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.
BRIDGE DESIGN SPECIFICATIONS FOR THE FUTURE
The American Association of State Highway and Transportation Officials (AASHTO)-sponsored National Coopperative Highway Research Program study to assess current U.S. bridge design specifications, foreign codes, and alternative specifications is discussed. The study findings led to the initiation of the NCHRP Project 12-33 to develop new bridge design specifications. The history of AASHTO Standard Specifications before and after the 1970s is reviewed including its modification to include the load factor design (LFD). The evolution of LRFD (load resistance factor design) specifications is described. LRFD-based specifications employ statistical methods and probability theory to define variations both in loading and material properties, and the likelihood that various combinations of loads will occur at the same time. It is anticipated that the final draft of the specifications will be considered for adoption by AASHTO in 1993. These specifications will result in construction of bridges that exhibit a more uniform level of safety and that provide better long-term serviceability and maintainability.
Application of 2μm Tm Laser on Biomedicine
Continuous wave Thulium laser emits at wavelength of 2.0 mm, which is well suited for tissue ablationand thermally stimulating cutaneous nerves due to its high absorption by water. 2 mm laser can be transmitted suffi-ciently by common quartz fibers and it is safe for eyes. A brief introduction of principle of 2 mm CW Tm Laser is giv-en, analyzing the photothermal modeling of thulium laser-tissue interaction, comparing 2 mm CW Tm Laser with tradi-tional laser.