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TÓM TẮT ĐÓNG GÓP MỚI CỦA LUẬN ÁN 1. Nghiên cứu đã khẳng định được sự cần thiết áp dụng kết cấu dầm đúc sẵn sử dụng bê tông cường độ cao trong xây dựng công trình cầu ở vùng Đông Nam Bộ. 2. Thiết kế được các cấp phối bê tông C60, C70, C80 có độ sụt cao sử dụng vật liệu địa phương khu vực Đông Nam Bộ, với cốt liệu thô sử dụng đá dăm Phú Mỹ - Bà Rịa và cốt liệu mịn phối trộn giữa cát sông và cát nghiền với tỉ lệ 60/40, phù hợp cho sản xuất dầm bê tông dự ứng lực đúc sẵn với quy mô công nghiệp. 3. Đối với các cấp phối C60, C70, C80 sử dụng vật liệu vùng Đông Nam Bộ, nghiên cứu đã đưa ra cách xác định một số chỉ tiêu cơ lý để phục vụ cho công tác thiết kế kết cấu dầm cầu bê tông dự ứng lực đúc sẵn khi sử dụng các cấp phối đó như mô đun đàn hồi, cường độ chịu kéo khi uốn, hệ số quy đổi khối ứng suất tương đương. 4. Đã đề xuất các thông số kích thước mặt cắt phù hợp đối với kết cấu dầm I cánh rộng sử dụng bê tông cường độ cao với các chiều dài nhịp 24m, 33m, 60m. 5. Khẳng định được tính hiệu quả của việc dùng dầm I cánh rộng với bê tông cường độ cao so với các loại hình dầm truyền thống sử dụng bê tông thông thường hiện nay trong khu vực Đông Nam Bộ: Giảm chiều cao dầm từ 150mm đến 450mm; giảm khối lượng vật liệu từ 10% đến 50%.
MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS VÕ VĨNH BẢO RESEARCH FOR APPLICATION OF PRECAST PRESTRESSED CONCRETE GIRDER WITH HIGH STRENGTH CONCRETE FOR TRAFFIC DEVELOPMENT IN THE SOUTHEAST REGION Majors: Transport Construction Engineering Code: 9580205 SUMMARY OF DOCTORAL THESIS HA NOI - 2022 The thesis was completed at: University of Transport and Communications Academic supervisors: Prof Dr Tran Duc Nhiem Assoc Prof Dr Nguyen Ngoc Long Reviewer 1: ……………………………………………… Reviewer ……………………………………………… Reviewer 3: ……………………………………………… The thesis will be defended in front of Doctoral-Level Evaluation Council at University of Transport and Communications At …… , ……, …… 2022 The thesis can be found at: University of Transport and Communications Library National Library INTRODUCTION The urgency of research In the South of Vietnam, the key economic area whose nucleus is the Southeast region has potential and resources for strong development, many new urban areas are quickly formed, and urbanization of the Southeast region is among the highest in the country, from which the demand for building technical infrastructure systems is also required To meet the needs of building an urban transport system in the Southeast region, it is necessary to have many beam structure solutions for urban bridge construction projects The type of prestressed concrete beam structure with high strength concrete has been applied by many countries in the world to traffic construction, the advantage of high strength concrete is that it can increase the bearing capacity of the structure thereby helping to design structures with smaller size, lighter weight, longer span and increased durability due to better concrete quality However, currently, in the Southeast region, bridge construction projects only use concrete with a strength of 50MPa or less This is an open issue and needs to be addressed With the available potential of the Southeast region in terms of materials to produce high-strength concrete, the study and application of high-strength concrete in the construction of traffic bridges in the Southeast region is a right direction Purpose of research - Research on manufacturing high-strength concrete using materials in the Southeast region and experimentally evaluate some important mechanical properties of the material such as elastic modulus, tensile strength in bending, development strength over time, to serve the design and manufacture of prestressed concrete beam structures - Analyze and select the type of precast concrete beam structure that is applicable to high strength concrete in the design and manufacture of precast concrete beams using materials in the Southeast region - Application to calculate and design typical girder structure for the type of beam selected in step using concrete mixed with concrete in step for application in traffic projects in the Southeast region The object and scope of the study of the thesis Materials: research of using local materials in the Southeast region to manufacture high-strength concrete mixes with suitable characteristics for the construction of pre-stressed concrete beams Structural: Research and application of wide-flange girder made of prestressed concrete with simple span for traffic development in the Southeast region About the load: The research load limit is a static load problem Research Methods The main research method is theoretical research combined with experimental research CHAPTER OVERVIEW 1.1 Traffic development demand in the Southeast region The SouthEast is a region with a high degree of urbanization and rapid development Population density is high in industrial zones and surrounding areas The provinces in this region have a very high urbanization rate, due to the income gap with other regions leading to massive migration from neighboring provinces to urban areas The general situation of these cities is: the demand for housing is large, the demand for personal transport and the large movement of goods exceeds the capacity of the existing infrastructure system In the existing urban areas, the land fund for traffic is still quite limited, the compensation and site clearance costs are very large, so the elevated roads and underground routes will be more focused on development 1.2 Types of precast - prestressed concrete beam structures are being applied and developed in bridge construction In Vietnam, with small and medium span bridges (length from 60m or less), simple girder span structure is the most applied span structure Table 1-1: Statistics of commonly used precast - prestressed beams in Vietnam No A B C D E Bridge girder type Fabricating method SLAB GIRDER Slab girder 9m Pre-tensioning Slab girder 12m Pre-tensioning Slab girder 15m Pre-tensioning Slab girder 18m Pre-tensioning Slab girder 21m Pre-tensioning Slab girder 24m Pre-tensioning T-SECTION BEAM T-beam 24m Post-tensioning T-beam 33m Post-tensioning I-SECTION BEAM I-beam 18,6m Pre-tensioning and Post-tensioning I-beam 24,54m Pre-tensioning and Post-tensioning I-beam 33m Pre-tensioning and Post-tensioning I-beam 42m Pre-tensioning SUPER-T SECTION BEAM Super-T beam 38,2m Pre-tensioning SOME NEW TYPES OF BEAM BEEN INTO VIETNAM Reverse T Beam 25m Pre-tensioning Currently in the world, types of prestressed concrete beams are being widely applied, including Bulb-Tee girder, Wide Flange Girder, U-Beam girder, Bath-Tub beam, Pi girder 1.3 Application situation and development trend of high strength concrete (HSC), high performance concrete (HPC) in bridge construction and repair High-strength concrete and high-performance concrete have been researched and widely applied in many countries around the world, led by the US, Germany, France, and Japan Many other countries are also very interested in developing high-strength concrete structures such as China, Korea, Australia, Norway, UK, Canada In the current bridge span structure design in Vietnam, concrete is commonly used with the usual strength range [4050]MPa for prestressed girder structures, for commonly used cast-in-place deck slabs concrete with strength [3035]MPa In the area of Ho Chi Minh City and neighboring provinces in the Southeast region, now many concrete factories have put into production high strength concrete up to 80MPa but still mainly used to manufacture precast - prestressed pile CHAPTER RESEARCH FOR PRODUCTION OF HIGH STRENGTH CONCRETE 60MPA TO 80MPA USING LOCAL MATERIALS IN THE SOUTHEAST AREA, APPLICATIONS FOR PRECASTED-PRESTRESSED GIRDER 2.1 Overview of high-strength concrete High-strength concrete is made based on the following adjustments: Reducing the ratio of water to cement (N/X): using a new generation of high water reducing additives, the N/X ratio can be greatly reduced while still ensuring the required slump Adding some products with high fineness: there are types of commonly used products: fly ash, silica fume and activated metakaolin 2.2 Research and design concrete mix composition of 60MPa to 80MPa strength using local materials in the SouthEast region The Southeast region has an abundant supply of good quality crushed stone The rock origin is mainly basalt, with strength ranges from 100Mpa to 200Mpa High intensity rock sources are concentrated in the areas of Tan Cang, Dinh Quan, Dong Nai province, Chau Pha in Ba Ria-Vung Tau, Di An in Binh Duong The main source of sand supplied in the Southeast region is from the Tien River, Tan Chau yellow sand (An Giang) is a popular material due to its abundant supply and low cost However, the modulus of magnitude is only about 1.75 (according to TCVN 7572-2:2006), if only river sand is used, it will not satisfy the requirements for grading Currently, in the Southeast region, crushed sand produced in Phu My, Ba Ria - Vung Tau province is a reasonable alternative and supplement for fine aggregates to manufacture high strength concrete The topic proposes to use fine aggregate with a mixing ratio of 60% river sand with 40% crushed sand for application in the next research sections Design of concrete mix C60 using materials in the Southeast region + Design requirements: - The 28-day compressive strength of the cylinder specimen: 60Mpa or more - Required slump: 160mm + Design steps: according to ACI211.4R-08 The design results are presented in Table 2-13 Kí hiệu BT C60 Table 2-13: C60 mix selected after testing FA SF Đ C N X N/CKD (kg) (kg) (kg) (lit) (kg) (kg) 0.3145 1120 720 150 477 PGSD (lít) Design of concrete mix C70 using materials in the Southeast region + Design requirements: - The 28-day compressive strength of the cylinder specimen: 70Mpa or more - Required slump: 160mm + Design steps: according to ACI211.4R-08 The design results are presented in Table 2-15 Kí hiệu BT C70 Table 2-15: C70 mix selected after testing FA SF Đ C N X N/CKD (kg) (kg) (kg) (lit) (kg) (kg) 0.264 1120 700 140 530 PGSD (lít) 4.77 Design of concrete mix C80 using materials in the Southeast region + Design requirements: - The 28-day compressive strength of the cylinder specimen: 80Mpa or more - Required slump: 160mm + Design steps: according to ACI211.4R-08 The design results are presented in Table 2-17 Table 2-17: C80 mix selected after testing Kí hiệu BT N/CKD Đ (kg) C (kg) N (lit) X (kg) C80 0.26 1120 780 140.4 540 FA SF (kg) (kg) 0 PGSD (lít) 5.2 Evaluation of compressive strength of test mix C60, C70, C80 using local materials in the Southeast region The characteristic compressive strength of the selected mix C60, C70, C80 is determined according to the results of compression test of a cylinder specimen of 15x30(cm) with the number of 12 specimen s for each mix The experimental results are shown in Table 2-19 Table 2-19: Results of determination of compressive strength for Concrete mix f’c (MPa) mix C60, C70, C80 C60 C70 67.2 74.3 C80 84.5 2.3 Research to determine some mechanical characteristics of concrete mix C60, C70, C80 using local materials in the Southeast region Modulus of rupture Modulus of rupture is determined by laboratory testing of beam samples of size 15x15x60 (cm), standard used for testing is ASTM C78-02, number of test samples used to determine tensile strength when bending is 12 samples for each mix Compare the value obtained from the experiment with the estimated value according to TCVN 11823 for grades C60, C70, C80 as follows: Mix Strength (MPa) C60 C70 C80 67,2 74,3 84,5 fr (TCVN 11823) (MPa) 5,16 5,43 5,79 fr from test (MPa) Difference (%) 8,867 7,284 7,640 171,84 134,14 131,95 The experimental values obtained are more than 30% higher than the estimate according to the formula of TCVN 11823:2017, so to estimate the elastic modulus value of concrete mix C60, C70, C80 accurately more precisely, the proposed bending strength estimation formula can be used as follows: f r 0,83 f 'c (Mpa) (2.29) Elastic modulus The modulus of elasticity is determined by testing a 15cm30cm cylinder with the number of test samples for each mix of C60, C70 and C80 being 12 samples/mix Standard use: according to ASTM 469/469M-10 The elastic modulus test results are shown in Table 223 Table 2-23: Test results of elastic modulus of cylinders C60 mix Sample C70 mix C80 mix Ec (Mpa) Sample Ec (Mpa) Sample Ec (Mpa) C60-M25 52580.0 C70-M25 54109.5 C80-M25 62751.0 C60-M26 53832.8 C70-M26 51866.0 C80-M26 56443.0 C60-M27 55815.9 C70-M27 51131.5 C80-M27 57818.9 C60-M28 54085.1 C70-M28 57881.9 C80-M28 58187.2 C60-M29 55441.7 C70-M29 60778.6 C80-M29 58541.7 C60-M30 56695.0 C70-M30 59997.1 C80-M30 52114.2 C60-M31 56754.3 C70-M31 58279.4 C80-M31 58169.2 C60-M32 67927.6 C70-M32 57878.2 C80-M32 61192.9 C60-M33 56754.3 C70-M33 54899.6 C80-M33 62727.4 C60-M34 55386.7 C70-M34 60454.9 C80-M34 59985.9 C60-M35 48569.5 C70-M35 59971.3 C80-M35 56113.3 C60-M36 52129.2 C70-M36 59913.0 C80-M36 58503.2 The process of testing 18 concrete samples with mixes of C60; C70; C80 obtained the results of 15 samples (1 sample with an error of the experimenter not storing the strain signal, samples with an error of the strain data series) With the results obtained, the topic evaluates and selects the type of equation used to represent the stress-strain relationship for high-strength concrete using materials in the Southeast region as follows: o ; is the parameter to be determined f c f 'c 1 o Parameter value is determined for each sample by the method of least squares, the results of parameter determination according to table 2-37 Table 2-37: Result of parameter based on experimental data Tên mẫu C60-M3 C60-M4 C60-M5 C60-M6 C70-M2 19.5 14.3 24.9 14.1 86.3 Tên mẫu C70-M3 16.9 C70-M4 53.4 C70-M5 16.9 C70-M6 72.1 C80-M1 9.0 Giá trị trung bình t/b = 28.08 Tên mẫu C80-M2 C80-M3 C80-M4 C80-M5 C80-M6 22.7 10.6 35.4 10.2 14.9 Based on the calculation results, the topic proposes to use the parameter value =28.1 To build a complete stress-strain relationship graph, it is necessary to determine the value of cu as well as the relative ratio of cu to o, so we consider the correlation between o and max according to the following table: Table 2-38: Summary of relative strain values o and max max o 100 No Sample o max o C60-M3 C60-M4 C60-M5 C60-M6 C70-M2 C70-M3 C70-M4 C70-M5 C70-M6 10 C80-M1 11 C80-M2 12 C80-M3 13 C80-M4 14 C80-M5 15 C80-M6 Average: -0.002436 -0.002134 -0.002400 -0.002329 -0.002252 -0.002121 -0.002358 -0.002164 -0.002206 -0.002338 -0.002123 -0.002267 -0.002616 -0.002588 -0.002100 -0.002295 -0.002496 -0.002364 -0.002404 -0.002478 -0.002313 -0.002384 -0.002396 -0.002387 -0.002280 -0.002421 -0.002232 -0.002480 -0.002619 -0.002716 -0.002269 -0.002416 2.5 10.8 0.2 6.4 2.7 12.4 1.6 10.3 3.4 3.6 5.1 9.4 0.1 4.9 8.0 5.4 Thesis suggest to use value max = 0.0023 for concrete mix C60, C70, C80 using materials in the SouthEast region, and the score cu o selected as 5% From that, the stress-strain relationship chart o when compressing of concrete mix C60, C70, C80 using materials in the SouthEast region is presented as shown in Figure 2-19 The format of the chart in Figure 2-19 can be used to determine the coefficients α1 and 1 of the equivalent compressive stress block for reinforced concrete beams with rectangular cross section by determining the parameters k1, k2 and k3 , the parameters are determined as follows: - k1 = 0.541; - k2 = 0.3365; kk 1 0.804 Hence: 2k 1 = 2k2 = 0.673 - k3 = f’c o=0.95max max=0.0023 Figure 2-19: The stress-strain relationship in compression of highstrength concrete with materials in the SouthEast region CHAPTER RESEARCH AND SELECTION OF PRECASTPRESTRESSED GIRDER WITH STRENGTH 60MPA TO 80MPA APPLICATION FOR TRAFFIC CONSTRUCTIONS IN THE SOUTHEAST AREA 3.1 Introduce This chapter also presents the calculation content of typical girder structure using concrete mix C60, C70, C80 with span lengths of 60m, 33m and 24m, using high strength concrete mix C60 , C70, C80 were presented in chapter 3.2 Selection of materials for precast-prestressed concrete girders and cast-in-place deck slabs The following types of materials are included in the audit calculation: Materials used for prestressed beams: + Prestressed strand: - Low relaxation strand Grade 270 - Nominal diameter 15,2mm + Regular steel reinforcement: - Yield strength fy = 400MPa + High-strength concrete mix C60: - Compressive strength f’c = 67,2MPa + High-strength concrete mix C70: - Compressive strength f’c = 74,3MPa + High-strength concrete mix C80: - Compressive strength f’c = 84,5MPa Materials used for deck slab: + Regular steel reinforcement: - Yield strength fy = 400MPa + Deck slab’s concrete: - Compressive strength f’c = 30MPa 3.3 Analysis and selection of type andcross-sectional dimensions of girder The type of beam is selected based on the following basic criteria: - Application for prefabricated structures - The ability to overcome great spans - The ability to construct cranes is not too difficult Analyzing the technical factors of various types of beams currently being applied domestically and internationally, the criteria can be evaluated according to the following table: Table 3-1: Summary and analysis of types of precast beams Type Response span length Girder spacing Stability in installation Difficulty of compaction Slab girder I girder T girder SuperT girder Reverse T girder Current traditional beam type 9m to 24m Small Fair 12.5m to 33m Average Poor 24m to 33m Average Average 38.2m Average Fair Easy Average Average Difficult 10m to 33m Difficult Average Average Modern type of beams in the world Bulb-Tee girder Wide flange girder U-beam girder Bath-tub girder 24m to 45m Average Average Average 24m to 60m Large Fair Average 23m to 36.5m Large Fair Difficult 24m to 36m Large Fair Difficult With the above analysis, it can be seen that the wide flange girder is the most suitable type to apply for bridge construction projects in urban areas in the SouthEast region Pre-tensioning concrete girder not have a genenerated tube arrangement on the beam side, but usually have rows of prestressed steel strands skewed at the beginning of the beam to reduce the tensile stress on the beam head and increase resistance for the beam head With the assumption that the girder must use shear reinforcement from 12mm to 18mm, the strand prestressed reinforcement has a nominal diameter of 15.2mm, the minimum thickness of the protective concrete layer allowed according to the procedure when using highstrength concrete is 25mm, the distance from center to center between the two strands is 51mm, inferring the minimum width of the beams according to the structural requirements is as follows: Table 3-5: Calculation of minimum value of beam width according to constituted law No Protective concrete thickness (mm) Shear reinforcement diameter (mm) Nominal diameter of strand (mm) Distance between strands (mm) Minimum girder width (mm) 25 25 25 25 12 14 16 18 15,2 15,2 15,2 15,2 51 51 51 51 140,2 144,2 148,2 152,2 Thus, the girder rib thickness should be chosen as 155mm to prevent some errors in the fabrication and installation of reinforcement With reference to the dimensions of the existing wide flange girder, the thesis proposes to use the following wide flange girder cross-sectional format: Table 3-6: Dimension data of WF2300 beams using high strength concrete Quantity Span length (m) Representative symbol L WF2300 60 Concrete strength (Mpa) f’c 67.2;74.3;84.5 No of strand 15.2mm ncap 74 s 2.5 Girder spacing (m) WIDE (m) Bottom flange wide b1 0.980 Bottom swiping wide b2 0.413 Web wide b3 0.155 Top swiping wide b4 0.548 Top flange wide b5 1.250 HEIGHT (m) Bottom flange height h1 0.180 Bottom swiping height h2 0.120 Web height h3 1.830 Top swiping height h4 0.090 Top flange height h5 0.080 Girder height H 2.300 The symbols in Table 3-6 are shown in Figure 3-1 Figure 3-1: Symbols of cross-sectional dimensions of wide flange girder Similarly, as on the wide flange girder with span lengths of 24m and 33m, the specific dimensions are selected as follows: Table 3-7: Dimensional data of beams WF800 and WF1200 Quantity Span length (m) Representative symbol L WF800 WF1200 24 33 Concrete strength (Mpa) f’c 67.2;74.3;84.5 67.2;74.3;84.5 No of strand 15.2mm ncap 32 38 s 2.5 2.5 Girder spacing (m) BỀ RỘNG(m) Bottom flange wide b1 0.980 0.980 Bottom swiping wide b2 0.413 0.413 Web wide b3 0.155 0.155 Top swiping wide b4 0.548 0.548 Top flange wide b5 1.250 1.250 CHIỀU CAO(m) Bottom flange height h1 0.130 0.130 Bottom swiping height h2 0.120 0.120 Web height h3 0.380 0.780 Top swiping height h4 0.090 0.090 Top flange height h5 0.080 0.080 Girder height H 0.800 1.200 3.4 Some main design content The detailed audit calculation tables of beams WF2300 with mix of C60, C70, C80 are presented in the appendix Calculation results are summarized in the following table: Table 3-8: Summary of calculation results for beams WF2300 SUMMARY OF CALCULATION RESULTS Representative WF2300 Quantity symbol Span length(m) L 60 Concrete strength f’c 67.2 74.3 (MPa) Resistance reserve factor (resistance/request) Deflection 1.59 1.64 Moment M 1.12 1.14 Shear V 2.89 3.21 84.5 1.71 1.16 3.62 Table 3-9: Summary of calculation results for beams WF1200 SUMMARY OF CALCULATION RESULTS Representative WF1200 Quantity symbol Span length(m) L 33 Concrete f’c 67.2 74.3 strength (MPa) Resistance reserve factor (resistance/request) Deflection 1.46 1.51 Moment M 1.24 1.25 Shear V 2.34 2.57 84.5 1.56 1.25 2.92 Table 3-9: Summary of calculation results for beams WF800 TỔNG HỢP KẾT QUẢ TÍNH TOÁN Đại lượng Ký hiệu WF800 Chiều dài nhịp (m) L 24 Cấp bê tông (MPa) f’c 67.2 74.3 Resistance reserve factor (resistance/request) Deflection 1.22 1.25 Moment M 1.27 1.28 84.5 1.3 1.29 Shear V 1.85 2.04 2.31 The audit results show that the values of internal force, stress and deformation of beams WF2300, WF1200 and WF800 when using high-strength concrete are within the allowable limits In the case of using 50MPa strength concrete, previous typical designs with wide flange girder proposed to use WF1300 beams for 33m span and WF900 for 24m span This thesis has experimental calculation and audit of beams WF800 and WF1200 to consider the responsiveness when reducing beam height, the results of the calculation and audit show that when using 50MPa strength concrete, the stress and deflection of beams is not satisfactory, therefore, reduction of beam height can only be done when using high-strength concrete Similarly, for a span of 60m using 50MPa grade concrete, the minimum height of I-beams with a width must be 2450mm to meet the requirements of stress audit From the above results, it can be seen that when using highstrength concrete with grades C60, C70, C80, the typical cross-section of wide flange girder can reduce the height when crossing spans of 60m, 33m, 24m is 150mm, 100mm and 100mm respectively compared to when using 50MPa normal strength concrete CHAPTER ANALYSIS AND EFFICIENCY OF ECONOMIC EFFICIENCY EFFICIENCY OF WIDE FLANGE GIRDER WITH HIGH STRENGTH CONCRETE COMPARISON WITH CURRENT PRECAST PRESTRESSED GIRDER 4.1 General For bridge construction with span length up to 60m, the popular simple span prestressed concrete beams not have corresponding designs, except for box girder which is not economically efficiency compared to profiled beams Therefore, the wide flange girder using high-strength concrete has a clear advantage in the segment of span lengths of 60m or more The comparison and evaluation in the content of this chapter focuses on evaluating the applicability of wide flange girder using high-strength concrete mix C60, C70, C80 compared with some types of conventional section beams with span lengths of 24m and 33m are span lengths commonly used in urban traffic construction projects in the SouthEast region 4.2 Comparative options The comparison and evaluation of economic-technical criteria are presented through the following case studies: Case study 1: compare the wide flange girder with the prestressed reinforced concrete slab girder with a span of 24m Precast prestressed slab girder is a typical beam commonly used with small span girders (12m, 15m, 18m, 21m and 24m) The advantage of the hollow girder type is that it has a low girder height, which helps to reduce the total height of the span structure, responds well to the problem of static under the bridge for urban overpasses, and helps to reduce the connecting road to the bridge leads to a reduction in project costs In this comparison, the study uses the data of a prestressed concrete girder bridge with a span of 24m The main girder is a typical slab girder with a girder height of 950mm The WF800 girder presented in chapter is used to compare with the 24m slab girder span According to the calculation results, the bridge cross section uses 05 main girders with a distance of 2.5m Case study 2: compare the wide flange girder with the 33m span post-tensioning I girder I girder made of prestressed concrete with a span of 33m is a typical type of girder widely used in traffic projects in recent years in the SouthEast region This comparison uses a bridge cross section of 12m wide, with a spacing of 2.4m between beams, corresponding to the widest main girder spacing applied in Vietnam for 33m I-beams To compare with the I33m beam, use the wide flange girder with WF1200 main girders, the main girder spacing is 2.5m as described in chapter 4.3 Comparative analysis of economic and technical indicators The resistance reserve capacity of the options in case study is presented in the following table: Table 4-1: Resistance reserve comparison of case study Comparative alternatives of case study Slab girder 24m WF800 girder Category End Middle End Middle section section section section Mr / Mu 1.664 1.29 Vr / Vu 2.25 3.20 2.31 2.47 Deflection 1.98 1.3 With the above results, the typical design of wide flange girder has lower moment reserve, shear force and deflection due to live loads compared to traditional hollow slab girders but still ensures the loadbearing requirements This result is the inevitable consequence of reducing the height of the wide flange girder, 800mm, compared with 950mm of the hollow slab girder over the same span length The comparison of resistance of the options in case study is presented in the following table: Table 4-2: Resistance reserve comparison of case study Comparative alternatives of case study I girder 33m WF1200 girder Category End Middle End Middle section section section section Mr / Mu 1.7 1.25 Vr / Vu 3.29 4.11 2.92 2.95 Deflection 2.07 1.56 With the above results, the typical design of wide flange girder has lower moment reserve, shear force and deflection due to live loads compared to traditional beams but still ensures the load-bearing requirements This result is an inevitable consequence of the reduction of the wide flange girder height To evaluate the economic and technical efficiency, it is possible to consider the amount of material used of the comparison options Comparative calculation results of case and are shown in the following tables: Table 4-3: Summary of 24m span comparison calculation results Girder type Slab girder (12 beams) WF800 girder (5 beams) Comparison Concrete mass (m3) beam span Strands mass (kg) beam span Reinforcement mass (kg) beam span 15.26 183.12 759.81 9117.72 1994.83 23937.98 10.75 53.76 845.57 4227.84 2216.96 11084.8 29.4% 46.37% 46.31% Table 4-4: Summary of 33m span comparison calculation results Girder type I girder (5 beams) WF1200 girder (5 beam) Comparison Concrete mass (m3) beam span Strands mass (kg) beam span Reinforcement mass (kg) beam span 23.73 118.65 1625.83 8129.15 3816.17 19080.85 17.09 85.47 1380.65 6903.27 3418.04 17090.22 72% 72% 84.9% 84.9% 89.6% 89.6% With the above comparison results, it can be seen that for normal span lengths, wide flange girder have more advantages in weight of span structure than traditional beams, thus reducing the load on the abutment system and bridge foundation Evaluation of other benefits of using wide flange girder with high-strength concrete In case study 2, the main girder height of the wide flange girder is 1200mm which is 450mm lower than the traditional I-beam height This is useful for constructions that need to pass static in urban areas, especially for overpasses at intersections Reducing the height helps to reduce the length of the ramp connecting the road to the bridge In case study 1, in addition to reducing the main girder height, the number of wide I-beam slabs used is only girders compared to 12 slab girders This, in addition to helping to reduce the amount of materials used, also helps reduce transportation and beam installation costs CONCLUSIONS AND SUGGESTIONS Conclusions The thesis has focused on research and has some main contributions as follows: - Research has confirmed the need to apply prefabricated beam structure using high strength concrete in bridge construction in the SouthEast region - Design concrete mix C60, C70, C80 with high slump using local materials in the SouthEast region, with coarse aggregate using Phu My - Ba Ria crushed stone and fine aggregate mixed between river sand and crushed sand with a ratio of 60/40, suitable for the production of pre-stressed concrete beams - For concrete mix C60, C70, C80 using materials from the SouthEast region, the study has provided a way to determine some mechanical and physical criteria to serve the design of precast prestressed concrete brigde girder when using those mix is as follows: Elastic modulus: Ec 3.385 105 w c2.55 (f'c )0.285 (Mpa) Modulus of rupture: f r 0,83 f 'c (Mpa) j ' fc28 Concrete strength by age: f cj' 0,84 0,97 j Block stress conversion factor: α1 = 0.804; 1 = 0.673 - The appropriate cross-sectional dimensions have been proposed for wide flange girder using high-strength concrete with span lengths of 24m, 33m, and 60m - Confirming the effectiveness of using wide flange girder with high-strength concrete compared to traditional types of beams using conventional concrete in the Southeast region: Reduce beam height from 150mm to 450mm Reduce material volume from 10% to 50% Suggestions To be able to complete the application in manufacturing prestressed concrete bridge girder with high strength concrete on an industrial scale, more long-term studies such as durability, creep and assurance studies on the ability to manufacture goods such as quality assurance or structural maintenance during the manufacturing process This study can be developed for some other types of beams using high-strength concrete On the other hand, beams can be manufactured and tested with real dimensions and evaluated experimentally on actual beam models THESIS RELATED PUBLICATION “Experimental study to propose a formula to determine the elastic modulus and modulus of rupture of high-strength concrete using materials in the Southeast region”, Transport Magazine, 01/2021 “Experimental study to determine the stress-strain curve of highstrength concrete from 60mpa to 80mpa using materials in the Southeast region”, Transport Magazine, 03/2021