Energy Saving with Rehabilitation Solutions for Existing Structures

SORIN DAN

Civil Engineering Department

"Politehnica" University of Timisoara

Str. T. Lalescu, No. 2, Timisoara

ROMANIA

sorin.dan@ct.upt.ro http://www.ct.upt.ro

Abstract: - The paper deals with aspects regarding energy saving of reinforced concrete existing structures

strengthened in seismic zones. Some case study and the rehabilitation of characteristic structures are analysed. The

rehabilitation solutions were chosen in accordance with the actual stage of building deterioration as well as function of

the actions characteristics. Classic (reinforced concrete and/or steel) and modern (Carbon Fibre Reinforced Polymers)

materials and technologies for strengthening have been used. Finally, the total cost of strengthening solution and the

energy used with raw materials are presented.

Key-Words: - Existing reinforced concrete structures; Seismic action; Strengthening; Classic rehabilitation solutions;

Modern rehabilitation techniques; Carbon fibre reinforced polymers (CFRP); Raw material; Embodied energy.

1 Introduction Sustainable construction has recently been identified as

one of lead markets for the near future of Europe

because of its high innovation potential, its ability to

respond to market needs, the strength of European

industry and the necessity to support it through the

implementation of public policy measures.

The main concept of sustainability regards buildings

with a long service life, low operating and maintenance

costs and high energy efficiency.

In addition the sustainability is based on the

environmental, economic and social components and

includes criteria such as technical process and site

quality. A global quantitative model for evaluating the

sustainability is difficult to be produced but for each

structural element or building it may be established. In

this paper the calculated components of sustainability

are: total cost of strengthening solution; the energy used

with raw materials.

The sustainability and the energy saving of the

strengthening solutions were slightly discussed in

comparison to the new buildings.

Three strengthening solutions will be analyzed in the

paper. The strengthened elements are existing reinforced

concrete columns as vertical structure of different

constructions.

The rehabilitation solutions are:

• steel bracing with four angle steel shapes

connected by flange plates;

• carbon fibre polymer composites (CFRP):

longitudinal strips and transversal wraps;

• jacketing by reinforced concrete using

longitudinal reinforcement bars and transversal

stirrups.

2 Rehabilitation Solutions

2.1 Structural rehabilitation using steel profiles

vs. carbon fibre reinforced polymers

2.1.1 Reinforced concrete silos

The assessment and rehabilitation solutions for a group

of silos owned by the SAB Miller Brewery Company

“Timisoreana” are presented. The silos (Fig.1) were built

40 years ago and stand 28 m high and 7.30 m in

diameter.

Fig.1. RC silos.

Initial silos inspection (1999) revealed large zones of

circular cells with concrete cover dislocated and

corrosion of circumferential steel reinforcement. Recent

silos inspection and assessment (2004) emphasized other

vulnerable parts: infrastructure and charging platform

(gallery).

ADVANCES in ENERGY PLANNING, ENVIRONMENTAL EDUCATION and RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 144 ISBN: 978-960-474-187-8

The silos infrastructure consists of foundation raft,

discharge funnel and its supporting columns and beams.

The main damages are due to water infiltration and

high humidity inside of each cell bottom part, which

caused important dislocated concrete cover and

corrosion of the columns steel reinforcement (Fig.2).

Fig.2. Reinforcement corrosion of discharge funnel

supporting columns.

Conexpand

M12/120/30

L 6

0X

60

X6

L

= 4

00

0 m

m

L 80x80x8

L 80x80x8

40x5...295

40x5...295

Co

ne

xp

an

d

M1

2/1

20

/30

Fig.3. Strengthening solution with steel profiles.

The strengthening of supporting columns for the

discharge funnel consists of steel profiles (Fig.3). This

solution has a smaller cost than CFRP materials. On the

other hand, steel profiles have a better buckling

behaviour than CFRP strips.

In order to have the comparison of sustainability and

energy saving criteria of the rehabilitation solutions, the

column strengthening was re-designed using CFRP as

follows (Fig.4):

• longitudinal strips S1012, on four sides, having a

width of 100 mm, a thickness of 1.2 mm and the

length of the column. The strips were anchored

in foundations and at the top joints;

• transversal confinement with a single layer of

wrap closed jacket at both ends of the columns.

The jackets had a width of 900 mm and a

thickness of 0.12 mm.

Fig.4. Strengthening solution with CFRP.

2.1.2 Reinforced concrete framed building

The Western University of Timisoara has many

buildings, among them the Main Building (Fig.5 and 6)

that is used as administrative part as well as classrooms

for students, was built in 1962-1963.

The RC structure consists of:

- transversal and longitudinal frames with eight storeys

and two spans of 5.6 m and eleven bays of 3.8 m;

- floors with girder mesh in two directions and a slab

of 10 cm;

- foundation with a thick slab and deep beams in two

directions.

ADVANCES in ENERGY PLANNING, ENVIRONMENTAL EDUCATION and RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 145 ISBN: 978-960-474-187-8

3.90

Strengthened columns at the first storey

Legend:

5.6

0

1

5.6

0

Stairs

3.80 3.80 3.80 4.00 3.80 3.80 3.80 3.80 3.80 3.90

2 123 4 5 6 7 8 9 10 11

A

B

C

SC 1 SC 2 SC 3 SC 4 SC 5 SC 6 SC 7 SC 8 SC 9 SC 10 SC 11 SC 12

SB 1 SB 2 SB 3 SB 4 SB 5 SB 6 SB 7 SB 8 SB 9 SB 10 SB 11 SB 12

SA 1 SA 2 SA 3 SA 4 SA 5 SA 6 SA 7 SA 8 SA 9 SA 10 SA 11 SA 12

Fig.5. Framing plan – ground storey

Fig.6. The Western University of Timisoara

On examination of the building and from non-

destructive measurements no important damages of the

RC structure were noticed. Some local damage due to

incipient reinforcement corrosion was detected at the

columns of the ground storey.

The analysis of the structure has been performed at

both combinations of actions: fundamental combinations

and special combinations including seismic action at

present-day level. From the analysis it was noticed:

- weakness of reinforcement and insufficient

anchorage of beam-positive reinforcement at the

beam-column joint, especially in the longitudinal

direction;

- the drift limitation conditions are not within the

admissible limits at the ground storey.

Rehabilitation solution consists in strengthening of

the columns located at the ground storey (Fig.7 and 8):

some columns were strengthened in 1999 to prevent the

local damages due to reinforcement corrosion; the other

columns were rehabilitated in 2004 for decreasing the

lateral displacements (drift limitation conditions) and for

a homogeneous columns stiffness at the ground storey.

SB 1, 12

550

90

0

100x10...900

100x10...550

100x10...550L100x100x10...5130

100x10...900

Fig.7. Strengthening solution with steel profiles.

Fig.8. Rehabilitation solution of columns.

ADVANCES in ENERGY PLANNING, ENVIRONMENTAL EDUCATION and RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 146 ISBN: 978-960-474-187-8

In order to have the comparison of sustainability and

energy saving criteria of the rehabilitation solutions, the

column strengthening was re-designed using CFRP as

follows (Fig.9):

• two longitudinal strips S1014, on each of the

four sides, having a width of 100 mm, a

thickness of 1.4 mm and the length of the

column. The strips were anchored in foundations

and at the top joints;

• transversal confinement with a single layer of

wrap closed jacket at both ends of the columns.

The jackets had a width of 1200 mm and a

thickness of 0.12 mm.

Carbodur

S1014

SB 1, 12

550

90

0

Sik

aw

rap

HE

X

23

0C

60

x5

0

Carbodur

S1014 Fig.9. Strengthening solution with CFRP.

2.2 Structural rehabilitation using reinforced

concrete The "Palace" structure (Fig.10) is a huge building

(underground floor, ground floor - restaurant, 3 storeys -

apartments, timber roof), built before 1900's with a

composite structure: masonry and reinforced concrete

framed structure (Fig.11).

Fig.10. The "Palace" building.

Fig.11. Longitudinal RC frames.

Initially it was an entire masonry structure, but later

the ground floor was changed: some resistance brick

walls were cut and two longitudinal RC frames were

erected to sustain all the vertical loads. Due to this

architectural operation the structure became more

vulnerable at seismic actions: by the transversal direction

main part of the ground floor became unstable at

horizontal actions because of some erected columns with

hinge connection at both ends (masonry wall supports

from the underground floor and ground storey). Other

vulnerabilities of the building consist of: overall lateral

stiffness values along the two main axes are different;

lack of seismic joints to divide building parts having

different dynamic characteristics; lack of straps at each

floor.

The building assessment emphasized some aspects:

concrete quality is very variable in structural elements,

having different classes (C8/10 - C16/20); some cracks

in longitudinal beams; corrosion of the slab

reinforcement; etc.

From the static and dynamic analysis a very

important conclusion could be drawn: the earthquake

capacity ratios R between the actual values of ultimate

bending moment (Mcap) and the necessary bending

moment (Mnec), given by the present-day seismic action

level, were very low for columns. That meant that the

building was characterized by a high risk of collapse at

seismic actions. Resulted the necessity of structural

rehabilitation.

In accordance to the structural analysis, the

strengthening of the ground floor was chosen in order to

obtain technical and economical advantages: safe

behaviour at seismic actions; slight change of the overall

structural stiffness; easy strengthening technology and

short period of refurbishment (December 2004 - June

2006).

The strengthening have been made on the following

structural elements:

ADVANCES in ENERGY PLANNING, ENVIRONMENTAL EDUCATION and RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 147 ISBN: 978-960-474-187-8

• strengthening by RC coating (7 cm on each side)

of masonry walls from the underground floor of

the building;

• new reinforced concrete floor with embedded

steel profiles (HEB 220) in two directions,

which stands as beams for the new structure;

• strengthening of half from the existing columns

(60x60m coated by RC to become 90x90cm –

Fig.12) and erecting of new transversal RC

beams in order to create new transversal frames

(Fig.13);

• strengthening by RC coating of existing

longitudinal beams;

• rehabilitation of some structural elements having

corroded reinforcement.

Fig.12. Strengthening of columns.

GLC 90x90GLC 90x90

GLB 90x90GLB 90x90

GLA 75x90 GLA 75x90

1,92

3,39

3,5

0,47 3,18 0,63,470,9

3,490,9 0,48

1,46

3,0

60

,39

1,741,61 3,2

0,6

3,35

0,61

0,46 3,57

5,9

3

5,9

3

5,9

3

3,390,94,720,644,840,9

4,124,15

0,6

0,6 0,38 1,5 0,4 0,63 3,51

4,71

0,8

4

4,66

0,6

5,1

20

,6

0,9

4,9

40

,6

0,62

1,9

4

0,9

1

1,86

0,6

0,6

5

2,7

9

11

,53

3,57

1,4

40

,4

3,26

0,7

1,4

4

S290x9090x90

S2 S290x90

90x90 S1 S1

90x90 S190x90

S190x90strengthened at 90x90cm

Existent longitudinal beam 60x80cm

GT

3 -

90

x8

0

GT

2 -

90

x8

0

NE

W B

EA

M

GT

1 -

90

x8

0

NE

W B

EA

M

NE

W B

EA

M

GT

3 -

90

x8

0

NE

W B

EA

M

GT

2 -

90

x8

0

NE

W B

EA

M

GT

1 -

90

x8

0

S190x90

S190x90

str

en

gth

en

ed

at

90

x8

0c

mE

xis

ten

t b

ea

m 6

0x

45

cm

strengthened at 90x90cmExistent longitudinal beam 60x80cm

strengthened at 75x90cm

Existent longitudinal beam 60x60cm

Fig.13. Ground floor rehabilitation.

3 Embodied Energy of Rehabilitation

Solutions The calculated characteristics of the five strengthening

solutions were: the total cost of strengthening solution;

the total energy for each solution, based on embodied

energy of raw materials. The results of the analysis are

presented in Table 1.

Table 1. Main characteristics of strengthening solutions.

Strengthening solution for columns Cost Energy

Total [€] Per m2 [€/m

2] Total [MJ] Per m

2 [MJ/m

2]

RC silos steel bracing * 33200 49 407265 598

CFRP ▲

71800 105 85536 126

RC frame steel bracing * 48200 102 590700 1249

CFRP ▲

76000 161 104544 221

RC jacketing * 21800 53 331380 804

Notes: * applied solutions; ▲

CFRP solutions designed for comparison;

- for the cost per m2 the total construction rehabilitated area was taken into account.

ADVANCES in ENERGY PLANNING, ENVIRONMENTAL EDUCATION and RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 148 ISBN: 978-960-474-187-8

The main conclusions from this data are:

• The energy saving regarding structural

strengthening is possible by using CFRP – strips

and wraps.

• The strengthening by steel bracing and RC

jacketing are energy consuming solutions in

comparison to the CFRP solutions.

4 Final Conclusion The main ideas which may emerge from these studies

are:

a) As structural rehabilitation for existing reinforced

concrete structures several strengthening

solutions may be used: steel bracing; carbon fibre

polymer composites (CFRP); jacketing by

reinforced concrete.

b) For energy saving is important to use building

materials with minimum embodied energy during

manufacturing process.

c) For strengthening of the existing structures the

energy saving is possible by using modern CFRP

materials (strips and wraps).

d) The manufacture time is also shorter in case of

using CFRP in comparison to classic

strengthening solutions (steel bracing or

reinforced concrete jacketing).

e) The cost of CFRP solutions for strengthening is

higher than other solutions.

f) Using of CFRP solution for strengthening of

columns may be inadequate in case of structural

stiffness increase demands.

References:

[1] Romanian Ministry of Public Works and Territory

Planning, Code for Seismic Design of Residential

Buildings, Agrozootechnical and Industrial

Structures P100-92, English version.

[2] Technical University Bucharest, Code for

Assessment of Existing Structures Safety to Seismic

Actions, 2002 (in Romanian).

[3] fib Bulletin 14, Externally Bonded FRP

Reinforcement for RC Structures, fib, Lausanne,

2001.

[4] A. Ghobarah, Seismic assessment of existing RC

structures. Progress in Structural Engineering and

Materials, 2000, Vol. 2, No. 1.

[5] Bob C., Dan S., Analysis, Redesign and

Rehabilitation of Reinforced Concrete Framed

Structures in Seismic Regions, fib Symposium:

Concrete Structures in Seismic Regions, Athens,

2003.

[6] Bob C., Dan S., Badea C., Iures L., Classic and

Modern Rehabilitation Techniques in Seismic Zones,

IABSE Symposium: Structures and Extreme Events,

Lisbon, 2005

[7] Dan S., Bob C., Gruin A., Analysis of Reinforced

Concrete Existing Structures in Seismic Regions,

WSEAS International Conference: Engineering

Mechanics, Structures, Engineering Geology

EMESEG’08, Heraklion, Greece, 2008.

[8] Bob C., Bob L., Sustainability of New and

Strengthened Buildings, WSEAS International

Conference on Sustainability in Civil Engineering

SSE’09, Timisoara, Romania, 2009.

ADVANCES in ENERGY PLANNING, ENVIRONMENTAL EDUCATION and RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 149 ISBN: 978-960-474-187-8