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تعداد صفحات این فایل: ۲۱ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Reinforced-concrete beam hinge joint fatigue assessment~~en~~

Abstract

A major highway underbridge has been subjected to a complex fatigue assessment to determine its present and future serviceability. Similar to approximately 100 other structures within Great Britain, reinforced-concrete deck hinge joints are positioned within longitudinal beams providing rotational flexibility. Concerns were raised as to the fatigue condition of the hinge joints considering repetitive rotations applied by traffic loading and pitting corrosion found on reinforcement bars. This paper describes the assessment work and associated research relating to this structure including finite-element analysis, laboratory models and space frame modelling of the structure. Comments are made on the applicability of current codes of practice for fatigue assessment of reinforced-concrete deck hinge joints.

۱ Introduction

۱۱ Background

A major highway underbridge was subjected to a complex assessment and category 3 check (by an independent company) to determine its present and future serviceability, regarding the fatigue condition of the reinforced-concrete hinge joints. The author was involved on behalf of the checking organisation and managed the laboratory testing regime. The initial assessment check followed the philosophy outlined in the draft Assessment Approval in Principle document, including plane stress finite-element analysis (FEA) but differing by using Abaqus software. Similar results to that of the principal assessor were established, confirming concerns over the fatigue condition of hinge joints. For a period of four years, the author performed progressively more detailed non-linear finite-element modelling and conducted laboratory research, which verified the quality thereof. This paper briefly describes the work conducted by the author on behalf of the checking organisation, Atkins, throughout the project.

۱۲ The structure

The in situ reinforced-concrete five-span twin-deck structure totals 135 m in length. Each deck is supported by four beams connected at the pier crossheads. Figure 1 shows general arrangement details of the underbridge. Each beam length includes reinforced-concrete beam hinge joints at the two points of contra-flexure in the central span and at the outer points of contra-flexure in the intermediate spans. The hinge joints transfer shear force and restrain longitudinal movement, but provide rotational flexibility at discrete points along the length of each beam. Thus, at the time of design, these points of contra-flexure were known and the structure would have been analysed as statically determinate, as shown in Figure 2. At hinge joints the beam decreases in depth to 432 mm (17 in), which is one third of that elsewhere, for a length of approximately 38 mm (1 1/2 in). Six triplets of bars cross through the joint, each including one horizontal dowel bar flanked by opposing ‘scissor’ bars inclined at 45° to the horizontal all of which have a diameter of 31·۷۵ mm (1 1/4 in). Scissor bars are referred to as ‘tension’ and ‘compression’ barswith respect to the predominant forces experienced in each under shear load. Shear bars, of diameter 22·۲۲ mm (7/8 in), referred to as ‘C-bars’, are positioned either side of the hinge throat, resisting cracking. Hinge details are shown in Figure 3. Such beam hinge details are also referred to as ‘thrust hinges’, and are similar to slab decks known as ‘deck hinges’.

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