Application of FRC/ECC in integral bridges

Abstract

The focus of this study is to research if ecc/frc is applicable for integral bridges. Integral bridge are bridges without or partly without intermediaries. A bridge normally consist of a substructure, superstructure and intermediaries. The superstructure comprises the bridge deck and the substructure consist of the abutments, piers and the foundation. The intermediaries are expansion joints and bearings which enables the bridge to deform and/ or to transfer the deformation and loading from the superstructure to the substructure. With or without intermediaries leads to different structural systems. A bridge with these intermediaries is called a ‘conventional bridge’ and a bridge without these intermediaries is called a ‘fully integral bridge’. There are also structural systems in between a conventional bridge and a fully integral bridge. (see chapter 1) Integral bridges have been built in the United States, Canada, Australia and several countries in Europe. The choice for an integral bridge over a conventional bridge depends strongly on the length of the bridge, the bridge location, the climate and the requirements of the bridge and the road. In some states of the U.S., integral bridges are preferred over conventional bridges. Hence, more than 1000 integral bridges have been built in the U.S. including the longest steel and concrete integral bridges. Some states in the U.S. prefer integral bridges over conventional bridges, because in their experience the elimination of expansion joints and bearings leads to a more durable structure and less maintenance. The maximum bridge length is disputed by the State engineers. Normally the allowable length is between 60 and 180 meter depending on the state limitations. (See section 3.1) Integral bridges are not used as a common practice in the Netherlands. The preferred structural system is a conventional bridge. The integral bridges that have been built, seem to be a choice of the designer. Most of the integral bridge that have been built, are single span bridges. (See section 3.1) All construction elements of an integral bridge are monolithically connected. This results in one integral system where there is interaction between the sub- and superstructure and between the bridge and the embankment soil. This is an important difference compared to a conventional bridge, where the sub- and superstructure function more like single structural systems. The structural system of an integral bridge can be schematized as a portal frame. In this case the beam of the portal frame is the superstructure and the columns comprise the substructure. In a portal frame, deformation in the beam will cause deformation in the columns. The deformation that occurs in the bridge deck of the integral bridge is caused by loading, temperature influences and time-related material effects. These loads and effects will cause the following rotations and displacements in the structure (see section 3.2): -Vertical displacement and rotation (weight of the bridge, asphalt, traffic) - Rotation (temperature gradient daily cycle) - Contraction (shrinkage, creep, elastic shortening prestressing) - Expansion (temperature yearly cycle) An integral bridge is a durable structure due to the absence of expansion joints and bearings. However, without expansion joints and bearings the bridge deforms into the soil due to the deformation of the bridge deck. The deformation of the bridge deck is caused by the temperature influences and time-related material effects. The time-related material effects are shrinkage, creep and elastic shortening in case of a prestressed concrete element. These effects are responsible for deformation of the bridge deck in time. The temperature influences lead to a cyclic behaviour. This behaviour could be divided in two cycles, namely a yearly and a daily cycle. Both cycles causes cyclic deformation of the bridge deck. This deformation of the bridge deck is only possible if the bridge is able to deform into the soil. This may imply certain problems, because the soil is not rheological. These problems are (See also section 0 and chapter 4): - Settlement of the soil close to the abutment ‘bump in the road’ - Asphalt/pavement problem - Foundation/piles - Early age cracking - Wing walls - Cracking of the abutment stem or the bridge deck at the abutment The major goal of this thesis is to investigate if the application of frc/ ecc in the connection of integral bridge has advantages. Fibre reinforced cementitious composites could be distinguished from conventional concrete due to the application of fibres. The application of fibres leads to some interesting properties, for example a higher strength, more ductility, more toughness, durability, higher stiffness and thermal resistance. FRC composites could be distinguished in ‘hardening and ‘softening’. An FRC composite has ‘hardening’ when the structural strength is equal to or greater than the cracking strength. This means that after the first ‘crack’ the tensile strength of the FRC composite is still increasing. This hardening can also occur under bending, and then the FRC composite is called ‘deflection-hardening’. When this hardening occurs under tension then the FRC composite is called ‘strain-hardening’. An FRC composites has ‘strain-softening’, when the tensile strength declines after the first crack. (see chapter 6) There is chosen to apply the FRC composites in the connection. A major motivation is to reduce reinforcement in the connection between the sub- and superstructure. This is firstly investigated by constructing strut-and-tie-models (STM) and string-panel model (SPM). The STM and SPM showed that influence of foundation pile on the connection is decisive. Two mechanisms could describe for the structural behaviour of the foundation pile in the connection. The first mechanism is the transfer of forces and moments by friction between the foundation pile and the surrounded concrete (Figure 7-4A) and the second mechanism is the transfer of forces and moments by a coupling force (Figure 7-4b). Both mechanisms are analysed by using the STM and SPM. This provided a good image of the flow of the forces and stresses in the connection. (See chapter 7 and appendix A) The 2D FEM is developed on basis of the results of the STM and the SPM and the building project ‘bridge Schokkeringweg’. The forces, the moment, the boundary conditions and the dimensions are based on the calculations of the ‘bridge Schokkeringweg’. The research focuses on the two mechanisms. Therefore, friction and cohesion between the foundation pile and the surrounded concrete and the horizontal reinforcement in this area are taken as variables. The results show that the strength of the connection depends mostly on the horizontal reinforcement and cohesion and friction have almost no influence. (More about the conclusions, see section 8.6) The next step was to investigate the effect of the FRC composites on the 2D FEM. The FRC composites used in this research are classified on basis of tensile strength, strain and ‘hardening or softening’. For this research, a 2D FEM with and without horizontal reinforcement in the area of the foundation pile is used. The results show that FRC composites leads to an improvement of the rotational stiffness of the connection and for 2D FEM without horizontal reinforcement also to a higher structural strength of the connection. However, the improvements are minor and therefore it is advised to not apply FRC composites in integral bridges. (see section 9.4)