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Background and Purpose
The purpose of the project is to apply engineering concepts from class to design an elevated house in a
certain location. The goal of the project was to build a lightweight substructure that can hold up the lux, withstand a
minimum lateral load of 35 lbs, and be economically viable. For the house, Structural International’s goal was to
build a structure that was both environmentally friendly and aesthetically pleasing. The roles of the team members
were Tak Lun Law as the Design Lead, Samuel Trejo as the Construction Lead, Pete Phathayakorn as the Design
Analyst, Eve Chutinuntanakul as the Lead Drafter, and Khristian Decastro as the Architect. The location was chosen
to satisfy TRITONS Real Estate Investment Association (TREIA) in obtaining clients who love offroading and dirt
biking during their vacation time. The location also gives the client the option of more relaxing activities such as
golfing and walking in the state park. Moreover, the design of the structure allows the client to view the precious
mountains for future adventures, the sunrise in the mornings as well as sunsets, and allow future clients to explore
the area’s casinos and restaurants. Figure 1 shows the site plan for the project while Figure 2 shows the zoomed in
view with dimensions.
Conceptual Design
The basis of the structure’s design consists of a
wooden frame with diagonal truss members for rigidity and
fixed restraints at the bottom of the substructure. The entire
structure was built using square balsa wood members that
were cut into appropriate lengths. The team’s design went
through a twostage process due to unforeseen circumstances
that occurred during construction.
Initially, the team decided on a square base that was
5x5 inches with 4 tapering columns that would span the
height of the tower. The top of the columns were fixed to a
smaller square that was designed to be 2x2 inches. This
braced frame structure was built using 1/4x1/4 balsa wood
sticks. The tapering of the tower was designed to resist
lateral forces applied to the top. For example, when a
horizontal force is applied to the top of a vertical member that
is fixed at the bottom, the member becomes an axiallyzero
force member and does not contribute to the rigidity of the
structure. This causes the majority of the load to be resisted
purely by a reactionary moment at the fixed joint. This
redistributes some of the load and causes less stress
concentration at the joint. Tapering the columns of the
substructure allows them to act as if they were truss members
themselves. This increases rigidity in cases where a lateral
load is applied to the top end of the substructure.
The substructure was sectioned into 3 levels due to
requirements dictating that no member be more than 6 inches
long. Between each level were horizontal beams that braced the
columns to each other. These horizontal beams were made with
1/4x1/4 balsa wood sticks. Within each level, diagonal trusses of 1/8x1/8 were used to form cross braces that acted
across each face of the structure.
During construction of the structure, however, it was deemed difficult to properly construct a frame that
tapered all the way to the top given the initial planned dimensions. As everything was hand made, accuracy in
obtaining the proper angles in 3 dimensions for the joints proved to be a struggle. After constructing the first level
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which had a 5x5 square base that tapered to a 3.75x3.75 top, the team decided to continue on with the second and
third levels with vertical columns instead of continuing to taper the columns upward. This modified design would
not have the theorized benefits of the original design, however the team decided that the benefits from a tapered
tower did not outweigh the risk of having improperly set joints and connections. As an extra precaution against joint
failure, exposed surfaces of the joints were covered with thin slices of balsa wood, acting as gusset plates.
The tower was fixed with aluminum plates on all four bottom sides.
These were glued on to the middle of the bottom horizontal beams with JB
Kwik epoxy on each face. Each plate then had 2 small holes,
approximately .10938 inches in diameter, drilled on opposite ends of the
plate’s length, both holes being .4 inches above the bottom of the plate and
their center. The holes are .5 inches away from the length ends. The top of
the structure featured 2 aluminum plates placed opposite to each other
and secured with JB Kwik. Each of the top plates had 2 holes
drilled into them, .25 inches in diameter, on opposite ends of the plate’s
length with each hole 1.5 inches away from the ends and in the center of
the plate’s width. Figure 3 shows the final design of the substructure
Engineering Principle
The team decided to apply slopedeflection concepts for the hand
calculations. The structure is a frame with trusses, yet the team had to
simply analyze at first in order to ensure SAP2000’s model match
theoretical values. Columns, beams, and diagonals were virtually separated
for analysis; given lateral, shear, and moment at each end. The team
decided to analyze a simple frame first in order to compare the accuracy of
SAP2000. Hand Calculations are in the Appendix. Figure 4 shows the
simple frame with each column and diagonal having fixedends. Table 1
shows the hand calculation and SAP2000’s result. Figures 5 and 6 show
SAP’s frame and deflection.
Table 1 : Comparison of Hand Calculation and
SAP2000 Calculation
Hand Calculation (in) SAP2000 calculation (in)
9.75 9.68
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Figure 5: Sample of Fixed
Frame
Figure 6: Sample
Deflection of Frame
Afterward, horizontal beams were attached and the
same concept was applied. Later, the team created
diagonals and connections to make up lateral
systems. The purpose of this lateral system is to
transfer the lateral load, from where force was
applied, to the ground without damaging the
substructure. Using fixedend moments for each
member, the team determined the deflection for the
test frame.
To determine the ultimate failure mode of
the structure, the stress and critical buckling for
diagonal members were determined since they were
constructed with a thinner cross sectional area. Since
the intersection between 2 diagonals were glued
together, the team assumed pinnedends for the worst case scenario of the substructure. Each analyzed diagonal had
half its length applied to the buckling equation since the intersection was considered a joint. This process was
applied to members facing the most stress on SAP2000 and were compared to their critical buckling values that
were determined by hand.
Structural Performance
By looking at the load combinations per ASCE 710, the team found that case 3, 1.2D+1.0E+L+0.2S,
governs the design. The values that the team used in finding the governed design are in Table 2. Figures 7 through 9
show the pattern of deflection for every case and Table 3 shows the max deflection for each case. While comparing
the deflections in Table 3 to the deflection the team obtained for the testing scenario with 35 lbs of lateral force and
the weight of the plate, the team found that the max deflection for the substructure is 0.15 in.
Table 2: Load Type and Value
Wind Load (lb) Live Load (lb) Dead Load (lb) Roof Live Load (lb) Earthquake Load (lb)
3 15.3 15.2 0.42 8
Figure 7: Case 1 Combination
Figure 8: Case 2 Combination
Figure 9: Case 3 Combination
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Table 3: Deflection for Different Load Combinations
Case 1 Deflection (in) Case 2 Deflection (in) Case 3 Deflection (in)
.0115 .0266 .0625
The loads that were applied to the structure during the testing are the dead load of the top plate and the
wind load applied by the actuator. From SAP2000 analysis, the team believed that the critical members would be the
sloped columns in the side farther away from the applied load, one of the top crossed braces, and the bottom crossed
braces from the two sides parallel to the direction of the wind load. These members would fail due to buckling when
applying the wind loads. The top diagonal member would receive the most compressive force because it would
resist the applied load. From the equation, , the critical load of this diagonal member is 15.56 lb. Due to crP = π EI2
(kL)2
the fact that the bottom diagonal members are longer than the rest, it would fail first. Their critical load is 9.7 lb.
This judgement was based by their length and cross sectional area. Hand calculations were performed to determine
the critical buckling force and only partial length was taken into account since the intersection of the diagonals was
glued. Hand calculations are in the Appendix. After determining the buckling value, different loading cases were
applied onto the structure and the team looked at the max applied stress to determine its force. Theoretically, the
substructure was able to handle over 35lbs of lateral load. Hence the team increased the load until reaching 40 lbs.
The team decided to lower the max load to 37.5 lbs since it was believed that manufacturing error would occur.
The load paths start at the top plate screwed into the structure. The wind load and the weight of the plate
went to the beams connecting to the two aluminum sheets. This load went to the connections and then the diagonal
members and the four columns. From the diagonal members, the load went through the bottom beams then onto the
columns. This process continued until the load reached the ground. However, because the substructure was being
pushed on one side, the load path of the right side would go up, while the bottom reaction force is pulling that side
down. Two of the diagonals in each floor would receive the upward load path as well because the columns would
pull the diagonals. The team assumed that all the connections are fixed connections because the connections
transferred the moment to the members. The connections transferred both the axial force and bending force. The
load path is shown in Figure 10 .
During testing, the substructure failed in the contact between the testing apparatus and balsa
woodaluminum sheet. This is because the team used JB Kwik instead of JB Weld glue; JB Kwik has significantly
less adhesive strength. . Hence the member failed due to not sustaining the shear force traveling along the member.
The applied load made half of the substructure receive
compression while the other half obtained tension. The side with
the applied force was in tension, as well as the blue diagonals in
Figure 12. The side farther away from the applied force was in
compression because the substructure deflected, as well as the
red diagonals in Figure 12. The critical connections of this
substructure were the connections between the slanted columns
and vertical columns. These connections would receive the most
stress due to the tension and compression of the columns. These
connections were solely held together by glue, which could break
under heavy stress.
Figure 10: Load Path of the Substructure
The team’s estimated PI value is 9852. Table 4 shows all predicted and actual values. The possible failure
modes were the buckling of the diagonal members and the breaking of the connections where the slanted columns
meet the vertical ones. To minimize the effects of these failure modes, the team glued the diagonal members
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together in order to reduce the length of the members, which in turn increased its critical load. To help reinforce the
connections, the team added small gusset plates to the side of the columns. During experimentation, the substructure
withstood 7.205 lbs. The experiment caused the bottom beam, which was parallel to the lateral force, to crack. The
team believes cracking occurred due to the glue used to fix the aluminum plate onto the bottom beam. To minimize
construction time, JB Kwik was used to contact the bottom beams with the aluminum plates. JB Kwik was
fastdrying, but this quick curing time compromised the strength mixture of the epoxy. The analysis did not
incorporate the aluminum plates in SAP2000 since the team believed no significant difference would occur.
Moreover, assuming no aluminum plates would provide the worst case scenario for the substructure.
Table 4: Comparison between Predicted and Actual PI
Cost ($) Weight
(g)
Predicted
Displ. (in)
Predicted
Force
(lbs)
Displ.
(in) @
20 lbs
Ultimate
Displ. (in)
Ultimate
Force
(lbs)
Predicted
PI
Actual
PI
12,380 97.6 .150 37.5 1.5 .124 7.205 9852 170.63
Figure 11: Failure Location of
Substructure
The result was fairly different from the predicted value
since the connections by JB Kwik did not perform as well as the
team predicted. When the JB Kwik epoxy gave in, the support
reaction moved inwards from the side of the structure. This caused
a bending moment in the the bottom horizontal member. Figure 11
shows the failure of the substructure under testing.
Figures 12 and 13 show the expected performance of the
structure with the predicted connection, while Figures 14 and 15
show what happened in the experiment. The errors in the
prediction were caused by the wrong assumption of the strength of
the epoxy. If the team were to use JB Weld, the structure would
have a higher ultimate force than 20 lbs, giving a higher stiffness
factor.
Figure 12: Predicted
Force Diagram of the
Substructure
Figure 13: Predicted
Deflection
Figure 14: Estimated
Force Diagram of the
Substructure after
Testing
Figure 15: Estimated
Testing Deflection
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Aesthetics
The structure was intended to blend into the desert environment to minimize disturbances to the natural
beauty of the surrounding landscapes. To do so, Structural International designed the truss system beneath the
structure to allow visitors to see the surrounding landscapes. Additionally, the team used sandstone on several walls
to help further the home’s blending into the environment. Different earth tones were used in the structure as well.
To keep up with the vastness of the desert environment, the architect designed vast open windows facing the east
and west, as well as an open deck on the structure’s west side to allow the client to feel one with the environment as
the sun rises and sets. To add on to this, each story has very high ceilings at a height of fifteen feet, and includes a
grand living and dining area that is two stories tall, as shown in Figure 16.
The significant volume of natural light entering the structure helps decrease the amount of electricity
needed to produce light throughout the day. To compensate for the expected very cool evenings and nights, the
twostory wall, facing east in the grand living room was painted black in order to absorb heat reflected off of the
inner surfaces; the same was done for the roof of the structure. To prevent the interior of the structure from heating
up too much, the team utilized tinted windows to prevent an uncomfortable amount of radiated heat from entering.
The sandstone exteriors are also meant to reflect light and be a strong insulator so as to strengthen prevention against
heat. The solar panels on top of the structure are curved in such a way that they follow the path of the sun’s
movement throughout the day, as the sun in the northern hemisphere typically sits toward the south for most of the
year. Figure 17 showcases the colors, textures, and environmental considerations in 3D from the Southwest.
Despite all the effort put into blending the structure into the environment, the team still wanted to maintain
a sense of uniqueness and did so by designing with hard lines and strong corners, thus providing the structure with a
hierarchy of shape against the smooth curves of the surrounding mountains. The mere scale of the building and its
elevation, also help stand out from the environment despite its desertinspired colors and textures. Altogether, the
structure aims to be simultaneously harmonious with the surrounding landscape as well as eyecatching enough to
catch the attention of passersby.
Figure 16: The Dimensions of the Structure from the South
Figure 17: 3D Model of the Structure
from the Southwest
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Project Challenges
One main challenge was trying to decrease the moment that the structure would experience from the lateral
force. Slanting the column toward the wind force helps reduce the moment on the substructure since the force
perpendicular to the cross sectional area of the column would decrease. The team realized that the more slanted the
columns are, the better the structure can reduce the moment at the bottom of the structure. However, in the original
design, the team could not decrease the angle anymore as doing so would risk decreasing the area at the top of the
structure to hold the vacation house on top, hence they were placed at 83 degrees.
Structural International faced a major setback during construction. Due to the complex geometry of the
original design, it was very difficult to construct the substructure with accuracy. After building the bottom section,
the Construction Leader realized that the complex shape could jeopardize the given criteria. The team was also not
wellequipped to accurately fabricate the beams needed to build the structure. In order to minimize costs, the Lead
Analyst kept the bottom section the same and redesigned the rest of the structure. Both leaders realized that one of
the most important elements of a structure under lateral is the connections. Having to conserve the cost and weight,
the team used balsa wood with a small surface area, creating challenges to make strong connections. To ensure that
the connections would not be a problem under loading, the team used TITEBOND III wood glue as well as adding
reinforcements on the joints.
The overall team dynamics on this project were outstanding. One challenge in team dynamics was that
there were strong opinions between team members on the design of the substructure. Samuel wanted a design that
would perform better, while Pete wanted another design that is more cost efficient. The entire team met to find a
design that satisfied each member’s preferences. The result was a design that can withstand sufficient force and was
economically efficient.
Team Responsibilities
Tak and Sam were responsible for the original design of the substructure, while Pete and Eve redesigned it
in order to reach a compromise between the team members’ interest. Sam was responsible for the SolidWorks model
of the substructure with the assistance of Tak. Eve’s task was producing the site layout and drawings through
AUTOCAD. Pete and Sam were responsible for the structural analysis and predictions. Khristian created the original
design of the house on SolidWorks, with revisions done by Pete and Tak to reach the final aesthetic design, which
Khristian in turn again modeled within SolidWorks. Pete and Khristian went out to buy necessary materials for
constructing the entire model. All the team members worked together throughout the construction of the entire
structure. The total hours the Eve, Pete, Sam, Tak, and Khristian put into this project are 48, 48, 49, 43,and 13 hours
respectively.
Conclusion
The team learned a huge difference between the strength of JB Weld and JB Kwik epoxy. Moreover, they
learned the importance of strong connections in the lateral system. Concepts such as SlopeDeflection were applied
for analysis to determine deflection and compare the accuracy of SAP2000. During the construction period, they
learned that the preconstruction planning is one of the most important processes for successfully constructing
without having to waste any time or material. Unfortunately the team was not able to test their structure to the full
limit due the poor connection by JB Kwik. The actual PI was 170.63 while Structural International expected 9852.
However the predicted PI assumes the entire structure was constructed properly. During the quarter, the team
became aware of how to accurately model in SAP2000 in order to maximize the efficiency of the program, how to
draw site plans using AUTOCAD, and create solid parts and assemblies in SolidWorks. They also knew the
limitations of computer programs and have taken that into account for their predictions, thus emphasizing the
importance of the engineer possessing knowledge and skills in the field in addition to computer analysis.
