CIVL3811 Post Tension Concrete Systems

Pre-stressing is the process of preloading a structure before applying design loads to improve its overall performance.

True

<p>freely</p> Signup and view all the answers

<p>Tendons are jacked to very high stresses prior to grouting. The reaction forces from the jacking process are applied to the ends of the concrete member and then transferred permanently to cast-in end anchors.</p> Signup and view all the answers

<p>The tendons are permanently pre-stressed in tension, and the concrete is permanently pre-stressed in compression.</p> Signup and view all the answers

<p>Tendon</p> Signup and view all the answers

<p>In pre-tensioned construction, tendons are tensioned before concrete pouring and bonded afterwards, while in post-tensioned construction, tendons are laid in ducts within the concrete and tensioned after it gains strength.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>Strands are jacked individually.</p> Signup and view all the answers

<p>Strand = A group of tendons assembled in a duct or anchorage. Tendon = A combined unit of high tensile wires woven together. Cable = The wire, strand, or bar intended to be pre-stressed. Pre-stressed = The tendons are tensioned prior to concrete pouring. Post-tensioned = The process of stressing both the concrete and tendons prior to service use. Pre-tensioned = Tendons are tensioned after the concrete gains strength.</p> Signup and view all the answers

<p>Grouting bonds the tendons to the concrete, effectively making them an integral part of the structure.</p> Signup and view all the answers

<p>bonded</p> Signup and view all the answers

<p>Wedges are used to apply tension to the tendons, creating the necessary pre-stress forces within the concrete.</p> Signup and view all the answers

<p>The construction sequence involves tendon placing, concreting, stressing, and grouting.</p> Signup and view all the answers

<p>Bonded tendons are grouted after stressing, creating a strong bond with the concrete, while unbonded tendons are not grouted and are typically encased in a plastic sheath.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>Pre-compression reduces cracking and deflection by applying compressive forces to the concrete prior to external loads.</p> Signup and view all the answers

<p>Tendons create the prestressing forces that induce compressive stresses in the concrete, effectively 'pre-balancing' the load and enhancing the structure's performance.</p> Signup and view all the answers

<p>'Draping' the tendon refers to its curved profile, which allows it to apply an upward load to the concrete, helping to carry a portion of the structure's self-weight.</p> Signup and view all the answers

<p>Reduced deflection and increased strength.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>External loads create a moment couple, which is resisted by the internal forces created by the prestressing forces, ensuring that the beam remains stable.</p> Signup and view all the answers

<p>The 'internal couple' approach is a simplified method for analyzing the behavior of a prestressed beam by considering the balancing forces created by external loads and the internal stresses introduced by prestressing.</p> Signup and view all the answers

<p>The characteristic value of concrete strength, denoted as f'c, represents the uniaxial compressive strength of test cylinders. This value is significant because it defines the strength that 95% of concrete samples should exceed.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>The typical range of compressive strength for prestressed concrete applications is between 32 MPa and 50 MPa.</p> Signup and view all the answers

<p>early transfer stress</p> Signup and view all the answers

<p>Creep and shrinkage are the two primary factors that cause time-dependent strain in concrete.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>The stress-strain curve helps to understand the relationship between the stress applied to the steel and its corresponding deformation.</p> Signup and view all the answers

<p>The 'characteristic breaking strength' (fpb) represents the maximum stress that a tendon can withstand before fracturing, and it is a crucial parameter for determining the design capacity of the tendon.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>Losses in prestressing force can significantly impact the structural performance of the pre-stressed element over time. Reducing these losses is crucial to ensure the intended design capacity of the structure and prevent premature failure.</p> Signup and view all the answers

<p>Elastic deformation of the concrete during stressing.</p> Signup and view all the answers

<p>Deferred losses are gradual losses that occur over time after the prestressing force is transferred to the concrete. They are primarily caused by factors like shrinkage and creep, while immediate losses occur during the initial tensioning and transfer phase.</p> Signup and view all the answers

<p>Load balancing in structural floor systems refers to the efficient transfer of gravity loads from the floor slab to the vertical support system, ensuring stability and minimizing stress concentrations.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>Ribbed slab and beam</p> Signup and view all the answers

<p>Band-beam and slab floor systems are commonly used for common office and car-park buildings.</p> Signup and view all the answers

<p>Flat plates are often used for residential buildings with smaller spans, while flat slabs are favored for larger areas, such as hospitals and office buildings.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>The L/D ratio (span-to-depth ratio) is a crucial parameter for pre-stressing design, as it provides a general guideline for determining the adequate depth of a member relative to its span length.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>When designing prestressed beams with simply supported conditions, it's essential to consider the load transfer mechanism and the potential for localized stress concentrations at the support points.</p> Signup and view all the answers

<p>The choice of P/A (prestress/area) ratio is influenced by factors such as the type of pre-stressed member (beam or slab), the specific loading conditions, and the required level of serviceability for the structure.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>The 'bay area', Ab, represents the area encompassed by the columns defining a particular load-carrying region within a pre-stressed structure. It's essential for determining the appropriate P/A value for the specific bay and ensuring adequate load distribution.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>A smooth transition is crucial to minimize stress concentrations and ensure a seamless transition between the straight tendon section in the span and the curved section near the supports, preventing potential cracking and structural failure.</p> Signup and view all the answers

<p>Practical tendon profiles with a smooth transition ensure a more efficient load distribution and minimize potential stress concentrations at the supports, leading to a more robust and durable structure.</p> Signup and view all the answers

<p>For three conditions: one with flexural cracks, one with web-shear cracks, and one with flexure-shear cracks.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>In region B, both moment and shear forces are relatively large, leading to the formation of flexure-shear cracks, a combination of flexural and shear cracking.</p> Signup and view all the answers

<p>Web-shear cracking occurs primarily in region C, where the shear forces are dominant, leading to the formation of cracks that extend across the web of the beam.</p> Signup and view all the answers

<p>Torsion in beams creates a diagonalized pattern of cracking around the perimeter of the beam, forming a crisscross pattern due to the twisting forces.</p> Signup and view all the answers

<p>Torsional reinforcement, typically in the form of closed ties, is used to supplement or add to the shear reinforcement in beams subject to torsional stresses, ensuring structural stability and preventing premature failure.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>'Determinate' structures allow all forces and moments to be determined using equations of static equilibrium. This makes them easier to analyze and predict their behavior under loads.</p> Signup and view all the answers

<p>'Indeterminate' structures have redundant restraints or members, making their analysis more complex. These structures require additional equations and methods beyond static equilibrium to determine forces and moments.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>Statically determinate beams primarily include simply supported beams, single-span beams with cantilever ends, and single-span cantilevers.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>The general approach for preliminary sizing of a simply reinforced beam involves starting with a standard design and gradually increasing the span-to-depth ratio (L/D) until the desired performance criteria are met.</p> Signup and view all the answers

<p>Post-tensioning allows for a reduction in the required depth of a beam compared to a simply reinforced beam for a comparable span. The depth can be reduced by approximately 70-80% while still meeting serviceability requirements.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>2.0-2.5 MPa</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>The 'bay area', Ab, is a key factor in calculating the P/A ratio. It represents the region between columns within a pre-stressed structure and influences the load distribution and overall structural capacity.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>A smooth transition near the supports is essential to prevent stress concentrations and minimize the risk of cracking. A gradual curvature allows for seamless transition, while a sharp change can lead to excessive stress and potential failure.</p> Signup and view all the answers

<p>Practical tendon profiles with a smooth transition offer greater efficiency in load distribution, minimizing stress concentrations. This translates to a more robust and longer-lasting structure, as the forces are managed more effectively.</p> Signup and view all the answers

<p>'Vuc' represents the component of shear carried by the concrete in a pre-stressed beam. Calculating 'Vuc' is essential to assess the shear capacity of the concrete and ensure that it can safely resist the applied loads.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>In region B, the combination of bending moments and shear forces is significant. This leads to the formation of flexure-shear cracks, a combination of flexural and shear cracking, creating a more complex cracking pattern.</p> Signup and view all the answers

<p>Web-shear cracking, predominantly found in Region C of a pre-stressed beam, is characterized by cracks extending across the web of the beam. This type of cracking occurs primarily due to dominant shear forces, while flexure-shear cracks are influenced by both bending moments and shear forces.</p> Signup and view all the answers

<p>Torsion introduces twisting forces in a beam, resulting in a diagonalized pattern of cracking. The twisting forces act perpendicular to the longitudinal axis of the beam, creating diagonal cracks that resist the torsional deformation.</p> Signup and view all the answers

<p>Torsional reinforcement is employed in beams subject to torsional stresses to prevent excessive cracking and ensure structural stability. It typically consists of closed ties placed at centers along the beam, acting as supplementary reinforcement to resist the twisting forces.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>They are easier to predict their behavior under loads.</p> Signup and view all the answers

<p>'Indeterminate' structures have redundant restraints or members, making their analysis more complex. These structures require additional equations and methods beyond static equilibrium to determine forces and moments. 'Determinate' structures have a simpler, predictable behavior because all forces and moments can be readily calculated using equations of static equilibrium.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>Pre-stressing is the process of preloading the structure before applying design loads to improve its overall performance.</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>Post-tensioned system</p> Signup and view all the answers

<p>All of the above</p> Signup and view all the answers

<p>Immediate losses and Deferred losses</p> Signup and view all the answers

<p>The method and equipment used for prestressing.</p> Signup and view all the answers

<p>Gradual losses that occur over time due to factors like creep, shrinkage, and stress relaxation.</p> Signup and view all the answers

<p>To support the loads and provide resistance to stresses.</p> Signup and view all the answers

<p>Strength, stiffness, and deflection.</p> Signup and view all the answers

<p>One-way spanning and two-way spanning.</p> Signup and view all the answers

<p>Ribbed slab and beam, beam and two-way slab, band-beam and slab, and flat slabs.</p> Signup and view all the answers

<p>Flat slab.</p> Signup and view all the answers

<p>Span to depth ratio.</p> Signup and view all the answers

<p>To smoothly transition the cable profiles over supports and prevent sharp curves or points.</p> Signup and view all the answers

<p>It allows for increased depth near the supports, improving load distribution and resistance.</p> Signup and view all the answers

<p>To resist shear stresses and prevent shear failures.</p> Signup and view all the answers