There are many examples explained in the book DESIGN AND CONSTRUCTION FAILURES by Dov Kaminetzky.For a single structural member the number of different sizes of bars shall be kept minimum.The location of construction joints shall be at the point of minimum shear approximately at mid or near the mid points.
For members subjected to torsion and for members likely to be subjected to reversal of stresses as in Seismic forces. The team consists of experienced structural engineers and IT experts, led by Apostolos Konstandinidis. Any concrete and rebars in between the compressive and tensile force are not effective in resisting the moment and hence, can be removed. Circular Cross Section Advantages Structures Download As PDFFrom: Structural Cross Sections, 2017 Related terms: Compressive Strength Fiber-Reinforced Polymer Reinforced Concrete Axial Capacity Bending Capacity Confined Concrete Strain Model View all Topics Download as PDF Set alert About this page Strengthening of reinforced concrete (RC) columns with fibre-reinforced polymer (FRP) composites J.G. TENG, T. JIANG, in Strengthening and Rehabilitation of Civil Infrastructures Using Fibre-Reinforced Polymer (FRP) Composites, 2008 6.2.5 Size effect It should be noted that the behaviour of FRP-confined concrete described above is mainly based on observations made on small-scale test specimens. For circular columns, the limited number of existing tests on large-scale columns ( Youssef, 2003; Carey and Harries, 2005; Mattys et al., 2005; Rocca et al., 2006; Yeh and Chang, 2007 ) have indicated that the size of columns does not have a significant effect on the observed behaviour. In other words, the behaviour of large-scale circular columns under concentric compression can be extrapolated from that of small-scale columns. For FRP-confined rectangular and elliptical columns, the effect of column size on the behaviour of the confined concrete is much more uncertain due to the very limited test data available ( Youssef, 2003; Rocca et al., 2006; Pantelides and Yan, 2007 ). The stressstrain models for FRP-confined concrete presented in the following sections do not account for the possible size effect, so caution should be exercised when they are used to predict the behaviour of large non-circular columns. Hence, a new expression was added to the second part of the curve while the first parabolic part remains the same. It is, however, not made clear how these effective confining pressures should be used. In ACI (2002), equations for the reinforcement ratio and the efficiency factor for square and rectangular sections are given, which can then be used to predict the compressive strength of FRP-confined concrete using the same equations as for circular columns. The confining effect of FRP is assumed to be negligible for sections with aspect ratios exceeding 1.5 or with face dimensions exceeding 900 mm unless their effectiveness is demonstrated by tests. In Concrete Society (2004), the compressive strength of FRP-confined concrete in rectangular columns is predicted by an equation developed by Lam and Teng (2001) with a modified effective area of confinement. ![]() Lam and Teng (2003b). A shape factor and an equivalent circular column are defined for use in this equation. The use of this equation is limited by the guideline to small sections with aspect ratios not exceeding 1.5 and with the smaller face dimension not exceeding 200 mm. Circular Cross Section Advantages Structures Full Chapter URLView chapter Purchase book Read full chapter URL: Response and Design of Column Cross-Sections Naveed Anwar, Fawad Ahmed Najam, in Structural Cross Sections, 2017 Effect of Cross-Section Shape on Column Strength The following guidelines (not rules) may be used to choose the initial shape and dimensions of column cross-section: Whenever practical, use square, rectangular, or circular columns. It is obvious that these shapes are the easiest to design and construct. They are often efficient when there is small moment or the relative value of biaxial moment is nearly the same. Circular columns are especially suitable for seismic prone areas where high strength and ductility are needed in all directions. It is much easier to confine the concrete using special reinforcement in circular columns (or square) than in other shapes. Avoid shapes requiring complicated formwork unless it can be reused several times. Complicated shapes such as chamfered or rounded rectangles, grooved sections, and complex polygonal sections are mostly used for architectural and esthetic reasons as well as bridge piers. Their use is justified if the columns form the integral part of the architectural design. Sometimes, precast cladding can be attached to the structural columns to obtain the descried effect and sometimes complicated shapes can be used for structural advantage as well as for material saving when several repetitions are needed. Use oblong shapes when the predominant moment in one direction is clearly much larger than in the other direction; however, the aspect ratio of the cross-section should be reasonable (0.25 h b Use hollow shapes or I shape or H shape when moment is much larger as compared to axial load, such as in high bridge piers or columns of portal frames. It is obvious that the moment capacity is predominantly provided by the lever arm between the tension and compression stress resultants in the cross-section.
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