Prestressed ultra-high performance concrete (UHPC) beams for reusable structural systems: design and testing (original) (raw)
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Structural Design with Ultra-High Performance Concrete
Structural Design with Ultra-High Performance Concrete, 2023
UHPC is a structural material that exhibits compelling structural behaviors. These behaviors are distinct from those exhibited by other more common materials used in the civil infrastructure, such as conventional concrete or steel. In comparison to conventional concrete, UHPC offers sustained postcracking tensile resistance, along with an increased compressive strength, an increased elastic modulus, and a decreased susceptibility to liquid permeation. To effectively engage the enhanced behaviors of UHPC, structural design guidance must rationally and conservatively provide a framework within which designers can appropriately conceive UHPC structures and proportion UHPC elements. With a look toward the future, UHPC can most likely allow for the design of novel structures whose composition is efficient, whose functionality is improved, and whose lifespan is extended. Until now, there has not been any formal design guidance in the United States for structural design with UHPC. Recent research and development-based advancements related to UHPC, and a growing interest from bridge owners in the possibilities presented by this material, have provided an opportunity for the bridge engineering community to consider and potentially adopt formal structural design guidance for UHPC structural elements. The main body of the report provides an overview of UHPC in the context of structural design. The report also contains three appendices. The first, Appendix A—Guide Specification for Structural Design with Ultra-High Performance Concrete, contains a draft structural design framework developed for consideration by AASHTO and presented in the format commonly used for AASHTO guide specifications. Section 1 of Appendix A focuses on structural design guidance, while Section 2 focuses material conformance guidance. To assist readers in understanding the potential application of the proposed structural design framework, a pair of design examples has been developed to demonstrate some of the basic concepts embedded in the framework. The first example focuses on using the methods in the design framework to analyze the behavior of a rectangular beam. This example can be found in Appendix B—Analysis of a Rectangular, Mild Steel Reinforced UHPC Beam. The second example demonstrates the design of a slab-on-stringer bridge superstructure using pretensioned girders. This example can be found in Appendix C—Design Example of a Pretensioned UHPC I-Beam Bridge with a Conventional Concrete Deck.
Experimental Study of Structural Behaviour of Beam using Ultra High Performance Concrete I
JETIR, 2018
UHPC (ultra-high performance concrete) is a relatively new type of concrete that exhibits mechanical properties that are far superior to those of conventional concrete and high performance concrete. The main characteristics that distinguish UHPC from conventional reinforced concrete are the improved compressive strength, the tensile strength, the addition of steel fibres, and the resistance to corrosion and degradation. The mechanical properties of UHPC allow for smaller, thinner, lighter sections to be designed while strength is maintained or improved. The use of UHPC has been limited to a few structure applications due to the high cost of the materials and the lack of established design guidelines. As the construction of superhigh structures and long span structures increases all over the world, strength and stiffness of structures are being improved by applying Ultra-high strength concrete. With such trends, demands to use 100Mpa or Ultrahigh strength concrete more than that are anticipated to spread out. Reinforced concrete is being used extensively in the construction industry all over the world. The use of Ultra high strength concrete has increased due to its obvious advantages like increased modulus of elasticity, chemical resistance, freeze thaw resistance, lower creep shrinkage and lower permeability.
Behaviour of Prestressed Ultra-High Performance Concrete I-Beams Subjected to Shear and Flexure
2013
Ultra-high performance concrete (UHPC) is a new type of concrete developed by selecting the particle sizes and gradation in the nano-and micro-scales targeting the highest possible packing. The resulting concrete with very high density is called UHPC. UHPC has very low permeability and hence it is very highly durable compared to traditional or high performance concrete (HPC). Micro reinforcement of UHPC by random distributed steel-synthetic fibers results in superior mechanical properties such as very high compressive and tensile strengths, high ductility, and high fatigue resistance. The material selection and early age curing processes, use of fiber reinforcement, and very high quality in production resulted in a very high initial cost of UHPC structures. In order to enable the mass production and cost effective use of the material, performance based design and optimization of UHPC structural members are required. This study is part of an NRC Canada research project to develop innovative, cost effective, and sustainable bridge structural systems using UHPC and other innovative materials. In this study, the estimation of shear and flexural capacities using the available approaches of international design guidelines of UHPC structures are comprehensively compared to a proposed truss models, linear and nonlinear finite element models. Several design trials intended to allow for an optimized use of the materials and a maximum load capacity was conducted for simply supported beams with one or two external loads, and having rectangular or I cross sections. Linear and non-linear finite element models are developed and their results were compared to the available international design recommendations. Truss models are proposed to simplify the stress analysis in the shear zone of the prestressed UHPC beams.
Optimization of Prestressed Precast Girders with Ultra High-Performance Concrete
Third International Interactive Symposium on Ultra-High Performance Concrete
Advances in research, several demands, and challenges of modern construction motivated the Ultra High-Performance Concrete (UHPC) development. High compressive and tensile strength, ductility, self-compacting, and high durability are characteristics of the UHPC. The mentioned material allows more durable structures with high possible slenderness and enables the reduction or elimination of passive flexural and shear reinforcements. In this context, this study presents a case study and a comparative analysis of prestressed girders with UHPC and with a 45-MPa concrete. The section height and area, material volume and weight, reinforcement, ultimate resistance bending moment, shear, deflections, and costs were assessed. It was possible to reduce the volume and weight by 48% and 42% for the beams designed with UHPC with nominal lengths of 20m and 35m, respectively. A total elimination of passive reinforcement the UHPC was considered, which is an essential factor to consider regarding cost. Although the initial cost of UHPC solution is relatively higher when compared to conventional concretes analyzing in the short term, its use has some advantages in relation to prestressed beams in class C45 concrete. Considering a long-term economy, it is believed that the high initial cost may dissolve with the lowest maintenance and repair needs over the structure lifetime, due to its high durability.
Flexural design of precast, prestressed ultra-high-performance concrete members
PCI Journal, 2020
Ultra-high-performance concrete (UHPC) is a special concrete mixture with outstanding mechanical and durability characteristics. It is a mixture of portland cement, supplementary cementitious materials, sand, and high-strength, high-aspect-ratio microfibers. In this paper, the authors propose flexural design guidelines for precast, prestressed concrete members made with concrete mixtures developed by precasters to meet minimum specific characteristics qualifying it to be called PCI-UHPC. Minimum specified cylinder strength is 10 ksi (69 MPa) at prestress release and 18 ksi (124 MPa) at the time the member is placed in service, typically 28 days. Minimum flexural cracking and tensile strengths of 1.5 and 2 ksi (10 and 14 MPa), respectively, according to ASTM C1609 testing specifications are required. In addition, strain-hardening and ductility requirements are specified. Tensile properties are shown to be more important for structural optimization than cylinder strength. Both buildin...
Structural Concrete, 2020
The increasing demands of sustainable design and construction with economical sections, reduced cover, and more efficient time schedule require more flexibility in the design methodologies. The development of ultra-high performance concrete (UHPC) have gained increasing interests as an attractive option for structural members with lightweight and superior performances. Concrete members reinforced with steel bars and fibers, generally known as hybrid reinforced concrete (HRC), offer a feasible solution in terms of reducing reinforcing materials and achieving desired structural performance. This paper proposes an analytical model to predict the flexural behavior of hybrid reinforced UHPC with steel reinforcements. Moment-curvature solutions are derived for reinforced sections based on parameterized tension-compression constitutive models. The approach is applicable to customized cross section and derivation of T-section is demonstrated. The moment-curvature response is further simplified as a tri-linear model, which is used for the development of full-range displacement solutions in analytical form. The proposed model is validated with the experimental data from literature covering a range of materials and member sizes. The full-range solutions may provide insights into the serviceability design approach based on the criterion of maximum crack width or allowable deflection.