Ans: F = 1410 kN; fT = 14.934 MPa, fB = -2.40 MPa 13 G. P. Ancog Prestressed Concrete Practice Problems Solution Section properties: A = bh = 300 x 750 = 225 x10 3 mm 2 I = 1 1 bh 3 = (300 )( 750 ) 3 = 1.0546875 x10 10 mm 4 12 12 In order to balance the load on the cantilever, the cgs at the tip must coincide with the cgc with a horizontal tangent. Prestressing tendons are susceptible to "Hydrogen Embrittlement" at higher voltages and extreme care and knowledge must utilized to avoid this issue that can result in sudden, brittle failure of the strands. Assuming n = 6, compute the stresses in the concrete immediately after transfer. Ans: 100.98mm Fig. This is why we offer the books compilations in this website. M = f 'I 4.13 (5.4 x10 9 ) = x10 6 = 74 .34 kN m c 300 Total moment capacity: M T = M 1 + M = 291 .78 + 74 .34 = 366 .12 kN m w= 8M 8(366 .12 ) = = 20 .34 kM / m L2 12 2 10. (18-3) reduces to: For post-tensioned members, the prestressing force in a tendon is applied through the anchorages as a concentrated force. Precast and prestressed concrete design is based on the provisions of ACI 318-05. If the value is inaccurate, it will have a bad effect on the quality of the project. The prestressed steel strand has slipped or broken wires. Jeffrey Luin. Ans: Initial condition: fT = 2.234 MPa, fB = 15.10 MPa; Final condition: fT = 13.803 MPa, fB = 0.975 MPa 45kN 4.50m 45kN 3.00m 4.50m 300 4 600 Fig. Design the slab following the provisions of the ACI code. Moment for zero tensile stress at the bottom: Q Qey My + =0 A I I 1296 .8 x10 3 1296 .8 x10 3 (125 )( 300 ) Mx 10 6 (300 ) 0= + 180 x10 3 5.4 x10 9 5.4 x10 9 M = 291 .78 kN m 8M 8( 291 .78 ) w= 2 = = 16 .21 kN / m L 12 2 fB = Top fiber stress: Q Qey My + A I I 3 1296 .8 x10 1296 .8 x10 3 (125 )( 300 ) 281 .78 x10 6 (300 ) = + 180 x10 3 5.4 x10 9 5.4 x10 9 = 13 .853 MPa fT = 2. Load Calculation: Consider only a 1 ft width of beam. The Australasian CP code limits the voltage of the strand to >-900mV (AgAgCl 0.5M at instant off). convergence. Inspection and Monitoring. Chapter 4: Operational Amplifiers the main factors for concrete used in psc are: ordinary portland cement-based concrete is used but strength usually greater than 50 n/mm2; a high early strength is required to enable quicker application of prestress; a larger elastic modulus is needed to reduce the shortening of the member; a mix that reduces creep of the concrete to minimize Determine the ultimate resisting moment. In most cases, these provisions are fol- . Assuming n = 6, compute the stresses in the concrete and steel immediately after transfer. Problem 4.9 This page intentionally left blank. ABSTRACT: The Softened Truss Model Theory applied to a prestressed concrete multiple cell box is developed in this study. 24. Assuming creep coefficient of cc = 723.75x25 1.8 and an due effective prestress of 830 MPa at that time. This had been emphasised in lectures. External prestressing is considered as an efficient system for strengthening existing structures, especially reinforced and prestressed concrete bridges. Let a trial thickness of 6.50 in. 4.2 Solutions If fc = fci = 34.4 MPa, n = 7, determine the stresses when the wires are cut between members. Prestressed concrete is a structural material that allows for predetermined, engineering stresses to be placed in members to counteract the stresses that occur when they are subject to loading. If the effective prestress value is too large when the load is applied to the prestressed steel bar, a high-stress state will appear, causing cracks in the steel bar due to deflection or tension, and at the same time, the plasticity will be reduced, and sudden brittle failure will easily occur. 1) When selecting corrugated metal ducts, perform quality inspection in strict accordance with (JG2252007) Corrugated Metal Ducts for Prestressed Concreteto ensure that its performance meets industry standards. 2. for cracking in the bottom fibers at a modulus of rupture of 4.13 MPa and assuming concrete to take up tension up to that value. Publication: Special Publication. Prestressed Concrete Practice Problems Solution Total tension of steel at rupture T = 937 .5 (1650 ) x10 3 =1546 .875 kN C =T .85 f c ' ba = T a= T 1546 .875 x10 3 = =176 .34 mm .85 f c ' b .85 (34 .4) ( 300 ) Ultimate moment M u = As f su ( d a 2 ) = 1546 .875 ( 500 176 .34 2 ) x10 3 = 637 .05 kN m 8. Spalling and Popouts. a problem of prestressed concrete pressure vessels: stress concentration adjacent to reinforced penetration under unidirectional stress. During normal construction, the initial strain and tightness of multiple prestressed steel strands are different when tensioning, and various problems are prone to occur, causing the prestress value to fail to meet the engineering needs, resulting in a decrease in the reliability and durability of the prestressed structure. Examples of failed prestress work include the use of lightweight aggregates as used in the Kenai River Bridge where the girders cracked and spalled; steam curing when a metal sheath is placed inside a beam, the metal acts as a radiator and cools the concrete cover causing cracks; and not taking into account temperature differentials on long casting beds, as in a New York viaduct were anchor bolts did not fit the templates after the beam was hoisted by crane. to ensure the standardization of the prestressed tension construction process. Design problems and typical solutions are presented for the following areas of containment design: foundation slab, intersection of wall and foundation slab, buttress, tendon configuration, large penetration, grouped penetrations, liner plate and corrosion protection. A hollow member is reinforced with 4 wires of 62.5 mm 2 each pretensioned fsi = 1030 MPa. It then looks at how failures in structural modelling can lead to big problems if they are not identified before construction is undertaken. It is pretensioned with 516mm2 of steel to an initial stress of 1040 MPa. ACI 318-05 PCI PrACtICE 2.2 Design of precast concrete moment frames is discussed in Chapter . A post-tensioned simple beam on a span of 12 m carries a superimposed load of 11.00 kN/m in addition to its own weight of 4.40 kN/m. Loss in prestress = creep strain x Es 4. Concrete Construction: Resources for contractors and specifiers including construction methods, materials and practices. Positive bending about a horizontal axis causes tension in the bottom . Copyright 2022 Zonda Media, a Delaware corporation. 2. Assume that there is no slack in the cable, that the shrinkage of concrete is 0.0002 at the time of transfer, and that the average compression in concrete is 5.50 MPa along the length of tendon. Music: 2.1 Driven to Succes by Scott Holmes, Source:. Example bridge 2.1 Bridge geometry and materials 2.2 Girder geometry and section properties 2.3 Effective flange width 3. l used solid65 for concrete, beam188 for reinforcing steels and link180 for prestressing strands. If the effective prestress value is too small, the brittleness of the concrete cannot be effectively restricted, and cracks are prone to occur. #PrestressedConcrete Principles of Prestressed Concrete Introduction Credits: 1. The most obvious type of failure occurs when high-strength steel fails because, in areas of corrosion pitting, its notched bar tensile strength is exceeded. Calculate the nominal moment strength of the prestressed member shown. 2) Before pouring concrete, make sure that the corrugated metal ducts are installed in the correct position, all accessories are installed firmly, and the sealing performance is normal, and fixed. Ans: Bonded condition: fs = 845.258 MPa, Unbonded condition: fs = 838.137 MPa wT = 11.00+4.40=15.40 kN/m Section properties: A = bh = 300x600 = 180000.00 mm2 I = bh3/12 = 300(600)3/12 = 5.4x109 mm4 c = h/2 = 600/2 = 300 mm Mo M x Parabolic moment diagram x y yo Parabolic y diagram Solution 1: Moment at mid-span: Mo = wL 2 15 .4(12 ) 2 = = 277 .2kN m 8 8 Moment at mid-span due to prestress: M s = Qe = (1612 .9 x830 )(125 ) x10 6 = 167 .34 kN m Net moment at mid-span: MN = 277.2 167.34 = 109.86 kN-m Stress in concrete at the level of steel due to bending: 7 G. P. Ancog Prestressed Concrete Practice Problems Using I for gross section My 109 .86 x10 6 (125 ) fc = = = 2.543 MPa I 5.4 x10 9 The stress in steel is increased by: f s = nf c = 6( 2.543 ) = 15 .258 MPa Resultant stress in steel: fsf = 830 + 15.258 = 845.258 MPa Solution 2: If the cable is unbonded and free to slip. The prestressing system works for a span greater than 35 m. Prestressing will increase the shear strength and exhaustion resistance of concrete. Problems with concrete include construction errors, disintegration, scaling, cracking, efflorescence, erosion, spalling, and popouts. Compute the length of shims required, neglecting any elastic shortening of the shims and any friction along the tendon. Ans: Case 1: w T =16.21 kN/m; Case 2: w T = 20.34 kN/m Solution Section properties: mmhc mmxbhI mmxbhA 3002600 2 104.5)600) (300(121 121 10180)600(300 4933 23 Prestress Q: kNxfAQ ss 8.129610)830(5.1562 3 1. A Prescon cable, 18.00 m long is to be tensioned from one end to an initial prestressed of 1040 MPa immediately after transfer. Prestressed Concrete Practice Problems and assuming concrete to take up tension up to that value. as well as a valuable reference for concrete structural design professionals in practice. l running static analysis on simply-supported prestressed concrete beam in ansys. B. Figure 1 Comparative free-body diagrams of a reinforced concrete (R.) beam and a prestressed concrete (P.) beam. grout to create problems. All rights reserved. concrete will not affect tendons since it will be taking place at the same time as tensioning and no loss of prestress force will take place. Determine the moment that can be carried at a maximum tension of 0.5(fc) and a maximum of fc = 0.45fc. Each case is analyzed to identify its cause and how it might have been prevented. 4. PRESTRESSED CONCRETE CONSTRUCTION MANUAL 3rd Edition April, 2017 NEW YORK STATE DEPARTMENT OF TRANSPORTATION OFFICE OF STRUCTURES About the Cover: Roslyn Viaduct over Hempstead Harbor Designer: Hardesty & Hanover, LLP Contractor: Tully Construction Co., INC. i April, 2017 China has become a world-class bridge building country. If the top fiber cracks and the concrete is assume to take no tension, compute the bottom fiber stresses. For post-tensioned unbonded beams, the net concrete section is the proper one for all stress calculation. DESIGN OF PRESTRESSE, Irwin, Basic Engineering Circuit Analysis, 10/E To use the least amount of pretsress, the eccentricity over the support should be a maximum. Specification for Installation of Prestressed Steel Strand, Replacement and Installation Principles of Bridge Expansion Joints, Address: No.12, Second Avenue, Kaifeng, China, Copyright 2022 HENAN ZHONGJIAO ROAD&BRIDGE ENGINEERING MATERIALS CO., LTD. Of prestressing technology is becoming more and more extensive cracks and the quality control is not accurate in! Es 4 over the support should be computed on the basis of transformed section the specimen problems Books compilations in this study 2 of steel that can be carried at a unit stress 1040. 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