Name: locating the beam’s highest deflection
Uploaded: 2024-05-23T13:00:03.000Z
Duration: 1 min 13 s
Channel: JoVE

Prenons l’exemple d’un train qui se déplace sur un pont. Ici, une charge asymétrique est appliquée à une poutre supportée où la déflexion maximale ne se produit généralement pas au milieu.
La déviation maximale de la poutre est calculée en identifiant le point O sur la courbe, où la tangente de la poutre est horizontale.
La pente de la tangente au point X est déterminée en calculant l’écart tangentiel entre les appuis et en le divisant par leur distance.
Comme la pente au point O est nulle, la pente entre O et X est égale à la pente négative en X.
Le premier théorème moment-aire est utilisé pour localiser le point O en mesurant une aire sous le diagramme M/EI égale à la pente négative au support X.
La déflexion maximale est égale à la déviation tangentielle de l’appui X par rapport au point O. Cette valeur peut être obtenue en calculant le premier moment relatif à l’axe vertical passant par X de l’aire entre X et O.

déflexion maximale

Lors de l’analyse de poutres soumises à des charges asymétriques, comme un train se déplaçant sur un pont, il est primordial de déterminer avec précision les points de contrainte et de déflexion maximales. Le processus consiste à identifier la déflexion maximale de la poutre, qui ne se produit pas toujours en son point médian en raison de la répartition inégale de la charge.

La déflexion maximale se produit en un point spécifique, appelé point O, où la tangente à la courbe de déflexion est horizontale. Pour trouver le point O, la pente de la tangente en tout point X donné le long de la poutre est examinée. La pente au point X peut être calculée en considérant l'écart tangentiel entre les supports et en le divisant par leur distance. Cette pente est nulle au point O, indiquant l'emplacement de la déflexion maximale.

Le théorème du premier moment d’aire joue un rôle clé dans la localisation du point O. Selon ce théorème, l'aire sous le diagramme des moments de flexion entre deux points quelconques le long de la poutre correspond au changement de pente entre ces points. Le point O peut être identifié en calculant cette aire jusqu'à la pente négative au niveau du support X.

Une fois le point O déterminé, la déflexion maximale est calculée en analysant la déviation tangentielle du support X par rapport au point O. Cette approche fournit une méthode systématique pour évaluer le comportement structurel des poutres sous chargement asymétrique, garantissant la sécurité et la stabilité des structures telles que les ponts ferroviaires.

Déflexion maximale

Prenons l’exemple d’un train qui se déplace sur un pont. Ici, une charge asymétrique est appliquée à une poutre supportée où la déflexion maximale ne se produit généralement pas ...

Education

Enseignement

JoVE Core

Mechanical Engineering

Génie mécanique

Unit 1

Unité 1

Deflection of Beams

Flèche des poutres

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Maximum Deflection

locating the beam’s highest deflection

Maximum deflection in a supported beam depends on where the load is placed. With an unsymmetrical load, such as a train moving across a bridge, the beam may bend most at a point that is not the midpoint. Finding that point is important for judging stress and deflection in the structure.

The point of maximum deflection is called point O. At point O, the tangent to the deflection curve is horizontal. That means the slope is zero there. To locate point O, the slope at any point X along the beam is examined.

The slope at point X can be found from the tangential deviation between the supports divided by the distance between them. When this slope becomes zero, point O has been reached. The First Moment-Area Theorem helps with this step. This theorem says the area under the bending moment diagram between two points equals the change in slope between those points.

Point O is identified by using that area up to the negative slope at support X. After point O is found, the maximum deflection is calculated by studying the tangential deviation of support X about point O. This method gives a clear way to analyze beams under unsymmetrical loading and helps support the safety and stability of structures like railway bridges.

Locating the Beam’s Highest Deflection

deformation of a beam under transverse loading

deformation-of-a-beam-under-transverse-loading

Beam Deflection from Loads and Supports

Beam deflection depends on the loads on a beam and the support conditions at its ends. For indeterminate beams, especially those with overhanging parts and multiple concentrated loads, careful analysis is needed to predict how the beam will bend. The first step is to draw an accurate free-body diagram. A free-body diagram shows the forces and moments acting on the beam. It helps reveal how the bending moment changes along the beam length. The bending moment diagram also shows how the beam...

equation of the elastic curve

Beam Deflection and Boundary Conditions

Beam deflection and boundary conditions help describe how a beam bends under load. In structural engineering, the curvature of a plane curve shows how sharply the beam bends. That curvature is found from the curve’s first and second derivatives. A cantilever beam with a point load at its free end is a common example. A diving board works like this type of beam. When slopes are small, the beam’s elastic curve becomes the main shape used in the analysis. The governing equation connects bending...

elastic curve from the load distribution

Beam Deflection Under Distributed Load

Beam deflection under distributed load is a key part of beam analysis in engineering. It helps predict how a beam bends and reacts when a load is spread along its length. Engineers use this relationship to judge whether a structure will stay safe and functional. The analysis starts with the link between load, shear force, and bending moment. These quantities can be written in differential form. When beam flexibility is treated as constant, further differentiation leads to a higher-order...

deflection of a beam

Beam Slope and Deflection by Singularity

Beam slope and deflection can be found with singularity functions when beam loading is hard to write as one simple equation. This method is useful in structural engineering because it helps describe beams under several loads without breaking the problem into many separate cases. Singularity functions are mathematical tools for showing discontinuities in a load, shear force, or bending moment equation. They are especially helpful when a load acts at a single point or over a set interval. In the...

method of superposition

Beam Deflection Under Combined Loads

Beam deflection under combined loads can be found with the method of superposition. This structural engineering method is used to analyze how multiple loads affect a beam. It works by finding the slope and deflection from each load separately, then adding those results together. The method applies only when the beam stays within its elastic limit. In that range, the material deforms in a linearly elastic way. That makes it valid to combine the effects of separate loads without changing the...

moment-area theorems

Beam Deflection Using Moment-Area Rules

The moment-area theorems help describe beam bending in structural engineering. They are often used for building floor supports and other beams under load. The theorems use the elastic curve, which is the shape a beam takes as it deforms. The first theorem links slope change to area on an M/EI diagram. Here, M is the bending moment, E is the modulus of elasticity, and I is the moment of inertia. When M/EI is plotted along the beam length, the area under the curve gives the total rotation...

beams with symmetric loadings

Moment-Area Method for Cantilever Deflection

The moment-area method is used in structural engineering to find the slope and deflection of a beam under load. It is especially useful for a cantilever beam with a concentrated load and a moment at the free end. The analysis begins with a free-body diagram. This diagram helps calculate the reactions at the fixed end. After that, the bending moment diagram is drawn to show how the bending moment changes along the beam. Points where the bending moment is zero are important in this step. Next,...

beams with unsymmetric loadings

Beam Deflection and Level Points

Beam deflection and level points can be found for a supported beam under unsymmetrical loadings using moment-area theorems. This type of analysis helps show how a beam bends when forces are spread unevenly along it. It is an important part of structural engineering because it links load patterns to beam response. The first moment-area theorem is used to find the slope at any point on the beam. It states that the change in slope between two points equals the area under the moment diagram over...

maximum deflection

Maximum deflection in a supported beam depends on where the load is placed. With an unsymmetrical load, such as a train moving across a bridge, the beam may bend most at a point that is not the midpoint. Finding that point is important for judging stress and deflection in the structure. The point of maximum deflection is called point O. At point O, the tangent to the deflection curve is horizontal. That means the slope is zero there. To locate point O, the slope at any point X along the beam...

key terms and concepts

Learn how unsymmetrical loads shift the point of maximum deflection in a supported beam and how the First Moment-Area Theorem helps locate it.

Locating the Beam’s Highest Deflection | JoVE K12

JoVE Core Mechanical Engineering offers concise, easy-to-understand animated videos covering key topics such as equilibrium, forces, truss analysis, and structural mechanics. Explore their real-world applications, and witness these concepts in action through scientist-led experiments.

mechanical engineering

Locating the Beam’s Highest Deflection

Description

Transcript

Tags