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& e. . Procedia
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Procedia Engineering 210 (2017) 109-119
www.elsevier.com/locate/procedia
6th International Workshop on Performance, Protection & Strengthening of Structures under Extreme Loading, PROTECT2017, 11-12 December 2017, Guangzhou (Canton), China
A review of experimental results of steel reinforced recycled aggregate concrete members and structures in China (2010-2016)
Jinjun XuA,C, —Zongping ChenB,C, Jianyang XueD, Yuliang ChenB, Zuqiang Liu13
A College of Civil Engineering, Nanjing Tech University, Nanjing 211816, China B College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China C Key Laboratory of Disaster Prevention and Structural Safety of China Ministry of Education, Nanning 530004, China D School of Civil Engineering, Xi'an University; of Architecture and Technology, Xi'an 710055, China
Abstract
A series of investigations on the structural performance of Steel Reinforced Concrete (SRC) members and frame structures realized employing Recycled Aggregate Concrete (RAC) have been performed in China from 2010 to 2016. The research achievements on Steel Reinforced Recycled Aggregate Concrete (SRRAC) structures are sufficient to review and share with investigators from other countries. This paper begins with an introduction of some research progeess made on the bond behavior between RAC and I-steel. Discussion is then turned to the static behaviors of SRRAC members, including the flexural and chear performances of beams and concentric and eccenteic compreesive properties of columns. Finally, research findings on the performance of SRRAC columns and the correaponding beam-column joints and frames under cyclic loads are presented and anaiyzhd.
© 2017 The Authors. Publrshed by Elsevier Lsd.
Pee^review under responsibility of the scientific committed of the 6th International Workshop dn Performance, Protection & Strengthening of Structures under Extreme Loading
Keyotrrds: Recycled aggregate concrete; steel reinforced concrete; bond behavior; static and cyclic performance
1. Introduction
Processing Construction and Demolition Wastes (CDW) and reintroducing them as recycled aggregates in new concrctc, referred to as Recycled Aggregate Concrete (RAC), can be an effective way to develop and implement environmental sustainable concrete for new constructions [1-3]. A review of existing literatures [4-8] has shown that much effort has been devoted to the investigation of mechanical properties and durability of RAC. A basic
* Corresponding author. Tel.: +86-1522-5171-689)1 E-mail a<6dress:jsx6_concrete@ 163. coni (J.-J. Xu), zpchen@gx62edu.cn (Z.-P. Chen).
1877-7058 © 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the 6th International Workshop on Performance, Protection &
Strengthening of Structures under Extreme Loading.
10.1016/j.proeng.2017.11.055
consensus is that the compressive and tensile strengths, elastic modulus and durability of RAC are in general lower than those of Natural Aggregate Concrete (NAC). Many investigators have demonstrated that the existence of residual mortar lumps adhering to the recycled aggregates as well as the formation of micro-cracks during the crushing process in recycled aggregate production can reduce the strength and increase the deformation in RAC materials [9-13]. Therefore, the development and applications of RAC in civil engineering applications are somewhat restricted due to the above-mentioned shortcomings.
Steel embedded into concrete structural members, also named Steel Reinforced Concrete (SRC, see Figure 1), can make full use of the properties of steel and concrete. As a kind of composite structures with higher carrying capacities and better seismic behavior, SRC structures have been widely used in high-rise buildings with good economic benefits [14-18]. It can be seen from Figure 1 that the reduced mechanical properties of RAC can be made equivalent or partially higher to NAC by employing steel shapes embedded into concrete. Hence, SRC members can be recognized as an effective mean to improve the mechanical behavior in terms of strength, stiffness, ductility and energy dissipation for the initial RAC deficiencies compared with NAC. These composite structures combining the material science and SRC structures have been developed for seven years in China from 2010 to 2016, and the concept of Steel Reinforced Recycled Aggregate Concrete (SRRAC) structures was firstly proposed by Cui [19].
Fig. 1. The details of different elements in Steel Reinforced Concrete members
In this context, a carefully review of the current knowledge on SRRAC members and the corresponding structures is needed in order to identify the field of research that reached a sufficient knowledge for practical application and implementation in Standards and Code of Practice. On the other hand, being this topic a relatively new one, it is important to point out the need for further research.
The objective of this paper is to summarize some important findings on the behavior of SRRAC members and the corresponding structures. In Section 2, with the aim to define the interfacial force transmission mechanism, it is reviewed the bond behavior between RAC and I-steel under push-out tests by considering different influencing variables such as RCA content, maximum RCA size, thickness of the protective layer and stirrup ratio. Then, the static performances of SRRAC beams (Section 3) and SRRAC columns (Section 4) are analyzed. Finally, the cyclic properties of SRRAC columns and the corresponding joints and frames are addressed in Section 5, Section 6 and Section 7, respectively.
2. Bond behavior between RAC and I-steel
Bond is an important structural behavior of Steel Reinforced Concrete and refers to the adhesion between steel shape and surrounding concrete which is responsible for transfer of axial force between these two elements thereby providing strain compatibility and composite action of concrete and steel. By push-out tests, Chen et al. [20] and Zheng et al. [21] studied the bond behavior between RAC and I-steel without surface preparation. Variables reported in their tests are the RCA content (r=0, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%), maximum size of RCA (20 mm and 32 mm), thickness of the protective layer to I-steel flange (40 mm, 50 mm, 60 mm and 70 mm) and stirrup ratio. It should be pointed out that the recycled coarse aggregates used in their studies were not pre-soaked, and the design water-cement ratios (w/c) were kept constant for all the specimens. Some critical experimental results of describing the bond strengths include the bond at initial slip (is), bond at ultimate point (Tu) and bond at residual point (Tr). These bond strengths presented in Figure 2 show that: the relative bond stresses, including ts,r/ts,0, Tu,r/Tu,0 and Tr,r/Tr,0, are generally improved as the increasing of RCA content, and this
tendency is basically concordant with the enhancement of concrete cubic compressive strength fcu influenced by RCA content. This is also confirmed by previous researches involved in RAC-filled steel tubes [22]. The reason can be attributed to a fact that the actual w/c in RAC is lower than the design w/c due to the strong water absorption capacity of recycled coarse aggregates without pre-soaked; hence, with an increase in RCA content, the lower w/c can lead to a higher bond strength between steel and concrete, which is positively related to the compressive strength in concrete. On the other hand, the bond strength on the contacting interface of I-steel and RAC is influenced by the size of recycled coarse aggregates, which means that the larger size of RCAs can lead to improve the bond strength in SRRAC. This can be explained that the larger size of RCA has more adhered mortar on the surface of aggregate compared to the smaller one, and the strong water absorption capacity of adhered mortar can reduce the design w/c, as a result, the bond strength in SRRAC can be enhanced due to the improvement of concrete strength. As also can be seen from Figure 2, both the ultimate bond strength and the residual bond strength can be improved by means of enlarging the thickness of the protective layer and increasing the stirrup ratio. As a matter of fact, these two kinds of measures have the same effect on strengthening the confinement to the encased I-steel, and the tightening pressure on the interface between I-steel and RAC can be significantly increased.
^ 2.0 ai
I 15 I 1.0
* 0.5 0.0
- rs,r / t s,0% [ Bond at initial slip] _ Tu,r / Tu,0% [Ultimate bond]
- t r,r / t r,0% [ Residual bond]
- f cu,r / f cu,0% [Concrete strength]
0 40 60 80 100 RCA content [%]
§ 1.5
■o § 10
w 0.5 E
2.5-i £ 1.5-
o 0 5. 0.0-
- Ultimate bond strength [rujl
- Residual bond strength [rr] I
Max RCA size [mm]
40 45 50 55 60 65 70 Thickness of the protective layer [mm]
Stirrup ratio [%]
Fig. 2. Effects of variables on the bond strength: (a) effect of RCA content; (b) effect of maximum size of RCA; (c) effect of thickness of the protective layer; (d) effect of stirrup ratio (data by Chen et al. [20] and Zheng et al. [21])
0 20 40 60 80 100 RCA content [%]
Fig. 3. Effect of RCA content on flexural moment and mid-span deflection (data by Chen et al. [23])
3. Mechanical performance of SRRAC beams
3.1 Flexural behavior of SRRAC beams
Chen et al. [23] carried out an investigation on the flexural behavior of simply supported SRRAC beams under two-point bending loads. The recycled coarse aggregates were not pre-soaked before fabricating specimens, and the design water to cement ratio (w/c) was kept as a constant value. The main test results are shown in Figure 3, in which two performance indices, including the flexural strength (Mu) and the corresponding mid-span deformation (Fu), are growing with the increasing of RCA content, and their influencing mechanisms are controlled by high water absorption capacity of RCA and RCA defects, respectively. As presented in Figure 3, concrete cubic compressive strength fcu increases as RCA content grows, which is on the material level to explain the structural strength characteristics. Hence, understanding the relationship between fcu and RCA water absorption characteristics is the key to illustrate the test phenomenon. As before-mentioned concrete configuration craft, RCAs used in the test were not pre-soaked and w/c was designed as constant, so that the real w/c was reduced due to the strong water absorption capacity of RCAs. As a result, the concrete strength can be improved. With respect to the mid-span
deformation, the initial damage and micro-crack defects in RCAs can lead to decrease the flexural stiffness of SRRAC beams, and the ability to resist deformation is correspondingly weakened.
3.2 Shear behavior of SRRAC beams
Shear behavior of SRRAC beams is also an important mechanism to practice RAC materials in SRC structure members. Chen et al. [24] conducted an experimental study on shear behavior of SRRAC beams by considering the effects of RCA content and shear-span ratio on their mechanical indices. The recycled coarse aggregates were not pre-soaked before fabricating concrete, and the design water to cement ratio (w/c) was kept as a constant value. According to the test results, it can be seen from Figure 4 that the effect of RCA content on the shear strength (Vu) and the corresponding mid-span deflection (Fu) of SRRAC beams is similar to the flexural strength and mid-span deflection of SRRAC beams influenced by RCA content (see Figure 3), hence, their reasons behind the test phenomenon are identical. In addition, the effect of shear-span ratio on ultimate shear capacity of SRRAC beams is illustrated in Figure 4, in which the shear strength decreases with expanding the value of shear-span ratio. This finding is coincident with the results obtained from conventional RC and SRC beams.
0 20 40 60 80 100 RCA content [%]
350 300 . 250 200 150
-□- r = 30% -O- r = 70% -A- r = 100%
1.0 1.2 1.4 1.6 1.8 Shear-span ratio
Fig. 4. (a) effect of RCA content on shear strength and mid-span deflection; (b) effect of shear-span ratio on ultimate shear capacity (data by
Chen et al. [24])
0 20 40 60 80 100 RCA content [%]
2000 1800 z 1600 <; 1400 1200 1000
- Diameter of stirrup = 8 mm
- Diameter of stirrup = 6 mm
80 100 120 140 160 180 200 Spacing of stirrup [mm]
Fig. 5. (a) effect of RCA content on compressive strength; (b) effect of stirrup ratio on compressive strength (data by Wang et al. [25])
4. Static property of SRRAC columns
4.1. Concentric loaded SRRAC columns
Wang et al. [25] investigated the influences of RCA content and stirrup ratio (including spacing of stirrup and diameter of stirrup) on the load carrying capacity of SRRAC columns when test specimens were subjected concentric loads. It should be noted that the recycled coarse aggregates used in the test were not pre-soaked and the design water-cement ratio (w/c) was constant for all the specimens. The relationship between ultimate axial load (Nu) and RCA content and concrete cubic compressive strength (fcu) versus RCA content are shown in Figure 5. In general, the effect of RCA content on Nu is similar to fcu influenced by RCA content, and this test result is again verifying the fact that non pre-soaked RCAs have a significant effect on improving the RAC material strength and the corresponding structural strength. Figure 5 also presents the effect of stirrup ratio on the compressive strength of SRRAC columns under concentric loads. From Figure 5, it can be summarized as follows: (1) regardless of
diameter of stirrup, expanding the spacing of stirrup leads to decrease the ultimate axial load of SRRAC columns; (2) regardless of spacing of stirrup, enlarging the diameter of stirrup is benefit for increasing the ultimate axial load of SRRAC columns. As a matter of fact, narrowing the spacing of stirrup and enlarging the diameter of stirrup are the two measures of increasing the stirrup ratio in SRRAC members, and they have an efficient influence on confining the inner concrete. As a result, the concentric load carrying capacity of SRRAC columns can be improved due to increasing the stirrup ratio.
4.2. Eccentric loaded SRRAC columns
Based on the eccentric loading test, Chen et al. [26] studied the effects of RCA content and eccentric degree (eo/h) on the structural behavior of SRRAC columns without pre-soaking the RCAs. With respect to the test results, it can be found from Figure 6 that the ultimate axial load, concrete cubic compressive strength and mid-height deflection of SRRAC columns generally increase with an increase of RCA content, and the mechanisms of bended SRRAC beams (see Figure 3) are still suitable for the eccentric loaded SRRAC columns. In addition, the relationship between eccentric degree and mechanical indices (ultimate axial load and mid-height deflection) is given in Figure 7. Figure 7 exhibits that an increase of eccentric degree leads to decrease the ultimate axial load but increase the mid-height deflection of eccentric loaded SRRAC columns. It can be explained that when eccentric degree grows, the second-order effect in the column can be expanded and it goes against the structural behavior.
1.0 u.
0 20 40 60 80 100 RCA content [%]
0 20 40 60 RCA content ['
I 1.5 a
(c) eo / h = 0.6 f cu/ / f c
Mid-span deflection
Axial strength
0 20 40 60 RCA content ['
1.5 1 1.0 ¿
Fig. 6. Effect of RCA content on compressive strength and mid-span deflection of SRRAC columns under eccentric loads: (a) eo/h = 0.2; (b) eo/h
= 0.4; (c) eo/h = 0.6 (data by Chen et al. [26])
80 100
1400 1200 z 1000 ¿ 800 600 400
-o- r = 30% -O- r = 70% r = 100%
0.3 0.4 0.5 e0 / h
0.4 e0 / h
Fig. 7. Effect of eccentric degree on compressive strength and mid-span deflection of SRRAC columns under eccentric loads: (a) axial load; (b)
mid-span deflection (data by Chen et al. [26])
5. Cyclic property of SRRAC columns
Understanding the seismic behavior of SRRAC columns under earthquake action is the key to develop and apply RAC materials in SRC structures in seismic regions. Hence, using anti-seismic experiments such as low cyclic reversed loading test and pseudo dynamic test are recognized as an efficient measure to reveal the seismic-induced failure mechanism of a structure. Ma et al. [27,28] conducted two batches of lateral low cyclic reversed loading tests on SRRAC columns by considering four variables, including the RCA content, axial load ratio, stirrup ratio and shear-span ratio. Also, the recycled coarse aggregates used in the test were not pre-soaked. Figure 8 presents the effect of RCA content on the shear strength and ductility of SRRAC columns. It can be found that the ultimate shear
load of SRRAC columns is larger than that of conventional SRC columns; and the ductility of test columns decreases when RCA content increases. This conforms the conclusions made by Chen et al. [29] in RAC-filled steel tubes, which are also the results of high water absorption capacity and brittleness of RCA influencing the shear strength and ductility on the material level, respectively. The effects of axial load ratio, stirrup ratio and shear-span ratio on the shear strength and ductility of SRRAC columns are given in Figures 9 and 10. It can be seen that: (1) the axial load ratio leads to improve the ultimate shear load but reduce the ductility; (2) the results show that a higher stirrup ratio has larger ultimate shear load and ductility; (3) increasing the shear-span ratio can decrease the ultimate shear load but increase the ductility in SRRAC columns. These findings are similar to the conventional RC and SRC columns influenced by axial load ratio, stirrup ratio and shear-span ratio, respectively.
0 20 40 60 80 100 RCA content [%]
Fig. 8. Effect of RCA content on strength and ductility of SRRAC columns (data by et al. [27,28])
Axial load ratio
350] 300-■ 250200150-
100-■ 0.5
- Shear-span ratio = 3.25
- Shear-span ratio = 1.40
1.0 1.5 2.0 Stirrup ratio [%]
1.5 2.0 2.5 3.0 Shear-span ratio
Fig. 9. Strength: (a) effect of axial load ratio; (b) effect of stirrup ratio; (c) effect of shear-span ratio (data by Ma et al. [27,28])
Axial load ratio
- Shear-span ratio = 3.25
- Shear-span ratio = 1.40
'■B 4-
1.0 1.5 2.0 Stirrup ratio [%]
1.5 2.0 2.5 3.0 Shear-span ratio
Fig. 10. Ductility: (a) effect of axial load ratio; (b) effect of stirrup ratio; (c) effect of shear-span ratio (data by Ma et al. [27,28])
6. Cyclic performance of SRRAC beam to SRRAC column joints
Xue et al. [30] tested four SRRAC beam-SRRAC column inner-frame joints under a constant axial load and lateral cyclic reversed loads by considering the RCA contents of 0, 30%, 70% and 100%. In this test, the recycled coarse aggregates were pre-soaked. The water to cement ratio (w/c) adopted were 0.44, 0.44, 0.43 and 0.42 corresponding to the RCA contents of 0, 30%, 70% and 100%. It should be noted that the design w/c decreases when RCA content increases, and the recycled coarse aggregates used in this test are pre-soaked, so that it can be judged from this test that the authors intended to control the actual w/c in the same level, and only to study the effect
of RCA defects on the behavior of beam-column joints. Test results such as the ultimate shear load, Pu, ductility coefficient, y., and equivalent viscous damping coefficient, he, are presented in Figure 11. From Figure 11, it can be seen that the shear strength, ductility and energy-dissipating capacity of SRRAC beam to SRRAC column joints reduce with the increasing of RCA content. The reason can be explained as: for the shear strength, the defects of recycled coarse aggregates such as the low strength of adhered mortar and micro-cracks during the crushing process in recycled aggregate production, can decrease the RAC strength when compared with NAC, which is confirmed by the tendency of fc-RCA content shown in Figure 11 (a). Hence, the lateral shear load of SRRAC beam-SRRAC column joints can be affected by RCA content due to its correlation with fu. With respect to the ductility and energy-dissipating capacity, the recycled coarse aggregates have a lot of micro-cracks, which can enlarge the brittleness of RAC materials and decrease the frictional effect on the interface of aggregates, so that on the structural level, the deformability and internal energy dissipation capacity of beam-column joints can be weaken.
1.05 1.10-r
1.00 o o .52 c ,0 1.05-
3= 1.00-
0.95 O
o 0.95-
0 90 cx
o E m 0.90-
0.85 TO 0 Q1 0.85-
0.80 0.80-L
0 20 40 60 80 100 RCA content [%]
(b) —0— heyr / hey,0% [Yeild point] —O— heur / heu,0% [Peak point] - hef,r/ hef,0% [Failure point]
20 40 60 80 RCA content [%]
Fig. 11. Effect of RCA content on seismic performance: (a) shear strength and ductility; (b) energy-dissipating capacity (data by Xue et al. [30]) 7. Cyclic performance of reinforced RAC beam to SRRAC column frames
Xue et al. [31] reported the cyclic performance of four 1/2.5-scaled reinforced RAC beam to SRRAC column frames fully infilled with RAC masonry blocks under constant axial loads and lateral low cyclic reversed loads. All the concrete fabricated in this test were the RAC with 100% RCA content. Test variables such as axial load ratio, spacing of tensile rebar in filled walls (tensile rebars were used to improving the confinement to infilled walls) and strength level of masonry blocks, were considered to evaluate the seismic behavior of reinforced RAC beam to SRRAC column frames.
Figure 12 shows the effect of axial load ratio on cyclic performance-based indices of test frames. From Figure 12, it can be seen that the axial load ratio has a positive effect on the lateral ultimate shear load but has a negative effect on the ductility and energy dissipation of reinforced RAC beam to SRRAC column frames. The reason is that higher axial load ratio makes the SRRC columns much stronger (see Figure 11a), while the ductility of SRRC columns can be reduced with increasing the axial load ratio (see Figure 11b); in addition, as for the energy dissipation of frames, the more compact of aggregates in concrete can hardly occur the friction between aggregate interfaces in concrete cracks, so that the generation of heat by friction relatively reduces under a relatively higher axial load ratio. Figure 13 illustrates that as the spacing of tensile rebar in filled walls increases, the ultimate lateral shear load, ductility and energy dissipation of test frames decrease. This phenomenon is actually based on the confinement degree of tensile rebars to infill walls, which means that reducing the spacing of tensile rebars can enhance the shear strength of masonry blocks and postpone their failure and cumulative damage.
The effect of strength level of masonry blocks on the ultimate lateral shear load, ductility and energy dissipation of reinforced RAC beam to SRRAC column frames is illustrated in Figure 14. These results show that the ultimate lateral shear load and energy dissipation can be improved by means of fabricating higher strength of RAC masonry blocks, while the tendency is on the contrary that a higher strength level of RAC masonry blocks has a lower coefficient of ductility. It is not difficult to understand that the relationship between shear strength of frames and strength level of RAC masonry blocks is positively related, and it is a common sense that higher strength of concrete leads to increase its brittleness on the material level. When it comes to the energy dissipation, it can be explained that micro-cracks under a higher strength level of RAC masonry blocks is approaching to be filled with sufficient mortar due to the density of cement-mortar stones, so that the friction between mortar and recycled aggregates in concrete cracks can be added, which is compared to the micro-cracks filled with insufficient mortar under the
conditions of lower strength level of RAC masonry blocks.
Ifl 0.18
it 0) 0.16
ik TO T 0.14
LU TD 0.12
- hey [Yeild point]
- heu [Peak point]
- hef [Failure point]]
0.3 0.4 0.5 0.6 Axial load ratio
0.3 0.4 0.5 0.6 Axial load ratio
0.4 0.5 0.6 Axial load ratio
Fig. 12. Effect of axial load ratio on (a) strength, (b) ductility and (c) energy dissipation (data by Xue et al. [31])
\r = 100%|
□- -□
|r = 100%
□-- --□
100 200 300 400 500 Spacing of tensile rebar in filled walls [mm]
100 200 300 400 500 Spacing of tensile rebar in filled walls [mm]
» C 0.18
° Ö o .2
IS 0.16
0.12 0.10
100 200 300 400 500 Spacing of tensile rebar in filled walls [mm]
Fig. 13. Effect of spacing of tensile rebar in filled walls on (a) strength, (b) ductility and (c) energy dissipation (data by Xue et al. [31])
MU3.5 MU5
Masonry block strength level
MU3.5 MU5
Masonry block strength level
0.20 0.18 0.16 0.14 0.12 0.10
MU3.5 MU5
Masonry block strength level
Fig. 14. Effect of strength level of masonry blocks on (a) strength, (c) ductility and (c) energy dissipation (data by Xue et al. [31]) (a)
Fig. 15. Failure mode of frames with different filling ratios: (a) no-wall; (b) half-wall; (c) full-wall (images by Xue et al. [32])
Ç 0.14
Jinjun Xu et al. /Procedia Engineering 210 (2017) 109—119 Fig. 16. Skeleton curves of frames with different filling ratios (data by Xue et al. [32])
2.0 I 1.5
a, 1 1.0
Fig. 17. Effect of filling ratio of infilled walls on (a) ultimate lateral load and (b) lateral stiffness (data by Xue et al. [32])
Later, Xue et al. [32] also investigated the lateral resisting ability of reinforced RAC beam to SRRAC column frames with respect to the filling ratio of infilled walls, highlighting the parameter of no walls, half walls and full walls. The failure mode of three types of frames is shown in Figure 15, and the load-displacement skeleton curves of test frames are sketched in Figure 16. It can be observed from Figure 16 that the skeleton shape of no-wall frame is similar to that of half-wall frame, while the skeleton shape of full-wall frame has a distinct peak point and then a sudden descending stage compared to those of no-wall and half-wall frames. It means that the reinforced RAC beam to SRRAC column frames fully infilled walls have two lines of defense to resist the earthquake action on their structures: (1) the first defense line is the infilled walls; (2) after the infilled walls failure, the pure frame starts to function its second defense line with no difference to no-wall frame and half-wall frame. Figure 17 shows the effect of filling ratio of infilled walls on the ultimate lateral load and lateral stiffness of reinforced RAC beam to SRRAC column frames. From Figure 17, it can be concluded that expanding the filling ratio of infilled walls has a positive influence on the ultimate lateral load and lateral stiffness in the loading process.
8. Conclusions
This paper presented a review of experimental results on the bond behavior between RAC and I-steel under push-out test, as well as the static and cyclic performances of SRRAC members and the corresponding joints and frames. The main conclusions can be summarized as follows:
(1) The bond strength between RAC and I-steel in general increases with an increase of RCA content, provided that the RCA used are not pre-soaked; The larger size of RCAs can lead to improve the bond strength in SRRAC.
(2) Flexural strength, shear strength and mid-span deformation of SRRAC beams are growing with the increasing of RCA content, and their influencing mechanisms are controlled by high water absorption capacity of RCA and RCA defects, respectively; the effect of RCA content on axial load carrying capacity is similar to concrete compressive strength influenced by RCA content, and the result is verifying the fact that non pre-soaked RCAs have a significant function on improving RAC material strength and the corresponding structural strength; the ultimate axial load, concrete cubic compressive strength and mid-height deflection of SRRAC columns are generally growing with an increase of RCA content; an increase of eccentric degree leads to decrease the ultimate axial load but increase the mid-height deflection of eccentric loaded SRRAC columns.
(3) The ultimate shear load of SRRAC columns is larger than that of conventional SRC columns; and the ductility of test columns decreases when RCA content increases, which is the results of high water absorption capacity and brittleness of RCA influencing the shear strength and ductility on the material level, respectively; the shear strength, ductility and energy-dissipating capacity of SRRAC beam to SRRAC column joints reduce with the increase of RCA content; the ultimate lateral shear load and energy dissipation in frames can be improved by means of fabricating higher strength of RAC masonry blocks, while the tendency is on the contrary that a higher strength level of RAC masonry blocks has a lower coefficient of ductility; the reinforced RAC beam to SRRAC column frames fully infilled walls have two lines of defense to resist the earthquake action on their structures; expanding the filling ratio of infilled walls has a positive influence on the ultimate lateral load and lateral stiffness of frames in the loading process.
Acknowledgements
The research reported in this paper was supported by the National Natural Science Foundation of China (Project Nos: 51708289 and 51578163), Postdoctoral Science Foundation of China (Project No: 2017M611796) and Key Project of Natural Science Foundation of Guangxi Province (Project No: 2016GXNSFDA380032).
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