Experimental Investigation on Flexural Behaviors in Framed Structure of PST Method
Existing underground pipe jacking methods use a reinforcing rod in a steel tube to obtain structural stiffness. However, some problems such as inconvenience of works and expensive materials resulted from limited working space and reinforcing works are existed. To resolve these problems, a new pipe jacking method, namely PST (Prestressed Segment Tunnel) method, was developed which used joint to connect the steel segment and form erection structure. For evaluating the flexural capacity of the PST method structure, a experimental test was conducted. The parameters considered in the test were span-to-depth ratio of segment, diameter of steel tube at the corner, prestressing force, and welding of joint. The flexural behaviours with the effect of load capacity in serviceability state according to different parameters were examined.. The frame with long segments could increase flexural stiffness and the specimen with large diameter of concave corner showed excellent resistance ability to the negative moment. In addition, welding of joints increased the flexural capacity. Keywords—PST method, Pipe jacking method, Flexural behavior, Prestressed concrete.
Deformation behaviour of tunnel face reinforced with longitudinal pipes—laboratory and numerical investigation
This paper presents the results of laboratory and numerical investigations on the deformation behaviour of tunnel face reinforced with longitudinal pipes. A series of reduced-scale model tests as well as 3D finite-element analyses were carried out with particular emphasis on the effects of reinforcement parameters such as density (number), length and stiffness of reinforcements on the face deformation behaviour. The results of the present study indicate among other things that the face reinforcement technique can significantly reduce not only face deformation but also ground surface settlements, suggesting that the face reinforcing technique can be effectively used as a positive means for ground movement control during urban tunneling. The study illustrates that the reinforcing effect is significantly influenced by the manner in which the reinforcements are distributed, and that there exists a critical value of each reinforcement parameter from which maximum reinforcing effect can be derived. Implications of the findings from this study are discussed in great detail.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.