Static behavior of stud shear connectors in elastic concrete–steel composite beams

Static behavior of stud shear connectors in elastic concrete–steel composite beamsContents lists available at ScienceDirect
Journal of Constructional Steel Research
Review
Static behavior of stud shear connectors in elastic concrete–steel composite beams
Qinghua Han a,b, Yihong Wang a, Jie Xu a,b,, Ying Xing a
a School of Civil Engineering, Tianjin University, Tianjin 300072, China b Key Laboratory of Coast Civil Structure and Safety of Ministry of Education, Tianjin University, Tianjin 300072, China
Corresponding author at: School of Civil Engineering, E-mail address: [email protected] (J. Xu).
http://dx.doi.org/10.1016/j.jcsr.2015.06.006 0143-974X/© 2015 Elsevier Ltd. All rights reserved.
a b s t r a c t
a r t i c l e i n f o
Article history: Received 30 December 2014 Received in revised form 19 May 2015 Accepted 15 June 2015 Available online xxxx
Keywords: Elastic concrete Composite beam Stud shear connectors Push-out test Crumb rubber content Ductility
Elastic concrete was first introduced into steel–concrete composite beams due to its superior deformability. The static behavior of stud shear connectors embedded in elastic concrete is studied in this paper. Eighteen push-out tests were conducted to evaluate the load-slip behavior, bearing capacity and ultimate slip of shear studs. Four different rubber contents, 0%, 5%, 10% and 15%were taken into consideration. Test results show that the ductility of stud improves significantly with the increasing rubber content. Especially, when the rubber content reaches 10%, the shear stud has relatively high bearing capacity, better deformation and better ductility. In specimens with 5% rubber content elastic concrete, shear stud shows amore ductile behavior embedded in lower compres- sive strength elastic concrete and the diameter has little influence on ductility and stiffness of studs. The equa- tions provided by AASHTO LRFD, Eurocode-4 and GB50017-2003 can still apply to shear studs embedded in elastic concrete. Compared with the experimentally obtained bearing capacities, AASHTO LRFD is confirmed to be the closest one.
© 2015 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 2. Material properties of elastic concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
2.1. Raw materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 2.2. Compressive strengths and elastic modulus of elastic concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 2.3. Compressive stress–strain curves of elastic concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 2.4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
3. Push-out test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 3.1. Test set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 3.2. Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
3.2.1. Modes of failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 3.2.2. Bearing capacity and ultimate slip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 4.1. Bearing capacity, stiffness and ductility of the shear stud in elastic concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
4.1.1. Effect of rubber contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 4.1.2. Effect of elastic concrete compressive strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 4.1.3. Effect of stud diameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
4.2. Stress mechanism of studs in push-out test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 4.3. Comparison between design codes and test results on ultimate strength of studs . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Tianjin University, Tianjin 300072, China.
jxuosai
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1. Introduction
Steel–concrete composite beams have been widely used in the field of bridge and building structures for decades [1]. As an important com- ponent of steel–concrete beams, stud shear connectors transfer the lon- gitudinal shear force on the surface between steel and concrete. The deformation ability of shear stud is a decisive factor to evaluate its duc- tility. Hence, it is of great importance to find a method to improve the deformation capacity of shear studs without sacrificing its bearing capacity. To this end, elastic concrete is introduced into composite beams in this paper.
Elastic concrete, also called crumb rubber concrete or recycled tire rubber-filled concrete, is a new environmental material in the last few years. According to previous studies, the deformability of concrete in- creases significantly after adding rubber crumb to it. Elastic concrete has ductile failure and better crack resistance. Moreover, it has superior acoustical properties, wearing resistance and aging resistance to ordi- nary concrete [2–4]. Nowadays elastic concrete is used in the paving of tennis courts and parking lots due to its superior properties, but it has never been used in composite beams. Hence, it is significant to study the performance of the elastic concrete and steel composite beams.
This paper presents an investigation on the shear studs in the elastic concrete and steel composite beams through push-out test. The push- out test has proven to be an effective method of determining the ulti- mate strength and deformation capacity of shear connectors. Since the first push-out test was devised in Switzerland in the 1930s [5], many experimental tests of shear connectors have been studied by numerous researchers. Viest [6] conducted 12 push-out tests and proposed the conception of “critical load”. He suggested that the shear bearing capac- ity of studs should be the load value when load-slip curves just entered nonlinear stage or the residual slip was 0.762 mm. Chapman [7] and Johnson [8] measured the shear performance of studs and developed a calculation model based on push-out tests. In 1966, Slutter and Fisher [9] tested the fatigue behavior of shear connectors and proposed the
Table 1 Proportions of elastic concrete with different rubber contents.
Group Rubber content
Crumb rubber (kg)
Water reducing (kg)
1 0% 0 295 1087 839 165 2.174 2 5% 50 400 703 1004 169 2.391 3 10% 100 590 1230 412 168 6.522 4 15% 150 590 1230 412 168 7.39 5 5%(S) 50 550 703 1004 169 5.652
Fig. 1. Raw materials and
fatigue design formula. In 1971, a design formula of static behavior of shear studs was proposed by Ollgaard [10] based on the push-out test results. The structure of the formula was adopted by most of national codes for nominal strength of studs. Changsha Railway Institute [11] conducted 15 push-out tests of studs based on Wuhu Bridge in China. An [12] investigated the different behaviors of studs between normal strength and high strength concrete through push-out tests. The results showed that the concrete compressive strength significantly affected the shear capacity of studs.
Recently a number of researchers have focused on the different as- pects of studs. In 2004, Lee and Shim [13,14] investigated the static and fatigue behavior of large stud shear connectors up to 30 mm in di- ameter, which were beyond the limitation of current design codes. A new stud system fastened with high strength pins was investigated ex- perimentally by Tahir [15]. Pavlovi [16] studied the different behaviors between bolted shear connectors and headed studs. W Xue [17] con- ducted 18 push-out tests to show the static behavior of single-stud. D Xue [18] investigated the different behaviors between single-stud and multi-stud connectors. According to the aforementioned research, the shear bearing capacity of studs depends on many factors, including the material and diameter of the stud itself and properties of the sur- rounding concrete slab. These factors are all included in several national codes [19–22].
People paymore attention to the bearing capacity of the shear studs, however few researchers have addressed the relationship between the deformation capacity of shear studs and the properties of the surround- ing concrete. This paperwill focus on this point.Moreover, the optimum efficiency of rubber content can be found after the experimental study.
The remainder of the paper is organized as follows. In Section 2, we present an introduction to the material properties of elastic concrete used in push-out tests. Section 3 details a total of 18 push-out tests an- alyzing failure modes, bearing capacity and ultimate deformation of studs. Three influence factors on the static behavior of studs, including rubber contents, elastic concrete compressive strengths and stud diam- eters are discussed in Section 4. The actual stress mechanism of studs in push-out tests and the comparison between the test results and three national codes regarding nominal strength of studs are also presented in this section. Section 5 presents some concluding remarks of this current paper.
2. Material properties of elastic concrete
Before push-out tests, the material properties of the different rubber mixed elastic concrete were studied experimentally. Note that the mixture ratios of elastic concrete discussed below were the same of those used in push-out specimens, introduced in Section 3 of this paper.
concrete test cubes.
Table 2 Results of the compressive strength and elastic modulus tests.
Group Rubber content
7 d (MPa)
28 d/(MPa)
120 d/(MPa)
Elastic Modula/(GPa)
1 0% 26.41 43.30 45.07 33.72 2 5% 25.75 36.27 38.67 27.90 3 10% 38.00 43.70 46.30 21.83 4 15% 28.85 35.13 38.46 14.45 5 5%(S) 35.98 48.40 50.83 29.12
117Q. Han et al. / Journal of Constructional Steel Research 113 (2015) 115–126
2.1. Raw materials
The rawmaterials used for test samples were fine aggregate, coarse aggregate, water and crumb rubber within 1–2 mm in diameters. In addition, the high range water-reducing admixture was adopted to
(a)
(c) (d)
Fig. 2. Typical damage shapes of concrete cubes. (a) Damaged concrete cubewith 0% rubber con 10% rubber content; (d) Damaged concrete cube with 15% rubber content; (e) Damaged concr
Fig. 3. Compressive stress
insure the high fluidity of concrete mixing. The mix proportions of crumb rubber followed the principle of volume percentage method and the rubber content was divided into four groups: 0% (the same as ordinary concrete), 5% (50 kg/m3), 10% (100 kg/m3) and 15% (150 kg/m3) [23]. These four groups were designed to be the same concrete grade level, C30. The compressive strength of C30 is between 35–45 MPa. In addition, a higher grade elastic concrete (C40) with 5% rubber content was designed to study the influence of different com- pressive strength on the performance of elastic concrete, and here this group was called 5% (S).
The optimalmix proportions of the rawmaterialwere achieved after 37 group testing, and the results are listed in Table 1. Eighteen standard concrete test cubes (150× 150× 150mm3) and nine prismatic concrete samples (100 × 100 × 300mm3) weremade together with the 18 spec- imens for push-out test according to Table 1. The specimenswere cured in the standard curing room (temperature is 20 ± 3 °C and relative
(b)
(e)
tent; (b) Damaged concrete cubewith 5% rubber content; (c) Damaged concrete cubewith ete cube with 5% (S) rubber content.
–strain curve testing.
Table 3 The ultimate stress and strain of concrete with different rubber contents.
Rubber content
Peak strain
Ultimate strain
0% 34.063 34.063 0.002725 0.003516 5% 26.833 26.833 0.002996 0.004223 10% 34.091 34.091 0.004323 0.006943 15% 29.412 29.412 0.004472 0.007104 5%(S) 37.762 37.762 0.003056 0.004024
Fig. 5. Stress–strain curves of concrete with different rubber contents.
118 Q. Han et al. / Journal of Constructional Steel Research 113 (2015) 115–126
humidity is above 90%) for the first 28 days and then under the condi- tion of room temperature. The raw materials and concrete test cubes are shown in Fig. 1.
2.2. Compressive strengths and elastic modulus of elastic concrete
According to the test methods of building material properties (GB/T50081-2002) [24] and (T0555-2005) [25], the compressive strength and elastic modulus of concrete were obtained. The results are listed in Table 2. Here, d refers to days and the push-out tests were conducted on 120 d. The damaged concrete cubes after the compressive strength tests are shown in Fig. 2.
From Table 2, it can be concluded that with the increasing rubber content, the elastic modulus of concrete declines. The largest drop am- plitude of elastic modulus is 57% for elastic concrete with 15% rubber content. Elastic modulus is a reaction of a material's deformability. Hence, with the increase of rubber content, it becomes easier to deform for the concrete in the elastic stage.
2.3. Compressive stress–strain curves of elastic concrete
A testing machine with a capacity of 5000 kN was adopted to apply load on the prismatic concrete samples in stress–strain curve testing. On the two surfaces of the concrete sample, the measuring points of longi- tudinal strain were arranged at the center of the trisection. The experi- mental details are shown in Fig. 3.
During the loading process, the tiny crack first appeared at the top of all specimens, and the crack propagated downwards gradually. The more rubbers mixed in concrete samples, the slower the tiny crack ap- peared and developed. When reaching bearing capacity, fragments from the ordinary concrete instantaneously ruptured, and the rupture was accompanied by a loud noise. Then the load quickly dropped. How- ever, there were less ruptured fragments for the elastic concrete, and the process of damage and unloading took more time. The details can be found in Table 3, and here the ultimate strain was defined as the strain value when the ultimate load dropped 15%.
As shown in Fig. 4, the typical damaged situation of prismatic concrete samples with different rubber contents very significantly.
(a)0% (b)5% (c)10
Fig. 4. Typical damaged situations of prismatic concret
There was one fatal penetrating crack on the surface when the crumb rubber content was 0%, and the top of the sample was badly damaged. When it had 5% rubber mixed in the concrete, there were multiple cracks rather than just one fatal penetrating crack, as shown in Fig. 4(b). When the rubber content reached 10%, the concrete sample maintained integrity with four relatively long cracks, uniformly distrib- uted on the surface. The condition of the concrete sample was even bet- ter when the rubber content was 15%.
2.4. Discussion
Compared with the ordinary concrete, the increasing ranges of peak strain in the elastic concrete with 5%, 10% and 15% rubber content are 10%, 60% and 65% respectively, and ultimate strain are 26%, 97% and 102%. Moreover, the descent stage of the stress–strain…