Construction Journal Submission Report Week Three: TIMBER CONSTRUCTION WORKSHOP Nicole Tan 641433 Aim: To construct a timber structure (from supplied materials) that can withstand the heaviest load. Description and photos of materials and tools used: SAW: Used to cut objects. Technique: Always cut on the push.
MEASURING TAPE: Used to obtain accurate dimension measurements
SLIDING BEVEL: Used to draw straight lines and/or angles
BENCH HOOK: Used to protect the benches
PLYWOOD: 3 ply therefore has 3 layers. Each layer alters grain direction. Strong in the lateral direction
CROSS AND STRAIGHT PEIN HAMMER: Used to drive nails into objects.
PINE (18X45): Clear, straight timber grain
PINE (35X35) Figure 18A. Photograph of workshop equipment used (Tan 2013).
SLIDING BEVEL
Figure 18B. Photograph of workshop equipment used (Tan 2013).
BATTERY DRILL: Has a ‘clutch’ which adjusts drill configuration depending on the type of screw. Figure 18C. Photograph of workshop equipment used.
Constructing Environments Journal | Nicole Tan
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Sketch of own design:
Figure 19. Sketch of timber structure and its components (Tan 2013).
Photos of three designs: Note: our tutorial class is a small class and hence only had three groups for this workshop DESIGN ONE (OWN DESIGN):
Figure 20. Our triangular timber structure using the concept of trusses (Tan 2013).
DESIGN TWO:
Figure 21. Group Two’s structure (Tan 2013).
DESIGN THREE:
Figure 22. Group Three’s structure (Tan 2013).
Constructing Environments Journal | Nicole Tan
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Photo and description of structural performance and failure of designs DESIGN ONE (OWN DESIGN):
Figure 23. Deformation of plywood due to tensile forces (in red) (Tan 2013)
Our design was very efficient and successful in withstanding a heavy load due to its ‘truss-like’, triangular structure which enabled an efficient load transfer between members. The plywood attached to the triangular structure was the first element to deform due to tensile stresses induced by the screws attached to the pine members (see Figure 23). From the practical, it can be concluded that the plywood did not contribute to the overall strength of the structure and was merely attached onto the pine members.
Figure 24. Stress fractures around embedded screw. (Tan 2013)
The pine members displayed high tensile and compressive strengths however eventually it became subject to shear forces. It was especially evident through the stress fractures especially evident near the weaker regions where the screws were embedded (see Figure 24).
Figure 25. Tear in plywood due to tension. Screws have also been misaligned (Tan 2013)
Constructing Environments Journal | Nicole Tan
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DESIGN TWO:
Figure 27. Deflection of a beam (Tan 2013)
Figure 26. Plywood deforming (Tan 2013)
Figure 26 demonstrates that the structure was not well constructed or designed as elements of the system worked against each other – the wooden blocks pushing against the plywood. Timber is always stronger when loaded parallel to the grains (Vassigh 2008) however in this case the load was perpendicular to the horizontal beams resulting in severe deflection (see Figure 27). Moreover, the presence of a knot in the beam (Figure 28) further weakened the structure and caused it to snap and fail.
Figure 28. Fractures and cracks originating from a knot (Tan 2013)
Constructing Environments Journal | Nicole Tan
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DESIGN THREE:
Figure 29. Plywood members unable to take the concentrated load (Tan 2013)
Design three was the weakest design. Although they attempted to incorporate the rigidity of the triangle into their design, their choice of materials resulted in a weak structure. By using the thin plywood as their primary members, the material itself could not withstand the heavy load which resulted in deflection and collapse of their structure. From Figure 29, it can be concluded that because of the design, the stronger pine members contributed received little of the concentrated load which led to the structure being weak.
Constructing Environments Journal | Nicole Tan
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Constructing Environments Journal | Nicole Tan
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