Design of Reinforced concerte (15.12.2008)

# Design of Reinforced concerte (15.12.2008) - Fall 08 Design...

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Design of Reinforced Concrete Residential Building Presented To Dr. Joseph Asaad Prepared By Freddy Saddik Rachel Samarani Rami Fayek Fall 08 CEN 330 Fall 08

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Chapter 4 Design of Rectangular Beams and One-Way Slabs 4.1- Load Factors Load factors are numbers, always larger than 1.0, used to increase the estimated loads applied to structures. Load factors for dead loads are much smaller than the ones used for live and environmental loads. The required strength U. U= 1.4 (D+F) U= 1.2 (D+F+T) +1.6 (L+H) + 0.5 (L r or S or R) U= 1.2D + 1.6 (L r or S or R) + (1.0L or 0.8W) U= 1.2D + 1.6W + 1.0L + 0.5 (L r or S or R) U= 1.2D + 1.0E + 1.0L + 0.2S U= 0.9D + 1.6W + 1.6H U= 0.9D + 1.0E + 1.6H 4.2- Design of rectangular beams Miscellaneous topics to be discussed. Include 1- Beam proportions. The most economical beam sections are usually obtained for shorter beams (up to 20 or 25 ft in length), when the ratio of D to b is in the range of 1 ½ to 2. for longer spans. Narrow sections are used. The depths may be as large as three or four times the widths. 2- Deflections. The ACI in section 9.5.2 provides minimum permissible beam and slab depths. These values are shown in Table 4.1. The purpose of such limitations is to prevent deflections of such magnitudes as would interfere with the use of or cause injury to the structure. For simply supported slabs, Summary of Chapters 4 through 8 Page 2
normal-weight concrete, and grade 60 steel, the minimum depth given when deflections are not computed equals.l/20. Where l is the span length of the slab. 3- Estimated beam weight. The weight of the beam to be selected must be included in the calculation of the bending moment to be resisted, because the beam must support itself as well as the external loads. You could calculate the moment due to the external loads only, select a beam size, and calculate its weight. From this beam size, you should be able to make a very good estimate of the weight of the final beam section. Another method estimating beam sizes is to assume a minimum overall depth h equal to the minimum depth specified by the ACI. After M u is determined for all of the loads, including the estimated beam weight, the section is selected. 4- Selection of bars. After the required reinforcing area is calculated, Appendix table A.4 is used to select bars that provide the necessary area. 5- Cover. Reinforcing is located at certain minimum distances from the surface of the concrete so called cover. The beams designed in examples are assumed to be located inside a building and thus protected from the weather. For this case the code requires a minimum cover of 1 ½ in. of concrete outside of any reinforcement. 6- Minimum spacing of bars. If the bars are placed in more than one layer, those in the upper layers are required to be placed directly over the ones in the lower layers and the clear distance between the layers must be not less than 1 in.

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