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Is there a reference to look at explaining the effect of bearing surface on loadpath?

For example, an existing structure has a suboptimal load transfer/distribution. A new support is added to add/improve integrity. How the loadpath will change, should the surface of the new support press hard against the existing structure or just slightly to guide the load?

See the diagram below.

loadpath sketch

Giuseppe Cimadoro
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1 Answers1

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Frame Action

If you attached the additional support snugly without releasing the built-in stresses in the original support structure, then the state of the bearing of the new support will depend on the load and the deformation that come after the addition. Note that the stresses in the original support will continue to increase, albeit at a reduced rate.

However, the entire load on the beam, including self-weight, will be shared equally by both the original and the additional supports, if the stress in the original support structure is fully released by "jacking" and "repositioning" operations prior to and after the addition is in place.

Composite Action

Another requirement to ascertain the proper transfer of loads from the existing structural element to the new element is to develop the composite action between the two elements through adding connectors/shear studs and careful grouting at the interface. Without such, while beam-column joint can be fully in contact, separation could occur in between the existing structure and the additional beam element, as they literally act independently from each other, thus the state of stress at the interface is highly uncertain.

r13
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  • Thanks, insightful. Essentially 1) over to me the constant deflection would load the new supports, 2) if the new support is properly connected it would start sharing the load immediately. That is my interpretation of your description. What is the place of the force follows stiffness in this case? – Giuseppe Cimadoro Mar 15 '22 at 12:40
  • Let's look from the side, even perfectly constructed, the wall will take more load than the steel frame because the latter will settle more, and the settlement will cause an additional moment on the brick cantilever. As a result, the load on the steel frame will decrease accordingly. But the effect is usually ignored in practice because the change in load is usually insignificantly small, – r13 Mar 15 '22 at 13:25
  • so, the new support would just aids in case the masonry stress due to bending moment would become unbearable? – Giuseppe Cimadoro Mar 15 '22 at 16:23
  • Yes, if the steel frame is placed loosely. Jacking the existing structure prior to frame installation, and lowering it after installing the frame will solve this issue. – r13 Mar 15 '22 at 16:46
  • to your knowledge are there theoretical resources about this process (i.e. releasing stress to move the load path of a structure?) – Giuseppe Cimadoro Mar 16 '22 at 17:39
  • This is a practical solution based on the understanding of the structural behaviors in/through theory. An engineering mechanics and structural analysis textbook will be a good start. Schooling is the most direct route. – r13 Mar 16 '22 at 17:57