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تعداد صفحات این فایل: ۱۰ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:ACOUSTIC EMISSION MONITORING OF CONCRETE HINGE JOINT MODELS~~en~~

Abstract

Currently in the United Kingdom there are over 100 bridges containing hinge joint components, introduced to simplify and standardise designs. Visual inspection of hinge joints noted bridge deck waterproofing failure, which can cause steel reinforcement bar corrosion. This reinforcement is crucial to the integrity of the joint, and the loss of reinforcement section can induce higher stresses leading to eventual failure by yielding. The Transport Research Laboratory created a model of two hinge joint assemblies typical of those found in reinforced concrete slab bridges. The model had notched reinforcement bars at the hinges. The aim of this investigation was to determine the effectiveness of the acoustic emission (AE) technique in detecting and locating the cracking of concrete at the throat. AE sensors were attached to the steel reinforcement bars using waveguides and to the concrete face of the model. The model was statically loaded until failure. To allow the visual inspection and logging of concrete cracking around the throat, the load was applied in stages with a brief hold period between each stage. AE results showed that it was possible to identify and locate cracking of the concrete around the throat and that this technique needs to be further evaluated on bridge structures under live loading.

۱ Introduction

Concrete hinge joints were introduced into bridge decks as a means of simplifying the design, and standardising details on bridges having a range of span and functional requirements. It is thought that the hinge joints transfer shear and accommodate small angular movements but restrict longitudinal movement (Wilson, 1995). The hinges also enabled the bridges to cope with possible differential settlement. The disadvantages with hinge joints are that they are not easily accessible for inspection or maintenance due to their form and their location over or under live traffic lanes. Previous attempts to investigate the deterioration of hinge joints by visual inspection, which involves the removal of structural concrete around the joint to expose the reinforcement bars, have noted particular defects; the majority have cracks running through the throat and a loss of waterproofing. Waterproofing failure can lead to chloride-rich seepage through the joint that can cause reinforcement bar corrosion leading to eventual failure. The Transport Research Laboratory (TRL) created a model, of two hinge joint assemblies. The model created was part of a larger testing programme commissioned by the Highways Agency to investigate the behaviour of the hinges under load (Daly, 2004). The hinge joint model is typical of those found in reinforced concrete slab bridges. The model reinforcement was notched at the hinge to ensure failure of the steel reinforcement. The investigation presented here reports the results the effectiveness of the acoustic emission (AE) technique in detecting both damage in the steel reinforcement and cracking of concrete at the throat in the notched hinge joint model.

۲ Experimental Procedure

The hinge joint specimen was restrained as shown in Fig. 1 and loaded using a hand-operated hydraulic actuator. Load was measured using a load cell and the vertical displacement of the centre span was measured using a displacement gauge. The model was loaded in 10 kN intervals to 125 kN followed by 15 kN interval to 290 kN and then 0.5 mm increases in deflection until failure. Following each load step there was a brief hold period to log cracking of the concrete. The position of the crack tip and the respective load was marked on the beam.

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