Selection of Structural Systems Flashcards
What is the typical spacing of wood joists? Typical maximum span?
Spacing: 12 in, 16 in, and 24 in OC
Span: 20 ft > 25 ft
What is the most common use of solid wood beam structural system? What is its typical max span?
Planks and beams framing = members of 4 in or 6 in nominal width span between girders or bearing walls at spacing of 4 ft, 6 ft, or 8 ft
Span = 10 ft > 20 ft
What are the advantages of glu-lam construction?
What are standard widths?
Spans?
Advantages =
Appearance: often are left exposed as part of architectural/structural expression
Shape: can be manufactured in tapered and curved beams and arches
Widths = 3 1/8”, 5 1/8”, 6 3/4”, and 8 3/4”
Spans = 15 ft < 60 ft
What is the main advantages of a lightweight I-joist (TJI)? When is it typically used?
Advantages:
Allows longer spans with a joist system because it is stronger and stiffer than standard wood.
Used in residential and light commercial construction
What is LVL?
What is it primarily used for?
What is its primary advantage?
Individual layers of thin veneer glued together.
Primarily used for:
- Headers over large openings
- Singly or built-up for beams
Advantages:
- Has higher modulus of elasticity than standard wood joist, so its allowable stress in bending is about twice that of a Douglas-fir joist.
When are wood trusses most often used?
What is its main advantage?
Typically used for residential and light commercial construction
Advantage = allow easy passage of mechanical ductwork through truss
What are typ spans of wood trusses?
Typ depths? Typ spacing?
Typical spans = 20 ft > 40 ft
Typical depths = 12 in > 36 in
Common spacing = 24 in on center
What is a box beam? When is it used?
Plywood panels are glued and nailed to solid wood members, typ 2x4
Uncommon but most often used where depth of member is not critical and other types of manufactured beams cannot be brought to the site
What is a stressed-skin panel? What type of assemblies can it be used for?
A type of wood construction where plywood is glued and nailed to both sides of solid 2x’s. Uncommon due to lack of availability and difficulty in on-site fabrication
Used for floor, roof or wall construction
What are 4 advantages of steel construction?
- High strength
- Availability
- Ability to adapt to a wide variety of structural conditions
- Ductility (able to tolerate some deformation and return to its original shape before breaking)
What type of construction is steel best suited for?
multi-floor construction due to strength and structural continuity
What are the two most common steel structural systems?
- beam-and-girder system
2. open-web steel joist system
What is the beam and girder steel structural system? What is the typical:
- beam span?
- beam spacing?
Larger girders span between vertical supports, and smaller beams are framed into them.
Typical beam span = 25 ft > 40 ft
Typical beam spacing = 8 ft > 10 ft on center
What is the open-web steel joist system?
What is the typical span? Long span? Deep long span?
What is the typical depth? Long depth? Deep long depth?
Open-web steel joists span between beams or bearing walls.
Standard open-web joist span = 60 ft
Standard depth = 8 in > 30 in
Long-span joist = 96 ft
Long-span depth = 18 in > 72 in
Deep long-span = 144 ft
What are 4 advantages of the open-web steel joist system? 1 disadvantage?
- Efficient structural members
- Well-suited for low-rise construction where overall depth of floor/ceiling is not critical
- Span long distances
- Mech/elec pipes and ducts can easily run through joists
Disadvantage:
1. Combustible construction
What are the two primary types of concrete structural systems?
- cast-in-place
2. precast
What are the advantages/disadvantages of cast-in-place construction? Of precast?
1. Cast-in-place Cons: - Require formwork - Take longer to build than precast Pros: - Can conform to almost unlimited variety of shapes, sizes, design intentions, and structural requirements
- Precast
Pros:
- Quality control is better since made in a factory
- Erection proceeds quicker
Cons:
- More limited in variety of shapes, sizes, design intentions, and structural requirements than cast-in-place
- Typically prestressed but can also be post-stressed. Sometimes mild reinforcing steel is used
What are two classifications of cast-in-place structural systems?
- one-way systems = slabs and beams are designed to transfer loads in one direction only (slab → beam → girder)
- two-way systems = transfer loads in 2 directions, all designed for use in rectangular bars where distance between columns is the same in both directions
What are 2 types of one-way cast-in-place structural systems?
- Beam-and-girder system = most common one-way system
- Concrete joist system = concrete members spaced 12 in or 36 in apart, running in one direction that frame into larger beams.
What is the typical span of a beam-and-girder cast-in-place structural system? What are 3 advantages of this system?
15 ft > 30 ft
- easy to form
- allows penetrations and openings in the slab
- most economical option for most applications
What is the typical span of a concrete joist cast-in-place structural system? What are 3 advantages of this system?
Typical spans = 20 ft > 30 ft
Typical depths = 12 in > 24 in
Easy to form
Good for light or medium loads where moderation distances must be spanned
What are 3 types of two-way cast-in-place concrete systems?
- Flat plate
- Flat slab
- Waffle slab
What is a flat plate concrete system?
Max span?
Typical thickness?
When it is most useful?
The simplest type of two-way system where a slab spans in both directions directly into columns.
Loads increase near columns but slab thickness is not increased or reinforced at columns so this system is limited to light loads and shorts spans.
Max span = 25 ft
Slab thickness = 6 in > 12 in
Useful when floor-to-floor height must be kept to a min or an uncluttered underfloor appearance is desired
What is a flat slab concrete system?
What is its max span?
A type of two-way system similar to a flat plate, except that drop panels are provided at columns to provide longer spans and accommodate heavier loads.
Max span = 30 ft
What is a waffle slab concrete system?
Is it precast or cast-in-place?
A type of precast two-way system that provides support for heavier loads at even longer spans.
Typ span = 40 ft
What are the most common precast forms? Why?
Single tee and double tee are popular forms because they provide both structure and floor or roof decking, and are easy/fast to erect.
- a 2” topping slab can be placed over the tees to provide uniform flooring and/or increased strength
When is post-tensioning used instead of pre-tensioning?
Pre tensioning is more common in prefab, but post tensioning is useful when high strength is required and it may be too difficult to transport precast members to job site.
what kind of assembly is masonry typically used?
Bearing walls