Flexural design of precast, prestressed ultra-high-performance concrete members (original) (raw)
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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.
State of the Art: Mechanical Properties of Ultra-High Performance Concrete
During the past decades, there has been an extensive attention in using Ultra-High Performance Concrete (UHPC) in the buildings and infrastructures construction. Due to that, defining comprehensive mechanical properties of UHPC required to design structural members is worthwhile. The main difference of UHPC with the conventional concrete is the very high strength of UHPC, resulting designing elements with less weight and smaller sizes. However, there have been no globally accepted UHPC properties to be implemented in the designing process. Therefore, in the current study, the UHPC mechanical properties such as compressive and tensile strength, modulus of elasticity and development length for designing purposes are provided based on the reviewed literature. According to that, the best-recommended properties of UHPC that can be used in designing of UHPC members are summarized. Finally, different topics for future works and researches on UHPC's mechanical properties are suggested.
Acta Polytechnica CTU Proceedings
With the aim to reduce the environmental footprint of buildings, this paper presents an original structural system concept for two-way slabs in residential and office buildings. The proposed system extends the best practice in terms of modularity, versatility, demountability, reusability, and durability. A finite set of elements can be used to form the main load-bearing system of multiple successively constructed buildings having different and unpredicted layouts and static systems. Ultra-High Performance Concrete (UHPC) was identified as one of the most promising materials for this application because of its high strength, extreme durability and the opportunities it opens for shape optimization and material consumption reduction. In the first part of this contribution, the main features of the new structural system and preliminary design assumptions for UHPC modules are briefly outlined. Then, the authors present and discuss the results of an experimental campaign on prestressed UH...
Mechanical Properties Of Ultra High Performance Concrete
2012
A research program is conducted to evaluate the mechanical properties of Ultra High Performance Concrete, target compressive strength at the age of 28 days being more than 150 MPa. The methodology to develop such mix has been explained. The material properties, mix design and curing regime are determined. The material attributes are understood by studying the stress strain behaviour of UHPC cylinders under uniaxial compressive loading. The load –crack mouth opening displacement (cmod) of UHPC beams, flexural strength and fracture energy was evaluated using third point loading test. Compressive strength and Split tensile strength results are determined to find out the compressive and tensile behaviour. Residual strength parameters are presented vividly explaining the flexural performance, toughness of concrete.Durability studies were also done to compare the effect of fibre to that of a control mix For all the studies the Mechanical properties were evaluated by varying the percentage...
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.
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.