Cyclic behavior and numerical study of PRC coupling beam with steel truss floor slab

The coupling beam with small span-to-depth ratio is prone to brittle shear failure under the action of earthquake, so it can not play its role as the first line of defense against earthquake. Therefore, this paper proposes a method for calculating the shear bearing capacity of PRC-connected beams with reinforced truss floor plates. A more rational calculation model should be adopted based on its mechanical mechanism. In this study, ABAQUS finite element software is utilized to explore the parameters of PRC-connected beams with steel truss plates, including the span-to-height ratio, reinforcement ratio of the internal steel plate, diameter of upper and lower chord bars, and diameter of abdominal bars. The analysis shows that the span-to-height ratio, steel plate ratio and concrete compressive strength have a significant effect on the seismic behavior of PRC coupling beams with steel truss floor slab. Based on the softened tension-compression bar model combined with the multi-strip model, the theoretical calculation method of the shear capacity of PRC connected beams with steel truss bearing plates is derived. The results of comparison test and simulation verify the accuracy of the calculation results, and provide a design basis for the engineering application of PRC connected beams with steel truss floor plates.


Introduction
Coupling beam is the key connecting member of coupled shear wall structure and core tube structure, which participates in the first energy dissipation of the structure under earthquake.In practical engineering, floors are frequently cast in conjunction with coupling beams.At present, only a few studies on coupling beams have considered the role of reinforced concrete (RC) floors [1].Deng Kailai et al [2] conducted a study on slotted reinforced concrete floors, and Deng Fuyuan et al [3] also investigated RC connected beams with floor slabs.All of these studies collectively demonstrate that RC floors have varying effects on stiffness degradation, strength degradation, and the failure process of connected beams.In recent years, with the rapid development of the housing industry, the ' industrialized 'residential structure system has gradually been accepted by the public.Among them, the steel truss floor slab is widely used in the industrialized residential building system because of its high production efficiency, good economic benefits, convenient installation, resource saving and convenient construction.
Therefore, in order to improve the seismic performance of small span-to-height ratio coupling beams, the researchers have conducted a lot of research and analysis.At present, The improvement methods are mainly as follows.New reinforcement methods are adopted.Paulay [4] first tried to adopt diagonal dark column reinforcement with diagonal cross reinforcement.Later, Tassios [5] conducted an experimental study using diagonal dark column reinforcement, and compared it with ordinary RC connected beams, the experiment showed that the deformation performance and ductility of connected beams were improved by setting diagonal dark column reinforcement.Galano [6] simplified the diagonal dark column reinforcement mode and carried out connected beam tests.The results all show that the new reinforcement mode improves the deformation performance and ductility of connected beams to a certain extent, and makes them more energy-dissipating than common reinforced connected beams.However, this method increases the difficulty of construction to a certain extent.By altering the fundamental composition materials of connected beams, Canbolat et al [7] introduced fiber-reinforced concrete (FRC) into the structure, while Park W S et al [8] incorporated steel fiber-polyethylene mixed fibers into the beams.The results revealed a significant enhancement in the shear capacity of these connected beams when compared to regular concrete-connected beams.However, it's worth noting that these modifications have also led to increased construction costs.By changing the section form of the connected beams, Liu C et al [9] proposed a new type of section form, that is, wide connected beams.Using replaceable or repairable beam, Fortney P J et al [10] put forward an innovative 'fuse' rigid beam, although it is less difficult to repair or replace after damage, and the cost is reduced, but compared with other methods, the construction is still difficult.Another method is to use steel-concrete composite beams.Subedi [11] initially introduced a new type of steel-concrete combined beam, which exhibited good load-bearing capacity.However, due to the ease of shear slip between the steel plate and concrete, these beams suffered early-stage damage.In response, Lam [12] proposed the classic steel-concrete composite beam with studs.The arrangement of studs effectively prevented slip between the steel plate and the concrete, significantly enhancing the anchorage of these materials and consequently improving the loadbearing capacity of the beam specimens.Later, Cheng [13], from the same institution, conducted a series of experimental studies on this innovative combined beam design.In summary, these methods can indeed enhance the seismic performance of connected beams with a small span-to-height ratio, but their effectiveness is limited.In contrast, employing a steel truss floor plate (PRC) connection beam proves to be a favorable option for seismic performance [13,14].
However, the floor slab and the coupling beam are poured together as a whole in real engineering applications, and the steel bar and concrete of the floor slab participate in the force on one side of the coupling beam and plastic deformation occurs [15].Most of the previous experimental studies do not consider this effect of the floor slab, which makes it different from the stress mechanism of the coupling beam in actual engineering, and the calculation results have certain errors [16,17].Even considering the function of the slab, the coupling beam test only selected the ordinary RC slab, which did not meet the requirements of the industrial residential building system.Steel truss floor slab has been widely used in industrial residential building system because of its high production efficiency, good economic benefits, convenient installation, resource saving, convenient construction and other advantages.
In this paper, the low-cycle reciprocating load tests of three PRC coupling beams (one without floor slab, one with ordinary RC floor slab and one with steel truss floor slab) are carried out, and the effects of failure forms, deformation properties and energy dissipation of PRC coupling beams with different floor types are compared and analyzed.ABAQUS finite element software is used to analyze the span-to-height ratio, steel plate ratio, longitudinal reinforcement ratio, and concrete compressive strength, upper and lower bar diameter and web diameter of truss of PRC coupling beam with steel truss floor slab.

Specimen design
In this experiment, three coupling beam specimens with a span-depth ratio of 1.5 were designed and fabricated, including one steel plate-concrete composite coupling beam specimen, one steel plate-concrete composite coupling beam specimen with RC floor slab, and one steel plate-concrete composite coupling beam specimen with steel truss floor bearing plate.The specific parameters of each specimen are shown in table 1.
The composition of the three specimens includes the end blocks at the upper and lower ends of the specimen and the composite coupling beam in the middle.The upper and lower end blocks are used to simulate the shear wall limb and have sufficient strength and stiffness to prevent the premature failure of the end blocks from affecting the test accuracy of the coupling beam.The size of the upper end block is 1020 mm × 600 mm × 300 mm, the size of the lower end block is 1720 mm × 600 mm × 300 mm, and the reinforcement of the upper and lower end blocks is shown in figure 1(a).The size of the connecting beam is l × b × h = 480 mm × 160 mm × 320 mm, which is reduced compared to the actual size.In reference to Lu Xianbin's test specimen [18] and its concrete protective layer thickness after scaling down, this paper also adjusts the thickness of the concrete protective layer for the connecting beam and  floor slab accordingly.This modification is made to prevent excessive thickness in the protective layer, which could lead to spalling.Therefore, the concrete protective layer is set at a thickness of 10 mm.Additionally, the thickness of the protective layer on the end block is 25 mm.For the joint action between steel plate and concrete, shear studs were welded on both sides of the steel plate.The longitudinal reinforcement of the three coupling beam specimens is 2D18 + 2D14, and the longitudinal reinforcement ratio is 1.67%.The stirrup is D8 @ 100, and the stirrup ratio is 0.63%.The anchorage length of the steel plate is 1.34 times the beam height.The size and reinforcement of each specimen are shown in figure 1.
Notes: l n /h is the span-depth ratio of the coupling beam, l n is the net span of the coupling beam, and h is the section height of the coupling beam ; ρ z is the longitudinal reinforcement ratio of the coupling beam, ρ t is the stirrup ratio of the coupling beam, D and t are the height and thickness of the steel plate of the coupling beam, ρ p is the plate ratio of the coupling beam, S1 is the ordinary RC floor, and S2 is the steel truss floor.

Material properties
The mechanical properties of the steel used in the test are obtained by the material test, and the specific performance parameters are shown in table 2. The strength grade of concrete is C35 grade commercial concrete, and the average compressive strength of the cube test block is 39.39 MPa.

Loading scheme
The test adopts a built-up combined test device [19].Each specimen is provided with a horizontal reciprocating load by a 1000 kN servo actuator through an inverted L-shaped loading steel arm, and the load line passes through the inflection point of the coupling beam.The upper end block of the specimen is connected with the loading steel arm.A four-link device is installed above the steel arm, which can make the specimen only move in the plane and prevent the specimen from rotating.The lower end block is connected with the rigid ground beam, and fixed devices are arranged on both sides of the upper and lower end blocks to prevent the overall slip and out-of-plane instability of the specimen.The test loading device is shown in figure 2.
The loading system of load-displacement hybrid control is adopted in the test.In the elastic stage, the reciprocating loading is carried out according to the load control.After the specimen is yielded, the reciprocating  loading is carried out according to the displacement control, and the loading is carried out according to the integral multiple of the yield displacement.The test contents of the test mainly include : horizontal relative linear displacement at both ends of the coupling beam, shear deformation at both ends of the coupling beam.The relative linear displacement at both ends of the coupling beam is measured by the hysteresis displacement meter A. The shear deformation at both ends of the coupling beam is calculated by the displacement deformation of the displacement meters B and C in the diagonal direction of the coupling beam.The test data is automatically collected by the IMP data acquisition system.The arrangement of the specimen displacement meter is shown in figure 3.

Experimental phenomena
When the horizontal load of PRC-NS1 is + 80 kN, the first diagonal crack in the diagonal direction appears at the left position of the upper part of the coupling beam.When a load of +120 kN is applied, diagonal cracks form along the lower part of the beam in the diagonal direction.Under a load of −120 kN, oblique cracks appear on the upper left side of the beam.With a load of −200 kN, numerous oblique cracks develop at the edge of the connected beam, while shear oblique cracks emerge in the middle part.Finally, under a load of +240 kN, an 8 cm flexural shear crack manifests at the base of the beam.When the load is + 320 kN, the coupling beam enters the displacement control stage.When the displacement load is Δ = 20 mm, the bearing capacity of the coupling beam decreases to below 85% of the peak load.At this time, the coupling beam has been destroyed.The failure mode of the coupling beam is shown in figure 4.
When the horizontal load of PRC-S2 is + 80 kN, the first oblique crack appears in the upper right position of the coupling beam.Simultaneously, a diagonal crack develops in the middle and lower part of the connecting beam, accompanied by a vertical crack approximately 6 cm in length at the junction of the beam wall.With a load of +120 kN, the cracks in the middle and lower part of the connecting beam continue to propagate.At this point, a crack emerges on the upper part of the floor's back.Under a load of +200 kN, the oblique crack in the middle of the beam widens and extends to the top.Upon reaching +280 kN, several oblique cracks appear on the left side of the specimen, with a crack width reaching 0.28 mm.When the load is − 360 kN, a gap through the coupling beam is generated at the upper part of the beam-wall junction and enters the displacement control stage.When the displacement loading Δ = 22 mm, the sound of concrete cracking appears inside the coupling beam, and the coupling beam is cut into many diamond-shaped blocks by oblique cracks.At this time, the bearing capacity of the specimen decreases to below 85% of the peak load, and the coupling beam has lost its bearing capacity.The failure mode of the specimen is shown in figure 5.When the horizontal load of the specimen PRC-S3 reaches-80 kN, a horizontal crack of about 8 cm is generated at the 6 cm junction of the lower beam wall of the right half of the back of the floor.When the load is −160 kN, a horizontal crack approximately 20 cm in length forms at the middle edge of the northern half of the floor.Simultaneously, the horizontal crack in the southern half extends 10 cm towards the edge.Under a load of +200 kN, two parallel and overlapping oblique cracks appear from the upper left part of the beam to the lower right part.The lengths of these cracks measure about 12 cm and 16 cm, respectively.At −240 kN, an inclined crack develops from the upper left corner of the beam, extending to the left edge.Additionally, an inclined crack approximately 16 cm long forms in the upper right middle part, while the lower right section shows a crack running from the lower middle to the middle root.Under a load of +280 kN, four diagonal cracks emerge along the left edge, from the upper left corner to the lower right corner.These diagonal cracks widen the previously formed cracks from the upper middle left side to the lower right side.With a load of +360 kN, three almost connected oblique cracks develop from the middle right to the upper left corner of the connected beam, measuring about 8 cm, 6 cm, and 3 cm in length, respectively.Additionally, several horizontal cracks appear above the southern half of the floor's back.Under a load of −360 kN, small cracks form on the right edge of the beam, and the maximum width of the cracks on the floor reaches 0.18 mm.When the load increases to +400 kN, no new cracks appear in the connected beam.However, the original crack widens significantly.At this point, the maximum width of the inclined crack in the connected beam reaches 0.31 mm.When the load is-400 kN, the inclined cracks that have appeared in the left position of the middle and lower part of the coupling beam extend to the lower left corner and the upper right corner respectively, and extend downward to the root to enter the displacement control stage.When the displacement loading Δ = 22 mm, the concrete protective layer at the lower part of the coupling beam is basically peeled off, and the welding between the floor slab and the floor bearing plate is broken.At this time, the bearing capacity of the coupling beam specimen decreases to below 85% of the peak load, and the coupling beam has been destroyed.The failure mode of the specimen is shown in figure 6.

Hysteresis loop
The hysteretic curves of PRC-NS1 ∼ PRC-S3 are shown in figure 7, where V and Δ are the load value and horizontal displacement value of the specimen, respectively.Through analysis, the following main conclusions are obtained: (1) The hysteresis loops of the three interconnected beams are complete, and there is no noticeable pinching phenomenon.This indicates a strong energy dissipation capacity of the connected beams.In the early stage of loading, the initial stiffness of the coupling beam is large, the hysteresis curve of each specimen is slender and narrow, and the load-displacement curve is approximately linear.
(2) As the load increases, the specimen has a certain degree of plastic damage, and the residual deformation begins to increase, resulting in the stiffness and bearing capacity degradation of the coupling beam during loading.At this time, the width of the inclined crack increases continuously, and the concrete cracks seriously and gradually withdraws from the work.(3) It is found that the peak load of PRC-S3 is 1.31 times and 1.18 times that of PRC-S2 and PRC-NS1, respectively.It can be seen that the PRC coupling beam with steel truss floor slab has higher bearing capacity.And the displacement of the specimen PRC-S3 is smaller than that of the specimen PRC-S2 when the peak load is reached, indicating that PRC-S3 has better ductility.

Finite element parameter analysis
ABAQUS finite element software is employed to construct the PRC coupling beam model with a steel truss floor slab.In this model, three-dimensional solid elements (C3D8R) represent the concrete, while three-dimensional linear truss elements (T3D2) depict the rebar.Additionally, shell elements (S4R) are used to model the embedded steel plate.To ensure the highest calculation accuracy, the Simpson integration method with 9 integral points is applied in the thickness direction.
In the material properties, the concrete unit employs the constitutive model within the ABAQUS software, which includes the plastic damage model.The compression model comprises the ascending straight line section, the ascending curve section, and the descending curve section.The ascending straight section is defined by the elastic limit points εc,e0 and σc,e0.The initial tangential modulus of concrete is calculated using formula (1): c e c e 0 0 0 In the formula, σ c,e0 = f c /3, where f c represents the axial compressive strength of concrete.The curve section is defined by the formula provided in Saenz [20].Where ε 0 is the strain corresponding to the peak stress σ 0 , ε u is the strain corresponding to the ultimate stress σ u , Es is the secant modulus at the maximum stress point given by E s = σ 0 /ε u , β is the coefficient, and its expression is as follows: The evolution equation for concrete compression damage is as follows: In this paper, the stress-fracture energy model is selected to define the tensile stress-strain relationship of concrete.To calculate the softening modulus during the tensile softening stage, the fracture energy of concrete can be determined by considering the 'stress-crack width' curve in the tensile softening section and the area enclosed by the coordinate axes.Consequently, the tensile softening modulus can be calculated as follows: The steel constitutive adopts the double broken line model, as shown in figure 8.The initial elastic modulus is E 0 , and the elastic modulus of steel after yield is 0.01E 0 .In addition, the initial elastic modulus of steel is obtained from the material test.
During the setting of boundary conditions, the model base is coupled to RP-2, and the setting is completely fixed.In the constraint setting, Lam [21] suggests that to mitigate the slip phenomenon resulting from cyclic loads between the concrete and the built-in steel plate, shear bolts are positioned on both sides of the steel plate.Therefore, for this simulation, the Embedded restraint mode is selected for the steel bars, built-in steel plate, and concrete.In the model, the steel arm and the upper end of the concrete block are set to Tie contact.Additionally, the steel gasket at the loading point of the steel arm is also in Tie contact with it.The loading point is placed 20 mm before the midpoint of the beam span of the steel arm to ensure that the force line of the actuator in the calculation passes through the beam span.The steel arm is rigidly coupled to the steel gasket.Regarding the grid division, the cell mesh size is set to 50 mm as it influences the calculation speed and accuracy.After several trial calculations, it was determined that a mesh size of 50 mm not only maintains the convergence speed but also ensures calculation accuracy.The PRC connected beam model and the grid diagram with the reinforced truss floor plate are illustrated in figure 1.To ensure improved convergence of the simulation analysis, a displacement control loading scheme is adopted.the finite element model is shown in figure 9.
Comparative analysis of simulation and experimental results.10 that the simulation curve of ABAQUS is in good agreement with the test skeleton curve, but the peak load of the simulation curve is slightly larger than the test skeleton curve.The error between the two is kept within 7%, which may be caused by the loosening of the device in the test.In the simulation, the specimen is an ideal boundary condition, so the peak load is slightly higher than the test value.It can be found from figure 13 that the final damage of the floor in the finite element simulation and the test occurs at the junction of the wallboard.The results of the two are in good agreement, and the simulation accuracy is high.
Parameter analysis of PRC coupling beam with steel bar truss floor slab On the basis of the test, in order to further explore the influence of the steel truss floor slab on the seismic performance of PRC coupling beams, the finite element software was used to analyze the parameters, including span-depth ratio, concrete compressive strength, longitudinal reinforcement ratio, stirrup reinforcement ratio, truss upper ( lower ) chord reinforcement diameter and truss web reinforcement diameter.

Span-to-height ratio
Ductility is a critical characteristic in the seismic performance of structures, often quantified by the ratio of ultimate displacement d u to yield displacement d , y referred to as the ductility coefficient.In this paper, the yield displacement d y is determined using the general yield bending moment method, as shown in figure 12.The ultimate displacement d u is defined as the displacement corresponding to the ultimate load, P u .
Figure 13 presents a comparison of load-displacement curves for different span-to-height ratios.The spanto-height ratio (l/h) is set to 1.0, 1.5, and 2.0.As observed in the figure, reducing the span-to-height ratio of connected beams leads to corresponding increases and decreases in shear-bearing capacity and ductility.Additionally, the displacement at peak load is smaller, indicating good plastic deformation performance.In comparison to specimens with a span-to-height ratio of 2.0, the ultimate bearing capacity of connected beams increases sequentially for span-to-height ratios of 1.0, 1.5, with increments of 4.24%.Ductility, on the other hand, decreases by 41.07% and 28.93% respectively.This demonstrates that the span-to-height ratio is a significant parameter.
Built-in steel plate ratio Figure 14 presents a comparison of load displacement curves for different internal steel plate distribution rates.The thickness of the steel plate is successively set to 6 mm, 8 mm, 10 mm, and 12 mm, with the corresponding steel plate allocation rates (ρ p ) being 3.71%, 4.95%, 6.19%, and 7.42%, respectively.As observed in the figure, increasing the proportion of the embedded steel plate significantly enhances the shear capacity of the specimen.However, the rate of increase in shear capacity gradually diminishes, indicating a reduction in the shear potential of the embedded steel plate.It is important to note that excessively large steel plate proportions should not be arbitrarily chosen.In comparison to specimens with a plate ratio of 3.71%, those with plate ratios of 4.95%, 6.19%, and 7.42% experienced increases in shear strength of 13.09%, 23.99%, and 32.84%, respectively.Additionally, ductility increased by 9.94%, 19.34%, and 33.15%.This underscores the significance of the internal steel plate ratio as an important factor.

Longitudinal reinforcement ratio
Figure 15 is the comparison of load-displacement curves of different longitudinal reinforcement ratios of coupling beams.The longitudinal reinforcement ratio ρ z of the he coupling beam is set to 1.23 %, 1.39 %, 1.59 %, 2.01 %, 2.22 % and 2.48 % respectively.It can be seen from the figure that compared with the specimens with longitudinal reinforcement ratio of 1.23 %, the shear capacity of the specimens with longitudinal reinforcement ratio of 1.39 %, 1.59 %, 2.01 % and 2.48 % increased by 1.3 %, 1.48 %, 2.4 %, 3.24 % and 3.67 % respectively, and the effect was not significant.It can be seen that the influence of the longitudinal reinforcement ratio of the coupling beam is limited.

Compressive strength of concrete
Figure 16 is the comparison of load displacement curves of different concrete compressive strength f cu, k .The compressive strength of concrete f cu, k is set to 30 MPa, 35 MPa, 40 MPa and 50 MPa.From the diagram, it can be seen that increasing the grade of concrete makes the shear capacity and ductility of the specimen increase and decrease accordingly.Compared with the specimens with compressive strength of 30 MPa, the shear bearing capacity of the coupling beams with compressive strength of 35 MPa, 40 MPa and 50 MPa increased by 5.56%, 11.46% and 19.15% respectively, and the ductility decreased by 5.19%, 6.49% and 8.66% respectively.Therefore, the compressive strength f cu, k of concrete is an important influence parameter.

Diameter of steel bar in web member
Figure 17 is the load-displacement curve of different truss web member steel bar diameters.Line comparison.The truss specification of the actual test is 10 mm × 8 mm × 4.5 mm ( the diameter of the upper chord is 10 mm, the diameter of the lower chord steel bar is 8 mm and the diameter of the web member steel bar is 4.5 mm ), which is selected as the basic model for parameter analysis.The diameter of the web member is set to 4 mm, 4.5 mm, 5 mm, 5.5 mm and 6 mm in turn.According to the comparison of the figures, compared with the specimens with a diameter of 4 mm, the shear capacity of the specimens with a diameter of 4.5 mm, 5 mm, 5.5 mm and 6 mm increased by 0.03%, 0.06%, 0.09% and 0.12% respectively.Diameter of upper and lower chord steel bar Figures 18 and 19 are the comparison of the load-displacement curves of different diameters of the upper and lower chords of the truss.The truss specification of the test is 10 mm × 8 mm × 4.5 mm ( the diameter of the upper chord is 10 mm, the diameter of the lower chord is 8 mm and the diameter of the web member is 4.5 mm ) as the basic model for parameter analysis.First of all, change the diameter of the upper chord steel bar, set it to 8 mm, 10 mm and 12 mm in turn, and the specific specifications are 8 mm × 8 mm × 4.5 mm, 10 mm × 8 mm × 4.5 mm, 12 mm × 8 mm × 4.5 mm ; after that, the diameter of the lower chord steel bar was changed to 8 mm and 10 mm respectively, and the specific specifications were 10 mm × 8 mm × 4.5 mm and 10 mm × 10 mm × 4.5 mm respectively.It can be seen from the figure that the influence of the diameter of the upper and lower chords of the truss is limited.Compared with the specimens with a diameter of 8 mm, the shear capacity of the coupling beams with a diameter of 10 mm and 12 mm increases by 0.48% and 0.91% respectively.The ductility increased by 1.52% and 1.02% respectively.Compared with the specimen with the diameter of the lower chord steel bar of 8 mm, the shear capacity of the specimen with the diameter of the lower chord steel bar of 10 mm increased by 0.52%.Ductility increased by 0.51%.It can be found that the diameter of the upper and lower chords of the truss has little effect on the bearing capacity and ductility of the coupling beam.

Conclusion
(1) The finite element software ABAQUS was employed to simulate three steel plate concrete composite beams, and the simulated displacement-to-load curves demonstrated a close alignment with the skeleton curves obtained from actual testing.A comparison between the simulated analysis and the real test results in terms of the loading mechanism and beam failure mode revealed a strong agreement, affirming the reasonableness of the model.
(2) The hysteresis loops of the three interconnected beams are complete, without any noticeable pinching phenomenon.This indicates that the connected beams possess a high energy dissipation capacity.
(3) While the placement of a floor slab can substantially alter the failure pattern of PRC connecting beams, it is noteworthy that the built-in steel plate within the connected beam exhibits superior shear resistance when compared to truss floor slabs with steel bars.In practical engineering, the inclusion of a truss slab with steel bars notably enhances the structural integrity and mitigates severe damage resulting from the interaction between the beam and the traditional RC slab.
(4) Utilizing the softened tension-compression bar model and the multi-strip model, a calculation method for the shear bearing capacity of PRC connected beams with reinforced truss slabs is developed.Subsequently, a comparison is made between the actual test results for shear bearing capacity, the finite element analysis results, and the calculated values obtained through this method.This comparison serves to validate the accuracy of calculating the shear bearing capacity of PRC connected beams with reinforced truss slabs.

Figure 1 .
Figure 1.Specimen size and reinforcement details: (a) Upper and lower end block size and reinforcement of coupling beam; (b) Coupling beam size and reinforcement diagram without floor(PRC-NS1); (c) Coupling beam size and reinforcement diagram with ordinary RC floor(PRC-S2); (d) Ordinary RC floor reinforcement diagram; (e) Size and reinforcement diagram of coupling beam with steel bar truss floor slab(PRC-S3); (f) Steel truss floor slab reinforcement diagram.

Figure 2 .
Figure 2. Test setup.(a) Diagram of loading device; (b) Main view of actual loading device; (c) Side view of actual loading device.

Figure 11 .
Figure 11.Comparison diagram of specimen floor damage.

Figure 13 .
Figure 13.Comparison of load-displacement curves of coupling beams with different span height ratio.(a) load-displacement curve; (b) ductility factor; (c) bearing capacity.

Figure 14 .
Figure 14.Comparison of load-displacement curves of different steel plate ratios of coupling beams.(a) load-displacement curve; (b) ductility factor; (c) bearing capacity.
Figures 10 and 11  are the PRC-S3 skeleton curve comparison diagram and the final damage comparison diagram of the floor respectively.It can be found from figure

Figure 17 .
Figure 17.Comparison of load-displacement curves of different truss web diameter of coupling beam.(a) load-displacement curve; (b) ductility factor; (c) bearing capacity.

Table 1 .
Main parameters of the specimens.

Table 2 .
Mechanical properties of steel.