Chapter 3 Design of Rectangular Beams and （章 3矩形梁和的设计）.PDF

Prof. Mohammed E. Haque, Ph.D., P.E. Rectangular Beams and One-way Slabs Page 1 of 9 Chapter - 3 Design of Rectangular Beams and One-way Slabs 12” h A 12” strip in a simply supported one-way slab b=12” h L Prof. Mohammed E. Haque, Ph.D., P.E. Rectangular Beams and One-way Slabs Page 2 of 9 Two Methods: 1. Allowable stress design or working stress design (WSD) 2. Strength Design or Ultimate-strength design (USD) Strength Design or Ultimate-strength design (USD) With strength design method, the working dead load (DL) and live load (LL) are multiplied by certain load factors (equivalent to safety factors), and the resulting values are called FACTORED LOADS. According to ACI 318-02: Factored load, U=1.4DL ; U = 1.2 DL + 1.6 LL U = 1.2 DL + 1.6 LL + 0.8 W; U=1.2DL +1.0 LL + 1.6 W U = 0.9 DL + 1.6 W (Where, W= wind load) Similarly for other loads combinations. Capacity Reduction Factors, ACI 318-02 = 0.90 for bending in reinforced concrete = 0.75 for shear and torsion = 0.65 for bearing on concrete Balanced Steel Ratio A beam that has a balanced steel ratio is one for which the tensile steel will theoretically start to yield and the compression concrete reach its ultimate strain (0.003) at exactly the same load. Under-reinforced Beams If a beam is under-reinforced and the ultimate load is approached, the steel will begin to yield even though the compression concrete is still under-stressed (strain 0.003). Over-reinforced Beams If a beam should be ove