Sculpting Bio-Synergies (UO Thesis Work): Week 8: Update/ Materials Research

This has been yet again another week from HELL. Our talk with Suenn at the end of studio on Friday helped me realize that I needed to reexamine my diagram/Concept, both at the urban scale and at the site/building level. I discovered that there were problems at the Urban level and it was keeping things from jiving at the building level.

As I have begun to flesh out that diagram/concept I am beginning to see what some of the reviewers were talking about. By calling my project a transit pavilion, it gives the connotation that it wants all of the transit modes to be adjacent to its site, which im my urban context is unfortunately not possible. So I can see why the reviewers were uneasy about where I have placed the variety of modes in relation to my building. I reminded myself that my thesis is about activating Gateway and using an urban space that transitions into a green street as a means for doing this.

Being as unbiased as I can, I have decided to rethink my thesis and diagram in the hopes to better inform my building parti and relation to there area. I know this has been frustrating for my instructors, but if the parti is strong as both a building and as an urban shaper it will make the rest of the building fall into place. It makes the most sense to resolve building problems at the Parti/urban level first while it is still a simple diagram, rather than trying to make revisions to a building that is composed of tons of program after the fact.

I am starting to feel the friction of my own design process (not perfect by any means) and the one that has been structured for our thesis studio. I think I have made the best of it, and have tried to approach each assignment open-minded. There comes a point where I need to edit what I am doing towards my project and weigh whether it will be beneficial or not, and if it is helping flesh out the ideas specific to MY thesis.

I am looking forward to the final review for this term and am excited to hear feedback that can help me strengthen my project. I feel confident that the time I spent this quarter really hatching out things at the urban level will allow me to easily slip into the building and move into design development full heartedly knowing that this building is in harmony with its context and doing what my thesis set out to do.

Materials Research: CAST-IN-PLACE CONCRETE

FORM+FUNCTION

In almost every commercial construction project more than likely one can find the use of cast in place concrete. Depending on the structure this subassembly can be used in many different ways; as the core of a building which is used for lateral strength or simply a wall to hold a companies logo. Cast in place is concrete which has been poured into a constructed form, (made of wood, steel, heavy plastics, or foam) which is then removed once cured to create a structure. The expression of form that is possible with c-i-p are only limited to the shape of the form constructed. Cast in place plays a very important role in the construction process in that certain structure pertinent to a building cannot be created using pre-cast. Structure such as caissons, spread footings, slabs on grade, elements too large or too heavy to transport, and slaps toppings over pre-cast floors are parts of construction that can not depend on pre-casting. These elements have to be cast as needed during the construction process.

Cast in place structures tend to be more of a massive construction process and can steer projects towards using either pre-cast or structural steel as an alternative if foundation loads are vital. Casting can also be time consuming, which can increase construction time. Each level of the building or elements must be first formed, then reinforce, poured, cured, and finally stripped of the forms before construction of any other levels can commence. Consequently, cast in place for most construction site takes place where weather is in constant contact with it, which at time can make it less structural than that of pre-cast and steel. These are manufactured most always in a controlled environment that insures the concrete or steel is as structurally sound as it possible can be. However, several technological advances have made casting in place one of the more favored building techniques of architects and engineers. Some limitations are now being eliminated by streamlined methods of material handling, using materials to make forms reusable, and extensive fabrication of reinforced elements.

METHODS OF ASSEMBLY

FORM TIE DETAIL
(Allen: Fundamentals of Building Construction)pg511

CASTING PROCES (Allen: Fundamentals of Building Construction)pg509

Walls that are cast at ground level usually rest on a foundation or a strip footing. The thickness of the footing and necessary steel reinforcements are determined by a structural engineer. While the concrete is wet strips of wood are placed where the wall will rest to create a key hole which will act as a mechanical connection. Inside this groove are placed vertically steel embeds such as rebar and j bolts which work as anchors connecting the wall to the foundation. Steel is used as an embed over other metals in that steel and concrete have very similar coefficients for thermal expansion. This means when the steel inside the wall expands or contracts due to temperature, it will not put any strain on the concrete and cause it to crack because the concrete will expand and contract at the same rate the steel does.

Next, vertical and horizontal pieces of re-bar are tied together to create a reinforcement for what is going to be a concrete wall. A wall may either require one re-bar frame located in the middle of the wall, or two located near the surface of the wall. This requirement is specified by the structural engineer. L-shaped horizontal bars are installed at corners to maintain structural continuity between two walls. If the top of the wall being poured will connect to either another floor slab or to another wall, rods will be left exposed from the form work. These rods will later act as a place to attach other reinforcing and will give the other parts strength.

Wall forms may be custom built of plywood, but it is more common these days to see the use of prefabricated panels. These panels are then coated in a release compound which will make removal of the forms easier. The forms are next placed on the footing, aligned and then braced with studs. Form ties are inserted through pre drilled holes which align with both sides of the forms. It is important that these tie rod do not touch the steel framing inside the form work. They need to be spaced from the re-bar far enough that both parts can be completely surrounded by the aggregate in the concrete. The form ties are next fastened to both sides of the form using a type of friction connection and horizontally placed studs called whalers. The wall is lastly secured with diagonal braces which are attached to slab or ground as extra strength to resist the hydraulic pressure from the pour. After the forms are inspected for straightness and plumpness the desired height is the marked inside the form all around. It is now the forms are ready to be filled with concrete.

Once the concrete is brought to the sight, test cylinders of concrete are made and a slump te st is conducted to test for proper pouring consistency. A large wall can be filled easily by using a concrete pump hose. Very large pours that may be too difficult to get to may require the use of a pump truck, which has a hose connected to a mechanical crane arm. Workers standing on planks or scaffolding facilitate the pouring into the form work. Other works use run vibrators through the freshly poured concrete to remove any air bubble that may have formed during the pour. The top of the pour is then covered with a protective plastic sheet or canvas which will shield the concrete from the elements while it is curing.

CONCRETE

The dimensions of concrete when being used as cast in place are virtually endless except to the structural standards necessary to make a building sound. When used as a residential slab concrete is poured to a thickness of 3 inches. For Industrial floors 6-8 inches and airport runways can be a thick as 1 foot. It is important when pouring large amounts of concrete to leave a controlled joint to allow for any cracking that may occur to not disfigure the concrete surface.

After concrete has been poured into place more often than not things need to be fastened to it. Some of these things may include interior partitions, hangers for pipes, ducts and conduit, suspended ceilings, stair railings, cabinets, and machinery. Thankfully there are several embed available for doing this. Some of these embed need to be placed into the concrete before it is poured. When ordering a pre-cast piece these things can be specified in details which will allow the manufacture to make sure these embeds are in the final product. However some fasteners can be drilled into the concrete after it has already been poured.

Embodied energy of normal reinforced concrete is pretty high but can be reduced by using recycled steel and aggregate. Cement from an efficient kiln and use of cement extenders can further reduce embodied energy. The embodied energy for cement is roughly 5.6 MJ/KG.

(Allen: Fundamentals of Building Construction) pg542

Concrete can be finished in several different manners. Most common is concrete that is cast against overlaid plywood which gives a smooth surface but slowly develops hairline cracks as it ages. Others include veneered plywood impressions, exposed aggregate, bush-hammered and finally made famous by Paul Adolph is ribbed and bush-hammered which is achieved bb placing ribs inside form work before pouring. Concrete can be given a nice aesthetic quality by adding a dye to the concrete when mixing to give it a stained color of desire.

By reducing the amount of water added when mixing concrete can increase concrete from weathering. The most potentially destructive weathering factor is freezing and thawing while the concrete is wet, particularly in the presence of deicing chemicals. Deterioration is caused by the freezing of water and subsequent expansion in the paste, the aggregate particles, or both. With the addition of an air entrainment admixture, concrete is highly resistant to freezing and thawing.

Typical cost of concrete per yard is $87.01 per yard

Light weight concrete construction has a fire rating based off the thickness that the concrete wall or slab is. Below is a table for determining fire rating for a cast in place slab.

Due to high density, concrete and concrete block walls have good TL values (STC's in the 40s and 50s for 4-8" thickness) but their weight, adds complexity of construction and poor thermal insulation tend to limit their use as viable materials in most residential wall construction, except in area where temperate climates, hurricanes and tornados are prone.

Like fire rating the R value of concrete is based off the thickness of the material. Poured concrete has a R value of .08 per inch, CMU has a R value of .8 for a 4” block, 1.11 for an 8” block and 1.28 for a 12” block. It is necessary to insulate concrete especially those which are exterior walls. Current code requirements call for an R value of 17 to 22 for exterior walls. Concrete has a thermal expansion coefficient of .0000055 in. /in. / ºF .

EVOCATIVE APPLICATIONS