IV. Question is Select the incorrect statement., Options are (A) The loss of prestress is more in pre-tensioning system than in post-tensioning system., (B) Pretensioning system has greater certainty about its durability., (C) For heavy loads and large spans in buildings or bridges, post-tensioning system is cheaper than pretensioning system, (D) none of the above, (E) , Leave your . Loss due to Relaxation:Relaxation is assumed to mean the loss of stress in steel under nearly constant strain at a constant temperature. Types of Losses in Prestress 2. var alS = 2002 % 1000; Loss of prestress due to friction occurs (AE 1997) A) Only in pre-tensioned beams. This loss is generally of the order of 2 to 8% of the initial stress. Theloss due to anchorage does not occur in pre-tensioned members. The pressure which is exerted by air around us is known as. Besides giving Questions and answers for Test: Prestress Concrete - 2, EduRev gives you an ample number of Online tests for practice. World's best MCQs website Civil Engineering, Consider the following factors :1. where [alpha] is the ratio of the prestress at the critical section to the fully effective prestress of the strands, which can be estimated as the distance ([l.sub.c]) from the member end to the critical section divided by the transfer length ([l.sub.t]) as shown in Figure 2. static frictionb. Wires of 5 mm or 7 mm are adopted. A pre tensioned concrete beam 100mm wide and 300mm Loss Due to Shrinkage:-deep, initial force of 150kn at an eccentricity of 50mm, 6 4 moment of inertia is 22510 mm , initial . Which of the following losses occurs only in post-tensioning pre-stressed concrete structures. Even during prestressing of tendons, and transfer of prestress, there is a drop of prestress from the initially applied stress. For prestressed concrete structural elements, high tensile steel is used primarily (AE 2010), a) because of the high modulus of elasticity. For prestressed concrete the high tensile wires are only used. ab. two of the above, 6 ) Which type of friction occurs between a paddle and the water?a. Thus the loss is 383.1 kN, which is 12.8% of the initial force. 4. In pre-stressed concrete, for post-tensioned members, the minimum 28 days compressive strength of concrete prescribed in IS 1343 (AE 2015), 19. The shrinkage of concrete can be reduced by reducing (AE-1999), 9. In prestressed concrete stress block is recommended with appropriate safety factors. Loss of pre-stress (fp) due to shrinkage = EP sh, Where Ep is the modulus of pre-stressing steel and. Initial losses occur during stressing operation and include anchor seating, elastic shortening, and friction between prestressing steel and post-tensioning ducts or tendon deviators and harped. R.C.C. the suns gravity is weaker than Earths.b. The box is lighter when it is sliding.b. 3 alone . if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[300,250],'physicsteacher_in-large-mobile-banner-2','ezslot_9',154,'0','0'])};__ez_fad_position('div-gpt-ad-physicsteacher_in-large-mobile-banner-2-0');5 ) A skydiver uses a parachute toa. 40 mm or maximum size of cables or bar of nominal maximum size of aggregate plus 5 mm. The number of wires in magnel cable varies between (AE 2018), 37. 1. The value of e is given by, For zero stress at top fibre, 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. 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. Loss of prestress due to elastic deformation of the concrete and relaxation of the steel need to be considered. 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. III. Cube strength of controlled concrete to be used for pre-tensioned and post-tensioned work respectively should not be less than (AE 1999), SHOW ANSWER b) 420 kg / cm2 & 350 kg / cm2, 25. forces of tension and compression change but lever arm remains unchanged, forces of tension and compression remains unchanged but lever arm changes with moment, both forces of tension and compression as well as lever arm changes, both forces of tension and compression as well as lever arm remains unchanged. Between the two ends, the spacing of the wires is maintained by spacers. It occurs when ball bearings are used.c. If fc= prestress in concrete at the level of steel. In prestressed concrete, a prestress force is applied to a concrete member and this induces an axial compression that counteracts all, or part of, the tensile stresses set up in the member by applied loading. Es= modulus of elasticity of steel. Loss of prestress affects - the strength of member and - member's serviceability [ Stresses in Concrete, Cracking, Camber and Deflection ] 7 8. It is similar to the creep of concrete. SHOW ANSWER a) Minimize elastic creep and shrinkage strains. increase air resistance.b. The loss of prestress due to elastic deformation of concrete depends on _____ a) Modular ratio and average stress . Estimate the percentage loss of stress due to elastic shortening of concrete. The decrease of stress in steel at constant strain is termed as (AE 2018), 40. window.ezoSTPixelAdd(slotId, 'stat_source_id', 44); A change in the external moments in the elastic range of a prestressed concrete beam results in a shift of the pressure line rather than in an increase in the resultant force in the beam. The full-scale strain (location 5.5-7.5 m) distribution of strand can be obtained by the BOTDA sensors. IV. = 40h = 0.2 m (iv) High strength concrete will have high modulus of elasticity of concrete(= 5000fck)and hence elastic and cracks strains are very low means creep strains are low, resulting in smaller loss of prestressing force. Load and moment in concrete are balanced by stressing the steel. 1. initial prestress A pre-stressed concrete induces artificially stresses in a structure before it is loaded. It took until the 1920s and '30s for its materials development to progress to a level where prestressed concrete could be used with confidence. Here it is asked minimum grade of prestressed concreteso it would be minimum of post-tensioning and pre tensioning. Initial prestress 2. The second category is the loss or gain due to additional loads, such as non-composite dead loads, composite dead loads and live loads that are applied after transfer. 100000120. 1343-1980, for pre-tensioned concrete is (AE 1998), 6. Force and Pressure Class 8 MCQs Questions with Answers. The following loss does not occur in Pre-tensioning of concrete. Manage Settings This loss is generally of the order of 2 to 8% of the initial stress. h = 200 mm, A prestressed concrete beam has a cross- section with the following properties: Determine the additional live load (kN/m) that the prestressed beam can sustain without concrete stresses exceeding . 1 alone Loss due to creep of concrete. But in the case of the arch, tensile stresses do not occur in the structure, all compressive forces evolve directly from the load due to its specially designed shape. slow the descent.d. Loss in Prestress Due to the Friction 3. Prestress Concrete MCQ 1. Then select the cables, choose Assign Cable Loads Target Force, then define the initial prestress forces for the cables. Loss of prestress due to effect of curvature, Loss of prestress due to wobble effect and frictional losses can be reduced by over tensioning the tendons by an amount equal to the maximum frictional loss and jacking the tendons from both ends of the beam adopted generally, when the tendons are long or when the angles of bearing are large. Advantages of Prestressed concrete. Table of Content 1. 3. a) Minimize elastic creep and shrinkage strains. (adsbygoogle = window.adsbygoogle || []).push({}); No loss due to elastic deformation if all the wires are simultaneously tensioned. It is similar to the creep of concrete. The cable is inserted into the duct. Loss due to shrinkage of concrete. var container = document.getElementById(slotId); The box has less friction when it is sliding. It is ITD's policy to ignore the effects of this . at the soffit of the beam, total stress at bottom fibre must be zero. Losses due to creep or relaxation of steel. The degree of pre- stress (0.68) is related only to the bend- ing moment of decompression, M,, in the tensile zone of the center span (see Table 2). 4. RMS CIVIL FACTORY What we are trying to quantify is the change in the strain. 50 Nc. 50 Nc. Introduction In prestressed concrete applications, most important variable is the prestress. This reduction in the prestressing force is called loss in prestress. These offer great technical advantages in comparison with other . I. Pre-stressed concrete structures are most economical. View full document. Which of the following post tensioning system adopts metallic sandwich plates, flat wedges and distribution plate for anchoring the wires? It is one in which a permanent and essentially horizontal compressive stress has been introduced prior to the application of any wheel loads. Total loss of prestress is around 15-20%. loss due to anchorage does not occur in pre-tensioned members. Time-dependent strain measured in an unloaded and unrestrained specimen at a constant temperature. D) None of the above. Losses in Prestress Due to Elastic Shortening of Concrete 5. 500 Nd. bc. SHOW ANSWERc) will change if loading in the beam is changed, 29. The class definition must include the words implements. Immediate Losses immediate losses occur during prestressing of tendons, and transfer of prestress to concrete member. Figure 14 illustrates the principle. (iii) With the use of high-strength concrete, shrinkage cracks are low. P/A = Pe/Z 1. Those which affect the ultimate moment capacity of a prestressed concrete beam would include. Therefore high tensile steel is made for prestress concrete. It is stronger than sliding friction.d. 31. Loss of prestress affects the strength of member and also See Page 1 . electric poles are generally made of (AE-2008), 12. \(\text{Total stress at bottom fibre} = \frac{P}{A} - \frac{M}{Z} +\frac{Pe}{Z}\)= 0, \( \frac{157\times 10^3}{150000} - \frac{M}{15\times 10^6} +\frac{157\times 10^3\times 100}{15\times 10^6} = 0\). 3. Producers who are interested in adding their name to the Prestressed Concrete Source Listing should review the Guidelines for Adding a Producer to the Materials/Producer Listings. bc. after transfer of the prestress force to the girder (loss due to prestress combined with gain due to the member self weight). rolling friction, 1 ) Gravity always causes objects toa. The bursting stresses in pre-stressed concrete members are developed at, (GROUP 1-1998). ins.style.display = 'block'; Bars provided with threads at the ends are inserted in the performed, Bond, Anchorage and Development Length MCQ, UKPSC Combined Upper Subordinate Services, Punjab & Haryana High Court Clerk Exam Dates, APPSC Assistant Motor Vehicle Inspector Apply Link Active, SSC CGL Divisional Accountant Exam Date Notice, Social Media Marketing Course for Beginners, Introduction to Python Course for Beginners. The gradual reduction of this introduced compressive stress in a prestressed member due to various reasons is called losses of prestress. To minimize the chances of deterioration of concrete from harmful chemical salts, the levels of such harmful salts in concrete coming from concrete materials, that is, cement, aggregates, water, and admixtures, as well as by diffusion from the environment should be limited. An example of data being processed may be a unique identifier stored in a cookie. Earth already orbits the sun.d. This loss is generally of the order of 2 to 8% of the initial stress. Prestressing is the process of introducing compressive stress to the concrete to counteract the tensile stresses resulting from an applied load. 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. Loss of pre-stress takes place due to the width effect. Types Loss of prestress is classified into two types: 1. The change of prestress loss is highly related to the distribution of cracks. Precast elements may be prestressed during the construction process (pre-tensioning) or structures may be stressed once completed (post-tensioning). the moon is closer to Earth. In concrete, if the reinforcement wires are stretched after the concrete has hardened, it is called (AE 2008), 28. Score: 4.7/5 (32 votes) . 2. For Posttensioning minimum cover to be used is 30 mm. Depth of cable from extreme compression fibre. lo.observe(document.getElementById(slotId + '-asloaded'), { attributes: true }); MCQ worksheet Force (Physics) | Multiple Choice Questions from the Force chapter physics, Buoyancy Worksheets - MCQ worksheet | Multiple Choice, Pressure Worksheets - MCQ worksheet | Multiple Choice, Current Electricity Worksheets - MCQ worksheet | Multiple, Newtons Laws of Motion Worksheets - MCQ worksheet |, Electronics - Worksheets MCQ | Multiple Choice Questions, Waves - Worksheets MCQ | Multiple Choice Questions from the, [pdf notes] Unit Systems in Physics grade 10 Notes download | class 11 physics notes on Unit System, Newtons Laws of Motion Worksheets MCQ worksheet | Multiple Choice Questions from the Laws of Motion chapter physics. Loss due to relaxation varies widely for different steels and the steel manufacturers based on test data may supply its magnitude. The prestress is induced in the cross-section of a pre-tensioned pre-stressed concrete member due to the (AE 2015), SHOW ANSWER a) bond between tendons and concrete, 20. Cover to be used in the design of prestressed concrete structure as per IS 1343 is as below: 1. The elastic shortening loss is quantified by the drop in the prestressing force in a tendon, due to the change in strain in the tendon. Final Gain = -9.96 ksi. To view the purposes they believe they have legitimate interest for, or to object to this data processing use the vendor list link below. The loss of prestress due to shrinkage is obtained by. 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. In addition to long-term losses due to creep, shrinkage and relaxation, an immediate drop in prestress force occurs due to elastic shortening of the concrete. which type of pre stressing is used in pre stressed concrete pavements? A.only in post-tensioned beams B.only in pretensioned beams C.in both post-tensioned and preten-sioned beams D.none of the above Answer & Explanation Related Questions on Design of Concrete Structures Mcqs 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. Creep of concrete. d, 7) Which pair of forces in question 5 produces a net force of zero?a. a) high tensile steel and ordinary concrete are used. The diameter of the bar is between 12 and 28 mm. a. has greater acceleration when it falls. loss of prestress. {\bf{e}}}}{{\bf{Z}}}\), \(\frac{{\frac{{{\bf{b}}{{\bf{d}}^3}}}{{12}}}}{{\frac{{\bf{d}}}{2}}} = \frac{{{\bf{b}}{{\bf{d}}^2}}}{6} = \frac{{300 \times {{900}^2}}}{6} = 40.5 \times {10^6}{\bf{m}}{{\bf{m}}^3}\), \(\frac{{700 \times {{10}^3}}}{{300 \times 900}}- \frac{{700 \times {{10}^3} \times 350}}{{40.5 \times {{10}^6}}}\), \(\text{P} = 4 \times \frac{\pi}{4}\times 10^2\times 500\), \( \frac{157\times 10^3}{150000} - \frac{M}{15\times 10^6} +\frac{157\times 10^3\times 100}{15\times 10^6} = 0\), \(\frac{{{\Delta f_p}}}{f} \times 100 = \frac{{60}}{{1000}} \times 100 = 6\%\), \(M = \frac{{\left( {w - P} \right){L^2}}}{8}\), \(\sigma = \frac{P}{A} + \frac{{My}}{I} - \frac{{Pey}}{I}\), \(\frac{{0.0001}}{{{{\log }_{10}}\left( {t + 2} \right)}}\), \(\frac{{0.0002}}{{{{\log }_{10}}\left( {t + 2} \right)}}\), \(\frac{{0.0003}}{{{{\log }_{10}}\left( {t + 2} \right)}}\), reductions of the prestressing force are termed as the losses in prestressing, loss due to friction does not occur in pre-tensioned members. For Pre-tensioning minimum grade of concrete used is M-40. none of the above. } Mention the losses that can occur in prestressed concrete ? Wherever possible, the total chloride content of the concrete should be determined. Mcqspage.com is a leading Website which provide Best online MCQ's solution with easy explanations for all competitive examination such as GK mcq question, english mcq question, arithmetic aptitude mcq question, Data Intpretation, Programing, Engeneering etc. It would be hard to ride a bike without it.b. ins.style.width = '100%'; 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. static frictionb. Choose the correct option. For Pre-tensioning minimum cover to be used is 20 mm. 4 ) Which statement about rolling friction is false?a. MCQ Geeks 0 : 0 : 1; . sliding frictiond. Ravindra and Markandeya Raju (2012) [34] formulated a procedure for finding loss of prestress in prestressing steel beams and studied the performance of prestressed steel I-beams and compound . The stress in concrete on top fiber is given by, \(\sigma = \frac{P}{A} + \frac{{My}}{I} - \frac{{Pey}}{I}\) (Signs are interchanged for bottom fibre). That reference gives simple equations for estimating losses of prestress which would enable the designer to estimate the various types of prestress loss rather than using a lump sum value. forced. The arch form is one of the earliest solutions to dealing with a material that has no tensile strength. Answer: Loss of prestressing in " pre-tensioned " members 1. 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. How are they constructed? b. has a weaker force of gravity. The increase in the resultant forces is due to a more or less constant lever arm between the forces, characterized by the properties of the composite section. and the stress variation in the nonprestressed reinforcement is about 130 Nlmm2 (18.9 ksi). area of the surfacesc. two of the above, 3 ) What does weight measure?a. In a pre-stressed member, it is advisable to use (AE-1998), C) Low strength concrete but high tensile steel, D) High strength concrete & high tensile steel, SHOW ANSWER D) High strength concrete & high tensile steel, 7. Loss due to elastic shortening of concrete. A partially pre-stressed member is one in which (AE 2018), a. limited tensile stresses and controlled cracking are permitted under service loads, b. mild steel is used in addition to prestressing steel, c. no tensile stresses are permitted under service loads, d. limited tensile stresses are permitted but no cracking under service loads, SHOW ANSWER a. limited tensile stresses and controlled cracking are permitted under service loads, 38. High strength concrete for prestressing is required due to the following reasons: (i) Due to the large prestressing force to be applied by tendons, large bearing stresses get developed in concrete at the end by anchoring devices. Determine the final concrete stress (MPa) at the bottom fiber of the midspan section when the beam sustains an additional live load of 10 kN/m. With PCP, the effective flexural strength of the concrete is increased by the induced compressive stress and is no longer limited in load-carrying capacity by the modulus of rupture of concrete. Relaxation of stress in steel. 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. If the loading on a pre-stressed rectangular beam is uniformly distributed, the tendon to be provided should be (AE 1999), SHOW ANSWER b) parabolic with convexity downward, 27. A partially prestressed member is one in which a) tensile stresses and cracking are permitted under service loads b) no tensile stresses are permitted under service loads c) mild steel is used in addition to prestressing steel d) tensile stresses are permitted but not cracking at service loads 6. two of the above, 2 ) Unlike friction, gravitya. The loss due to friction does not occur in pre-tensioned members because there is no concrete during the stretching of the tendons. McGraw-Hill Dictionary of Architecture and . Please see the attached Screenshot for more information. ins.style.height = container.attributes.ezah.value + 'px'; Cables consist of wires in multiples of 8 wires. This is in contrast to an RC beam section where an increase in the external moment results in a corresponding increase in the tensile force and the compressive force. Answer (1 of 2): * PSC is basically concrete in which internal stress of suitable magnitude & distribution are introduced so that stress resulting from the external load is counteracted to a desired degree. two of the above, 3) If gravity pulls you down toward the center of Earth with a force of 500 N, how much upward force does the ground exert on you?a. Get Instant Access to 1000+ FREE Docs, Videos & Tests. 2. It is similar to creep of concrete. Upward pressure provided by the parabolic cable = 8Ph/L2 Consider the statement (AE 2013) b) Maximize elastic creep and shrinkage strains. Loss of Prestress 3. depth of cable from extreme compression fibre Transportation of prestressed concrete is also a big challenge . 2. ESE Previous year Civil Engineering Question Papers, GATE Previous year Civil Engineering Question Papers, Other TNPSC PREVIOUS YEAR QUESTION PAPERS. fewer required joints and less probability of cracking, resulting in less required maintenance and longer pavement life. For Post tensioning minimum grade of concrete used is M-30. 23. Explanation: The prestressing of concrete members is done to reduce the compressive stresses developed in the concrete members to the required extent while tensile stresses is the stress state where the length of member tends to expand in tension side while the volume remains constant, shear forces and bending stresses force of weight pressing on the surfacesd. Loss due to relaxation of stress in steel. T. 5000 N, 5 ) There is gravity between you anda. two of the above, 3 ) If you pick up and carry a piece of heavy furniture, which type of friction do you have with the floor?a. SHOW ANSWERb) high strength concrete and high tensile steel are used. Total Prestress Losses = (13.65 + 20.3) - 9.96 = 23.99Ksi. An override declaration can change the accessibility of the virtual method. Loss in prestress = Initial prestress - effective prestress. Profile of the prestressing steel in prestressed concrete members follows thebending moment diagram. 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. * In pre-tensioning wires are tensioned then concrete is cast after concrete attains suf. 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. 2. ins.id = slotId + '-asloaded'; cd. moving object to change direction.d. This lecture is a part of CS3001 Concrete Engineering subject for the third year Civil Engineering students at James Cook University, Townsville Australia. It is obvious from Hooke's law, that if we have a change in strain, there will be a change in the stress. When we load the beam we have equal and opposite vertical forces that cancel each other. Why does prestressed concrete have high tensile strength? Strain in concrete at zero stress is called (AE 1999), 10. In the calculation of the design forces in tendons at various stages considered in design, allowance should be made for the appropriate losses of prestress resulting from: b) the elastic deformation and subsequent shrinkage and creep of the concrete; c) slip or movement of tendons at . is less affected by gravity.d. 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. ins.style.minWidth = container.attributes.ezaw.value + 'px'; The maximum cube strength of concrete used for a pre-stressed member is (AE 2013), 16. Initial prestress 2. To modify the behavior of the member or structure in such a way so as to make it more suitable for its intended purpose.
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