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MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS INVESTIGATION OF THE FLEXURAL AND SHEAR BEHAVIOUR OF SANDWICH PANELS USING TEXTILE REINFORCED CONCRETE AND LIGHTWEIGHT CONCRETE FOR FLOOR PANELS Major: Special Construction Engineering Code No: 9580206 SUMMARY OF DOCTORAL THESIS Name of PhD Student : MSc HIEP Vu Van Name of Supervisors : Prof Dr QUANG Ngo Dang Prof Dr TRINH Nguyen Thi Tuyet HA NOI - 2023 PREFACE Introduction Sandwich panels are laminated composites made of many layers arranged in a specific order to maximize the load-bearing capacities of component materials The outer layers, known as the face sheets or skin, are typically made of high-strength material to primarily resist the external load The core layer is made of low-strength and lightweight material, which helps to keep the structure stable and provides sound and thermal insulation Sandwich structures with this combination have a high load-bearing capacity, high stiffness, and are lightweight, making them suitable for building wall or slab panels Many new materials, such as textile reinforced concrete (TRC) and lightweight concrete using expanded clay aggregate (LCEC), have been considered suitable for the face sheets and core of sandwich panels Textile reinforced concrete is a composite material composed of finegrained concrete (FGC) and multiple-axial fabric made of carbon or alkali resistant glass, basalt, TRC has many outstanding characteristics, such as high strength and durability, because it is made up of high-strength and non-corrosive materials LCEC is a type of concrete that contains lightweight keramzit aggregate Keramzit is a lightweight granular aggregate made from expanded clay Keramzit particles also increase the strength of conventional lightweight concrete Previous research has focused on developing sandwich panels for wall panels using TRC and lightweight materials with low load-bearing capacity The research on sandwich panels made of TRC and LCEC has not yet been accomplished As a result, to develop a sandwich panels made of TRC and LCEC with high load-bearing capacity in the application of floor panels, structural principles, calculation methods, and design for these types of sandwich panels must be investigated Research objectives To develop a sandwich panel made of TRC and LCEC with high loadcarrying capacity in the application of floor panels, this thesis is carried out with the following objectives: (a) Proposing a sandwich panel made of TRC and LCEC in the application of floor panels (b) Developing the analytical models for determining of the flexural and shear behavior of sandwich panels made of TRC and LCEC in the ultimate limit state and serviceability limit state Subjects, scopes, and research method The research subject of the thesis is a sandwich panel using TRC and LCEC in the form of a prefabricated panel The panel functions as a oneway simply supported beam Research scopes: • Flexural and shear behavior of sandwich panels made of TRC and LCEC when applied to a simply supported one-way concrete beam or floor subjected to short-term static loads • TRC has a compressive strength of up to 60 MPa; • LCEC has a compressive strength of up to 20 MPa and a weight density of approximately 1300 kg/m3; • Carbon textile reinforcement with a tensile strength of up to 3000 MPa The thesis is based on three main methods: theoretical research, experimental investigation, and numerical simulation Contents The thesis contains four chapters, an introduction, and concluding remarks and suggestions for future work - The introduction chapter explains the reasons for choosing the topic, the research’s objectives, the scope, the research method, and the scientific and practical significance of the topic - Chapter introduces the current research conducted on sandwich panels in Vietnam and around the world, and the introduction of TRC and LCEC The proposed research direction and the contents of this thesis are clarified based on the previous literature - Chapter proposes a design of a sandwich panels made of TRC and LCEC in the form of a one-way prefabricated floor panel It also develops calculation models to determine the flexural and shear behavior of sandwich panels made of TRC and LCEC - Chapter describes the experimental results used to determine some of the main mechanical properties of TRC and LCEC, such as compressive strength, flexural tensile strength, elastic modulus, and bond behavior between the two materials Experimental investigations of the flexural and shear behavior of one-way sandwich panels using TRC and LCEC were also carried out These findings will be used to validate the calculation models developed in Chapter - Chapter presents the parametric studies on the effect of the strength of the LCEC core layer and material layers’ thickness on the load-bearing behavior of the sandwich panels This chapter also introduces the design of a sandwich panel made of prefabricated TRC and LCEC for the use of floor panels - Concluding remarks and suggestions for future work summarize the main conclusions of the thesis and suggestions for future research Scientific and practical significance - The scientific significance of the thesis: This thesis proposes a prefabricated floor panel sandwich panels made of TRC and LCEC This is a new structure made of high-performance materials such as textile reinforcement, fine-grained concrete, and lightweight concrete using expanded clay aggregate - The practical significance of the thesis: This thesis investigated the flexural and shear behavior of sandwich panels made of TRC and LCEC in the application of floor panels CHAPTER OVERVIEW OF CURRENT RESEARCH 1.1 Sandwich panels and their applications in construction projects A sandwich panel is a system with an optimal load-bearing capacity that combines two or more types of materials or structures with different and sometimes contradictory load-bearing characteristics (Figure 1-1) Figure 1-1 Design of a 3-layer sandwich panel Sandwich panels are classified according to the simultaneous working of material layers There are several groups of sandwich panels as below: • "Unconjugated sandwich panels" has a very weak bond between material layers Each material layer in this sandwich panels operates almost independently; • “Partially composite sandwich panels” has a limited bond between layers of materials When sandwich panels are loaded, the layers of materials separate; however, the skin continues to resist the load; •“Completely composite sandwich panels” has a perfect bond between the layers of materials The bond between the layers does not influence the failure of the sandwich panels In practice, sandwich panels have been widely used in a variety of construction projects, including civil, industrial, and transportation infrastructure (Figure 1-2) Figure 1-2 Several types of sandwich panels in construction projects 1.2 Textile reinforced concrete TRC is a composite material made of fine-grained concrete (FGC) and high-strength textile fiber (Figure 1-3) FGC is an inorganic cementitious matrix with small aggregates (less than 1mm in diameter) Textile reinforcement is created by weaving small carbon fiber or glass fiber into a mesh Figure 1-3 The structure of TRC 1.2.1 Component materials 1.2.1.1 Textile reinforced concrete Textile reinforcement is made up of basic fibers (filaments) with diameters ranging from a few micrometers to several millimeters As reinforcement for concrete, textile fiber is woven into a mesh (Figure 1-4) The fibers are coated with a very thin layer of polymers such as epoxy or styrene butadiene rubber (SBR) to strengthen the bond between the basic fibers and the fibers with FGC Figure 1-4 Textile mesh and basic fibers 1.2.1.2 Fine-grained concrete Fine-grained concrete is composed of cement, fly ash, silica fume, and aggregate with a diameter of less than 0.6 mm, high-strength plasticizer, and water Brockmann proposed a mixture for FGC with compressive strength ranging from 40 to 135 MPa and elastic modulus ranging from 22 to 32 GPa In Vietnam, Cuong Le Minh proposed a mixture for FGC with compressive strength ranging from 40 to 80 MPa 1.2.1.3 Bonding properties between textile reinforcement and FGC The bonding properties between textile reinforcement and FGC are critical factors influencing the simultaneous work of the two materials in textile reinforced concrete Because textile reinforcement is made up of thousands of basic fibers, the bonding properties of the textile reinforcement with FGC are determined by the adhesion of the basic fibers together as well as the adhesion of the outer fibers to the FGC The bond strength between the textile reinforcement and FGC depends on the surface coating of the basic fibers Krüger and Ortlepp built experimental models to determine the bond strength value between textile reinforcement and FGC The experiment proposed by Krüger was reliable and was included in the German technical instruction Zulassung Z-31.10182 1.2.2 Tensile behavior of textile reinforced concrete plate The tensile behavior of the TRC slab can be used to simulate the operation of textile reinforcement in FGC However, because textile reinforcement is heterogeneous, the strength of textile reinforcement immersed in FGC is reduced when compared to the individual fiber Curbach's research on axial tensile reinforced concrete panels revealed that the maximum tensile strength of the textile reinforcement is significantly lower than the total tensile strength of the individual filament 1.2.3 Surface bonding properties between TRC and the core of sandwich panels The ability to work simultaneously between the face sheet and the cores in sandwich panels is dependent on the bond between the layers This bond is formed by the material layers self-bonding or by anchors and shear reinforcement With TRC skin and core layers, this bond is formed by the adhesion force of the cement paste to the aggregate or the surface of each layer The bond properties of the TRC slabs and the based concrete were determined using the tensile test according to RILEM 250-CSM instructions 1.3 Lightweight concrete 1.3.1 Introduction TCVN 9029:2017 specifies lightweight concrete (LC) as having a weight density of less than 1800 kg/m3 The density of concrete is reduced by replacing a portion of the solid material in the concrete with air The amount of gas (pores) in the concrete increases, causing the strength to decrease Aerated concrete or foam concrete, cavity concrete or concrete without sand, and lightweight aggregate concrete are all examples of LC 1.3.2 Lightweight aggregate concretes Lightweight aggregate concretes are lightweight and have high strength The lightweight aggregates are polystyrene foam particles, keramzit, etc Polystyrene foam particles are porous materials with densities ranging from 10 to 20 kg/m3 Keramzit hollow aggregate is made from swollen clay and has a weight density of 800 to 900 kg/m3 The strength of lightweight kezamit concrete (Figure 1-5b) is greater than that of porous concrete, aerated concrete, or recessed concrete Figure 1-5 Lightweight aggregate concretes 1.4 Introduction of sandwich panels with TRC face layers 1.4.1 Research on sandwich panels with TRC face layers Currently, research on sandwich panels with TRC face sheets combined with lightweight core layers has been developed Most of the sandwich panels used lightweight materials such as EPS foam (Expanded Polystyrene, EPS), XPS foam (Extruded Polystyrene, XPS) (Figure 1-6), solid PU foam (polyurethane, PU), porous concrete as the core material Figure 1-6 Sandwich wall panels using TRC-EPS (Finzel) 1.4.2 Calculation models for flexural and shear resistance of sandwich panels Junes proposed a model to calculate the flexural resistance of sandwich panels made of TRC and foam concrete by the multilayer division method The assumptions of this method are as follows Firstly, the stress in each layer is constant Secondly, the bond between the skin and the core layer is perfect The bending moment is determined by the equilibrium equation Djamai proposed a model to determine the flexural behavior of sandwich beams by TRC and foam concrete into stages corresponding to the axial tensile behavior of TRC plate They are the elastic phase, crack forming stage, and stable crack stage, taking into account the tensile stiffening effect Ali Shams proposed a calculation model to determine the relationship between the bending moment and deflection of sandwich beams using TRC - EPS In this model, the deformation of the structure takes into account both the bending moment and the shear force Also, the skin and core materials are considered isotropic The bond between the skin and the core is assumed to be perfect Nguyen proposed an approximate formula for calculating the shear resistance of sandwich panels by TRC – EPC taking into account the influence of shear slenderness (a/d) of the beams The coefficient k(a/d) was determined by statistical analysis of experimental data 1.4.3 Applications of TRC and LC in sandwich panels TRC has been investigated and developed by several research centers and enterprises in Europe to manufacture a variety of prefabricated panels applied as wall panels for buildings The typical projects are Eastsite VIII building (Germany) and EASEE building in Cinisello Balsamo (Italy) The wall panels have a TRC skin combined with a porous concrete core 1.5 Research orientation and contents In recent years, sandwich panels have been researched and developed with a face sheet made of TRC and a core layer of lightweight materials in the application of wall panels These sandwich panels are lightweight and have low load-bearing capacity As the core layer of lightweight materials has low strength and elastic modulus, the load-bearing capacity of the sandwich panels is small Currently, the study on sandwich panels with high load-bearing capacity in the application of floor panels is not yet available In addition, there are few calculation models for sandwich panels The available models only present specific types of sandwich panels There are no design standards for sandwich panels made of TRC and LC Therefore, to develop a sandwich structure with high load-bearing capacity in the application of floor panels, it is recommended to study and apply a sandwich structure with face sheets made of TRC and a core layer by LCEC The objective of this thesis is to develop a prefabricated sandwich panels made of TRC and LCEC in the application of floor panels The research tasks include proposing the design and calculation models for sandwich panels, conducting experimental studies to determine the mechanical properties of materials, flexural and shear behavior of sandwich panels, and implementing parametric studies on several types of sandwich panels in the application of floor panels CHAPTER PROPOSED DESIGN AND ANALYTICAL MODELS TO DETERMINE THE FLEXURAL AND SHEAR BEHAVIORS OF SANDWICH PANELS MADE OF TRC AND LCEC 2.1 Research purposes A sandwich panels composed of TRC and LCEC is a new type of structure To safely and effectively apply sandwich panels made of TRC and LCEC, this chapter presents a study on analytical models to determine the flexural and shear behavior of the sandwich panels made of TRC and LCEC 2.2 Proposed design of sandwich panels made of TRC and LCEC in the application of floor panels The design of sandwich panels in the application of floor panels including the face layer of TRC in tension, the face layer of FGC in compression, and the core layer of LCEC is shown in Figure 2-1 Figure 2-1 The design of sandwich panels using FGC – LCEC – TRC Materials: FGC has a compressive strength from 60 MPa to 70 MPa; carbon textile reinforcement has a tensile strength of about 3000 MPa; LCEC has a compressive strength from 10 MPa to 20 MPa Cross-sectional dimensions: Height: h L 45 25 where L is the span of the panel, h ≥ 100 mm The thickness of the TRC and FGC layers should be chosen as a multiple of mm and should be larger than 10 mm The thickness of the protective concrete layer is mm 2.3 Calculation models to determine the flexural behavior of sandwich panels made of TRC and LCEC 2.3.1 Flexural resistance The flexural resistance of the sandwich section is calculated by the method of layering The material layers are divided into several layers with small thicknesses o FGC is not cracked, o FGC layer cracks at the position of the first crack Figure 2-3 Stress and strain in uncracked cross-section of sandwich panels The calculation of tensile stress in the uncracked concrete area will explain the crack development process In addition, due to the bond between the layers of materials, there is a force transfer between the material layers along the longitudinal direction (as shown in Figure 2-4) Along the transmission length, as the tensile stress reaches the tensile strength, the next crack may appear Based on the equilibrium conditions of force and bending moment, the shortest length of force transmission will be determined so that the tensile stress reaches the tensile strength of the concrete Then, the location of the following cracks on sandwich panels will be predicted according to the first crack location Figure 2-4 Stress diagram in sandwich panels when FGC cracks 11 The procedure to predict the formation and development of cracks in sandwich panels is shown according to a block diagram as shown in Figure 2-5 Figure 2-5 The procedure to predict the formation and development of cracks in sandwich panels 2.4 Calculation model of the shear resistance of sandwich panels made of TRC and LCEC according to the method of bar diagram 12 2.4.1 The strut and tie method The strut and tie method models force flows in the structure by simple truss members (Figure 2-6) Figure 2-6 The strut and tie method for short beam according to ACI 318-19 2.4.2 Modeling of sandwich panels made of TRC and LCEC according to the strut and tie method The sandwich panels is modeled according to the strut and tie method (Figure 2-7): the TRC face sheet is modeled as a tensile member, the LCEC is modeled as a compression member, and the intersection area between the above members is modeled as node region (Figure 2-8, Figure 2-9) Figure 2-7 The strut and tie model in sandwich panels with small a/d Figure 2-8 Node at mid-span Figure 2-9 Node at the supports 13 The shear resistance of the sandwich panels is calculated as: V P C sin T tan 2.5 Conclusion of Chapter This chapter presents a proposal design of sandwich panels made of TRC and LCEC in the application of floor panels The flexural resistance of sandwich panels made of TRC and LCEC is determined by the multilayer division method From the analysis result, a predicted model of crack formation and development in sandwich panels made of TRC and LCEC is developed The model considered the geometrical properties of the cross-section, mechanical properties of materials, bond characteristics between textile reinforcement and FGC, and bond characteristics between FGC and LCEC The chapter also built a model to calculate the shear resistance of sandwich panels made of TRC and LCEC using the strut and tie method 14 CHAPTER EXPERIMENTAL INVESTIGATION OF FLEXURAL AND SHEAR BEHAVIORS OF SANDWICH PANELS MADE OF TRC AND LCEC 3.1 Research purposes The experimental research investigates some important mechanical properties of the TRC face sheet and LCEC core layer of sandwich panels They are the bond between the textile reinforcement and FGC, and the bond between FGC and LCEC This chapter also presents experiments to determine the flexural and shear behavior of sandwich panels made of TRC and LCEC and to verify the proposed calculational models 3.2 Mechanical properties of materials 3.2.1 Fine-grained concrete In this study, FGC is a compound of quartz sand, quartz powder, PC40 cement, fly ash, silica fume, water, and high-strength plasticizer The compressive strength and flexural strength of FGC are 64.06 MPa and 6.75 MPa, respectively The elastic modulus of FGC is 31568 MPa 3.2.2 Lightweight keramzit concrete LCEC is a compound of yellow sand, keramzit aggregate, PC40 cement, water, and high-strength plasticizer The compressive strength and tensile strength of LCEC are 18.6 MPa and 1.47 MPa, respectively The elastic modulus of LCEC is 7693 MPa 3.2.3 Textile reinforcement Carbon textile reinforcement SITgrid004 is manufactured by V.FRAAS (Germany), which has a dimension of m × 1.25 m for each The fiber has a fineness of 1600 tex The tensile strength of single yarn and textile reinforcement immersed in concrete are 3550 MPa and 2700 MPa, respectively The elastic modulus of textile reinforcement is 225 GPa 3.2.4 Bond behavior between textile reinforcement and FGC Bond behavior between FGC and textile reinforcement was determined according to the instructions in Zulassung Z-31.10-182 The average bond strength between SITgrid004 carbon textile and FGC is approximately 1.95 MPa, corresponding to the anchor length of 152 mm 3.2.5 Bond behavior between FGC and LCEC The bond behavior between FGC and LCEC was determined according to the experimental instructions in RILEM 250-CSM The average bond strength between FGC and LCEC is 2.39 MPa 3.3 Study on the flexural and shear behavior of sandwich panels made of TRC and LCEC 15 3.3.1 Design of tested specimens Experimental sets SW1, SW2, and SW3 are designed for 4-point bending test, and experimental sets SW4 and SW5 are designed for 3-point bending test with dimension parameters as shown in Table 3.1 Figure 3-1 4-point bending test of sandwich panels Table 3.1 Dimensions of sandwich panels in the experiment Table 3.2 Flexural and shear resistance of test specimens according to the theoretical model Table 3.3 Predicted results of crack patterns in test specimens according to the theoretical model 16 3.3.2 Flexural behavior of sandwich panels Experimental sets SW1, SW2, and SW3 fail as textile reinforcement is torn apart The difference between experimental and theoretical flexural resistance is less than 5.4% The crack spacing in test specimens ranges from to times of the theoretical results The values range from 46 mm to 107 mm (Figure 3-5) Figure 3-2 Load-deflection curve of SW1 specimens Figure 3-4 Load-deflection curve of SW3 specimens Figure 3-3 Load-deflection curve of SW2 specimens Figure 3-5 Crack distribution in pure bending area in SW1 specimens 17 3.3.3 Shear behavior of sandwich panels Experimental sets SW4 and SW5 fail mainly because LCEC is damaged by inclined cracks (see Figure 3-6 to Figure 3-9) The difference between experimental and theoretical shear resistance is less than 9.2% Figure 3-6 Load-deflection curve of SW4 specimens Figure 3-7 Load-deflection curve of SW5 specimens Figure 3-8 Failure modes of SW4 specimens Figure 3-9 Failure modes of SW5 specimens 3.4 Conclusions of Chapter This chapter presents experimental results to determine some mechanical properties of materials including compressive strength, flexural strength, the elastic modulus of FGC, bond behavior between textile reinforcement and FGC; bond behavior between FGC and LCEC, compressive strength, tensile strength, and elastic modulus of LCEC The calculational models developed in Chapter were verified by experimental results The calculated results by the theoretical model are approximately the same as the experimental results The deviation of the flexural resistance model is less than 5.4% and the deviation of the shear resistance model is less than 9.2% 18 CHAPTER PARAMETRIC STUDY OF INFLUENCE PARAMETERS AND DESIGN OF SANDWICH PANELS IN THE APPLICATION OF FLOORS 4.1 Research purposes The parametric study of influence parameters plays an important role in developing the design of sandwich panels made of TRC and LCEC The study analyzes the requirements of material and dimensions and proposes the appropriate parameters to create a safe and effective sandwich panels 4.2 Parametric study of the influence parameters by analytical method 4.2.1 Parametric study of the thickness of material layers on the sandwich’s cross-section A parametric study of the thickness of material layers is carried out on the cross-section of the SW1 group with unchanged material parameters Table 4.1 Sandwich panels with different thicknesses of material layers The parametric results (Table 4.1) show that as the thickness of the face sheet increases, the load-bearing capacity of the sandwich panels is almost unchanged However, the stiffness of the structures increases significantly The resistance of the cross-section is determined by textile reinforcement In this case, the face sheet with a minimum thickness of 10 mm can meet the requirements for sandwich panels 4.2.2 Parametric study of LCEC core layer’s strength The parametric study of the LCEC core layer’s strength is carried out on the cross-section of the SW1 specimens with varied strength and unchanged cross-section The results in Table 4.2 and Table 4.3 show that sandwich panels made of a low-strength LCEC core layer have a poor sandwich effect As a result, the sandwich panels is damaged when it does not reach load bearing capacity of FGC and TRC In this case, the LCEC core layer should have a minimum compressive strength of 10 MPa 19 Table 4.2 Results of the parametric study in the plane cross-section Table 4.3 Results of the parametric study based on the bar diagram model 4.3 Parametric study of influence parameters by finite element method 4.3.1 Numerical simulation A parametric study of influence parameters is carried out on the simulation model by ATENA software (Figure 4-1) The models are simulated with the available parameters of the experimental specimens in Chapter Figure 4-1 Discrete model of sandwich panels in ATENA software Figure 4-2 Simulated results of SW1 specimens Figure 4-3 Simulated results of all tested specimens 20 Figure 4-4 Load patterns of SW1 specimens before failure The results show that the behavior of the sandwich panels in the simulation is similar to that of the experiment The deviation of loadbearing capacity is less than 10% The distribution of cracks on the simulation models and the experimental specimens is the same (Figure 4-4) 4.3.2 Parametric study of influence parameters by ATENA software A parametric study of material layers’ thickness and the strength of the core material is carried out by ATENA software with the same parameters in the theoretical model 4.3.2.1 Parametric study of material layers’ thickness The simulation results show that the sandwich models have the same behavior The failure occurs as textile reinforcement tears apart The loadbearing capacity of the sandwich panels does not change significantly as the thickness of face sheets varies Resistance values are approximately equal to analytical results with the maximum difference is 4.7% Figure 4-5 Simulation results of sandwich panels with different layer’s thickness 4.3.2.2 Parametric study of core layer material’s strength The results show similar behavior of sandwich panels in simulation and analytical models In case LCEC has a compressive strength below 10 MPa, sandwich panels fail before the failure of the face sheets 21 Figure 4-6 Simulation results of sandwich panels with different core layer’s strength 4.4 Design of sandwich panels made of TRC and LCEC in the application of floor panels The sandwich panels is intended to be used as floor panels in the context of this thesis It is built as a prefabricated panel with a width of m and a span length ranging from m to m As shown in Figure 4-7, the sandwich panels is made up of three layers of materials FGC has a compressive strength of 64.04 MPa and an elasticity modulus of 31.5 GPa LCEC has a compressive strength of 18.6 MPa and an elasticity modulus of 6.8 GPa SITgrid004 carbon textile reinforcement has a tensile strength of 2700 MPa, and 35.2 mm2/m cross-sectional area (calculated with 1-meter width of the member) Figure 4-7 Design of 1-meter sandwich panels The floor panel is designed with a simply supported beam diagram and tested with TCVN2737-2020 under static and live loads The parameters of the sandwich panels in the application of floor panels are shown in Table 4.4 22 Table 4.4 Design of prefabricated sandwich panels in the application of floor panels in construction projects 23 4.5 Conclusion of Chapter The thickness of the material layers and the strength of the LCEC core layer are investigated in this chapter to determine the load-bearing capacity of the sandwich panels The stiffness of the structures can be increased by increasing the thickness The load-bearing capacity of the structures, however, remains unchanged The load-bearing capacity of sandwich panels is significantly reduced when the LCEC core layer has low compressive strength LCEC with compressive strengths ranging from 10 MPa to 20 MPa is appropriate for sandwich panels with FGC strengths ranging 64.04 MPa Sandwich panels made of TRC and LCEC are simulated by ATENA software taking into account the material’s nonlinearity, the bond properties between the textile reinforcement and FGC, and the bond between FGC and LCEC The simulation results of the load-bearing behavior of the sandwich panels are consistent with the experimental results The sandwich panels is designed as a prefabricated panel in the application of m wide floor panels The spans of the panel are m, m, m, and m Table 4.4 shows the design parameters for floor panels 24 CONCLUDING REMARKS AND SUGGESTIONS Following the implementation of research contents in accordance with the stated objectives, the thesis achieved the following main results: (1) Proposing the design of a sandwich panels made of TRC and LCEC in the application of floor panels The sandwich panels includes two layers of FGC and LCEC as a core (2) Determining the flexural resistance of sandwich cross-sections made of TRC and LCEC using the multilayer division method (3) Developing a calculated model for the shear resistance of sandwich panels made of TRC and LCEC using the strut and tie method (4) Developing a model to predict the process of crack formation and development in sandwich panels made of TRC and LCEC when it is subjected to bending moment (5) Providing experimental data on the mechanical properties of FGC and LCEC manufactured in Vietnam; mechanical properties of TRC; and the flexural and shear behavior of sandwich panels made of TRC and LCEC SUGGESTIONS The results of theoretical research, parametric study, experimental analysis, and numerical simulation in the scope of this thesis are the basic steps for applying this sandwich panels in practice Future research on a sandwich panels made of TRC and LCEC can be listed as follows: - Investigation of sandwich panels subjected to repeated loads, impact loads, and large local loads - Investigation of the long-term behavior of TRC and LCEC - Investigation of the behavior of the sandwich panels when subjected to high temperatures Furthermore, it is necessary to continue developing technical instructions for the design and construction process of sandwich panels made of TRC and LCEC 25 ... 3-layer sandwich panel Sandwich panels are classified according to the simultaneous working of material layers There are several groups of sandwich panels as below: • "Unconjugated sandwich panels"... sandwich panels made of TRC and LCEC 2.2 Proposed design of sandwich panels made of TRC and LCEC in the application of floor panels The design of sandwich panels in the application of floor panels... models for sandwich panels The available models only present specific types of sandwich panels There are no design standards for sandwich panels made of TRC and LC Therefore, to develop a sandwich