JACQ UI DA NIEL I RYAN TRETOW I A LI TRUWIT

PRELIMINARY BRIDGE DESIGN:

We designed our bridge to be efficient and structurally sound rather

than focusing on aesthetics. We began by designing the bridge within

the dimensional parameters of the assignment, and then further

reduced the depth and weight of the bridge to maximize the bridge

efficiency and give Team Bridgiant the greatest opportunity to win.

Our bridge is designed to hold 90+ lb load at a weight of less than 4

FURTHER DESIGN DEVELOPMENT:

With further development, we realized we would need to maximize

the stability of our bridge. To do so, we added gussets plates to all ·~---of our member joints to reduce stress at the joints and allow for

a stronger connection from member to member. Additionally, we

devised ~ ed, laminated member method to enhance the strength

of our lower arched member and create a continuous bent member:

ounces. Our bridge is composed of 37 total members; 20 of which effectively reducing the number of joints and individual member in

comprise the perimeter of the bridge and are 1/4"x1/4" . The remaining the total bridge assembly. We also aaded 1" tabs on the end of our

members are 1/8"x1/8", allowed the bridge to support a large amount truss assemblies to aid in the secure fitment of our bridge within the

of weight while remaining very lightweight. Further, we designed the official testing frame, which provided solid footing for our bridge to

bridge to be inverted to leave a clear, open roadway deck to stack the hold weight beyond what was initially anticipated.

winning amount of weight. The oridge rests on two fixed supports

that can resist vertical and horizontal forces as well as the moment(s) After initial design of our bridge, Me also concluded that we would

at each end. These fixed supports are representative of the provided need to find additional weight reduction strategies to ensure our

testing frame. bridge met spec. To reduce weight. we prepared an ultra-thin

MEMBER SIZING:

20 - 1/4" x 1/4" Basswood Members

17 - 1/8" x 1/8" Basswood Members

WEIGHT:

Approx. 3.8 oz

+ 10% For Glue Weight

EXPECTED MAX LOAD:

90+ lbs

·~

road decking solution and strategically placed cross members for ·-----=----maximum strength and resistance to torsion while controlling and

monitoring overall weight of bridge construction. As a result, our

team precisely met the weight specifications at 4.0 ounces.

BRIDGE ADJUSTMENTS:

Besides the edits noted above, our initial bridge design was largely

satisfactory based on the results of the preliminary report. Therefore,

our initial design remained relatively unchanged.

MEMBER SIZE ADJUSTMENTS:

Our member sizes, placement and quantity met bridge weight

spec and exceeded carrying ca acity requirements so we chose

to maintain our member sizing strategy and design in an effort to

maximize the bridge 's ability to hold a winn ing amount of weight.

IMPACT OF PRE-ANALYSIS ON FINAL DESIGN:

After initial design of our bridge, we also concluded that we would

need to find additional weight reduction strategies to ensure our

bridge met spec. To reduce weight, we prepared an ultra-thin

road decking solution and strategically placed cross members for

maximum strength and resistance to torsion while controlling and

monitoring overall weight of bridge construction. As a result, our

team precisely met the weight specifications at 4.0 ounces.

We were planning for the bridge to maximize its weight to strength

ratio to the greatest extent possible and therefore initially weighed

in at 4.2 ounces. Through a bit more weight reduction measures

at the location of gussets, we were able to meet the final weight

requirement and offset the final unknown of how the glue weight

would add to the total weight of our bridge in the end. In summary,

our careful preparation during the preliminary design phase, we

were able to execute very accurately on our initial proposal. The

carefulness of our initial efforts allowed us to efficiently construct a

successful bridge and have confidence that we as a team, and our

bridge, would perform excellent under pressure.

REVISED BRIDGE DESIGN ANALYSIS:

MEMBER SIZING:

20 - 1/4" x 1/4" Basswood Members

17 -1/8" x 1/8" Basswood Membey

WEIGHT:

Approx. 3.8 oz

+10%~eight -EXPECTED MAX LOAD:

90+ lbs

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DERIVATIONS OF MEMBER AREAS:

1/8"

Compression to Grain (T) 5.78

Compression to Grain (II) 73.91

Tension to Grain (II) 70.31

Shear to Grain (II) 15.47

1,'4"

23.1 25

295.63

281.25

61.86

PREDICTION OF CAPACITY:

Based on this revised design, the bridge could hold a total weight of

901bs

MODE OF FAILURE:

Based on the below calculated conditions, the bridge will fail at the

bottom member of each end reaction location

Estimated Weight 3.0 ounces + 10% Glue Weight

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MEMBER SIZING

FROM AVAILABLE STOCK:

JOINT CALCULATION: 6.ll lB / 3~ 3 "-2 + 2,1 A 2 = 3,65 A 2

SLOPE= 2.1 / 3

... USING SIMILAR TRIANGLES: Fx = 40.447 lb

... USING PYTHAGORE S THEOREM: Fy = 81.1 lb

-\0

CRUSHING CALCULATIONS:

With 1/8" members, our weakest member is

the lower member at the location of the end

reactions, which is the member calculated at

the left. If utilized as shown and calculated, the

bridge would fail at this location and have a ~

capacity of 90 lbs of total weight. This is based

on Dr. Frame illustration shown above as well as

derivation of member areas listed above on this

page.

F=P/A 7

ILLUSTRATION OF TESTED (REVISED FROM PRELIMINARY) DESIGN

*SEE DR.FRAME FOR MEMBER STRESSES

ELEVATION

PLAN

4.rr

SECTION

2.69"\1 ' X1/4")

TESTING RESULTS

WEIGHT GR

WEIGHT OZ

HEIGHT

LOAD CAPACITY KG

LOAD LB

MEMBERS

JOINTS

PANELS

HEIGHT /LENGTH_ RATIO

LOAD/WEIGHT_ RATIO

TYPE

SCORE

PICKS

OBSERVATIONS OF TESTING:

11 3.398

4

6.5

56.699

125

44

4

10

0.216667

1.95312

Deck Bridge

72.5

20

The bridge successfully held iµell beyond the minimum requirement

of 50 pounds, with a total capacity of ~ nds. We utilized a

strategy of evenly placed weight blocks during the testing period, and

in hindsight see the potential to place the weight differently to reduce

overall stress on bridge trusses. Perhaps, had we placed more weigh

towards the ends, instead of a large number of weights at the center,

we may have been able to hold a greater number of 51b bricks.

BEFORE

AFTER

DESCRIPTION OF MODE OF FAILURE:

The bridge tailed as expected, due to a strategic reduction of cross

members and non-critical members to ensure that the bridge

efficiently met the overall weight requirement. Due to this, we were

able to predict the areas of fai lure (via torsion of the bridge assembly)

and as such, the bridge failed at the I cation of the horizontal and

angled between-truss cross members.

Based on the integrity on our pair of truss assemblies (based on

initial analysis in Dr. Frame) we knew it would be critical to place the

weights as carefully as possible to red ice the above mention effects.

We were able to do so up to 125Ibs in total weight, before the weight

stacks got too tall to be resisted by truss assembly. We know this

based on resulting integrity and limited failure of the arched trusses

and associated member connections. and the specific and focused

failure of the bridge at the area of the ultra-thin deck and limited cross

sectional width bracing.

FOLLOWING THE GUIDELINES:

Our bridge met the guidelines in all aspects which include bridge

material (solely basswood) , bridge weight ( <4.0 ounces), and bridge

capacity which exceeded the minimum requirement by an additional

75Ibs. The bridge trusses were constructed of individual hand cut

members in consideration of the direction of the grain of the wood tor

maximum force capabilities. It spanned the 30" gap with an extra inch

on either side. The bridge contained a flat, continuous, non-perforated

deck with a 4" width.

IMAGES OF FAILURE:

' (

POST-TESTING ANALYSIS:

In comparison of the bridge testing results and the preliminary design

predicted capacity, we exceeded the predicted capacity by 35Ibs;

and we exceeded the project requirement by 75Ibs. The location(s)

of failure were also successfully predicted by our team, due to the

focus on strength of primary truss assemblies and reduction of

cross member quantities and road deck thickness as a weight saving

measure; because in fact, the cross members were the precise

location of failure. These correct predictions are further verified

by the resulting broken bridge parts, where we had only two truss

member connections split out of both trusses, but nearly all of our

cross bracing separate from the trusses as well as a split down the

center of the road deck.

Thusly, the bridge broke under the twisting force of the Sib steel

bricks on the bridge due to the reduction of cross bracing. Further,

the discrepancies between the results and preliminary design

occurred as expected, and other than holding much more weight

than expected, our results went better than expected due to increased

overall capacity .

. IMPROVEMENTS:

Our design could have looked at a reduction of intermediate

members to 8 or less total bays, for example (instead of 10) to

reduce overall weight and maintain carrying capacity. We also could

have omitted at minimum, one 1/16"x1/4" basswood laminations

from our bottom custom laminated curved member to reduce weight

of basswood and glue in the assembly. This member proved to be

our strongest component and saw zero structural failure after testing

and therefore could have been reduced proportionally.

FURTHER IMPROVEMENTS:

Most importantly, we should have added more cross bracing and

angle bracing to add stability to the pair of trusses as a total bridge

assembly. We also (unintentionally) relied on the road deck to keep

the top of the trusses in parallel, since we omitted any bracing

between trusses directly below the road deck. In hindsight, we

should have added bracing in this location beneath the road deck

to ensure further structural integrity of our design. With the edits,

we believe the bridge would have performed even better than the

actual results, at a total capac ity of at or above double the anticipated

weight capac ity. (1 80+ lbs or more)