ANALYSIS & DESIGN OF
PRESTRESSED TRANSFER PLATE
Ir. LOW HF PhD.Eng (Monash)
PEPC, MIEM, C.ENG MIStructE, MIEAust, CPEng,
MIES, APEC Eng, ASEAN Eng, IntPE
INTRODUCTION
TRANSFER STRUCTURE is required when the layout of shear walls or
columns for the tower block and the podium floor are different
This is to enable the transition of the load from the smaller grid structures
in a tower block to the larger column spacing at the podium and
subsequently to the building foundations.
Transfer beams have
traditionally been
used as transfer
structures to support
the tower blocks.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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INTRODUCTION
PRESTRESSED TRANSFER PLATE = A Thick Prestressed (Post-Tensioned)
Concrete Slab used to transfer shear wall loads to the supporting columns
Design of Prestressed Transfer Plate by Ir Dr Low HF
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PACIFIC PLACE, HONG KONG (1988)
• First documented Prestressed Transfer Plate at Pacific Place Tower in Hong
Kong (1988)
• Alternative Design to use 4.5m thick PT Transfer Plate to support 61 storeys
of hotel/ residential units (74mm per floor)
• Rebars were reduced from 500kg/m3 to 180kg/m3 + 22kg/m3 of tendons
• Built in 3 layers with first 1.5m was designed to support the subsequent pour
Source: Section 5.2 (fib Bulletin 31, 2005)
Design of Prestressed Transfer Plate by Ir Dr Low HF
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SANDWICH CLASS HOUSING- MARINA HABITAT
• Prestressed Transfer Plates to support 3 towers of 42 storeys of
residential units in Ap Lei Chau built in1996
• Alternative Design reduced RC Transfer Plates from 4.2m to 3.2m using
Post-Tensioning (76mm per floor)
• It was casted in 2 layers with the first layer of 1.3m was designed to
support the subsequent casts
Source: Section 5.2 (fib Bulletin 31, 2005)
Design of Prestressed Transfer Plate by Ir Dr Low HF
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Max Span
Length
(m)
PT Plate
Thickness
(mm)
Span/
Depth
Ratio
Plate Thickness
Required for each
supported level
(mm)
Item
Project
Location
No. of Floors
Supported
Above, n
1
Hong Kong
61
9.3
4500
2.1
74
Hong Kong
43
10.5
3200
3.3
74
Hong Kong
47
10.8
3200
3.4
68
Hong Kong
37
11.6
3500
3.3
95
USA
30
6
Pacific Place Building
Sandwich-Class Housing Development,
Ap Lei Chau
Robinson Place4
Residential Block@Tai Ho Road, Tsuen
Wan4
One Eleven Building, Chicago (Unbonded
Tendons)
Nanjing Lou Zi Xiang Service Apartment
China
25
8.0
2000
4.0
80
7
Shanghai Qian Hong Yuan Building6
China
20
8.4
1000
8.4
50
8
9
10
Guangzhou Jia He Yuan Building6
China
China
China
17
22
47
9.0
8.4
1200
1700
2000
7.5
4.9
71
77
43
China
30
India
India
India
India
India
India
Malaysia
12
42
35
13
12
28
30
11.0
9.0
10.5
11.0
12.0
Malaysia
Malaysia
24
Mercury Apartment, Sentul Village9
Alila Bangsar Apartment, KL9
PPAIM Apartment@ Precinct 17
Cyberaya9
Sky Habitat Condo@ Meldrum Hills,
Johor Bahru9
Solstice Apartment@ Pangeo, Cyberjaya9
25
2
3
4
5
11
12
13
14
15
16
17
18
Baoding Kang Le Mall6
Ningbo Zhe Hai Building6
Changzhou Lai Meng City Commercial
Complex
Classic Mall, Chennai
Delhi One, Noida, Delhi8
Aether by Romel Group, Mumbai8
Kapil Tower, Hyderabad8
Phoenix Market City, Chenna8
Vasant Oasis, Mumbai8
Concerto Kiara, Mon't Kiara, KL
1500
50
1800
60
8.0
1000
3000
1250
1000
1250
1800
1400
11.0
3.0
8.4
11.0
9.6
0.0
5.7
83
71
36
77
104
64
47
26
41
10.6
11.5
1800
2600
5.9
4.4
69
63
Malaysia
26
8.7
1200
7.3
46
Malaysia
23
9.3
1200
7.8
52
Malaysia
31
8.4
1500
5.6
48
Twin Arkz Condo@ Bukit Jalil, KL9
Malaysia
29
9.4
1800
5.2
62
26
I-Marcom Condo@Kia Peng, KL9
Malaysia
42
11.8
2700
4.4
64
27
28
The Bay Residence, Kota Kinabalu, Sabah9
Malaysia
Malaysia
18
32
8.4
8.5
1000
1500
8.4
5.7
56
47
19
20
22
23
d'Pristine Medini, Johor9
[1]Source: Section 5.2 (fib Bulletin 31, 2005).
[5] Source: Research and Application of Thick Plate Transition Floor in Tall Building
[4] Source: Table 1-1: Transfer Plate for High-rise Building (Su J. H., 2007) – in Mandarin.
[7] Courtesy of OSD Consultants (M) Sdn Bhd & Utracon India
[3] Source: One Eleven Prestressed Transfer Deck@ www.amsyscoinc.com (Amsysco, 2015).
(He P. L., 2007) – in Mandarin.
6
CURRENT TREND OF PT TRANSFER PLATE
• General rule of thumb, prestressed transfer plate thickness can be taken as
50mm for each level transferred above; normally governed by punching
shear design (max allowable shear stress)
ie. to support a 30 storeys apartment above, initial transfer plate
thickness can be taken as 30 storeys * 50mm/ storey = 1500mm thick
• For typical prestressed transfer plate (7.5 to 8.5m grid) the following
poundage may be applicable.
Rebar = 75 ~ 85kg/m3
Tendon = 20 ~ 30kg/m3
• Minimum concrete grade for prestressed structures allowed is G35; but
concrete grade 45 is commonly used in Malaysia due to punching shear
consideration
Design of Prestressed Transfer Plate by Ir Dr Low HF
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ADVANTAGES OF PT TRANSFER PLATE
• Cost Saving as compared to conventional RC Transfer Beams
• Reduced Concrete Weight => Lower equivalent
concrete thickness compared to conventional RC
beams, reduced load on foundation and amount of
formwork.
• Faster Construction => no complicated transfer
beam reinforcements & simpler bottom formwork
• Aesthetic => provide a flat and pleasing soffit
Design of Prestressed Transfer Plate by Ir Dr Low HF
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RC TRANSFER BEAMS VS PRESTRESS TRANSFER PLATE
CONVENTIONAL RC TRANSFER BEAMS => LARGE BEAMS OF 1500W BY 1800D
PRESTRESSED TRANSFER PLATES => FLAT SLAB OF 1000 THICK
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SPECIAL FEATURES OF A PT TRANSFER PLATE
• Complicated Load Path
2-way Behaviour to transfer shear wall loads in all directions; Irregular shear
wall orientation; => FEM software to predict load path and design
• Interaction with Shear Walls
Transfer plates are relatively less stiff compared to RC transfer beams.
Interaction effect with shear walls (arching effect) are more significant
• First Cast to Support Second Cast
Prestressed transfer plates are casted in layers with the first cast designed to
support the subsequent casts => it experiences changes in section properties
and stresses throughout various construction stages
Design of Prestressed Transfer Plate by Ir Dr Low HF
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BEHAVIOUR OF A PRESTRESS TRANSFER PLATE
Two-Way Slab Behaviour
Line of
Zero Shear
2-way Behaviour to transfer shear wall loads in
all directions; Irregular shear wall orientation;
=> FEM software to predict load path and design
* Sagging at midspan normally governs the design;
except at long cantilevers
Design of Prestressed Transfer Plate by Ir Dr Low HF
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BEHAVIOUR OF A PRESTRESS TRANSFER PLATE
Two-Way Slab Behaviour
Modes of Failure
Source: Practical Yield Line Design by G. Kennedy & C. H. Goodchild
Design of Prestressed Transfer Plate by Ir Dr Low HF
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METHOD OF TRANSFER PLATE MODELLING
• Two type models of analysis modelling for Transfer Plate:
(a) Complete Model considering shear wall interaction effect
(b) Separate Model without shear wall interaction effect
• Complete Model normally considers stage construction analysis; ie no shear
walls are erected during stressing of the transfer plate
• Separate Model transfers the shear wall reactions from one analysis model
to another analysis model of prestressed transfer plate as line loads
Design of Prestressed Transfer Plate by Ir Dr Low HF
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BEHAVIOUR OF A PRESTRESS TRANSFER PLATE
• Shear Wall – Transfer Plate Interaction Effect
Transfer plates are relatively less stiff compared to RC transfer beams.
Interaction effect with shear walls (arching effect) are more imminent
Shear Wall Interaction Effect on Transfer Plate design:
Shear Wall Active
Interactive Zone, L
• Helping effect on Transfer Plate Bending
• Helping effect on Punching Shear/ Localised load below the 2 wall ends
• Redistribution of Column Reaction Loads below Transfer Plate
Span Length, L
(Support to Support)
Deep Beam “hanging”
the transfer plate
Reference: Variation of Wall Vertical Stress Along its Length for Various Wall Heights (Kuang & Zhang, 2003)
Design of Prestressed Transfer Plate by Ir Dr Low HF
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BEHAVIOUR OF A PRESTRESS TRANSFER PLATE
• Shear Wall – Transfer Plate Interaction Effect on Punching Shear
When the shear walls are supported directly onto the column supports, direct
transfer of load from shear walls to columns, reducing the punching shear
force in the transfer plates
When the shear walls are supported away from column supports, localised
forces are developed at the 2 ends of the shear walls due to arching effect.
Source: Punching Shear Stress in PT Transfer Plate of Multi-Story Buildings by Byeonguk Ahn, Thomas HK Kang, SM Kang & JK Yoon
Design of Prestressed Transfer Plate by Ir Dr Low HF
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COMPARISON OF STRESS CONTOUR IN FEM WITH VS
WITHOUR SHEAR WALL INTERACTION EFFECT
Stress contour without shear wall interaction (line load) in X-direction (left) & Y-direction (right)
Stress contour considering shear wall interaction in X-direction (left) & Y-direction (right)
Design of Prestressed Transfer Plate by Ir Dr Low HF
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BEHAVIOUR OF A PRESTRESS TRANSFER PLATE
• Shear Wall – Transfer Plate Interaction Effect on Column Axial Force
• Complete Model considering shear wall interaction effect and Separate
Model (line load) have different column axial force distribution; more
significant for columns near to the core walls (eg. Col 3, 4 & 10)
• If Separate Model is used, it is recommended to consider transfer of
load through the core walls in the analysis model of the Transfer Plate.
Source: Punching Shear Stress in PT Transfer Plate of Multi-Story Buildings by Byeonguk Ahn, Thomas HK Kang, SM Kang & JK Yoon
Design of Prestressed Transfer Plate by Ir Dr Low HF
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BEHAVIOUR OF A PRESTRESS TRANSFER PLATE
• Locked-In Stresses due to Staged Construction & Sequential Stressing
Prestressed transfer plates are casted in layers with the first cast designed to
support the subsequent casts => it experiences changes in section properties and
stresses throughout various construction stages
This type of locked-in or residual stresses cannot be disregarded because it will
add on to the stresses of the complete composite structure.
d
d/3
Z= BD2/6
= B (d/3)2 / 6
= Bd2 / 54
Z= BD2/6
= B (d)2 / 6
= Bd2 / 6
For a 1.5m deep transfer plate (full Section),
M = (1.5m*24kN/m3) * 8.4m ^2 /12;
Z = 1.0*1.5^2 / 6
=> Stresses due to self weight = 0.56MPa
Since Stress= M/Z
Staged casting incurs
9 times tensile stresses
due to self weight
For a 0.5m deep transfer plate (d/3 Sec)
M = (1.5m*24kN/m3) * 8.4m ^2 /12;
Z = 1.0*1.5^2 / 54
=> Stresses due to self weight = 5.04MPa
This locked-in stresses should be taken care by extra tendons in the first cast;
cannot rely on the minimum rebar in the transfer plate which will not help in
terms of stress at SLS
Design of Prestressed Transfer Plate by Ir Dr Low HF
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PT TRANSFER PLATE RESEARCH WITH STRAIN GAUGES
Together with Dr Daniel & Dr Kong of Monash University, we have done the first
experimental research on a prestressed transfer plate that was constructed with
staged casting and sequential stressing.
A total of 131 units of strain gauges (vibrating wire) were cast into the prestressed
transfer plate at various locations to record the concrete strain throughout the
19
tower construction
Design of Prestressed Transfer Plate by Ir Dr Low HF
CONCRETE STRESSES MEASURED AT SITE IN
COMPARISON WITH NUMERICAL FEM MODELS
•
In order to obtain the total stresses from various FE numerical models to
simulate staged construction, Principle of Super-position was adopted during
the combination of stresses from one stage (1st model) to the next (2nd Model).
•
The total stresses from FEM models are compared with the site data.
•
The measured concrete stresses at site demonstrated the similar behavior as
predicted by the numerical FEM models
Combining Stresses of Different FE Models by
Principle of Super-Position
Design of Prestressed Transfer Plate by Ir Dr Low HF
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Variation of Concrete Stresses Across Transfer Plate Thickness
STRESS VARIATION VS DEPTH AT POINT 16B
STRESS VARIATION VS DEPTH AT POINT 6B
•
Sudden changes of stress across the interface joints between the first cast and
second cast were recorded by the strain gauges
•
The observation confirmed the locked-in stresses in the prestressed transfer plate
due to staged construction in line with the construction method (first cast prestressed
to support the second cast of wet concrete) and sequential tendon stressing.
•
These residual stresses were frequently ignored in the design of prestressed transfer
plate. Thus, computation method needs to be established for a safe design in future.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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LIMITATION OF CURRENT DESIGN APPROACH FOR
PRESTRESSED TRANSFER PLATE
•
Separate Model is widely adopted by local consultants
•
The transfer plates are designed-&-built or alternative design proposed by a
prestressing specialist contractor
•
Consultants need to interface the tower and podium design carefully in order
to ensure consistency of load path from the design of tower structure to
transfer plate, and subsequently to the foundation.
•
Common shortfalls:
1.
The transfer plate in the Separate Model is not designed for complete
forces rather than just the gravity loads.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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LIMITATION OF CURRENT DESIGN APPROACH FOR
PRESTRESSED TRANSFER PLATE
•
2.
Common shortfalls:
Not check back the column forces (axial and bending) after alternative
design to convert transfer beams into prestressed transfer plate
Suspended
Shear Walls
Columns
Core Walls
Columns to be checked for buckling and extra slenderness, particularly
double/triple volume, when converted into transfer plate
Design of Prestressed Transfer Plate by Ir Dr Low HF
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LIMITATION OF CURRENT DESIGN APPROACH FOR
PRESTRESSED TRANSFER PLATE
•
Common shortfalls:
3.
Inconsistency in the design assumption for shear walls and transfer plate;
ie, consider the helping effect from the shear wall- transfer plate
interaction, but only design the shear wall for axial loads (without
considering the arching effect – strut-&-tie action)
⇒ reinf. not detailed accordingly.
4.
Not consider the restraint effect (prestress losses) due to the shear walls
if multiple stage stressing are proposed for the transfer plate.
ie, only stress 50% of the tendons during transfer; 2nd stage stressing after
completion of 10 floors above
5.
Not consider induced forces into the transfer plates due to differential
column shortening effect.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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Ir. LOW HF PhD.Eng (Monash)
PEPC, MIEM, C.ENG MIStructE, MIEAust, CPEng,
MIES, APEC Eng, ASEAN Eng, IntPE
Handphone : 019-3571163
Email : lowhf@osdconsultants.com.my
Website : www.osdalliance.com.my
Learn Prestressed Design
https://www.facebook.com/
groups/271051748340014
CODES & DESIGN GUIDELINES
• BS8110-1: 1997: Sec 4 only covers prestressed beams and one-way
spanning slabs; but not flat slab or plate
If a transfer plate were to be designed as
prestressed one-way slab of concrete G45,
then the design flexural tensile stresses
would be
½(5.0 + 5.8) * 0.7 = 3.78N/mm2
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TECHNICAL REPORT, TR43
• Prestressed Transfer Plate behaves as two-way slabs and thus specialist
literature shall be referred.
• Reference is commonly made to Technical Report 43: Post-Tensioned
Concrete Floors Design Handbook by UK Concrete Society
• TR43 allows normalisation of peak stresses of a prestressed flat slab across a
tributary width; and compare with the allowable tensile and compressive
stress
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TR43: 1st Edition VS 2nd Edition
• Two editions of TR43 were issued;
1st Edition issued in 1994 to compliment BS8110
2nd Edition issued in 2004 to compliment EC2
• Both require prestressed design to SLS, whereby
BS:
Load Comb of 1.0DL + 1.0LL
EC: Load Comb of 1.0DL + 1.0LL (Characteristic); if LL reduction
Load Comb of 1.0DL + 0.7LL (Frequent); if NO LL reduction
• At ULS bending capacity and punching shear check
BS:
Load Comb of 1.4DL + 1.6LL
EC: Load Comb of 1.35DL + 1.5LL
• Punching Shear Design to
•
TR43 (1st Edition):
PT Beam Formula for Section Cracked in Flexural
TR43 (2nd Edition):
Prestressed Flat Slab Punching Shear Formula
Both editions do NOT cover Interface Shear Design
Design of Prestressed Transfer Plate by Ir Dr Low HF
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ALLOWABLE STRESS TO TR43 (1ST Edition)
• First edition of TR43 (1994) allows normalisation of stresses across the full
panel (entire tributary width)
• For flat slab design, first edition of TR43 (1994) recommends to adopt
allowable
Tensile stress of 0.45√fcu ; and
Compressive stress of 0.33fcu at midspan and 0.24fcu over support.
• During transfer, TR43 allows tensile stress of 0.36√fci and compressive stress
of 0.5fci.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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ALLOWABLE STRESS TO TR43 (2nd Edition)
• In TR43 2nd Edition (2004), two methods of normalising the stresses are
allowed; (1) Across Full Panel ; (2) Column Strip – Middle Strip Method
= 2.89N/mm2
< 0.45 √fcu
** Spacing of Rebars or Tendons < 500mm; otherwise stress for “without bonded reinf.“ shall be used.
fctm = 0.30* fck 2/3 for concrete C50/60 or below;
eg fcu = 45 => fck = 35 =>fctm = 3.2MPa
Design of Prestressed Transfer Plate by Ir Dr Low HF
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ALLOWABLE STRESS TO TR43 (2nd Edition)
• In TR43 (2nd Edition), two methods of normalising the stresses are allowed;
(1) Across Full Panel ; (2) Column Strip – Middle Strip Method
= 0.57 √fcu
** Spacing of Rebars or Tendons < 500mm; otherwise stress for “without bonded reinf.“ shall be used.
fctm = 0.30* fck 2/3 for concrete C50/60;
eg fcu = 45 => fck = 35 =>fctm = 3.2MPa
Design of Prestressed Transfer Plate by Ir Dr Low HF
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COMPARISON OF ALLOWABLE STRESSES
For comparison purposes, let’s take prestressed transfer plate of
>1000mm thick with concrete G45 (fck, cube)
• Allowable Compressive Stress
Location BS8110
TR43 (1st Edition) TR43 (2nd Edition)
ACI 318M-14
Support
0.33fcu (14.8MPa) 0.24fcu (10.8MPa)
0.3fck (10.5MPa)
0.45fck (15.7MPa)
Span
0.33fcu (14.8MPa) 0.33fcu (14.8MPa)
0.4fck (14.0MPa)
0.45fck (15.7MPa)
• Allowable Tensile Stress
Location
Span/
Support
BS8110
3.78MPa
TR43
(1st Edition)
Full Panel
0.45√fcu
(3.02MPa)
SLS Load Comb:
TR43 (2nd Edition)
Full Panel
Column-Middle Strip
0.9fctm
(2.89MPa)
1.2fctm
(3.85MPa)
ACI 318M-14
Clause R24.5.2.1
Full Panel
0.5√fck
(2.96MPa)
BS8110 = 1.0DL + 1.0LL
EC2 =
1.0DL + 1.0LL (Characteristic)
ACI318 = 1.0DL + 1.0LL (Total Load)
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE ANALYSIS
•
Complicated Load Path
2-way Behaviour to transfer shear wall loads in all directions; Irregular shear wall
orientation; => FEM software to predict load path and design
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE DESIGN FOR SLS
• The critical condition for a prestressed structure is
• During Transfer when the load is minimum and prestress
force is largest
• At Service when the load is maximum and prestress force
is minimum (after losses)
• With these conditions, the following formulas can be written with
limiting stresses for top and bottom fiber for each transfer and
service stage.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE DESIGN FOR SLS
Discussion: Are we supposed to check width based on the normalized stresses
across the full panel?
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE DESIGN FOR REBARS
Q1: Why do we need minimum top reinf. at support?
Q2: Do we need to provide minimum bottom reinf.?
Q3: How to arrange the minimum reinf.?
0.2L
0.2L
1.5d+Col+1.5d
A2: Arching effect in the shear wall causes load
concentration at the 2 wall edges. This point load
effect may cause localized cracking at the soffit
which requires effective mean for crack control
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE PUNCHING SHEAR DESIGN
What’s Punching Shear?
Punching shear is a type of failure of reinforced concrete slabs
subjected to high localized forces. In flat slab structures, this
occurs at column support points. The failure is due to shear.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE PUNCHING SHEAR DESIGN
Effective Punching Shear Force
The critical consideration for shear in flat slab structures is that of punching shear
around the columns.
The shear stresses are increased to allow for the effects of moment transfer.
x
Design of Prestressed Transfer Plate by Ir Dr Low HF
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EXTRACTING PUNCHING SHEAR FORCES FROM FEM
ANALYSIS MODEL FOR DESIGN
When extracting the shear stress from the FEM shell elements, engineers have to
ensure the cut-lines go through the perimeter nodes to avoid “missing” shear force.
If use column reaction to design, the helping effect from the shear wall interaction
will not be realised.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE PUNCHING SHEAR DESIGN
Shear Capacity of Prestressed Elements is made up from
•
•
•
(TR43 2nd Edition)
Concrete shear component, VRd,c (including helping effect of concrete precompression)
Shear steel component, VRd,s
Vertical component of tendons, Vp
When calculating the contribution of prestressing force at ULS, both the direct stress, σcp, and
the beneficial effects due to vertical component of prestress force, should be multiplied by an
appropriate safety factor, γp. *** γp in UK National Annex is taken as 0.9.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE PUNCHING SHEAR DESIGN
Vertical Component of Tendon Force
-reduce the applied shear force at column due to catenary action
-only those tendons passing within 0.5h of the column face can be
considered and the angle of the tendon considered should be that at
0.5h from the column face.
-value should remain constant for outer perimeters
Vp ~ Peff * 8a/S
Where
a = tendon drape (highest profile – lowest profile)
S = tendon span
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE PUNCHING SHEAR DESIGN
Design of Prestressed Transfer Plate by Ir Dr Low HF
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UNDERSTANDING INTERFACING SHEAR
Longitudinal Shear force occurs in between different layers of the structure
=> Develop horizontal shearing stress
Consider two timbers are put together without any glue or nails in between
d
d/2
d/2
d/2
d/2
If they are glued together, the glue will prevent 2 timbers from sliding past each
other
d
This resistance to sliding at the horizontal surface of the interface generates
shear stress which can cause failure if they are weak
If this happens, the strength and stiffness of the structure will be substantially
reduced from d3 to 2*(d/2)3 = d3/4, or 4 times weaker.
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE INTERFACING SHEAR DESIGN
Computing Interfacing Shear Stress
using Linear Elastic Approach
For equilibrium, σc . dA + ∆H = σd . dA
Concrete Area
of 2nd cast, A
y
νh = V. Q / Ib
(N/mm2)
Where
V = vertical shear force
Q = A. y ; refer diagram above
I = moment of inertia
b = width of interface
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE INTERFACING SHEAR DESIGN
Computing Interfacing Shear Stress
using Non-Linear Approach (ULS)
EQ 6.24: BS EN 1992-1-1 (2004)
Where
β = Ratio of longitudinal force in new concrete
area and the total longitudinal force either
in compression or tension zone, both
calculated for the section considered
VEd = Transverse Shear Force (Normal Shear)
z = Lever arm of composite section
bi = width of interface
Concrete 2nd cast
within
Compressive Zone
εcu
y
Concrete 2nd cast
within Tensile Zone
0.85fck
0.4x
Fcd
0.8x
x
z
Apt
Ast
(a) Section
εst
εpt
(b) Strain
Fpt
Fst
β within compressive zone
= y / (0.8x)
β within tensile zone
= Fst / (Fst+Fpt)
(c) Idealised Stress Block to EC2
Flexural Behaviour of Prestressed Beam at Ultimate with Idealised Stress Block to EC2
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE INTERFACING SHEAR DESIGN
BS8110
Nominal links should be of cross section at least 0.15% of the contact area. Spacing should not
exceed 4 times the minimum thickness of the second cast nor 600mm whichever is greater.
As,h /Sh = νh . b / 0.87*460 ; Sh = radial spacing of interfacing links
Design of Prestressed Transfer Plate by Ir Dr Low HF
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TRANSFER PLATE INTERFACING SHEAR DESIGN
BS EN 1992-1-1 (2004)
Design of Prestressed Transfer Plate by Ir Dr Low HF
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COMPARISON OF HORIZONTAL SHEAR CAPACITY
BY DIFFECT CODES VS EXPERIMENTAL RESULTS
Experiments results were compared with the computed
horizontal shear stress capacity by various codes based on
the upper characteristic concrete tensile strength without
material factor
~1.5 times higher than other codes
Design of Prestressed Transfer Plate by Ir Dr Low HF
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PRESTRESS TRANSFER PLATE
DESIGN FLOW CHART
1. Select Stress Limit & Decide on Concrete Grade
2. Member Sizing & Modelling
3. Analysis of Structure
4. Select Prestress Force and Eccentricity
5. Design to comply Allowable Stress Limit at SLS
6. Calculate Prestress Losses
7. Check Deflection at SLS
8. Check Ultimate Moment of Resistance
9. Design for Punching Shear
10. Design for Interfacing Shear (if few times castings)
Design of Prestressed Transfer Plate by Ir Dr Low HF
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Design of Prestressed Transfer Plate by Ir Dr Low HF
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