a PhD thesis at the College of Engineering at the University of Basrah discussing (studying the strength and bending behavior of composite concrete beams)
The thesis submitted by the student Haider Kadhem Udday dealt with conducting the research to study the behavior of
Flexion and shearing of two-layered lintels. Fitted beams for bending test: Twelve concrete beams were evaluated with two different layers of concrete as a simple study under four loading points. The lintels are constructed from two different types of layers
concrete, one of which is of normal weight concrete (NWC) and the other of light weight concrete (LWC).
The studied variables are the ratio of the thickness of the lightweight concrete layer to the total depth of the lintel (hew/h)
, compressive strength of concrete regular and lightweight. The lintels were divided into four groups. The first was based on the ratio of the thickness of the lightweight aggregate concrete layer to the total depth of the lintel, while the second and third groups were for a study. 
The effect of compressive strength of ordinary and lightweight aggregate concrete in the compressive zone. 
The last study was conducted to study the compressive strength of lightweight aggregate concrete in the tensile zone. 
The thesis aims to study the compound reinforced concrete beams. 
The thesis concluded that the ratio of the theoretical value to the experimental value
It has a maximum value of 104% and a minimum value of 94% with an average value of 98%.
Regarding the strength of the shear beams, the results of the finite element method were in agreement with the experimental results.
The average value of the final experimental to theoretical load ratio is 105%.