T beam design by WSD method


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T beam design by WSD method

  1. 1. Presented by Khandaker Mehedi Hasan Student ID: Department of Civil Engineering AUST,Dhaka
  2. 2. Course Teachers Lecturer Mr. Galib Muktadir Assistant prof. Ms. Sabreena Nasrin Department of Civil Engineering Ahsanullah University of science and Technology
  3. 3. A T-Beam is a beam that supports a slab and the slab is built integrally with the beam.
  4. 4.  Concrete floor slabs and beams are normally tied together by means of stirrups and bent-up bars if any and then are cast form one mass of concrete. Such a monolithic system will act integrally i.e., it is allowed to assume that part of the slab acts with the beam and they form what is known as a flanged beam, Fig. 1.1  The part of the slab acting with the beam is called the flange, and it is indicated in Fig. 1.2 by the area Bts. The rest of the section confining the area (t-ts)b is called the stem or web. As Fig. 1.2 indicates. Fig:1.1 Fig:1.2
  5. 5. Various Possible Geometries of T-Beams Single Tee Twin Tee Box
  6. 6. Square T beam Tapered T beam Inverted L(Spandrel) Beams
  7. 7. Analysis of Flanged Section Floor systems with slabs and beams are placed in monolithic pour. Slab acts as a top flange to the beam; Tbeams, and Inverted L(Spandrel) Beams.
  8. 8. Analysis of Flanged Sections Positive and Negative Moment Regions in a T-beam
  9. 9. Analysis of Flanged Sections If the neutral axis falls within the slab depth analyze the beam as a rectangular beam, otherwise as a T-beam.
  10. 10. Analysis of Flanged Sections Effective Flange Width Portions near the webs are more highly stressed than areas away from the web.
  11. 11. ACI Code Provisions for Estimating beff From ACI 318, Section From ACI 318, Section 8.10.2 8.10 T Beam Flange: beff L 4 16hf bactual Isolated T-Beams bw hf beff bw 2 4bw
  12. 12. Design of T-Beam T-Beam may be singly reinforced or doubly reinforced. When steel is provided only in tensile zone (i.e. below neutral axis) is called singly reinforced t-beam, but when steel is provided in tension zone as well as compression zone is called doubly reinforced t-beam. The aim of design is: To decide the size (dimensions) of the member and the amount of reinforcement required. To check whether the adopted section will perform safely and satisfactorily during the life time of the structure. 
  13. 13. Methods of Design Allowable Stress – WSD (ASD) Examples: WSD Actual loads used to determine stress Allowable stress reduced by factor of safety Ultimate Strength – (LRFD) Loads increased depending on type load Ultimate Strength Factors: DL=1.4 LL=1.7 WL=1.3 U=1.4DL+1.7LL Strength reduced depending on type force Factors: flexure=0.9 shear=0.85 column=0.7
  14. 14. Working Stress Design(WSD) Method Assumptions: – – – – Plane sections remain plane Hooke’s Law applies Concrete tensile strength is neglected Concrete and steel are totally bonded Allowable Stress Levels – Concrete = 0.45f’c – Steel = 20 ksi for gr. 40 or gr. 50 = 24 ksi for gr. 60 Transformed Section – Steel is converted to equivalent concrete.
  15. 15. Procedure for Design of Singly Reinforced Beam by Working Stress Method Given : (i) Span of the beam (l) (ii) Loads on the beam (iii)Materials Grade of Concrete and type of steel. i.e. f'c & fy
  16. 16. Now, Selecting the suitable diameter of bar calculate the number of bars required As Singly reinforced T-beam
  17. 17. Reasons for Providing Compression Reinforcement Reduced sustained load deflections.      Creep of concrete in compression zone transfer load to compression steel reduced stress in concrete Architectural design & view less sustained load deflection
  18. 18. Reasons for Providing Compression Reinforcement Effective of compression reinforcement on sustained load deflections
  19. 19. Layout of doubly reinforced T-beam Doubly reinforced T-beam