Constructing Environments LogBook (Wk 2)

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WK2 – Studio Report During this weeks studio, the exercise we had to complete was to build a bridge out of a limited amount of materials that could span across a 150cm gap. The diagram on the left shows a few of the ideas that my group initially had about a design.

We looked at top bracing and bottom bracing, and the possibility of using an arch to distribute the load that would be tested on our bridge at the end of the studio.

Our group decided to use bridge number 2 from the diagram above as our actual design. We would construct a main base from 3 pieces of balsa wood and support it with trusses along both sides that would connect up to a secondary beam above the main base. The image on the bottom left of this page shows our Sinal design alongside the Sinal design of another group in the class.

The other groups bridge (the bridge on the right) was much wider than out bridge and did not have any upwards bracing. Instead the group decided to reinforce their bridge with horizontal struts that joined two main beams. Although this gave their bridge support from sideways compression, it was not as efSicient in carrying a load at the middle of the bridge, with bending occurring.

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The materials we were given i n c l u d e d a d h e s i v e s ( g l u e , blutack, pins and tape) and a 60x10cm piece of balsa wood.

Because we had a very limited amount of construction material (the balsa wood) and a wide gap for the bridge to span, our group decided to make a very thin bridge compromising of a main base and support. The balsa wood was split into the elements shown in the diagram below.

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WK2 – Studio Report

In order to create a bridge that would be able to span the 150cm gap multiple 60cm beams had to be joined together. The three base strips that our group cut from the balsa wood were 60x2cm large each and when joined together, would span approximately 180cm. This page shows what methods were used to connect these 3 base pieces.

When deciding how to join the base pieces together, a group suggested using a tongue and groove system that would lock 2 ends of different pieces together. We decided that this method of joining the base pieces would create the most structurally stable joint, as it fused two different pieces of balsa together, rather than just attaching the two pieces together. We created 1.5cm tongues on the ends of each base piece and began joining them together.

The diagram on the right shows the details of our tongue and groove system.

We wanted the joints to be really secure, so we used 2 types of adhesive as well as gluing a backing piece to the backs of the 2 joints. The backing piece is shown in the image to the right.

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The image below show how the 3 base pieces were connected, using tongue and groove joints. Glue and pins were used for this joint.

WK2 – Studio Report

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Load path for current model of the bridge (3 base pieces)

The bridge at this stage was just a long base strip that spanned across the 150cm gap. The diagram above shows the load path on this design, and we can see that because there is structural bracing, the bridge bends when any loads are added as the this load is not efSiciently distributed to the ground at the ends of the bridge. To Six this, bracing and support needed to be added to the base piece.

The diagram in the bottom left shows the method of joint construction. Initially our group wanted to use one long pin to attach two pieces of balsa together, however the length of the pins meant that we instead had to use 2 pins every time we wanted to attach wood together.

The result of double pinning pieces is shown in the photo before where arrows show position and orientation of pins.

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The support that we added to the bridge came in the form of side trusses.

We talked about using only one set of trusses glued to the middle of the base piece instead of using two one both sides of the base piece (to save materials to further re-­‐enforce the structure), but decided to go with this design.

Our group used pins to attach the trusses to the base piece and used a ruler to measure the gaps in between each set of trusses. A problem that we ran into, was running out of balsa wood.

Limited supply of materials meant that our group was forced to only add trusses to the center of the bridge, stopping about 30cm from both ends, compromising on strength and stability of the bridge.

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WK2 – Studio Report Once our support structure was completed the load path of the bridge was reassessed. With these re-­‐enforcements, the bridge was much more stable with more load being distributed through the structure. However, because the support structure did not span the entire length of the bridge, load distribution was far less efSicient than it could have been. A load path is shown in the image on the left.

In order to get the trusses over the largest span of the bridges base, the group decided to leave very large gaps in between the trusses. The diagram in the top right hand corner of the page shows the difference between the two. Although having larger gaps between the trusses created a less structurally stable bridge, this was compensated by the fact that the gaps allowed the trusses to cover a larger area of the bridge.

The tutor suggested that we try using the bridge upside down (shown in the photograph on the left) to see whether or not it made a difference to the design. Both versions led to bending in the middle of the bridge.

When our bridge was tested out, it was clear that not being able to Sinish the support structure that attached to the main base affected the strength of our bridge. The increase in weight at the middle of the bridge was not matched with increased support at the ends of the bridge, causing there the bending. At the end of the lesson, we tested this by cutting off the ends of the base piece so that the bridge was the same length as the support structure. This shorter bridge was much stronger than the original bridge, as loads were able to be transferred through the structure all the way to the ground, rather than having to go through the base beam.

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WK2 – Learning Loop Structural Joints

Structural Systems

SOLID – Stone, mud brick. Compression is main structural action found. Arches are efSicient features. Loads spread evenly through structure and all blocks are load bearing.

SURFACE – SKELETAL – Very common. EfSicient way of transferring loads.

Loads are focused on points.

MEMBRANE – EfSicient and cheap.

Construction Systems

> Enclosure system [shell of structure. Roof, walls, facade] > Structural system [system that holds the building up. Skeleton] > Service system [Gas lines, plumbing, AC] Choosing materials guided by: Performance requirement, Aesthetic qualities Economic ef:iciency, Environmental Impacts Common ESD strategies: -­‐ Local materials

-­‐ Thermal mass

-­‐ Solar energy

-­‐ Cross ventilation -­‐ Insulation

-­‐ Material efSiciency -­‐ Night air purging -­‐Wind energy -­‐ Smart sun design -­‐ Water harvesting

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1. Roller Joints -­‐ Most simple joint.

-­‐ Loads transferred in only 1 direction and pushing the load in any direction will move the load.

1. Pin Joints -­‐ Very common in construction.

-­‐ Modes of action possible in 2 ways.

1. Fixed Joints -­‐ Very complex because bending can occur.

-­‐Restricts vertical, horizontal and rotational movement.

WK2 GLOSSARY

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ESD – Environmentally Sustainable Design.

Recyclability – Potential for a product/material to be reused or transformed into a new product.

Carbon footprint – Measure of amount of greenhouse gas is generated during fabrication, transport and use of a product. The larger the product, the more positive/less detrimental affect it has.

Structural Joint – Joint where two or more structural elements meet.

Column – Vertical element of a structure that can be separate from main part of the structure. Usually load bearing.

Frame – A type of construction system. Consists of beams, columns and bracing.

Bracing – Element of a structure that braces (supports) another element/part.

Span – Length/full extent of something from one end to the other. The amount of space something covers.

ENVS10003 Constructing Environments