Behavior of Three-Span Continuous Pre-stressed Concrete Girder for Precast Construction of Monorail Transit System

Abstract

This study presented the results of an experimental and finite element analysis programme conducted on a newly proposed Full-scale Precast Post-tensioned Continuous (FPPC) girder for straddle monorail. The investigated FPPC girder represents the actual size, design and construction details for a newly designed monorail transit system (Yellow Line and Pink Line Monorail) in Bangkok, Thailand. The salient features of the newly proposed girder system include lightweight, low-cost, easy and fast construction. The newly proposed FPPC girder is mainly comprised of three reinforced concrete (RC) hollow haunched girders, four piers or supports, two pier segments, four wet joints, and four bearings at each support. The FPPC girder was constructed at the casting yard of Sino-Thai Engineering and Construction Public Company Limited (STECON), Thailand. In the first part of this study, the FPPC girder was tested under different loading conditions (such as service and ultimate loading conditions). Both service and ultimate loads were applied as two-point loadings. Service load in a monotonic manner was applied on the right exterior span (two-point), middle span (two-point), and on the left exterior span and middle span (four-point). Meanwhile, the ultimate load in a monotonic manner was applied only on the left exterior and middle span as a four-point loading scheme. The test results indicate that the behaviour of the FPPC girder under service load conditions is elastic. Further, cracking of the concrete was not observed at any location. The observed maximum deflections under service load conditions were less than the permissible limits at all locations. Further, the maximum ultimate load-carrying capacity was observed to be much greater than the design load under ultimate loading conditions. This is an indication that the design details and construction procedure of FPPC girder are appropriate and further that this system could be used effectively to construct straddle monorail transit systems. In the second part of this study, small-scale reinforced concrete hollow (RCH) beams were also constructed and tested at the laboratory environment to ascertain the efficiency of Carbon Fiber Reinforced Polymer (CFRP) in enhancing flexural response of hollow section reinforced concrete (RC) beams. Nine beams were tested under four-point bending in 3 groups. Beams were categorized to reflect the presence or configuration of CFRP sheet. Each group consisted of 3 beams: 1 with solid section, 1 with a square 50 x 50 mm opening, and 1 with 100 x 100 mm opening. Beams in 1st group were tested in as-built condition. Beams in 2nd group were strengthened with a single CFRP sheet bonded to their bottom sides. Configuration of CFRP sheet was altered to U-shape applied to the tension side of 3rd group beams. Inclusion of openings, regardless of their size, did not result in degradation of ultimate load and corresponding deflections. However, cracking loads were found to decline as opening size increased. Regardless of the opening size and CFRP configuration, ultimate loads of beams increased with the application of CFRP. However, this improvement was limited to the de-bonding and rupture of CFRP in group 2 and 3 beams, respectively. A comparison in the behavior of group 2 and 3 beams revealed that the application of U-shape CFRP sheet yielded better flexural performance in comparison with flat-CFRP sheet bonded to the bottom of beams. At the end of this study, finite element analysis of FPPC monorail bridge girder was also performed by using a computer program ATENA which is a computational tool for nonlinear engineering analysis of bridges and culverts. The finite element analysis results indicate that the computer program ATENA is well capable to predict the ultimate load carrying capacity, displacement and cracking patterns of FPPC girder.

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