Week 3:!
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Serve to “support and anchor the superstructure above and transmit its loads safely into the earth.”! Loads! - dead and live vertical loads of superstructure! - natural elements - wind-induced sliding, overturning, uplift, earthquakes! - pressure imposed by surrounding soil mass and groundwater on basement walls! - thrust from arched or tensile structures! Settlement! - “gradual subsiding of a structure as the soil beneath its foundation consolidates under loading”! Shallow and deep foundations! - depend on the quality of soil, deep foundations extend through unsuitable soil until they reach hard rock, dense sand or gravel!
Strip footings - “the continuous spread footings of foundation walls” ! Stepped footings - multi-leveled strip footings !
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Image source: http://www.builderbill-diy-help.com/strip-footing.html
Week 3 Studio - On Site (Take one):!
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For the week 3 studio we visited ten sites on campus to study their structural composition and learn more about built scale and construction in general.! The first site we visited was one of the campus cafes. Here many of the structural systems were visible, such as the utilities, enclosure system and the components that were in fact structurally integral to the building. Predominantly the site is composed of concrete columns and slabs that allow for efficient construction of this simple design. The enclosure system was almost entirely glazing - at least on the wall we observed. We discussed the steel beam shown to the left of the photo here and arrived at the conclusion that it is purely aesthetic. !
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Another site we visited was simply a concrete wall that formed part of one of the lecture theatres. Here we concentrated particularly on the details of the wall that were of structural significance. Shown in the photos is a weep hole - a small gap in the rendering that allows water that penetrates the brick layer to escape back out of the building - and a flexible movement joint - a layer of springy rubber glue, of which there are several interspersed throughout the wall, which allows for the expansion and movement that naturally occurs in brick walls. !
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We also examined the supporting structure of one of the university car parks. Here we found that the structure is composed of many separated concrete columns that each bare the weight of a certain section of the floor above. Essentially the columns were composed of huge pre cast sections of concrete that were then stuck together on site. Concrete is shown here to be a good material for creating large supporting structures, however, one of it’s weaknesses was also highlighted. On one of the columns water was shown to have penetrated the concrete and had begun to erode it as the supporting steel frame was rusted and deteriorated. This problem, we were told, is fairly common and incredibly difficult and expensive to repair. !
Another site included a stair case with several ties connecting to a protruding beam that appeared to be in tension - though their structural significance was debated. This framework structural system was interesting as it showed to what lengths people go to create optical illusion, such as this idea that the stairs were suspended, in construction. !
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We also visited one of the canopies that cover one of the eating areas. This membrane system consisted of a thin plastic sheet that was pulled tight and held in position by metal wires that had been stitched into it and connected to large steel columns on the edge of the area. In the centre of the canopy it dipped and a hole was created to allow for water run off and wind penetration to minimise pressure build up and degradation.
Week 4: Floor Systems!
! Ching 04! !
Floor systems are the horizontal planes that must support both live loads (furniture, people etc.) and dead loads (weight of the construction). Must transfer loads horizontally towards supporting beams, columns or walls. !
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May consist of a series of linear beams and joists overlaid by sheathing or decking, or simply a slab of reinforced concrete. Depth of floor slabs is determined by the services that may be required within the structure, i.e. electrical, plumbing etc., and also by other factors that may need to be controlled, i.e. noise control and fire safety. !
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Steel:! Steel beams support steel decking or precast concrete planks! Beams may be supported by girders, columns or load bearing walls! Typically an integral part of skeleton frame system! Steel decking or wood planks have relatively short spans! Can be heavy gauge or light gauge! Girders (main beams) and joists (smaller beams)!
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Concrete! Slabs of various types may span the joists - one way slab, two way slab! Slab thickness is roughly equal to the span of the slab supporting joists divided by 30! Precast - created off site, or In Situ - created on site!
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Timber! Bearers (main beams) and joists (smaller beams)! Span of bearers determines the spacing of the piers or stumps! Spacing of bearers equals span of the joists!
Week 5 - Frames and Walls:!
! Ching 2.17 (Frames)! !
“A beam simply supported by two columns is not capable of resisting lateral forces unless it is braced. If the joints connecting the columns and beam are capable of resisting both force and moments, then the assembly becomes a rigid frame.”!
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Fixed frames - more resistant to deflection than hinged, more sensitive to support elements, thermal expansion and contraction.!
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Hinged frames - connected with pin joints, prevent high bending stresses as frame can rotate as a unit and flex slightly given changes in temperature.!
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Three hinged frame - two rigid sections connected to each other and its support by pin joints, sensitive to deflection, least affected by thermal stresses and support elements.!
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Loadbearing Wall:! “If we fill in the plane defined by two columns and a beam, it becomes a load bearing wall that acts as a long, thin column in transmitting compressive forces to the ground.”! Loadbearing walls are strongest when carrying coplanar loads as compared to perpendicular loads. ! For lateral stability loadbearing walls must rest on buttressing; pilasters, cross walls, transverse rigid frames or horizontal slabs.! Openings in loadbearing walls must be supported by a lintel or arch above - allows the compressive stresses to flow around the opening to adjacent sections of the wall.!
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Week 5 Studio - Model of the Oval Pavilion:!
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For this tutorial we built models of a given section of the Oval Pavilion - based on the drawing sets. This was both an introduction to model making in this subject, as well as to reading construction and architectural drawings. !
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Our section of the site was part of the canopy roofing structure from the front of the building. Essentially it is just a skeleton frame structural system, and it consists of timber and sections of supporting steel. Our model was made from balsa wood however, and shows only the integral structural frame, not the enclosure system of wood cladding. !
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Working from the drawings was initially confronting, as it is a new and demanding skill, but a system and pattern was eventually devised. This allowed for easy separation of the separate components of the structure so that it could be created efficiently. All joints in the structure are fixed joints to create an overall very rigid structure. !
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The problem we encountered was the difficulty in creating a rigid model, and as such it was left without a base because no suitable solution for getting the model to stand up could be found. Other than this, the model was quite successful in representing the section of the canopy at a 1:20 scale, and gives a good impression of the nature of the skeletal frame of the structure. !
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Compared to other groups our structure was more intricate, as it involved several members, but less structurally sound, due largely to the choice in material and model making competency. ! Overall the activity was useful in highlighting the complexity of architectural drawings and increasing our understanding of how constructions are intricately interdependent and structured.!
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Week 6 - Roof Systems:!
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Ching 06! “The roof system functions as the primary sheltering element for the interior spaces of a building. The form and slope of a roof must be compatible with the type of roofing… Like floor systems, a roof must be structured to span across a space and carry its own weight as well as the weight of any attached equipment and accumulated rain and snow.”!
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Loads - transferred to supporting structure:! Live occupancy loads - flat roofs ! Gravity loads! Lateral wind and seismic forces! Uplifting wind forces!
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Flat roofs (pitch 1º to 3º):! Require a continuous membrane roofing material! Minimum recommended slope of 1/4” per foot (1:50)! Slope usually leads to interior drains!
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Sloping/pitched roofs (pitch > 3º):! Low slope roofs - up to 3:12! Medium/high slope roofs - 4:12 to 12:12! Roof slope affects material choice, requirements for underlayment and eave flashing, design wind loads! Low slope roofs require roll or continuous membrane roofing! Medium and high slope roofs may be covered with shingles, tiles or sheet materials!
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Concrete:! -Generally flat plates of reinforced concrete! -Roof is sloped towards drainage - a waterproofing membrane is required for finishing!
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Structural Steel:! -Flat roofs! •combination of primary and secondary roof beams - for heavier roofing systems! •combination of roof beams and perlins - lighter roofing systems! -Sloping roofs! •Roof beams and perlins with metal sheeting! -Portal frames! •series of braced rigid frames (two columns and a beam) with perlins for the roof and girts for the walls! •usually finished with metal sheeting!
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Trussed roofs - framed roofs constructed from a series of open web type steel or timber elements.
Week 7 - Detailing for Heat and Moisture:!
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For water penetration ALL of the following conditions must be met:! An opening! Water present at the opening! A force to move water through the opening!
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Three strategies to remove water penetration:! Remove openings (via sealants or gaskets - deteriorate over time) OR! Keep water away from opening (gutters, downpipes and storm water systems & overlapping cladding and roofing elements & window/door sills and flashing) OR! Neutralise the forces that move water through openings - i.e. gravity, surface tension/capillary action, momentum, air pressure differential - using slopes and overlaps typically, a drip or a break is used between surfaces to prevent capillary action!
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Controlling heat:! Thermal insulation! Thermal breaks - generally made from rubber! Double glazing! Radiation - controlled by reflective surfaces and shading systems!
Week 8 - Openings:!
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Door frames:! Timber! Aluminium! Steel - often used in combination (offers impact protection) !
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Windows: ! Offer ventilation and sunlight.! Double glazed ! - Decrease heat transfer! - Decrease sound transfer! - Filled with argon gas! Glass! - Flat glass! - Shaped glass! - Float glass - clear float glass, tempered glass or laminated! -Tinted! -wired! -patterned! -curved! -photovoltaic! -glass channels! -slumped and formed! -glass fibres
Construction Workshop (5 May):!
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The task for the construction workshop was to build a structure - of any shape - from the given materials that spanned at least 1 metre and was no taller than 400mm. We worked in groups of three and were given an hour to construct our objects before they would be tested for their strength by being crushed. !
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Our materials included two 1.2m lengths of pine and two 1.3m lengths of thin plywood. Our design was devised fairly quickly and it involved a simple triangular shape, spanning 1.1m (to allow margin for error). This triangle shape was then going to be braced by the thinner plywood we were given and supported by a length of pine directly in the centre of the structure.!
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Our construction (shown in the bottom left and right corners) lasted quite well under the weight. It achieved a compression of 53mm and withstood an applied load of 253kg. The plywood bracing began buckling very quickly and proved to do very little in terms of support. The strongest component of the structure was in fact the vertical pine column in the centre. The final break came when the triangle points broke away from the bottom beam.!
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Other groups went for different, rectangular structures. These didn’t seem to last as well as they essentially depended on the integral strength of the pine beam alone.
Active Loads - Ching 2.09!
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“Wind loads are forces exerted by the kinetic energy of a moving mass of air.”!
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Structure must be designed to resist sliding, uplifting or overturning! Wind exerts positie pressure on the windward vertical faces of a building ! Wind exerts negative pressure or suction on the sides not facing windward!
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All information obtained comes from: ! LMS Weekly Learnings - presented by Clare Newton and Rebecca Cameron OR! Where referred to; “Building Construction Illustrated (Fourth Edition)” Ching, Francis D.K., 2008, John Wiley & Sons, Inc., Hoboken, New Jersey,!
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