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Stress-strain model for confined fiber-reinforced concrete under axial compression

Sabariman B., Soehardjono A., Wisnumurti, Wibowo A., Tavio

Archives of Civil Engineering

2020

Vol. 66, nr 2

119--133

Confinement in concrete can improve the descending branch of the stress-strain relationship of concrete. The addition of steel fiber in concrete can also improve the descending branch of the stress-strain relationship of concrete. The combination of the use of both can double the impact significantly on the post-peak response. It can be seen from the trend of the post-peak response that the values of both 0.85fccf and 0.5fccf can be well predicted. The study involved an experimental investigation on the effect of confinement on square column specimens reinforced with steel fiber. From the experimental program, it is proven that the use of combination of confining steel and steel fiber works very well which is indicated by the better improvement on the post-peak response. The proposed equations can predict the actual stress-strain curves quite accurately which include the effects of confinement parameters (Zm) and steel fiber volumetric parameter (Vf).

Optimizing static and dynamic stiffness of machine tools spindle shaft, for improving machining product quality

Prakosa T., Wibowo A., Ilhamsyah R.

Journal of KONES

2013

Vol. 20, No. 4

363--370

Automotive industries in Indonesia have grown up fast, and in-line with it, machine tools population has also grown up. Nevertheless, most of these machines are imported, because there are only few machine tools industries in Indonesia. Based on this situation, Indonesia has started to build its own machine tools industry in order to support mostly, automotive industries. This paper deals with an activity in machine tools performance improvement researches in Indonesia, that is, improving spindle static and dynamic stiffness. Spindle shaft is the weakest point in machine tools structure, increasing its stiffness will further increase machine tools accuracy and machining product quality as well. Moreover, high productivity needs machine tools with high speed machining capability, which leads into unavoidable dynamic effects that occur in the machine tool spindle during production process such as regenerative chatter. A study has been conducted on developing mathematical model for calculating static and dynamic stiffness of machine tools spindle shaft and studying changes of spindle shaft static and dynamic stiffnesses, by varying bearings preload, number of bearings, bearings span and spindle length. The study was conducted theoretically and experimentally on a national-built CNC vertical milling machine. The study shows that the machine tools spindle shaft stiffness can be increased by optimizing the parameters aforementioned.