The group analyzed a 3D concrete overpass using MSC Patran/Nastran software. They applied a distributed load of 4,000 lb/in to simulate traffic, finding a maximum stress of 3,540 psi for the test geometry. Additional geometries were also analyzed. Applying a load of 80,000 lb/in to simulate a tractor-trailer resulted in complete failure at 71,000 psi. The analysis suggests using a semicircular archway, as it had the lowest stress of around 2,750 psi due to a larger cross-sectional area.

1. To: Professor Xu
From: Rudy Bores, David Carver, Joshua Allison
Subject: MET 411 Group Project: 3D Concrete Overpass
Date: 5/5/2015
EXECUTIVE SUMMARY:
To complete this project MSC Patran/Nastran software was used to analyze a solid concrete
overpass. To create this overpass the geometry from the overpass in exam two was used. This
geometry was utilized to create a surface that was use to create the 3D solid analyzed. This solid
was divided into sections using the plane break feature to create an area to apply the distributed
load along the tire track width of an average car. The average weight of a motor vehicle was
found to be roughly 4,000 lb and this force was applied as a distributed load along the top of the
tire track planes. This load was to simulate a worst case scenario of heavy traffic continually
moving across the bridge. The bottom surfaces of the overpass were constrained for no
displacement to simulate the base of the structure. The overpass was defined as being
constructed of portland cement and containing no additional materials or structural steel
supports. The results of this analysis produced a maximum deflection of 0.12 in and a maximum
stress of 3540 psi. This value for stress is almost half of the compressive strength of portland
cement which is 6,000 psi. This analysis was performed utilizing three additional geometries to
observe the change in the stress and deflection patterns. The geometries utilizing the rectangular
and semicircular overpass produced the lowest maximum stress values due to their larger cross
sectional areas compared to the test geometry. These two geometries produced a very similar
stress values of roughly 2,750 psi. The last geometry utilized, flush archway, attempted to move
the semicircular archway higher to reduce the cross sectional area. This analysis proved that the
cross sectional area had been reduced too much and the maximum stress produced was almost
4,400 psi. This stress occurs in two areas along the top of the overpass and are centered between
the two sets of tire tracks. This geometry threatens to cause tensile stresses at the bottom to the
archway and should be avoided. The results of this analysis seem to suggest that by lowering the
height of the flush geometry to increase the cross sectional area, the maximum stress produced
can be lowered and the structural geometry can be optimized. A final analysis was performed on
the test geometry using a distributed load of 80,000 lb/in to simulate the maximum legal load of
a tractor-trailer without any additional permits. This load produced an analysis that shows
complete failure for the overpass and producing a maximum stress of roughly 71,000 psi. This
stress is well above the compressive strength of the portland cement.

2. PROBLEM STATEMENT:
For this project it was decided that the concrete overpass structure from exam two would be
analyzed as a 3D solid structure. This solid structure is assumed to be made entirely of portland
cement and has no structural steel components. The maximum stress and displacements of the
birge will be analyzed assuming average loading conditions. The archway geometry will be
changed in an attempt to optimize the loading conditions.
FINITE ELEMENT ANALYSIS:
I) Geometry: The geometry of the concrete overpass is base off of the geometry given in exam
two. The geometry was created in MSC Patran by creating a rectangular surface and then
utilizing the subtract command to create the archway. Once the surface had been created the
extrude feature was utilized to create a 3D solid 564 in thick. Once the solid had been created it
was separated into 9 sections, to simulate the load application area, utilizing the plane break
feature. This planes were created using the 3 Point create plane feature using the input points
shown below. Alternate geometries analysed can be viewed in the additional figures section.
FIGURE 1: Overpass Geometry

3. II) Meshing : The Overpass geometry was meshed by creating a uniform solid mesh using Tet
element shape, IsoMesh mesher, Tet10 topology, and a global edge length of 24”. The resulting
mesh created 21,500 elements and 32,650 nodes.
III) Boundary/Load Conditions : The base of the overpass was constrained in all directions
for zero displacement in translational and rotational planes. This simulates the overpass being
anchored to the ground. A uniform distributed load of 4,000 lb/in was applied to the top surface
of the overpass along the designated tire tracks. This load is to simulate continual traffic across
the bridge. A maximum load of 80,000 lb/in was applied to the test geometry only.
FIGURE 2: Overpass Meshing, Boundary, & Load Conditions
IV) Material Properties: The overpass is made of portland cement and the material
properties can be viewed in the table blow.

4. RESULTS:
The results of the MSC Patran/Nastran analysis can be viewed in the tables and figures below.
The analysis shows that the maximum stress magnitudes are usually located near the intersection
of the circular archway and the support legs as can be seen in Figure 3. With the rectangular
geometry the maximum stress is located at the right angle created by the archway. For the
geometry that only used the semi-circular archway the maximum stresses were located along the
tire tracks. Finally for the flush archway geometry used the maximum stress was located in
between the two tire track loading planes created. The maximum deflection for the overpass was
located at the center of the innermost tire track for all geometries analysed except the flush
archway. The flush geometry maximum displacement is located in between the tire tracks
created. The magnitudes and nodal location of the maximum stresses and displacements can be
observed in table 4. For the final analysis a distributed load of 80,000 lb/in was used to simulate
the maximum load expected.
FIGURE 3: Overpass Stresses

5. FIGURE 4: Overpass Displacements
CONCLUSION:
The test geometry used performed well when the average load was applied. This load was
applied along the surface of the tire track sections created to attempt to simulate continuously
moving traffic across the bridge. When under this load the test geometry showed a maximum
stress of 3,540 psi. This load occurred at the intersection of the archway cutout and is a stress
caused by compressive forces. This stress would produce a factor of safety of 1.69 for the test
geometry which is relatively low. For a bridge that would experience consistent repeated loads a
factor of safety over 3 would be preferable. The use of the semicircle for the archway produced
the best results when observing the factor of safety. This is believed to be due to the increased
cross sectional area caused by the use of this geometry. This same trend can be observed in the
use of the rectangular archway. The use of the rectangular geometry is not efficient because of
the high stress concentration caused by the sharp intersection of the archway. When observing
the flush geometry for the archway it can be seen that the stress plot pattern changes and the
maximum stress is located centered between the respective tire tracks. This could result in tensile
stresses in the bottom of the bridge and should be avoided. If the height of the flush archway was

6. decreased the surface area of the cross section could be increased. This group believes that this
could be a possible alternative to the use of the test geometry or the use of only the semicircular
archway geometries.
ADDITIONAL FIGURES:
FIGURE 5: Overpass Stress (Max Load)
FIGURE 6: Overpass Displacements (Max Load)

7. FIGURE 7: Overpass Semi-Circle Only (38,019 Nodes, 25,455 Elements)
FIGURE 7: Overpass Displacements (Semi-Circle Only)
FIGURE 8: Overpass Displacements (Semi-Circle Only)

8. FIGURE 7: Overpass Rectangular Archway (36,667 Nodes, 24,552 Elements)
FIGURE 9: Overpass Displacements (Rectangular Archway)
FIGURE 10: Overpass Displacements (Rectangular Archway)

9. FIGURE 7: Overpass Flush Archway (31,927 Nodes, 20,892 Elements)
FIGURE 11: Overpass Stress (Flush Archway)
FIGURE 12: Overpass Displacements (Flush Archway)

10. FIGURE 13: Overpass (Alternate Geometries)
FIGURE 14: Overpass (Plane Separations)