Doubling the width of the platform of the San Pedro bridge in Spain

The San Pedro Bridge has six spans and is 750 m (2460 ft) long, 88 m (290 ft) high, 12 m (39 ft) wide, and curved with a radius of 700 m (2300 ft). It was built in 1993 using the cantilever method. Its super - structure is a prestressed concrete box girder with main spans of 150 m (490 ft). In 2008 and 2009, the width of the platform was enlarged to 23 m (75 ft) using five movable sets of scaffolding. The bridge remained open to traffic during construction. The original platform was widened 6 m (20 ft) on each side by connecting a new lightweight concrete cantilever to the original upper slab. These cantilevers were supported by steelstruts. The tie into the upper slab was made with new transverse post-tensioned tendons. The original superstructure was strengthened to resist the additional dead load of the expansion and live loads of the extra traffic. An additional new central web and a composite concrete-steel section were constructed and connected to the concrete box and central web using vertical high-strength post-tensioning bars. Also, external post-tensioning cables were implemented. It was also necessary to strengthen the connection of the original concrete box section to the piers. Detailed calculations were performed to evaluate the load distribution transmitted to the piers by the webs and by the original inclined concrete walls of the box girder. Finally, a detailed second-order-analysis of the complete structure was made to guarantee the resistance of the piers compared with actual loads

An analysis of transfer and development lengths for pretensioned concrete structures /

"December 1994."

Compilation and evaluation of results from high-performance concrete bridge projects /

"HRDI-06/10-06(1M)E"--p. [4] of cover.

Static tests on prestresed concrete beams using 7/16 in. strands.

Mode of access: Internet.

Analysis and design of partially prestressed beams to satisfy serviceability criteria /

Mode of access: Internet.

Technological review of prestressed pavements /

Mode of access: Internet.

High stress monitoring of prestressing tendons in nuclear concrete vessels using fibre-optic sensors

Maintaining the structural health of prestressed concrete nuclear containments is a key element in ensuring nuclear reactors are capable of meeting their safety requirements. This paper discusses the attachment, fabrication and characterisation of optical fibre strain sensors suitable for the prestress monitoring of irradiated steel prestressing tendons. The all-metal fabrication and welding process allowed the instrumented strand to simultaneously monitor and apply stresses up to 1300 MPa (80% of steel's ultimate tensile strength). There were no adverse effects to the strand's mechanical properties or integrity. After sensor relaxation through cyclic stress treatment, strain transfer between the optical fibre sensors and the strand remained at 69%. The fibre strain sensors could also withstand the non-axial forces induced as the strand was deflected around a 4.5 m bend radius. Further development of this technology has the potential to augment current prestress monitoring practices, allowing distributed measurements of short- and long-term prestress losses in nuclear prestressed-concrete vessels. © 2014 Elsevier B.V.

Precast Concrete Panel Thickness for Epoxy-Coated Prestressing Strands, HR-353, Interim Report, 1994

A recommended minimum thickness for prestressed concrete (P/C) bridge deck panels containing 3/8-in. diameter, 270-ksi, low-relaxation, grit-impregnated, epoxy-coated prestressing strands is being evaluated by testing prototype panel specimens. As of January 1994, specimens from ten castings have been tested. The specimens in the first five castings were constructed to establish a preliminary minimum thickness for P/C panels. The specimens in the last five castings were constructed to 1) confirm the minimum panel thickness requirement, 2) measure the development length of epoxy-coated strands in specimens containing multiple strands, 3) measure the development length of uncoated strands in specimens containing multiple and single strands, 4) observe if concrete cracks form in thin panel specimens that have a raked top surface and are reinforced with welded wire fabric and either epoxy-coated or uncoated strands, 5) measure the transfer length for specimens containing a single uncoated strand, and 6) observe the seating characteristics of the grips used for uncoated strand and epoxy-coated strands. These tests have produced several initial findings. The preliminary recommended thickness for P/C panels containing grit-impregnated, epoxy-coated strands is 3 in. and the tentative development length for uncoated and coated multiple strands is approximately 45 in. and 24 in., respectively. Further tests will address confirmation of the recommended P/C panel thickness and establish the transfer and development lengths of single and multiple, uncoated and grit-impregnated epoxy-coated strands.

Investigation of the Impact of Dual-Lane Axle Spacing on Lateral Load Distribution, 2016

The spacing of adjacent wheel lines of dual-lane loads induces different lateral live load distributions on bridges, which cannot be determined using the current American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) or Load Factor Design (LFD) equations for vehicles with standard axle configurations. Current Iowa law requires dual-lane loads to meet a five-foot requirement, the adequacy of which needs to be verified. To improve the state policy and AASHTO code specifications, it is necessary to understand the actual effects of wheel-line spacing on lateral load distribution. The main objective of this research was to investigate the impact of the wheel-line spacing of dual-lane loads on the lateral load distribution on bridges. To achieve this objective, a numerical evaluation using two-dimensional linear elastic finite element (FE) models was performed. For simulation purposes, 20 prestressed-concrete bridges, 20 steel bridges, and 20 slab bridges were randomly sampled from the Iowa bridge database. Based on the FE results, the load distribution factors (LDFs) of the concrete and steel bridges and the equivalent lengths of the slab bridges were derived. To investigate the variations of LDFs, a total of 22 types of single-axle four-wheel-line dual-lane loads were taken into account with configurations consisting of combinations of various interior and exterior wheel-line spacing. The corresponding moment and shear LDFs and equivalent widths were also derived using the AASHTO equations and the adequacy of the Iowa DOT five-foot requirement was evaluated. Finally, the axle weight limits per lane for different dual-lane load types were further calculated and recommended to complement the current Iowa Department of Transportation (DOT) policy and AASHTO code specifications.

Creep and Shrinkage Properties of Lightweight Concrete Used in the State of Iowa, HR-136, Phase I, 1968

In February of 1968 a cooperative research project by the Iowa State Highway Commission (Project No. HR-136) and the University of Iowa, Iowa City, Iowa was initiated in order to determine experimentally the creep and shrinkage characteristics of lightweight-aggregate concrete used in the State of Iowa. This report is concerned with Phase 1 of the Project as described in the Prospectus for the project submitted in November of 1967: "The State Highway Commission is planning to conduct pilot studies in prestressed-lightweight structures fabricated with materials that are proposed for use in bridge structures in the near future. Thus, Phase will have as its immediate objective, investigating the materials to be used in the above mentioned pilot studies.” (1) The work described in this report was also carried out in conjunction with a second cooperative project: "Time-Dependent Camber and Deflection of Non-Composite and Composite Lightweight-Prestressed Concrete Beams" (Project No. HR-137).

Projeto de estabilidade da alteração de um edifício de habitação multifamiliar

Trabalho de Projeto para obtenção do grau de Mestre em Engenharia Civil Estruturas

Determing the Effect of Thermal Treatment Timing on Ultra-High Performance Concrete Beams

The loss of prestressing force over time influences the long-term deflection of the prestressed concrete element. Prestress losses are inherently complex due to the interaction of concrete creep, concrete shrinkage, and steel relaxation. Implementing advanced materials such as ultra-high performance concrete (UHPC) further complicates the estimation of prestress losses because of the changes in material models dependent on curing regime. Past research shows compressive creep is "locked in" when UHPC cylinders are subjected to thermal treatment before being loaded in compression. However, the current precasting manufacturing process would typically load the element (through prestressing strand release from the prestressing bed) before the element would be taken to the curing facility. Members of many ages are stored until curing could be applied to all of them at once. This research was conducted to determine the impact of variable curing times for UHPC on the prestress losses, and hence deflections. Three UHPC beams, a rectangular section, a modified bulb tee section, and a pi-girder, were assessed for losses and deflections using an incremental time step approach and material models specific to UHPC based on compressive creep and shrinkage testing. Results show that although it is important for prestressed UHPC beams to be thermally treated, to "lock in" material properties, the timing of thermal treatment leads to negligible differences in long-term deflections. Results also show that for UHPC elements that are thermally treated, changes in deflection are caused only by external loads because prestress losses are "locked-in" following thermal treatment.

A non-linear dynamic analysis of heavy haul track line sleepers under wheel flat

Significant wheel-rail dynamic forces occur because of imperfections in the wheels and/or rail. One of the key responses to the transmission of these forces down through the track is impact force on the sleepers. Dynamic analysis of nonlinear systems is very complicated and does not lend itself easily to a classical solution of multiple equations. Trying to deduce the behaviour of track components from experimental data is very difficult because such data is hard to obtain and applies to only the particular conditions of the track being tested. The finite element method can be the best solution to this dilemma. This paper describes a finite element model using the software package ANSYS for various sized flat defects in the tread of a wheel rolling at a typical speed on heavy haul track. The paper explores the dynamic response of a prestressed concrete sleeper to these defects.

Rapid growth of nanotubes and nanorods of wurtzite ZnO through microwave-irradiation of a metalorganic complex of zinc and a surfactant in solution

Large quantities of single-crystalline ZnO nanorods and nanotubes have been prepared by the microwave, irradiation of a metalorganic complex of zinc, in the presence of a surfactant. The method is simple, fast, and inexpensive (as it uses a domestic microwave oven), and yields pure nanostructures of the hexagonal wurtzite phase of ZnO in min, and requires no conventional templating. The ZnO nanotubes formed have a hollow core with inner diameter varying from 140-160 nm and a wall of thickness, 40-50 nm. The length of nanorods and nanotubes varies in the narrow range of 500-600 nm. These nanostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods and nanotubes are found by SAED to be single-crystalline. The growth process of ZnO nanorods and nanotubes has been investigated by varying the surfactant concentration and microwave irradiation time. Based on the various results obtained, a tentative and plausible mechanism for the formation of ZnO nanostructures is proposed.

Altered ultrastructure of rinderpest virus and its nucleocapsids induced by 5-fluorouracil

he ultrastructure of purified rinderpest virus and intracellular viral nucleocapsids from infected vero cells treated with a subtoxic dose of 5-fluorouracil (5-Fu) (1 mug/ml), has been analysed by transmission electron microscopy, and compared with that of normal virus particle and nucleocapsids. The results reveal dramatic alterations in the structure of both virions and nucleocapsids. The surface glycoprotein projection of virions was not seen or present at a much reduced level. The intracellular nucleocapsids showed pronounced structural changes,with respect to size, shape and fine structure. The length of treated nucleocapsids is much smaller as compared to the control. The central hollow core is missing in case of drug-treated nucleocapsid and the herring bone structure is replaced by a 'beads on string' structure. The presence of N protein, which is a major structural component of nucleocapsids was seen in 5-Fu-treated cells, but it was associated with a predominantly diffused form of nucleocapsids as seen by immunoelectron microscopy. We report here the first definitive and visual evidence of altered structure of virions and their nucleocapsids after 5-Fu treatment