Analysis And Limit State Design Of Concrete Filled Steel Tube Through Arch Bridge

Abstract

In trying to arrive at a suitable definition for an arch we may look no further than Hooke's anagram of 1675 which stated "as hangs the flexible line, so but inverted will stand the rigid arch". This suggests that any given loading to a flexible cable if frozen and inverted will provide a purely compressive structure in equilibrium with the applied load. Basic principles of arch construction have been known and used successfully for centuries. Based on the same, magnificent stone arches constructed under the direction of engineers of the ancient Roman Empire are still in service after 2000 years. Innovations in material science has brought changes in structural behavior and its design techniques. It is always beneficial to adopt advance material with regards to load carrying capacity and sometimes cost. By the end of the nineteenth century many new materials has been brought into construction industry. During middle of nineteenth century many analytical technique also developed including Castigliano (1879) developed strain energy method which could be applied to arches provided they remained elastic. Recent arch bridges have become increasingly sophisticated combining modern materials like Compos- ite tubes and modern analytical techniques. Concrete Filled Steel Tube(CFST) Arch ribs can replace conventional steel box section and study has shown that different types of sections like dumbbell shaped, triangle shaped and rectangular shapes of arch rib having CFST tubes connected with plates have performed extremely well under load application. Uniform permanent load on whole span, which causes compression in arch ribs and neg- ligible bending moments but any slight variation in the loading will result in a moment being induced in the arch. So it is the matter of arriving at appropriate proportions of arch depth to accommodate the range of eccentricities of the thrust line that is the chal- lenge to the bridge engineer. Study of comparison of Arch Bridge with steel and CFST rib will help to select type of bridge and span of bridge. In the project work, Analysis and Limit state design of through arch bridge has been carried out. Study of cost of Steel rib through arch bridge and CFST rib through arch is done on basis of material required and comparison of both the type of bridge has been carried out. For this, span variation ranging from 50m to 90m with interval of 10m has been chosen. Cost comparison and unit load comparison is done which can be useful to select type of arch bridge and its optimum span. For the problem formulated, Results shows that the cost of CFST circular rib through arch bridge is less up to 70m span and it is more for 80m and 90m span. As Circular tube is having concrete in it, Weight of CFST circular rib arch bridge is more compared to steel arch rib bridge. Use of dumbbell shaped, triangular trussed shape CFST rib will further cut the cost and weight of arch bridge. CFST rib being stiff compared to steel rib arch bridge, Steel rib arch bridge requires larger member sizes to limit displacement within permissible limits.