡 ≤ 𝑀𝑀𝑀𝑀𝑀𝑀 (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠), �𝑏𝑏𝑤𝑤 + 20 × ℎ𝑓𝑓.𝑡𝑡� for bottom flange (1a)
𝑏𝑏𝑓𝑓.𝑐𝑐 ≤ (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) for top flange (1b)
4.2 Design for flexural effectsThe imposed UDL induces flexure in the webs and a combination of flexural and axial load effects in the flanges. This requires satisfying the requirements of Clause 3.5 of AS1720.1 –2010, for combined bending and axial load effects. The equations below apply to a simplysupported beam and would need to be interpreted correctly for use with continuous beams.
Bending capacity of the section above the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡 (2a)
Bending capacity of the section below the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑏𝑏𝑡𝑡𝑡𝑡 (2b)
Where: k4, k6, k9 and k12, will all normally equal 1.0
Axial capacity (compression) of the top flange is given by:
𝑀𝑀𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘12𝑓𝑓′𝑐𝑐𝐴𝐴𝑓𝑓.𝑐𝑐 (3a)
Axial capacity (tension) of the bottom flange is given by:
𝑀𝑀𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘11𝑓𝑓′𝑡𝑡𝐴𝐴𝑓𝑓.𝑡𝑡 (3b)
for bottom flange (1a)
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
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4 Design procedureThe design procedure has three fundamental stages:
1. Identifying the geometric characteristics of the cross-section of the composite beam. 2. Evaluation of the strength capacity.3. Assessment of the serviceability limit states.
4.1 Cross-section characteristicsIn cases where the flanges and webs have differing properties (such as the use of cross laminated timber), it is necessary to determine the modular ratio and apply this to determine effective widths of members, prior to determination of the section properties.
For irregular sections (e.g. where the top and bottom flanges are different) the location of the centroid must be determined, in order to calculate the relevant section properties.
It is strongly recommended that the c/c web spacing be such that shear lag effects do not occur in the flanges. This is normally met by satisfying Equation 1.
𝑏𝑏𝑓𝑓.𝑡𝑡 ≤ 𝑀𝑀𝑀𝑀𝑀𝑀 (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠), �𝑏𝑏𝑤𝑤 + 20 × ℎ𝑓𝑓.𝑡𝑡� for bottom flange (1a)
𝑏𝑏𝑓𝑓.𝑐𝑐 ≤ (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) for top flange (1b)
4.2 Design for flexural effectsThe imposed UDL induces flexure in the webs and a combination of flexural and axial load effects in the flanges. This requires satisfying the requirements of Clause 3.5 of AS1720.1 –2010, for combined bending and axial load effects. The equations below apply to a simplysupported beam and would need to be interpreted correctly for use with continuous beams.
Bending capacity of the section above the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡 (2a)
Bending capacity of the section below the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑏𝑏𝑡𝑡𝑡𝑡 (2b)
Where: k4, k6, k9 and k12, will all normally equal 1.0
Axial capacity (compression) of the top flange is given by:
𝑀𝑀𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘12𝑓𝑓′𝑐𝑐𝐴𝐴𝑓𝑓.𝑐𝑐 (3a)
Axial capacity (tension) of the bottom flange is given by:
𝑀𝑀𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘11𝑓𝑓′𝑡𝑡𝐴𝐴𝑓𝑓.𝑡𝑡 (3b)
for top flange (1b)
4.2 Design for flexural effectsThe imposed UDL induces flexure in the webs and a combination
of flexural and axial load effects in the flanges. This requires
satisfying the requirements of Clause 3.5 of AS1720.1 – 2010, for
combined bending and axial load effects. The equations below
apply to a simply supported beam and would need to be interpreted
correctly for use with continuous beams.
Bending capacity of the section above the centroid is given by:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
6
4 Design procedureThe design procedure has three fundamental stages:
1. Identifying the geometric characteristics of the cross-section of the composite beam. 2. Evaluation of the strength capacity.3. Assessment of the serviceability limit states.
4.1 Cross-section characteristicsIn cases where the flanges and webs have differing properties (such as the use of cross laminated timber), it is necessary to determine the modular ratio and apply this to determine effective widths of members, prior to determination of the section properties.
For irregular sections (e.g. where the top and bottom flanges are different) the location of the centroid must be determined, in order to calculate the relevant section properties.
It is strongly recommended that the c/c web spacing be such that shear lag effects do not occur in the flanges. This is normally met by satisfying Equation 1.
𝑏𝑏𝑓𝑓.𝑡𝑡 ≤ 𝑀𝑀𝑀𝑀𝑀𝑀 (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠), �𝑏𝑏𝑤𝑤 + 20 × ℎ𝑓𝑓.𝑡𝑡� for bottom flange (1a)
𝑏𝑏𝑓𝑓.𝑐𝑐 ≤ (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) for top flange (1b)
4.2 Design for flexural effectsThe imposed UDL induces flexure in the webs and a combination of flexural and axial load effects in the flanges. This requires satisfying the requirements of Clause 3.5 of AS1720.1 –2010, for combined bending and axial load effects. The equations below apply to a simplysupported beam and would need to be interpreted correctly for use with continuous beams.
Bending capacity of the section above the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡 (2a)
Bending capacity of the section below the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑏𝑏𝑡𝑡𝑡𝑡 (2b)
Where: k4, k6, k9 and k12, will all normally equal 1.0
Axial capacity (compression) of the top flange is given by:
𝑀𝑀𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘12𝑓𝑓′𝑐𝑐𝐴𝐴𝑓𝑓.𝑐𝑐 (3a)
Axial capacity (tension) of the bottom flange is given by:
𝑀𝑀𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘11𝑓𝑓′𝑡𝑡𝐴𝐴𝑓𝑓.𝑡𝑡 (3b)
(2a)
Bending capacity of the section below the centroid is given by:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
6
4 Design procedureThe design procedure has three fundamental stages:
1. Identifying the geometric characteristics of the cross-section of the composite beam. 2. Evaluation of the strength capacity.3. Assessment of the serviceability limit states.
4.1 Cross-section characteristicsIn cases where the flanges and webs have differing properties (such as the use of cross laminated timber), it is necessary to determine the modular ratio and apply this to determine effective widths of members, prior to determination of the section properties.
For irregular sections (e.g. where the top and bottom flanges are different) the location of the centroid must be determined, in order to calculate the relevant section properties.
It is strongly recommended that the c/c web spacing be such that shear lag effects do not occur in the flanges. This is normally met by satisfying Equation 1.
𝑏𝑏𝑓𝑓.𝑡𝑡 ≤ 𝑀𝑀𝑀𝑀𝑀𝑀 (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠), �𝑏𝑏𝑤𝑤 + 20 × ℎ𝑓𝑓.𝑡𝑡� for bottom flange (1a)
𝑏𝑏𝑓𝑓.𝑐𝑐 ≤ (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) for top flange (1b)
4.2 Design for flexural effectsThe imposed UDL induces flexure in the webs and a combination of flexural and axial load effects in the flanges. This requires satisfying the requirements of Clause 3.5 of AS1720.1 –2010, for combined bending and axial load effects. The equations below apply to a simplysupported beam and would need to be interpreted correctly for use with continuous beams.
Bending capacity of the section above the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡 (2a)
Bending capacity of the section below the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑏𝑏𝑡𝑡𝑡𝑡 (2b)
Where: k4, k6, k9 and k12, will all normally equal 1.0
Axial capacity (compression) of the top flange is given by:
𝑀𝑀𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘12𝑓𝑓′𝑐𝑐𝐴𝐴𝑓𝑓.𝑐𝑐 (3a)
Axial capacity (tension) of the bottom flange is given by:
𝑀𝑀𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘11𝑓𝑓′𝑡𝑡𝐴𝐴𝑓𝑓.𝑡𝑡 (3b)
(2b)
Where: k4, k6, k9 and k12, will all normally equal 1.0
Axial capacity (compression) of the top flange is given by:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
6
4 Design procedureThe design procedure has three fundamental stages:
1. Identifying the geometric characteristics of the cross-section of the composite beam. 2. Evaluation of the strength capacity.3. Assessment of the serviceability limit states.
4.1 Cross-section characteristicsIn cases where the flanges and webs have differing properties (such as the use of cross laminated timber), it is necessary to determine the modular ratio and apply this to determine effective widths of members, prior to determination of the section properties.
For irregular sections (e.g. where the top and bottom flanges are different) the location of the centroid must be determined, in order to calculate the relevant section properties.
It is strongly recommended that the c/c web spacing be such that shear lag effects do not occur in the flanges. This is normally met by satisfying Equation 1.
𝑏𝑏𝑓𝑓.𝑡𝑡 ≤ 𝑀𝑀𝑀𝑀𝑀𝑀 (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠), �𝑏𝑏𝑤𝑤 + 20 × ℎ𝑓𝑓.𝑡𝑡� for bottom flange (1a)
𝑏𝑏𝑓𝑓.𝑐𝑐 ≤ (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) for top flange (1b)
4.2 Design for flexural effectsThe imposed UDL induces flexure in the webs and a combination of flexural and axial load effects in the flanges. This requires satisfying the requirements of Clause 3.5 of AS1720.1 –2010, for combined bending and axial load effects. The equations below apply to a simplysupported beam and would need to be interpreted correctly for use with continuous beams.
Bending capacity of the section above the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡 (2a)
Bending capacity of the section below the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑏𝑏𝑡𝑡𝑡𝑡 (2b)
Where: k4, k6, k9 and k12, will all normally equal 1.0
Axial capacity (compression) of the top flange is given by:
𝑀𝑀𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘12𝑓𝑓′𝑐𝑐𝐴𝐴𝑓𝑓.𝑐𝑐 (3a)
Axial capacity (tension) of the bottom flange is given by:
𝑀𝑀𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘11𝑓𝑓′𝑡𝑡𝐴𝐴𝑓𝑓.𝑡𝑡 (3b)
(3a)
Axial capacity (tension) of the bottom flange is given by:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
6
4 Design procedureThe design procedure has three fundamental stages:
1. Identifying the geometric characteristics of the cross-section of the composite beam. 2. Evaluation of the strength capacity.3. Assessment of the serviceability limit states.
4.1 Cross-section characteristicsIn cases where the flanges and webs have differing properties (such as the use of cross laminated timber), it is necessary to determine the modular ratio and apply this to determine effective widths of members, prior to determination of the section properties.
For irregular sections (e.g. where the top and bottom flanges are different) the location of the centroid must be determined, in order to calculate the relevant section properties.
It is strongly recommended that the c/c web spacing be such that shear lag effects do not occur in the flanges. This is normally met by satisfying Equation 1.
𝑏𝑏𝑓𝑓.𝑡𝑡 ≤ 𝑀𝑀𝑀𝑀𝑀𝑀 (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠), �𝑏𝑏𝑤𝑤 + 20 × ℎ𝑓𝑓.𝑡𝑡� for bottom flange (1a)
𝑏𝑏𝑓𝑓.𝑐𝑐 ≤ (𝑏𝑏𝑤𝑤 + 0.1 × 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠) for top flange (1b)
4.2 Design for flexural effectsThe imposed UDL induces flexure in the webs and a combination of flexural and axial load effects in the flanges. This requires satisfying the requirements of Clause 3.5 of AS1720.1 –2010, for combined bending and axial load effects. The equations below apply to a simplysupported beam and would need to be interpreted correctly for use with continuous beams.
Bending capacity of the section above the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑡𝑡𝑡𝑡𝑡𝑡 (2a)
Bending capacity of the section below the centroid is given by:
𝑀𝑀𝑑𝑑 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘9𝑘𝑘12𝑓𝑓′𝑏𝑏𝑍𝑍𝑏𝑏𝑡𝑡𝑡𝑡 (2b)
Where: k4, k6, k9 and k12, will all normally equal 1.0
Axial capacity (compression) of the top flange is given by:
𝑀𝑀𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘12𝑓𝑓′𝑐𝑐𝐴𝐴𝑓𝑓.𝑐𝑐 (3a)
Axial capacity (tension) of the bottom flange is given by:
𝑀𝑀𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑘𝑘11𝑓𝑓′𝑡𝑡𝐴𝐴𝑓𝑓.𝑡𝑡 (3b) (3b)
The axial force induced in each flange as a result of the bending
action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b)
(4a)
Axial load induced (tension) in the bottom flange is given by:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b)
(4b)
Combined bending and compression – top flange:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b)
(5a)
and
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b)
(5b)
Combined bending and tension – bottom flange:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b)
(5c)
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b)
(5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of
floor beams. However, a check of the web for shear is recommended:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b)
(6)
Connection details recommended for achieving fully composite
design behaviour are specified in Section 5. The first moment of
shear area and hence the shear flow at the interface between web and
the flanges can be checked using the following equations:
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b)
(7a)
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
7
The axial force induced in each flange as a result of the bending action is calculated using the following equations:
Axial load induced (compression) in the top flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ − ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4a)
Axial load induced (tension) in the bottom flange is given by:
𝑁𝑁𝑐𝑐∗ = 𝑀𝑀∗ × �ℎ𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� × 𝐴𝐴𝑓𝑓.𝑐𝑐 ÷ 𝐼𝐼 (4b)
Combined bending and compression – top flange:
�𝑀𝑀∗
𝑀𝑀𝑑𝑑�2
+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5a)
and
𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑐𝑐∗
𝑁𝑁𝑑𝑑_𝑡𝑡𝑡𝑡𝑡𝑡≤ 1.0 (5b)
Combined bending and tension – bottom flange:
𝑘𝑘12𝑀𝑀∗
𝑀𝑀𝑑𝑑+ 𝑁𝑁𝑡𝑡
∗
𝑁𝑁𝑑𝑑_𝑏𝑏𝑡𝑡𝑡𝑡≤ 1.0 (5c)
𝑀𝑀∗
𝑀𝑀𝑑𝑑− 𝑍𝑍
𝐴𝐴× 𝑁𝑁𝑡𝑡
∗
𝑀𝑀𝑑𝑑≤ 1.0 (5d)
4.3 Design for shear effectsShear is generally not a limiting state for strength in these types of floor beams. However, a check of the web for shear is recommended:
𝑉𝑉𝑐𝑐 = ∅𝑘𝑘1𝑘𝑘4𝑘𝑘6𝑓𝑓′𝑠𝑠𝐴𝐴𝑠𝑠 (6)
Connection details recommended for achieving fully composite design behaviour are specified in Section 5. The first moment of shear area and hence the shear flow at the interface between web and the flanges can be checked using the following equations:
𝑄𝑄𝑐𝑐𝑐𝑐𝑡𝑡 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7a)
𝑄𝑄𝑏𝑏𝑐𝑐𝑐𝑐 = 𝐴𝐴𝑓𝑓.𝑐𝑐�ℎ𝑐𝑐 − ℎ𝑓𝑓.𝑐𝑐/2� (7b) (7b)STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
8
𝑞𝑞𝑡𝑡𝑡𝑡𝑡𝑡 = 𝑄𝑄𝑡𝑡𝑡𝑡𝑡𝑡 × (𝑉𝑉∗ ÷ 𝐼𝐼) (8a)
𝑞𝑞𝑏𝑏𝑡𝑡𝑡𝑡 = 𝑄𝑄𝑏𝑏𝑡𝑡𝑡𝑡 × (𝑉𝑉∗ ÷ 𝐼𝐼) (8b)
4.4 Design for deflection & dynamicsLimits on the deflection and dynamic behaviour need to be determined to suit the functional requirements of the flooring system, in accordance with Guidelines presented in Appendix Bof AS1720.1 – 2010.
5 Manufacturing provisionsThe recommended procedure for connecting flanges to webs is “gluing and screwing”. The design philosophy behind this is that the glue creates an infinitely stiff bond to resist serviceability load events, whilst the screws provided a mechanical connection that can ensure composite action occurs at the design ultimate load events.
In the beams tested, the glue bond was a PURBOND polyurethane glue, fastened using 14G Type 17 screws (as indicated in Figure 3) at nominal centres of 400mm c/c along the entire length of the web.
Figure 3: Dimensions of the Type 17 screws used for manufacture
(8a)
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2
8
𝑞𝑞𝑡𝑡𝑡𝑡𝑡𝑡 = 𝑄𝑄𝑡𝑡𝑡𝑡𝑡𝑡 × (𝑉𝑉∗ ÷ 𝐼𝐼) (8a)
𝑞𝑞𝑏𝑏𝑡𝑡𝑡𝑡 = 𝑄𝑄𝑏𝑏𝑡𝑡𝑡𝑡 × (𝑉𝑉∗ ÷ 𝐼𝐼) (8b)
4.4 Design for deflection & dynamicsLimits on the deflection and dynamic behaviour need to be determined to suit the functional requirements of the flooring system, in accordance with Guidelines presented in Appendix Bof AS1720.1 – 2010.
5 Manufacturing provisionsThe recommended procedure for connecting flanges to webs is “gluing and screwing”. The design philosophy behind this is that the glue creates an infinitely stiff bond to resist serviceability load events, whilst the screws provided a mechanical connection that can ensure composite action occurs at the design ultimate load events.
In the beams tested, the glue bond was a PURBOND polyurethane glue, fastened using 14G Type 17 screws (as indicated in Figure 3) at nominal centres of 400mm c/c along the entire length of the web.
Figure 3: Dimensions of the Type 17 screws used for manufacture
(8b)
4.4 Design for deflection & dynamicsLimits on the deflection and dynamic behaviour need to be
determined to suit the functional requirements of the flooring
system, in accordance with Guidelines presented in Appendix B of
AS1720.1 – 2010.
A more rigorous dynamic assessment can be carried out based
on the fundamental frequency of the timber floor – noting that this
formula predicts the behaviour of an individual beam element, which
will generally be conservative as a prediction of the floor system
behaviour. Prediction of the first fundamental frequency of simply
supported timber floor beam is based on an empirically derived
methodology, which is summarised in the formula below:
4.4 Design for deflection & dynamics Limits on the deflection and dynamic behaviour need to be determined to suit the functional requirements of the flooring system, in accordance with Guidelines presented in Appendix B of AS1720.1 – 2010. A more rigorous dynamic assessment can be carried out based on the fundamental frequency of the timber floor – noting that this formula predicts the behaviour of an individual beam element, which will generally be conservative as a prediction of the floor system behaviour. Prediction of the first fundamental frequency of simply supported timber floor beam is based on an empirically derived methodology, which is summarised in the formula below:
Nat Freq (Hz) =
where: EIeff is the effective stiffness of the timber beam cross-‐section and will need to be derived based on the modular ratio if the web and flanges have different properties, G is the self-‐weight and all units are in N mm.
Currently accepted design methods for timber floors such AS 1684, are generally based upon the assumption that acceptable performance of the floor is considered to occur when the fundamental frequency exceeds 8 Hz. However, this is a simplification and recent studies (Hamm, et al. 2012) indicate that lower frequencies in the 3.5 to 5.5 Hz range, may also be acceptable. A more comprehensive assessment of the dynamic performance of the floor where the dynamic performance is deemed to be critical can be undertaken based on quantifying a “Response Factor” (Willford and Young 2009 and Smith et al. 2006). This method is based on concrete and steel-concrete composite floor design but is considered to be equally applicable to timber floors. However, the method will normally require the use of finite element modelling to establish the dynamic parameters of the floor such as natural frequencies, mode shapes and damping. Ammendment to Notations: EIeff - effective stiffness of timber floor cross-section G - self-weight
where: EIeff is the effective stiffness of the timber beam cross-section and will need to be derived based on the modular ratio if the web and flanges have different properties, G is the self-weight and all units are in N mm.
Introduction Design requirements Notation Design procedure Manufacturing provisions
9
Currently accepted design methods for timber floors
such AS 1684, are generally based upon the assumption that
acceptable performance of the floor is considered to occur when
the fundamental frequency exceeds 8 Hz. However, this is a
simplification and recent studies (Hamm, et al. 2012) indicate that
lower frequencies in the 3.5 to 5.5 Hz range, may also be acceptable.
A more comprehensive assessment of the dynamic performance of
the floor where the dynamic performance is deemed to be critical can
be undertaken based on quantifying a “Response Factor” (Willford
and Young 2009 and Smith et al. 2006). This method is based on
concrete and steel-concrete composite floor design but is considered
to be equally applicable to timber floors. However, the method will
normally require the use of finite element modelling to establish the
dynamic parameters of the floor such as natural frequencies, mode
shapes and damping.
5. Manufacturing provisions
The recommended procedure for connecting flanges to webs is
“gluing and screwing”. The design philosophy behind this is that the
glue creates an infinitely stiff bond to resist serviceability load events,
whilst the screws provided a mechanical connection that can ensure
composite action occurs at the design ultimate load events.
In the beams tested, the glue bond was a PURBOND
polyurethane glue, fastened using 14G Type 17 screws (as indicated
in Figure 3) at nominal centres of 400mm c/c along the entire length
of the web.
Figure 3: Dimensions of the Type 17 screws used for manufacture
4.4 Design for deflection & dynamicsLimits on the deflection and dynamic behaviour need to be determined to suit the functional requirements of the flooring system, in accordance with Guidelines presented in Appendix B of AS1720.1 – 2010.
5 Manufacturing provisionsThe recommended procedure for connecting flanges to webs is “gluing and screwing”. The design philosophy behind this is that the glue creates an infinitely stiff bond to resist serviceability load events, whilst the screws provided a mechanical connection that can ensure composite action occurs at the design ultimate load events.
In the beams tested, the glue bond was a PURBOND polyurethane glue, fastened using 14G Type 17 screws (as indicated in Figure 3) at nominal centres of 400mm c/c along the entire length of the web.
Figure 3: Dimensions of the Type 17 screws used for manufacture
STIC 2013-44 Timber Design Procedures - ver May 16 2013 Rev 2.pages
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Introduction Design requirements Notation Design procedure Manufacturing provisions