|M.Sc Student||Elmelech David|
|Subject||Analysis and Design of Composite Bridges - Plate Girder|
with Concrete Deck
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Yeoshua Frostig|
|Full Thesis text - in Hebrew|
Composite bridges made of concrete slab and steel girders combine the advantages of the two materials, namely, the high tensile strength of the steel beams and the compressive strength of the concrete slab. The high ratio of the steel strength to its own weight makes it possible to execute bridges of large spans and provides design flexibility (for example the use of launching, hoisting and casting on site) with minimalist appearance, high engineering efficiency, simpler sub-structure in areas of weak soil conditions, reduction of the superstructure weight which leads to the reduction of earthquake forces, high quality of work and reduced on-site working time.
In Israel, composite bridges are rarely executed due to several reasons, such as the lack of knowledge, inexperience and inaccurate preconceptions regarding maintenance requirements.
This thesis reviews various aspects related to the design, analysis and construction of composite bridges from European and American standards, research and current practical international experience, since the execution of an efficient, elegant and economical composite bridge is dependent on both the accurate knowledge of the intricacies found within the standards and regulations as well as further knowledge and engineering experience.
Generally, the execution of the superstructure is divided into two main stages. The first stage consists of the steel beams that are launched into their position throughout the bridge spans or alternatively are hoisted and positioned in their final location . The second stage is casting of the concrete slab.
The casting stages are very important since they influence the response of the structure deformations, stiffness, shrinkage, creep etc. Therefore, the Eurocode EN1994-2 requires to examine the influence of each casting at Service Limit State (SLS), Ultimate Limit State (ULS), and to perform global analysis for each of the different types of sections.
The functionality and structural resistance of the composite bridge is strongly dependent on the chosen connection method between the two materials. If the connections are not fully fixed, cracks will be formed at the interface between the two materials at low stress.
The time effects on the composite bridge are associated with the variability of stresses and stiffness through the beam height due to creep and shrinkage. The variability in stiffness may be explained by:
• The cracked concrete above the piers, as such the concrete in this zone cannot lose its stiffness over time.
• The effect of creep and shrinkage over time on the compressed concrete slab in the middle of the spans that decreases the slab stiffness.
• The redistribution of the moments and forces from the span to the piers
Owing to these advantages, composite bridges provide a superior alternative to concrete bridges especially in seismic regions and are efficient, elegant and cost- effective.