Dynamic Properties of Timber–Concrete Composite Beams with Crossed Inclined Coach Screw Connections: Experimental and Theoretical Investigations

: Due to the low density and stiffness of wood, traditional timber ﬂoor systems are prone to producing large vibration responses. By combining timber beams with concrete ﬂoors, timber– concrete composite (TCC) ﬂoor systems show stronger bearing capacity, higher bending stiffness, and better thermal and sound insulation behaviors when compared with traditional timber ﬂoor systems. In this study, the vibration performance of TCC beams with crossed inclined coach screw connectors was investigated using dynamic tests. The inﬂuence of the screw diameters and slab dimensions on the dynamic performance of the composite beams was evaluated. The test results demonstrated that TCC beams show good dynamic performance when used as a ﬂoor component and meet the preliminary requirements of ﬂoor vibration comfort for fundamental frequency. The fundamental frequency and damping ratio of TCC beams decreases with the increase in slab dimensions. The bending stiffness and natural frequency of TCC beams decrease smoothly when reducing the screw diameter from 16 to 12 mm. Additionally, two theoretical models were used to predict the natural frequencies of the TCC beams, and the predicted values show good consistency with the measured ones.


Introduction
Timber members, characterized by light mass and high strength, are easily fabricated and assembled in construction [1][2][3].However, compared to concrete or steel, timber shows apparent disadvantages in density and modulus of elasticity.Timber floors easily produce annoying vibrations, which affect the comfort of users, and even cause resonance that endangers the safety of the structure.Therefore, scholars have focused on the vibration problem of timber floors since the 1970s, forming a series of design methods and controlling indicators [4,5].The controlling vibration factors include deformation modal parameters and excitation responses, such as deflection d, fundamental frequency f, speed v, and acceleration a, under dynamic load [6][7][8][9][10].
Existing investigations found that adding concrete to timber beams can significantly improve the vibration performance of the floor system.Compared to pure timber floors, timber-concrete composite (TCC) floors show significant improvement in the sound insulation effect and in reducing the sensitivity of vibration comfort, by means of increasing the stiffness of the components through the composite action [11][12][13].
Studies on TCC structures are mainly focused on static properties, but there are limited studies on vibration behavior.Deam et al. [14] experimentally investigated the dynamic performance of laminated veneer lumber (LVL)-concrete composite beams.Their study showed that the concrete slab is beneficial in reducing fundamental frequency and acceleration sensitivity when compared with pure timber floors, which can effectively avoid the sensitive perception range of people.Mertens et al. [15] conducted dynamic tests both on timber floors and TCC floors and evaluated vibration comfort according to the European standard EN 1995-1-1 (Eurocode 5) [10].They found that TCC floors could meet the requirements of fundamental frequency and that TCC connections are crucial to the vibration response of TCC floors.Rijal et al. [16] discussed the influences of different connection types on the dynamic performances of TCC beams.Through experimental research, they found that different shear connectors influence beams' natural frequencies and damping ratios.
The interlayer connection is a crucial aspect of research in timber-concrete composite structures.Various types of fasteners have been reported for TCC structures.Chybi ński and Polus [17] developed an aluminum-timber composite connection with hexagonal head wood screws and reinforced with toothed plates.Through an experimental study, it was found that bearing strength can be significantly improved after strengthening with a toothed plate.Lukaszewska et al. [18] developed a novel composite floor system by connecting prefabricated concrete slabs to timber joists.They developed and tested various types of shear connectors for the floor system, including metal plates, dowels, toothed metal plates, and hexagonal head wood screws with steel tubes.Through experiments and numerical analysis, they found that the connections all have good structural performance, especially the coach screws and notch connections.Szumigała et al. [19] developed new connectors for timber-concrete composite structures, consisting of a headed stud and a steel screw.Through experiments and analyses, it was found that the significant advantage of the new connection is ductility.Tao et al. [20,21] studied the feasibility of glued perforated steel plates in prefabricated timber-concrete composite structures.Their results showed that the glued perforated steel plate connections have high slip stiffness and shearing capacity.Gutkowski et al. [22] studied a composite concrete-wood floor system using a novel notched shear key/anchor connection.Their results indicated its structural merit compared with ordinary mechanical connectors.
In this study, connections with crossed inclined coach screws were used for TCC beams considering their high construction efficiency and good shear performance [23].Wen et al. [24] investigated the vibration performance of timber-lightweight aggregate concrete composite beams using three different connection methods.Among them, the natural frequency of composite beams connected with crossed inclined screw connections is lower than those with notch-screw connections or glued-steel plate connections.There are limited studies available in the literature on the dynamic performance of TCC beams with crossed inclined coach screw connections.Therefore, this study aimed to investigate the dynamic properties of TCC beams that utilize crossed inclined coach screws.Experimental investigations were conducted to evaluate the modal dynamic properties of TCC beams, including their fundamental frequency and damping ratio.Moreover, the effects of concrete slab dimensions and screw diameter on the dynamic performance of TCC beams are discussed.

Timber
The glulam beams were made with Douglas fir lumber from North America.The lumber has a density of 456 kg/m 3 and a moisture content of 11.2%.Their moisture content was determined using tests according to GB/T 1931-2009 [25], and their density was measured following the GB/T 1933-2009 [26] guidelines.For the tests, a drying oven with machine model DHG-9140(A) (101-2), produced by Yiheng Scientific Instrument Co., LTD., Shanghai, China, was used.The basic mechanical properties of glulam were obtained using material tests according to EN 408 [27].The dimensions of the samples used in the tensile, compressive, and shear tests were 30 mm × 10 mm × 300 mm (height × width × length), 50 mm × 50 mm × 300 mm, and 55 mm × 32 mm × 300 mm, respectively.A testing machine produced by MTS System (China) Co., Ltd.(Shanghai, China) with a maximum capacity of 300 kN, was used for the material tests.The corresponding test results are shown in Table 1.Notes: E t is the modulus of elasticity, f cl is the compression strength in the longitudinal direction, f tl is the tension strength in the longitudinal direction, and f tp is the shear strength parallel to the grain.

Concrete
The concrete slabs were poured with C40 grade cast in situ concrete.The compression tests were conducted on the concrete cubes with a side length of 150 mm under natural curing for 28 days.The Young's modulus and the tensile strength of the concrete were obtained via tests according to GB50010-2010 [28].The tests were conducted using a Microcomputercontrolled automatic pressure tester produced by Sansi Instrument Manufacturing Co., Ltd.(Shanghai, China).The basic mechanical properties of the concrete are shown in Table 2. Notes: E c is the elastic modulus of concrete, f c is the compression strength, and f t is the tension strength.

Steel
The steels used in this test mainly include the reinforcing bars, bearing supports, and coach screws.The strength grade of the steel made for the reinforcing bars and coach screws was S355 with a yield strength of 345 MPa and a modulus of elasticity of 200 GPa.The bearing supports were manufactured with high strength steel with a yield strength of 640 MPa and a modulus of elasticity of 210 GPa.The diameter of the reinforcing bars was 8 mm at a spacing of 150 mm.The thickness of the bearing support plate was 30 mm.Coach screws with diameters of 12 mm or 16 mm and a length of 200 mm were used as the timber-concrete interfacial connections, as shown in Figure 1.The concrete slabs were poured with C40 grade cast in situ compression tests were conducted on the concrete cubes with a side len under natural curing for 28 days.The Young's modulus and the tensile concrete were obtained via tests according to GB50010-2010 [28].T conducted using a Microcomputer-controlled automatic pressure tester Sansi Instrument Manufacturing Co., Ltd.(Shanghai, China).The bas properties of the concrete are shown in Table 2.

Steel
The steels used in this test mainly include the reinforcing bars, bea and coach screws.The strength grade of the steel made for the reinforcing screws was S355 with a yield strength of 345 MPa and a modulus of elastic The bearing supports were manufactured with high strength steel with a of 640 MPa and a modulus of elasticity of 210 GPa.The diameter of the re was 8 mm at a spacing of 150 mm.The thickness of the bearing support pla Coach screws with diameters of 12 mm or 16 mm and a length of 200 mm the timber-concrete interfacial connections, as shown in Figure 1.The predrilling diameter for CBIS16-200 was 12 mm, while that for CBIS12-200 was 9 mm.The screws were inserted using an electric wrench with a maximum torque moment of 200 N•m.A multifunctional testing device with a maximum load capacity of 250 kN produced by Hangzhou POPWIL electromechanical control engineering co., ltd.,China was used for the test.The test setup for the push-out test is shown in Figure 3.
To evaluate the shear performance of the crossed inclined coach push-out tests were carried out in preliminary tests according to EN268 groups of specimens with 3 samples in each group were analyzed in adopting screws with different diameters.The specimens with 16 mm dia were named CBIS16-200 and those with 12 mm diameter screws were name The length of the screws was 200 mm and the inclined angle was 45°.The shown in Figure 2. The predrilling diameter for CBIS16-200 was 12 mm, CBIS12-200 was 9 mm.The screws were inserted using an electric w maximum torque moment of 200 N•m.A multifunctional testing device wit load capacity of 250 kN produced by Hangzhou POPWIL electromech engineering co., ltd.,China was used for the test.The test setup for the pu shown in Figure 3.

Timber-Concrete Composite (TCC) Beams
To evaluate the effects of concrete slab dimensions and screw dia dynamic performance of the TCC beams, five TCC beam specimens were dimensions of the timber beams were 5000 mm × 150 mm × 400 mm (len height), and the dimensions of the concrete slabs were 4800 mm in length widths and heights.
To explore the influence of concrete slab width on vibration performan widths of 930 mm, 1395 mm, and 1860 mm were designed under the clear mm.The parameter bc/l is the width-to-span ratio, which was 0.2, 0.3, a To evaluate the shear performance of the crossed inclined coac push-out tests were carried out in preliminary tests according to EN26 groups of specimens with 3 samples in each group were analyzed in adopting screws with different diameters.The specimens with 16 mm di were named CBIS16-200 and those with 12 mm diameter screws were nam The length of the screws was 200 mm and the inclined angle was 45°.The shown in Figure 2. The predrilling diameter for CBIS16-200 was 12 mm, CBIS12-200 was 9 mm.The screws were inserted using an electric w maximum torque moment of 200 N•m.A multifunctional testing device wi load capacity of 250 kN produced by Hangzhou POPWIL electromech engineering co., ltd.,China was used for the test.The test setup for the p shown in Figure 3.

Timber-Concrete Composite (TCC) Beams
To evaluate the effects of concrete slab dimensions and screw di dynamic performance of the TCC beams, five TCC beam specimens were dimensions of the timber beams were 5000 mm × 150 mm × 400 mm (len height), and the dimensions of the concrete slabs were 4800 mm in length widths and heights.
To explore the influence of concrete slab width on vibration performa widths of 930 mm, 1395 mm, and 1860 mm were designed under the clea mm.The parameter bc/l is the width-to-span ratio, which was 0.2, 0.3,

Timber-Concrete Composite (TCC) Beams
To evaluate the effects of concrete slab dimensions and screw diameter on the dynamic performance of the TCC beams, five TCC beam specimens were designed.The dimensions of the timber beams were 5000 mm × 150 mm × 400 mm (length × width × height), and the dimensions of the concrete slabs were 4800 mm in length with different widths and heights.
To explore the influence of concrete slab width on vibration performance, three slab widths of 930 mm, 1395 mm, and 1860 mm were designed under the clear span of 4650 mm.The parameter b c /l is the width-to-span ratio, which was 0.2, 0.3, and 0.4 in this study.Therefore, the TCC beams were named after b c /l, which are TCC0.2,TCC0.3, and TCC0.4,respectively.Also, this study tested two different concrete slab heights, 100 mm and 120 mm.The TCC beam with a 100 mm high concrete slab was designated as TCC0.4; while the TCC beam with a 120 mm thick concrete slab was specified as TCC0.4-hc120.
The timber beams and the concrete slabs were connected with crossed inclined coach screws.The test explored two sizes of coach screws, the beam with 12 mm diameter screws was named TCC0.4-CO12,and the others were all 16 mm.The spacing between the connectors was 300 mm in length of beam and 70 mm in width.The details of the parameters of the TCC beams are listed in Table 3, and an example of the TCC beam is shown in Figure 4. TCC0.4,respectively.Also, this study tested two different concrete slab heights, 100 mm and 120 mm.The TCC beam with a 100 mm high concrete slab was designated as TCC0.4; while the TCC beam with a 120 mm thick concrete slab was specified as TCC0.4-hc120.
The timber beams and the concrete slabs were connected with crossed inclined coach screws.The test explored two sizes of coach screws, the beam with 12 mm diameter screws was named TCC0.4-CO12,and the others were all 16 mm.The spacing between the connectors was 300 mm in length of beam and 70 mm in width.The details of the parameters of the TCC beams are listed in Table 3, and an example of the TCC beam is shown in Figure 4.

Test Set-Up
All of the TCC beam specimens were tested under the same boundary conditions, with one hinge support at one end and a roller support at the other end, as shown in Figure 5.The specimens were placed in the central line of the supports, and the clear span of all beams was 4650 mm.

Test Set-Up
All of the TCC beam specimens were tested under the same boundary conditions, with one hinge support at one end and a roller support at the other end, as shown in Figure 5.The specimens were placed in the central line of the supports, and the clear span of all beams was 4650 mm.
The timber beams and the concrete slabs were connected with crossed inclined coach screws.The test explored two sizes of coach screws, the beam with 12 mm diameter screws was named TCC0.4-CO12,and the others were all 16 mm.The spacing between the connectors was 300 mm in length of beam and 70 mm in width.The details of the parameters of the TCC beams are listed in Table 3, and an example of the TCC beam is shown in Figure 4. Notes: bc is the concrete slab width, hc is the concrete slab height, l is the span of the beam, and bc/l is the concrete slab width-to-span ratio.

Test Set-Up
All of the TCC beam specimens were tested under the same boundary conditions, with one hinge support at one end and a roller support at the other end, as shown in Figure 5.The specimens were placed in the central line of the supports, and the clear span of all beams was 4650 mm.Buildings 2023, 13, 2268 6 of 14

Equipment and Experimental Procedure
Acceleration sensors were arranged equidistantly along the central line of the upper surface of the concrete slabs, as shown in Figures 6 and 7.The dynamic test was stimulated using a pulsed hammer.The response signal was collected using the dynamic signal test system TST3828E, and the modal analysis of dynamic properties was performed using the signal processing software DASP-V11.To improve the accuracy and reliability of the data, each TCC beam was tested twice, and the dynamic properties were determined using the average values from the two tests.stimulated using a pulsed hammer.The response signal was collected usin signal test system TST3828E, and the modal analysis of dynamic p performed using the signal processing software DASP-V11.To improve th reliability of the data, each TCC beam was tested twice, and the dynamic p determined using the average values from the two tests.
The TCC beams were tested under bending load, and the test set-u Figures 8 and 9.The testing equipment comprises a hydraulic jack a produced by OVM Machinery Co., Ltd. in Liuzhou, China and Jiangsu Gu Detection Instrument Technology Co., Ltd. in Nanjing, China, resp hydraulic jack with counter-force frames provided the load, and the values forces were recorded with the load cell.The deflections of the TCC beans with linear variable displacement transducers (LVDTs).signal test system TST3828E, and the modal analysis of dynamic properties was performed using the signal processing software DASP-V11.To improve the accuracy and reliability of the data, each TCC beam was tested twice, and the dynamic properties were determined using the average values from the two tests.
The TCC beams were tested under bending load, and the test set-up is shown in Figures 8 and 9.The testing equipment comprises a hydraulic jack and a load cell produced by OVM Machinery Co., Ltd. in Liuzhou, China and Jiangsu Guo Yan Li Zhun Detection Instrument Technology Co., Ltd. in Nanjing, China, respectively.The hydraulic jack with counter-force frames provided the load, and the values of the applied forces were recorded with the load cell.The deflections of the TCC beans were recorded with linear variable displacement transducers (LVDTs).The TCC beams were tested under bending load, and the test set-up is shown in Figures 8 and 9.The testing equipment comprises a hydraulic jack and a load cell produced by OVM Machinery Co., Ltd. in Liuzhou, China and Jiangsu Guo Yan Li Zhun Detection Instrument Technology Co., Ltd. in Nanjing, China, respectively.The hydraulic jack with counter-force frames provided the load, and the values of the applied forces were recorded with the load cell.The deflections of the TCC beans were recorded with linear variable displacement transducers (LVDTs).

Push-Out Test of Connectors
According to the European standard EN26891 [29], the load, interfaci slip stiffness of the connector were obtained.The shear properties of the c listed in Table 4.

Push-Out Test of Connectors
According to the European standard EN26891 [29], the load, interfacial slip, and the slip stiffness of the connector were obtained.The shear properties of the connections are listed in Table 4. Notes: Ks is the slip modulus of the connection at the serviceability limit, Ku is the slip modulus of the connection at the ultimate state, and Fmax is the shear capacity of the connection.

Dynamic and Bending Test of the TCC Beams
The TCC beams were stimulated with a hammer, and the time domain signals of

Push-Out Test of Connectors
According to the European standard EN26891 [29], the load, interfacial slip, and the slip stiffness of the connector were obtained.The shear properties of the connections are listed in Table 4. Notes: K s is the slip modulus of the connection at the serviceability limit, K u is the slip modulus of the connection at the ultimate state, and F max is the shear capacity of the connection.

Dynamic and Bending Test of the TCC Beams
The TCC beams were stimulated with a hammer, and the time domain signals of acceleration responses (as shown in Figure 10) were collected from sensors.The time domain signals were subjected to fast Fourier transform (FFT); then, the natural frequencies (as shown in Figure 11) and damping ratio of the TCC beams could be calculated.The symbol f 1(exp) denotes the measured values of fundamental frequencies of the first flexural modal, and ζ 1 was used to indicate the first modal damping ratio of the TCC beams.The specific test results are listed in Table 5.The load (P) was applied at the rate of 20 kN/min using a hydraulic jack with counterforce frames.The deflections were recorded via the LVDTs, and the load-deflection curves are shown in Figure 12.The bending properties at the serviceability state of the TCC beams are also listed in Table 5, including the mid-span deflection d and the bending stiffness (EI) (exp) .The beams were tested to the ultimate load; P u is the ultimate load and presents the failure mode, as shown in Figure 13.The load (P) was applied at the rate of 20 kN/min using a hydra counterforce frames.The deflections were recorded via the LVD load-deflection curves are shown in Figure 12.The bending pro serviceability state of the TCC beams are also listed in Table 5, including deflection d and the bending stiffness (EI)(exp).The beams were tested to the Pu is the ultimate load and presents the failure mode, as shown in Figure 1

Analytical Investigation
Studies have shown that people are most likely to feel uncomfortable is characterized by low-frequency vibrations, especially for frequencies i The load (P) was applied at the rate of 20 kN/min using a hydra counterforce frames.The deflections were recorded via the LVD load-deflection curves are shown in Figure 12.The bending prop serviceability state of the TCC beams are also listed in Table 5, including deflection d and the bending stiffness (EI)(exp).The beams were tested to the Pu is the ultimate load and presents the failure mode, as shown in Figure 1

Analytical Investigation
Studies have shown that people are most likely to feel uncomfortable is characterized by low-frequency vibrations, especially for frequencies i 4-8 Hz [31].Combined with research and ISO standards [32,33], schola

Analytical Investigation
Studies have shown that people are most likely to feel uncomfortable when the floor is characterized by low-frequency vibrations, especially for frequencies in the range of 4-8 Hz [31].Combined with research and ISO standards [32,33], scholars have given relevant indicators to control the vibration of timber floors for comfort.An important one of which is that the fundamental frequency (f 1 ) should be greater than 8 Hz.If f 1 is lower than 8 Hz, it is easy to cause discomfort to the users, and even footfall will cause resonance of the floor, causing safety problems [6,7,32,33].For example, Eurocode 5 [10] stipulates that the f 1 should be greater than 8 Hz.If the f 1 of the floor is estimated to be lower than 8 Hz, special analysis and design should be carried out.As one of the important indicators of the dynamic properties of the floor, the fundamental frequency is an important indicator to evaluate whether the vibration performance of the floor is good.Therefore, the analysis of the f 1 of the TCC beam is an important task of this study.

Theoretical Calculation
Eurocode 5 provides a calculation model for estimating the fundamental frequency (f 1 ) of the floor system, as shown in Formula (1): where EI is the bending stiffness of the TCC beam; l is the span of the TCC beam; and m is the unit length mass of the TCC beam, including the beam self-weight and other permanent loads.In addition, the bending stiffness of the partially composite beams uses the effective bending stiffness (EI) eff , which is based on the 'γ-method', as shown in Formula ( 2): where the subscripts c and t designate the concrete and timber, respectively; E is the modulus of elasticity; I is the moment of inertia; γ is the reduction coefficient for the combined action; A c and A t are the section area of concrete slab and timber beam, respectively; a c and a t are the distance between the centroid of concrete slab or timber beam to the neutral axis of the composite section, respectively; s is the distance of shear connectors; K is the slip stiffness of shear connections; and L is the clear span of beams.
Murray [34] also provides a calculation model that could estimate the fundamental frequency (f 1 ) of the simply supported beams, as shown in Formula (4): where g is the acceleration of gravity; EI is the bending stiffness of the TCC beam; L is the clear span of the beam; and w is the uniformly distributed load in unit length.The parameters adopted in the theoretical calculation are shown in the previous text.It is worth noting that Table 4 shows the shear properties of the connectors.K s and K u are the slip moduli of the connector at the serviceability limit and the ultimate state, respectively.When studying the vibration behavior of beams, the values of K s were used to calculate the (EI) eff of TCC beams in the serviceability limit state.Using the Eurocode 5 and Murray methods, the semi-theoretical predicted values f 1(EC5) and f 1(M) of the fundamental frequencies of the TCC beams can be obtained, respectively, as shown in Table 6.Additionally, Tao et al. [23] have provided a theoretical calculation method of connector stiffness.Based on the connection stiffness calculation method, the full-theoretical predicted values of the fundamental frequencies can be obtained, as the values of f 1(EC5) and f 1(M) shown in Table 6.Notes: (EI) eff is the bending stiffness of the TCC beams calculated based on the γ-method, (EI) (exp) is the experimental bending stiffness of the TCC beams, f 1(EC5) is the fundamental frequency calculated according to Eurocode 5 with the experimental stiffness of the connector, f 1(M) is the fundamental frequency calculated according to Murray [34] with the experimental stiffness of the connector, f 1(EC5) is the fundamental frequency calculated according to Eurocode 5 with the theoretical stiffness of the connector, and f 1(M) is the fundamental frequency calculated according to Murray [34] with the theoretical stiffness of the connector.

Fundamental Frequency
As shown in Table 6, the fundamental frequencies of the five composite beams ranged from 18 Hz to 26 Hz.If the TCC beams are considered as one-way floors, the control requirements of f 1 > 8 Hz for the floor can be satisfied.From the comparison between the measured values and the calculated values, the value of the maximum difference between experimental frequency and full calculated frequency is 2.13 Hz, it can be seen that the calculation methods in the Eurocode 5 and Murray methods have good reliability.

Effect of the Dimensions of Concrete Slabs
From the data in Table 6, as the width of the slab increases, the flexural stiffness (EI) eff and (EI) (exp) of TCC beams increases, while the fundamental frequency decreases both in the calculated value and in the measured value.According to Equation (1), although the stiffness of the concrete slab increases with the increase in the slab width, the increase in self-weight caused by the increase in slab width still reduces the fundamental frequency of the TCC beams.Similarly, when the slab heights of the concrete are increased from 100 mm to 120 mm, the flexural stiffness (EI) eff of the TCC beam also increases significantly, but its fundamental frequency still decreases.Therefore, it can be preliminarily identified that the self-weight of concrete slab changes, caused by the dimension change, has a greater effect on the fundamental frequency of the TCC beams than the flexural stiffness (EI) eff , and the values of fundamental frequency using the Murray method have a similar pattern.In addition, the damping ratio decreases significantly as the width and height size of the concrete slab increase.

Effect of the Connection
This study tested two different connectors for the TCC beams.It can be seen in Tables 4 and 6 that the flexural stiffness (EI) eff and (EI) (exp) of the TCC beam decreases when reducing the shear stiffness of the connectors.Meanwhile, when changing the screw diameter from 16 mm to 12 mm, the fundamental frequency of the TCC beams decreases smoothly, but the damping ratio increases notably, according to Table 6.This indicates that under the same conditions, the natural frequency of the specimen is inversely proportional to the damping ratio.

Conclusions
In this study, five TCC beams with a clear span of 4650 mm were tested under dynamic excitation.The vibration behavior of the TCC beams was evaluated based on the fundamental frequency and damping ratio.The fundamental frequency of the TCC beams was predicted and calculated using the calculation models in Eurocode 5 and the Murray method, respectively.The calculated values and the experimental values were compared and discussed.The generalized conclusions are as follows: The TCC beams in this study can be used as the one-way floor unit and meet the requirement of f 1 > 8 Hz for floor comfort.
The increase in the dimensions of the concrete slab can increase the flexural stiffness of the TCC beams, but the consequent increase in the self-weight of concrete causes a reduction in the fundamental frequency.The fundamental frequency of the composite beams decreases with the decrease in the connection shear stiffness, while the damping ratio increases with the reduction in the connection stiffness.
Both the methods provided by Eurocode 5 [10] and Murray [34] have certain reliability in predicting the vibration behavior of the TCC beams, but their calculation values are smaller than the experimental values.Therefore, a more in-depth study needs to be conducted, and our next research plan will try to optimize the existing predictive method.

2. 2 .
Specimens 2.2.1.Shear Connectors To evaluate the shear performance of the crossed inclined coach screws, the push-out tests were carried out in preliminary tests according to EN26891 [29].Two groups of Buildings 2023, 13, 2268 4 of 14 specimens with 3 samples in each group were analyzed in this study by adopting screws with different diameters.The specimens with 16 mm diameter screws were named CBIS16-200 and those with 12 mm diameter screws were named CBIS12-200.The length of the screws was 200 mm and the inclined angle was 45 • .The test sample is shown in Figure 2.

Figure 3 .
Figure 3.The push-out test for the shear connector.

Figure 3 .
Figure 3.The push-out test for the shear connector.

Figure 3 .
Figure 3.The push-out test for the shear connector.

Table 3 .
Parameter details of TCC beams.Notes: b c is the concrete slab width, h c is the concrete slab height, l is the span of the beam, and b c /l is the concrete slab width-to-span ratio.

Table 3 .
Parameter details of TCC beams.bc is the concrete slab width, hc is the concrete slab height, l is the span of the beam, and bc/l is the concrete slab width-to-span ratio.

Figure 5 .
Figure 5.The supports of the test: (a) the hinge support; (b) the roller support.

Figure 5 .
Figure 5.The supports of the test: (a) the hinge support; (b) the roller support.

Figure 5 .
Figure 5.The supports of the test: (a) the hinge support; (b) the roller support.
EI)(exp) is the bending stiffness, d is the mid-span deflection at 0.4 Pu, Pu is t f1(exp) is the measured values of fundamental frequencies of the first flexural mod first modal damping ratio of the TCC beams.

Table 1 .
Mechanical properties of timber.

Table 2 .
Mechanical properties of concrete.

Table 1 .
Mechanical properties of timber.Et is the modulus of elasticity, fcl is the compression strength in the longitud is the tension strength in the longitudinal direction, and ftp is the shear strength par 2.1.2.Concrete Notes:

Table 2 .
Mechanical properties of concrete.

Table 3 .
Parameter details of TCC beams.

Table 4 .
Shear properties of connectors.
Notes: Ks is the slip modulus of the connection at the serviceability limit, Ku is the s the connection at the ultimate state, and Fmax is the shear capacity of the connection3.2.Dynamic and Bending Test of the TCC Beams

Table 4 .
Shear properties of connectors.

Table 4 .
Shear properties of connectors.

Table 5 .
Measured values of bending and dynamic properties of TCC beams.

Table 5 .
Measured values of bending and dynamic properties of TCC beams.Notes: (EI) (exp) is the bending stiffness, d is the mid-span deflection at 0.4 P u, P u is the ultimate load, f 1(exp) is the measured values of fundamental frequencies of the first flexural modal, and ζ 1 is the first modal damping ratio of the TCC beams.

Table 6 .
Bending stiffness and dynamic properties of TCC beams.