Structural Engineering Slide Library

Set D: Truss Structures

This set of slides illustrates many of the important aspects of truss systems as used in bridge and building construction. Sets B: Arch Structures and C: Cable and Suspension Structures have already illustrated the use of trusses in arch and suspension structures, as both of these systems being inherently flexible need to be stiffened to resist shear and moment. Slides from both of these sets can be used effectively in discussing the use and geometry of trusses. This set features structures where the prime load-carrying mechanism is the truss; hence the emphasis is on medium and long-span bridges, tall buildings, or buildings where spans are large or loadings are heavy. This set covers the following general topics:

• Truss geometry and response
• Bridge trusses: Pin-jointed
• Bridge trusses: Lift bridge
• Bridge trusses: Simply supported
• Bridge trusses: Bascule truss bridge
• Bridge trusses: Cantilever
• Bridge trusses: 3-pinned truss bridge
• Bridge trusses: Cantilever and suspended span
• Bridge trusses: Continuous
• Crane structure
• Building trusses: Simply supported
• Building trusses: Two-directional
• Building trusses: Balanced cantilever
• Building trusses: Bracing for vertical shear
• Building trusses: Bracing for horizontal shear
• Building trusses: Space frames

Understanding the arrangement of members in a truss and their function is essential for a thorough understanding of truss systems. This is best accomplished by taking sections and using statics on free body diagrams. Many of the slides in this set are ideal for this purpose as their geometry is relatively simple even though the structures may be large. In many of the modern high-rise buildings, the shear bracing for wind or seismic forces is visible and shows clearly the importance of a continuous shear system from the point of origin of loading to the point of support. Large bridges tend to look more complex on account of the need for bracing compression members against buckling, but a careful study will reduce the complexity to the essentials of the framing geometry. As such they are amenable to the same simple free-body approach.

This set starts with a statically determinate five-span bridge to introduce many of the aspects of truss design. It is a Warren truss and includes a simply supported lift span, cantilever and suspended span side spans. The towers include both Warren and K-bracing. Close-up details include hinged and rocker supports, and pinned and riveted connections. From this structure the slides progress through truss bridges and buildings and end with more complex examples of highly indeterminate space frames.