(See Design Step 5.5.1 for commentary explaining how to proceed if "c" is greater than the deck thickness. Compression ( Table 23 ) Stage 1. a simply supported prestressed concrete Y beam which carries a 150mm thick concrete The CivilWeb Prestressed Concrete Beam Design Excel Spreadsheet draws a handy diagram showing the designer the tendons chosen profile. When the deck slab The difference between Service I and Service III limit states is that Service I has a load factor of 1.0 for live load while Service III has a load factor of 0.8. 0.5fci ( 0.4fcu) = 20 N/mm2 max. Diameter of stirrup, 0.5 in The steps in the design of a reinforced concrete beam are as follows; (a) Preliminary sizing of members. Now change the Limit State: field to ULS Persistent/Transient to carry out the calculations for vertical shear where we will determine the requirement for shear links. Compression (1.25 Table 22) These jurisdictions provide reinforcement at the bottom of the beams at intermediate diaphragms to resist the factored positive moment at these locations. After a short while a warning message will appear indicating that the limiting strains in the concrete slab at ULS do not comply as they are primarily in compression. Hurst 2017-12-21 Prestressed concrete is widely used in the construction industry in buildings, bridges, and other structures. Recall that the centers of gravity of a wedge, a prism with all rectangular faces, a prism with a triangular vertical face and a pyramid are at one-third, one-half, one-third and one-quarter the height, respectively. + 0.408 750 [ 50 ( 0.9 358 + 0.15 366 ) + 240 ( 1.2 In these tests, the failure always occurred in the girder. It is used when building slabs, beams, decks, sleepers and tanks. Set the UDL Intensity Start and End as 1410.213kN/m. 0.408 1000 [ 150 ( 3.0 502 + 5.25 527 ) ] 10-6 + Actions to be considered at the service limit state are cracking, deformations, and concrete stresses, as specified in Articles S5.7.3.4, S5.7.3.6, and S5.9.4, respectively. Max live load bending (with associated shears) and shear effects (with associated moments) have been prepared in an external ASCII file as envelopes. Slab C32/40 fcu = 40 N/mm2. Also change the Job Number: to 5.2 and add your initials to the Calculated by data item if necessary. Reinforcement bars are placed in a form and stressed by the stretching of the bars at each end, inducing tension in the bar. = 24kN/m 3 Set the UDL Intensity Start and End as 2.5kN/m then click OK to generate the load effects. Minimum concrete cover: 1.5 in. The spreadsheet then calculates the tensile and compressive stresses acting on the beam and the tendons. endstream However, if we can provide props during the construction of the deck, its weight will be born by the props without transferring to the prestress beam. = Initial prestressing force taken from Table 5.5-1 (kips), = Distance between the neutral axis of the noncomposite girder and the center of gravity of the prestressing steel (in. The Shear Resistance of the beam needs to be determined in accordance with clause 6.3.4. and compared with the ultimate shear load at critical sections. Section properties of Y5 beam were obtained from a Paper by Taylor, Clark and Banks (download .pdf extract from paper by The design is based on AASHTO LRFD Bridge Design Specifications 3rd Edition 2004. If an Owner chooses to invoke deflection control, the following principles may apply: If the Owner invokes the optional live load deflection criteria, the deflection should be taken as the larger of: According to S2.5.2.6.2, the deflection criteria for vehicular live load limits deflection to L/800. Civil Engineering Design (1) Dr. C. Caprani10 1.5 Methods of Prestressing There are two methods of prestressing: Pre-tensioning: Apply prestress to steel strands before casting concrete; Post-tensioning: Apply prestress to steel tendons after casting concrete. Prestressed Concrete Analysis and Design - Antoine E. Naaman 2004-01-01 Prestressed Concrete Design - M.K. Click the Add Load Component button and enter the UDL Intensity Start and End as 1410.213kN/m. <> In this example we have taken a prestressed beam created in a previous example and applied load to it for a series of design load cases. Design data: Dead load: 1500 lb/ft. At the end of the optimisation, the program produces an error message and provides a summary on the right hand side of the form. The calculated live load deflection determined by using computer software is 0.324 in. Area of tendon = 139mm2 Element designs with notes and discussions have added to get comprehensive knowledge. Now, we can calculate the stress in the section as follows. endstream This textbook presents a detailed description and explanation of the behaviour of prestressed concrete members and structures both at service loads . Stresses in the tensile face and the compression face of the beam shall be checked in accordance with the relevant standards. of designing the beam (See BS 5400 Pt2, or DB 37/01 for full Self weight of beam and 382 + 1.35 397 ) ] 10-6 Key Words Prestressed Concrete, LRFD, Design, Bridge Girders, U54 Prestressed reinforced concrete is the used when building bridges because it allows bridges with bigger spans to be built and for floors in high-rise buildings. Initially, we place the prestressed beam on the abutment. This is why it is important to ensure that the other load cases are absolute shears. 4260) / 28 = 135mm On the Pre-tensioned Beam Analysis form set Time Considered: to t = and the Fibre Stress: field to Minimum top. Using Figure S5.4.2.3.2-1 or SC5.4.2.3.2-1, the correction factor, kc, is taken to be approximately 0.759. Prestressed Concrete Example Problem - Free download as PDF File (.pdf), Text File (.txt) or read online for free. Presence of a longitudinal compr essive force ac ting on a concrete beam . Finally it is necessary to remove the temporary construction loads. The beam Things to Remembered in Concrete Construction, Prestressed Composite Beams [design aspects], There is a significant reduction in the construction time, Low strength concrete can be used for in situ concrete. 9 0 obj All strands are fully bonded at this location. This reflects observations made during girder tests in the past. 17. To translate this article, select a language. 25 units of HB to be considered at SLS for load combination 1 only (BS 5400 Pt4 Cl. The UDL intensity is 13.4306kN/m which applies a total load of 282.0426kN to the beam. Now lets see how do we calculate the service stressed in a composite beam with an example. <> Therefore, the difference between the maximum haunch thickness at the support and the minimum haunch thickness at the center of the beam should equal the final camber, i.e., 1.79 in. The cracking stress is taken as the modulus of rupture specified in S5.4.2.6. It is suggest reading the article Bridge Design to BS 5400 for further information on calculating the stress in the section. The span of the beam is 24.0m centre to centre of bearings and the beams are spaced at 1.0m intervals. Civil Engineering Design (1) Example. Downloads: 248. The first prestressed concrete bridge was built in 1948 under the Assam Rail Link Project. To achieve this we need to adjust the shear calculation parameters. By integrating the tensile stress in Figure 5.6-2 over the corresponding area of the beam, the tensile force may be calculated as: Minimum allowable number of bars = 7 #5 bars, Figure 5.6-2 - Stress at Location of Maximum Tensile Stress at Transfer, Figure 5.6-3 - Longitudinal Reinforcement of Girder Top Flange. The moment from internal compressive concrete forces shown in Table 5.6-3 is equal to the force multiplied by the distance from the neutral axis to the location of the force. www.in.gov. concrete has cured then any further loading (superimposed and live Set the Shrinkage strain to 0.00025, the Long term losses occurring before composite to 20%, the Differential shrinkage to 0.0001 and the Creep coefficient to 1.5. - 0.408 300 ( 200 0.45 270 - 150 0.45 283 ) 10-6 ), Level 2, combination 1 : f = - 0.98 + 1037 / 89.066 + 1310 / 242.424 + 1.64 = 17.71 (< 25 O.K. Nominal tensile strength = fpu =1670 N/mm2 Restraint moment Mcs = -439 0.502 = -220.4 kNm. Given: A simply supported reinforced concrete beam is supporting uniform dead and live loads. 2) Zlevel 2 gives : P >= A (20 Zlevel 1 - 1.0 Zlevel 2) / (Zlevel 1 + Zlevel 2), P = 449.22 103 ( 20 116.02 - 89.066) / ( 116.02 + 89.066) 10-3 = 4888 kN, Allow 10% for loss of force before and during transfer, then the initial force Po = 4888 / 0.9 = 5431kN, Using 15.2mm class 2 relaxation standard strand at maximum initial force of 174kN (0.75 Pu) All compression stresses and allowables use negative sign convention. Click OK on the warning message and click OK to close the Tendon Optimisation form. MEGA FLOOR,the Prestressed slab. PRE-Stress is an advanced prestressed concrete design software that helps you run calculations and analysis on many types of structural prestressed concrete elements including hollowcore slabs, solid slabs, wall panels, beams, sloped beams, double tees and most recently "sloped" TT beams.. In the fck field, change 40 to 50 to increase the strength. The span of the beam is 24.0m centre to centre of The bridge owner may select to invoke this criteria if desired. This is often preferable where durability is a concern. This behavior is due to the confinement of the diaphragm concrete in the connection zone provided by the surrounding concrete. 202-366-4000. However, sample calculations are provided for this example. )OV?WS 1 HMKW]O0dK7L C@O97vJG''y+`-sd6Igv;H#OR3{:hstxJO`1@{.SD90x eG)g{,uM Factored flexural resistance in flanged sections (S5.7.3.2.2). Click OK on the Define Property Details form to save the change. The change in the prestressing steel force is typically small and was ignored in the following calculations. A composite pre-tensioned pre-cast beam and concrete slab is shown below. Click on the Add Load Component button again and enter the UDL Intensity Start and End as 1.4kN/m. We can now investigate this. Only strands that are fully bonded are used for the positive moment connection. Select the supplied file EU Live Loads.sld and click Open. Final stresses due to prestress after all loss of prestress at : Level 1 f1,0.82P = 0.82 20.89 = 17.08 N/mm2, Level 2 f2,0.82P = 0.82 - 1.20 = - 0.98 N/mm2. curvature due to temperature strain : Structural Guide 2022. Material properties relevant to design are presented and discussed in Chapter 4. (See Figure 4-16). When a load is applied on beam, cracks still occur in the concrete, but the tension is carried by the steel reinforcement. Click on the Analyse for drop down and select Shear for gr 1b-gr5 1. Use the default values for all the other fields on the form and click on the Design Optimised Layout button. The stiffness of the overall section can be taken into account in composite design. ), NA, = specified compressive strength of concrete at 28 days, unless another age is specified (ksi), = width of the effective compression block of the member (in.) Change the ULS and SLS Load Factors to 1.35 and 1 respectively and set the Component Ref. (20.89 N/mm2 is slightly greater than the allowable of 20 N/mm2 so a number of tendons will need to be debonded near the ends of the beam). In the Ultimate Compressive Strain, cu field enter 0.002.". - 0.408 [ 150000 ( 3.6 502 + 2.3 527 ) + 27000 ( 0.9 ", Click the Add Load Component button and repeat the process (remembering to make ULS and SLS Load Factors negative), this time setting the Start Dimension to 19.95m, the End Dimension to 20.05m and the Component Ref. Lets see what are the stresses we need to calculate. For example: Since that time, there has been extensive research on human response to motion, and it is now generally agreed that the primary factor affecting human sensitivity is acceleration as opposed to deflection, velocity, or the rate of change of acceleration for bridge structures, but the problem is a difficult subjective one. Calculations are made from the top of the total thickness and include the integral wearing surface in the total thickness of slab. In order to resolve the first warning and get a solution we will try increasing the strength of the precast concrete material and adjusting the strain limit of the cast in place concrete. <> The next step will be to import some results from a separate live load analysis by using a text file that is formatted in a certain way. Fc > Ft therefore reduce depth to neutral axis and repeat the calculations. Beam C40/50 fcu = 50 N/mm2, fci = 40 N/mm2 stream 1.25 0.4fcu = 25 N/mm2, Tension = 0 N/mm2 (class 1) & 3.2 N/mm2 (class 2 - Table 24). Prestressed concrete is structural concrete in which internal stresses have been introduced to reduce potential tensile stresses in the concrete resulting from loads. Set the Results Point of Interest to 20 and Note the stresses and repeat for the other three Fibre Stress: conditions. Since we are placing the concrete on concrete that already harden, there will be differential shrinkage. Though the new concrete shrink, concrete in the prestress beam will not shrink. = - 385.9 - 19.3 - 295.1 = - 700.3 kN, Moment M about centroid of section to restrain Loss of force after transfer due to : Concrete shrinkage = (cs Es Aps ) = 300 10-6 196 32 139 = 262, Concrete creep = ( ct fco Es Aps ) = 1.03 48 10-6 12.76 196 32 139 = 550, Final force after all loss of prestress = Pe = 5067 - 923 = 4144 kN (Pe/P = 0.82).
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