Prestressed Concrete Design Mahidol-Books Pdf

Prestressed Concrete Design Mahidol
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Principle of Prestressing Principle of Prestressing. Prestressing is a method in which compression force is applied to the Stress in concrete section when the prestressing force is applied at the c g. reinforced concrete section of the section simplest case. The effect of prestressing is to reduce the tensile stress in the section to. the point that the tensile stress is below the cracking stress Thus the. concretet does, d nott crack, It is then possible to treat prestressed concrete as an elastic material. The concrete can be visualized to have 2 force systems. Internal Prestressing Forces, External Forces from DL LL etc. These 2 force systems must counteract each other, 2010 Praveen Chompreda 5 2010 Praveen Chompreda 6. Principle of Prestressing Historical Perspective, Stress in concrete section when the prestressing force is applied The concept of prestressing was invented centuries. eccentrically with respect to the c g of the section typical case ago when metal bands were wound around wooden. pieces staves to fform a barrel, Smaller Compression.
e0 Source Wikipedia 2006, The metal bands were, S ll Compression. F A Fe0y I MDLy I MLLy I tighten under tensile stress. which creates compression, Cross Prestressing Stress Stress Stress. Force ffrom DL ffrom LL Resultant, between the staves. allowing them to resist, internal liquid pressure, Source Naaman 2004. 2010 Praveen Chompreda 7 2010 Praveen Chompreda 8, Historical Perspective Historical Perspective.
Eugene Freyssinet 1879 1962, 1879 1962 was the first to propose. that we should use very high strength steel which, permit high elongation of steel The high steel. elongation would not be entirely offset by the, Source Naaman 2004 shortening of concrete prestress loss due to creep. and shrinkage, The concept of prestressed concrete is also not new In 1886 a patent was Source Wikipedia 2006. granted for tightening steel tie rods in concrete blocks This is analogous to First prestressed concrete bridge. modern day segmental constructions in 1941 in France. First prestressed concrete bridge, E l attempts, tt t were nott very successful.
l strength, t th off steel, t l att in US Walnut Lane Bridge in. that time Since we cannot prestress at high stress level the prestress Pennsylvania Built in 1949 47. losses due to creep and shrinkage of concrete quickly reduce the meter span. effectiveness of prestressing, 2010 Praveen Chompreda 9 2010 Praveen Chompreda 10. Applications of Prestressed Concrete Classifications and Types. Bridges Pretensioning v s Posttensioning, Slabs in buildings. g External v s, v s Internal, Water Tank, Linear v s Circular. Concrete Pile, Thin Shell Structures End Anchored v s Non End Anchored.
Offshore Platform Bonded v s Unbonded Tendon, Nuclear Power Plant Precast v s Cast In Place v s Composite. Repair and Rehabilitations Partial v s Full Prestressing. Source Wikipedia 2006, 2010 Praveen Chompreda 11 2010 Praveen Chompreda 12. Classifications and Types Classifications and Types. Pretensioning vs, vs Posttensioning, In Pretension the tendons are tensioned against some abutments before. the concrete is pplace After the concrete hardened the tension force is. released The tendon tries to shrink back to the initial length but the. concrete resists it through the bond between them thus compression. force iis iinduced, d d iin concrete P, Pretension. i iis usually, i h precast, Pretensioned Prestressed Concrete.
Casting Factory, Source Naaman 2004 2010 Praveen Chompreda 13 2010 Praveen Chompreda 14. Classifications and Types Classifications and Types. In Posttension the tendons are tensioned after the concrete has Precast Segmental. hardened Commonly metal or plastic ducts are placed inside the Girder to be. Posttensioned In, concrete before casting After the concrete hardened and had enough. strength the tendon was placed inside the duct stressed and anchored. against concrete, concrete Grout may be injected into the duct later. later This can be, done either as precast or cast in place. Source Wikipedia 2006, 2010 Praveen Chompreda 15 2010 Praveen Chompreda 16.
Classifications and Types Classifications and Types. l vs IInternall Prestressing, Prestressing may be done inside or outside End Anchored vs Non End Anchored tendons. In Pretensioning tendons transfer the prestress through the bond. Linear vs Ci, l P Prestressing, actions along the tendon therefore it is non end anchored. Prestressing can be done in a straight structure such as beams linear. prestressing or around a circular structures such as tank or silo In Posttensioning tendons are anchored at their ends using mechanical. circular prestressing devices to transfer the prestress to concrete therefore it is end. anchored Grouting or not is irrelevant, Bonded vs Unbonded Tendon. The tendon may be bonded to concrete pretensioning or posttensioning. with grouting or unbonded posttensioning without grouting Bonding. helps prevent corrosion of tendon, tendon Unbonding allows readjustment of. prestressing force at later times, 2010 Praveen Chompreda 17 2010 Praveen Chompreda 18.
Classifications and Types RC vs PPC vs PC, Partial vs Full Prestressing. Prestressing tendon may be used in combination with regular. reinforcing steel Thus it is something between full prestressed. concrete PC and reinforced concrete RC The goal is to allow. some tension and cracking under full service load while ensuring. sufficient ultimate strength, We sometimes use partially prestressed concrete PPC to control. camber and deflection increase ductility and save costs. Source Naaman 2004, 2010 Praveen Chompreda 19 2010 Praveen Chompreda 20. RC vs PPC vs PC RC vs PPC vs PC, Source Naaman 2004 2010 Praveen Chompreda 21 Source Naaman 2004 2010 Praveen Chompreda 22. Advantages of PC over RC Design Codes for PC, Take full advantages of high strength concrete and high.
strength steel ACI 318 Building Code, Need less materials Chapter. Smaller and lighter structure, Use the entire section to resist the load. Better corrosion resistance AASHTO LRFD, G d fforr water. Good ater tanks and nuclear, n clear plant, lant Chapter 5. Very effective for deflection control, B tt shear, Better h resistance.
Other related institutions, PCI Precast Prestressed Concrete Institute. PTI Post Tensioning Institute, 2010 Praveen Chompreda 23 2010 Praveen Chompreda 24. Design Principles Stages of Loading, In RC we primarily design the member for either service limit Unlike RC where we primarily consider the capacity of the structure at. states Working stress design method or ultimate limit one stage i e during service we must consider multiple stages of. construction in Prestressed Concrete, states Ultimate strength design. The stresses in the concrete section must remain below the maximum. PC both service limit states and ultimate limit states must li it att allll ti. limit times, be checked, In service limit states, states section must have stresses below the allowable.
stress limits, In ultimate limit states the moment and shear capacity. p y must be greater, than the ultimate factored loads. Source Wikipedia 2006, 2010 Praveen Chompreda 25 2010 Praveen Chompreda 26. Stages of Loading, Typical stages of loading considered. Part II Materials and, Initial Immediatelyy Transportation.
p Service Hardwares for Prestressingg, after Prestress Erection Prestress loss has. Transfer Partial loss of fully occurred, Full prestress force prestress force DL SDL. DL SDL LL LL, May or may not DL Concrete, include DL Different support. pp Prestressing Steel, depending on conditions during. construction type erection from Prestressing Hardwares. 2010 Praveen Chompreda 27 2010 Praveen Chompreda 28. Concrete Concrete Compressive Strength, Mechanical properties of AASHTO LRFD.
concrete that are relevant, to the prestressed concrete For prestressed concrete f c at. g includes y should be 28 70 MPa, Compressive Strength f c For reinforced concrete f c at 28. Modulus of Elasticityy E, c y should be 16 70 MPa, Modulus of Rupture fr Concrete with f c 70 MPa can. be used only when supported by, Source Wikipedia 2006. 2010 Praveen Chompreda 29 2010 Praveen Chompreda 30. Concrete Modulus of Elasticity Concrete Modulus of Rupture. Modulus of elasticity can be, Indicates the tensile capacity of.
obtained directly from test or, concrete under bendingg. ti t d ffrom compressive i, strength AASHTO secion 5 4 2 4 Tested simply supported concrete. beam under 4 point bendingg, 0 043 c1 5, configuration. c in kg m3, fr My I PL bd2, ff c in MPa, Modulus of rupture can also be. For normal weight concrete we, estimated from compressive.
can use a simplified equation, strength AASHTO section 5 4 2 6. Ec 4800 f c 0 5 MPa, fr 0 63 f c 0 5 MPa, 2010 Praveen Chompreda 31 2010 Praveen Chompreda 32. Concrete Summary of Properties Prestressing Tendons. Source Naaman 2004, Prestressing tendon may be in the form of strands wires. round bar or threaded rods, High Strength Steel, Fiber Reinforced Polymer FRP Composites glass or carbon fibers. 33 2010 Praveen Chompreda 34, Tendons Prestressing Steel.
Common shapes, of prestressing, Most Popular, 7 wire Strand. Source Naaman 2004, Source Naaman 2004 2010 Praveen Chompreda 35 2010 Praveen Chompreda 36. Prestressing Strands Prestressing Strands, Prestressing strands have two grades. Grade 250 fpu 250 ksi or 1725 MPa, Grade 270 fpu 270 ksi or 1860 MPa. Types of strands, Stressed Relieved Strand, Low Relaxation Strand lower prestress loss due to relaxation of.
Source AASHTO 2000, 2010 Praveen Chompreda 37 2010 Praveen Chompreda 38. Prestressing Strands Prestressing Strands, Source Naaman 2004. Modulus of Elasticity, 197000 MPa for Strands, 207000 MPa for Bars. The modulus of, elasticity of strand is, lower than that of. steel bar because, strand is made from, twisting of small wires.
Source AASHTO 2000, 2010 Praveen Chompreda 39 2010 Praveen Chompreda 40. Hardwares Prestressing Equipments Pretensioned Beams. Pretensioned Members, Hold Down Devices, Posttensioned Members. Anchorages, Stressing Anchorage, Dead End Anchorageg. Posttensioningg Procedures, Source Wikipedia 2006, Source Naaman 2004. 2010 Praveen Chompreda 41 2010 Praveen Chompreda 42. Pretensioning Hardwares Posttensioned Beams, Hold Down Devices for.
Pretensioned Beams, Source VSL 2006, Posttension Hardwares. St i A Anchorage, Dead End Anchorage, Duct Grout Tube. Source Naaman 2004 Source Naaman 2004, 2010 Praveen Chompreda 43 2010 Praveen Chompreda 44. Posttensioning Hardwares Anchorages Posttensioning Hardwares Anchorages. Source VSL 2006, 2010 Praveen Chompreda Source VSL 2006. 45 2010 Praveen Chompreda 46, Posttensioning Hardwares Anchorages Posttensioning Hardwares Ducts.
Source VSL 2006, Source VSL 2006, 2010 Praveen Chompreda 47 2010 Praveen Chompreda 48. Posttensioning Procedures Posttensioning Procedures. Grouting is optional, p on the system, Source VSL 2006 Source VSL 2006. 2010 Praveen Chompreda 49 2010 Praveen Chompreda 50. Prestress Losses, Prestress force at any time is less than that during jacking. Part III Prestress Losses Sources of Prestress Loss. of Concrete, Sources of Prestress Losses, S Estimation. E i i off P, Prestress Loss, Elastic Prestress Prestress.
Shortening Relaxation, 2010 Praveen Chompreda 51 2010 Praveen Chompreda 52. Prestress Losses Prestress Losses, Sources of Prestress Loss Sources of Prestress Loss cont. Friction Friction in the duct of posttensioning system causes stress at. f end d to be, j ki end d Thus, Th theh average, Elastic Shortening Caused stress over the entire tendon is less than the jacking stress. byy concrete shorteningg, when the prestressing force. is applied The tendon, causing a stress loss, Source VSL 2006.
g Set The wedge g in the, anchorage may set in slightly to lock. the tendon causing a loss of stress, 2010 Praveen Chompreda 53 2010 Praveen Chompreda 54. Prestress Losses Prestress Losses, Source Naaman 2004. Sources of Prestress Loss cont Sources of, Shrinkage g Concrete shrinks Prestress Loss. over time due to the loss of, water leading to stress loss cont.
on attached, tt h d tendons, t d Steell R, St Relaxation. Creep Concrete shortens Steel loss its stress, over time under compressive with time due to. stress leading to stress loss, on attached tendons. elongation the, elongation, larger the stress, the larger the loss. 2010 Praveen Chompreda 55 2010 Praveen Chompreda 56. Time Line of Prestress Loss Prestress Loss By Types. Posttensioning, ES Pretensioned Posttensioned, Jacking Initial Effective.
Instantaneous Elastic Shortening Friction, fpjj fpii fpe Anchorage Set. Elastic Shortening, Pretensioning SH Time Dependent. Time Dependent Shrinkage Concrete Shrinkage Concrete. AS CR Creep Concrete Creep Concrete, RE Relaxation Steel Relaxation Steel. Jacking RE ES, against Release Initial Effective, abutment cutting. strands fpi fpe, Instantaneous Losses Time Dependent Losses.
57 2010 Praveen Chompreda 58, Prestress Loss Pretensioned Prestress. Prestressed Concrete Bridge Design Basic Principles Naaman 2004 The concept of prestressed concrete is also not new shortening of concrete

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