H30 Academic Year, Department of Architecture and Civil Engineering, Research Presentation Day 2019.02.26
Sustainability Evaluation of Reinforced Concrete Members
No. 0162281
1.
Introduction
In recent years, in construction field there is a tendency of
change in evaluation of structure from the idea of focusing on
“safety” to sustainability idea which comprehensively evaluates
the balance of “social aspect”, “economical aspect” and
“environmental aspect”. For example, the fib (International
Federation for Structural Concrete) and ACI (American
Concrete Institute) have proposed the importance of
introduction of sustainability in required performance of each
design standard.
The objective of this research is to do a sustainability
evaluation on reinforced concrete’s members (RC members). In
detail, changes of (1) diameter of rebars, (2) compressive
strength of concrete, (3) yield strength of rebars, (4) effective
height and (5) production method of steel were made to a basic
designed beam, and influences of these causes on “strength”,
“cost” and “CO2 emission amount” were found by numeric
calculation and researching on various documents.
2.
Sustainability Design of RC members
where，𝐴 ：area of rebars, 𝑓 ：yield strength of rebar，𝑑 ：
effective height, 𝑝 : balanced steel ratio， 𝑓 ：compressive
strength of concrete.
By the way， since flexural failure which consists of
toughness must precede, design bending strength was set to be
smaller than design shear strength.
C.
Basic elements of RC beam for numeric calculation is
shown in Figure.1.
Calculation Method of Cost
Cost = cost of rebars + cost of stirrups + cost of concrete
(2)
where，cost of steels = M ×L× Cs× N
(2.1)
cost of concrete = (Cv − Rs )×Cc
(2.2)
and, M[kg/m] : unit mass of steel, L[m] : length of steel,
Cs[¥/kg] : unit price of steel, N : number of steel，Cv[m3] :
volume of concrete, Rs[m3] : volume of steel, Cc[¥/m3] : unit
price of concrete.
D.
2.1 Elements of RC member
I Uoy PEN
Calculation Method of CO2 Emission
CO2 = CO2 by rebars + CO2 by stirrups + CO2 by concrete (3)
where，CO2 by steels = M × L × COs × N
(3.1)
CO2 by concrete = (Cv − Rs )×C×COc
(3.2)
and，M, L, N are the same as shown in equation (2.1)，
COs[kgCO2/kg] : unit CO2 emission of steel, Cv, RS are the same
as shown in equation (2.2)，C[kg/m3] : unit mass of cement，
COc[kgCO2/kg] : unit CO2 emission amount of cement.
3.
Calculation’s Results and Discussions
3.1 Influence of Rebars
Figure.2 shows relationship of the three elements when
diameter of rebars were changed. When diameter of rebars
became bigger, increasing tendency of the three elements can be
Figure.1: Cross section plan of RC beam
seen.
While,
strength
and
cost
increased
with
high
magnification, increasing rate of CO2 emission amount was
2.2 Numeric Calculation
A.
Conditions of Calculation
The representing elements for sustainability’s three aspects
are: “strength (for simplification purpose, only design bending
strength was used)” for social aspect, “production cost” for
economical aspect, and “CO2 emission amount” for
environmental aspect.
comparatively small.
Furthermore, the ranges of change for each method are :
D8 to D29 for diameter of rebars, 18 N/mm2 to 30N/mm2 for
compressive strength of concrete, SD295 to SD490 for yield
strength of rebars，blast furnace and electric furnace for steel’s
production methods.
B.
Calculation Method of Strength
Design bending strength 𝑀
=𝐴 𝑓 𝑑 1−
𝑝 𝑓
∙
1.7 𝑓
(1)
Figure.2: Relationship between the three elements
H30 Academic Year, Department of Architecture and Civil Engineering, Research Presentation Day 2019.02.26
3.2 Influence of Concrete’s Compressive Strength
Figure.3 shows relationship of the three elements when
compressive strength of concrete was changed. When
compressive strength of concrete became bigger, increasing
tendency of the three elements can be seen. While, strength and
cost increased with almost the same magnifications, increasing
rate of CO2 emission amount was comparatively big.
Figure.5: Strength - effective height relationship
3.5 Influence of Steel’s Production Methods
Table.1 shows the different amounts of CO2 emission
by production methods of steel. By changing from blast
furnace to electric furnace, amount of CO2 emission can be
reduced. On the other hand, from equation (1), strength is
irrelative with steel’s production methods. Due to lack of
documents, in this case cost was unknown.
Figure.3: Relationship between the three elements
3.3 Influence of Rebar’s Yield Strength
Table.1: CO2 emission by steel’s production methods
Production
Methods
CO2 emission amount in 1 ton of steel production
when yield strength of rebars were changed. When yield
Blast furnace
Steel production
process
about 2 tons
strength of rebars became bigger, increasing tendency of
Electric furnace
about 0.5 tons
Figure.4 shows relationship of the strength and cost
the two elements can be seen. And, strength increased in
Main materials transportation
process
α (constant)
about α/35 to α /125
[出典]東京製鐵株式会社：東京製鐵の鋼材 Q & A, 2015
larger magnification than cost did. Though, due to lack of
documents related to influence of rebar’s yield strength on
CO2 emission, in this case CO2 emission was unknown.
4. Conclusions
(1) The relationship between the three elements of
sustainability which are strength, cost and amount of
CO2 emission changes according to each cause.
(2) Preparation of inventory data related to relationship
between yield of rebar with amount of CO2 emission
and price of steel made by blast furnace or electric
furnace is necessary in further research.
References
1)
堺孝司，横田弘：コンクリート構造物のサステ
イナビリティ設計「地球環境と人間社会の不確
実性への挑戦」
，技報堂出版，2016
Figure.4: Strength, cost - rebar’s yield strength
3.4 Influence of Effective Height
Figure.5 shows relationship between strength and
effective height. When effective height got bigger,
increasing tendency of strength can be seen. Besides, from
equations (2.1), (2.2), (3.1) and (3.2) cost and CO2 emission
amount is irrelative with effective height.
2)
Shibata T, Kata K, Kasuga A, Sakai K : Sustainability
evaluation of butterfly web bridge, Structural
Concrete, 2017;1-18