Interim Submission Journal Entries: Weeks 5, 6 + 7 Constructing Environments India McKenzie 639 234
week 5 Constructing Environments India McKenzie 639 234
Principles, planning and construction
WK 5_JOURNAL
This screenshot is from this weeks E-learning content and described the various timber beam structures. These examples are markedly different from our design which emphasised the design faults in ours which will be discussed in the next section.
The brief: The task we were given was
to construct a beam to span one metre that was to be subjected to extreme compressive forces. Each group was given different combinations of two types of timber; bracing ply 1200mm x 4mm and radiator pine (NZ) 42mm x 19mm. We were also given access to a hammer, a drill and various sizes of common bolts and nails. Our group was given 3 lengths of the pine and one length of the ply. First of all, we assessed the compressive and tensile strength of the two timber types. The ply was much thinner and more flexible thus making it an excellent tensile plank. Conversely, the pine was much more solid and stiff and was less effective in coping with tension. Image courtesy of R. Zuzek
Our finished beam
For this reason, we chose to cut one of our pine lengths into 6 equal parts and stack to create a block like structure. Our aim was to bolster the horizontal pine lengths with stabilising blocks. The ply wood was nailed to the bottom of the span as the bottom rail would be under the most tension as the top rail would be under compression once the force was applied.
LOAD
COMPRESSION
TENSION
In our planning stages, we consulted Ching (2011) for ideas, primarily looking through the chapters on floor, wall and roof systems. On page 4.35, “Wood Beams�, the various styles of beam construction are illustrated and describes the forces working on solid sawn timber beams. Ching, F.D.K, 2011, Building Construction Illustrated, 4th Edition, John Wiley & Sons. Diagram of sketch design
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Testing process Our beam was spanned between two chocks that propped up the beam. A metal plate was then placed inbetween the beam and the load bearing needle so that the needle would not burrow into the beam as had been an issue in the past. The needle was then wound down through a threaded spindle axis. The exerted force was measured in kilograms that was displayed on the screen as seen on this page.
The beam withstood over 100kg of pressure before serious stress began to show. The ruler as pictured below allowed us to measure the degree of deflection as the beam bowed under the concentrated load of the machine. From the neutral origin, the beam deflected over 5cm before it began to splinter. The first thing we noticed was a slippage of the blocks that we had stacked inbetween the top and bottom members. The reason for this was partly to do with our selection of fixtures. Our choice of nails proved to be ineffective as they can resist shear but not axial pressure as was being exerted on the deflecting beam. The fastener (nail) dislodged from its place and the blocks began to slip laterally as the top lateral member exerted considerable compressive force on the blocks below. The ruler illustrating delection. Image courtesy of R. Zuzek
Our beam tolerated a maximum load of approx. 250kg before splintering entirely. Interestingly, the ply board had not fully fractured which emohasises the tensile capabilities of the thin bracing ply as opposed to the relative stiffness of the thicker pine. It also suggests that the ply has a much higher ultimate stress point than the pine. This image shows that the blocks we placed in between the members proved to be ineffective at providing support. Rather infact, they created a detrimental weakness along the edges of the blocks as can be seen by the splintered breakage in the image to the right. From the Interactive Structures module on “Connections and Structural Systems�, we were instructed to consider the timber species, angle of load in relation to the grain, the wood moisture content and the number, spacing and position of fasteners. The latter point would have been of most influence in our design as more tactical placement of fasteners and support structures could have increased the ultimate stress point of our beam.
WK 5_JOURNAL The E-learning video this week that focuses on the material properties of timber proved to be rather telling when evaluating the effectiveness of our beam design. Both Hamish in the workshop and Claire on the video emphasised the importance of grain direction and imperfections in the wood in order to ensure that each length of timber is strong. This screen shot on the left shows the irregularities in timber that can cause fractures and splintering when put under considerable tension. Being able to identify these weaknesses in the wood remains a critical part of our material selection.
The image on the right showed the bowing of the ply in a lateral direction. The principles of this traditional box-beam are sound how Glenferrie Rd (Hawthorn) ever the construction process created weaknesses in the wood. The sheer number of nails and bolts in the elements of the beam created weak point at every disruption of the grain and thus, when placed under even just 80kg, the vertical ply wood that enclosed the beam deflected laterally. This began the discussion of fixtures, connections and construction methods and Hamish suggested that perhaps a strong adhesive would have been a more suitable fixture for this design. Althought we were restricted to just the two fastening options (nails and bolts), we were able to acknowledge the intent of their design as well as recognise the inherent weakness of nails and bolts as a timber fastener when placed under extreme compressive loads.
Image courtesy of R. Zuzek
The most successful beam was this semi-box beam construction as seen in the picture above. Bearing up to 550kg, this design proved to be the most efficient at coping with a concentrated load. The weakness in this design was once again the nail fixtures as they were unable to cope with the axial load. Interetingly, the irregular number and placement of the fixtures on each of the panels allowed us to identify the most effective strategy for fixing the two elements together. The panels that connected to the lateral beams with a one-nail connection allowed the top and bottom beams to deflect in opposite directions whilst the panels that were fixed at all four corners were less effective in that they restrained the flexing of the top and bottom rails and eventually disconnected from the main members.
Image courtesy of R. Zuzek
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Working Drawings
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Working Drawings
WK 5_JOURNAL NOTE: this scan corrupted. original hard copy available.
Working Drawings
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Working Drawings
week 6 Constructing Environments India McKenzie 639 234
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Structural Concept
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Structural Concept
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Structural Concept
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Structural Concept
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Structural Concept
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Structural Concept
Structural Concept
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Primary Structural Systems! Pad and pile footings! In-situ Concrete Slab ! Precast concrete panel! Wooden Roof beam! Columns !
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Secondary Structural Systems ! Steel stud wall! Roof rafters ! Roofing materials (waterproof system) ! Brick wall (double thick) !
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Structural Materials! Wood! Concrete ! Steel joists! Bricks !
Joints and Fixings! Nails and Bolts are prominent on the build as it is mostly wood to wood or wood into fixed joints ! (Fixings used in Emporium are shown below) !
Bolts secure steel and wood into existing structures (mostly brick walls and existing flooring!
This graphic denotes how the timber beams will support the roof. The beam is fixed in place with steel hangers and bolts to the wall (precast concrete slabs). Wooden battens are then placed on top of the beam using nails !
To secure the lateral structures to the horizontal framing steel flanges/ hangers are used and connected with two bolts !
Most connections between two wooden pieces are made using nails as they will not be subject to tensile forces !
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Structural Concept
Sustainability & Environmental Analysis: Steel ! ! The carbon emission of steel and concrete are high (figure below) compared to wood. Given that the main structural component of the building is concrete (with minimal wooden roof beams), it would imply the carbon footprint is also high, increasing the environmental impact of the building. Conversely, as the building is made of concrete it will also be durable and not need replacing or additional work. So the carbon footprint will wane overtime, and therefore compensate its sustainability. ! !
Economic Implications! ! The building is comprised using many quick building techniques (pre-cast concrete panels, exposed concrete slabs as finishes, using existing structures). Although the materials used may be costly, using these techniques will significantly reduce the build schedule and hence the amount needed for labor (which would primarily be the most costly part of the project). Therefore making the build more economically viable. !
week 7 Constructing Environments India McKenzie 639 234
Modelling Task
WK 7_JOURNAL
Internal Elevations (A.12 Emporium & Bar) Drawing no. A702
Internal Elevations (A.12 Emporium & Bar) Drawing no. A703
The segment of the redevelopment that we chose to analyse was the emporium bar section as is showed the connection of the planned building to the pre-existing structure. The room also uses a wide variety of materials and structural systems and therefore had scope for investigation. The internal elevations below show more detail than we wish to include but the human figure gave us a sense of proportion and scale when conceptualising the space. The drawings, combined with the architectural floor plans and the engineeers detail drawings allowed us understand the various systems and materials in play here and identify the key structural members and the supporting secondary members. We selected just the primary structural members to model.
Internal Elevations (A.12 Emporium & Bar) Drawing no. A704
Modelling Task: Overview
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The segment of the drawing shows the area of focus for our model making. We selected a 1:20 scale as the most approrpiate sise for our model as this size allowed for an acceptable degree of detail as well as being suited to our selection of materials. Our materials consisted of balsa wood of many varying shapes and widths which allowed us to represent different materials and construction methods in the model. We chose this segmenet to model as it showed both the existing wall form of the double brick cavity wall as well as the introduction of two new wall systems, the timber stud wall and the precast concrete slab wall. The model also integrates the roof system that here shows the roof beam with a single span rafter. The very slight gradient of the roof (only 2 degrees) faciliatates the use of the box gutter which has been used to great effect in the construction of the new addition to the site.
Timber stud wall Pre-cast conrete wall
The foundation system beneath the ground was also rather varied in that we could identify the pre-existing pad footing system of the existing building and the strip footing along the new built area.
Double brick cavity
Solid masonry columns Internal Elevations (A.12 Emporium & Bar) Drawing no. A701
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Modelling Task: Roof System
This drawing below shows the specific section that we were replicating on a 1:20 scale. We began by converting the measurements from the architectural drawings into our own scale and sketching out a scaled elevation similar to this shown. Although scaled disproportionately here to show detail, the architectural drawings were completed in a 1:100 scale which would not have allowed for enough details with our selected material. This section also indicates the roofing style which we replicated.
Rafter
Low slope Box gutter
Roof joists
Given the depth of our section, we included just one rafter but indicated the spacing by the distance from the stud wall as pictured on the left. The roof is supported by the roof beams that span between the double brick wall and the precast concrete wall. Unlike the gable and hip roofs of the existing building, this part of the addition adopts a flat roof style which is used primarily to facilitate interior drains as outlined in “roof slopes” on page 6.03 of Ching’s “Building construction illustrated. This section of the book also categorises roof slopes of 3 degrees or less as a “low slope” and therefore, with the 2 degree slope, can be classified as such. There is a need for a continuous membrane for the roof sheath. The way the roof achieves its “low slope” is through the tapering of the roof joists that sit on top of the rafter and underneath the roof sheathing. This could also be referred to as “purlins” however, roof joists is a more commonly used term. The drainage system used here also differs from the pre-existing drainage system. This is most likely due to the change in slope as the higher sloped roofs used the “half-round” open gutters that are common of buidlings of that era. The new internal drainage system is in keeping with the slick new aesthetic of the redevelopment. Ching, F.D.K, 2011, Building Construction Illustrated, 4th Edition, John Wiley & Sons.
Continuous membrane
Box gutter
Modelling Task: Wall System
WK 7_JOURNAL
Top plate Wall Cladding Stud
Noggins
Bottom plate Stud wall
Pre cast concrete
Double brick cavity
More commonly used in small-scale residential construction, the timber stud wall is a versatile lightweight internal wall structure. In the commercial context, it is more likely that steel studs would be used either in the form of c-studs or channel studs as seen on page 5.39 “light-guage steel studs” of Ching’s ‘Building construction illustrated’. Although not used in this instance, it is also common to have a diagonal steel strap bracing for added lateral support. The cavity that is created by the stud framework and the cladding is able to be used for utilities and insulation and offers a wide range of finishes.
The ingenuity of precast concrete walls is that it reduces the on-site labour required to construct the walls. As ‘precast’ would suggest, the panels are formed and set off site and brought in and simply slotted into place. Although this is a relatively expensive option, and has a comparatively high embodied energy, the longevity of the material offsets the initial carbon and financial expense. In this situation, the precast panel is only minor and connected to lightweight timber stud walls. The use of concrete also assists in sound/noise control which is an important factor for the emporium/bar.
This wall remains intact from th pre-existing building on the site and is typical of the era in which the original building was constructed. Benefits of this type of construction include the load-bearing capacity of the compressive masonry as well as being non-combustible. The cavity space inbetween the two wythes “enhances the thermal insulation value of the wall and permits the installation of additional thermal insulation material” (Ching, 2011, p 5.17). The cavity space also acts as a barrier against water penetration if it is left clear and if adequate weep holes and flashing are provided as described in detail on page 7.22.
Ching, F.D.K, 2011, Building Construction Illustrated, 4th Edition, John Wiley & Sons.
However whilst the double brick cavity wall may have numerous functional benefits as an external wall, the addition to the existing structure makes this part of the interior structure and thus many aspects are neglible. The aesthetic is arguably outdated and has an inefficient construction process in terms of manual labour. This is probably the reason why this construction method has not been used for the new parts of the building. It does however have a certain authentic charm and creates a fitting dichotomy between the old and the new in the emporium space.