Prestressing

ABSTRACT An experimental testing program was conducted at Kansas State University (KSU) to test the bond characteristics of various 5.32 mm-diameter, Grade 270 low-relaxation steel wires used in prestressed concrete railroad ties. This un-tensioned pullout test could serve as a quality control test similar to the NASP (North American Strand Producers) Strand Bond Test that has been developed for pre-tensioned strands. A total of twelve (12) wires produced by six different steel manufacturers were used to develop the wire pullout test. All of the wires were tested in their " as-received " condition and have different indent geometries. It is generally accepted that indentations in the wire improve the bond between the steel and concrete. However, there are currently no commonly accepted quality control tests that accurately predict a wire's bond characteristics in a pre-tensioned application. The un-tensioned pullout test developed is comparable to the NASP [Strand] Bond Test. The specimens consist of a 4 in. (100 mm) outer-diameter tube with a total length of 8 in. (200 mm) and a steel plate welded to the bottom. The 5.32 mm-diameter wire was centered in the tube and the sand-cement mortar was placed and allowed to cure. The flow of the mortar was measured for consistency and 2 " x 2 " (50 mm x 50 mm) mortar cubes were used to determine the compressive strength of the mortar. The specimens were tested when the compressive strength of the mortar was between 4500 and 5000 psi (31.0 MPa and 34.5 MPa). Each batch of mortar contained 12 pullout specimens; one with each wire type. Each wire was tested six times leading to a total of six batches and a total of 72 mortar specimens. During testing, the wires were loaded in force control at the bottom, while continuously monitoring and recording the movement (slip) of the wire with respect to the mortar at the opposite (top) end. The force verses end-slip data of the six tests for each wire type were numerically combined to obtain the average bond performance. These average results from the un-tensioned pullout tests were then compared to transfer length measurements from accompanying pre-tensioned concrete prisms. In general, the wire end slip measurements from the pullout tests were found to have good correlation with the measured transfer length. For all 12 wires, a coefficient of determination (R 2) of 0.872 was found between the average pullout force (at 0.10-inch (2.54 mm) of wire free-end slip) and average transfer length measurements from the accompanying concrete prism tests. However, when only the indented wires were considered, the R 2 increased to 0.913.

In Present days the pretensioning and post tensioning systems are very popularly using in the major constructions of a structure. The Pre-tensioning and Post-tensioning both methods are used under pre-stressing process. In which has few edges over the orthodox non-stressed structures like greater span to depth ratio, higher moment and shear capacity. These methods are generally adopted in the making of PSC girders, sleepers, Bridges, Slabs in buildings, Concrete Pile, Repair and Rehabilitations, Nuclear Power Plant etc.

Two major multifunctional sports arenas, where post-tensioned reinforced concrete structural elements were applied, have recently been opened in Europe -the Zagreb Arena in Croatia and the Sports Arena Lodz in Poland. The Zagreb Arena is a multi-functional complex with a seating capacity of 15,200 and hosted the 2009 Men's World Handball Championship. The shell shape follows the structure logic -it partly covers the inner space with curved columns. Basic shape and structural elements are prestressed prefabricated reinforced concrete columns with heights of up to 37 m. Eighty-six columns surround the hall, support grandstands and carry the facade, as well as the suspended steel roof structure. Architectural cables carry the roof that has a main span of 110 m. The Zagreb Arena was the outright winner of the 2009 structural design category at the World Architecture Festival.

As cortinas atirantadas são estruturas de contenção que requerem o trabalho conjunto das propriedades de resistência do concreto armado com tirantes protendidos, envolvendo também as do solo de base para ancoragem, tudo isso de modo a impedir o escorregamento do maciço de terra. Apesar da complexidade envolvendo o projeto desse tipo de contenção, O Método Brasileiro de Atirantamento desenvolvido em 1957 pelo prof. Eng. Ântonio J. Costa Nunes, incentivou e difundiu o emprego desse tipo de estrutura no Brasil. Daí esse trabalho ter por objetivo evidenciar os principais aspectos de projetos a serem considerados, por meio da investigação e descrição das especificidades de cada um dos materiais envolvidos (concreto armado, aço protendido e solos) e como eles interagem estruturalmente de modo a garantir o bom desempenho e segurança da obra de contenção. Isso é demonstrado a partir do desenvolvimento de um exemplo prático de dimensionamento de cortina, buscando elucidar de maneira objetiva a sequência de cálculos a ser executada, utilizando o Método Brasileiro de Atirantamento para análise de estabilidade, orientações da NBR 5629:2006 para dimensionamento dos tirantes e a NBR 6118:2014 para dimensionamento do paramento. Muito embora exista uma norma brasileira dando orientações para a execução de tirantes ancorados no solo, ainda não existe uma metodologia de cálculo bem definida a ser executada e o fato do solo ser um material extremamente heterogêneo, dificulta a assertividade da modelagem do problema, de modo que conta-se muito com a experiência do projetista.

In this study, the effects of low-velocity impact on the preloaded E-glass/ epoxy-laminated composites were investigated. Unidirectional reinforced E-glass/epoxy-laminated composite materials, [0/90] 2s , were manufactured and tested. Dimensions of the specimens are 140 × 140 mm and its thickness is 2 mm. Impact tests were conducted in a vertical drop weight test device, which was specially manufactured. Impactor has geometry with a semi-spherical end of diameter 12 mm and weight 3.1 kg. In the tests, tension–tension, tension–compression (shear), and compression–compression preloads were applied on the specimen and low-velocity impacts were applied in the middle of the plate for the specimens under preload and the differences with regard to damage were specified. Force–time graphs obtained from the test specimens are given and discussed. Other graphs namely energy–time and force–displacement are calculated from the force–time graphs.

Currently in vogue fast track construction has encouraged the adoption of pre-tension technology for urban flyovers. After having successfully experimented pretensioned spans for River Bridge upto span of 30 m in Hadakiya Bridge in Gujarat, the technology was first time extended upto 35m spans for Beas and Sutlej river bridges in Punjab. The inherent peculiarities such as single stage prestressing, transfer of prestress through bond between concrete and cables by obviation of grouting and sheathing ducts, tensioning of tendons before the concrete is cast and transfer of prestress after the attainment of required strength in concrete derive certain advantages in favour of pretensioning in terms of durability, quantity reduction, construction speed, design and construction expediency. However, in the Indian scenario there are no codal guidelines accounting for these peculiarities for bridges. The enumeration with illustration is intended to provide basis for formulating guidelines for pretensioning in bridge building. The Paper also deliberates on optimization of beam cross section in relation to lateral stability during transfer of prestress accounting for casting imperfections, handling and erection of beams before the beams are transversly stiffened by deck slab which may help the code makers to have fresh look on the guidelines for lateral stability of the prestressed beams. The project consisted of design and construction of high-level bridge across the river Sutlej including approaches and guide-bunds connecting Nakodar and Jagraon. The construction of the bridge facilitates in reduction of the distance between the towns by 50 km, reduction in traffic of NH-1 due to traffic from Rajkot, Maler Kotla and Jalandar and reduction of traffic in the city of Ludhiana. The bridge proper, 810 m long between the inner faces of dirt walls is made up of 23 spans of 35.20 m, while the approaches of lengths 1369 m and 1115 m on Nakodar side and Jagraon side respectively flanked the bridge proper. The main flow is confined and guided through the bridge linear waterway without causing damage to the bridge and its approaches by provision of divergent guide-bunds along the river flow, upstream and downstream on both the banks. The superstructure of 35.20 m span bridge consisted of 6-nos. precast pretensioned concrete beams spaced at 2.15 m centres and cast-in-situ RCC deck slab. The width of the carriageway has been kept 7.50 m flanked either side by 2 m wide cycle track making the total width of the bridge deck to be 12.95 m including crash barriers and steel railings. The vehicular way is separated from cycle ways by crash barriers while cyclists are protected by steel railings from being toppled over. The beams were simply supported on POT-cum-PTFE bearings having slab steel expansion joints between the spans. The abutments were solid non spill-through types to go with same family of plate type piers flaring towards pier cap in the direction of river flow (transverse) to minimise the size of the RCC cap. The piers were founded on 6 m dia well foundations while the abutments were resting on 7 m dia wells. The detail of the general features of the bridge is given in Fig. 1. 2. DETAILS OF THE CONTRACT Punjab Infrastructure Development Board, on behalf of Punjab PWD provided developmental outline proposal with the condition that the contractor should submit his own proposal with the approximate dimensions of various components of the bridge structure to fairly establish that the technical requirement were met with. The tender proposal of the contractors were to include certain obligatory conditions such as length of the bridge, approaches and guide-bunds, carriageway and cycle track width requirements, linear water way and vertical clearance and type of foundations, and formation levels. The departmental outline proposal had the span of 40.50 m and the variation in span length was permitted up to ±20 per cent. The contractor had to give detailed design calculations and drawings in support of his proposal after the award of the work to comply with the design requirements stipulated in tender documents. Qualified engineers supplemented by independent quality control consultant in line with ISO requirements were supervising the execution of the job. Some of the salient design parameters specified in the tender documents are as below: River hydraulics

ABSTRACT An experimental testing program was conducted at Kansas State University (KSU) to test the bond characteristics of various 5.32 mm-diameter, Grade 270 low-relaxation steel wires used in prestressed concrete railroad ties. This un-tensioned pullout test could serve as a quality control test similar to the NASP (North American Strand Producers) Strand Bond Test that has been developed for pre-tensioned strands. A total of twelve (12) wires produced by six different steel manufacturers were used to develop the wire pullout test. All of the wires were tested in their " as-received " condition and have different indent geometries. It is generally accepted that indentations in the wire improve the bond between the steel and concrete. However, there are currently no commonly accepted quality control tests that accurately predict a wire's bond characteristics in a pre-tensioned application. The un-tensioned pullout test developed is comparable to the NASP [Strand] Bond Test. The specimens consist of a 4 in. (100 mm) outer-diameter tube with a total length of 8 in. (200 mm) and a steel plate welded to the bottom. The 5.32 mm-diameter wire was centered in the tube and the sand-cement mortar was placed and allowed to cure. The flow of the mortar was measured for consistency and 2 " x 2 " (50 mm x 50 mm) mortar cubes were used to determine the compressive strength of the mortar. The specimens were tested when the compressive strength of the mortar was between 4500 and 5000 psi (31.0 MPa and 34.5 MPa). Each batch of mortar contained 12 pullout specimens; one with each wire type. Each wire was tested six times leading to a total of six batches and a total of 72 mortar specimens. During testing, the wires were loaded in force control at the bottom, while continuously monitoring and recording the movement (slip) of the wire with respect to the mortar at the opposite (top) end. The force verses end-slip data of the six tests for each wire type were numerically combined to obtain the average bond performance. These average results from the un-tensioned pullout tests were then compared to transfer length measurements from accompanying pre-tensioned concrete prisms. In general, the wire end slip measurements from the pullout tests were found to have good correlation with the measured transfer length. For all 12 wires, a coefficient of determination (R 2) of 0.872 was found between the average pullout force (at 0.10-inch (2.54 mm) of wire free-end slip) and average transfer length measurements from the accompanying concrete prism tests. However, when only the indented wires were considered, the R 2 increased to 0.913.

Résumé/Abstract This paper presents the effects of the number of transverse diaphragms and the level of transverse post-tensioning forces using unbonded carbon-fiber-reinforced-polymer (CFRP) strands on the behavior of side-by-side box-beam bridges. An experimental program, consisting of load-and strain-distribution tests, was conducted on a half-scale, 30-deg-skew, side-by-side box-beam bridge model. The bridge model was tested under three different phases: uncracked deck slab, cracked deck slab, and replaced beam. An ultimate ...