![]() In many such cases it will be more economic to use plate girders.Ĭomposite plate girders can be used for the great majority of medium span bridges. However, Universal Beams can only be used for spans close to the upper end of these ranges if girder spacings are reduced considerably. 1.3 Range of ApplicationĬomposite bridges with Universal Beams can span up to 30 m for simple spans and up to 35 m for continuous construction. One of the more specialist applications is in the design of ramps for access to roll-on/roll-off ferries. Non-composite steel plate girder and beam bridges can be used to carry highway, railway or pedestrian loadings. The deck may either be concrete, supported by and usually acting compositely with steel cross-girders, or orthotropically stiffened steel.Ĭomposite girder bridges are primarily used for highway or footbridges. More commonly non-composite plate girders are used for the half-through or through girder bridges shown in Figure 2. Such structures can only be justified where there is an overriding need to minimise the structural weight. Non-composite bridges can adopt any of the structural forms shown in Figure 1 with the concrete slab replaced by an orthotropic steel deck. However this system does require substantial cross-bracing which considerably reduces the overall economy. The longitudinal shear resistance from the two main girders is now limited to the minimum required. The stringer, much shallower than the main beams, has to be supported by robust cross bracing. The presence of the stringer reduces the slab support spacing to that for multiple girder bridges. There is effectively no upper limit to the width of this form of construction.Īs an intermediate solution the twin girders with intermediate stringer cross-section shown in Figure 1d has also been developed. Cross girders are therefore introduced, as shown in Figure 1c. These are now much more widely spaced, and the slab will usually be haunched to provide sufficient transverse bending resistance.Īt larger girder spacings the required slab thickness is increased beyond its economic limit. In Figure 1b the economy in shear has improved considerably because there are only two girders, the minimum number possible. If the webs are reduced in thickness so that they are more highly stressed they will require considerable, expensive stiffening. However, its economy is reduced because there is much more shear capacity than is required, i.e. This form of construction is very simple and is widely used. In Figure 1a the closely spaced main girders directly support a deck of uniform thickness. ![]() Figure 1 shows the basic types of composite bridges. ![]() Plate girders and beams are utilised in a range of bridge forms. The distribution of material within the beam or plate girder cross-section is carefully selected to meet this requirement: material required to carry bending stresses is located at the upper and lower extremities of the cross-section for maximum efficiency, whilst the (usually deep) web panel separating the flanges is normally assumed to resist the full shear load applied to the section.ĭepending on the spans involved, the loading intensity, costs of steelwork fabrication and any particular geometric and/or aesthetic requirements of the structure, a decision must be taken as to whether commercially available rolled beam sections or fabricated girders are to be used. Unlike the arch, the beam supports applied loads primarily in flexure and associated shear. The simple beam is perhaps the most basic though not necessarily the most efficient form of bridging member. It offers guidance for detailed design from global analysis to important details. It discusses the means by which girders can be stabilised against lateral-torsional and distortional buckling. It gives guidance for initial sizing of the most popular forms of construction. It discusses overall layouts, types of continuity, girder proportions, longitudinal and cross girder spacings and choice of deck slabs. This lecture identifies the principal types of composite and non-composite plate girder bridges that are used for highway, railway and pedestrian bridges. Lecture 15B.12: Introduction to Bridge Construction SUMMARY Lecture 15B.11: Splices and other Connections in Bridges Lecture 8.4.3: Plate Girder Design - Special Topics Lecture 8.4.2: Plate Girder Behaviour and Design II ![]() Lecture 8.4.1: Plate Girder Behaviour and Design I To introduce the design of plate girder and beam bridges for highway, railway and footbridge applications. STRUCTURAL SYSTEMS: BRIDGES Lecture 15B.4: Plate Girder and Beam Bridges OBJECTIVE/SCOPE
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