Long_Span_Structures Flashcards
(26 cards)
What is the advantage of trusses for long spans?
They allow increased depth using less material due to open webbing.
Why are precast T and double-T beams useful for long spans?
They offer significant depth and pre-stressing to handle tension and compression efficiently.
What structural role does concrete play in a T-beam?
It resists compression, especially at the top of the beam.
What structural role does steel play in a T-beam?
It resists tension, especially at the bottom of the beam.
What is the typical topping thickness for a precast T system?
About 2 inches.
How far can single or double-T precast concrete members typically span?
60–120 feet.
What is the typical width and depth range of precast T-beams?
Widths: 6–10 feet; Depths: 18 inches–4 feet.
What type of loading are concrete members designed to handle best?
Compression.
Where are single-T and double-T beams most commonly used?
Parking decks.
Why are double-T beams easier to erect than single-Ts?
They are self-supporting and don’t need bracing.
What is camber in precast elements?
An upward curvature to compensate for deflection under load.
Why must precast elements be transported upright?
To prevent additional sag that could cause failure.
What is the difference between pre-stressed and post-tensioned concrete?
Pre-stressed is tensioned before concrete sets (in precast); post-tensioned is tensioned after concrete sets (in site-cast).
When is precast preferred over site-cast concrete?
When speed of construction is critical.
What is a major advantage of site-cast concrete for complex forms?
It allows custom shaping without costly, reusable formwork.
What is the main logistical disadvantage of precast long-span elements?
Transportation and crane requirements.
How does pre-stressing benefit concrete elements?
It compresses the concrete, increasing load capacity and span.
How does post-tensioning work in site-cast beams?
Tendons are tensioned after concrete cures using hydraulic jacks and then grouted in place.
What are pneumatic structures?
Air-pressurized membranes used for low-cost, temporary large-span enclosures.
What is a thin-shell concrete structure?
A minimal-thickness concrete form shaped to stay in compression, often arched.
What is a tensile structure?
A structure using stretched membranes held in tension by cables and supports.
What is a space frame?
A 3D truss system made of small members that span long distances in multiple directions.
What is a lamella roof?
A barrel-vault pattern formed from overlapping short members to span large spaces.
Who is known for thin-shell concrete structures?
Candela and Nervi.
