m8l19 - Module 8 Reinforced Concrete Slabs Version 2 CE...

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Unformatted text preview: Module 8 Reinforced Concrete Slabs Version 2 CE IIT, Kharagpur Lesson 19 Two-way Slabs Version 2 CE IIT, Kharagpur Instructional Objectives: At the end of this lesson, the student should be able to: • determine the shear force of two-way slabs subjected to uniformly distributed loads, • state the two types of two-way slabs mentioning the differences between them, • determine the preliminary depth of two-way slabs of different support conditions from the span to effective depth ratios as given in IS 456, • explain the provisions of torsion reinforcing bars at two types of corners of a restrained two-way slab, • design the two types of two-way slabs applying the different methods explained in this lesson and draw the detailing of reinforcing bars. 8.19.1 Introduction Lesson 18 explains the various types of slabs with different support conditions, plan forms, horizontal/inclined etc. Moreover, sec. 8.18.2 of Lesson 18 illustrates the sharing of uniformly distributed loads to the supporting beams of both one and two-way slabs including the profiles of deflection (Figs.8.18.4a and b). It is, thus, understood that two-way slabs span in both directions having the aspect ratio of l y /l x up to 2, considering l x as the shorter span. This lesson presents the different aspects of analysis and design of two-way slabs. Many of the stipulations of IS 456 are the same as those of one-way slabs. While mentioning the common stipulations with their respective section in Lesson 18, this lesson presents other relevant requirements regarding the analysis, design and detailing of two-way slabs. Numerical problems are also solved to illustrate the applications of the theory in the design of two-way slabs. 8.19.2 Two-way Slabs Two-way slabs subjected mostly to uniformly distributed loads resist them primarily by bending about both the axis. However, as in the one-way slab, the depth of the two-way slabs should also be checked for the shear stresses to avoid any reinforcement for shear. Moreover, these slabs should have sufficient depth for the control deflection. Thus, strength and deflection are the requirements of design of two-way slabs. Version 2 CE IIT, Kharagpur 8.19.3 Design Shear Strength of Concrete Design shear strength of concrete in two-way slabs is to be determined incorporating the multiplying factor k from Table 8.1 of Lesson 18 in the same manner as discussed in sec. 8.18.3 of Lesson 18. 8.19.4 Structural Analysis 8.19.4.1 Computation of shear force Shear forces are computed following the procedure stated below with reference to Fig.8.19.1. The two-way slab of Fig. 8.19.1 is divided into two trapezoidal and two triangular zones by drawing lines from each corner at an angle of 45 o . The loads of triangular segment A will be transferred to beam 1-2 and the same of trapezoidal segment B will be beam 2-3. The shear forces per unit width of the strips aa and bb are highest at the ends of strips. Moreover, the length of half the strip bb is equal to the length of the strip aa. Thus, the shear forces in both strips strip bb is equal to the length of the strip aa....
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m8l19 - Module 8 Reinforced Concrete Slabs Version 2 CE...

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