1. National Timber Bridge Design Competition – 2017
College or University name: University of Kansas
Student Chapter (ASCE or FPS): ASCE
Address: 1530 West 15th street Lawrence, KS 66045
Website Address:
Faculty Advisor: Robert Lyon
Phone:
Faculty Advisor: Robert Lyon
Phone:

2. Hour Spent on this project
Student: 120
Faculty: 10
Cost of Materials
Donated: $280
Purchased: $200

3. 1. Abstract
    We have considered some conventional truss types and narrowed down the alternative as per their individual advantages and disadvantages in terms of strength, weight and stiffness. We initially investigated 7 truss types. These include Howe Truss, Burr arch Truss, Susquehanna truss, Pratt truss, Warren truss, Multiple Kingpost and Partridge truss types and selected 3 panel Warren truss. Each configuration was evaluated for the prescribed loading through a FEM software, SAP2000. LRFD timber design manual, NDS 2015 has been used to calculate the design strengths of the timber members of different sizes. Preliminary member sizes have been obtained and evaluation matrix has been used to calculate the advantage of one truss type over the other. Criteria for this matrix are maximum bridge deflection, maximum deck deflection, ease of construction, connections, substitution of steel members, aesthetics and total weight. The 3 paneled Warren truss came out as an efficient choice for this type of loading and deflection limit.
The chord members were doubled to increase the strength, ease of construction and efficiency of connection as the diagonals were sandwiched between two chord members and this connection was perceived to be better than a single chord member with truss plate connection to diagonals. A three panel deck with 2X6s as deck members was envisaged in the initial stage. Both longitudinal and transverse alignment of deck members have been investigated and longitudinal alignment was selected. After further evaluation of stiffness vs weight of the bridge, the deck has been modified to 5 deck panel with 1X6s running longitudinally. A deck stiffener has been added in the central deck panel to increase the stiffness of the deck as it has maximum panel length of 1000 mm. Deck members were spanned between floor beams running in between the bottom chords. Double 2X6s have been used in the central deck panel and connected by joist hangers.

4. 2. Deflection Table (Deflection – millimeters rounded to 2 decimal places)
1. Loading Increment
2. Bridge
3. Beam
LEFT
4. Beam
RIGHT
5. Average
(L & R)
6. Gross Deck
7. Net Deck
5 kN
2.59
0.91
1.75
3.66
1.91
10 kN
4.93
3.81
4.37
7.37
3.00
15 kN
6.73
6.96
6.85
11.18
4.33
20 kN – 0 min.
8.64
10.03
9.33
15.04
5.70
20 kN – 15 min.
8.89
10.41
9.65
15.37
5.72
20 kN – 30 min.
8.94
9.68
15.44
5.77
20 kN – 45 min.
9.14
10.54
9.84
15.49
5.65
20 kN – 60 min.
9.30
10.59
9.94
15.60
Loading Increments
Bridge – As measured at midspan of the longitudinal beam receiving greatest loading.
Beam L – As measured under the longitudinal beam to left of selected deck monitoring point.
Beam R – As measured under the longitudinal beam to right of selected deck monitoring point.
Average (L & R) – Average of 3 and 4, above.
Gross Deck – As measured under the loading point expected to experience maximum deflection.
Net Deck – Column 6 minus Column 5.
Deck Span:
Longitudinal distance between two deck beams = _1000_mm ÷ 100 = _10_mm = maximum allowable net deck deflection.

5. 3. Materials List
Kgs
294.84
35.38

6. 4. Summary – Describe Bridge and its Behavior Under Load (max
4. Summary – Describe Bridge and its Behavior Under Load (max. 500 words)
The bridge was designed using three panel Warren truss. For the bottom chord to meet the stiffness and strength criteria, two 2X6s were used and for the top chord two 2X4s were used and the diagonals were sandwiched between the chord members at the joint. Five deck panels were considered with deck members running longitudinally over floor beams and floor beams were connected to the bottom chords. The efficiency of the connection between chord members and diagonals were improved by using a sandwich mechanism. A deck stiffener has been provided below the central deck panel to increase the stiffness of the deck to meet the deflection criteria. The test loads were directly transferred to the floor beams as they are located right below the loading points because of the five panel deck configuration. Lag screws were used to make the connection between chord members and diagonals and splice plates were used with a filler piece to splice the bottom chords.
The loading blocks as mentioned in the project rules were steel plates welded to the steel I girder with a distance of mm between them and two such girders were aligned longitudinally and spaced as per the regulations. After weighing each member used for loading we achieved initial 5kN load by adding some more additional steel angles each weighing around 25 lbs. After that a long steel beam girder was places on the top of this angles to achieve 10kN load. Later by adding more steel angles and some salt bags of 50 lbs. each we could achieve a full loading of 20kN. Deflection reading were taken at all the regulated point while testing. As per the results the bridge had deflected more during the initial loading and this could account for the actual bridge deflection and the imperfections in the connections as we apples the torque in the screws manually, we may have some slippage in the connections during the initial loading. In the right chord the pattern of deflection is consistent and it reached to 10.59mm which is 111.5% of the maximum allowable deflection. In the left chord even though had higher deflections in the earlier loading which may be due to the slip in the splice connection, the final deflection was under permissible limits. At the full loading the deflection hardly changed during the one-hour loading time. The maximum net deflection in the deck was observed to be 5.7mm which is less than the permissible limit of 10mm.

7. Side Drawing

8. End Drawing

9. Trimetric Drawing

10. Drawing Clearly Showing Location of Loading and Deflection Gauge Points in Relation to Longitudinal Members
Note: Repeat slide if loading setup was moved to measure deck deflection

11. Drawing Clearly Showing Location of Loading and Deflection Gauge Points in Relation to Transverse Members
Note: Repeat slide if loading setup was moved to measure deck deflection
Gauge 1 is at the middle of Left side Bottom Chord
Gauge 2 is at the middle of deck stiffener under the middle deck panel
Gauge 3 is at the middle of Right side Bottom Chord

12. Photos showing the Trimetric view of Loading setup for measuring Bridge Deflection
Note: Repeat Slide if loading setup was moved to measure deck deflection

13. Photos showing the End view of Loading setup for measuring Bridge Deflection
Note: Repeat Slide if loading setup was moved to measure deck deflection

14. End photo of Finished Bridge

15. Side photo of Finished Bridge

16. Trimetric photo of Finished Bridge

17. Team photo (with bridge in the foreground)

18. Briefly describe each bridge components, as applicable
6. Bridge Component Details
Briefly describe each bridge components, as applicable
Bottom Chord
Each chord comprises two 2X6s timber beams and each beam has two 2X6s, 1.93m long each and spliced with a small 2X6 filler piece (1 ft. long)
Top chord
Each chord comprises two 2X4s timber beams and each beam has two 2X6s, 1.85m & 0.85m long and are spliced with a small 2X6 filler piece (6 in. long)
Diagonals
Diagonal are made by 2X4s
Deck
1X6s were used for decking, each decking member was run along the length of the bridge spanning over floor beams. Five deck panel lengths were used with the maximum being 1000 mm.
Floor Beams
2X6s were used for floor beams. Below the largest deck panel the one in the middle, two 2X6s were used.
Deck Stiffener
A diagonal deck stiffener of 2X4 was used below the largest deck panel
Unique Components
Lag screws were used to connect diagonals to the top and bottom chords, Splice plates have been used in the connection of bottom chord

19. 7. Preservative Treatment
    We receive all the timber for this project as a donation from Westar Energy Green Team. Therefore, all the wood used in this project are from recycled power poles. All of the poles used by Westar Energy are pentachlorophenol pressure treated before being used as utility poles. The pentachlorophenol pressure treatment, often called P35 treatment, is used to keep the insects away and prevent the decay of the wood. This treatment did not present any special problem for us. We ourselves did not add any special treatment on the wood members. We believe that our bridge will be able to withstand the Kansas weather for a very longtime..

20. 8. Special Considerations – End use of Bridge
    The end use of our timber bridge will be used as the crossing for one of the trails in the Baker Wetlands, located in Lawrence, Kansas. Our bridge will be placed near the Discovery Center of Wetlands where it will cross over a small pond. The bridge will be supported by footings that will be complete in the spring of  Once the bridge is in place, we would gladly share photos of the bridge if requested

21. 9. Summarize the Team’s Experience from participation in the Competition. Was it beneficial? What steps you recommend to improve the experience?
Design competition is always a great platform to learn how our calculated design is going to act under real load testing. From the very first day our team was really excited about this competition. We were a team of three group members. Each member contributed the same amount of dedication and hard work. In this competition we were supposed to design, build and perform a non-destructive load test of our timber bridge. We first decided to design it as a timber truss bridge. Around 12 types of historical trusses were analyzed using SAP 2000 AND RISA under given load to find out the most efficient truss type and sections. At last we decided to design it as a Howe truss bridge. Our primary concern was to develop a lightweight and cost effective design. After finalizing our initial design, we decided to start building our bridge in lab. I must say it was a great experience. After started working in lab, we had made many changes in our design to make our bridge more efficient. For example, we figured out that about 60% of our bridge weight is taken by the deck as in our initial design we choose 2x6 cross section as our bridge deck members. So we decided to reduce the thickness of our deck members (use 1X6) and use diagonal bracings to make it more stiffer. By this change we were able to reduce the self-weight of the bridge around 30% from our initial design. After building our bridge we tested it under 20 KN with 4-point loads. Our test went really well though our beam deflections were higher than our software calculated value. By that incident we realize that software result doesn’t consider construction errors in analysis. So the lab values are different. Though one deflection went to 111% of permissible limits, could be due to the loosening of bolts in the splice connection while transferring the bridge for testing. This competition was a great experience and learning for our team.
We could have made the bolted connections sufficiently tight after the transportation of bridge to the test location. All in all we could improve our working schedule throughout this work. As we are graduate students and taking different classes, it was really hard to manage a common time for our team.

22. Photos of Bridge Weighing

23. One photo of each deflection at full loading, with identification sign indicating Deck, Beam Left and Beam Right
Gauge 2 (Deck)
Gauge 1 (Beam Right)
Gauge 1 (Beam Left)

24. Add as many photos as you wish showing the bridge construction process
Add as many photos as you wish showing the bridge construction process. Especially consider photos of internal structural components that may not be visible to judges from observing the finished bridge.