| Summary: | 博士 === 中興大學 === 土木工程學系所 === 99 === Freeway NO. 6, Nantou section, C605 main stem (STA. 13+750~STA. 14+135) was established out of cutting. The local road, ShiZhuo-lane, STA.14+090, was constructed as a bridge in order to maintain its own traffic function. ShiZhuo-lane across bridge was 57 m long. The upper part of the bridge was constructed as hollow version of the beam using sedimentary light weight aggregate, with its concrete compressive strength (f’c) being 350 kgf/cm2, manufactured with Field caster method.
Due to it was the first bridge composed of light weight aggregate concrete (LWAC) in Taiwan, the field design and constructing experience were still scarce. The current study used ShiZhuo-lane across bridge as target, developing a series of research, including the basic properties of LWAC, the mechanics behavior of LWAC prestressed beams, and the measurement of ShiZhou-lane across bridge performance behavior.
The current study used a series of test results and values of actual measurement to determine the structure behavior of LWAC applied to prestressed concrete beam and its time-dependent properties, with a normal concrete set as control. The study were divided into three parts: Part I, the hardened properties and engineering properties of concrete were tested. Part II, the flexure behavior, stiffness and ductility tests of 4.2 m prestressed concrete beams were executed. And, time-dependent derformation behavior of 20.5 m prestressed concrete beams were observed. Part III, the structure behavior of the actual application of LWAC were tested. The measurement of the bridge behavior was took along with the construction process, including Deflection, Prestressed losses, length change and natural frequency.
According to the results of the prestressed concrete beam test, the ultimate flexural strength of beam stored outdoor for a year didn’t differ from those of 28 days. As for the time-corresponding ductility, the member displacement ductility factor of prestressed beams of normal concrete was 1.38 times of those of 28 days, where as the factor of LWAC was 1.33 times. The result showed that with the same design strength, the ductility of both LWAC and normal concrete were better than those of 28 days. The member displacement ductility factor of LWAC beam were generally smaller than those of normal concrete beam.
As regards the results of the observation of time-dependent derformation of prestressed concrete beams, for 180 days after prestressing, the prestress loss is about 14.1% for prestressed lightweight concrete beam and about 16.8% for prestressed normal concrete beams. It reveals that, by means of proportioning the suitable lightweight concrete mixture to improve the volume stability, an outstanding benefit could be achieved for controlling the prestress loss of prestressed lightweight concrete beams.
According to the results of ShiZhuo-lane test measurement, the subsidence degree of the central of the bridge fitted our expectation. The creep behavior increased the subsidence degree, but the tendency also eased off, as expected. The maximum subsidence amount was 19.9 mm, smaller than the legislated maximum amount 36.2 mm.The natural frequency of the bridge was 3.9 Hz, close to the simulated value 3.65. Furthermore, the simulated stiffness of the bridge was 12.0 tonf/mm, close to the value gained form the loading test, 13.7 tonf/mm. This result showed that the current engineering simulation result could still apply to LWAC engineering.
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