Prestressed Concrete: Principles & History

<p>The concrete behaves more like an elastic material. (D)</p> Signup and view all the answers

<p>Uniform compressive stress. (D)</p> Signup and view all the answers

<p>To counteract external stresses from applied loads. (B)</p> Signup and view all the answers

<p>A combination of direct stress and bending stress. (D)</p> Signup and view all the answers

<p>High compressive strength. (C)</p> Signup and view all the answers

<p>Grade 270 strands have a higher minimum ultimate strength. (C)</p> Signup and view all the answers

<p>To straighten the wire when subjected to tension. (C)</p> Signup and view all the answers

<p>To serve as a pathway for the tendons to be inserted and stressed. (D)</p> Signup and view all the answers

<p>The introduction of specific alloying elements and cold working. (C)</p> Signup and view all the answers

<p>Stressing the steel tendons <em>after</em> the concrete has hardened . (C)</p> Signup and view all the answers

<p>To maintain the position of the tendons during the concrete pouring process. (D)</p> Signup and view all the answers

<p>To permanently secure the tendon at the end opposite the stressing anchorage. (A)</p> Signup and view all the answers

<p>A twisted arrangement, typically in a 7-wire strand. (D)</p> Signup and view all the answers

<p>The low strength of steel available at the time resulted in significant prestress losses due to creep of the steel. (C)</p> Signup and view all the answers

<p>Applying tensile stress to encircle and compress materials. (A)</p> Signup and view all the answers

<p>Tendons are tensioned against abutments before the concrete is placed. (C)</p> Signup and view all the answers

<p>Walnut Lane Bridge (C)</p> Signup and view all the answers

<p>Pretensioning involves tensioning tendons before concrete placement; post-tensioning involves tensioning after concrete hardening. (D)</p> Signup and view all the answers

<p>To effectively apply a large initial tensile force that can induce compressive stress in the concrete. (D)</p> Signup and view all the answers

<p>Creep and shrinkage characteristics of the concrete. (C)</p> Signup and view all the answers

<p>$f_r = \frac{PL}{bd^2}$ (B)</p> Signup and view all the answers

<p>To create compression between the staves allowing them to resist internal liquid pressure; prestressing uses tensioned tendons to compress the concrete. (C)</p> Signup and view all the answers

<p>The use of primarily precast concrete elements manufactured off-site. (D)</p> Signup and view all the answers

<p>The shape of the structural member. (B)</p> Signup and view all the answers

<p>Prestressed concrete beams are designed to have minimal to no deflection under service loads, and may even exhibit upward deflection (camber). (D)</p> Signup and view all the answers

<p>Strand is made from twisting small wires together. (C)</p> Signup and view all the answers

<p>The tensile capacity under bending. (D)</p> Signup and view all the answers

<p>$f_r = 0.63 \sqrt{f'c}$ MPa (A)</p> Signup and view all the answers

<p>Creep and shrinkage of the concrete. (A)</p> Signup and view all the answers

<p>To provide corrosion protection to the strand. (D)</p> Signup and view all the answers

<p>To enhance corrosion protection at the joints. (B)</p> Signup and view all the answers

<p>To withstand the large tensile forces during prestressing. (B)</p> Signup and view all the answers

<p>The plug. (A)</p> Signup and view all the answers

<p>It is suitable for mass production of precast members. (D)</p> Signup and view all the answers

<p>To facilitate the transfer of prestress to the concrete through bond. (A)</p> Signup and view all the answers

<p>When the anchor nuts are under tension (D)</p> Signup and view all the answers

<p>Corrosion inhibiting compound. (A)</p> Signup and view all the answers

<p>Shorer System. (A)</p> Signup and view all the answers

<p>Plug. (B)</p> Signup and view all the answers

<p>Grooved sandwich plates and wedges. (A)</p> Signup and view all the answers

<p>Each wire is stressed independently using a double-acting jack. (B)</p> Signup and view all the answers

<p>Helical spring inside the cable (C)</p> Signup and view all the answers

<p>Nuts tightened against bearing plates (C)</p> Signup and view all the answers

<p>Thermoplastic material (A)</p> Signup and view all the answers

<p>Embedding steel in concrete made of expanding cement. (B)</p> Signup and view all the answers

<p>Pretensioning (C)</p> Signup and view all the answers

<p>The location of the prestressing tendons. (B)</p> Signup and view all the answers

<p>Liquid containment tanks (C)</p> Signup and view all the answers

<p>$f = -P / A_c$ (B)</p> Signup and view all the answers

<p>By the bond between the steel and concrete. (D)</p> Signup and view all the answers

<p>-10 MPa (A)</p> Signup and view all the answers

<p>It applies force longitudinally, suitable for beams (B)</p> Signup and view all the answers

<p>Wrapping cylindrical structures to resist bursting. (C)</p> Signup and view all the answers

<p>Gifford-Udall System (D)</p> Signup and view all the answers

A reinforced concrete type that uses compression forces to reduce tensile stresses.

Introduced the concept of prestressing in 1904 to enhance concrete's resistance to tensile forces.

Concrete that incorporates steel bars to improve tensile strength and resist cracking.

Concrete's ability to resist tension, typically considered as zero in design.

The stress level beyond which concrete begins to crack under load.

Applying pre-compression in concrete to prevent cracking from tensile loads.

Forces induced within concrete to counterbalance external applied forces.

Applying prestressing forces off-center from the centroid of the section.

The first prestressed concrete bridge was built in 1941 in France.

The first prestressed concrete bridge in the US, built in 1949, with a 47-meter span.

A method where tendons are tensioned before concrete placement, creating a pre-compression effect.

A method where tendons are tensioned after concrete has hardened.

Posttensioning can be classified as external or internal, and bonded or unbonded.

Full prestressing applies maximum tension, while partial prestressing uses less to alleviate some stresses.

Granted in 1886 for tightening steel rods in concrete blocks, resembling modern segmental construction.

Ec=4800(f’c)0.5 MPa for normal weight concrete.

Indicates tensile capacity of concrete under bending.

Deformation over time at constant stress or load.

Creep strain depends on time, mix, humidity, curing, and age.

Can be strands, wires, round bars, or threaded rods.

High strength steel used in prestressing for stability.

197,000 MPa, lower than bar due to wire twisting.

Conducted under a 4-point bending configuration.

Strands are wires used in prestressing, sized from 0.25 in to 0.60 in diameter.

Cable stress relief through heat treatment after stranding.

Two grades: Grade 250 (250,000 psi) and Grade 270 (270,000 psi) indicate strength.

Manganese, silicon, and chromium increase the strength of alloy steel bars.

Cold work further increases the strength of steel bars during manufacture.

Devices used for securing pretensioned beams during the tensioning process.

Types of anchorages in posttensioning, including stressing and dead-end anchorages.

Steps involved in applying posttensioning to beams after hardening.

A protective layer around tendons in prestressing to prevent corrosion.

A substance used to prevent rust and degradation in metal components.

Anchors designed with corroded protection and easier installation in concrete.

A sleeve that shrinks when heat is applied, providing protective covering for cables.

A pretensioning system used for mass production of concrete members.

A system where multiple concrete elements are cast in a single line and framework.

A method using a high-strength steel tube to transfer prestress from wires to concrete.

A posttensioning method that utilizes hydraulic jacks for tensioning wires.

Hollow passages in concrete where tendons are placed for tensioning.

Ongoing safeguarding methods to protect metal parts from corrosion.

A post-tensioning system using sandwich plates to anchor wires.

A method that originated in Great Britain involving independent wire stressing.

A system where steel bars are tensioned in ducts and tightened with nuts.

Method using electric current to heat coated bars for elongation and stress.

Applies stress through expanding cement embedding steel, elongating it.

Prestressing applied externally using abutments that support the force.

Applying prestress through tendons inside the concrete member.

Prestressing force applied along the member's axis.

Hoop stress applied around cylindrical structures to counter internal pressure.

The transfer of force from steel to concrete after hardening.

Stress experienced by concrete beams due to applied prestressing force.

Special device used to pull and anchor wires in prestressing systems.