L2: Building Structures

Question 1

What is the main function of buildings?

Answer 1

To protect occupants from weather

Question 2

What is the excess margin modern safety factors call for and what does this cover?

Answer 2

50-150% increase in structural capacity; covers minor material flaws, inaccuracies and other unavoidable errors

Question 3

How does structure impact design for short/high rise buildings?

Answer 3

Short - design is common sense

High - structure highly affects design and appearance

Question 4

What three items must be present in a building structure?

Answer 4

Stability
Strength and stiffness
Economy

Question 5

What causes unstable structures to form?

Answer 5

Unbalanced forces

Question 6

What do stable structures do under realistic loads?

Answer 6

Remain at rest

Question 7

How stiff is wood compared to steel

Answer 7

Wood is less than 16 times steel’s stiffness

Question 8

What are the types of building loads?

Answer 8

Dead (fixed), live (moving, weather)

Question 9

What do forces do?

Answer 9

Exert motion or stress within a structural member

Question 10

How can loads be distributed?

Answer 10

Uniform or concentrated

Question 11

What are the types of forces?

Answer 11

Vertical
Horizontal
Moment (rotational)

Question 12

How are vertical and horizontal forces balanced by a structure?

Answer 12

Vertical - with building foundation (accumulative)

Horizontal - bracing of structural frame (each floor separate)

Question 13

What is stress and what stress occurs within materials?

Answer 13

Internal resistance to an applied force; compression, tension, shear, bending

Question 14

What is compression and what strain does it cause?

Answer 14

Crushing/squashing causing shortening

Question 15

What is tension and what strain does it cause?

Answer 15

Pulling/stretching causing lengthening

Question 16

What is shear and what strain does it cause?

Answer 16

Force perpendicular to long axis; two forces moving against each other causing compression and tension (shortening/lengthening)

Question 17

What is bending (moment) and what strain does it cause?

Answer 17

Compression above and tension below the theoretical mutual axis causing deflection (compression and tension)

Question 18

What impacts the amount of bending?

Answer 18

Distance from point of rotation stiffness of materials

Question 19

Where is bending stress greatest in a uniform load, point load, and cantilever (uniform or point)

Answer 19

Uniform - midspan
Point - at point
Cantilever - at support

Question 20

What is the strain of materials?

Answer 20

The external reaction to an applied load

Question 21

What determines a structures resistance to compression, tension and shear

Answer 21

Strength of material and cross sectional area

Question 22

What stresses are steel good in?

Answer 22

All

Question 23

What stress is concrete good in and what must be done to handle the other stresses?

Answer 23

Good in compression

Reinforced with rebar to handle tension
Reinforced with stirrups to handle shear

Question 24

What determines a structures resistance to bending?

Answer 24

Moment of inertia; higher proportion of depth to width decreases deflection

Efficiency in shape - material bulk at centre is inefficient and adds dead load

Question 25

What is a bearing wall?

Answer 25

A wall that supports any vertical load in addition to its own weight; system of compression materials most efficient if loaded uniformly

Question 26

What are bearing walls limited by?

Answer 26

Height - would need thick base to support cumulative loads

Question 27

Where are bearing walls used?

Answer 27

Common wood frame house - exterior and some interior walls support vertical loads Tilt-wall construction (eg. shopping centres) - reinforced concrete formed and poured on ground and then lifted into position Arches

Question 28

Explain the forces in arches

Answer 28

Keystone sends compression loads to base of arch; these have vertical components which go into the ground and horizontal components which cause outward thrust

Question 29

How is outward thrust handled?

Answer 29

Counterweighted - more mass alongside arch or arches placed in series (oppose) Tied - tension cable/rod placed at base

Question 30

What is a post and beam structure?

Answer 30

A system of horizontal and vertical members subject to bending, compression and shear; not laterally stable

Question 31

What is the structural element hierarchy

Answer 31

``` Floor slab/deck Joists Beams Girders (Vertical) columns ```

Question 32

What does a floor slab/deck do?

Answer 32

Initially receives live loads

Question 33

What do joists do?

Answer 33

Directly support slab/deck | quite flimsy, closely spaced

Question 34

What do beams do?

Answer 34

Receive loads from joists (or directly support floor if no joists)

Question 35

What do girders do?

Answer 35

Receive loads from beams

Question 36

What do columns do?

Answer 36

Receive loads from beam/girders and above columns to transfer to foundation

Question 37

What are trusses?

Answer 37

Triangular spanning elements with axial tension and compression, commonly used to support roofing