Papers by Keyword: Prestressed Concrete

Abstract: The important characteristic in the creation of longitudinal splitting cracks in pretensioned concrete members has found to be the geometry of the pre-stressing wire indents. Longitudinal splitting along prestressing tendons can result in severe splitting of prestressed member in the field under loading over time. The research evaluated the influence of wire type indentation on the longitudinal splitting in prestressed concrete members fabricated with different concrete mixtures and different compressive strength of concrete. A key objective was to find the best type of wire to avoid failures in the field. A study was conducted at Kansas State University to understand the effect of wire type on the longitudinal splitting between prestressing steel and prestressed concrete. Three different types of wires will be presented in this paper denoted as “WB”, “WF” and “WQ”. The wires have different parameters which include indent depth, indent width, indent sidewall angle, indent pitch and indent volume.

Abstract: This research was focused on evaluating the influence of the different variables that affectsplitting in prestressed concrete members, particularly prestressed concrete ties. These include the thickness of concrete cover, release strength of concrete, and the type of wire indentation. Different combinations of these variables can affect splitting. This research was focused on finding the best possible material characteristics to avoid potential failures in the field. The objective of this research was to set the minimum value of the thickness of concrete cover, for different wire types used in manufacturing having given types of aggregate for concrete mixture. The importance of this research was to identify the best materials and the best system (concrete, wire, cover) designs before the production of prestressed concrete ties. Splitting test results presented in this research were focusedon three different thicknesses of concrete cover, three different concrete mixes, a 4500psi concrete release strength, and seven different indented wire types.

Abstract: This paper deals with prestressed foundation - soil interaction. For interaction task is used FEM model of thick slab with shear influence which is supported by structural strength modified elastic half-space. The calculation of deformations, internal forces and contact stresses in subsoil is performed iteratively by means of isoparametric element and numerical integration. The results of settlement and stress of non-prestressed/prestressed slab - subsoil interaction are compared on example.

Abstract: Building collapses from the seismic pounding of two adjacent buildings have been found in many past earthquakes. For the two buildings with different story height, the pounding induces impact load and local stress at column mid-height where the provided column reinforcement is normally lesser than the column’s edge. This paper aims to investigate the impact responses of reinforced concrete columns with different axial load and shear capacity by using numerical simulation method. Sixteen reinforced concretes columns were subjected to an impact load created by dropping 300 kg hammer at the height of 1,200 mm above the mid-span of the column. Every specimen has an identical cross section of 220 mm by 220 mm, with 3,000 mm of clear span length. Both ends of the column were fully restrained. The magnitude of the axial load varies from 0% to 40% of the ultimate axial capacity of the concrete section. Shear reinforcement spacing varies from @200 mm to @60 mm. It is found that the axial loads have a great effect on the impact responses of the RC columns. The specimens with high axial load yield higher peak impact force value and less mid-span deflection. Shear cracks were observed on the specimens with low axial force, but the cracks were relatively decreased when increasing the axial load.

Abstract: Northeast Extreme Tee (NEXT) beams have been recently developed for the accelerated bridge construction. The skew effect on live load distribution in a NEXT beam bridge, especially with integral abutments, is not clear and shall be assessed. In this paper, various skew NEXT beam bridges are evaluated through validated finite element (FE) analyses with solid brick elements. Parameters as studied include beam section, span length, and skew angle. Per AASHTO LRFD specifications, one- and two-lane loaded cases are examined to obtain the maximum tensile strains in beam stems under the design live loading (HL-93). Unskewed bridges are used as control specimens to compute skew reduction factors (SRF) for moment from the obtained FE strains. The FE- and LRFD-SRFs for moment are compared in terms of figures, which indicate the LRFD-SRFs have good agreements with the FE-SRFs at large. For the majority of the bridges, LRFD-SFRs govern the FE-SRFs. The research findings from this paper are useful for practicing engineers to safely design a skew NEXT beam bridge with integral abutments.

Abstract: Thermal load, especially vertical temperature gradient, is an important factor that should be considered during the bridge design procedure. In the world, several researches focusing on temperature gradient was made, mostly in USA and China, but only a few analyzed actual temperature gradients measuring at European bridges. In this paper, short overview of temperature loading of bridge structures is described. Then, the temperature measurement of prestressed concrete box girder bridge built by launching method is analyzed. Recorded temperature gradient has been compared with temperature gradients for the concrete box girder cross section recommended by Eurocode design specifications.

Abstract: The purpose of this article is to describe the construction of the bridge spanning the Chomutovka river valley as a part of the road I/27 bypassing the village of Velemyšleves. The investor of this project is Ředitelství silnic a dálnic ČR, správa Chomutov (Directorate for Roads and Motorways of the Czech Republic, division Chomutov). The general constructor of the entire project is the association of companies Silnice Group a.s. and AZ sanace a.s., the constructor of the foundations and the pile foundation is AZ Sanace a.s. and the constructor of the bridge is SMP CZ, a.s. The project execution documentation was carried out by the planning agency NOVÁK & PARTNER s.r.o. The designer and lead construction engineer of the project is Doc. Ing. Lukáš Vráblík, Ph.D.The structure is a seven-span bridge with a total length of 537 m. The load bearing structure, constructed using cantilever casting and supporting construction, consists of a seven-span continuous box girder with two frame connections. The whole structure is to be opened for public use by the end of this year.

Abstract: This paper describes an experimental investigation of the effect of early age prestressing on the ultimate geometry and the load bearing capacity of precast concrete elements. The experimental is performed with a small-scale T-beam which are prestress at three different ages. The experimental results obtained after seven days after prestressing are compared with calculated estimations on the shrinkage and creep according to B3 model.

Abstract: For a long-span prestressed concrete box-girder bridge erected by the double-cantilever segmental method, concrete of segmental joints and concrete in their nearby area may be different from integrally-cast concrete in structural performances. For example, the stiffness of segmental joints could be weakened significantly. To reveal influences of weakening in the stiffness of segmental joints on the deflection at mid-span of box girder, a typical continuous rigid frame bridge in China was taken as the analysis example, and its finite element models were established. In these models, weakening joints were simulated. After the validity of finite element models were warranted, the deflection in the completed construction stage and the long-term deflection in the running period of box girder were calculated, and then the variation of these deflections with the stiffness reduction in all segmental joints was described. Results showed that, compared with the shearing stiffness reduction in segmental joints, the bending stiffness reduction played more significant role in affecting the deflection of box girder. When the weakening times of joint stiffness arrived at 100, deflection values of the box girder increased significantly. However, in the practical engineering, the determination of stiffness reduction in segmental joints according by their damages, and the incorporation of weakening segmental joints into the bearing capacity assessment for existing box girders were all worth further study.

Abstract: The paper deal with the design and construction of cable stayed bridge in the city Natal in Brazil. The bridge has total length of 280m and consists of two approaches and main cable-stayed part with spans of 2x60m. The cable-stayed part is formed by one pylon with two planes of stays. The superstructure of approaches is formed of precast beams and concrete composite deck. Parapet girder has been used for the superstructure design of cable stayed part. The pylon has a ”V” shape because of the plan curvature of the bridge. Strasky, Husty a partneri company has developed the detailed design of the bridge. The bridge construction has finished in June 2014.