# Questions tagged [beam]

Questions about the theory and applications of structural elements designed to resist bending.

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### Is it structurally sound to cut an I beam to a T on one end?

I'd like to confirm whether the replaced beam in the attached picture is structurally sound given the end was cut to a T instead of an I. I had a qualified structural engineer approve the work but I'm ...
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### Easy nonlinear model for large deformation of a beam

I have a beam subject to twisting and/or bending forces as well as linear compression force along its main axis. It is modelled as an isotropic beam, but if anisotropic is not too far off then that's ...
6k views

### At what point does an I-beam becomes a H-beam?

According to BS5950, a beam section can be classified as plastic, semi-compact, compact or slender. For the same section area, a H-beam can take axial compression (without buckling) better than an I-...
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### How do I calculate the forces on a desk and its legs?

I have a design for a desk, and I'd like to not just guess at how strong it'll be, but I can't find an explanation on how to figure out all the forces involved that doesn't assume I already know a lot ...
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### Buckling: Do buckling mode shapes of n > 1 occur in reality?

In the buckling of columns we know that: $$P = \dfrac{n^2\pi^2EI}{L^2}$$ The smallest value of P occurs when $n=1$ which gives a simple buckling shape (one wave): $$P_{cr} = \dfrac{\pi^2EI}{L^2}$$ ...
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### Strength of a welded steel gate with vertical bars vs. crossed diagonal bars

Looking for some hints on how to create a rough estimate for the following problem. Given two steel gates with the same dimensions, same material - e.g. everything is the same. The only difference ...
6k views

### Why is it unwise to choose cylindrical horizontal beam

I heard that it is unwise to choose cylindrical horizontal beam. My question is why?
33k views

### How to deal with a point force acting right on the hinge of a beam?

I have been attempting to solve a question where there is a point force acting on the hinge of a beam. Here is the problem: I am not sure how to deal with the 2 kN point force at $C$ ($C$ and $E$ are ...
4k views

### How do you select the correct area to consiser for first moment of area calculations?

I have just begun studying mechanics of materials and I am struggling to understand intuitively how to select the area in first moment of area calculations. I was hoping someone has a relatively easy ...
3k views

### Derivation of the weak form for the euler-bernoulli beam equations

I am master student and doing an assignment of Finite element method. In the instruction I could not understand the derivation of the weak form, which should not be difficult. I'm sorry for posting ...
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### Unbraced Length for Lateral Torsional Buckling vs. Yield Strength

The AISC 360-10 Specification for Structural Steel Buildings gives provisions for calculating the maximum unbraced length of a compression flange that separates yielding moment from lateral torsional ...
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### Large deflection of a cantilever beam with distributed normal load

I have a strip of stainless steel encastree'd at one end to which is applied a constant pressure on one side, and I need to know what the deflection equation y = f(x) is at equilibrium. If the ...
910 views

### Design of transverse reinforcement in a wide beam

Besides satisfying nominal bar provision in the code, is there any special requirement in the provision of transverse reinforcement to ensure that the longitudinal reinforcement is fully effective in ...
820 views

### Tolerance for Beam With Cope End

I need to have some beams fabricated with copes on the ends. They will be set on top of existing steel trusses, and used to replace undersized purlins to shore up existing rafters (hence the need ...
432 views

### What does it mean when actual member reaction is 100% of allowed?

I received construction documents for an extensive residential remodel and looking at the engineering there's a glulam drop beam with a calculated member reaction that is 100% of allowed (3965 lbs @ 5 ...
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### Are linear beam element solutions ever exact and when are they used in practice?

In qualifying the results of a Finite Element (FE) beam model, I'm realizing that I dont understand FE beam elements as well as I should. Is there a procedure to determine what order beam element is ...
154 views

### Undesired vibration of a beam under foot traffic

The other day I was in the waiting room of a doctor's office in a new building as part of UCLA medical complex. A new construction as part of multi million dollar extension of existing medical complex ...
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### Deriving the deflection force equation for a beam that is fixed on both ends

I want to calculate the force-displacement equation for a beam that is fixed at both ends. I think I should use the superposition principle but I am not very sure how to get started. I know that for,...
172 views

### Is the order of operations in jacking a cable relevant?

If you have a prestressed concrete beam or slab and are jacking a cable from both ends, does the order of operations alter the result? For a symmetric curve, the tension diagram along the cable's ...
117 views

### Deformation of two perpendicular beams with parabolic properties

I want to calculate the deformation of the following structure: I have numbered the vertical beam 1 and the horzontal beam 2. The hight of beam 2 is given by: $h(x)=h\sqrt{1-x/L_2}$ So I thought I ...
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### Why do we assume the moment is zero when analyzing a simply supported beam?

When calculating the reactions of a simply supported beam under any type of loading we assume that the moment about the reaction points is zero. What if our assumption is wrong and in actual practice ...
116 views

### Why does concentrated shear force on a beam influence the whole beam?

This might be a silly question but can someone explain how this shear force on the right side of the beam causes Qy throught the whole beam? I understand it mathematically but not conceptually so I ...
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### Determining stiffness of a beam w/varying moment of inertia

I need to calculate $K$ or equivalent stiffness of a beam that has a varying $I$ across its length. $I$ has been given to me as a function of $x$, or length. I have been unable to find a proper ...