Aims Subject

Chapter 6. Equilibrium of rigid bodies

A rigid body is said to in equilibrium if the resultant of all forces and all their moments taken about any and all points are zero.

Free body diagram (FBD): depiction of an object with ALL the external forces acting on it.

Reactions coming from the supports: usually a body is constrained against motions using supports. It is essentially to correctly estimate the number and type of reactions that a support can provide.

equilibrium-of-rigid-body from Rudi Wicaksana

A slide-share presentation about equilibrium can help you to understand the key concepts of this chapter:

Aims Subject

Chapter 11. Structural members: beams


11.1 Isostatic beams. Introduction.

11.2 Reactions at supports.

11.3 Types of loads on beams.

11.4 Internal forces in beams. Sign convention.

11.5 Loads, shears and axial forces.

11.6 Bending moments.

11.7 Graphical analysis of a beam.

11.8 Elastic curve of a beam.

You should learn to solve any isostatic plane beam after the theoretical lectures, the problem sessions and the homework you did during this part of the subject. Chapter objectives can be  summarized as follows:

  • To show how to use the method of sections to determine the internal loadings in a member.
  • To generate this procedure by formulating equations that can be plotted so that they describe the internal shear and moment throughout a member.
  • To draw the shear and moment diagrams for any isostatic plane beam.

The next video explains how to solve a beam using the method of sections (Spanish from a Professor at the Universitat Politècnica de València).


Rodes Roca, J. J., Durá Doménech, A. i Vera Guarinos, J., Fonaments físics de les construccions arquitectòniques (Publicacions de la Universitat d’Alacant, Alacant, 2011). Capítol 12.

Rodes Roca, J. J., Exercicis i problemes dels fonaments físics d’arquitectura. I. Vectors lliscants i geometria de masses (ECU, Alacant, 2009)

Rodes Roca, J. J. i Durá Doménech, A., Exercicis i problemes dels fonaments físics d’arquitectura. II. Estàtica aplicada a les estructures (Col·lecció Joan Fuster 154, Universitat d’Alacant, 2013)

Tipler, P. A. i Mosca, G., Física per a la ciència i la tecnologia, Volum 1 (Reverté, Barcelona, 2010). Capítols 1 i 12.