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Questions and Answers
What is the main structural analogy used for designing torsion?
What is the main structural analogy used for designing torsion?
- Solid beam
- Thin-walled tube (correct)
- Space frame
- Rigid plate
In the thin-walled tube analogy, where is the torsional resistance primarily assumed to be provided from in a cracked reinforced concrete beam?
In the thin-walled tube analogy, where is the torsional resistance primarily assumed to be provided from in a cracked reinforced concrete beam?
- Closed stirrups and longitudinal bars near the surface
- Center of the beam
- Core concrete cross-section
- Outer skin of the cross-section around the stirrups (correct)
When a beam subjected to torsion has cracked, where is the torsional resistance primarily provided in the thin-walled tube analogy?
When a beam subjected to torsion has cracked, where is the torsional resistance primarily provided in the thin-walled tube analogy?
- Near the center of the beam
- At the edges of the beam
- At the core of the beam
- On the surface around closed stirrups (correct)
What is the approximate threshold for torques that do not cause a structurally significant reduction in either flexural or shear strength?
What is the approximate threshold for torques that do not cause a structurally significant reduction in either flexural or shear strength?
In the thin-walled tube analogy, how is cracking torsion under pure torsion derived?
In the thin-walled tube analogy, how is cracking torsion under pure torsion derived?
When does cracking occur according to the thin-walled tube analogy?
When does cracking occur according to the thin-walled tube analogy?
In a non-prestressed beam loaded with torsion only, what is equal to the principal tensile stress?
In a non-prestressed beam loaded with torsion only, what is equal to the principal tensile stress?
What part of a reinforced concrete beam is neglected in the thin-walled tube analogy for torsion?
What part of a reinforced concrete beam is neglected in the thin-walled tube analogy for torsion?
How is a reinforced concrete beam idealized geometrically in the thin-walled tube analogy?
How is a reinforced concrete beam idealized geometrically in the thin-walled tube analogy?
Which part of the reinforced concrete beam provides most of the torsional resistance after cracking according to thin-walled tube analogy?
Which part of the reinforced concrete beam provides most of the torsional resistance after cracking according to thin-walled tube analogy?
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Study Notes
Design for Torsion
- The design for torsion is based on the thin-walled tube, space truss analogy.
- In this analogy, the core concrete cross section in a solid beam is neglected.
- A reinforced concrete beam's torsional resistance is provided primarily by closed stirrups and longitudinal bars near the surface after cracking.
- The thin-walled tube analogy assumes the resistance is provided by the outer skin of the cross section, roughly centered on the closed stirrups.
Idealization of Sections
- Both hollow and solid sections are idealized as thin-walled tubes before and after cracking.
Torque Limits
- Torques that do not exceed approximately one-quarter of the cracking torque (Tcr) can be ignored.
- Such torques do not cause a structurally significant reduction in flexural or shear strength.
Cracking Torsion (Tcr)
- Cracking torsion under pure torsion (Tcr) is derived by replacing the actual section with an equivalent thin-walled tube.
- The tube has a wall thickness (t) of (0.75 Acp / Pcp) prior to cracking.
- The area enclosed by the wall centerline (Ao) is equal to (2/3) Acp.
Cracking Criteria
- Cracking is assumed to occur when the principal tensile stress reaches −c f λ 33.0.
- In a non-prestressed beam loaded with torsion alone, the principal tensile stress is equal to the torsional shear stress (Ï„ = T/(2Aot)).
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