Thu, 2014-05-08 12:50 — Riyad Abdel-Karim

Research Title:

Finite Element Analysis of Reinforced Concrete Cross-vault Shells Research Abstract:

Thousands of years ago, man had discovered the idea
of using vault systems, built in stone to cover large areas. The Romans used
the vault system widely especially in the construction of roofs of thermae.

One vault system is that system which is constructed by two intersecting cylindrical
vaults known as cross-vault system.

Muslims also used this system especially to cover large areas of the
holly places (mosques) and it became a tradition in the construction of mosques
for hundreds of years. In modern architecture, shell structures occupy a place
of increasing importance because of their strength, economy, and architectural
form.

At the end of previous century and the beginning of
this century, some scholars started to study the distribution of stresses in
plates and shells. Their studies showed that in most cases the shells are under
compression.

The vast use of concrete nowadays, which has good
strength under compression and weak strength under tension, encourages the use
of concrete as a new material for the old structural conception of shells.

Prior to the 1970s engineers used the membrane
theory to analyze cross-vault shells. Based on a statically determinate
analysis neglecting bending stresses, this theory gives uniform in- plane
shearing stress resultants on all element sections parallel to the edges. At
45° from the boundaries these forces resolve into the principal compressive
stresses resultants in the convex parabolas implying that the hyperbolic shell
carries the vertical load through arch action.

In this paper , the Finite Element Linear Analysis is used to study the stress
distribution in cross vault shell model and finding the best geometry of this
type of structures that leads to the minimum tensile stresses at the surface of
the shell, and puts all elements in that surface under compression

The Finite element analysis is made using an available
and widely used software program called STAAD III and a triangular three noded
element is assumed in the analysis.

Finite element analysis have shown that the shape
of the cross-vault shell is very proper in getting compressive stresses only
and membrane theory assumption for the behavior of cross vault shells is
incorrect at certain sections, and the junction between two shell surface leads to a large stress
concentration So, this paper proposes a des. Based on these observations in
which small crown beams at the shell junctions introduced and material is added
near the supports to reduce high stress concentryti that results at this corner
and free edges for the shell.