Analys av plattrambroar med krökta ramben

Abstract

One of the most common types of bridges in Sweden is the integral bridge. What characterizes the integral bridge is the lack of bearings and expansion joints. The advantage of this construction is that the horizontal forces can be distributed throughout the structure. A problem is the restraint forces that occur due to, for instance, changes in temperature. Integral bridges are now often designed with horizontally curved abutment walls. This is because they are perceived as safer as this enables more light. These bridges should be analyzed three dimensionally and this increases the effect of the restraint forces. The aim of this study was to establish basic differences between integral bridges with straight respectively curved abutment walls through finite element analysis. Loads which have negative effect on the section forces have been identified. How the geometrical properties on bridges affects the section forces have been investigated, and different ways of modeling the ground attachment have been exanimated.

This study has included the permanent loads, self-weight, earth pressure, support displacement and shrinkage. The included variable loads was traffic load, breakand acceleration force, different temperature loads, increased earth pressure due to overload and due to movement of the construction. The load combinations described are STR-A and STR-B.

Analyses were carried out in a finite element program called BRIGADE/plus. The finite element method is a numerical calculation which gives approximate results.

To identify the loads with negative effect, sections forces in an integral bridge with straight abutment walls was compared with the section forces for an integral bridge with curved abutment walls. The loads which have been found to have negative effect were temperature loads and shrinkage.

Thereafter the bridges geometrical impact on the section forces from the
shrinkage was analyzed. Shrinkage had been found to have the most negative effect on the section forces. With reduced curvature radius increases the section forces. It is also found that the ratio between width and length affects the section forces. The section forces that were affected most by the curvature of the abutment walls were the normal forces in both directions.

The stress distributions in bridges exposed to ultimate state loads was examined. Bridges with different curvature radius where analyzed and differences between the stresses was investigated. Differences in the stress distribution when the abutment walls were designed with a curvature are found compared to straight abutment walls. Decreasing radius resulted in increasing stresses.

The ground attachment was modeled in five different ways to investigate how this affects the stress distribution. The different methods is; fixed supports, fixed in a cylindrical coordinate system, fixed in a girder without the capacity to resist normal force, modeling of the ground slabs and modeling the ground slab with a girder. The strategy with fixed supports resulted in largest stresses.

This study illustrated some problems that occur when an integral bridge is
designed with curved abutment walls. Stress levels increases but was seemingly manageable.

• author: Hult, Frida
• supervisor: Kent Persson; Tore Nilsson; Fredrik Carlsson
• organization: Structural Mechanics
• course: VSM820 20111
• year: 2011
• type: H3 - Professional qualifications (4 Years - )
• subject: Technology and Engineering
• publication/series: TVSM-5000
• report number: TVSM-5180
• ISSN: 0281-6679
• language: Swedish
• id: 3202845
• date added to LUP: 2012-11-26 12:40:14
• date last changed: 2013-10-07 13:22:11