The diameter of the bar is between 12 and 28 mm. ESE Previous year Civil Engineering Question Papers, GATE Previous year Civil Engineering Question Papers, Other TNPSC PREVIOUS YEAR QUESTION PAPERS. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. The slight variation could be due to the application of successive prestressing in all the cables. The Final Total Prestress loss shown in the Leap Conspan output is calculated as follows. Prestressed Concrete Structures Basic Online 1 Prestressed Concrete Structures MCQ Questions PDF with easy explanations will prepare you for various types of written exams and clear them with good scores. Detailed Solution for Test: Prestress Concrete - 2 - Question 3 Let the dip of the cable be h. Upward pressure provided by the parabolic cable = 8Ph/L 2 In order this upward pressure may fully balance the external loading. 50 Nc. PART B 16marks (CE6702 Prestressed Concrete Structures Question Bank) 1. The primary purpose of prestressing steel is to apply a force to a concrete, either by bond or by means of special anchoring devices. IV. To view the purposes they believe they have legitimate interest for, or to object to this data processing use the vendor list link below. Loss of stress due to relaxation of steel is influenced by, Loss of stress due to relaxation of steel. Initial Loss = 13.65 ksi (Elastic Shortening) Long Term Loss = 20.3 ksi. This method was introduced by a famous engineer. container.style.width = '100%'; Answer: a Clarification: The loss due to elastic deformation of concrete depends on the modular ratio and the average stress in concrete at the level of steel, consider a post tensioned member which is prestressed by a single tendon and the shortening of concrete occurs till the tendon is jacked and no shortening of concrete is observed after it. SHOW ANSWERc) will change if loading in the beam is changed, 29. Between the two ends, the spacing of the wires is maintained by spacers. Where, t - age of concrete at transfer in days. If a concrete beam is subjected to an eccentric prestressing force of magnitude p, at an eccentricity e, the stress developed at the bottom fiber of the beam is (FC 2018), 44. This loss occurs only in the post tensioned members. Introduction In prestressed concrete applications, most important variable is the prestress. your desk.d. The various limit state of collapse as per IS 1343: 2012are: The various limit state of serviceability as per IS 1343: 2012are: Reference: IS 1343 - 2012 (Page 42:, Clause 23), Loss of pre-stress is not directly related to, 1. It would be hard to ride a bike without it.b. In pre-stressed concrete, for post-tensioned members, the minimum 28 days compressive strength of concrete prescribed in IS 1343 (AE 2015), 19. From the above factors, we can say thatLoss of pre-stress is not directly related to the grade of concrete. repel each other.b. Loss due to relaxation of stress in steel. The spacing of stirrups in a pre-stressed beam should not exceed (AE 2015), c) 0.75 times the effective depth of the beam, d) 0.3 times the effective depth of the beam, SHOW ANSWER c) 0.75 times the effective depth of the beam, 18. What we are trying to quantify is the change in the strain. Consider m = 6. The crack width in the center span is between 0.1 and 0.15 mm (0.004 and 0.006 in.) 2. (c) muscular force. 7. friction.c. Answer. Theminimum clear spacing between groups of cables or ducts of grouped cables shall be greaterof the following: b) 5 mm plus the maximum size of aggregate, As per IS code, the minimum grade of concrete for the design of prestressed concrete structure is:-. b) Maximize elastic creep and shrinkage strains. What is his weight on Earth?a. cushion the landing.c. However ,if a prestressed concrete member is cracked , it behaves in a manner similar to that of a reinforced concrete sections. 23. Even during prestressing of tendons, and transfer of prestress, there is a drop of prestress from the initially applied stress. The loss of prestress due to shrinkage is obtained by. acts between objects that are not touching.d. two of the above, 3 ) What does weight measure?a. Consider the statements: (AE 1999) The locus of the point of application of the resultant force at any given section of a prestressed concrete beam is the (2019 AE), SHOW ANSWER (B) pressure line or thrust line, 47. Losses in Prestress Due to Creep of Concrete 6. Prestressing is the process by which a concrete element is compressed, generally by steel wires or strands. The friction between tendons and surrounding materials is not small and may be considered partly a length effect (wobble effect) and partly a curvature effect. The box has less friction when it is sliding. See Page 1 . Loss due to relaxation varies widely for different steels and the steel manufacturers based on test data may supply its magnitude. 4) In the following sketch, what is the net force acting on the box?if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[320,50],'physicsteacher_in-box-4','ezslot_2',148,'0','0'])};__ez_fad_position('div-gpt-ad-physicsteacher_in-box-4-0'); 5) Which diagram represents balanced forces? acceleration.d. It is ITD's policy to ignore the effects of this . surfaces in contact generate heat.c. Losses due to creep in concrete 4. Pages 324 This preview shows page 310 - 313 out of 324 pages. window.ezoSTPixelAdd(slotId, 'stat_source_id', 44); A prestressed concrete sleeper produced by pre- tensioning method has a rectangular cross-section of 300mm 250 mm (b h). pre-stressed concrete structures are subjected to impact and vibration. var lo = new MutationObserver(window.ezaslEvent); The lever arm for a given pre-stressed concrete beam section (AE 2010), c) will change if loading in the beam is changed. Loss due to the relaxation of strands is categorized as a long-term loss of pre-stress in a pre-stressed concrete member. The approximate value of shrinkage strain for design shall be assumed as follows (IS 1383): initial Prestressing force, Po = 300 kN, Area = 300 mm2, Initial stress, f = Po/A = 300000/300 = 1000 N/mm2, Loss of pre-stress due to shrinkage,(fp) = EP sh, Loss of stress (%) =\(\frac{{{\Delta f_p}}}{f} \times 100 = \frac{{60}}{{1000}} \times 100 = 6\%\). Save my name, email, and website in this browser for the next time I comment. It is one in which a permanent and essentially horizontal compressive stress has been introduced prior to the application of any wheel loads. Let us discuss the types of losses in prestress given in the article below. 7 ) An object with greater massa. ins.style.width = '100%'; For Post tensioning minimum grade of concrete used is M-30. Tendon force P x at the distance x from the jacking end can be expressed as . Total number of loss is more in Post-tensioned concrete compare to Pre-tensioned concrete. Loss of pre-stress (fp) due to shrinkage = EP sh, Where Ep is the modulus of pre-stressing steel and. It is subjected to a prestressing force at an eccentricity e so as to have a zero stress at the top fibre. Your email address will not be published. For pre-stressed concrete, it is desirable to use (AE-1998), A) High strength concrete and high tensile strength steel, B) Low strength concrete and low tensile strength steel, C) High strength concrete and low tensile strength steel, D) High strength concrete and low tensile strength steel, SHOW ANSWER A) High strength concrete and high tensile strength steel, 3. Based on the initial applied prestressing force in tendons and the calculated existing prestressing force, loss of prestress can be worked out during last 10 years as given below in Table -4: The loss observed is quite uniform throughout. In the case of small span pre-stressed unsymmetrical I-section members thinner webs of about ____ may be used (2019 AE Nilgiri), SHOW ANSWER (C) 60-80 mm(Tentative Answer), 50. bc. ab. lo.observe(document.getElementById(slotId + '-asloaded'), { attributes: true }); The function of reinforcements is pre-stressed Concrete is to (2019 AE), (C) Provide sufficient torsion resistance, (D) Produce initial compressive stresses in concrete in the torsion zone, SHOW ANSWER (D) Produce initial compressive stresses in concrete in the torsion zone, 46. Considering the parabolic tendon upward force & moment is given by, \(w = \frac{{8Py}}{{{L^2}}}\)&\(M = \frac{{\left( {w - P} \right){L^2}}}{8}\). \(\text{Total stress at bottom fibre} = \frac{P}{A} - \frac{M}{Z} +\frac{Pe}{Z}\)= 0, \( \frac{157\times 10^3}{150000} - \frac{M}{15\times 10^6} +\frac{157\times 10^3\times 100}{15\times 10^6} = 0\). 500 Nd. (b) atmospheric pressure. The minimum prestress force occurs at the right-hand end of the beam: P(x=50)=3000 exp [0.19(0.469+5010450)] Figure 4.7 . Cover to be used in the design of the prestressed concrete structure as per IS 1343 is as below: The grade of concrete used for prestressed member lies in the range of: Hence it can be seen thatgrade of concrete used for prestressed member lies in the range of M30 to M60. 3. 1343-1980, for pre-tensioned concrete is (AE 1998), 6. 31. The change of prestress loss is highly related to the distribution of cracks. The total acid-soluble chloride content should be calculated from the mix proportions and the measured chloride contents of each of the constituents. As per IS 1343 1980, the minimum 28 days compressive strength for pre-tensioned member is: the minimum 28 days compressive strength for pre-tensioned member is: M 40 or40 N/mm2, The purpose of reinforcement in prestressed concrete is. The high tensile steel tendon in a prestressed concrete member (FC 2018), b) Does not remain under a constant condition of either stress or strain, SHOW ANSWER b) Does not remain under a constant condition of either stress or strain, 43. rolling friction, 1 ) Gravity always causes objects toa. But total loss of prestress is more in Pre-tensioned concrete compare to Post-tensioned concrete. 2) Losses due to creep or relaxation of steel: Important PointsLosses in Post-tensioning, High-tensile bars threaded at ends are used in. 1 and 2 . prestress. High strength concrete is used in prestressed concrete to (GROUP 1-1998). T. It is stronger than sliding friction.d. 1 Crore+ students have signed up on EduRev. What is maximum bending moment that can be applied to the section WITHOUT causing tension at soffit of the beam? 2. Basically the load-carrying mechanism is comprised of a constant force with a changing lever-arm as in case of prestressed concrete sections and a changing force with a constant lever arm prevailing in reinforced concrete sections. Depth of cable from extreme compression fibre. Copyright 2022 All rights reserved. There are small frictional losses in the jacking equipment. Material/Producer Listing. which type of pre stressing is used in pre stressed concrete pavements? Post tensioning: 1. It has a higher modulus of elasticity and smaller creep strain. Officer, Patna Civil Court Reader Cum Deposition Writer, MP Vyapam Horticulture Development Officer, Option 3 : To impart initial compressive stress in concrete, Option 2 : forces of tension and compression remains unchanged but lever arm changes with moment, Option 3 : loss due to relaxation of strands, Copyright 2014-2022 Testbook Edu Solutions Pvt. concrete is 23.5 kN/m3, Unit weight of The properties of the double-tee section are: Area 220,000 mm2 1 1890 x 106 mm4 y 90 mm b 2.5 m y2 270 mm y 75 mm Simple span, L -8 m Dead load 2.5 kPa Live load 6 kPa Service loads on floor: 161. As a result, the loss of prestressing is small. Allahabad University Group C Non-Teaching, Allahabad University Group A Non-Teaching, Allahabad University Group B Non-Teaching, NFL Junior Engineering Assistant Grade II, BPSC Asst. The prestressing force in each tee is 750 kN. If a simply supported concrete beam, prestressed with a force of 2500 kN, is designed by load balancing concept for an effective span of 10 m and to carry a total load Of 40 kN/m, the central dip of the cable profile should be, Let the dip of the cable be h. The moment of resistance of rectangular sections in which the neutral axis lies within the flange m to be obtained in prestressed concrete beams as, 35. in the presention system the prestress is imparted to concrete by (AE 2018), SHOW ANSWER b) the bond between steel and concrete, 36. stationary object to start moving.b. 3. depth of cable from extreme compression fibre The loss of prestress due to elastic deformation of concrete depends on _____ a) Modular ratio and average stress . A concrete beam is pre-stressed by a cable carrying an initial pre-stressing force of 300 kN, the area is 300 mm2. 3 alone . 1. i.e M30 grade. d, 1) Friction occurs becausea. Which of the following are necessary for Run-time Polymorphism? loss of prestress. McGraw-Hill Dictionary of Architecture and . As initial prestress is around 1500-2000 N/mm2. The maximum cube strength of concrete used for a pre-stressed member is (AE 2013), 16. The initial prestress force of a cable is calculated using below empirical formula: where F is the initial prestress force, is the yield stress of the cable, and A is the cross-sectional area of the cable. Wherever possible, the total chloride content of the concrete should be determined. Initial prestress 2. Loss in prestress = Initial prestress - effective prestress. (iii) With the use of high-strength concrete, shrinkage cracks are low. 1. Profile of the prestressing steel in prestressed concrete members follows thebending moment diagram. Transportation of prestressed concrete is also a big challenge . 1.LOSS DUE TO ELASTIC DEFORMATION OF CONCRETE: The loss of prestress due to elastic deformation of concrete depends on the modular ratio and the average stress in concrete at the level of steel. To modify the behavior of the member or structure in such a way so as to make it more suitable for its intended purpose. In concrete, if the reinforcement wires are stretched after the concrete has hardened, it is called (AE 2008), 28. In the field of bridge engineering, the introduction of prestressed concrete has aided the construction of long-span concrete bridges. Modulus of Elasticity of Steel - (Measured in Pascal) - Modulus of Elasticity of Steel or elastic modulus is the resistance of the structure or object from being deformed elastically when a stress is applied. 2. Precast elements may be prestressed during the construction process (pre-tensioning) or structures may be stressed once completed (post-tensioning). Friction loss has two components, including the length or wobble effect and the curvature effect. High strength concrete is necessary in prestressed concrete, as the material offers high, resistance in (FC 2018), SHOW ANSWER c) tension, shear, bond, and bearing, 42. Loss due to relaxation varies widely for different steels and the steel manufacturers based on test data may supply its magnitude. minimum clear spacing between groups of cables or ducts of grouped cables shall be greater, \(\frac{{\bf{P}}}{{\bf{A}}} - \frac{{{\bf{P}}. d) does not exist in the absence of live loads. Advantages of Prestressed concrete. 4 ) Which statement about rolling friction is false?a. If the loading on a pre-stressed rectangular beam is uniformly distributed, and supported at either end, the tendon to be provided should be (2019 AE), SHOW ANSWER (B) Parabolic with convexity downward, 49. It occurs when ball bearings are used.c. 7 ) An object with greater mass. Those which affect the ultimate moment capacity of a prestressed concrete beam would include. Loss in Prestress Due to the Friction 3. Tendon force is greatest at the jacking end, and decreases with distance from the end because of the friction which occurs during jacking between the tendon and the duct. Here is how the Loss of Prestress due to Slip calculation can be explained with given input values -> 4 = 5E-05* (200000000000*0 . Prestressing compensates for the tensile stresses introduced when the element is loaded. 24. The prestress loss due to elastic shortening in pre-tensioned members is taken as the concrete stress at the centroid of the prestressing steel at transfer, f cgp, multiplied by the ratio of the modulus of elasticities of the prestressing steel and the concrete at transfer 2) Losses due to creep or relaxation of steel: Loss of pre-stress takes place due to the width effect. To improve the resistance of the member to the dead and live loads. Besides giving Questions and answers for Test: Prestress Concrete - 2, EduRev gives you an ample number of Online tests for practice. Depth of cable from extreme compression fibre. The acceptable limit for the safety and serviceability requirements before failure occurs is called a limit state. When the friction loss data of prestress is obtained by tests, the corresponding friction coefficient can be got according to the prediction equation of prestress. sizeb. 2. Moreover, high-strength concrete is less subjected to shrinkage cracks. Where, P = force applied on tendon, A = Cross-section area, M = moment on beam, y = Tendon distance from neutral axis, e = eccentricity and I = moment of inertia. Which of the following losses occurs only in post-tensioning pre-stressed concrete structures. Figure 14 shows the 3-D time-dependent prestress loss of the loaded beam measured by the BOTDA sensors in the smart steel strand at the normal service limit state. Prestressed concrete is a system devised to provide sufficient precompression in the concrete beam by tensioned steel wires, cables, or rods that under working conditions the concrete has no tensile stresses or the tensile stresses are so low that no visible cracking occurs. at the soffit of the beam, total stress at bottom fibre must be zero. This reduction in the prestressing force is called loss in prestress. {\bf{e}}}}{{\bf{Z}}}\), =\(\frac{{700 \times {{10}^3}}}{{300 \times 900}}- \frac{{700 \times {{10}^3} \times 350}}{{40.5 \times {{10}^6}}}\). The full-scale strain (location 5.5-7.5 m) distribution of strand can be obtained by the BOTDA sensors. Hence the concrete generally remains in compression. Required fields are marked *. Es= modulus of elasticity of steel. In most tensioning systems, when the cable is tensioned and the jack is released to transfer pre-stress to concrete, the friction wedges employed to grip the wires, slip over a small distance before the wires are finally housed between the wedges. In prestressed concrete, the reduction of the prestressing force which results from the combined effects of creep in the steel and creep and shrinkage of the concrete; normally does not include friction losses but may include the effect of elastic deformation of the concrete. ins.className = 'adsbygoogle ezasloaded'; High strength steel wires of 5 mm or 7 mm diameter, numbering 8 or 12 or 16 or 24 are grouped into a cable with a helical spring inside. The value of e is given by, For zero stress at top fibre, Loss of pre-stress takes place due to creep of steel. Fully pre-stressed concrete beams (AE 1997), a) Resists the full live load by pre-stress, b) Resists all the working loads by pre-stress, c) Resists a part of the load of pre-stress, SHOW ANSWER b) Resists all the working loads by pre-stress, 21. In prestressed concrete stress block is recommended with appropriate safety factors. 22. Prestressing is done to reduce or eliminate the internal tensile stresses by applying an initial compressive axial force to the concrete. There are two types of the anchorage device in this system: The Freyssinet system was introduced by the French Engineer Freyssinet and it was the.

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