Walls

On today´s lesson we talked about walls. Walls are often used to support loads, to insulate the building and to works as a climatic  enclosure, protecting the building from wind, rain and snow.

Walls can be load bearing so support the floor and roofs or non load bearing, but they always separate a place from another, so they work like filters in space. That is why their qualities affect so much the space they create.

There are different types of walls made from different materials, according to the requirements of the context and the clients wishes. A wall can be a solid wall that carries its loads in compression throughout its length and so it requires supporting beams or a continuous foundation. Wall can also be a stressed skin around a framework, that act in tension.

Concrete walls can be cast in site or be a composition of prefabricated panels or blocks. Concrete is great in compression but lousy in tension, so it is often reinforced with steel bars. It is called a composite.

Modular panels can be produced off site,  in other words prefabricated. They can have many different finishes and forms, depending on the form-work it was cast.

Examples of cement finishes.

As when molded on site, cement blocks can be reinforced with steel bars.

Masonry walls are made of piled up modular blocks, usually made of clay, stone or concrete. They are various ways a masonry wall can be stacked and they create different patterns. Usually they are hold together with the help of mortar that is made of sand, cement and water. In the past masonry walls were stacked without mortar, relying completely on gravity forces.

Cavity walls are made of two skins of block and brickwork that are tied together with metal ties. In the between of these two skins remains a 10 cm wide gap that contains insulation and prevents humidity from entering the building.

The thickness of a wall depends on the diameter of load bearing elements, and their frequency and the height of the building.

Timber wall´s core is a timber frame that is composed of different members that keep the structure stable and secure. They are presented in the drawing below

These frames can be coated with timber cladding or panels or even another material like metal.

When renovating a 100-year-old timber house different elements were found.

Glass structural walls are very popular in the contemporary architecture since they allow natural light into the building, and have a beautiful uniform surface that goes along the facade without disruptions. Freeing the facades from bearing the loads, revolutionized architecture and the interior spaces.

Glass panels are attached to a framework via variety of fitting options, architect chooses the right one depending on the economic, aesthetic and environmental issues.

Glass facade of Dtansted airport

 

 

Bibliography:

Silver, P., McLean, W. (2008) Introduction to Architectural Technology, Laurence King Publishing, London

Benedetti C., Bacigalupi, V. (2005) Materiali & Progetto, Edizioni Kappa, Roma

Balfour Beatty Ground Engineering (Internet) Available at: http://www.bbge.com/?page=DiaphragmWall (accessed 01.03.2012)

Institute of structural engineers (Internet) Available at: www.istructe.org/…/75af4a72-36ac-4765-bd90-9f37db85b814.pdf (accessed 01.03.2012)

Pro Interior Design (Internet) Available at: http://prointeriordesigner.com/construction/walls/ (accessed 01.03.2012)

Metro GlassTech (Internet) Available at: http://www.metroglasstech.co.nz/catalogue/139.aspx (accessed 01.03.2012)

 

Images:

Texture King (Internet) Available at: http://www.textureking.com/index.php/category/concrete (accessed 01.03.2012)

Texture Zine (Internet) Available at: http://texturezine.com/textures/rock-stone/concrete-textures.html (accessed 01.03.2012)

Copyright free images (Internet) Available at: http://www.copyright-free-images.com/textures-and-patterns-copyright-free-images/concrete-texture-copyright-free-images/concrete-surface.jpg.html (accessed 01.03.2012)

Devian art (Internet) Available at: http://agf81.deviantart.com/art/Concrete-Texture-8-197981630 (accessed 01.03.2012)

RGB Stock (Internet) Available at: http://www.rgbstock.com/photo/mif5zcQ/concrete+art+texture (accessed 01.03.2012)

Integrated publishing (Internet) Available at: http://constructionmanuals.tpub.com/14043/css/14043_234.htm (accessed 01.03.2012)

Pro Interior Design (Internet) Available at: http://prointeriordesigner.com/construction/walls/ (accessed 01.03.2012)

House-Energy (Internet) Available at: http://www.house-energy.com/Walls/Cavity-Insulation2.html (accessed  01.03.2012)

Stability

Stability is a very important factor when designing buildings. Lateral loads such as the wind and seismic loads  and the ground  type have to be taken under consideration.

When considering structures stability, cost and strength become the main focuses. The aim is to create a structure, with minimum use of material, that  supports its own weight and withstands external forces applied to it.

As we already know triangle is the simplest geometric for that does not change its shape when the lengths of its sides are fixed. So it needs the minimum material, does not deform easily and it is able to balance stretching and compressive forces inside the structure.

A simple test with an A4 paper that resisted much more than its own weight when folded to triangular shapes.

There are three ways to stabilize a structure and augment its resistance to lateral forces: Braced frames, rigid frames and sheer walls.

Bracing is a method to reinforce buildings via transferring horizontal loads trough diagonal elements, so basically creating triangles. This frees the walls from resisting loads and can be reduced to minimum. Bracing can be applied to any rectangular structure. It maximizes the weight of loads that a structure is able to support.

There are different types of bracing such as Cross bracing, K (Chevron) bracing and Eccentric bracing.

The cross bracing is the most common type of bracing. It is composed of diagonal supports that intersect with each other forming an X. They support compression and tension forces.

Cross bracing at the Stansted Terminal

The K (Chevron) and the Eccentric bracing are very similar,they are made of  V-shaped diagonal elements that do not cross each other and so offer more possibilities for openings (doors and windows). The eccentric bracing, commonly used in seismic regions, unlike in the K bracing, the diagonal elements do not meet in the beam they end up in.

Rigid walls, also known as moment frames offers even more possibilities for openings but are more expensive and time-consuming option since they need stronger more detailed connections. The moment frames support vertical loads in bending, and then return to their former state, like an elastic banner without causing harm to the construction.

Often braced frame and rigid frame can be combined and so result even in a higher resistance.

Portal Frames are usually used in low buildings housing a large open space. The most common materials are steel or steel inforced concrete. Portal frames are made of columns and beams attached together with strong and rigid joints. These joints carry bending forces and transfers horizontal loads first to rafters and then to the columns and ground.

Shear walls are composed of braced panels, also known as the shear panels.  They are used to stiffen structural frames. The shear wall should resist forces directed along the length of the wall and  have the strength and stiffness to support the forces

The structure nature of the sheer walls make them impossible to be cut open or moved. The work as a rigid core of the structure that support the floors plates and usually houses staircases or elevators of the building.

Masonry walls carry a great compressive strength but is weak in tensile strength so twisting and stretching. Openings effect the stability. especially openings in corners can result in instability. A masonry wall can be reinforced, either by thickening the wall, applying a steel enforcement or vertical columns at intervals.

In ordinary domestic construction, usually the internal walls and floors are sufficient enough to support the walls effected by lateral loads. This is called diaphragm action. A horizontal gravity load element (roof, floor) transfer lateral loads to the shear walls or frames through in-plane share tress.

Shear walls and floor used as a diaphragm in Stansted Terminal

Bibliography:

Silver, P., McLean, W. (2008) Introduction to Architectural Technology, Laurence King Publishing, London

WordPress (Internet) Available at: http://capitalsteelbuildings.wordpress.com/2010/10/10/the-stability-of-steel-frame-buildings/ (accessed 02.02.2012)

Tata steel (Internet) Available at:  http://www.tatasteelconstruction.com/en/reference/teaching_resources/architectural_studio_reference/history/the_development_of_the_steel_frame/bracing/ (accessed 02.02.2012)

Slide share (Internet) Available at: http://www.slideshare.net/nadimnit/bracing-connections (accessed 02.02.2012)

Maths in the city (Internet) Available at: http://www.mathsinthecity.com/sites/most-stable-shape-triangle (accessed 02.02.2012)

Wise geek (Internet) Available at: http://www.wisegeek.com/what-is-a-shear-wall.htm (accessed 02.02.2012)

Abag (Internet) Available at: http://www.abag.ca.gov/bayarea/eqmaps/fixit/ch3/sld002.htm (accessed 02.02.2012)

Wikipedia (Internet) Available at: http://en.wikipedia.org/wiki/Shear_wall (accessed 02.02.2012)

Sheld blog (Internet) Available at: http://shedblog.com.au/what-is-a-portal-frame/ (accessed 02.02.2012)

Wikipedia (Internet) Available at: http://en.wikipedia.org/wiki/Portal_frame (accessed 02.02.2012)

Tata steel (Internet) Available at: http://www.tatasteelconstruction.com/en/reference/teaching_resources/architectural_studio_reference/technology/the_fabrication_and_erection_of_steelwork/lateral_stability/ (accessed 02.02.2012)

Wikipedia (Internet) Available at: http://en.wikipedia.org/wiki/Diaphragm_%28structural_system%29 (accessed 02/02/2012)

Images:

modified image, original from All Posters (Internet) Available at: http://www.allposters.com/-sp/Stansted-Airport-Terminal-Stansted-Essex-England-United-Kingdom-Posters_i2662690_.htm (accessed 02.02.2012)

AISC (Internet) Available at: http://www.slideshare.net/nadimnit/bracing-connections (accessed 02.02.2012)

Wikipedia (Internet) Available at: http://it.wikipedia.org/wiki/File:London_Stansted_Airport_Terminal_Model_1.jpg (accessed 02.02.2012)

 

 

Trusses

testing truss model´s load bearing in the class

A truss can be considered a beam. But a truss is composed of straight separate elements. Trusses comprise one or more triangles, that are structured by separate members whose ends are connected at joints.

Triangle is the simplest geometric form that does not alternate its shape when the lengths of each side is fixed. A rectangular shape can be alternated much easier by forces.

Trusses are ideal for larger scale projects since they are using less material than solid beam. This results in lightweight and more economic solution.

It is assumed that external forces act only at the joint instead at intermediate points of the separate parts.  The forces applied to the singular elements are axial forces that work in tension or in compression (or in both). Which element carries which forces depends on the direction of the bending and the truss type.

A patt truss. -vertical elements respond to compression -horizontal members to tenstion -longer diagonal members work in tension for gavity load effect

The members of a truss are: chords ties and struts.

Chords are considered the horizontal elements that carry load in tension and compression. The truss web is composed of vertical and diagonal members that carry the shear force. Struts are parts of the structure that has a tensile force acting upon it and a tie has a compression force acting upon it.

examples of ties and struts

Types of trusses

A planar truss is a truss where all the members lie in a two-dimentional plane, when a space truss reaches three-dimesionality.

A simple truss is completely made out of triangles.

A pitched or also known as the common trusses are characterized by the triangle and are often used in roof structures. Parallel chord trusses are often used for flooring. If you combine these two you get a truncated truss that are used in hip roofs.

truss types

 

There are many different types of trusses with various compositions. Depending on the purpose of the structure and its requirements (needs of openings, aesthetics ect,) , you choose the right kind of truss type. Chord and web sizes are determined by the span, load and spacing of the structure. The depth so the distance between the top chord and the bottom chord is essential when aiming for the optimum efficiency of the structure.

Trusses are used in a huge variety of purposes and projects. Here are some interesting projects, from our field trip to Rome, realized with a truss structure.

Gas holder "Il Gasometro" Ostiense

 

"Palazzo del nuoto" Olympic swimming stadium by Calatrava

Basic Structural Principles: Load Paths

LOADS & LOAD PATHS

There are various loads that apply to a building. They get categorized into live and dead loads. The latter is also known as dead load, meaning the weight of all of the components of the building such as the building materials. Live loads are components that change in time such as the people who use the building or the wind.

These loads acting upon the building from different directions, horizontally and vertically, may take various paths in the building but their common destination is foundation in the ground. The ground works or should work as an opposite, equal force to these loads in order to keep the building stable.

A structural engineer works for transferring different loads to the ground and equalize  opposite forces to assure a stable and secure structure.

In our first blog entry we were to choose a building and look at its structure and how its loads act upon it.

I chose the Stansted Terminal from  Foster + Partners because I find the building fascinating with its the structure in sight.

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The structure is composed of 36 structural steel “trees” that form a grid system throughout the building.

the grid

This grid forms the lightweight roof that has a reticular structure. It has four primary beams on each side of the block, that hold a metal grid inside.

The roof is supported by the tree columns that are composed of four columns that transfer load in compression. They are attached together by vertical beams that are much smaller since their function is to transfer load in tension, prevent bending.                                From each of the four columns departs a diagonal cable that arrives until the corner of each block of the ceiling structure.

From each column departs also a smaller chord. These chords meet in the center, above the columns and tie them together, again preventing the four beams from bending. From this knot parts other four always smaller cables that arrive in the corners of the ceiling block.

the structural tree and vertical load paths

The vertical loads transfer through the corners of each ceiling block to the diagonal chords and then to the columns, that arrive until the ground and end with cement foundation. The load transfers through these elements to the ground.

The pavements of the ground floor is supported by another separate structure around the previous one.

the floor supporting structure and how loads apply to it

The floor is based on primary beams that form a square around the other structure. From the primary beams depart secondary beams that hold the pavement. The floor transfers load in bending.

From the central primary beams part four columns that end with cement blocks foundation below the ground. These columns transfer various loads directly to the ground. The is possible because the pavement is made of concrete.

The Lateral loads are supported and transferred to the ground through the column trees, the metal grid of the walls and the stiff cement floor.