International Concrete Abstracts Portal

SP-188 This volume presents 24 papers from the Fourth International Symposium and represents a significant expansion in the state of knowledge that has occurred since the First Symposium in 1993.

This paper presents the results of a pilot study to apply externally bonded CFRP sheets to strengthen a simple span reinforced concrete solid slab bridge. The objective was to remove the current load posting. This bridge is a load posted structure on a heavy truck route. Strengthening with CFRP sheets was accomplished in three days without traffic interruption. Preparation consisted of light sandblasting and no concrete repair. The University of Missouri at Rolla conducted the pilot study for the Missouri Department of Transportation. The testing procedure included the construction of two test beams, to simulate bridge deck performance with and without strengthening. Laboratory setup, instrumentation and test results of two full-scale test beams are presented. Field load tests of the bridge were performed by the University of Missouri at Columbia to verify the increase in flexural strength achieved with the application of externally bonded CFRP. The method used to instrument and field load test the bridge along with the subsequence load-deflection characteristics is presented. Comparisons are made between the analytical model, laboratory beam specimens strengthened with CFRP, and in situ field tests of the actual bridge before and after strengthening.

In-situ lateral load tests of reinforced concrete bridge bents were conducted to determine the strength and ductility of existing and retrofitted bents with Carbon Fiber Reinforced Polymer (CFRP) composites. The CFRP composite retrofit included three columns, the cap beam and the three cap beam-column joints. Existing design guidelines were used for retrofit of the columns with CFRP composites. New design guidelines were developed for retrofit of cap beam-column joints. The design of the CFRP composite retrofit was based on doubling the displacement ductility of the bent. The CFRP composite was able to strengthen the cap beam-column joints effectively for an increase in shear stresses of 35 percent. The bent retrofitted with the CFRP composite reached a system displacement ductility of 6.3 as compared to the bent in the as-is condition, which reached a ductility of 2.8. The peak lateral load capacity was increased by 16 percent.

Bridge rehabilitation is becoming as much an art as a science. The design of new bridges involves the application of current aesthetic principles and the latest engineering tools to create a new structure. Bridge rehabilitation, on the other hand, takes the bridge as it is, warts and all, and tries to bring it back to health. The science of bridge rehabilitation includes load assessment and structural and member analysis. The art of bridge rehabilitation includes the condition assessment and the judgement needed to determine the most appropriate treatment required. Usually, the bridge rehabilitation engineer is faced with a number of options and a balance has to be reached between the extent and cost of repair work, and the estimated remaining life of the repaired structure. Rehabilitation engineers try to account for this by using fairly subjective, life cycle cost analysis techniques. Often, however rehabilitation decisions are based on factors other than engineering ones. Intuition, which Winston Churchill called 'logic in a hurry', and experience usually play a major role in the art of bridge rehabilitation. This paper describes a bridge rehabilitation project in the Canadian Prairies, where the extreme climate plays an important part in the design and construction of bridges. It outlines the engineering steps followed in assessing the strength of the bridge and the strengthening measures adopted. It shows how bridge rehabilitation engineers are constantly searching for new ways to meet the challenge of bridge care, and introduces the carbon fiber reinforced polymer (CFRP) strips as a method of deck strengthening.

The aim of this project is the production of a 28 m high CFRP-prestressed spun concrete pylon as a support for electric lines at the 110 kV voltage level (Duralight concept). It is intended to use this pylon as a support mast in a section of the 110 kV line of the Nordostschweizerische Kraftewerke (NOK, Power Company of North East Switzerland) Beznau-Baden. The fundamental advantage of this new design is the low weight in combination with an optimum corrosion resistance. The high corrosion resistance of the CFRP prestressing and shear reinforcement allows minimization of the concrete cover so that a cross-sectional wall thickness in the region of only 4 cm (1.6 inches) can be obtained. This is at present about 10 cm (4 inches) if steel reinforcement is used. The low weight of the CFRP reinforcement (the density of CFRP is only 1.6 g/cm3, which is a fifth of the density of steel) and its high tensile strength (CFRP pretensioning rods have a tensile strength of 3000 MPa, which is twice that of a prestressing steel) are also noteworthy. These two factors permit a weight reduction on the reinforcement side of 90% compared with conventional pre-stressed concrete construction. On the matrix side, high-strength spun concrete of strength class B110 is used. Owing to its high strength, it helps to achieve the stated minimization of the cross-sectional dimensions. The envisaged pylon weight of 4730 kg means a 45% weight reduction compared with the traditional steel reinforced spun concrete pylon. The transport and installation costs are thus lower and the expected life without maintenance is 50 years. This paper describes the technical fundamentals studied in a four year research program at the Swiss Federal Laboratories for Materials Testing and Research EMPA for designing and manufacturing this prototype pylon. The presented pilot project results from a close co-operation of the spun concrete element production plant SACAC with EMPA and the power company NOK.