The Hong Kong Polytechnic University
Material Science and Technology in Engineering Conference Frontiers of Sustainable Materials
Embodied Carbon of Concrete / Steel - Building
Structures using Nonlinear Optimization
Ir Julian LEE Manager - Research, Construction Industry Council
Siu-Lai CHAN, Han YU Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University
25 June 2015
Dept. of Civil and Environmental Engineering
The Hong Kong Polytechnic University
The Hong Kong Polytechnic University
2
1 Background
2 Research Aim and Scope
3 Methodology
4 Results Discussion
5 Conclusions and Prospects
Outline
The Hong Kong Polytechnic University
#1. Building and Construction (>40%)
#2. Transportation (~20%)
#3. Industry (~20%)
Source: International Energy Agency (2012) CO2 Emissions from Fuel Combustion
Buildings in Hong Kong accounted for 60% of total local GHG emissions.
3
Buildings and Construction
Contribution to Global GHG Emissions
The Hong Kong Polytechnic University
• Actions Taken towards Energy Efficiency Worldwide
4
Building Energy Use & Actions Taken
Sources:
Asia Business Council (ed.) (2007) Building Energy Efficiency – Why Green Buildings are Key to Asia’s Future.
European Insulation Manufacturers Association (Eurima). (ed.). (2011). Energy Efficiency in Buildings: Tackling Climate Change.
U.S. Department of Energy (ed.) (2012) Buildings Sector. Buildings Energy Data Book. Energy Efficiency & Renewable Energy.
• Energy Consumption by Building Sector Worldwide
The Hong Kong Polytechnic University 5
Construction sector accounts for second largest carbon footprint
85% of carbon emission is embodied in upstream materials and services
Construction Material Consumption
& Carbon Footprint by Construction Sector in HK
Source: WWF-Hong Kong (2011), Hong Kong Ecological Footprint Report 2010, Paths to Sustainable Future, Hong Kong
California Integrated Waste Management Board (CIWMB) (2000). Designing with Vision: A Technical Manual for Materials Choices in Sustainable Construction.
Among various economic sectors, the construction industry consumes 40% of materials entering the global economy.
The Hong Kong Polytechnic University
6
UK USA KOREA CANADA
JAPAN FRANCE N. AMERICA TAIWAN
Carbon Footprint & Actions Taken
The Hong Kong Polytechnic University 7
CIC Carbon Labelling Scheme for Construction Products
Cement Rebar Structural Steel
Aim: Provide verifiable and accurate information on the carbon footprint of construction materials for users to make informed decision thereby to combat the climate change.
Material Coverage
Ready-mixed Concrete
The Hong Kong Polytechnic University 8
Development of the Scheme
CIC has commissioned HKU to conduct a research on:
Establishment a Hong Kong Based Carbon Labelling Framework
for Construction Materials (the “Research”)
Prof. Thomas NG, Department of Civil Engineering, HKU
Research period: 15 months; completed in late 2012
Two of the key functions of the Construction Industry
Council (CIC):
To promote green building practices and sustainable
construction
To encourage research activities and the use of innovative
techniques and, to establish or promote the establishment of
standards for the construction industry
The Hong Kong Polytechnic University
Development of the Scheme
9
Inspiration of Carbon Labelling for construction products 2009
HKU developed the carbon labelling framework for 6 types of construction products 2012
CIC Carbon Labelling Scheme Launched and open for applications Jan 2014
Research Phase II commences (covering 10 additional product types incl. concrete, stainless steel, asphalt, etc.) Mar 2014
Implementation& Development
Promote the application and the use of low carbon materials
Low-carbon design/construction
Carbon tendering
Export service on carbon certification
The Hong Kong Polytechnic University
Involved Stakeholders / Organisations
10
The Hong Kong Polytechnic University 11
Concrete is everywhere. It is the second
most consumed material after water, the
most widely used man-made material and
it shapes our built environment.
Reinforcing bar and structural steel are
extensively used in the construction
industry as they are the “bones” of
buildings.
Concrete vs. Steel (Lower Carbon?)
(Direct Industrial CO2 Emission, 2006)
Concrete
Source: Industrial Development Report, 2011
Embodied Carbon Footprint
Ready-mixed Concrete vs. Steel
Material Type Carbon Footprint (kg CO2 e/kg) * a general range collected from worldwide data sources
Concrete 0.1 ~ 0.2 depending on strength, SCM rate, cement carbon footprint, etc.
Virgin Steel 1.5 ~ 3.5 depending on the manufacturing furnace type, fuel type and use, etc.
Recycled Steel 0.5 ~ 1.5 depending on recycled scrap usage, furnace type, fuel type and use, etc.
The Hong Kong Polytechnic University 12
What is missing?
What is missing:-
Least Material Consumption ≠ Least Carbon Emissions
Optimised Structure Design ≠ Lowest Carbon Footprint of Structure
Selection and Use of Low Carbon Material ≠ Lowest Carbon Footprint of Building Structure
Smart Integration of Structural Design and Low Carbon Materials
Lowest Carbon Footprint of the Whole Building Structure?
What we know:-
Building & Construction – Consumes Much Energy and Generates GHG Emissions
Building Design – Structural Safety, Economic Efficiency & Environmental Sustainability
Material Use – Associated with Embodied Carbon (EC) & Energy
What we are doing:-
Energy Supply Increase Energy Efficiency Improvement (Green Building (GB) techniques, GB rating tools, etc.)
Optimised Structural Design is Saving Material Consumption
Carbon Labelling Scheme is Promoting Use and Manufacture of Low Carbon Materials
The Hong Kong Polytechnic University
• This study aims to examine the potential of embodied carbon reduction through optimising different steel and reinforced concrete structural designs (typical Hong Kong Layout with local geological condition, loading & design requirements such as wind load).
The Nonlinear Optimization Method will be used to optimise the structural design of building structures which enables the safety, economic efficiency as well as environmental sustainability.
The embodied carbon footprint data of ready-mixed concrete and steel (virgin / recycled) will be used to calculate the overall carbon footprint of optimised building structure
Comparison will be conducted to investigate the influence of structure design and material usage on the building's overall carbon footprint.
13
Research Aim and Scope
The Hong Kong Polytechnic University 14
Methodology
Building Model Configurations
Steel • Steel Beam + Steel Columns
• Coupled with Concrete Corewall
Reinforced Concrete
The Hong Kong Polytechnic University 15
Methodology
Building Model Configurations (Cont.)
Steel Building • Steel Beams+Steel Columns • Concrete Core Wall (Beams)
RC Building • RC Beams+RC Columns • Concrete Core Wall (Beams)
Both types are in 25 floors Maximum Height = 97.6m Plan Area = 27.69m x 23.26m
The Hong Kong Polytechnic University 16
Methodology
Computer Analysis Method
Steel Building • Second-order plastic (P-Δ-δ) analysis RC Building • Linear elastic analysis
3-D analysis and modeling are used in determining the capacities and forces in members and connections.
Computer Programme Used • NAF serious – Nonlinear Integrated
Design and Analysis (NAF-NIDA) version 9
All design shall be in accordance with the BD of the Hong
Kong SAR Government. All aspects of the structural design
shall comply with:
1. Hong Kong Building (Construction) Regulations 1990
2. Code of Practice for Structural Use of Concrete 2004
3. Code of Practice for the Structural Uses of Steel, 2011
4. Code of Practice on Wind effects in Hong Kong, 2004
5. Code of Practice for Fire Resisting Construction 1996
6. BS8007 Design of Concrete Structures for Retaining
Aqueous Liquid
7. BS4466:1989 Schedule, dimensioning, bending and
cutting of steel reinforcement for concrete
8. Practice Notes for AP/RSE/RGE No. APP-68 (PNAP 173)
Design and Construction of Cantilevered Concrete
Structures
9. Eurocode-3, EN 1993-1-8, Design of joints, 2005
The Hong Kong Polytechnic University 17
Methodology
Computer Analysis Method (cont.)
Load combinations for ultimate limit state (ULS) and serviceability limit state (SLS) checking are considered
Second-order analysis of constant load Newton-Raphson method is employed to account for both P-Δ and P-δ effects, as well as initial imperfections
Only section capacity check by is adequate No need of traditional member design
Fc(Δx+δx) & Fc(Δy+δy) - Additional moments due to frame & member deflections including effects of initial imperfections; Member lateral-torsional buckling check is carried out by replacing Mcx in Equation (1) by the buckling resistance moment Mb.
(1)
(2)
No plastic moment re-distribution is
allowed in the “Advanced Analysis”
in accordance with HKSC2011
The Hong Kong Polytechnic University 18
Methodology
Control of Variation
Comparison 1: Superstructure Only (Sup) • Steel Building (Core wall in C60, C80, C100; Steel Section / Bar in Virgin, 39% recycled
scrap, 59% recycled scrap)
• RC Building in C60 (Steel Bar in Virgin, 39% recycled scrap, 59% recycled scrap)
• RC Building in C80 (As above)
• RC Building in C100 (As above)
Comparison 2: Superstructure + Foundation (Sup + F) Variation the same as above in Comparison 1 • Steel Building • RC Building in C60 • RC Building in C80 • RC Building in C100
The Hong Kong Polytechnic University
• Due to the limited data collected from Hong Kong local industry and market, this study firstly applies the carbon footprint data obtained from Inventory of Embodied Carbon & Energy (ICE), a comprehensive carbon footprint database for construction materials developed by UK.
• Concrete (C20 – C50;
100% OPC; PFA 15% / 30% replacement; GGBS
25% / 50% replacement).
• Steel (Section, Bar, pipe, plate;
100% virgin;39%, 59% recycled scrap)
19
Methodology
Embodied Carbon Database
Avg value
C 60, C80, C100
The Hong Kong Polytechnic University
Concrete Grade 100% OPC (Upper Limit) 50% GGBS (Lower Limit) Average Value
C60 491 306 413
C80 598 381 507
C100 * 598 381 507
20
*The carbon footprint value of super high strength concrete will not be increased with the increasing strength but tending to be steady. It is assumed that the carbon footprint of C100 the same as the C80.
The Carbon footprint data of concrete applied in this study (unit: kg CO2e/m3) :
The Carbon footprint data of steel applied in this study (unit: kg CO2e/kg) :
Steel Type 100% virgin steel 39% recycled scrap 59% recycled scrap
Section 3.03 2.03 1.53
Bar 2.77 1.86 1.40
Methodology
Embodied Carbon Data
The Hong Kong Polytechnic University 21
Results Discussion
1.1 Superstructure(Sup) Total Weight
Weight (kN) Steel Building RC Building in C60 RC Building in C80 RC Building in C100
Section 8654 0 0 0
Concrete 47636 98239 86560 76668
Bar 5163 10893 10001 9640
Total 61452 109132 96561 86308
8654
0
0
0
47636
98239
86560
76668
5163
10893
10001
9640
0 20000 40000 60000 80000 100000 120000
Steel
C60
C80
C100
WEIGHT (KN)
TOTAL WEIGHTS COMPARISON
Section Concrete Bar
The Hong Kong Polytechnic University 22
Results Discussion
1.2 Sup In Different Concrete Grades
Steel Building, 5.13
Steel Building, 4.97
Steel Buiilding, 4.75
RC Building, 5.13
RC Building, 4.80
RC Building, 4.35
0.00 1.00 2.00 3.00 4.00 5.00 6.00
C60 UL
C60 Avg
C60 LL
CO
NC
RET
E V
AR
IETY
ICE Virgin Steel with Different Concrete
Steel Building, 5.34
Steel Building, 5.16
Steel Building, 4.90
RC Building, 5.02
RC Building, 4.69
RC Building, 4.23
0.00 1.00 2.00 3.00 4.00 5.00 6.00
C80 UL
C80 Avg
C80 LL
CO
NC
RET
E V
AR
IETY
Steel Building, 5.34
Steel Building, 5.16
Steel Building, 4.90
RC Building, 4.67
RC Building, 4.37
RC Building, 3.96
0.00 1.00 2.00 3.00 4.00 5.00 6.00
C100 UL
C100 Avg
C100 LL
ECe value (10^6 kgCO2e/m3)
CO
NC
RET
E V
AR
IETY
Concrete Steel
Concrete Grade Increases---
• Total Embodied Carbon
decreases
• The Difference of Total EC values between RC and Steel Buildings increases
• Same trends apply to models using recycled steel
RC Building Steel Building
The Hong Kong Polytechnic University 23
Results Discussion
1.3 Sup In Different Kinds of Steel
Steel Building, 5.13
Steel Building, 3.76
Steel Building, 3.08
RC Building, 5.13
RC Building, 4.12
RC Building, 3.60
0.00 1.00 2.00 3.00 4.00 5.00 6.00
VIR
GIN
39
%R
59
%R
ECe Value (10^6 kgCO2e/m3)
Stee
l Var
iety
C60 UL with Different Steel
Steel Building, 4.97
Steel Building, 3.61
Steel Building, 2.92
RC Building, 4.80
RC Building, 3.79
RC Building, 3.28
0.00 1.00 2.00 3.00 4.00 5.00 6.00
VIR
GIN
39
%R
59
%R
ECe Value (10^6 kgCO2e/m3)
Stee
l Var
iety
C60 Avg with Different Steel
Steel Building, 4.75
Steel Building, 3.39
Steel Building, 2.71
RC Building, 4.35
RC Building, 3.34
RC Building, 2.83
0.00 1.00 2.00 3.00 4.00 5.00 6.00
VIR
GIN
39
%R
59
%R
ECe Value (10^6 kgCO2e/m3)
Stee
l Var
iety
C60 LL with Different Steel
Recycled Content of Scrap in Steel Products Increases--
• Total Embodied Carbon
decreases
• The advantage of steel building in terms of total EC increases
• Same trends apply to models in C80 & C100
The Hong Kong Polytechnic University
Applicant Region Product Category Carbon Footprint Value Rebar and Structural Steel Unit: tonne CO2e/tonne
Thailand Section 0.55 Mainland China Pipe 2.95
Taiwan Section 1.37 Middle East Rebar 2.08
Middle East Section 2.36
Hong Kong
Ready-mixed Concrete Unit: kg CO2e/m3 concrete C30s 240 C40s 308 C40s 209 C40s 229
C40s 233
C40s 255
C40s 287 C40s 282 C60s 310 C60s 240
24
Results Discussion
CIC Carbon Labelling Applicant Data
The Hong Kong Polytechnic University
Steel Bldg, 4.97
Steel Bldg, 3.61
Steel Bldg, 2.92
Steel Bldg, 2.42
RC Bldg, 4.80
RC Bldg, 3.79
RC Bldg, 3.28
RC Bldg, 4.03
0.00 1.00 2.00 3.00 4.00 5.00 6.00
VIR
GIN
3
9%
R
59
%R
H
K
AP
PLI
CA
NT
ECe Value (10^6 kgCO2e/m3)
Stee
l Var
iety
C60 Avg with Different Steel
25
Results Discussion
1.3 Sup In Different Kinds of Steel
• Keep the Embodied Carbon Data for C60 from ICE unchanged
• Data for steel section and steel rebar obtained from CIC Carbon Labelling Applicants (certain content of steel is using recycled scrap as raw material)
Steel Section ECe = 0.55 kgCO2e/kg Steel Rebar ECe = 2.08 kgCO2e/kg
Steel Bldg, 5.13
Steel Bldg, 3.76
Steel Bldg, 3.08
Steel Bldg, 2.57
RC Bldg, 5.13
RC Bldg, 4.12
RC Bldg, 3.60
RC Bldg, 4.36
0.00 1.00 2.00 3.00 4.00 5.00 6.00
VIR
GIN
3
9%
R
59
%R
H
K
AP
PLI
CA
NT
ECe Value (10^6 kgCO2e/m3)
Stee
l Var
iety
C60 UL with Different Steel
Steel Bldg, 4.75
Steel Bldg, 3.39
Steel Bldg, 2.71
Steel Bldg, 2.20
RC Bldg, 4.35
RC Bldg, 3.34
RC Bldg, 2.83
RC Bldg, 3.59
0.00 1.00 2.00 3.00 4.00 5.00 6.00
VIR
GIN
3
9%
R
59
%R
H
K
AP
PLI
CA
NT
ECe Value (10^6 kgCO2e/m3)
Stee
l Var
iety
C60 LL with Different Steel
The Hong Kong Polytechnic University
-25%
-20%
-15%
-10%
-5%
0%
5%
10%
15%
200 250 300 350 400 450 500 550 600
Stee
l Bu
ildin
g A
dva
nta
ge E
ffec
t
Concrete ECe (kgCO2e/m3)
Steel Building Advantage Effect to RC Building with Concrete in Different Grades
Virgin 0%R C60 39%R C60 59%R C60
Virgin 0%R C80 39%R C80 59%R C80
Virgin 0%R C100 39%R C100 59%R C100
39%
0%
26
Results Discussion 1.4 Sup Steel Building Advantage Effect
• As the Concrete with higher ECe in use
The advantage effect of Steel
Building presents especially when
recycled steel is in use
• Recycled Content of Scrap in Steel
Products Increases—
The advantage of steel building
in terms of total EC increases
RC Building still wins with high
strength concrete in use.
LL
Avg
UL
C60 C80
C100
59%
• Under what condition, Steel Building’s carbon footprint would be lower than RC Building?
The Hong Kong Polytechnic University
41.30% 40.51% 39.19%
-25%
-15%
-5%
5%
15%
25%
35%
45%
200 250 300 350 400 450 500 550 600
Stee
l Bu
ildin
g A
dva
nta
ge E
ffec
t
Concrete ECe (kgCO2e/m3
Steel Building Advantage Effect to RC Building with Concrete in Different Grades
Virgin 0%R C60 39%R C60 59%R C60
Virgin 0%R C80 39%R C80 59%R C80
HK Applicant C60
27
Results Discussion 1.4 Sup Steel Building Advantage Effect
• Keep the Embodied Carbon Data for C60 from ICE unchanged
• Data for steel section and steel rebar obtained from Applicants in HK
• Steel Section’s Embodied Carbon Value is as low as 0.55 kgCO2e/kg
• By using the steel with low ECe value, the steel building design option has absolute advantage in terms of carbon footprint over RC building.
LL Avg UL
59%
39%
0%
The Hong Kong Polytechnic University 28
Comparison
1.5 Sup Total EC Values Comparisons
0
1
2
3
4
5
6
-10% 0% 10% 20% 30% 40% 50% 60%
Tota
l EC
e (
10^6
kgC
O2/
kg)
Percentage of Recycled Steel Included in Whole Building
Total Carbon Emission Equivalent Values Comparison for Steel and RC Buildings in C60 Avg (Superstructure Only)
• The more recycled steel used, the more environmental friendly the design will be.
• However, it is not practical to use recycled steel in the whole building structure due to size limitation of recycled steel products.
• Q: How much percentage of the recycled steel accounts for in the overall steel consumption could make the Steel Building be lower carbon than RC Building?
• < 28% of Recycled Steel RC Bldg
• > 28% of Recycled Steel Steel Bldg
0
1
2
3
4
5
6
-10% 0% 10% 20% 30% 40% 50% 60%
Tota
l EC
e (
10^6
kgC
O2/k
g)
Percentage of Recycled Steel Included Whole Building
Total Carbon Emission Equivalent Values Comparison
Steel C60 Avg
RC C60 Avg
Steel C80 Avg
RC C80 Avg
Steel C100 Avg
RC C100 Avg
The Hong Kong Polytechnic University
0
1
2
3
4
5
6
-10% 0% 10% 20% 30% 40% 50% 60%
Tota
l EC
e (
10^6
kgC
O2/
kg)
Percentage of Recycled Steel Included in Whole Building
Total Carbon Emission Equivalent Values Comparison for Steel and RC Buildings in C100 Avg (Superstructure Only)
St100
RC100
29
Comparison 1.5 Sup Total EC Values Comparisons (cont.)
0
1
2
3
4
5
6
-10% 0% 10% 20% 30% 40% 50% 60%
Tota
l EC
e (1
0^6k
gCO
2/kg
)
Percentage of Recycled Steel Included in Whole Building
Total Carbon Emission Equivalent Values Comparison for Steel and RC Buildings in C80 Avg (Superstructure Only)
St80
RC80
• ?% of Recycled Steel RC Bldg
• < 54% of Recycled Steel RC Bldg
• > 54% of Recycled Steel Steel Bldg
The Hong Kong Polytechnic University 30
Results Discussion 1.6 Sup+F Total EC Values Comparisons
• From 28% (Sup) to 5% (Sup + F) • < 5% of Recycled Steel RC Bldg • > 5% of Recycled Steel Steel Bldg
• From 54% (Sup) to 32% (Sup + F) • < 32% of Recycled Steel RC Bldg • > 32% of Recycled Steel Steel Bldg
By adding foundation, the concrete usage dramatically increases:
0
1
2
3
4
5
6
7
-10% 0% 10% 20% 30% 40% 50% 60%
Tota
l EC
e (1
0^6
kgC
O2/
kg)
Percentage of Recycled Steel Included in Whole Building
Total Carbon Emission Equivalent Values Comparison for Steel and RC Buildings in C60 Avg (Superstructure+Foundation)
0
1
2
3
4
5
6
7
-10% 0% 10% 20% 30% 40% 50% 60%
Tota
l EC
e (
10^6
kgC
O2/k
g)
Percentage of Recycled Steel Included in Whole Building
Total Carbon Emission Equivalent Values Comparison for Steel and RC Buildings in C80 Avg (Superstructure+Foundation)
St80 RC80
St80+F RC80+F
The Hong Kong Polytechnic University 31
Results Discussion 1.6 Sup+F Total EC Values Comparisons (cont.)
If Foundation is included, an interception might be found at around 62% • <~62% of Recycled Steel RC Bldg • >~62% of Recycled Steel Steel Bldg
0
1
2
3
4
5
6
7
-10% 0% 10% 20% 30% 40% 50% 60%
Tota
l EC
e (1
0^6
kgC
O2/
kg)
Percentage of Recycled Steel Included in Whole Building
Total Carbon Emission Equivalent Values Comparison for Steel and RC Buildings in C100 Avg (Superstructure+Foundation)
St100 RC100
St100+F RC100+F
The Hong Kong Polytechnic University
• RC Building vs. Steel Building (Which one is lower carbon?)
Material type and constitutes (recycled/virgin steel, recycled percentage, concrete with SCM such as PFA or GGBS, etc.); Combination of material (concrete, rebar, structural steel)
Design (performance requirement, local factor, approach of optimisation)
Material, structural and geotechnical (foundation) condition.
• Composite Structure Building? To be investigated
• More Carbon Footprint Data of Locally Used Material Needed
CIC Carbon Labelling Scheme
• Carbon Footprint Benchmark of Different Building Types
Caron Footprint Index CO2e / GFA
32
Conclusions
The Hong Kong Polytechnic University 33
Future Study
Comparison 3: Superstructure Only – Vary the Building Heights • Steel Building in 15 Floors • RC Building in C60 in 15 Floors • Steel Building in 35 Floors • RC Building in C60 in 35 Floors
Comparison 4: Superstructure + F – Vary the Building Heights • Steel Building in 15 Floors • RC Building in C60 in 15 Floors • Steel Building in 35 Floors • RC Building in C60 in 35 Floors
Comparison 5: Change to Composite Floor System • Steel Building in 12 Floors (Sup+F) • RC Building in C60 in 12 Floors (Sup+F)
Apply more Hong Kong local values instead of ICE Database to examine the practicability of the study; Provide a guidance for environmental structure system optimization; Link the integrated environmental structural design optimisation with BEAM Plus to easily assess the overall carbon footprint of green building.
The Hong Kong Polytechnic University
Future Development: Think Low Carbon
Low Carbon / Green Materials
Low Carbon / Environmental
Structural Design
Green Building Design and Promotion
G r e e n C u l t u r e
34
The Hong Kong Polytechnic University
Future Development: Think Low Carbon
Low Carbon /
Green Materials
Low Carbon / Environmental
Structural Design
Low carbon design
G r e e n C u l t u r e
Green Building Design and Promotion
35
Identify the low carbon material
options
Propose Structural
Design Options
Compute and compare alternative
structural and material options
Optimize the design to achieve low carbon , low cost and safety
Integrate the design with BEAM Plus to assess the green
performance of the building
Implement the design for construction and further promotion of
green building
The Hong Kong Polytechnic University
Green moving towards a low-carbon city
Green Construction
Green Building
sources of photos:
http://widedscreen.com/3d-architecture-wallpaper-2/
http://www.maximizingprogress.org/2008/11/singapore-green-buildings-in-garden.html
http://www.globalmayorsforum.org/en/citiesdetails.aspx?tid=115&id=129
The Hong Kong Polytechnic University
Thank You
Ir Julian LEE Manager - Research, Construction Industry Council
25 June 2015