Just a quick update. After spending 12 months researching Masonry arch bridges I have completed part one of my dissertation which can be viewed here.
Conclusions from my dissertation are below:
"The use of finite element analysis along with calculations
using Pippard’s method with varying load spread angle, verify that the way the
load is distributed through the fill in the masonry arch bridge structure is of
key importance. When the load is concentrated at the crown of the arch, the
stresses and allowable axle load are lower than those than when the load is distributed through the fill.
If the fill material is of poor quality the load will have a
greater load spread angle distribution and will effectively act as a point load
at the crown of the arch as assumed in Pippard’s elastic method, which as shown
in the calculations in Table 3.2 the permissible axle load increase as the angle
of distribution becomes shallower the load increase, this is due to the load
being transmitted directly to the foundations of the arch.
When the fill is of good quality and well compacted, a fill
such as a limestone material the distribution of load over the length, ls becomes greater, therefore
allowing the load to be transmitted to the foundations, or in analysis terms to
the the supports, this allows a larger permissible load for the arch as
demonstrated in Table 3.2 and the arch
model shown in Figure 4.5,m the stresses with in the arch arch of considerable
difference to that in Figure 4.3, the reduction in stress is almost 50% for a
distribution at 45o modeled by two point loads at the extremities."
(to see the figures or tables referenced above please view the full dissertation on the link above)
For the second part on my dissertation I have decided to focus more on the hand calculations, consolidate them and gain a further understanding by using ansit to model the lateral pressure of the soil using horrizantal springs and supports and using different stiffness of soil to fully evaluate the stress distribution within the soil and the soil arch interaction within a Masonry Arch Bridge. Hand calculations will be based on two pin arch analysis.
I will publish more information about this later in 2013. If you would like to be kept informed please complete the contact form here.
