State-of-the-art review on steel-concrete composite walls

: Steel-concrete composite walls, valued for their capacity to combine the strengths of steel and concrete, have become a prevalent construction choice. During the past few decades, the performance of steel-concrete composite walls has been studied by means of structural tests, theoretical analysis, and numerical simulation. Different types of steel-concrete composite walls have been proposed by researchers to satisfy miscellaneous structural requirements. Meanwhile, new forms were continually being developed to further improve the mechanical performance. This review paper examines research conducted over the past few years on these versatile structural elements. The paper categorizes steel-concrete composite walls according to the arrangement of steel plates and concrete, along with the configurations of steel plates. It delves into the unique characteristics of each type and analyzes their performance under various loading conditions, including axial, cyclic, shear, fire, dynamic, impact, and joint loads. Additionally, existing design recommendations for these walls are summarized. To conclude, the paper offers insights into potential future developments in steel-concrete composite wall technology.


Introduction
Composite structures have become ubiquitous across various engineering disciplines, playing a vital role in modern construction practices [1,2].Their exceptional performance stems from the combined action of different materials, each contributing properties that they might not possess individually.Steel-concrete composite structures are the most prevalent example in civil engineering, with their use dating back to the early 20th century, particularly in America, Japan, and Europe [3].Recent decades have witnessed a surge in the development of various composite systems and components, including composite columns, plates, beams, and walls [4][5][6][7].
The shear wall is an important lateral resistance component in structures [8,9], which are responsible for bearing shear forces and dissipating seismic energy during earthquakes, thereby becoming a significant component in the buildings.With the development of high-rise building systems, the height of the structure continues to increase and the layouts become more complex.This requires a higher performance of shear wall components.As a result, new shear wall structures with excellent performance of seismic resistance and load-bearing capacities are increasingly needed.The reinforced concrete (RC) shear wall and steel plate shear wall (SPSW) are two common forms of the traditional shear wall.Although the RC structures have good durability performance [10][11][12], the large wall depth reduces the effective usable area with large self-weight.Therefore, RC shear walls are not appropriate for ultra-high-rise structures.Besides, the RC shear wall is easy to concrete crush under cyclic loads, exhibiting poor ductility.In contrast, the SPSW has good ductility, but its durability and fire resistance are relatively poor.For thick SPSWs, the residual stress and deformation after welding are commonly large, resulting in a great reduction in their mechanical properties.The large consumption of steel and high cost also limit the application of thick SPSWs.For thin SPSWs, the steel plate is easy to buckle under seismic effects.It should be mentioned that thin SPSWs have a large out-of-plane deformation accompanied by noise after buckling.Although these phenomena have little effect on structural safety, they can easily make people feel uncomfortable.
Studies have shown that the steel-concrete composite wall presents significant environmental benefits [13].The composite wall can effectively combine the advantages of both steel and concrete materials, resulting in a high utilization efficiency of materials and a composite effect greater than the sum of their individual performances.The high durability and longevity of the composite wall minimize the requirement for frequent maintenance and replacement, reducing material waste and resource consumption.Besides, steel is a highly recyclable material, allowing for the potential recovery and reuse of components at the end of the life cycle of the composite wall, promoting a sustainable circular economy.As a result, the steel-concrete composite walls have great load-bearing capacities, high ductility and durability, and excellent environmental friendliness [14,15].Due to these advantages, steel-concrete composite walls have gained extensive practical application, as illustrated in Fig. 1.
This paper presents a review of various types of steel-concrete composite walls to provide a clear vision for researchers.Firstly, the steel-concrete composite wall was classified according to the arrangement of steel plates and concrete, along with the configurations of steel plates.Then, research works on the structural behavior of steel-concrete composite walls subjected to different types of loading, e.g.axial compression, lateral loads, cyclic loads, fire resistance, dynamic loads, impact loads, and joint performance, are summarized.The design criteria are analyzed as well and some typical studies are introduced in detail.Finally, based on the review of existing studies, the development trend of steel-concrete composite walls in the future is discussed.

Classification of steel-concrete composite walls
According to the arrangement of steel plates and concrete as well as the configurations of steel plates, the steel-concrete composite wall can be classified into five groups as shown in Fig. 2, including steel plate reinforced concrete composite wall (SPRCCW), double-skin flat plate composite wall (DFPCW), double-skin corrugated plate composite wall (DCPCW), multi-celled concrete-filled steel tubular wall (MCFSTW) and multi-celled corrugated-plate concrete-filled steel tubular wall (MC-CFSTW).
As described in Fig. 2(a), the SPRCCW consists of a steel plate embedded within reinforced concrete.To strengthen the interaction between steel and concrete, shear connectors are applied, such as shear studs and steel bars [18].The presence of the steel plate significantly improves the ductility of the SPRCCW, while maintaining a reduced wall depth for equivalent strength and stiffness [19].Besides, the concrete restrains the buckling of steel plates, thereby increasing the strength of the wall.The use of external concrete also provides sound and temperature insulation [20].However, concrete is easy to crack or even spall under loads, leading to the development of the double-skin composite wall.According to the shape of steel plates, the double-skin composite wall can be divided into DFPCW and DCPCW, as depicted in Fig. 2(b) and (c), respectively.Both DFPCW and DCPCW are composed of two external steel plates filled with concrete, exhibiting good structural performances [21,22].On the one hand, the concrete is confined by external steel plates, enhancing its axial compression strength.On the other hand, the concrete restrains the inward deformation of the steel plates, increasing their buckling load capacity [23].The steel plates can be used as the permanent template of concrete, improving construction efficiency.To ensure the composite action of steel and concrete and prevent local buckling of steel plates, shear connectors are employed [24].For DFPCWs, dense arrangement of shear connectors to maintain the mechanical properties of the flat steel plates, which imposes higher requirements on the fluidity of the concrete [25].Simultaneously, it is not conducive to the economic design.Since the bending stiffness is small for the flat steel plate, additional lateral supports may be required to prevent its buckling.
To restrain the local buckling of external steel plates, the corrugated steel plate has been applied in the composite wall [26].Compared with DFPCWs, the DCPCWs have a better bonding effect between steel plates and concrete, owing to the existence of corrugation.This reduces the demand for shear connectors [27].Moreover, the bending stiffness of corrugated steel plate about the strong axis is greater than that of flat steel plate with the same thickness by two or three orders of magnitude, which offers stronger confinement for the concrete and meet the rigidity requirements during transportation and installation [28].
As presented in Fig. 2(d), the most widely used MCFSTW consists of a rectangular steel tube and multiple U-shaped steel tubes infilled with concrete [29,30].The diaphragm plates in MCFSTWs eliminates the need for shear connectors, which improves construction convenience compared with DFPCWs.Through reasonable design, the steel plate can yield before buckling, ensuring effective interaction between steel and concrete.Since the strength and stiffness of the MCFSTW can be adjusted by the quantity of U-shaped steel tubes, the cross-sectional dimensions of the U-shaped steel tubes are 000035-4 limited to a few modular sizes in practice, which is beneficial for industrialized construction [31].Though the MCFSTW exhibits high performance in the practical design, the large steel consumption limited its development.As plotted in Fig. 2(e), the MC-CFSTW was proposed by introducing the corrugated steel plates into multi-celled structures [32].The MC-CFSTW consists of CFSTs and corrugated cells connected alternately.The diagram of the MC-CFSTW is shown in Fig. 3. Compared to MCFSTWs, U-shaped steel tubes (typically 4 mm in thick) are replaced with corrugated steel plates (typically 1.5 mm in thick), significantly reducing steel consumption.Since the corrugated steel plates are positioned horizontally, the corrugation trough tends to deform inward, providing active confinement on the concrete [33].The presence of corrugations also reduces the self-weight of the composite wall.However, it also increases the difficulty of concrete pouring and imposes higher welding requirements.Additionally, the ultimate resistance of the MCFSTW relies on the trough section, resulting in underutilization of the material strength at the crest section.
Table 1 summarizes the characteristics of five types of steel-concrete composite walls, and numerous research works have been carried out.As described in Fig. 4, research works focused on compression performance, cyclic performance, fire performance, dynamic performance, flexural performance, and joint performance of composite walls.
3 Research on steel plate reinforced concrete composite wall

Compression performance
Though SPRCCWs were usually designed as lateral resistance members, they were still subjected to axial loads.To investigate their axial behavior, an experimental test was conducted by Hao et al. [34].Two different shear connectors were involved, including shear studs and vertical stiffening ribs.As described in Fig. 5, the concrete near the top end of the wall with shear studs crushed suddenly at the peak load.For specimens with vertical stiffening ribs, the brittle performance improved significantly.

Cyclic performance
Research works on the SPRCCW mainly focus on its seismic performance.Wang et al. [18] carried out comprehensive tests on 16 specimens of the SPRCCW, revealing that the failure modes varied with the aspect ratio and depth of the wall.Bending failure occurred in the wall with large aspect ratio and small depth, while the wall with small aspect ratio and large depth exhibited bending-shear failure, as presented in Fig. 6.Numerical analyses were conducted by Wang et al. [35] to further study the the seismic performance of the SPRCCW, and the results indicated that increasing steel plate ratio and decreasing axial compressive ratio could enhance the ultimate resistance and deformation capacity of the SPRCCW.Experimental studies on T-shaped SPRCCW under combined axial compression and cyclic lateral loads were conducted by Ke et al. [16].Comparied to I-shaped walls, the T-shaped SPRCCW demonstrated more favorable seismic performance.Ke et al. [19] also proposed a novel type of SPRCCW with partially encased composite columns.Seismic tests on seven specimens were performed, revealing that the SPRCCW with diagonal distribution reinforcement exhibited a 6.5% increase in cracking load and a 13.6% increase in ductility compared to those with orthogonal distribution reinforcement.Considering that the SPRCCW might be subjected to combined tensionbending actions, tests on seven specimens under tension-bending loads were conducted by Wang et al. [36].Besides, the stud performance was investigated by Qi et al. [37].Based on the numerical analysis, the stud shear force demand was proposed.Fig. 6.Typical failure modes of SPRCCW under cyclic lateral loads [18].
With the development of material, high-performance material has been introduced in the SPRCCW.Seismic behavior of three specimens with varying steel plate yield strengths was investigated by Lou et al. [38].It was indicated that the higher steel yield strength could increase the yield and ultimate loads and corresponding displacements of the wall, but it had negative effects on the ductility.Xiao et al. [39] carried out cyclic tests on 18 SPRCCWs with high-strength concrete, revealing that the performance of SPRCCW with high-strength concrete was improved obviously.Jiang et al. [40] also conducted tests on SPRCCW with high-strength concrete, and similar test results were obtained.During the test, the composite wall showed smaller and more dispersed cracks compared to the traditional RC shear walls.Both Xiao et al. [39] and Jiang et al. [40] suggested that the axial compression ratio should be kept below 0.5.The gangue concrete was introduced into SPRCCW by Zhang et al. [41].It was concluded from the test that the SPRCCW with gangue concrete had excellent load-bearing capacity and ductility, accompanied by limited strength and stiffness degradations.New forms and constructions were proposed to further improve the performance of SPRCCW.By combining the SPRCCW with steel side columns, a 1/4 scaled five-story specimen was tested under cyclic lateral loads by Ma et al. [42], as presented in Fig. 7(a).The coupled system exhibited excellent ductility, deformation capacity, and energy dissipation capacity.To simplify fabrication, Dong et al. [43] suggested a novel construction of SPRCCW using multiple smaller steel plates, as shown in Fig. 7(b).Seismic tests revealed that the wall demonstrated a remarkable capacity for energy dissipation.It was known that the concrete was easy to crush under large deformation.To offer this challenge, boundary CFST columns were used by Hu et al. [44] (Fig. 7(c)).The test phenomena revealed that the concrete crushing was significantly improved.
Another effective method was to use corrugated steel plates.Wang et al. [45,46] investigated the behavior of SPRCCWs with embedded corrugated steel plates.The existence of corrugations enhanced the interaction between steel plates and concrete, resulting in improved initial stiffness, ductility, and energy dissipation capacity.SPRCCWs with vertical corrugated plates exhibited higher load-bearing capacity than SPRCCWs with horizontal corrugated plates.On this basis, Li et al. [47] analyzed the stress distribution of SPRCCW with vertical corrugated plates, and design formulas were proposed to predict the curvatures of the wall.To fully develop the capacity of steel plates and boundary columns, Luo et al. [48] suggested that the shear ratio of the column to the steel plate should to be larger than 1.45.Moreover, Song et al. [49] and Wang et al. [50] investigated the bond-slip performance between corrugated steel plates and concrete with and without studs, respectively.Bond-slip constitutive models were then established, showing good accuracy with test results.Numerical analysis on the shear resistance of the SPRCCW was carried out by Zhou et al. [51].The impacts of the shear span ratio, steel ratio, concrete strength, axial compression ratio, and reinforcement ratio were evaluated.

Fire resistance
Xie et al. [52] studied the cyclic performance of SPRCCWs before and after fire exposure.As illustrated in Fig. 8, the spalling of concrete occurred in all specimens in the fire test, and the concrete spalling in SPRCCW was more serious than that in the traditional RC shear wall.Compared with the SPRCCW using an entire steel plate, the discrete steel plates effectively mitigated the propagation of diagonal cracks and the influence of fire exposure was less significant, which exhibited flexural failure.Although the load-bearing capacity of the SPRCCW were reduced due to the high temperature, the energy dissipation capacities were similar for SPRCCWs before and after fire exposure when the the drift ratio was less than 1/120.

Dynamic Performance
A numerical analysis was investigated by Ren et al. [53] to study the dynamic performance of a 20-story building with SPRCCWs.The SPRCCW was simulated by a multilayer shell model, and the simulation results indicated that the internal force redistribution could significantly influence the behavior of the structures.Moreover, nonlinear numerical analysis on the seismic responses of fourstory and six-story buildings using SPRCCWs was conducted by Dey and Bhowmick [54].It was observed that the period of the building obtained from the existing design codes was shorter than that obtained from the numerical analysis.A modified formula to predict the fundamental period of SPRCCWs was then proposed.
The DFPCW is the most widely used composite wall [55,56].The DFPCW was first applied as the floor in marine structural systems [57,58], and then it was developed in residential and office buildings as lateral resistance components, attracting the attention of researchers.The DFPCW can fully develop the advantage of steel and concrete.Additionally, shear connectors are employed to ensure the interaction between steel and concrete.As shown in Fig. 9, different types of shear connectors are used in DFPCWs, including tie bar [59], shear stud [60], T-shaped stiffener [61], intermediate bolt [62], Jhook [63] and batten plate [23].Studies on the performance of DFPCW under different loads have been conducted.

Compression Performance
The performance of DFPCWs under axial loads has been widely considered by researchers.In 1998, axial compression tests on DFPCWs with tie bars were conducted by Takeuchi et al. [64].The structure exhibited high ultimate resistance and great ductility.Furthermore, they conducted an analysis on the failure mechanism of the composite wall.Yan et al. [25,65,66] conducted tests on DFPCWs with different shear connectors, including C-shaped channel steel, J-hook, and shear studs, and the typical failure mode is described in Fig. 10.The load-bearing capacity of DFPCWs can be increased by enhancing the height of headed studs and the thickness of steel plates.Notably, the impact of steel plate thickness is more obvious when the length of headed studs was short.The stability performance under axial compression was studied by Qin et al. [67], who utilized the steel truss composed of angle steel and kinked rebar as shear connectors, as depicted in Fig. 11(a).Increasing the thickness of steel plate effectively delayed its local buckling, thereby enhancing the buckling stress and axial stiffness.As presented in Fig. 11(b), Shi et al. [61] introduced a novel type of DFPCW using steel-bars truss as connectors.The axial compression tests demonstrated that the steel-bars truss effectively restrained local buckling of the external steel plates.Stability tests on DFPCWs with intermediate bolts were carried out by Chen et al. [68], and when the height-to-depth ratio was larger than 12, overall instability could be observed accompanied by the local buckling of steel plates.Due to the poor stability of the external steel plates, the local buckling performance of steel plates was concerned by researchers.The axial compression test on ten specimens was carried out by Yang et al. [69] to investigate the impacts of key parameters on the axial performance of DFPCWs, including the width-to-thickness ratio of steel plate, spacing between shear studs and stud arrangement.Fig. 12 illustrates the local buckling deformation of steel plates observed in the tests.Combined with numerical analyses, it was suggested that the shear connector spacing to the steel plate thickness (s/t) should be less than 0.91√ s   ⁄ , where Es is and fy are the elastic modulus and yield strength of steel plate.Hu et al. [70] designed 12 specimens with intermediate bolts and conducted axial compression tests, and a calculation formula to present the ultimate and residual resistances of steel plates were proposed.The correlation between the shear stud stiffness and the local buckling performance of DFPCWs was studied by Harmon and Varma [71], revealing that the buckling mode of steel plates was significantly affected by the shear stud stiffness.Axial compression tests on DFPCWs with different shear connectors were carried out by Shi et al. [72,73], demonstrating that the limit of s/t could be taken as 0.91√ s   ⁄ for DFPCWs with shear studs, while the limit of s/t could be increased to 1.67√ s   ⁄ for the DFPCW with both shear studs and additional stiffening ribs.

Cyclic Performance
As an excellent lateral resistance component, the seismic performance of DFPCWs is worth studying.Ozaki et al. [74] derived the calculation formula of the in-plane shear resistance of the DFPCW.The accuracy of this formula was successfully validated against the test results.The seismic performance of isolated and coupled DFPCWs with I-and T-shaped sections was experimentally explored by Eom et al. [62].The study revealed that the failure of coupled DFPCWs was mainly attributed to the local buckling of steel plates and the weld fracture between the composite walls and coupling beams, as illustrated in Fig. 13.Nie et al. [23] conducted seismic tests on DFPCWs with vertical stiffeners and two boundary CFST columns, and high-strength concrete was considered.The results demonstrated that the reasonable arrangement of vertical stiffeners effectively mitigated the occurrence of local buckling in steel plates.Yan et al. [75] developed a new DFPCW with shear studs and boundary elements, which proved to improve the ductility of tall buildings, and all specimens showed local buckling of steel plates, fracture of boundary column, and crush of concrete.Moreover, the cyclic performance of DFPCWs with steel-bar space trusses and boundary CFSTR columns was experimentally investigated by Shi et al. [76], and a theoretical formula to predict the lateral resistance was presented.

Fire Resistance
The safely of structures exposed to fire has attracted much attention [77].Fire tests on 12 DFPCW specimens were conducted by Wei et al. [78].As depicted in Fig. 14, three typical phenomena were observed in the tests for the composite wall uniformly exposed to fire, including local buckling of steel plates, weld fracture, and global instability.For the composite wall exposed to single-sided fire, no obvious damage could be observed at 2.5 hours of fire exposure.Taghipour et al. [79] carried out numerical analyses to investigate the impact of key parameters on the fire resistance of the DFPCW.To enhance the failure time of the composite wall, it was suggested that the ratio of shear connector spacing to the steel plate thickness (s/t) should be less than 1.2√ s   ⁄ .Hu et al. [80] found that the out-of-plane stiffness of the composite wall was significantly affected by the fire exposure.A fitting formula to calculate the initial out-of-plane stiffness was presented.Besides, Du et al. [81] performed fire tests on DFPCWs with truss connectors.The test results indicated that the fire resistance of the wall was significantly influenced by the axial compression ratio and truss spacing.

Flexural Resistance
McKinley and Boswell [82] conducted three-point bending tests on 16 specimens of DFPCW.For DFPCWs with tie bars, the failure of composite wall primarily attributed to the occurrence of local buckling in steel plates, while the DFPCWs with shear studs exhibited failure as a result of the shear studs pulling out of the concrete.The test results proved that the DFPCW with tie bars showed higher resistance and larger deformation compared to the DFPCW with shear studs.Besides, Sener et al. [83,84] investigated the flexural performance of DFPCWs experimentally.The investigation revealed that the out-of-plane flexural strength of the structure was not influenced by the shear span-to-depth ratio and slenderness of steel plates, while the yield strength of steel plates had a significant impact.Varma et al. [85] study the flexural behavior of DFPCW in nuclear structures.It was suggested that the tensile strength and spacing of shear connectors should be carefully designed to prevent non-ductile failure of the wall.A four-point bending test was conducted by Yang et al. [86] to evaluate the buckling behavior of steel plates in DFPCWs under bending loads.It was indicated from test results that the stiffening ribs and tie plates could significantly improve the buckling stress of the steel plates, as described in Fig. 15.

Research on Double-skin Corrugated Plate Composite Wall
The DCPCW was first proposed by Wright et al. [87], serving as the flooring system.As shown in Fig. 16, various types of corrugated plates have been applied in the DCPCW, including trapezoidal corrugation, sinusoidal corrugation, and re-entrant corrugation.

Compression Performance
Due to the special section shape of DCPCWs, the sectional strength and stability performance under axial compression were studied by researchers.In 1998, axial compression tests were carried out by Wright [88] to analyze the failure mode of DCPCWs.The ultimate resistance of DCPCW was affected by the local buckling of corrugated steel plates and section shape of concrete.A design formula to evaluate the sectional strength of DCPCW was then proposed, where a reduction factor was introduced to consider the influence of the above two factors.In engineering practice, openings for doors and windows are required, which may lead to the perforation of DCPCW.To investigate the axial compression performance of pierced DCPCWs, tests on 19 specimens were conducted by Hossain et al. [89].The influence of corrugation dimensions, types of shear connectors, opening dimensions, and strength enhancement devices are evaluated.It was concluded that strengthening the boundary of the opening was the most effective approach to improve the behavior of pierced DCPCWs.Uy et al. [90] conducted tests on the DCPCW with re-entrant corrugation subjected to eccentric compression, where the local buckling of the corrugated plate was observed.On this basis, Tong et al. [91,92] conducted numerical and theoretical analyses to to further examine the performance of DCPCWs.The analyses concluded that the material strength, wall depth, and steel plate thickness had positive effects on the axial and bending resistance of the wall.The interaction curves between axial and flexural capacities were then proposed.
As described in Fig. 17, a new type of DCPCW with boundary CFST columns and intermediate bolts was proposed by Guo et al. [26] in recent years.It was found from the test and simulation by Zhu et al. [28] that the corrugated steel plate between bolts was prone to buckle, which was described in Fig. 18(a).Therefore, the axial resistance of the wall was proposed, where the stability coefficient of the corrugated steel plate was considered.Zhou et al. [93] studied the performance of this new type of composite wall subjected to combined axial compression and in-plane bending.A theoretical model was presented to evaluate the cooperative effect between corrugated steel plates, concrete, and boundary elements, and the N-M correlation curve was presented.Moreover, the stability performance under axial compression was carried out by Guo et al. [26], as presented in Fig. 18(b).Combined with stability tests and numerical simulations, the stability curve was proposed.For T-shaped DCPCW, axial compression tests and numerical analysis were conducted by Wang et al. [94] to further investigate the performance of the composite wall under axial loads, bending loads, and combined axial and bending loads.The numerical results revealed that the load shared by steel plates ranged from 50% to 80% subjected to eccentric compression.Furthermore, Wang et al. [95,96] also evaluated the flexural and flexuraltorsional buckling behavior of T-shaped DCPCW under axial loads.The stability design method was then developed.Besides, the stability performance under combined axial compression and biaxial bending loads was investigated using the same method [97].Condiering the restraint provided by the infilled concrete against the inward buckling of corrugated steel plates in DCPCWs, the corrugated steel plate between intermediate bolts was simplified as a four-edge fixed steel plate by Wang et al. [27].The stability curve of the four-edge fixed steel plate was proposed.

Cyclic Performance
As a lateral resistance component, the performance of DCPCW under shear loads was analyzed.Hossain and Wright [98][99][100] conducted shear tests on corrugated concrete plates and analyzed their failure modes.On this basis, shear tests on DCPCWs were performed and the theoretical models to calculate the shear capacity and initial stiffness of DCPCWs were proposed.Rafiei et al. [101] studied the shear behavior of DCPCWs using intermediate bolts.It was found that increasing the intermediate bolt number could increase the shear capacity of the DCPCW until the critical bolt spacing is reached, where the yielding of the corrugated plate occurred before buckling.The high-performance concrete was introduced into DCPCW instead of normal concrete by Rafiei et al. [102].The test results proved that high-performance concrete could improve the ductility of DCPCWs.Based on the studies of the shear performance of DCPCWs, the seismic performance was further investigated.Hossain et al. [104] conducted tests on six specimens subjected to cyclic lateral loads, revealing that the utilization of mild-strength steel enhanced the ductility of the wall.Zhao et al. [105] compared the seismic performance of DCPCWs and DFPCWs.DCPCWs showed better initial stiffness and energy dissipation capacity than DFPCWs when the bolt spacing was 50% larger than the limit in design codes.The seismic behavior of DCPCW with boundary CFST columns shown in Fig. 17 was evaluated by Zhu et al. [106].The test results on eight specimens revealed that the specimens were all subjected to compression-bending failure.Increasing the shear span ratio could enhance the ductility of the wall, while it was negatively correlated with the shear resistance.On this basis, the theoretical formula was developed to predict the ultimate resistanc of DCPCWs.Moreover, Zhou et al. [103] conducted hysteretic tests on 15 specimens, and three types of failure modes were concluded as described in Fig. 19.The results confirmed that the DCPCW with vertical corrugations exhibited much better hysteretic performance than the DCPCW with horizontal corrugations.

Fire Resistance
Le et al. [107] investigated the axial compression performance of the DCPCW at ambient and elevated temperatures.The tests indicated that the DCPCW exhibited ductile failure at ambient temperature, but the ductility of the wall decreased with the increase of temperature.Besides, the temperature also showed a negative effect on the axial resistance of the wall.Since the composite wall was subjected to single-sided fire, the effective centroid would be affected by the temperature gradient, which influenced the failure plane of concrete.To further understand the performance of DCPCWs exposed to single-sided fire, Le et al. [108] proposed an analytical model considering the non-uniform stiffness and non-linear temperature gradient.The proposed model exhibited good accuracy with the experimental results, which could be used to predict the stress and curvature of the structures.

Impact Performance
Rafiei et al. [109] studied the impact shear resistance of DCPCWs.It was found that the shear strength after impact loads was not reduced and the stiffness was only reduced by 8%.Thus, the DCPCW had great impact shear resistance.

Research on Multi-celled Concrete-filled Steel Tubular Wall
According to previous studies, the diaphragm connectors ensure the development of composite action in MCFSTWs.As illustrated in Fig. 20, various types of MCFSTW have been developed.Many scholars have carried out detailed research on its performances, including axial compression performance, seismic performance, fire resistance, and joint performance.

Compression Performance
In 1995, Link and Elwi [110] conducted tests on MCFSTW which was used in offshore structures.Considering the action of waves and moving ice, the MCFSTW was tested under axial and out-of-plane loads, proving the good ductility of the composite wall.Guo et al. [111] and Li et al. [112] respectively performed tests on MCFSTWs with normal concrete and self-compacting concrete, and the deformations are presented in Fig. 21.It was found that the strength failure occurred for stub MCFSTWs accompanied by obvious local buckling of steel plates.Furthermore, Li et al. [112] employed ultrasonic testing to monitor the progression of concrete damage.The residual strength and ductility index were investigated by Zhang et al. [113], and it was concluded that these two parameters demonstrated positive correlations with the confinement factor.Based on the tests and numerical simulations, fitting formulas were presented to predict these two parameters.For slender MCFSTWs, stability tests under axial compression were conducted by Wang et al. [114] and Zhou et al. [31].Parametric analysis showed that increasing steel plate thickness and decreasing material strength could improve the stability performance of the MCFSTW, while it was hardly affected by the wall width.Besides, Zhou et al. [17] conducted stability tests on MCFSTWs with three simply-supported edges under axial compression.As shown in Fig. 22, The three specimens all exhibited global instability where the out-of-plane deflection of the free edge was observed.By using orthotropic plate theory, the elastic buckling load was proposed, and then the stability curve was presented.By using the same theoretical method, the stability performance of MCFSTWs with four simply-supported edges was evaluated [115].

Cyclic Performance
Zhang et al. conducted experimental tests to assess the mechanical properties of the MCFSTW when subjected to combined axial compression and lateral cyclic loads.Zhang et al. [29,30] carried out tests to evaluate the mechanical properties of the MCFSTW when subjected to combined axial compression and lateral cyclic loads, including seven specimens with an Ishaped section and five specimens with a T-shaped section.Combined with the failure modes shown in Fig. 23, the energy dissipation capacity, ductility, stiffness, and ultimate strength of the wall were analyzed in detail.The results revealed that an increase in the axial compression ratio resulted in accelerated degradation of strength and stiffness, while it has little effect on the yield and peak strengths.It was widely recognized that the skeleton curves obtained from tests generally contained the secondorder effect of axial loads which was calculated separately in the structural design software.To apply the test results to structural design, Zhou et al. [116] proposed a method to modify the skeleton curve that excluded the second-order effect, and a more accurate ductility for practical design was obtained.A new type of MCFSTW consisting of CFST columns and steel plates infilled with concrete was developed by Huang et al. [117].The seismic tests on five specimens showed that the structure had good hysteretic performance.Subsequently, a fitting formula was presented to calculate the lateral bearing capacity of the wall, taking into account the confinement effect of the infilled concrete.Furthermore, tie-bolts were introduced into the MCFSTW by Tong et al. [118], and the tie-bolts were proved to suppress the local buckling half-wavelength of the steel plate.Based on test results, two simplified models of the hysteretic curves were presented.Li et al. [119] studied the performance of Lshaped MCFSTWs.The weld cracking was observed at the bottom end of webs when the wall flange was width, while only local buckling of webs occured for the MCFSTW with a narrow flange.Chen et al. [120][121][122] presented an innovative composite wall where the diaphragm was replaced by two Lshaped connectors.Theoretical formulas were developed to estimate the wall bending strength and the local buckling stress of the steel plate.To reflect the requirement of MCFSTWs under earthquake more accurately and reasonably, Wang et al. [123,124] proposed a new loading protocol for quasi-static tests.

Fire resistance
Compared with the mechanical performance under other loads, the research works on the fire resistance of the MCFSTW are limited.Liu et al. [125,126] conducted tests on eight specimens under axial loads when exposed to fire.The test indicated that the inner force distribution and the stress and strain distribution of the MCFSTW exhibited similarities to those of traditional CFST columns.Since the diaphragm connectors were inside the composite wall, they were not significantly affected by the fire.Thus, the presence of the inner diaphragm with lower temperatures was found to be crucial in enhancing the load-bearing capacity of the wall and reducing the occurrence of local buckling in the steel plates.Combined with the test results and refined FE simulation results, a simplified calculation formula to predict the fire resistance of the MCFSTW and a method for determining the fire protection thickness were proposed.

Joint performance
Joint performance is a critical aspect of structural design.Recognizing that butt joints are susceptible to tensile fractures, Tong et al. [127] introduced a novel butt joint configuration, where the T-shaped connector was applied.Tensile tests on 12 specimens were carried out, among which six specimens had web plates and the other six did not have web plates.The test results demonstrated a significant enhancement in the tensile strength and ductility of the butt joint when the additional welding seam was introduced between the web plate and connector.For wall-beam joints of MCFSTW, Tong et al. [128] explored its bending strength and stiffness.According to the yield line analysis, the design formulas to calculate the initial stiffness and bending resistance were proposed.The theoretical formulas proved to have good accuracy with simulation results.Guo et al. [129] conducted tests on four MCFSTW-beam joints with double side plates.The results proved that both types of joints with discrete and consecutive double side plates could provide satisfactory collapse resistance.To improve the prefabrication degree of the joint, An et al. [130] proposed an anchored prefabricated wall-beam joint.Based on the hysteretic test on four specimens, the joint was confirmed to have good seismic performance.Besides, an innovative joint was investigated experimentally by Xu et al. [131] which could be used between replaceable coupling beams and walls.A design formula was presented to calculate the strength of this joint.

Compression performance
As a new composite wall with excellent performance, the behavior of MC-CFSTW under axial compression was investigated by Tong et al. [33].As shown in Fig. 24, it was evident that local buckling occurred in both the steel tubes and corrugated steel plates during the test.A numerical study was then conducted by Yu et al. [132].Increasing the thickness and yield strength of the steel tube resulted in the increment of both the ultimate and residual strengths of the wall, while increasing corrugated cell width and wall depth could increase the ultimate strength of the wall but reduce its ductility.A formula to calculate the sectional strength of the MC-CFSTW was fitted, which was a function of the equivalent confinement factor of the wall.Furthermore, Tong et al. [133] explored the stability performance of the composite wall, and a stability test on six slender MC-CFSTWs was conducted.By comparing with the existing design curves, it was found that the formulas specified in design codes were not suitable for MC-CFSTWs.Therefore, a new stability curve was proposed with good accuracy.Li et al. [134] presented a novel type of MC-CFSTW, where the composite wall consisted of CFST components and corrugated plates connected alternately, and the CFST component was composited by two flat plates and two corrugated plates infilled with concrete.Experimental and numerical analyses were conducted to study the axial compression behavior of the CFST components.The results revealed good composite action of the wall with strength indexes of all specimens exceeding 1.17.

Cyclic performance
Except for the axial compression performance, the cyclic performance of MC-CFSTWs was also studied [135].Based on the seven full-scaled specimens, the hysteretic performance of the wall was found to be significantly effected by the axial compression ratio.Specifically, global buckling failure occurred in the post-ultimate stage with the axial compression ratio larger than 0.55, as described in Fig. 25.Moreover, the ductility of the MC-CFSTW was compared with that of the MCFSTW developed by Tong et al. [118] and Zhang et al. [29].Though the steel consumption was reduced by about 20%, the ductility of the MC-CFSTW was similar to that of the MCFSTW.In the study conducted by Tong et al. [136], eight specimens of MC-CFSTWs using interval flat plates subjected to cyclic loads with different axial compression ratios were tested.The MC-CFSTWs with boundary flat plates demonstrated flexural failure modes in the test, whereas those with boundary H-shaped or CFST columns exhibited shear failure modes.The MC-CFSTW could also be applied in underground pipe gallery projects to subject withstand out-of-plane loads.The experimental study was performed to study the out-of-plane flexural performance of the wall [32].As described in Fig. 26, the mid CFST showed significant local deformation due to the tensile force exerted by the corrugated steel plate.Therefore, the deflection of the specimen was regarded as the combined action of overall bending deformation and local deformation.Based on the theoretical analysis, the prediction formulas to calculate the initial stiffness and ultimate bending capacity were proposed.

Joint performance
Duan et al. [137] proposed a wall-beam joint for MC-CFSTWs.Numerical analysis revealed that the width-to-thickness ratio of steel tubes and the hole diameter of the horizontal diaphragm had negative effects on the rotational stiffness of the joint.Conversely, increasing the axial compression ratio and concrete strength enhanced its rotational stiffness.Moreover, the yield strength of steel plates had no influence on the joint stiffness, which could significantly affect the joint bending strength.Utilizing the yield line analysis method, a design formula was presented to calculate the bending resistance of the joint.

Shear resistance
Different types of composite walls have different methods to calculate their shear resistance.For SPRCCW, the superposition principle is applied, and the design formula can be expressed as in which V is the shear capacity of the SPRCCW; Vc, Vb, Vp, and Vr are the shear capacities of concrete, boundary elements, embedded steel plate, and steel rebars, respectively; and VN is the contribution of axial compression loads.The calibration factors of different components were proposed according to the numerical and experimental results, and Eq. ( 1) can be further expressed as  where  is the shear span ratio of the composite wall;  is the steel plate ratio; s is the stability coefficient of corrugated steel plates; fcu is the cubic strength of concrete; and nd is the axial compression ratio.
For the other four types of steel-concrete composite walls, it is recommended to disregard the contribution of concrete.As a result, the shear capacity can be expressed as in which fvs and As are the shear yield strength and area of the steel plate in the composite wall, respectively.
Besides, when the height-to-width ratio is large, the composite wall exhibits bending failure modes [18,106,136].For the bending resistance of the steel-concrete composite wall, the sectional analysis method [19] was used.The position of the neutral axis could be calculated through the balance of forces.Based on the assumption of plane sections, the stress distribution was obtained, and hence, the bending moment of the sections was further calculated.
where fc' and Ac are the compressive strength and cross-sectional area of concrete in the composite wall, respectively; fys and fus are the yield strength and tensile strength of steel plate, respectively.
Based on the above design codes, the axial compression capacity can be expressed as in which 1 and 2 are calculation factors.
Different calculation factors have been proposed for various forms of composite walls.For the SPRCCW, the concrete strength can be determined based on the cylinder compressive strength.However, for the other four types of composite walls, the concrete strength is often estimated using the confined concrete strength, considering the confinement effect of steel plate and steel reinforcement bars.Yan et al. [25,65,66] proposed a method for calculating concrete strength under the confinement of different shear connectors.The confined concrete theory proposed by Mander et al. [144] was suggested to determine the confined concrete strength [34].For the steel material, it was suggested that the vertical stress should be reduced due to the confinement effect of steel on the concrete.However, it was difficult to determine the vertical stress of steel plates theoretically, and its value varied greatly from existing literature [33,145].In many studies, the strain gauge data observed in the test were used to determine the vertical strain of steel plates when the specimen reached peak load, thereby obtaining the vertical stress of the steel plates.

Stability resistance
The load-bearing capacity of the composite wall with large slenderness ratio is controlled by its stability.The stability curves of various types of composite walls are different.Chen et al. [68] suggested that the stability curve of DFPCWs with intermediate bolts could be calculated as: where 0 is the normalized slenderness ratio; and is the stability coefficient.However, due to the lack of experimental results, the stability curve with a normalized slenderness ratio greater than 0.6 should be modified.Qin et al. [146] proposed the stability curve of DFPCWs with steel truss under axial compression through tests and numerical simulations, and the stability curve could be expressed as Similarly, Guo et al. [26] and Zhou et al. [31] proposed the stability curves of DCPCWs and MCFSTWs, respectively, as shown in Eqs. ( 7) and ( 8).Tong et al. [133] explored the stability performance of MC-CFSTWs, and the stability curve could be calculated by Eq. ( 9).
The stability curves of different types of composite walls are compared in Fig. 27, revealing that the utilization of truss connectors significantly enhances the stability performance of DFPCWs.The stability curves of DCPCWs and MC-CFSTWs are close.However, when compared to MCFSTWs, both DCPCWs and MC-CFSTWs demonstrate worse stability performance.Pre-fabricated structures offer numerous advantages, including reduced material waste, environmentally friendly construction, flexible structural arrangements, high degree of industrialization, and rapid construction.Fabricated steel structures align with the concept of life-cycle design for green buildings.The widespread application of pre-fabricated steel structures represents a significant way to achieve building industrialization.In recent years, research has increasingly focused on the prefabricated structure, but the absence of reliable design codes and standards limits its development.Additionally, modular construction has attracted increasing attention.Modular steel construction and modular concrete construction have been applied in many regions such as Hong Kong and Singapore, while modular composite construction is few and requires detailed scientific research for further advancements

High performance and sustainable materials
Researchers have conducted numerous analyses in recent years to investigate the mechanical properties of steel-concrete composite walls.However, the current studies focus on normal strength materials, with limited research on high performance and sustainable materials.High-strength materials have been extensively explored in CFSTs, enabling steel yield strengths of up to 780 MPa and concrete cylinder strengths of up to 190 MPa [147].Consequently, high-strength materials can also be introduced in composite walls to further reduce cross-sectional dimensions and enhance the load-bearing capacities of the structural elements.
Furthermore, the utilization of lightweight concrete can effectively decrease the self-weight of structures, particularly in high-rise buildings.Previous investigations have revealed that concrete in SPRCCWs is prone to cracking under load.Therefore, the utilization of high-toughness concrete can help prevent cracks and enhance durability [148].Moreover, recycled aggregate concrete agrees with sustainability goals and has attracted much attention [149][150][151], which can be used in composite structures.The existing literature shows limited investigations on composite walls using high performance and sustainable materials, which provides a direction for future research.

Load types and design provisions
Although existing studies have extensively analyzed the behavior of steel-concrete composite walls under different load conditions, there are clear gaps in the current literature.For instance, few studies were conducted on the effect of dynamic loads, which directly reflect the characteristics of structures during earthquakes.Additionally, the impact of thermal loads, impact loads, and explosion loads can be further explored as supplementary areas of research.
Moreover, the deficiency of standards significantly affects the application of steel-concrete composite walls.Despite the progress made in studying novel structural forms, an integrated system of design methods has not been formed.On one hand, the design formulas proposed in existing literature lack universality.On the other hand, the design formulas provided by current standards fail to fully reflect the advantages of the novel types of composite walls in load-bearing performance.Thus, comprehensive and universally applicable design methods that effectively reflect the benefits of innovative composite walls are required.

Conclusion
Compared to traditional reinforced concrete shear walls and steel plate shear walls, steel-concrete composite walls offer several advantages.These include high load-bearing capacity, good energy dissipation, and significant deformation capacity, making them ideal for high-rise buildings.
This review summarized the research on various steel-concrete composite wall types.We classified these walls into five categories based on their cross-section and the relative positions of steel and concrete.These categories include steel plate reinforced concrete composite wall (SPRCCW), double-skin flat plate composite wall (DFPCW), double-skin corrugated plate composite wall (DCPCW), multi-celled concrete-filled steel tubular wall (MCFSTW) and multi-celled corrugated-plate concrete-filled steel tubular wall (MC-CFSTW).The reviewed research highlighted several key findings: (1) Limited research on non-static loads: Existing research primarily focuses on axial compression and cyclic performance, with less emphasis on the effects of dynamic, thermal, and impact loads.
(2) Concrete failure and confinement: For SPRCCW walls under axial compression, concrete crushing and spalling can reduce structural ductility.However, walls where concrete is confined between steel plates (DFPCW, DCPCW, MCFSTW, and MC-CFSTW) exhibit limited concrete spalling due to the steel plates, leading to improved ductility.
(3) Seismic performance and influencing factors: The composite action between steel and concrete contributes to excellent seismic performance.While increasing the axial compression ratio reduces deformation capacity and ductility, a higher steel ratio enhances wall stiffness and strength.
(4) Connectors and their role: Connectors are instrumental in ensuring composite action between steel and concrete.Researchers are continuously developing new connector types to improve overall wall performance.
(5) Design considerations: Scholars have proposed design formulas for different composite wall types under various loads.While testing has verified the accuracy of these formulas to some extent, their universal applicability requires further investigation.
Future research to promote the wider use of composite walls include: pre-fabrication and modular construction techniques, exploration of alternative and sustainable materials, and the development of new design theories.

Table 1 .
Characteristics of different types of steel-concrete composite walls Types Advantages Disadvantages SPRCCW Steel plate without local buckling; High durability and fire resistance Easy cracking of concrete; Low construction efficiency DFPCW Steel plate served as the permanent template; Improving compressive strength of concrete Easy buckling of steel plates; A large number of connectors DCPCW Improving buckling resistance of steel plate; Improving compressive strength of concrete Limited thickness of corrugated steel plate; Difficulty of welding of corrugated steel plate MCFSTW Improving compressive strength of concrete; Without additional connectors Large steel consumption; Heavy welding workload MC-CFSTW Improving compressive strength of concrete; Reducing steel consumption Difficulty in concrete pouring; High welding requirements

Table 2 .
) in which ft is the tensile strength of concrete; dw and bw are the wall depth and effective width, respectively; N0 is the axial load, which is less than 0.2fcbwdw; fyb is the yield strength of boundary elements; Ab is the cross-sectional area of single-side steel boundary column, taken as the smaller area of two boundary columns; fyp and Ap are the yield strength and area of embedded steel plate, respectively; fyr and Ar are the yield strength and area of horizontal steel rebars, respectively; hr is the configuration width of steel bar; s is the spacing between two horizontal steel rebars; and 1 to 5 are the calibration factors.The calibration factors specified in design codes and literature are summarized in It is found that the design formula specified in the code cannot predict the shear capacity accurately with the development of new types of structures.However, these calibration factors are obtained by fitting tests and FE results, which are only applicable to specific structures and lack universality.It is still worthy of further study.

Table 2 .
Design formulas for the shear capacity of SPRCCW

Table 3 .
Design codes for steel-concrete composite structures