ie School of Architecture

By 1830, the use of cast iron as internal structure was a fact. However all the buildings had an external enclosure, to protect the building from
weather, fire, and they provided the building against overturning. The skeleton frame has not enclosure at all, and it needs by itself to bear the loads and provide stability.

They afford this with 4 different methods:
1- Rigid connections between columns and beams (Hungerford Fish Market,1833 by Charles Fowler). Usually accomplished by interior masonry (or concrete) stair towers and elevator shafts that creates a vertical rigid core that resists deformation and torsion of the building due to external lateral forces.
2-Shear Walls - Exterior (or interior) walls built of masonry or concrete that act as a vertical cantilever beam resisting lateral loads. Problems - may interfere with exterior windows, labor intensive, heavy.
3-Moment-Resisting Beam-to-Column Connections - Typically accomplished by fabricating extra connection angles, welds and bolts that greatly increase the rigidity of the connection. Problems - extremely labor intensive and expensive.
4-Diagonal Bracing: The addition of diagonal "X" or "K" bracing that resists lateral loads. Problems - may interfere with exterior windows.. It was very used in railway stations
(Pennsylvania State railway, 1910).
Crystal Palace, with no enclosure at all, just glazing, Paxton, 1850. As an skeleton frame we can include the Eiffel tower, 1886.

The skeleton frame made the curtain walls and glazing possible, since all the dead loads are in the internal structure and not in the enclosure anymore.

The advantages of steel skeleton frame:
1. Can build very tall and wide (tallest buildings in the world)
2. Light weight and strong (much lighter and stronger than concrete)
3. Prefabricated - frames assemble quickly
4. Precise and predictable (excellent quality control)

Disadvantages of steel skeleton frame:
1. Steel is an expensive material (much more expensive than masonry or concrete)
2. Frames are unstable
3. Needs fire protection
4. Needs separate "skin" (walls and floors).

Connections while making a skeleton frame:
1 Rivets - Generally not used any more for reasons such as low strength, safety and poor quality control.
2 Bolts - Come in two varieties - carbon steel and high-strength. The carbon steel bolts obtain their strength through shear (or tension) along the shaft of the bolt only.
3 Welding - Welding is accomplished by mechanically joining steel together by heating electrodes into a molten state, which forms one piece from two. Creates extremely rigid connections. The most common type of weld used for building structures is the "fillet" weld, which joins pieces at right angles. It is common to shop-weld connection angles to beams and columns, then field-bolt them together at the job site.

ie School of Architecture lo descubrió en diciembre de 2009

listas: learning_CONCEPTS , s_XIX

etiquetas: skeleton frame , steel

Home Insurance Building was erected in 1885, Illinois. The rchitect was William Le Baron Jenney, an engineer.

This building is the begining of curtain wall, as it is the first offices building in using a Skeleton frame made out of steel and iron.
The skeleton consists in horizontal beams and vertical columns, all made out of metal. It is said that it is not a pure steel framed structure since it rested partly on granite piers at the base and on a rear brick wall, to hold the building against wind.
It had 12 stories high, and it is consider as the first skyscraper.
Jenney discovered that steel frame could support a tall building as well as the stone walls could. The buildng weighed one-third as the same one built in masonry.
As the skeleton supported all dead loads in the building it was possible to start thinking about glazing skyscrapers, and do more and more openings until reach a completely glazed skyscraper.

ie School of Architecture lo descubrió en diciembre de 2009

listas: s_XIX , use_OFFICE_WORK_SPACES

etiquetas: curtain wall , home insurance , le baron jenney , skeleton frame , steel