Scholarly article on topic 'Effect of tension lap splice on the behavior of high strength self-compacted concrete beams'

Effect of tension lap splice on the behavior of high strength self-compacted concrete beams Academic research paper on "Civil engineering"

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Bond / Lap splice / Concrete / High strength / Self-compacted / Casting position

Abstract of research paper on Civil engineering, author of scientific article — Mahmoud A. El-Azab, Hatem M. Mohamed, Ahmed Farahat

Abstract Construction using concrete is spreading widely and there is a need for concrete that is capable of flowing under its own weight without mechanical vibration or compaction and fill the places between reinforcement and the complicated form shapes. From here, Self-Compacted Concrete (SCC) appears for the first time. Limited attention has been directed toward the bond between High Strength Self-Compacted Concrete (HSSCC) and spliced bars in beams [1–8]. This research studies the bond between HSSCC and spliced tension bars in beams. It is focused on observing the effect of some factors such as; reinforcement bar diameter and ratio, splice length and casting position on the beam flexural behavior. An experimental program consisting of sixteen simply supported beams divided into four groups is considered. All beams are of 1800mm span and 200×400mm cross-section cast with HSSCC. In twelve beams, the tensile steel was spliced in the constant moment zone, and four control beams without splice for comparison purpose. During testing; ultimate capacity, deflection, crack pattern and mode of failure have been recorded. Test results had been compared with proposed values in the Egyptian code of practice, other international design codes and recorded values of other researchers.

Academic research paper on topic "Effect of tension lap splice on the behavior of high strength self-compacted concrete beams"

A] -

Alexandria Engineering Journal (2014) xxx, xxx-xxx

Alexandria University Alexandria Engineering Journal

www.elsevier.com/locate/aej www.sciencedirect.com

ORIGINAL ARTICLE

Effect of tension lap splice on the behavior of high strength self-compacted concrete beams

Mahmoud A. El-Azab 1, Hatem M. Mohamed *, Ahmed Farahat 2

Faculty of Engineering, Cairo University, Cairo, Egypt

Received 7 December 2013; revised 24 January 2014; accepted 29 January 2014

KEYWORDS

Bond; Lap splice; Concrete; High strength; Self-compacted; Casting position

Abstract Construction using concrete is spreading widely and there is a need for concrete that is capable of flowing under its own weight without mechanical vibration or compaction and fill the places between reinforcement and the complicated form shapes. From here, Self-Compacted Concrete (SCC) appears for the first time. Limited attention has been directed toward the bond between High Strength Self-Compacted Concrete (HSSCC) and spliced bars in beams [1-8].

This research studies the bond between HSSCC and spliced tension bars in beams. It is focused on observing the effect of some factors such as; reinforcement bar diameter and ratio, splice length and casting position on the beam flexural behavior. An experimental program consisting of sixteen simply supported beams divided into four groups is considered. All beams are of 1800 mm span and 200 x 400 mm cross-section cast with HSSCC. In twelve beams, the tensile steel was spliced in the constant moment zone, and four control beams without splice for comparison purpose. During testing; ultimate capacity, deflection, crack pattern and mode of failure have been recorded. Test results had been compared with proposed values in the Egyptian code of practice, other international design codes and recorded values of other researchers.

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* Corresponding author. Address: Structure Eng. Department, Faculty of Engineering, Cairo University, 48 Gezeeret El Arab, El Mohandeseen, Giza, Egypt. Tel.: +20 2 02 33043850, mobile: +20 122 318 5801; fax: +20 2 02 33024645.

E-mail addresses: mahmoudelazab@hotmail.com (M.A. El-Azab), hatem_amn@yahoo.com (H.M. Mohamed), dr_frahat@yahoo.com (A. Farahat).

1 Tel.: +20 01003017368.

2 Tel.: +20 01223226904.

Peer review under responsibility of Faculty of Engineering, Alexandria

1. Introduction

Adequate bond between concrete and reinforcing bars in a splice is an essential requirement in the design of reinforced concrete structures. In the last 25 years, The Interest in HSSCC grows rapidly and now it is widely used in bridges and high rise building construction. This concrete was described as high-strength concrete (HSC) since it has higher strength than the usual normal-strength concrete (NSC) that has been produced for almost a century with 28-days strength in the range of 20-40 MPa. A typical application example of Self-compacting concrete is the two anchorages of Akashi-Kaikyo Bridge opened in April 1998 and the

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suspension bridge with the longest span in the world (1991 m).

Many researches were reported on bond strength between concrete and deformed bars for both normal strength and high strength concrete. Experimental tests were done and analytical equations were proposed by some researchers.

Various investigations have been carried out in order to make self-compacting concrete a standard one [9]. The items to be solved are summarized as, self-compactability testing method, mix-design method including, acceptance testing method at job site, and new type of powder or admixture suitable for self-compacting concrete. The European Guidelines for Self-Compacting Concrete [3] represents a state of the art document addressed to those specifiers, designers, purchasers, producers and users who wish to enhance their expertise and use of SCC. The Guidelines have been prepared using the wide range of experience and knowledge available to the European Project Group.

During the last ten years, few researches were conducted on bond strength of self-compacting concrete [1-7]. In 1990, Ato-rod Azizinamini et al. [1] tested a total of 18 beam specimens with two or three bars spliced. The main variables were (a) Concrete compressive strength fc, (b) Splice length; and (c) Casting position. The results showed that normalized bond strength decreases as concrete compressive strength increases with a rate of decrease increases as the splice length increases. In the case of normal strength concrete, the top bar demonstrated approximately 8% reduction in bond capacity compared to bottom cast bars. As indicated by comparison with the results, top bars, as defined by the ACI 318-11 [10], produce higher bond capacity when HSC is utilized.

Yerlici and Ozturan [2] conducted a research program for testing 53 eccentric pullout test specimens. Tested specimens were divided into four groups, where only a single parameter varied in each group. For the first three groups, the variable parameters were the concrete compressive strength, the reinforcing bar diameter, and the thickness of clear concrete cover. These parameters varied as 60, 70, 80, and 90 MPa (8700, 10,150, 11,600, and 13,050 psi), 12, 16, 20, and 26 mm (No. 4, 5, 6, and 8), and 15, 20, 25, and 30 mm (5/8, 3/8, 1, and 1-1/8 in.), respectively. The variable parameter of the fourth test group was the amount of web reinforcement that was made up of three closed stirrups spaced at 30 mm (1-3/ 16 in.), center-to-center, transversely crossing the anchorage length of the longitudinal bars. The amount of web reinforcement varied from none to having stirrups made of 3, 4, and 6 mm (D-1, D-2, and D-4) diameter steel wires. It was indicated that the average anchorage bond strength varies with the compressive strength of concrete, as (fc)2=3. The ACI Code slightly underestimates the effect of concrete strength on anchorage bond resistance when extended to HSC, while it overestimates the effect of concrete cover on anchorage bond resistance when extended to HSC.

The research project of Chan et al. [4] included the testing of a full-scale RC wall as the pullout specimen in which pullout reinforcing bars and transverse reinforcement were installed, some walls were SCC while others were cast from ordinary compacted concrete. The main variables were; (a) Concrete compressive strength fc, (b) Height of pull out bar (effect of top bar), and (c) Age of Concrete from 17 h to 28 days. It was concluded that compared to normal concrete NC, SCC exhibits higher bond to reinforcing bars and lower reduction in bond strength due to the top-bar effect. The slow develop-

ment of compressive strength and bond strength in SCC at early age is generally due to the retarding effect of the carbox-ylic high-range water-reducing admixture used.

Almeida et al. [5] tested 66 special set up beam specimens made from 3 SCC mixes. The main variables were (a) Maximum aggregate size, and (b) SCC fluidity. It was found that the bond resistance was not affected by the SCC lack of fluidity. It was also found that high performance concretes have a fragile rupture of the bond connection. Also, unless some confinement reinforcement is provided, the splitting of the concrete surrounding the bar will occur as the concrete tension strength is reached. Finally, the desirable failure mode, with yielding or slip of the bar, will not occur. The behavior of the beams was similar in the 3 series of tests, even considering the low fluidity of one of the 3 mixes.

Twelve full-scale beam specimens (2000 x 300 x 200 mm) were tested in positive bending [6] with the loading system designed to determine the effect of self-compacting concrete (SCC) and the diameter of reinforcement on bond-slip characteristics of tension lap-slices. The specimens of lap-splice series were tested with lap-spliced bars centered on the midspan in a region of constant positive bending. The results showed that load transfer within the tension lap-spliced bars embedded in SCC in a reinforced concrete beam was better than that of the tension lap-spliced bars embedded in NC. The beam specimens produced from SCC had generally longer cracks in length than the beams produced from NC regardless of the reinforcing bar diameter.

The project of Cattaneo and Rosati [7] included the testing of 27 pullout specimens containing one embedded reinforcement bar. The main variables were reinforcement bar diameter, fiber existence and confinement. Two types of tests were considered: unconfined and confined pullout. The tests showed a significant size effect on bond strength: the smaller bar diameter exhibited a higher strength than the larger one. The bond strength of self-consolidating concrete was found to be higher than normal strength concrete. The concrete cover, 4.50, where 0 is the bar diameter, was not sufficient to prevent splitting failure in SCC.

2. Experimental work

This research is a part of an experimental investigation [8] which studies bond between high-strength self-compacting concrete (HSSCC) and reinforcing bars in splices in beams. A total of sixteen concrete beams were fabricated and tested in this experimental program. The specimens were divided into four groups each has four specimens. The objectives of this program are to examine the effect of some factors such as; reinforcement bar size, reinforcement ratio, tension lap splice length and casting position on the beam flexural behavior.

A three-part notation system was used to indicate the variables of each beam. The first part of the notation indicates the casting position: B and T for bottom and top casting respectively. The second part indicates the splice length as a factor of the bar diameter with two different bar diameters: LM x N for splice length of M times bar diameter and N is the diameter of reinforcement bar. The third part is the reinforcement ratio: R.295 and R.424 for AS/(b x d) equal to 0.295% and 0.424% respectively. The specimens with no splice are referred to as the control specimens. The objectives of this

experimental program are to determine (I) Beam Capacity; (II) crack pattern and crack propagation; and (III) mode of failure of beams casted using high strength self-compacting concrete (HSSCC) with lap-splices in tension zone.

2.1. Test specimens

Tests were carried out on sixteen high strength self-compacting concrete beams reinforced with high grade steel bars spliced -if any - in the constant moment region and designed to start failure in tension zone (under reinforced sections). Test beams were simply supported with 2000 mm span (1800 mm Center line to Center Line of supports) and 200 mm x 400 mm cross-section and they were tested in four point bend configuration. The specimens were divided into four groups; each group consisted of four specimens. The details of the tested specimens are shown in Table 1.

Group (I): This group consists of four specimens having the same reinforcing ratio 0.295% and casting position (Bottom) but different in the splice length (0, 20, 30, and 40) times bar diameter 10 mm. Group (II) consists of four specimens having the same reinforcing ratio 0.295% and casting position (Top) but different in the splice length (0, 20, 30, and 40) times bar diameter 10 mm. The main difference between groups (I) and (II) is the casting position. The third group (III) consists of four specimens having the same reinforcing ratio 0.295% and casting position (Bottom) but different in the splice length (0, 20, 30, and 40) times bar diameter 12 mm. The main difference between group (I) and (III) is the bar diameter. Finally, group (IV) consists of four specimens having the same reinforcing ratio 0.424% and casting position (Bottom) but different in the splice length (0, 20, 30, and 40) times bar diameter 12 mm. The main difference between groups (III) and (IV) is the reinforcement ratio. Fig. 1a and b shows the reinforcement details of the tested beams.

2.2. Materials

The mix used to cast the specimens was developed by trial batching in the concrete research laboratories at Cairo Univer-

sity and Ain-Shams University. The materials used in the mixes are Ordinary Portland cement, natural clean sand; coarse aggregate, Silica fume and a super-plasticizer. The chosen mix for casting the specimens was designed to develop cube strength of 59.4 N/mm2. Table 2 shows the weights required to cast one cubic meter of the chosen concrete mix.

2.3. Test procedure

Static hydraulic loading jack with an electrical load cell was used to apply the concentrated vertical loads. A digital load indicator with 1 kN accuracy was used to measure the applied load. Each beam was centered on the testing machine, while loads were applied with increment of 5 kN. Fig. 2 shows a photograph for the general test arrangement, and Fig. 3 shows a schematic view of the test arrangement. Specimens cast in a top cast position were turned upside down before being placed on the test frame.

At every load increment, cracks were observed and marked and continuous recording for deflection, steel strains and load value from the loading cell using data accusation system. Failure was considered to occur when the load could not be increased further.

The deflections were measured at the mid-span of the beam by a LVDT instrument gauge of 0.01 mm accuracy. The crack propagation was plotted on the concrete beams during loading. The steel strains at mid-span were measured using 10 mm gauge length for one deformed bar in the splice region.

2.4. Test results

Tests were performed on sixteen beams cast using high strength self-compacted concrete reinforced with lap splice in mid-span (tension zone), which were subjected to incremental load up to failure. The design parameters taken into consideration include casting position, splice length as a factor of the bar diameter with two different bar diameters, and reinforcement ratios.

Effect of the previous parameters on the splice length in self-compacted high strength concrete beams will be discussed

Table 1 Details of test specimens.

Group No. Specimen designation Casting position Splice length Rft. Bar biameter (mm) Rft. ratio (%)

I 1 M-B-L0x10-R.295 Bottom - 10 0.295

2 M-B-L20x10-R.295 Bottom 200 10 0.295

3 M-B-L30x10-R.295 Bottom 300 10 0.295

4 M-B-L40x10-R.295 Bottom 400 10 0.295

II 5 M-T-L0x10-R.295 Top - 10 0.295

6 M-T-L20x10-R.295 Top 200 10 0.295

7 M-T-L30x10-R.295 Top 300 10 0.295

8 M-T-L40x10-R.295 Top 400 10 0.295

III 9 M-B-L0x12-R.295 Bottom - 12 0.295

10 M-B-L20x12-R.295 Bottom 200 12 0.295

11 M-B-L30x12-R.295 Bottom 300 12 0.295

12 M-B-L40x12-R.295 Bottom 400 12 0.295

IV 13 M-B-L0x12-R.424 Bottom - 12 0.424

14 M-B-L20x12-R.424 Bottom 200 12 0.424

15 M-B-L30x12-R.424 Bottom 300 12 0.424

16 M-B-L40x12-R.424 Bottom 400 12 0.424

9010075

3 ï 10@ 150

9010075

Specimen M-B-L0xl0-R.295

9010075

3 010® 150

9 010@75

Specimen M-B-L20xl0-R.295

901O@75

3 01O@15O

9 010075

Specimen M-B-L3QxlO-R.295

9010075

3 0100150

9010075

Specimen M-B-L40xl0-R.295

t200 Section

f2^ Section

Section

Section

9010075

30100150

9010075

Specimen M-T-LOxlO-R.295

^ 200 ^ Section

9010075

3® 10® 150

9010075

Specimen M-T-L20xl0-R.295

^ 200 t Section

9010075

3010®150

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Specimen M-T-L30xl0-R.295

J00^ Section

901O@75

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Specimen M-T-L40xl0-R.295

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Specimen M-B-L0xl2-R.295

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3 0100150

9010075

Specimen M-B-L20xl2-R.29S

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9010075

30100^50

9010075

Specimen M-B-L30xl2-R.295

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3 010^150

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Specimen M-B-L40xl2-R.295

^ 200 ^ Section

Specimen M-B-L0xl2-R.424

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Specimen M-B-L20xl2-R.424

_f00^. Section

Specimen M-B-L30* 12-R.424

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9010075

3 0100

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Specimen M-B-L40xl2-R.424

^ Section

Figure 1 (a and b) Typical elevation and sections of specimens.

Table 2 Design of the concrete mix (per m3).

Material Weight (kN) Material Weight (kN)

Coarse aggregate (Gravel) 7.50 Fine aggregate (Sand) 7.50

Cement 4.25 Water 1.60

Silica fume 0.50 Super plasticizer (Sikament R2002) 0.10

Figure 2 Test instrumentation.

Figure 3 Schematic view of the test arrangement.

in this section. The discussion of results will focus on the crack propagation, crack pattern, and failure mode.

The cracking and failure loads of the specimens will also be discussed as well as load-deflection relationship. In addition, load-reinforcement's strain relationship and ductility of the beams will be examined.

2.4.1. Crack pattern, cracking and failure loads For each beam during the test, a continuous recording of loading, midspan deflection, and strains using computerized data accusation system was carried out. During the loading operation, continuous plotting for the cracks and marking their corresponding load, the crack propagation, crack pattern and failure mode were listed. Table 3 gives the cracking and ultimate failure loads with the corresponding mid-span deflection while Fig. 4 shows the crack pattern at failure for each specimen.

As noticed from table and figures, a short splice length (200) led to slippage failure while - in general - a moderate

splice (300) and a long splice (400) led to flexure failure as no-splice specimens. Also, as noticed from Fig. 4, the crack pattern is mainly a flexure and shear cracks for all specimens. Flexure cracks started inside the middle third of the beam (zone of constant maximum moment) and increased in number and width all over the beam length with load increase while shear cracks started near supports after first flexure crack occurred. Slippage cracks occurred in short splice specimens.

2.4.2. Results classification

A subgroup system will be used to discuss the effect of the studied parameters on the beam behavior. Each subgroup consists of 2-4 specimens from the main groups (I, II, III and IV) and has the same properties except the studied variable. The subgroups will have a notation A, B, C or D. Subgroups (A1, A2, A3 and A4) focus on the effect of the splice length while subgroups (B1, B2, B3 and B4) focus on the effect of reinforcement bar diameter. Subgroups (C1, C2, C3 and C4) and (D1, D2, D3 and D4) focus on the effect of casting position and reinforcement ratio respectively.

2.4.3. Cracking and failure loads

2.4.3.1. Effect of splice length. Comparing the results obtained from Table 3 and Figs. 5-8 for subgroups (A1, A2, A3 and A4), short splice length (200) decreases both the cracking and failure loads by an average of 15% with respect to no-spliced specimens. For moderate splice (300) a decrease in cracking load of about 10% was recorded while an increase of about 9% was recorded in failure load values. There was no increase in the cracking loads for specimens with (400) splice, while only 6% increase was recorded in failure load values.

2.4.3.2. Effect of bar diameter. Comparing the results of groups (I and III) given in Table 3 and Figs. 9-12 for subgroups (B1, B2, B3 and B4), there is no change in the average cracking load while an average decrease in failure load of about 11% was recorded. Bond strength decreases with the decrease in the reinforcement total surface areas and since increasing bar diameter from 10 mm to 12 mm with the same reinforcement ratio led to decreasing of reinforcement total surface areas, the beam failure load decreased.

2.4.3.3. Effect of casting position. Comparing the results of groups (I and II) given in Table 3 and Figs. 13-16 for subgroups (C1, C2, C3 and C4), an average decrease in both cracking and failure loads of about 29% and 22% respectively was recorded. As known, bond strength between Rft. and concrete varied according to bar location. For top steel reinforcement, bond strength decreased by about 23% with respect to bottom reinforcement.

Table 3 Cracking and ultimate loads for HSSCC beams.

Group no. Beam Cracking stage Final stage Failure mode

Cracking load (kN) Deflection (mm) Failure load (kN) Deflection (mm)

I M-B-L0X10-R0.295 90 0.73 245 23 Flexure

M-B-L20X10-R0.295 50 0.55 230 5.5 Slippage

M-B-L30X10-R0.295 80 0.7 290 13 Flexure

M-B-L40X10-R0.295 90 1.43 270 34 Flexure

II M-T-L0X10-R0.295 80 0.8 220 38 Flexure

M-T-L20X10-R0.295 60 0.9 195 7.5 Slippage

M-T-L30X10-R0.295 40 0.65 200 12 Flexure

M-T-L40X10-R0.295 40 0.3 195 24.5 Flexure

III M-B-L0X12-R0.295 50 0.75 230 37.5 Flexure

M-B-L20X12-R0.295 90 1 195 5 Slippage

M-B-L30X12-R0.295 90 1.1 260 36 Flexure

M-B-L40X12-R0.295 80 1.3 230 24 Flexure

IV M-B-L0X12-R0.424 110 1.05 320 32 Flexure

M-B-L20X12-R0.424 85 0.95 245 4.1 Slippage

M-B-L30X12-R0.424 90 0.9 355 34.5 Slippage

M-B-L40X12-R0.424 120 0.8 380 32 Flexure

2.4.3.4. Effect of reinforcement ratio. Comparing the results of groups (III and IV) given in Table 3 and Figs. 17-20 for subgroups (D1, D2, D3 and D4), an average increase in both cracking and failure loads of about 30% and 42% respectively was recorded due to the increase in the Rft. ratio of about 44%.

2.4.4. Load-deflection relationship

Load-midspan deflection curves for all specimens according to subgroup classifications are shown in from Figs. 5-20.

2.4.4.1. Effect of splice length. Figs. 5-8 shows Load-Deflection relationship for subgroups (A1, A2, A3 and A4). As noticed from figures, the results obtained from beams with splice length equal to 20 times bar diameter always have deflection values bigger than those without splices at the same load value. The values obtained for beams with 30 and 40 times bar diameter splice length show behavior similar to beams without splices with failure loads equal or greater than beams without splice. This is because while 20 times bar diameter splice length was not enough to make Rft. act as non-spliced Rft., 30 and 40 times bar diameter spliced Rft. act together as a main tension Rft. and carries part of the tension stresses occurred due to flexure.

2.4.4.2. Effect of bar diameter. It was noticed from Load-Deflection relationship for subgroups (B1, B2, B3 and B4) shown in Figs. 9-12 that the results obtained from beams with bar diameter 12 mm always have deflection values greater than those with bar diameter 10 mm at the same load value.

2.4.4.3. Effect of casting position. It was noticed from Load-Deflection relationship for subgroups (C1, C2, C3 and C4) shown in Figs. 13-16 that the results obtained from top cast beams always have deflection values greater than bottom cast beams at the same load value.

2.4.4.4. Effect of reinforcement ratio. Comparing the results of groups given in Figs. 17-20 for subgroups (D1, D2, D3 and

D4), low deflection values at the same load level due to an increase in the Rft. ratio by about 44%.

2.4.5. Ductility of specimens

Ductility of specimen could be represented by the area under Load-Deflection curve. The bigger area under the curve, the more ductile behavior specimen has. Effect of each parameter on beam ductility will be discussed below.

2.4.5.1. Effect of splice length. Figs. 5-8 show Load-Deflection relationship for subgroups (A1, A2, A3 and A4). As noticed from figures, all specimens with 20 times bar diameter behavior were brittle. The area obtained under the curves for these beams smaller than those without splices by an average of 75%. The values obtained for beams with 30 and 40 times bar diameter splice length bigger than beams without splices by about 30% and 50% respectively.

2.4.5.2. Effect of bar diameter. It was noticed from Load-Deflection relationship for subgroups (B1, B2, B3 and B4) shown in Figs. 9-12 that the results obtained from beams with bar diameter 10 mm always have ductility more than those with bar diameter 12 mm by an average value of 25%.

2.4.5.3. Effect of casting position. It was noticed from Load-Deflection relationship for subgroups (C1, C2, C3 and C4) shown in Figs. 13-16 that the results obtained from top cast beams always have ductility more than those from bottom cast beams by an average value of 35%.

2.4.5.4. Effect of reinforcement ratio. Comparing the results of groups given in Figs. 17-20 for subgroups (D1, D2, D3 and D4), higher ductility by about 60% was recorded due to an increase in the Rft. ratio by about 44%.

2.4.6. Codes formulae for splice length

As given in Appendix A, ECP-203 [11] gives an equation for calculating the minimum splice length for tension splice taking into consideration concrete strength (fcu), steel yield stress (fy),

Crack Pattern of M-B-L30X10 R0.295

Crack Pattern of M-B-L40X10 R0.295

(a) Crack Pattern and Failure Mode for Group (I) Beams

Crack Pattern of M-T-L30X10 R0.295

Crack Pattern of M-T-L40X10 R0.295

(b) Crack Pattern and Failure Mode for Group (II) Beams

Crack Pattern of M-B-L30X12 R0.295 Crack Pattern of M-B-L40X12 R0.295

(c) Crack Pattern and Failure Mode for Groups (III) Beams

Crack Pattern of M-B-L30X12 R0. 424 Crack Pattern of M-B-L40X12 R0. 424

(d) Crack Pattern and Failure Mode for Groups (IV) Beams

Figure 4 Crack pattern and failure mode for beams.

bar surface shape (b factor), bar end shape (a factor) and bar location (top or bottom bar as g factor). However, ACI318M-11 [10] gives another equation taking into consideration concrete strength (fcu), steel yield stress (fy), coating factor (We),

location factor (Wt) and concrete type factor (k) for lightweight or normal weight concrete.

Using research data, the calculated required splice length by ECP-203 is about 360 for bottom casting and 470 for top

— 300

L0X10-

R0.295

0 10 20 30 40 50 Deflection (mm)

Figure 9 Load-deflection curves for subgroup (B1).

10 20 30 40 Deflection (mm)

Figure 5 Load-deflection curves for subgroup (A1).

0 10 20 30 40 50 Deflection (mm)

-M-B-L0X12-R0.424 ■M-B-L20X12-R0.424 M-B-L30X12-R0.424 ■M-B-L40X12-R0.424

Figure 6 Load-deflection curves for subgroup (A2).

■M-B-L20X12-R0.295

L20X10-

R0.295

10 20 30 40 50 Deflection (mm)

Figure 10 Load-deflection curves for subgroup (B2).

0 10 20 30 40 Deflection (mm)

Figure 7 Load-deflection curves for subgroup (A3).

„ 300 z

~ 250 •a

S 150 € S

10 20 30 40 Deflection (mm)

Figure 11 Load-deflection curves for subgroup (B3).

0 10 20 30 40 50 Deflection (mm)

■M-T-L0X10-R0.295 ■M-T-L20X10-R0.295 M-T-L30X10-R0.295 ■M-T-L40X10-R0.295

Figure 8 Load-deflection curves for subgroup (A4).

10 20 30 Deflection (mm)

Figure 12 Load-deflection curves for subgroup (B4).

0 10 20 30 40 50 Deflection (mm)

L0X12-

R0.424

10 20 30 40 Deflection (mm)

Figure 13 Load-deflection curves for subgroup (C1).

Figure 17 Load-deflection curves for subgroup (D1).

•M-T-L20X10-R0.295

M-B-L20X10-

R0.295

10 20 30 40 Deflection (mm)

Figure 14 Load-deflection curves for subgroup (C2).

■M-B-L20X12-R0.424

-M-B-L20X12-R0.295

10 20 30 40 Deflection (mm)

Figure 18 Load-deflection curves for subgroup (D2).

10 20 30 40 50 Deflection (mm)

Figure 15 Load-deflection curves for subgroup (C3).

10 20 30 40 Deflection (mm)

Figure 19 Load-deflection curves for subgroup (D3).

10 20 30 Deflection (mm)

Figure 16 Load-deflection curves for subgroup (C4).

0 10 20 30 40 50 Deflection (mm)

Figure 20 Load-deflection curves for subgroup (D4).

casting while the required splice length by ACI 318M-11 is 440 for both top and bottom casting.

As noticed from results, the best obtained results have been recorded in case of specimens with 400 splice length for both top and bottom casting which too close to those recommended by the both codes.

3. Conclusions

Based on the analysis of the results of the studied cases, the following conclusions can be obtained,

• Splice length of 20 times bar diameter is not sufficient to make the tension reinforcement act efficiently as no spliced reinforcement. All specimens having splice length 20 times bar diameter failed in a brittle mode under low loads with respect to specimens without spliced reinforcement.

• Splice length of 30 times bar diameter is critical to be taken as a sufficient splice length since beams sometimes started cracking and failed at a load smaller than those without splice.

• Splice length of 40 times bar diameter is almost the minimum splice length to be taken as a sufficient splice length since beams started cracking and failed at a load equal or higher than those without splice.

• The use of smaller bar diameter with the same reinforcement amount increases both the beam capacity and ductility.

• Top casting decreases both the beam capacity and ductility by about 22% and 35% respectively.

• Increasing reinforcement ratio by about 44% increases both cracking and failure loads by about 30% and 42% respectively with an increase in the beam ductility by about 60%.

Finally, it is recommended - for generic conclusions - more studies for different structural configurations and loadings such as long term loading should be carried out.

Also, it is recommended in the future to study more specimens experimentally and analytically with variable splice lengths and variable splice locations in beam to propose an equation for calculating the required splice length taking into consideration all variables.

Appendix A

A.1. ECP 203-2007

Lap splice can be calculated using the following equation:

Ld — a ■ b ■ g(fy/Vs)/(4fbu) (A.1)

where g = 1.3 for splices near top surface of beams during casting, g = 1 for splices near bottom surface of beams, b = 0.75 for deformed bars, a = 1 for straight bars, Fbu — 0.3^55/1.5 = 1.817 N/mm2, Ld — 1x4°x7158x117xg x 105 ffi 360

for bottom reinforcement, Ld — 1x4'x715 8i173x x -i40!! ffi 470 for top reinforcement.

A.2. ACI 318M-11

According to article 7.10.4.5, lap splices not less than the larger of 300 mm and 48db for deformed uncoated bar or wire.

According to article 12.2.3, for deformed bars or deformed wire, lap splice can be calculated using the following equation:

Ld =(fyWWJ2.1\Jf)db

where Wt is the traditional reinforcement location factor to reflect the adverse effects of the top reinforcement casting position, We is a coating factor reflecting the effects of epoxy coating if any, k shall not exceed 0.75 for lightweight concrete and k = 1.0 for normal weight concrete.

In studied case:

We = 1.0,uncoated reinforcement

Wt = 1.0 for regular bottom cast beams and Wt = 1.3 for

top cast beams.

The ACI code required (Wt • We) not less than 1.7, and so,

400 x(1. 7)

For bottom cast beams Ld —

2.1 x 1 x \/55 '

x db = 44di

For top cast beams Ld _ 400 x(1-7) x db ffi 44db 2. 1 x 1 x V55

References

[1] Atorod Azizinamini, Mark Stark, John J. Roller, S.K. Ghosh, Bond performance of reinforcing bars embedded in high-strength concrete, ACI-Struct. J. 90 (5) (1993) 554-661.

[2] Vedat A. Yerlici, Turan Ozturan, Factors affecting anchorage bond strength in high-performance concrete, ACI-Struct. J. 97 (3) (2000) 449-507.

[3] The European Guidelines for Self-Compacting Concrete, specification, Production and Use, EFNARC, Farnham, UK, EFNARC, May 2005.

[4] Yin-Wen Chan, Yu-Sheng Chen, Yi-Shi Liu, Development of bond strength of reinforcement steel in self-consolidating concrete, ACI-Struct. J. 100 (4) (2003) 490-498.

[5] M. Almeida Filhoa, B.E. Barraganb, J R. Casasc, A.L.H.C. EL Debsd, Variability of the bond and mechanical properties of SCC, IBRACON 1 (1) (2008) 31-57, ISSN 1983-4195.

[6] Kazim Turk, Ahmet Benli, Yusuf Calayir, Bond strength of tension lap-splices in full scale self-compacting concrete beams, Turkish J. Eng. Environ. Sci. 32 (Nov. 2008) 377-386.

[7] Sara Cattaneo, Gianpaolo Rosati, Bond between steel and self-consolidating concrete: experiments and modeling, ACI-Struct. J. 106 (4) (2009) 540-550.

[8] Mahmoud Ahmed El-Azab Abd El-Halim, Effect of Tension Lap Splice on the Behavior of High Strength Self-Compacted Concrete Beams, MSc Thesis, Faculty of Engineering, Cairo University, 2013.

[9] Okamura Hajime, Ouchi Masahiro, Self-compacting concrete, J. Adv. Concr. Technol. 1 (April) (2003) 5-15, Japan Concrete Institute.

[10] American Concrete Institute, ACI 318-11 Metric Building Code Requirements for Structural Concrete and Commentary, American Concrete Institute, Farmington Hills, Mich., USA, 2011, 503 pp.