long_span Flashcards
(28 cards)
What defines a short-span system?
Spans around 14–16 feet, typically 2x wood joists used in single-family homes.
What defines a medium-span system?
Spans of 25–35 feet, typically using steel or concrete for commercial/retail.
What defines a long-span system?
Spans of 60–250 feet, used where column-free spaces are critical (e.g., auditoriums, gyms).
Why are long-span systems more expensive?
They require high strength, have fewer members (less redundancy), and require greater safety factors.
What structural form is commonly used in long-span systems?
Trusses, due to their triangulated load distribution and depth efficiency.
What is the relationship between depth and efficiency in trusses?
More depth increases stiffness and reduces material cost.
What’s a risk of using fewer, longer spanning elements?
A single failure could cause catastrophic collapse due to lack of redundancy.
What materials can trusses be made from?
Steel, wood, or a combination of both.
Why are trusses often built on-site?
Their large size makes transport difficult.
What connections are typically used in trusses?
Pinned connections (conceptually), often bolted or welded.
What are the typical span ranges for trusses?
60 to 250 feet.
What is a castellated beam?
A wide flange beam cut and re-welded in a zigzag pattern to increase depth and allow MEP routing.
What is a Vierendeel truss?
A rectangular-frame ‘truss’ with moment connections, allowing openings but not using triangulation.
What are open web steel joists?
Lightweight, steel trusses used repetitively for economical long spans.
Why are open web steel joists advantageous?
Lightweight, readily available, open for routing ducts/pipes.
What is a major con of open web steel joists?
They bounce significantly under live loads.
Where are open web joists best used?
Roof structures where deflection is less critical.
What affects joist spacing?
Joist load capacity and steel deck spanning ability.
What is typical spacing for open web joists?
Ranges from 4 to 10 feet, depending on load and deck type.
What is the K-Series joist span range?
20–60 feet.
What is the LH-Series joist span range?
50–80 feet.
What is the DLH-Series joist span range?
60–100+ feet, deeper and stronger than LH.
Why is steel a preferred material for long spans?
It’s strong and ductile, allowing movement without failure.
Why is cast iron rarely used structurally today?
It’s strong but brittle, prone to sudden failure.
