Danielle Shetler - Structural option Courtyard by Marriott Lancaster, PA - 19 - Structural Analysis Overview: During the structural analysis of the Courtyard by Marriott in Lancaster, Pa, a redesign of the lateral and gravity system from masonry bearing and shear walls to a staggered truss system was performed. The building’s foundation was kept as spread footings and the floor system remained as 8” pre-cast hollow core planks. The basic layout of the building was changed to accommodate the staggered truss systems efficiency. The layout of the building is now a 74’ x 252’ rectangular shape in order to yield the most efficient economical and structural results from the staggered truss system. The height of the building was also altered slightly. The 52’ building was increased in height by 1’ to obtain equal floor to floor heights and provide a higher first floor height. Another change made to the structure of Courtyard by Marriott in the structural analysis was the roof. It was transformed to a flat roof with a green roof system incorporated into it. For the analysis of this building with the staggered truss system, hand calculations were done following the Steel Design Guide 14: Staggered Truss Framing Systems in order to design a typical truss member for this building (which can be found in the appendix) and a computer analysis was also done using ETABS. Lateral Loads: In using the IBC 2003 to determine the new lateral, it was found that the seismic load case still governs over the wind load case. The wind forces remained relatively the same as the existing structure, as well as the seismic forces. The seismic force decreased slightly overall. This is because of the extra load presented on the roof of the building from the 8” pre-cast hollow core plank and green roof addition. The hollow core planks add an extra 65 psf, while the green roof will add an extra 25 psf.
19
Embed
Danielle Shetler - Structural option Courtyard by Marriott ... · Danielle Shetler - Structural option Courtyard by Marriott Lancaster, PA - 19 - Structural Analysis Overview: During
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Danielle Shetler - Structural option Courtyard by Marriott
Lancaster, PA
- 19 -
Structural Analysis
Overview:
During the structural analysis of the Courtyard by Marriott in Lancaster, Pa, a redesign
of the lateral and gravity system from masonry bearing and shear walls to a staggered
truss system was performed. The building’s foundation was kept as spread footings
and the floor system remained as 8” pre-cast hollow core planks. The basic layout of
the building was changed to accommodate the staggered truss systems efficiency.
The layout of the building is now a 74’ x 252’ rectangular shape in order to yield the
most efficient economical and structural results from the staggered truss system. The
height of the building was also altered slightly. The 52’ building was increased in
height by 1’ to obtain equal floor to floor heights and provide a higher first floor
height. Another change made to the structure of Courtyard by Marriott in the
structural analysis was the roof. It was transformed to a flat roof with a green roof
system incorporated into it.
For the analysis of this building with the staggered truss system, hand calculations
were done following the Steel Design Guide 14: Staggered Truss Framing Systems in
order to design a typical truss member for this building (which can be found in the
appendix) and a computer analysis was also done using ETABS.
Lateral Loads:
In using the IBC 2003 to determine the new lateral, it was found that the seismic load
case still governs over the wind load case. The wind forces remained relatively the
same as the existing structure, as well as the seismic forces. The seismic force
decreased slightly overall. This is because of the extra load presented on the roof of
the building from the 8” pre-cast hollow core plank and green roof addition. The
hollow core planks add an extra 65 psf, while the green roof will add an extra 25 psf.
Danielle Shetler - Structural option Courtyard by Marriott
Lancaster, PA
- 20 -
The existing system has a much lighter roof system which consists of metal deck with
concrete and cold-form trusses. Another reason for the similar seismic loads in the
two systems is that the seismic response factor used fot the staggered truss system
was 3 and the seismic response factor used for the reinforced masonry shear walls was
3.5. A seismic response factor of 3 for the staggered truss systems is a more
conservative value for the overall behavior of the system. Also, if this value is used in
steel buildings, then there is no need to design special seismic connections. Since the
building is located on the east coast, there is no need to consider special seismic
connections. The following tables and figures show the results of the new wind and
seismic load cases.
Wind Loads
V = 90 mph Exposure B
I = 1.0 h = 53 ft
Height (ft) Windward Force (psf) Leeward Force
(psf) Total Wind Force
(psf)
N/S & E/W N/S E/W N/S E/W
0-15 6.83 -6.13 -3.06 12.96 9.89
20 7.43 -6.13 -3.06 13.56 10.49
25 7.92 -6.13 -3.06 14.05 10.98
30 8.39 -6.13 -3.06 14.52 11.45
40 9.11 -6.13 -3.06 15.24 12.17
50 9.71 -6.13 -3.06 15.84 12.77
60 10.19 -6.13 -3.06 16.32 13.25
Table 4. New Wind Loads
Danielle Shetler - Structural option Courtyard by Marriott
Lancaster, PA
- 21 -
Seismic Loads
R = 3 Seismic Design Category B
Seismic Use Category II Seismic Factor = 1.0
Level wx (k) hx (ft) wxhxk Cvx Fx
Roof 1870.2 53 99,121 0.344 216.7
5 1689.4 43 72,644 0.252 158.7
4 1689.4 33 55,750 0.193 121.6
3 1689.4 23 38,856 0.135 85
2 1689.4 13 21,962 0.076 47.9
1 0 0 0 0 0
Σ = 1 629.9
Figure 8. New Wind Story Shear - N/S Direction
Table 5. New Seismic Loads
Danielle Shetler - Structural option Courtyard by Marriott
Lancaster, PA
- 22 -
Gravity Loads:
With the changes to the roofing system of the building, the gravity loads for the new
system remain relatively similar to the existing system. The new total dead load
equals 122 psf, while the dead load of the existing system is 121 psf. If the roof
changes were not being considered and the roof from the existing system were to
remain in the new system, the total dead load case would reduce to 89 psf. The
following table provides all loads that contribute to the gravity loads of the building.
Figure 9. New Seismic Story Forces
Danielle Shetler - Structural option Courtyard by Marriott