International Concrete Abstracts Portal

Wacker Drive in Chicago is a double-deck viaduct constructed along the Chicago River. Because of severe moisture-driven deterioration, the section of the elevated road between Randolph Street and Michigan Avenue are being reconstructed using a post-tensioned slab produced of high-performance concrete topped with a replaceable latex-modified concrete overlay. In order to verify the adequacy of the road way design, a full scale prototype was built and a test program was executed to evaluate the structural performance of the superstructure and its elements. Specifically, the following structural performance characteristics were evaluated: Positive and negative flexural strength Shear strength Live load stress range in concrete and post tensioning tendons Cracking at service load, overload and ultimate load Deflection at service load, overload and ultimate load Overlay bond strength and interaction between overlay and substrate Dynamic response This paper describes the prototype construction, analysis and testing.

This paper presents the results of an investigation on the fatigue performance of two full-size pre-cracked prestressed concrete bridge girders. One AASHTO Type III girder and one AASHTO Type V girder were tested under 1,000,000 cycles of repeated service load intermingled with 2,500 cycles of repeated overload. The behavior of the girders was monitored after each 200,000 cycles of service load as well as each 500 cycles of overload. At the end of the fatigue tests, the girders were tested to failure to determine their ultimate strengths. The test results demonstrated that the fatigue loadings had virtually no effect on the girder behavior. The girders showed no degradation in stiffness or strength after 1,002,500 cycles of fatigue loading. Both girders showed considerable ductility, and their ultimate loads and maximum deflections exceeded the predicted values.

The pier supporting Canada Place Cruise Terminal in Vancouver, British Columbia was constructed in the 1920s. Repairs and upgrading of the reinforced concrete structure were completed in the early 1980s for the 1986 World Expo, to provide hotel and convention centre facilities and a terminal for cruise ships. Since 2000, the Port of Vancouver has undertaken major renovations and expansion to increase the capacity of the facility and meet demands of the expanding cruise ship market. The extension to the existing pier added a third berth and provided additional passenger handling facilities. The expansion required the aprons of the original deck to carry wheel and outrigger pad loads in excess of load ratings previously in use. In the absence of detailed drawings, design data and material specifications to allow assessmetn of the load carrying capacity of the original structure, full scale structural load tests were performed in accordance with Canadian Standards Association CAN/CSA-A23.3 procedures. All thirteen tests were successful, confirming adequacy of the structure to carry the new loads. This paper presents the structural parameters, methodology and results of the test load programme.

A unique large-scale testing apparatus has been designed and built to facilitate the stressing and testing of 18.3 m lengths of steel prestressing strand. The strands are tested in a draped configuration to simulate the load and boundary conditions typical of an unbonded monostrand tendon in a post-tensioned concrete slab. Individual wires can be cut to simulate the occurrence of wire breaks due to corrosion. The apparatus consists of a steel wide flange beam with a parabolic profile plate that aligns the tendon in a draped configuration while providing access along the entire length for strain gauges. The overall length was selected, using mechanical models presented elsewhere, so that complete strain recovery could be observed in a wire with a break at the tendon mid-length. Other geometric variables were set to mimic the typical drape-to-span ratio of an unbonded monostrand tendon in a post-tensioned slab. Test results for intact 7-wire monostrand tendons correspond well to those predicted using the mathematical model of Machida and Durelli. Standard errors of 220 N and 133 microstrain were determined for the tendon load and wire strains, respectively. Thus, the apparatus can be used to accurately measure the mechanical response of unbonded 7-wire tendons.

During the last decade dozens of concrete bridges were raced in The Netherlands that had suffered from alkali-silica reaction (ASR). Since the bridge decks were not provided with vertical reinforcement, their shear capacity fully depends on the concrete tensile strength. To study the effect of ASR on the shear capacity, six beams sawn from two viaducts were loaded in bending till failure. Failure occurred at about 75% of the theorectical shear capacity of undamaged concrete. Contrary to what normally would be expected, failure was not attended with the development of inclined bending cracks, but with diagonal cracks that originated at mid-depth. Hence, the tensile strength reduction due to ASR resulted in a change of the failure mechanism from flexural shear into diagonal shear. To explain the observed crack development and shear strength, the influences of a longitudinal compressive stress due to the restraint of ASR-induced expansion and an orientation dependent tensile strength were taken into consideration.