fixed and pinned supports

[abdallah hamdan]

if I have a beam with pin supports (columns) as in fig (1)

Is having a weight P due to the existence of upper floors on the beam sides as in fig 2, lead the beam to act as there is fixed support on both ends?

 

[BAretired]

I might add that the same confusion arises with the term "pinned". A beam may be pinned to a column. That does not mean that the beam has a pinned support, because the joint may translate when the column bends. A pinned support permits free rotation, but prevents translation.

BA

 

[dik]

Concur... but with a slab to a stair or elevator core, the relative stiffness of the slab to the core, nearly makes them fixed.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EngDM]

Wl/8 midspan, Wl/16 at supports. That should do it, unless the support is truly fixed, which is rare.

Depending on the conditions the concrete is poured (monolithic or otherwise) with end conditions the negative bending an be greater than WL/16 for concrete beams.

CDH 4th Edition

 

[human909]

I think some clarification is needed. The OP is referring to Fig. 7.14A of SP34, "Handbook on Concrete Reinforcing and Detailing" in which the term "FIXED" is used.

A beam may be fixed to a column, meaning that the beam and column are rigidly connected, hence have equal rotation. That does not mean the beam has a fixed support, because, as hokie66 pointed out, the joint will rotate when load is applied to the beam. The amount of rotation depends on the stiffness of all members meeting at the joint.

I might add that the same confusion arises with the term "pinned". A beam may be pinned to a column. That does not mean that the beam has a pinned support, because the joint may translate when the column bends. A pinned support permits free rotation, but prevents translation.

Agreed. This difference seems to have ended up with different answers in both this thread and the "moment / fixed connection" thread also discussed in the last couple of days.

Part of the difference comes down to peoples work flow. If your design approach does not incorporate full frame analysis then assuming joints as fixed can lead to unconservative outcomes even if the connection itself is effectively fixed.