Constructing Environments Logbook Week 2 Summary
Construction Challenge: Span The design challenge for this week was to construct a beam that was able to span a distance of 1.5 meters. Materials made available to us included a 600mm X 100mm piece of balsa wood; super glue; a box of matches and a roll of sticky tape. Upon successful completion of spanning the gap our beam was to be tested for its load bearing capability. A series of loads in increasing increments would be placed on the structure to achieve a point where the beam will fail.
Design
Detail 1: Matchstick Lintel
Measuring the balsa wood before cutting.
Our initial design discussion centred on how we would span the distance whilst also creating the strongest possible structure. We identified the joins between the members as being the most likely element to fail. These would need to be reinforced using the available materials. A design using two parallel beams connected at several points was chosen as we believed this would provide the strongest beam possible.
1
Detail 2: Reinforced join without matchstick lintel in place.
Samuel Hill
Constructing Environments: Week 2 Logbook
Student Number: 722052
Construction Each joint consisted of the four intersecting long beams, laminated between 4 smaller pieces, two on each side of the main beam. Super glue was used as the bonding agent between each layer of timber. Additional supports were constructed out of the matchsticks. 4 of the square pieces were laminated together with glue and allowed to set. These were then glued to the bottom and top of each join to provide additional support. Once each support was constructed they were wrapped at several points in a few layers of sticky tape. This helped tie all of the elements together as we did not believe the glue to be strong enough.
Final beam showing support bracing between.
Beam joint in construction. Showing the matchstick lintels.
Dead Load When loading the structure we discovered we had not given enough consideration to how the beam would be attached to the supports. When load was placed on the middle of the structure it resulted in a rotational force being applied to the structure making the entire beam unstable and unable to support the load. We needed to hold the beam down manually in order to proceed with the test. The lateral force deformed the beam to the extent that it was no longer structurally able to support the load it was subjected to.
Samuel Hill
Constructing Environments: Week 2 Logbook
Student Number: 722052
Rotational Load In large part due to our inability to anchor to the supports our beam was initially not very good at supporting load. Each time we attempted to load the beam it would rotate and fall off. With some success after holding down the load we were able to ascertain the beam was quite strong. However was not able to support itself laterally therefore was susceptible to rotational forces.
Compression and Tension As can be seen in the adjacent photos when load was placed on the beam the top is in compression whilst the bottom is in tension. Both forces need to be taken into account in order to design a successful structural member. We discussed stringing a few lengths of tap from end to end to provide additional support however run out of time. With more time I would have liked to explore this theory. There was the potential for this to add unnecessary weight to the beam therefore making it even more unstable.
Failure The beam failed due to a lack of ability to secure each individual member together at the join. The matchstick lintels were efficient in adding additional structural support. In the end the beam failed at the join. The two end pieces (on the right had side of the adjacent picture) rotated inside the join until they were no longer supported by the tape bindings.
The failed join of the beam. Left side showing the structural support. Right side showing the unhinged member. Samuel Hill
Constructing Environments: Week 2 Logbook
Student Number: 722052
Glossary of terms Structural Joint: Rigid or fixed joints; Pinned joints and Roller joints are the 3 main type of structural joints. The way a structural system performs as a whole depends on how loads a transferred from one element to the next.
Column:
‘Are rigid, relatively slender structural members designed primarily to support axial compressive loads applied to the ends of members’. ‘Failure occurs when the direct stresses from an axial load exceeds the compressive strength of the material available in the cross section. (Ching, 2014).
Tension: Tension is a force applied to a structural part of the construction. When a load is placed onto a member often it will put a portion of the support into tension. Creating strength. Often combined with bending stresses.
Frame: A frame is most effective when supporting a dead load if it is braced adequately, otherwise it is susceptible to lateral forces. A rigid frame is rigid only in its plane, therefore if lateral forces are applied the frame needs to be appropriately braced.
Bracing: Vital to the integrity of a structure when attempting to overcome lateral forces is bracing. This can be achieved in many ways. The installation of knee bracing; K-brace; cross bracing as well as cable bracing. (See image below)
(Ching, Page 2.14)
Span: The distance between two supports. A beam will need to be constructed long enough in order to bridge the gap between these two supports.
Reference List Ching, F, D, K. (2014). Building Construction Illustrated. Hoboken, New Jersey: John Wiley & Sons.
Samuel Hill
Constructing Environments: Week 2 Logbook
Student Number: 722052