Seismic Behavior of Reinforced Normal Strength Concrete and Reactive powder Concrete Eccentrically Loaded Frames

Seismic Behavior of Reinforced Normal Strength

Concrete and Reactive powder Concrete Eccentrically

Loaded Frames

Ali Sabah Al Amli

1

_{, Aamer Najim Abbas}

2

_{, Tamara Adnan Qasim3, Nadhir Al-Ansari}

4

Civil Engineering Depar tment, Al-Mustansiriyah University, Baghdad, 0096 4, Iraq

1

Water Resources Engineering Department, Al-Mustansiriyah University, Baghdad, 00964, Iraq

2

_.

Lecturer, Department of Civil Engineering, Al-Mustansiryah University, Baghdad, Iraq

3

Lulea Uni versity of Technology, 97187 Lulea, Sweden

4

_.

Abstract— The purpose of this inv estigation is to study the effect of repeated load on reinforced concrete beam-column connections. Eight specimens were adopted in this investigation; four spec imens were poured with normal strength concrete, and other four specimens were poured with reactive po wder concrete. The frames dimensions are constant; 280 mm and 200mm of beam height and width respectively with 1000mm beam length and 200mm square column with 700mm height. The load was applied at mid-span and at a distance 150mm from the mid-span of beam. The reduction in frame capacity reached to 53.3% due to eccentricity. All tested specimens were failed at cycle 5 with different load level; . the decrease in stiffness of cyclically loaded frames of normal strength concrete was higher than that of reactive powder concrete frames. The deflections of cyclically loaded frames higher than that of statically loaded frames. In brief, the frames with eccentrically and cyclically loading give lowest ultimate strength, first crack load and stiffness with highest deflections.

Keywords— Frame, Beam-column Connection, Eccentric Load, Cyclic Load, Stiffness.

1. Introduction

Reinforced concrete buildings are a common construction for residential and commerci al buildings in areas near earthquake activity. Reinforce d concrete frameworks consisting of columns and beams are usually considered as main structural eleme nts in the design process[1]. The philosophy of seismic design is based on a structure that provides sufficient rigidity in structures that can receive seismic energy. In the case of inelastic deformation, the actual material properties are outside the elastic limit, so damage to this area is obvious. A plastic hinge is an expected position in which structural damage can occur due to large deformation. Connecting columns with beams in reinforced concrete frames for lateral displacement caused by an earthquake can lead to high shear stresses, which can lead to severe joint damage and loss of structural rigidity. Several works were present ed a recommendations for shear stress and design of reinforced concrete structures; Hanson and connor (1967 )[2], Hanson(1971) [3], Meggat and Park (1971)[4], Uzumeri and sekin (1974)[5], Meinhait and Jirsa (1981) [6] Durrani and White (1985) [7] and Ehsani and W hite (1982) [8].

Emre E. et. al. [9] tested three spec imens of external connections in two way story of reinforced concrete structures. JABBARI Ilyas [10] cond ucted three tests, these tests depend on how to beam is fastened, as well as on the number and shape of tran sverse stiffeners provided at the joint, the frames w ere damaged in the joint zone due to severe destruction of the main concrete and the destruction of reinforcement. Geraldine S. C. and H. S. lew [11] conducted an experimental study of prestressd concrete frames under cyclic loading. The aim is to make precast concrete components durable, economical and easy to manu facture. The results show that it is durable and ductile after it is strengthened in the form of monolithic frame. Two types of loads were used in the experimental studies conducted by Park, Y. J. and Ang, A.H.S. [ 12]. A useful result

value of frame loaded cyclically. The current recommendations of ACI-ASCE 352 (2002) [13] included

three main Parameters affects the joint behavior; 1) requirements for restrictions; 2)assessment of shear

strength; 3) Fixity the beams and columns at a joint; if these parameters are available the displacement

capacity will be adequate.

2. Experimental Works

2.1 Materials Properties

2.1.1 Cement (OPC)

Type (I) Ordinary Portland Cement was employed in the production of normal concrete and reactive powder

concrete. The cement properties are shown in Table 1 and Table 2, the chemical and physical properties are

conformed the American Standard ASTM C-150 [14].

Table 1

Physical properties

Test results

Fineness using Blain air

293

permeability apparatus (m2/kg)

Soundness using autoclave

0.13%

method

Setting time using Vicat’s

instrument

187

Initial (min.)

4.7

Final (hr.)

Compressive strength for cemen t

paste cube(70.7mm) at:

3 days(Mpa)

22.71

7 days(Mpa)

29.99

Table 2

Chemical

No.

Compound composition

compositi

Weight (%)

on

1

Lime

CaO

61.22

2

Silica

SiO2

21.22

3

Alumina

Al2O3

5.54

4

Iron oxide

Fe2O3

3.09

5

Magnesia

MgO

2.83

6

Sulfate

SO3

2.48

7

Loss on ignition

L.O.I

1.07

8

Insoluble residue

I.R

0.73

9

Lime saturation factor

L.S.F

0.87

10

Tricalcium aluminates

C3A

8.95

11

Tricalcium silicate

C3S

42.05

12

Diacalcium silicate

C2S

28.90

13

Tricalcium alumoma ferrite

C4AF

9.57

2.1.2 Fine Aggregate

In the production of concrete, the maximum aggregate size of sand was (4.75mm). The sieve analysis results and physical properties of the sand are shown in Table 3 and Table 4 respectively, the grading and physical properties of the sand are conformed the Standards of BS 882 [15].

Table 3

7

Pan

0

No .

Sieve size

Passing (%)

1

4.75 mm

93.82

2

2.36 mm

82.33

3

1.18 mm

62.75

4

600 μm

40.39

5

300 μm

15.89

6

150 μm

2.67

Physical properties

Test results

S pecific gravity

2.59

Sulfate content(so3)

0.43 %

Absorption

1.69 %

Table 5

2.1.3 Coarse Aggregate

The gradation of gravel is shown in Table 5. The gravel maximum size was (10mm) us ed in the production of concrete, the properties of gravel are conformed the British Standards of BS 882 [15].

No.

Sieve size

Passing (%)

1

20 mm

100

2

10 mm

89.79

3

5 mm

4.33

4

2.36mm

2.76

5

1.18 mm

1.4

6

pan

0

2.1.4 Steel Reinforcement

Table 6

The steel bars specifications that u sed in reinforcing beam-column joints are shown in Table 6, the test

methodology was performed according to ASTM A615 [16].

[Table 7]

Steel specimens

Diameter of bar

Yield stress

Ultimate strength

Modul us of elasticity

(mm)

(N/mm2)

(N/mm2)

(N/mm2)

1

10

466

498

222000

2

8

483

519

220000

2.1.5 Silica Fume

To improve concrete properties, a silica fume was used as an admixture to concrete to produce modified reactive powder concrete. The silica fume fineness modulus was 20000 m2/kg. The che mical compound of the silica fume conforms to the AST M C 1240-04[17], as shown in Table 7. [Table 8]

Compound

Che mical

Oxide

Limit of specification

composition

comp osition

content (%)

requirement (ASTM C 1240)

Lime

C aO

0.5

ـــــــــ

Iron oxide

Fe2O3

1.4

ـــــــــ

Alumina

Al2O3

0.5

ـــــــــ

Silica

SiO2

92.1

85(min.)

Magnesia

M gO

0.3

ـــــــــ

Sulphate

SO3

0.1

ـــــــــ

Potassium

K 2O

0.7

ـــــــــ

Sodium

Na2O

0.3

ـــــــــ

202

2.1.6 Steel Fiber

0.4% of total volume Hook end steel fibers with aspect ratio (100) was used in modified reactive powder concrete mix to increase its tensile strength. Table 8 summarized the specifications of steel fiber. [Table 9]

Property

Specification

Density.

7860 kg/m3

Ultimate strength

1500 MPa

Modulus of elasticity

2*105MPa

Possions ratio

0.28

Length

50 mm

Diameter

0.5mm

Aspect ratio

100

2.2 Mix Proportions

Table 9 contains the quantity of each components in concrete mixture that used in this work, the mix were

designed according to ACI 211.1-91 [18].

[Table 10]

Type of concrete

Cement

Sand

Gravel

Water

Superplastizer

Kg/m3

Kg/m3

Kg/m3

Lt/m3

Liter/m3

NSC

400

600

1200

188

ـــــــ

RPC

530

575

1000

163

4

2.3 Compressive Strength of Concrete

The compressive strength of tested joints are shown in Table 10, three cubes and three cylinders were poured and tested at the same age of joint specimens, the compressive strength of each tested specimen is the average of

compressive strength of three specimens [19]. [Table 11]

Beam

Cylinder compressive

Cube compressive strength

symbol

strength (N/mm2)

(N/mm2)

F1-30

29.19

34.48

F1C-30

29.45

34.81

EF1-30

28.58

35.91

EF1C-30

29.29

35.61

F1-70

66.53

77.98

F1C-70

63.88

76.85

EF1-70

65.26

79.57

EF1C-70

71.83

83.78

2.4 Specimens Details

Eight reinforced concrete frames were manufactured, each frame represent a model of beam to column connection, four of frames were poured with normal strength concrete, and other four specimens were poured with reactive powder concrete. Two load configurations were applied on column; central load at the mid span of the beam and eccentric load was applied at a distance 150mm from the mid span length of beam, two types of loading were applied; static load and repeated load. These frames are classified depending on type of concrete and applied load configuration; static centrally loaded on normal strength concrete (F1-30), cyclic centrally loaded on normal strength concrete (F1C-30), static eccentrically loaded on normal strength concrete (EF1-30), cyclic eccentrically loaded on normal strength concrete (EF1C-30), static centrally loaded on reactive powder concrete (F1-70), cyclic centrally loaded on reactive powder concrete (F1C-70), static eccentrically loaded on reactive powder concrete (EF1-70), and cyclic eccentrically loaded on reactive powder concrete (EF1C-70). All frames have the same dimensions of 280mm total height and 200mm of width of the beam and 200x200mm of column section dimensions. The overall span of beam is equal to 1000mm and the effective span is 900mm, and the column height is 700mm. Fabrication details of the tested Frames are presented in Table 11, also Fig. 1 and Fig. 2 show specimens details of centrally and eccentrically loaded frames. [Table 12]

Frame

Type of

Position of column

Type of

designation

conc rete

loadin g

F1-30

NS C

at Mid-span

Stati c

EF1-30

NS C

at 150mm from Mid-span

Stati c

F1-70

RP C

at Mid-span

Stati c

EF1-70

RP C

at 150mm from Mid-span

Stati c

F1C-30

NS C

at Mid-span

Repeated

EF1C-30

NS C

at 150mm from Mid-span

Repeated

F1C-70

RP C

at Mid-span

Repeated

140 120 100 250 200 150 L o ad ( k N )

3.

Results and Discussions of Experimental Works

3.1 Statically Loaded Frames

3.1.1 Load Versus Deflection Response

Fig. 3 and Fig. 4 show the evaluation of the beam deflection as a function of applied load. Three stages can be seen from the load –deflection diagram; stage one that the specimen in elastic state, it starts with starting of load application up to appearance of the first crack. The values of deflections of centrally and eccentrically loaded frame appeared closed together at initial loading stages. Centrally loaded frames seems more elastic than eccentrically loaded frames. Due to transferred moment, the first crack of eccentrically loaded frames appeared before the centrally loaded frame. The second stage; is the stage in which the reinforcing steel yields, this stage characterized by increasing the number, depth and width of cracks , thus causing gradual decrease in specimen stiffness due to lack of bond between steel bars and concrete. The third stage appeared significant increase in deflections due to a variation of shear modulus in the beam behavior that the failure occurred by shear. Briefly, the eccentrically loaded frame appeared low first crack load, low yield load and low ultimate load with high deflections. (k N ) ₈₀ F1-30 60 L oa d 40 EF1-30 20 0 0 2 4 6 8 Deflection (mm) EF1-70 100 F1-70 50 0 0 2 4 6 8 Deflection (mm)

3.1.2 Failure and First Crack Loads

Table 12 illustrates the failure and first crack loads and corresponding deflections. The ultimate loading capacity of (F1-30) frame was (53.3%) higher than frame (EF1-30), while the ultimate load of (F1-70) frame was (39.28%) higher than frame (EF1-70); frames F1-30 and F1-70 were centrally loaded frames with normal strength concrete and modified reactive powder concrete respectively, while frames EF1-30 and EF1-70 were eccentrically loaded frames with normal strength concrete and modified reactive powder concrete respectively. The ultimate load enhancement seemed to be proportional to the decrease in the eccentrically.

The ultimate deflection of (F1-30) frame was (5.15 mm) while frame (EF1-30) recorded (5.85 mm) ultimate deflection. The ultimate deflection o f frame (F1-70) was 15.04% higher than corresponding (EF1-70) frame. From Table 12, it can be concluded that, the first crack load of frame (F1-30) was (70 KN). However , the frame with eccentrically of (150mm) , the first crack load decreased up to (55.5%). Also, the first crack load of eccentrically modified reactive powder concrete frame was decreased (64%) in compa rison with centrally loaded specimen. Consequently, it w as also found a significant difference obtained bet ween the deflections at first crack load of tested frames, t he deflection at first crack load of frame (F1-30) was approximate (0.68 mm). While, the frame with eccentricity of 150mm (frame (EF1-30)) recorded (0.57 m m) deflection at first crack load. On the same way, with increasing the eccentricity, the deflection at first crack load of frame (EF1-70) was (0.84 mm), while frame (F1-70) achieved (1.23mm) deflection

at first crack load. [Table 13]

Ultimate

Ultimate

First

Deflection

Frame

load

deflection crack

at first

designation

(KN)

(mm)

load crack

(KN)

(mm)

F1-30

115

5.15

70

0.68

EF1-30

75

5.85

45

0.57

F1-70

195

5.05

82

1.23

EF1-70

140

5.85

50

0.84

3.1.3 Failure Pattern of the Joints

Flexural cracks were observed in th e beam portion during early stage of loading. Then a diagonal cracks were observed in the connection zo ne. The behavior of interior joint up to failure can be divided in to two stages; at the early loading stage up to initiation of diagonal cracks in connection zone followed by propagation of diagonal cracks up to failure ,see Fig. 5 to Fig. 8. The first crack usu ally appeared at the beam –column junction, but the maj or structural crack was always the diagonal shear crack. The transferred bending moment on either sides of the column eliminate each other. But in case of ec centric column, the transferred moment cases premature appearance of first flexural crack and diagonal shea r crack.

After formation of diagonal shear cr acks, the joint is able to carry more load depending on the strength of concrete and percentage of reinforc ement. With increasing the load, a substantial deterioration in the joint through cracks propagations the join t is not able to carry more load as in centric loading. The largest flexural cracks occur at the connection can bee distinguished in eccentric loading frame.

206

3.1.4 Stiffness Characteristics of Tested Frames

According to Table 13, all eccentrically loaded frames show a decrease in stiffness in comparison with centrally loaded frames, the decrease in stiffness was 42.6% in specimen EF1-30 with respect to specimen F1-30 , and 38.1% in specimen EF1-70 with respect to specimen F1-70. The degradation in stiffness is most possibly attributed to its lower flexural capacity. All specimens appeared degradation in its stiffness, but the amount of decreasing in stiffness is significantly affected by column position. Specimen EF1-30 showed higher stiffness degradation (83.3%), while specimen F1-70 showed lower stiffness degradation. Note that the degradation rate may gives an indication on amount of absorbed energy of tested frames before failure. [Table 14]

Frame

Stiffness at

Decrease in

Stiffness at first

Decrease in

designation

ultimate load

stiffness at ultimate

crack (kN/mm)

stiffness (%)

(kN/mm)

load of different

specimens

F1-30

22.3

R*

102.9

78.4

EF1-30

12.8

42.6

78.9

83.8

F1-70

38.6

R*

66.7

42.1

EF1-70

23.9

38.1

59.5

59.8

Fig. 9 to Fig. 12 show the applied force versus beam deflection of tested frames. Note that the cycle 5 was distinct decrease in deflections of tested specimens, the specimen FIC-30 have maximum deflection 1.05

mm at inflection point, the corresponding deflection in static load test was 0.81 mm, there was a 22.9% decrease in deflection due to loading cyclically. The specimen (F1C-70) was able to carry repeated load up to 5 cycles, the specimen record 2.43 mm deflection at the end of cycle 5, while the statically loaded specimen (F1-70) recorded 2.14 mm deflection at the same load level of cycle 5, 13.5% reduction in deflection when loaded the specimen under repeated load. The eccentrically loaded normal strength concrete specimen (EF1C-30) failed under 5 cycles, it was achieved ultimate deflection (0.8mm), the corresponding statically loaded specimen (EF1-30) achieved 0.63 mm deflection at the same loading level of cycle 5, it was recorded a reduction in ultimate deflection about 21.25%. Specimen (EF1C-70) failed under 5 load

Cycles at 3.95 mm deflection, while statically loaded specimen (EF1-70) recorded deflection 2.65 mm at same load level of cycle 5. The deflection of eccentrically loaded specimen (EF1-30) under the ultimate static load higher than eccentrically loaded specimen (EF1-70). While, the deflection of eccentrically loaded specimen (EF1C-30) under the ultimate cyclic load lower than eccentrically loaded specimen (EF1C-70).

160 140 120 100 80 60 40 First Cycle Second Cycle Third Cycle Fourth Cycle Fifth Cycle 20 0 0 150 100 50 First Cycle Second Cycle Third Cycle Fourth Cycle Fifth Cycle 0 0 80 60 40 20 First Cycle Second Cycle Third Cycle Fourth Cycle Fifth Cycle 0 0 1 2 3 Deflection (mm) 60 50 40 30 20 10 0 0 200 First Cycle Second Cycle Third Cycle Fourth Cycle Fifth Cycle 0.5 1 Deflection (mm) 1 2 3 4 5 Deflection (mm) 100 0.5 1 1.5 207 Deflection (mm) L o ad ( k N ) L o a d ( k N ) L o ad ( k N ) L o ad ( k N )

208

The first crack of tested specimens was observed at initial loading state (static loading). The specimens F1C-30, EF1C-30, F1C-70 and EF1C-70 were recorded the first crack at loads 70 KN, 45KN, 82KN and 50 KN respectively, see Table 12. In next loading state (repeated loading), new cracks were detected at a different distances from the face of column, these cracks gradually increased in length and width in each cycle, these cracks named a flexural cracks, the eccentrically loaded frames have number of cracks larger than centrally loaded frames, the crack width is restricted by loading and unloading state, the crack width was not reached 1mm for all states. The MRPC frames have flexural crack width thinner than that of normal strength concrete frames; its width was not reached to 0.6mm for all states.

The main diagonal crack was about 0.6 mm wide increased to 2.4 mm wide was initiated at a distance (d)

from column face, then extend diagonally (about 45) to the column face. The diagonal cracks were initiated

after 4 cycles, 3 cycles, 3 cycles and 2 cycles of loading for specimens F1C-70, EF1C-70, F1C-30, and

EF1C-30 respectively, see Fig. 13 to Fig. 16.

3.2.3 Stiffness

Table 14 shows the stiffness of tested frames under the effect of repeated load. The eccentrically loaded frames appeared a decrease in stiffness in comparison with centrally loaded frames; eccentrically loaded normal strength concrete frames EF1C-30 achieved stiffness 62.5 kN/mm, the corresponding centrally loaded frames F1C-30 achieved stiffness 71.43 kN/mm. On the other hand , Statically loaded MRPC frames EF1C-70 achieved stiffness 44.3 kN/mm, while the stiffness of corresponding centrally loaded frames F1C-70 was 53.49 kN/mm.

209

Table 15

Frame

Stiffness at

Decrease in stiffness

designation

failure (kN/mm)

(%)

F1C-30

71.43

R*

EF1C-30

62.5

12.5

F1C-70

53.49

R*

EF1C-70

44.3

17.18

4. Conclusions

The following conclusions can be achieved from this experimental study:

1. There is a decrease in ultimate strength of frames due to eccentricity of load in static and cyclic

loadings.

2. The eccentric cyclically loaded frames achieved minimum first diagonal crack load.

3. There is a significant decrease i n stiffness of eccentrically loaded frames.

4. It is observed that there is an increase in deflections of cyclically loaded frames in comparison with

statically loaded frames.

5. The first crack load of eccentrically loaded frames was lower than that of centrally loaded frames in

two cases of static and cyclic lo ads.

5. References

[1] H. A. Nilson, D. Darwin and W. C. D olan. Design of Concrete Structures. USA: McGraw-Hill, 2010.

[2] N. Hanson , H. Connor, “Seismic R esistance of Reinforced Concrete Beam-column Joints, Proc. ASCE, Jo. Str. Div., Vol.93, No.ST5, USA, 1967 , pp. 533-560.

[3] N. W. Hanson, “Seismic Resistance of Concrete Frames with Grade 60 Reinforcement, Jou rnal of the Structural Division, ASCE, Vol. 97, No. ST 6, , 1971, PP. 1685-1700.

[4] L. M. Megget, and R. Park, “Rein forced Concrete Exterior Beam-Column Joints under Seismic Loading, New Zealand Engineering (Wellington), Vol. 26, No. 11, 1971, PP.341-353.

[5] S. M. Uzumeri, and M. Seckin, “B ehavior of Reinforced Concrete Beam-column Joints Subjected to Slow Load Reversals, Department of Civil Engineering, University of Toronto, Toronto, Ontario, C anada, Report 74-05, 1974.

[6] D.F. Meinheit, and J.O. Jirsa, “Shea r Strength of RC Beam-column Connections, Proc. AS CE, Jo. Str. Div., vol. 107, no. ST11,USA, 1981, pp. 2227-2244.

[7] A.J. Durrani and J.K.Wight, “Behavior of Interior Beam-to-column Connection under Earthquake-type Loading, ACI Jo., No. 82-30, May-June., 1985, PP. 343-350.

[8] M.R. Ehsani and J.K. Wight, “Exte rior R/C Beam-to-column Connections Subjected to Earthquake-type Loading, ACI Jo., No. 82-43, July-Aug., 19 85, PP. 421-428.

[9] E. Emre , A. Bengi and B. E. Ome r, “Experimental Assessment of RC Beam-column Con nections with Internal and External Strengthening Techn iques, Advances in Civil Engineering, Vol. 2019: 12, 20 19.

[10 I. Jabbari, “Investigation of the Behavior of Beam-to-column Joints in Seismic Areas, Master Thesis, Ingénieur Civil Des Constructions, Université de Liège, Napoli, 2015.

[11] S. Geraldine , H. S. L Cheok, “Performance of Precast Concrete Beam-to-column Connect ons Subject to Cyclic Loading, PCI Journal, Vol. 36,Issue 3, 1991, PP. 56-67.

[12] Y. J. Park, and A.H.S. Ang, “ Mechanistic Seismic Damage in Reinforced Concrete, Journal of Structural Engineering, Vol. 111, No. 4, 198 5, PP. 722-739.

[13] ACI-ASCE Committee 352. Rec ommendation for Design of Beam-column Joints in M onolithic Reinforced Concrete Structures, 2002.

[14] British Standards. Standard Specifi cation for Portland Cement, ASTM C-150, 2015.

[15] British Standards. Specification for Aggregate from Natural Source for Concrete, BS 882-1992, 1992.

[16] American Standards for Testing Materials. Standard Specification for Deformed and Plain Carbon-steel Bars for Concrete Reinforcement, ASTM A615, 2009.

[17] American Standards for Testing M aterials. Standard Specification for Silica Fume Used in Cementitious Mixture, ASTM C 1240-04, 2004.

Concrete, ACI 211.1-91, ACI 211.1–91, Reapproved 2002.

[19] British Standards. Method for Determination of Compressive Strength of Concrete Cubes, BS 1881, 1983.

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