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Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.Nghiên cứu cải tiến hình thức kết cấu hệ dàn cửa van phẳng kéo đứng nhịp lớn cho công trình kiểm soát nước vùng triều.MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT THUYLOI UNIVERSITY TRAN XUAN HAI RESEARCH ON IMPROVING THE TRUSS STRUCTURAL FORM OF LARGE SPAN VERTICAL LIFT GATES FOR.
MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT THUYLOI UNIVERSITY TRAN XUAN HAI RESEARCH ON IMPROVING THE TRUSS STRUCTURAL FORM OF LARGE-SPAN VERTICAL LIFT GATES FOR WATER LEVEL CONTROL WORKS IN TIDAL REGIONS Major: Hydraulic Engineering Code: 9580202 SUMMARY OF TECHNICAL DOCTORAL DISSERTATION HANOI, 2023 The work was completed at ThuyLoi University Scientific supervisor 1: Assoc Prof PhD Vu Hoang Hung Science supervisor 2: Prof PhD Ha Van Khoi Reviewer 1: Prof PhD Nguyen Van Le - Vietnam Association of structural Engineering and Construction Technology Reviewer 2: Prof PhD Truong Dinh Du - Vietnam Irrigation Association Reviewer 3: Assoc Prof PhD Vo Thanh Luong - Military Technical Academy The dissertation shall be defended ahead the Dissertation Examiners meeting at ThuyLoi University at 8:30 am on 06 July 2023 Dissertation can be found at: - National Library - Library of ThuyLoi University INTROUCTION Rationale of the study The large span vertical lift gate is one of the gate designs that may control water flow in tidal zones The structural form for this kind of gate is quite varied to meet the requirements of a large span while functioning as a typical vertical lift gate At the moment, the gate serves as both a large span steel structure and a hydraulic mechanical device As a result, it's crucial to balance mechanical and structural requirements, also known as strength and stiffness, while determining the design Large span vertical lift gates have been used extensively recently However, the truss's structural design continues to adhere to the conventional structural design employed in Germany's River Ems project It is necessary to put this type of structure through practice and demonstrate with scientific evidence that certain aspects of its design calculation, such as the selection of structural form, structure optimization, strength, stiffness, and service life in particular tidal conditions with local specificity, are different from those of other similar gates in the world Therefore, the study for the improvement of structural form of trus for large span vertical lift gate for water control works in tidal zones will contribute to the system of specialized scientific reasoning as well as provide designers with the necessary tools to be able to calculate for works with similar conditions Study objective Studying the stress-strain state of the large span vertical lift gate's structure when working in two directions Studying the effect of changing the form of the main frame's oblique bar structure on the durability and stiffness of the large span vertical lift gate when the valve gate is working in the closed state Studying the behavior of the large span vertical lift gate's structure when subjected to seismic loads taking into account the mutual effect of the water mass before and after the valve gate is in the closed state Study on fatigue life of the large span vertical lift gate valve when subjected to water level fluctuations before and after the valve gate Object and scope of study The bearing structure in the form of a space steel pipe arch of the large span vertical lift gate's structure in the tidal zone water control project has been, is and will be built in Vietnam Study approach and methods The dissertation uses a combination of advanced study methods with high reliability, specifically: - Method of relevant document collection and synthsis - Field survey method - Theoretical study method - Mathematical modeling method Scientific and practical significance 5.1 Scientific significance Clarification of the influence of the system form on the stiffness of large span vertical lift gate system when working in two directions The change in the form of the bearing structure of the large span vertical lift gate meets the requirements of stiffness when working in two directions Structure of Dissertation The dissertation, in addition to the Introduction and Conclusion, 86 references, 04 published author documents and 04 Appendixes, the main content of the dissertation is presented in 04 Chapters including 141 pages, 118 drawings and 39 tables CHAPTER OVERVIEW OF LARGE SPAN GATE AND AND PROBLEMS TO BE STUDIED WITH THE DISSERTATION 1.1 Large span gate 1.1.1 The concept of large span gate Large span gates are frequently employed as gates in intercepting dams or tidal intercepting dams with large cross sections They have a width of water barrier B that is significantly more than their height H As a result, the dissertation specifies the standards under which a gate will be deemed a large span gate if its width is greater than 30 meters 1.1.3 Large span vertical lift gate The large span vertical lift gate used in Vietnam today is mainly in the form of the German Ems river gate with the structure as shown in Figure 1.4 Figure 1.4 Structure of large span vertical lift gate The basic structure of the vertical lift gate includes: (1) face plate; (2) Longitudinal sub-beams; (3) T-section vertical beams; (4) The main bearing on the opposite side; (5) Weight bearing; (6) The adjacent pier is a compound Isection (7) Cylinders placed vertically at both ends The main load acting on the large span vertical lift gate is the static water pressure from both sides (Figure 1.5) and the gate‘s own weight, in addition, there are wave pressure, hydrodynamic pressure, wind pressure, and wave pressure, hydrodynamic pressure, wind pressure, opening and closing force, earthquake etc These loads should be considered on a case-by-case basis Headrace Elevation (HE) Headrace Elevation (HE) Tailrace Elevation (TE) Tailrace Elevation (TE) Figure 1.5 Diagram of static water pressure on lift gate The steel pipe truss, capable of functioning in both directions, subject to the difference in water pressure from both sides, opening and closing even when there is a difference in water level, gives the large span vertical lift gate a considerable bearing capacity 1.2 Studies related to the calculation of gate structure The dissertation limits the study to only the working scope of steel structures Therefore, the general problems are only related to the calculation of valve steel structure 1.2.1 Optimization of the gate structure Studies on typical optimization methods such as Nguyen Trong Ha (2014), Hoang Anh Pham (2016), Pham Van Hung, Doan Van Duan (2017), TV Hung, SE Kim (2018), Le Hoai Nam (2020), Adil Baykasoğlu, Cengiz Baykasoğlu (2021), MahdiAzizi , Uwe Aickelin (2022) The study of lift gate optimization has Wang and Zhang (2002), Lluis Gil, Antoni Andreu ( 2001) For the specific study of two-plane single-span spatial staging , there is Alemseged Gebrehiwot Weldeyesus (2020) Slection of a simple and effective calculation method for optimizing truss weight based on constrained conditions of truss bar stress, conditions on the overall displacement and application in common software is the problem that needs to be raised for the dissertation 1.2.2 Structural oscillation of gate Studies on the oscillation characteristics of the gate due to the flow action at the bottom of the typical gate include Kolkman (1980), Georg Göbel (2019), Seong Haeng Lee (2014) Study on simulating the interaction of water block dynamics - gate structure based on common mathematical analysis software including Xue Huifang et al (2012), YAN Genhua et al (2020), Jijian Lian (2020) There are not many studies on the interaction between the vertical lift gate and the water block ahead and behind the gate, the most recent being the study of Khuc Hong Van (2018) Most of the studies are performed on the ANSYS popular finite element analysis software, which shows the superiority of the software in simulating the dynamics of water block - structure interactions The dissertation poses the problem that it is necessary to calculate the oscillations of the large span vertical lift gate under the impact of earthquake acceleration over time, considering the interaction of water blocks ahead and behind the gate for a case study 1.2.3 Fatigue failure of gate steel structure Some studies on fatigue failure of gate steel structures such as Shi Zhezhu (2008), Feng Hui Dong (2017), Matttheus Lucassen (2019), Jian Zhang (2013), Aswathi Dev.KK (2015), Akhil V Raj (2016) The joint fatigue calculation can be performed on ANSYS software with the change of joint shape and size quite easily All studies suggest to use the beam element model to consider the overall truss structure, then use the submodel built by the cover element with boundary conditions taken from the overall model for detailed consideration at truss joints This method ensures accuracy at the required locations but saves computing resources and computation time This is the basis to be applied to the selection of the structure of the truss connection and the calculation of the fatigue of the large span vertical lift gate proposed as a study object in the dissertation 1.3 Problems and study directions The large span vertical lift gate is being used quite a lot in water control works in the tidal zone and structural shape still follows the tradition of two main trusses with a curved arch and usually has a fairly large strength reserve, making the gate weight large compared to the load-bearing requirements Therefore, the study of optimizing the structural form and cross-sectional dimensions of the truss bar is proposed for the dissertation The truss bar after optimization have large thinness, are very sensitive to dynamic loads even with small accelerations; therefore, the dissertation poses the problem of considering the influence of the earthquake acceleration on the gate vibration when there is the interaction of the water block ahead and behind the gate for a typical work in the study area In addition, the problem of fatigue failure of gate steel structure currently has not been much studied both at home and abroad This is also a problem posed for the dissertation when calculating for a typical work in the study area 1.4 Conclusion Chapter Even with the progressively large scale of the gate as it is today, the problem of whether the structural form of the bearing truss of this gate is indeed optimal or not remains unsolved or has not been properly studied The study related to the large span vertical lift gate mainly focuses on optimizing the gate structure shape, gate vibration under dynamic load, water block interaction and gate structure, gate structural fatigue when subjected to cyclic loads These are all new problems for vertical lift gates in the specific conditions of Vietnam CHAPTER THEORETICAL BASIS AND CALCULATION TOOLS 2.2 Structure optimization 2.2.1 Structure optimization overview In the actual design, in addition to the test problem, we also face the problem of determining the structural shape and the necessary size of the cross section of the structural elements that are reasonable for a known load system in order to satisfy the requirements for strength, stiffness, stability, and the least amount of material use This problem is known as weight-optimization of the structure The quantities to be minimized, such as the structure's weight, volume, cost, etc., are often represented by the objective function Equilibrium conditions and conditions for continuous deformation are often constraints in the form of equalities Conditions of strength, stiffness, yield, etc., are frequently constraint conditions that take the form of inequalities Depending on the structure and method of solution, the objective function and constraint condition might take on different forms Therefore, when using different calculation techniques like the force method, displacement method, or finite element method, the optimization issue and the solution method have distinctive characteristics 2.2.2 Basic formula of structure optimization problem An objective function that has to be optimized and is frequently constrained by equality and/or inequality requirements makes up the fundamental formulation of a structural optimization problem Under the conditions of optimally chosen design variables, the objective and constraint functions are either hidden or visible The general formula is presented as follows f(x) (2-1) g i(x) 0, ∀ i = 1, … , m; with the condition h j(x) = 0, ∀ j = 1, … , p; where x Rn are the design variables; f(x) is the objective function; g(x) Rm are inequality constraints; h(x) Rp are equality constraints 2.2.3 Problem of optimal calculation of steel truss of large span vertical lift gate A module that optimizes the size and form of the bar structure is now available in the ANSYS popular finite element analysis software 2.3 Structural dynamics 2.3.1 Overview of structural dynamics Structural dynamics is the study of the calculation of structures that are subjected to dynamic loads in order to identify the internal forces resulting from dynamic loads, dynamic displacements, dynamic speeds, dynamic accelerations, and natural vibrational frequencies in order to avoid resonance and identify vibrationreducing techniques The structural system's equation of motion is: [𝑀]𝑢̈ (𝑡) + [𝐶]𝑢̇ (𝑡) + [𝐾]𝑢(𝑡) = 𝑝(𝑡) (2-7) where : [M], [C], [K] are mass matrix, resistance matrix and stiffness matrix, respectively; 𝑢̈ (𝑡), 𝑢̇ (𝑡), 𝑢(𝑡)are the acceleration vector, speed vector and displacement vector , respectively; p is the external force vector Currently, there are two methods of solving equations of motion: the step-by-step direct integration method and the oscillating superposition method 2.3.2 Integral method directly solves structural dynamics problems The method's fundamental idea is discrete time domain The structural system's dynamic response produced the provided state vector.The direct integration method is often divided into the explicit method or the implicit method The fundamentalimplicit method has the Newmark and Wilson method 2.3.3 Problem of calculating the dynamics of the large span vertical lift gate structure A three-dimensional spatial finite element model that has been solved on a computer is the only way to determine acceleration, speed, and displacement at every spot on the gate over time since large span vertical lift gates are complicated spatial structures with an unlimited number of degrees of freedom The ANSYS popular finite element analysis software can simulate the threedimensional structure, which is made up of a variety of different types of elements, pretty effectively Solving differential equations of motion at time steps in the software is done by the extended Newmark method Figure 2.15 Block diagram of the optimal calculation process in ANSYS software 2.6.4 Calculation technique of structural dynamics Dynamic problems may all be thoroughly and dependably resolved, including structural vibration characteristics, time-varying load effects, cyclic excitation loads, etc by ANSYS software 2.6.5 Calculation technique of water block-structure interaction Fluid Structure Interaction (FSI) with various boundary conditions may be effectively simulated using ANSYS software Assign FSI to the interface between the two environments in accordance with the overall water block and structural model The water block will interact with the structure in vibrational patterns as it vibrates 2.6.6 Calculation techniques for fatigue failure of steel structures There is a separate module in the ANSYS program to compute the fatigue failure of the structure under repeated loads over an extended period of time such as Strain Life and Stress Life 11 2.7 Conclusion Chapter The dissertation is based on the results of calculating the internal force and stress in the truss bar from the spatial finite element model of the gate structure to carry out the iterative solution calculation to determine the optimal shape and size according to the stress constraint with the minimum gate weight objective function It is crucial to take into account how the water block interaction in front of and behind the gate affects its oscillation characteristics when subjected to dynamic stresses By estimating the fatigue age of the joint based on the size of the stress concentration at the crack initiation location (intersection of truss members) and the material's S-N curve, the overall strength of the gate's structure is assessed CHAPTER STUDY ON CHANGING FORM AND OPTIMAL CALCULATION OF TRUSS STRUCTURE FOR LARGE SPAN VERTICAL LIFT GATE SYSTEM 3.2 Study on improvement of the structural form of the large span vertical lift gate system 3.2.1 Proposal to improve the structural form of the system The dissertation proposes to change the lattice layout of the main system by using an inverted curved bar to support the deck to replace the rectangular bars in the system plane as shown in Figure 3.4 to reduce the stiffness difference of the system in both directions Figure 3.4 Main system form of the vertical lift gate proposed to improve 12 The basis for making this form is as follows: When there is a sea level difference greater than the river side (Figure 3.5a), the lower chord (1) is tensile, the upper chord (2) is compressible and vice versa when the river level difference is larger than the sea side (Figure 3.5b), the lower chord (1) is compressible, the upper chord (2) is tensile, which will promote the effect of the arch when the bars are mainly subjected to longitudinal forces In addition, when changing the form of truss, the thinness of the compression bar decreases due to the reduction in the calculated length of the compression bar, the number of truss joints increases, but the structure is simpler due to the reduction in the number of connecting bars at the joint Sea Compressible River Tensile River Tensile Sea Compressible Figure 3.5 Bearing principle of the two-dimensional work platform 3.2.2 Building a program to calculate gate structure Proceed to build a gate calculation program according to the traditional model and the proposed model named LIFTGATE.MAC and LIFTGATE_OP.MAC respectively The program is run on ANSYS Mechanical V16 software Due to the study limitation of the dissertation only in the scope of steel structure, the gate model is built in the condition that the gate is working normally to prevent water or the gate is closed, the cylinder is not working Boundary conditions of the model, in addition to the horizontal support single links at the sliding surface, there are vertical supports connecting the bottom of the gate with the threshold at the two gate ends To ensure sufficient linkage for the three13 dimensional model, place additional longitudinal links of the gate on the symmetrical plane at the middle of the gate length (in fact the side wheels) 3.2.3 Calculation results of gate structure In order to have a basis to compare the calculation results of the two traditional and proposed models, input data is taken to be similar (1) Calculation results according to the traditional model: The total weight of the gate is 197,155 tons (2) Calculation results according to the proposed model: The total weight of the gate is 187,873 tons 3.2.4 Summary of calculation results and comments The displacement in the flow direction of the two models is approximately the same or the gate stiffness is almost unchanged, but the weight is reduced by nearly 10 tons, equal to 4.73% of the total weight of the gate and 13.59% of the total weight of the truss With the proposed model, the compressive force in the lower chord when the gate keeping freshwater is reduced by 10.77%, that proves the efficiency of the inverted curved bar in tension supports the lower chord under compression With this result, it shows the feasibility of the proposed model when the gate works in two ways Table 3.7 Comparison of calculation results by two models Model Traditional model Proposed model Difference Traditional model Proposed model Difference Combination 1 2 Displacement in Z direction (mm) 16.10 16.34 +1,49% -11.39 -11.46 +0.61% Longitudinal force of lower chord (kN) 1957 1938 -0.97% -1291 -1152 -10.77% 3.3 Study and selection of appropriate size of the truss The influence of the truss structure dimension parameters such as: Main truss height: B1 (sizes B2, B3, B4 according to size B1) 14 G (ton) 197.16 187.87 4.73% 197.16 187.83 4.73% Distance between two main truss: H1 (sizes H2, H3, H4 according to size H1) The position of the upper chord relative to the lower chord: X1 (X2, X3 according to X1) The size of the truss is considered reasonable when the self-weight is the smallest but still ensures the condition of strength and rigidity Figure 3.17 Dimensions of truss 3.3.1 Effect of main truss height on internal force and truss displacement When the height of the main truss increases, the displacement of the gate in the direction of flow decreases is consistent with the rule, the displacement decreases quickly when the height of the truss is small and slows down when the height of the truss is large (about 5.5 m onwards) The longitudinal force in the lower chord is similar For the upper chord of the lower truss, in both combinations, the force is pulled and decreases as the height of the truss increases According to the condition of stiffness, the relative displacement of the gate in the flow direction (Z direction) must not exceed the allowed relative displacement According to the condition of durability, with all main truss heights, the condition of durability is satisfied 3.3.2 Effect of the distance between two lower chords of the main truss on the internal force and displacement of the truss When the distance between the two lower chords of the main truss increases, the displacement of the gate in the flow direction increases but is not linear The longitudinal force in the lower chord is reduced but not significantly For the upper chord of the lower truss, in both combinations, it is tensible and reduced gradually as the distance between two lower chords of the main truss increases For the upper 15 chord of the upper truss, in both combinations, it is compressible and reduced gradually as the distance between two lower chords of the main truss increases 3.3.3 Effect of curvature of the upper chord of the main truss on internal force and truss displacement When the curvature of the upper chord decreases, the displacement of the gate in the flow direction increases; the tensible axial force in the lower chord decreases with water level combination 1, the compressive axial force in the lower chord increases with combination This shows that the large curvature of the upper chord is beneficial for displacement and longitudinal force in the lower chord For the upper chord, in both combinations, when the curvature decreases, the internal force increases 3.3.4 Selection of angle of inclination of the two main trusses From the graphs of the relationship between the vertical displacement and the distance between the two ends of the truss, the smallest displacement corresponding to the case H1 = 3.5m; For the vertical force in the upper chord, the minimum distance between the two ends of the H1 = 2.8 m; For the axial force in the lower chord landing bar, the distance is smallest when the distance between the two ends of the H1 = 3.3 m Combining the above conditions, it is recommended that the reasonable range of the distance between the two ends of the truss lies between 2.0 m and 4.0 m, corresponding to the tilt angle of the truss plane from 12.5o to 2.5o from the horizontal 3.4 Study on selection of cross-sectional dimensions of truss bar 3.4.1 Optimal calculation plan Carry out calculations with options of bar groups: Option includes groups of bars: lower chord (DK01), vertical connecting bar (DK02), vertical bar + upper chord + horizontal truss bar (DK03), cross bar (DK04) Option includes groups of bars: lower chord (DK01), vertical connecting bar (DK02), vertical bar + upper chord (DK03), cross bar (DK04), horizontal truss bar (DK05) 16 Option includes groups of rods: lower chord (DK01), vertical connecting rod (DK02), vertical bar (DK03), cross bar (DK04), horizontal truss bar (DK05), upper chord (DK06) Vertical bar (DK03) Upper chord (DK06) Horizontal truss bar (DK05) Lower chord (DK01) Vertical connecting bar (DK02) Cross bar (DK04) Figure 3.38 Groups of truss bars 3.4.2 Results of optimal calculation of the cross-sectional dimensions for the options In order for the gate to meet in both working cases and in accordance with the pipe steel fabrication specifications, based on the optimal calculation results corresponding to the options of the bar group, the dissertation proposes the crosssectional size of the truss bars given in Table 3.18 Table 3.18 Dimensions of the proposed truss bar section according to options Parameters Initial DKO1 (m) DKO2 (m) DKO3 (m) DKO4 (m) DKO5 (m) DKO6 (m) TO1 (m) TO2 (m) TO3 (m) TO4 (m) TO5 (m) TO6 (m) WT (tons) % Optimal 0.762 0.457 0.457 0.457 Option Basic Basic 0.588 0.500 0.345 0.312 0.322 0.397 0.278 0.398 Option Basic Basic 0.501 0.500 0.315 0.300 0.301 0.300 0.202 0.200 0.396 0.383 0.020 0.014 0.014 0.014 0.018 0.012 0.013 0.013 0.019 0.012 0.013 0.014 0.014 0.012 0.012 0.011 0.014 0.014 0.012 0.012 0.010 0.013 68.368 45.522 33.4 47.371 30.7 32.067 53.1 31.458 53.9 Option Basic Basic 0.500 0.500 0.300 0.300 0.300 0.313 0.219 0.200 0.338 0.400 0.480 0.395 0.0140 0.0140 0.0124 0.0120 0.0123 0.0120 0.0120 0.0114 0.0139 0.0140 0.0139 0.0139 26.961 26.632 60.6 61.0 Proposal 0.500 0.300 0.400 0.250 0.400 0.500 0.016 0.014 0.014 0.012 0.014 0.016 39.038 42.9 The large span vertical lift gate system according to the proposed model is classified into groups: Lower chord (DKO1) + Upper chord (DKO6): D500 17 16; Vertical connecting bar (DKO2): D300 16; Vertical lattice (DKO3) + Horizontal bar (DKO5): D400 14 ; Top cross bar (DKO4): D250 12 3.5 Conclusion Chapter In order to maximize the efficiency of the truss in both working directions, the dissertation proposes to improve the form of the large span vertical lift gate system using a combination of reverse curved bars to support the deck to increase the rigidity of the truss in both directions of bearing With the proposed model, the gate stiffness is almost unchanged, however, the weight is reduced by nearly 10 tons, equal to 4.73% of the total weight of the gate and 13.59% of the total weight of the truss The longitudinal force in the lower chord when the gate is tidal in the two cases is approximately the same, however, with the proposed model, the compressive force in the lower chord when the gate keeps freshwater is reduced by 10.77%, that proves the efficiency of the reverse curved bars in tension supporting the lower chord under compression The ability of the lower chord to destabilize under compression is reduced After optimal calculation, the weight of the truss structure is reduced by 42.9% compared to the traditional one Although the strength and stiffness reserve factor of the gate is still quite large, but due to the structural requirements and to ensure that the center of gravity is not too close to the deck, it cannot be reduced to less than the cross-sectional size CHAPTER RESEARCH AND APPLICATION OF THE LARGE SPAN VERTICAL LIFT GATE FOR NGUYEN TON THANH SLUICE WORKS 4.1 Project introduction The work consists of an M300 reinforced concrete open-air sluice with a drainage width of B = 40 m, a threshold sluice gate of -5.50 m, the top elevation of the pin pole +3.00 m S355JR flat steel sluice gate operated by vertical hydraulic cylinder, gate height +2.50 m The dissertation recommends using vertical lift gate proposed in Chapter for Nguyen Tan Thanh culvert with the size of 40 8 m 18