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Structural Concrete, Vol. 8, no. 3, September 2007

The use of prestressed concrete piles to support integral abutments

E.G. Burdette, University of Tennessee, Knoxville, USA
S.C. Howard, University of Tennessee, Knoxville, USA 
J.H. Deatherage, University of Tennessee, Knoxville, USA
D.W. Goodpasture, University of Tennessee, Knoxville, USA

The Tennessee Department of Transportation (TDOT) in the United States has become the national leader in the design and construction of jointless bridges with abutments which are integral with the bridge deck. While TDOT criteria call for limits of length of 152 m (500 ft) and 244 m (800 ft) for steel and concrete bridges, respectively, they have on more than one occasion exceeded these limits significantly. TDOT's desire to address any questions raised about the efficacy of using prestressed concrete piles to support integral abutments and perhaps to extend the limits on bridge length led to the tests reported in this paper. Four full-size abutments, 3.05 m (10 ft) wide, were built and tested in the field. The description and results of these tests are reported and discussed. Of particular interest are the testing of one pile to failure and the cyclic tests performed on one pile. The conclusions drawn were, first, that prestressed concrete piles are appropriate to use to support integral abutments and, second, that the TDOT criteria for bridge lengths are reasonable and conservative. 

Structural Concrete, Vol. 8, no. 2, June 2007

Shear strength in the new Eurocode 2. A step forward?

A. Cladera, University of Balearic Islands, Palma de Mallorca, Spain
A.R. Mari, Technical University of Catalonia, Barcelona, Spain

The shear strength of reinforced concrete beams with stirrups has been a highly controversial matter since Ritter and Mörsh proposed the first truss models. Since then, different analytical models have been discussed, such as truss models with concrete contribution, shear/compression theories, truss models with variable angle of inclination, and compression field theories. However, some of these models were too complex to be implemented in a code of practice and they had to be simplified. As Regan has pointed out, for simpler models the problem is mostly that of the need to neglect some factors, considered secondaries. However, what is secondary in one case may be primary in another. With the release of the new Eurocode 2 (prEN 1992-1-1:2003) the controversy has been raised again. The EC-2 proposes a very simple formulation based on a truss model. However, the authors think that it is a gross oversimplification of a complex problem as it neglects important key variables. In this paper the new EC-2 shear procedure predictions are compared to empirical tests and to other simplified formulations. It is concluded that the EC-2 procedure is very easy to use by practising engineers but it presents a great scatter of results. On the one hand, it may be too conservative for slightly shear-reinforced beams or for prestressed beams. On the other, it may be slightly unconservative for heavily reinforced members. 

Structural Concrete, Vol. 8, no. 2, June 2007

Output-only dynamic testing of bridges and special structures

Á. Cunha, University of Porto, Portugal
E. Caetano, University of Porto, Portugal 
F. Magalhães, University of Porto, Portugal

This paper stresses the important role that output-only dynamic testing of bridges and special structures can play in the assessment of dynamic structural behaviour by presenting a set of applications recently performed at several Portuguese bridges (railway, roadway and pedestrian bridges), as well as at the new Braga Sports Stadium suspended roof, and briefly referring to the most important tools developed for that purpose at the Laboratory of Vibrations and Monitoring at the Faculty of Engineering of the University of Porto. 

Structural Concrete, Vol. 8, no. 2, June 2007

Shear and torsion in prestressed hollow core units: finite element analyses of full-scale tests

H. Broo, Chalmers University of Technology, Göteborg, Sweden
K. Lundgren, Chalmers University of Technology, Göteborg, Sweden
B. Engström, Chalmers University of Technology, Göteborg, Sweden

The present calculation methods for shear and torsion in prestressed hollow core slabs add stresses from various influences without taking into account deformations and compatibility, the softening of cracking concrete, or restraint at the boundaries; therefore, they are most likely conservative. The main purpose of this work is to establish three-dimensional finite element models, which can be used both to analyse the effect of parameters that influence the shear and torsion response and to be included in global models of complete floors. An important aspect was therefore to simplify the models to avoid time-consuming analyses. Coarse meshes with solid elements were combined with beam elements. The established models were validated by simulating a series of full-scale tests conducted on both 200 mm and 400 mm thick hollow core units subjected to various combinations of shear and torsion. In general, although very coarse meshes were used, the finite element analyses of the tests succeeded in describing the overall behaviour, crack pattern, failure mode, and maximum load, with a reasonably good agreement. 

Structural Concrete, Vol. 8, no. 1, March 2007

Integral abutment bridge concept applied to the rehabilitation of a simply supported concrete structure

B. Briseghella, University of Architecture in Venice, Italy
T. Zordan, University of Architecture in Venice, Italy

A case study aiming to transform a simply supported pre-stressed concrete flyover into a frame structure throughout its full length, through refurbishment, is presented. Hogging moment resistance is achieved at the piers by the construction of a rigid transverse cast-in-place concrete diaphragm connected to the piers and to the beams of adjacent bays, in an attempt to fulfil the requirements of the integral abutment bridge (IAB) concept specified. All former bearings and expansion joints are eliminated resulting in an improved durability of the structure and greater comfort for the users. According to the IAB concept, hogging moment resistance is obtained by the flow of tensile forces through the concrete slab thanks to an increased ratio of reinforcement and the transmission of compressive forces directly through the concrete. Shear transmission is ensured by the installation of a convenient number of concrete-to-concrete shear studs on the webs of each of the beams forming the deck. Experimental tests were used to investigate the behaviour of shear studs. The possibility of making a simply supported deck continuous for a certain length depends on the soil-structure interaction and, consequently, on a wide number of parameters, varying from case to case, that will not be investigated in the present paper. 

Structural Concrete, Vol. 8, no. 1, March 2007

Metallic fabric jackets: an innovative method for seismic retrofitting of substandard RC prismatic members

G. E. Thermou, Demokritus University of Thrace, Greece 
S. J. Pantazopoulou, Demokritus University of Thrace, Greece 

This paper presents the results of a recent experimental research study where metallic (high-strength steel cord) fabric jackets (MF jackets) were utilised for the seismic upgrading of substandard reinforced concrete members. The proposed intervention method and its practical application are described in detail. Specimens were cantilevers with a square cross-section, representing a typical building column at half scale. The length of the test region corresponded to half the span of a typical storey building column under lateral sway. Due to lack of adequate seismic detailing the specimens were susceptible to various modes of failure such as web shear failure, buckling of compression reinforcement or failure in the lap splice region. The as-built specimens were first damaged up to failure after being subjected to combined axial loading and cyclic lateral displacement reversals simulating seismic loading. In the next phase, specimens were retrofitted with both composite and metallic fabric jackets and then tested again under the same load history. The results of this preliminary experimental research programme show that the metallic fabric jackets performed in an excellent way compared to glass- and carbon-fibre reinforced polymer jackets, increasing substantially both the strength and the deformation capacity of the repaired members. The excellent mechanical performance of the metallic fabrics combined with many of the advantages of the synthetic wraps (easy handling, no change in member dimensions) and the intrinsic favourable properties of steel (fire resistance), underline the potential of this novel material in repair/strengthening of reinforced concrete as an alternative option for jacketing applications. 

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