Reinforcing existing timber beam

[mats12]

Hello,

The existing timber roof beam in 18/20 cm - the span is 6 m.

The existing beam will be reinforced with additional timber beam beneath and steel channels as shown in the attached image.

Question: can reinforcing elements start/end at the face of the support (drawing A) or it should continue on top of the support (drawing B)?
Regarding bending moments I think the drawing A is sufficient but I'm not so sure about shear forces near the support.
Is there a way to solve this without removing parts of the existing wall - supports?

 

[mats12]

Any help?

 

[milkshakelake]

You assumed pinned, so you have zero moment at ends and your reinforcement doesn't necessarily need to continue over the support. However, I would check shear separately with the unreinforced section only. If shear doesn't work with that, then you need to extend the reinforcement over the wall, or provide some kind of other way to resolve that shear into the wall.

In my experience, the shear might fail without the reinforcement. With steel, shear may pass over an unreinforced support because of the high amount of shear resistance provided by a steel beam web. With wood, it's not the same case. Shear might very well control. The way I see you doing the reinforcement, I'm like 90% sure shear will fail in the unreinforced area by visual inspection. However, I can't read kN, so who knows (I'm a silly American). The numbers look high to me, that's all.

 

[KootK]

Question: can reinforcing elements start/end at the face of the support (drawing A) or it should continue on top of the support (drawing B)?

The trick to this is to recognize that, if the reinforcing does not extend over the supports, then there will be a concentrated demand for fastening at the ends of the reinforcing. Both shear and tension. So you may need grouped fastening at the ends (which you are already showing). This is precisely why we take the reinforcing over the supports whenever that is practical.

The closer the reinforcing gets to the supports, the less will be the demand for concentrated forcing. So you'll probably be in pretty great with what you already have planned.

 

[AKSherpa]

If needed I would consider extending the upper portion of the reinforcing steel over the existing end suports in effort to gain adequate shear strength without removing part of the existing wall. If necessary the steel over the supports could be "beefed up" to provide additional shear strength.

 

[XR250]

Are you trying to get composite action between the upper and lower wood members? If so, I would be concerned about a in-plane grain failure. Looks like you have room for larger channels. May make sense to do non-composite with just the original beam and the channels.

 

[north_man]

The trick to this is to recognize that, if the reinforcing does not extend over the supports, then there will be a concentrated demand for fastening at the ends of the reinforcing. Both shear and tension. So you may need grouped fastening at the ends (which you are already showing). This is precisely why we take the reinforcing over the supports whenever that is practical.

The closer the reinforcing gets to the supports, the less will be the demand for concentrated forcing. So you'll probably be in pretty great with what you already have planned.

Is the fastening just based off the shear force diagram?