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This paper presents the results of an extensive numerical and analytical study to re-investigate the mechanism of load introduction into concrete-filled tubular column through shear connection. The new mechanism of load introduction revealed from this research indicates that the shear load from the connection is introduced through the column length above and within the connection. This is different from the currently assumed mechanism of load introduction from underneath the connection. In fact, a simple free-body diagram analysis would demonstrate that the currently assumed load introduction mechanism is not possible. The results of the numerical simulations also indicate that the load introduction length above the connection is unlimited and can be as long as the entire column height. Based on the new load introduction mechanism and the numerical simulation results, the maximum amount of load introduced into the concrete core can be calculated as the bond strength multiplying the entire steel tube/concrete core contact surface area for the entire column length above and including the connection. Under the new load introduction mechanism and using representative values of column dimensions and concrete cylinder strength, it has been demonstrated that complete load introduction can be achieved in almost all practical arrangements of concrete filled tubular construction. [ABSTRACT FROM AUTHOR]

Ballast plays an important role in the stability of railway track systems. The effectiveness of the ballast in maintaining the track stability is very much dependent on its mechanical conditions. The available ballast maintenance approaches are mainly based on only track geometry conditions (such as track profile) which do not sufficiently reflect the ballast mechanical behaviors. That is, the ballast potential of degradation (i.e., ballast long term behaviors) has been omitted. This makes the effectiveness of the current ballast maintenance approach questionable, indicating a need for a more comprehensive and effective ballast conditions assessment technique. In response to this need, two ballast condition indices based on ballast geometry degradation (BGI) and the level of ballast fouling (BFI) as the main indicators of ballast mechanical behavior were developed. The BGI is a function of the standard deviations of track alignment, unevenness and twist. The BFI was developed based on the data obtained from the ground penetration radar (GPR). Making use of the new indices, a more reliable maintenance algorithm was developed. Through illustrations of the applicability of the new maintenance algorithm in a railway line, it was shown that the new algorithm causes a considerable improvement in the maintenance effectiveness and an increase in the life cycle of railway tracks by making more effective allocation of resources and more accurate maintenance planning. [ABSTRACT FROM AUTHOR]