Structural Systems

Question 1

What are the typical spanning ranges for wood joists?

Answer 1

Usually 20ft, but can be up to 25ft.

Question 2

What is the maximum recommended spacing for wood joist bridging?

Answer 2

8ft

Question 3

What is “plank-and-beam” construction? What is it’s typical spacing?

Answer 3

Large solid wood beams span between girders or bearing walls, with planks or laminated boards between beams.

Typically spaced at 4-8ft and spanning 10-20ft.

Question 4

What are the typical dimensions and spans for glulams?

Answer 4

3/4” or 1-1/4”
by
3-1/8” …. 5-1/8” …. 6-3/4” …. 8-3/4”

Span 15-60ft

Question 5

What are the typical dimensions of a engineered wood I-joist? What else can it be called?

Answer 5

1-3/4” -to- 5-1/5” wide

9-1/2” -to- 20” deep

“Manufactured” / “lightweight” “I-shaped joist”

Question 6

What are the typical dimensions for an LVL?

Answer 6

1-3/4” wide by almost any depth

Question 7

What are the typical dimensions, spacing, and span of wood trusses?

Answer 7

3-1/2” wide
12” -to- 36” deep

Typically 24” O.C.

Span 24-40ft

Question 8

What are the typical spans for the various types of wood members?

Answer 8

Solid wood joists —— 20-25ft

Solid wood beams —– 10-20ft

Glulams —————– 15-60ft

Wood truss joists ——- 24-60ft

Question 9

What are the typical spacing and spans for “beam-and-girder” steel construction?

Answer 9

Span 25-40ft

Beams spaced at 8-10ft

Question 10

What are the typical dimensions and spans for the different types of “open-web steel truss” construction types?

Answer 10

• *Standard Trusses**
• span up to 60ft
• 8-30” deep
• *Long-Span Trusses**
• span up to 96ft
• 18-72” deep
• *Long-and-Deep Trusses**
• span up to 144ft
• 18-72” deep

Question 11

What are te typical spacings for the different applications of “open-web steel truss” construction?

Answer 11

Floor joists: 2-4ft

Roof joists: 4-6ft

Question 12

What is the process of “lift-slab” construction?

Answer 12

Concrete slabs are cast on the ground (usually all at once) around the columns, and are then lifted up to floor height and fixed in to the columns.

Question 13

What are the typical spans for two types of one-way concrete systems?

Answer 13

Beam-and-girder system ………………. 15-30ft

Concrete joist (“pan joist”) system … 20-30ft

Question 14

What are the typical spans for the three types of two-way concrete systems?

Answer 14

Flat plate: up to 25ft

Flat slab: up to 30ft

Waffle slab: up to 40ft

Question 15

What is the process of pre-cast concrete pre-stressing?

Answer 15

Cables are put under tension and then councrete is poured into the form. Once the concerte reaches a certain strength, the cables are released, which transferers their stress into the concrete.

Often results in a “camber” in the members before they are placed and loaded.

Question 16

What is the “slenderness ratio”?

Answer 16

The ratio of the vertical member’s unsupported height to its width.

It indicated the members ability to resist buckling under compression.

Question 17

What are the primary structural concerns of attaching a facade wall to a building structural system?

Answer 17

• How it will support itself and/or hang off the primary structural system
• How it will transfer lateral loads into the primary structural system
• How it will handle expansion and differential shifting

Question 18

What are the typical spans for arches of different materials?

Answer 18

Wood arches: 50-240ft

Concrete arches: 20-320ft

Steel arches: 50-500ft

Question 19

What are the three hinge types of arches?

Answer 19

Fixed arch

Two-hinged

Three-hinged

Question 20

What is the typical span of a “space-frame” system?

Answer 20

Up to 350ft

Question 21

What is the typical span of a “folded-plat” system?

Answer 21

30-100ft (longer for reinforced concrete)

Question 22

What are the general aspects of “thin-shelled” systems?

Answer 22

• Include domes, barrel vaults, typical paraboloids or hyperbolic paraboloids
• Typically of concrete
• Since (theoretically) the shape prevents any bending/moment forces, the structure can be very thin
• Span from 40-200ft (30-160ft for hyperbolic paraboloids)

Question 23

What are the primary aspects of “stress-skinned” systems?

Answer 23

• One or two layers of sheathing attached to rows of web members
• Typically of wood, but can be made form steel as well
• Typically span from 12-35ft

Question 24

What are the three primary types of loads that a building must resist?

Answer 24

“Dead Loads”
Weight of the building itself

External loads
Such as wind, snow, eathquake

“Live Loads”
Loads from building use, such as occupants, furniture, equipment, ETC

Question 25

What are the primary determining factors in selecting a building structural system?

Answer 25

• Effective resistance to loads
• Material efficiency in resisting the types of loads that are expected*
• Building function
• How the use may make certain systems more advantageous, even if they are not the most efficient*
• Integration with other building systems
• Cost
• Including the cost of labor to construct and cost to fire-rate the structural system*
• Fire resistance
• What fire resistance rating is required by code*
• Schedule
• Delivery time of materials and assembly time by on-site labor*
• Construction complexity
• Does it need specialized labor or equipment to assemble? Does it demand certain construction sequencing or additional planning*
• Aesthetics
• Context
• Does the neighborhood or local context of the building demand or prefer a certain system*