Structures - Test 2

what is force?

a physical influence, caused by a load which changes, or tries to change, the state of rest in a body
form may also deform or deflect a material body

how do we observe the results of force?

in the form of movements or deformations of a body

what does the move SPACE ODYSSEY show about force?

the rotating wheel space station creates/generate an environment of artificial gravity

how do tuning force show force?

they can resonate with each other, transferring the invisible force causing the vibrations

what has to occur for equilibrium to exist?

for every action (force) there is an equal and opposite reaction (reaction force)

what is the most fundamental observation of equilibrium?

forces have direction

if a body is at rest on a horizontal plane, it certainly exerts a pushing force on the surface of that plane, the force being __gravity force__

what maintains equilibrium on the body?

there must be another force acting on the body which maintains equilibrium (the body at rest) - **this is the reaction force**

how do the three dimensional planes in the **organ of balance** work together?

they cover all the degrees of movement in the joints (ankles, knee, elbows, shoulders and jaws) in the same plan as the organ of balance

what is the line of action?

force acting along the same line are in the same line of action

the line of action force and the reaction force can maintain equilibrium if they are equal

how do forces act on a body to cause ROTATION?

both the magnitude of the forces causing the rotation, and the distance from the force to the point (or axis) through which the rotation takes place, are relevant parameters that explain the action

what is **the moment of a force, M?**

both force and a distance are involved

moment = force x distance

M = P x L

Moment M = Force (P) x Lever Arm/ Distance (L)

what is the moment arm?

the perpendicular distance between the line of action of the force and the point/axis about which rotation occurs

what is the **lever principle?**

illustrates the effects of moments

because of the differences between the lengths of the moment arms **a** and **b, a** being much longer, the magnitude of the necessary applied force **A** will be significantly smaller than the weight **W** to be lifted

the forces involved are proportionally related as the inverse ratio of the corresponding lengths

torsional moments - door handle

is is perpendicular to the door, rotates to unlock, while also acting outside the plane of the elements involves, a distance **a** from the axis of rotation

when and how did the United Arab Emirates use concrete?

6500 BC in the United Arab Emirates area

structures by the Nabataea traders in regions of Syria and Jordan

concrete floors, housing structures and underground cisterns

when and how did Egypt and China use concrete?

3000 BC

Egypt: mud mixed with straw to bind dried bricks (used gypsum mortars and mortars of lime in the pyramids

China: the Great Wall of China was built with a form of cement

when and how did Rome use concrete?

600 BC Rome

re-discovered by the ancient Romans while quarrying limestone for mortar on the slopes of Mount Vesevius

were the first to utilize the material at a major scale (widespread) and are created to have *discovered* it

accidentally re-discovered silica and alumina-bearing mineral that, when mixed with limestone and burned, produced a cement that exhibited a unique property

what was special about the concrete used in Rome?

when mixed with water and sand, it produced a mortar that could harden underwater as well as in the air

this mortar was stronger, harder, much more adhesive and cured much quicker than the ordinary lime mortar to which they were accustomed

what does recent research say about roman concrete?

research has found that concrete mixes from the roman empire are the world’s longest lasting, even when compared to modern mixes

the concrete seawalls constructed to form a coastal defense __**continued to strengthen**__ because of the minerals and their natural chemistry

explain the chemical reaction that occurs with roman concrete

the chemical reaction between saltwater and volcanic ash used in the mix generates interlocking minerals that get stronger on a daily basis due to the waters tide, allowing the concrete to be much more durable (less cracking)

roman concrete vs modern concrete

modern concrete will corrode over time when exposed to salt water

roman concrete strengthens wen exposed to saltwater

what examples of new architectural possibilities did concrete aid in?

roman baths, Caracalla and Diocletian

barrel vaults and their intersection possibilities

pantheon

roman colosseum

what is reinforced concrete?

concrete in which steel bars are embedded to resist tensile forces

when did reinforced concrete come into widespread use?

when a French gardener *Joseph Monier* obtained a patent for reinforcing concrete flowerpots in 1867 and went on to build concrete water tanks and bridges

what was the first house made in reinforced concrete?

francois coignet house 1853

built in a very traditional way with the supporting walls in compression and with limited window openings

approximately what time did engineers begin to experiment with *prestressing?*

by the end of the 19th century

what did Eugene Freyssinet do?

in the 1920s he established a __scientific basis__ for the design of *prestressed concrete* structures

patented in 1928

how is prestressed concrete produced?

produced by mixing course and fine aggregates, Portland cement and water and allowing the mixture to harden

what happens during the hardening process when making prestressed concrete?

during the hardening process (called the curing process) considerable heat (heat of hydration) is given off as the cement combines chemically with water to form __strong crystals__ that bind the aggregates together

what happens during the curing process of prestressed concrete?

as excess water evaporates from the concrete due to the generated heat, the concrete shrinks slightly

what is consolidating concrete (SCC)?

a concrete that fills forms completely without requiring vibration or any other method of consolidation

how is consolidated concrete formulated?

formulated with more fine aggregates than coarse ones, a reversal of the usual proportions, and it includes special **superplasticizing** admixtures

how does consolidated concrete flow and where is it used?

this mix flows much more freely and may be used where forms are crowded with steel reinforcing

portland cement type 1

normal standard use

portland type 1A

normal, air entraining

portland cement type 2

moderate resistance to sulfate attack

portland cement type 2A

moderate resistance, air entraining

portland cement type 3

high early strength

portland cement type 3A

high early strength, air entraining

portland cement type 4

low heat of hydration

portland cement type 5

high resistance to sulfate attack

when do you use cement that has a resistance to sulfate attack (type 2 + 5)

used where the concrete will be in contact with water that has a high concentration of sulfates (salt)

when do you use concrete that has high early strength (type 3)?

it hardens much quicker than the other types and is used where a reduced *curing* period is desired (ex. cold weather) in the precasting of concrete structural members, or when the construction schedule must be accelerated

when is concrete that has a low heat of hydration used (type 4)?

used in massive structures such dams where the heat is emitted by curing concrete may raise the temperature of the concrete to damaging levels

concrete admixtures: air entraining

increase the workability of the wet concrete, reduces freeze-thaw damage and when used in large amounts, creates very lightweight nonstructural concrete with thermal insulating properties

concrete admixtures: water-reducing

allows a reduction in the amount of mixing water while retaining the same workability, which results in a higher strength concrete

concrete admixtures: high-range water-reducing or superplasticizers

organic compounds that transform a stiff concrete mix into one that flows freely into the forms. used either to facilitate placement of concrete under difficult circumstances or to reduce the water content of a concrete mix in order to increase strength

used in self consolidating concrete

concrete admixtures: accelerating

cause concrete to cure much faster

concrete admixtures: retarding

slows its curing to allow for more time for working with the wet concrete

concrete admixtures: coloring agents

dyes and pigments used to alter and control the colour of concrete for building components whose appearance is important

how is the “concrete slump test” performed?

1. fill a standard cone 1/3 full and tamp 25 times with rod
2. fill cone 2/3 full and tamp 25 times then fill full and tamp 25 times, screed off excess flush with top
3. lift cone off concrete, measure the amount the concrete slumps below the top of the cone

what does *quality* concrete refer to?

concrete designed to fulfill the requirements of its specific use under which it must serve

what is a *paste* refer to in terms of concrete?

portland cement (the “glue”) and **clean** water create a chemical reaction

what are the different kinds of *aggregates?*

fine - dust - 1/4 inch

course - 1/16 to whatever size is needed for specific construction

what does the quality of the paste determine?

strength, durability, water tightness and abrasion resistance

what is strength and water tightness determined by?

the water cement ratio

more water = weaker concrete

less water = stronger concrete (compressive strength), better quality, durability, less damage due to __freeze thaw cycles__

curing time determines…

strength (it is kept moist)

7 days, 28 days, 90 days, 6 months

hardened concrete…

expands and contracts due to temperature

what are the 5 essential requirements of quality concrete?

1. proper selection of materials
2. correct proportioning in mixing and transportine
3. careful placing and consolidation
4. skillful finishing


1. adequate curing

what are the 2 primary ways of producing concrete structural components?

precast - primarily done in a factory in a controlled environments and then the product is transported to the site

\
or cast-in-place

what are the elements of precast concrete?

slabs

beams

girders

columns

wall panels

what is critical to the precasting process?

joinery\`

what advantages does precasting have over site casting?

1. conveniently cast at ground level
2. highly mechanized mixing and poring operation and frequently carried out under shelter (especially in difficult or sever climates)
3. better control of the quality of materials and workmanship (generally)
4. the excellent control of the formwork surface properties can offer high-quality finish surfaces
5. high reuse of formwork - lower cost
6. formwork is equipped to pretension the steel in the precast elements for greater structural efficiency, which translates into longer spans, lesser depth, and lower weights than for comparable reinforced concrete elements
7. concrete and steel of superior strength are used in precast elements - due to the excellent quality control
8. faster curing due to the use of type 3 portland cement (high early strength)


1. **steam cured** elements - the steam furnishes heat, accelerating the hardening of the concrete and moisture for full hydration

what is introduced with prestressed, precast concrete?

with compression forces introduced into the concrete cross-section by pre-tensioning steel strands before the concrete is cast

this **pre-tensioning** will counter the actual loading that will be on the structural member

who built boats with reinforced concrete?

Joseph L. Lambot

who tested reinforced concrete beams?

Thaddeus Hyatt

what was the first reinforced concrete skyscraper?

15 story Ingalls Building, Cincinnati, Ohio by E.L Ransome

what does prestressing concrete eliminate/reduces?

possible cracks

the structural action is more efficient than that of a reinforced beam

uses less material (beam size is reduced)

what are the two ways pre-stressing can be done?

pre-tensioning and post-tensioning

prestressing concrete: pretensioning

1. stretch the steel prestressing strands tightly across the casting bed
2. concrete is cast around the stretched strands and cured (the concrete bonds to the strands)
3. when the strands are cut the concrete goes into compression and the beam takes on a camber

prestressing concrete: post tensioning

done primarily on site, using draped strands to aproximately follow the flow of tensile forces in the beam


1. the concrete is not allowed to bond to the steel strands during curing
2. after the concrete has cured, the strands are tensioned with a hydraulic jack and anchored to the ends of the beam. if the strands are draped, as shown here, higher structural efficiency is possible than with straight strands

what is cast-in-place concrete?

concrete that is directly poured on site and allows for monolithic structural systems in a variety of possible shapes with appropriate formwork

what are form ties?

keeps the two halves of the formwork from separating due to the outward pressure of the wet concrete when poured. this pressure leaves an imprint of the form-ties on the surface of the hardened concrete. the location of the form-ties is critical if it will be exposed as part of the design

how are the form tie supports oriented?

they are in a grid that can be exposed

what is fiber-reinforced concrete (FRC)?

contains fibers instead of steel rebars

the fibers are uniformly distributed an randomly oriented throughout the concrete

the fibers can be very short steel strips or glass or synthetic filaments

the use if fibers allows for the manufacturing of very thin structural shells (i.e., prefabricated shells)

what is ferrocement?

mortar is put by hand over several layers of wire mesh, resulting in a dense matrix of mortar within the mesh

this allows for thin and delicate structural members with a hard and dense surface texture

what do control joints do?

provides a location for the slab to crack without being visible or running at angles

what are construction joints?

occur where two concrete pours meet

what are isolation joints?

separate a pour from wall, column or other adjoining form

what is concrete slab action?

the flow the loads through the slab, beams and wall or column supports

one way slab action

loads on this floor slab have a one way axial direction to be transferred over to the two support walls

one axial direction with two possible direction towards one wall or the other

two way slab action - without beams

loads have two way axial directions to be transferred over to the four support columns

two axial directions with four possible directions towards the supports

note: the slab steel reinforcement follows these directions which is why the slab actins performs this way

le corbusier’s prototype for an open floor plan

concrete floor slabs with thin reinforced concrete columns

corbusier: what does column grid plan vs full bearing plan allow (windows)

grid plan - allows for full strip windows

bearing wall plan - allows for limited window openings

corbusier: what does column grid plan vs full bearing plan allow (plan)

grid plan - allows for “free” planning of walls

bearing wall plan - allows for a rigid plan

corbusier: what does column grid plan vs full bearing plan allow (support)

grid plan - allows for columns to support the building above the ground

bearing wall plan - wall foundation excavated into the earth

corbusier: what does column grid plan vs full bearing plan allow (light)

grid plan - allows more light to enter from the exterior with full strip windows

bearing wall plan - allows for limited light to enter from the exterior

both plans show light zones getting darker away from the windows

trampoline and embodied awareness

the stretchable mat and springs (in tension) push up on the person (the weight/load) that has landed. this resulting pushing force from the “springboard” is used by the gymnast to do acrobatics or gymnastic exercises

how is force generated with post and pre tensioning?

the tension cable is creating a force across the beam that pushes up from within to resist the loading that it will be subjected to. this is very similar to the force that pushes up on the gymnast from the trampoline “springboard”

what did camille polonceu do?

french engineer and builder exploited the principle of how a slender beam can be reinforced by adding a small transverse compression member below its center and tying the lower end of this strut by means of tension rods to the ends of the beam

what did polonceu design?

inclining two reinforced beams towards each other and further connecting the ends of the two compression struts with a horizontal member in tension, he designed a very effective structure for **large roofs**

what is the “self-similar” construction process?

the process of alternating twisting from the *yarns* to the *strands* to the rope, and to the cable

what is a structure?

a material element or a number of such elements working together, providing *strength, stiffness and stability* so that loads can be supported overhead

what is a our need for a shelter?

function is to make sure that snow, wind and gravity loads remain right where they attack the shelter and do not cause it to collapse and fall on us

what do structural elements and structural members refer to?

the individual parts of an overall structural form, like the **compression strut** or **the tension tie** of the polonceu truss

what is a structural system?

refers to the whole set of structural arrangements in a building made up of many structural elements and members

what are the different types of structures?

horizontal span structures

vertical structures

straight, planar or curved structures

elastic properties: rigid and non-rigid structures

massive structures vs skeletal structures

basic structural actions: elongation/stretching

resulting from tension within the element, two loads pulling away from each other in opposite directions

basic structural actions: shortening

resulting from a compression force acting within the element

compression - two forces pushing against each other