AL-Mustansiriyah University Reinforced Concrete Design II Civil Department \ 4th
class
Collage of Engineering Undergraduate / Course Ass. Prof. Dr. Hadi Nasir AL-Maliki
Semester I [90] 2018 /
2019
Yield Line Theory
Introduction:
An elastic analysis of a reinforced concrete slab gives no indication of its ultimate load
carrying capacity and further analyses have to be made for this condition. An exact
solution for the ultimate flexural strength of slab can be found only rarely, but it possible
to determine upper and lower bounds, to the true collapse load.
The yield line method of analysis gives an upper bounds to the ultimate load capacity of
a reinforced concrete slab by a study of assumed mechanisms of collapse. This method
developed by JOHANSON (1940s), is powerful tool for estimating the required bending
resistance and hence the necessary reinforcement especially for slabs of non-regular
geometry or loading.
Two approaches are possible in yield line theory:
1-Energy Method:
External work done by the loads during the small virtual displacement of the collapse
mechanism is equated to the internal work done by the resisting moments.
2-Equilibrium Method:
Equilibrium of the segments or parts of slab into which the slab is divided by the yield
lines.
Plastic Analysis:
Plastic behavior of the material describes the deformation of the body undergoing
nonreversible changes of shape in response to applied forces. The main task of the
structural engineering is to design the structural members so they can carry the loads
under all possible conditions including ultimate limit states. The elastic distribution of
stresses can be obtained by solution of the elasticity problem. However the structural
elements do not behave elastically near ultimate load and bending capacity of section is
based on a plastic analysis.
