Frame bridge – Handling instruction for the conversion from existing bridges to integral bridges

Starting point / motivation

In comparison to conventional bridges with bearings and expansion joints, the integral bridges exhibit many advantages in regard to the construction procedures and costs. With integral bridges, a lower life-cycle cost is achieved. It can be found that the popularity of the integral bridges clearly increases internationally. In numerous countries, guidelines were published to facilitate the use of this kind of structural system and construction method.

However, these issues are mostly limited to the construction of new bridges. For the adaptation of existing buildings, no generally approved approach is available.

Furthermore it can be assumed that with the situation of the existing bridges and the fact that Austria has already disposed of the compact road and railway system, the main focus in close future will lie in the rehabilitation or refurbishment of existing bridges and not in erection of new construction.

Accordingly, the focus of this research project is on the adaptation of existing bridges. However, the gained knowledge can be transferred without further advancement in the design of new constructions.

Contents and goals

The adaptation of conventional bridges with bearings and expansion joints to integral bridges means an essential change of the static system. In this occasion, as a function of boundary condition like building length, ground conditions, etc strengthening can be necessary at different places of the structure.

If the extent of the strengthening is very big, the economic efficiency of the elective measure could not be realized any more compared to building a new structure. Generally, rehabilitation should not be more expensive than the construction of a new structure.

With the help of the evaluation of the results from a literature review and a collection of experiences gained at the road administrations and engineering consultants as well as an extensive structural analysis taking into account essential parameters, a recommendation was carried out for the adaptation of the conventional bridges to integral bridges.

Methods

Essential construction details (e.g., frame corner and concrete hinge) were examined considering the possibility for the usage of high performance concrete for the optimization of the load bearing capacity as well as the durability.

The design rules for the construction details were also suggested. The development of a deformable slip plate for integral bridges with large length is in another focus of this research project. With the results of this project the road administrations as well as structural engineers should be decisively supported by their search to achieve an optimal solution to the rehabilitation and strengthening of existing bridges.

Results and Conclusions

According to the results of the realised parametric study the necessity of supplementary measures for the conversion of conventional bridge structures into integral structures could be verified. Furthermore it was shown that a more detailed analyse is important to avoid the formation of crack by the lowering of constraining forces. Thus, resulting in a spare of unneeded reinforcements, which is special useful for components with little dimensions.

Based on the results, more planning reliability will be reached for the realization of integral bridges.

• Univ. Prof. Dr. Viet Tue Nguyen, Technical University Graz – Institute for concrete construction
• Technical University Vienna – Institute for supporting structure– concrete construction

Technical University Graz - Institute for concrete construction
Univ. Prof. Dr. Viet Tue Nguyen
Tel.: +43 (316) 873-6190
E-Mail: tue@tugraz.at