Concrete, allowable compressive stress

If the force is exerted in the compressive direction, then it is a compressive force. Dividing by the cross-sectional area gives the compressive stress. Materials such as concrete and diamond have relatively high allowable compressive stress values. Others, such as mud or flesh, have low allowable compressive stress values. 

Ar = area required, base plate, in. f = ultimate 28-day strength, psi fu = bearing pressure, psi fi = equivalent bearing pressure, psi Fb = allowable bending stress, psi Ft = allowable tension stress, psi F, = allowable compression stress, psi E, = modulus of elasticity, steel, psi Ec = modulus of elasticity, concrete, psi n = modular ratio, steel-concrete n = equivalent cantilever dimension of base plate, in. Bp = allowable bearing pressure, psi Ki,2,3 = factor... 

Fb = allowable bending stress, psi Fc = allowable compressive stress, concrete, psi (see Table 3-35)... 

The results tabulated indicate that the stresses are well within the limiting cases. Hence reinforcement design based on 500 psi tension allowed for 15°C temperature cross fall on the outer face is safe. It is of interest to note that compressive stress on the inside face of the vessel due to above combination of loads is well within the allowable compressive stress, i.e. 2200 psi for Hunter-ston B concrete mix of 5400 psi cube strength at 28 days. 

The allowable compressive stress of concrete is taken from Table 12.3. 

The value of K represents the location of the neutral axis between the anchor bolts in tension and the concrete in compression. A preliminary value of K is estimated based on a ratio of the allowable stresses of the anchor bolts and concrete. From this preliminary value, anchor bolt sizes and numbers are determined and actual stresses computed. Using these actual stresses, the location of the neutral axis is found and thus an actual corresponding K value. A comparison of these K values tells the designer whether the location of the neutral axis he assumed for selection of anchor bolts was accurate. In successive trials, vary the anchor bolt sizes and quantity and width of base plate to obtain an optimum design. At each trial a new K is estimated and calculations repeated until the estimated K and actual K are approximately equal. This indicates both a balanced design and accurate calculations. 

Allowing no tension in the concrete (compressive stress in the reinforcement steel = 125N/mm )... 

S = code allowable stress, tension, psi N = number of anchor bolts Fp = allowable bearing pressure, concrete, psi Fy = minimum specified yield stress, sldrt, psi Fs = allowable stress, anchor bolts, psi fLT = axial load, tension, Ib/in.-circumference fLc= axial load, compression, Ib/in.-circumference Ft = allowable stress, tension, sldrt, psi Fc = allowable stress, compression, sldrt, psi Fb = allowable stress, bending, psi... 

In one such prestressing technique, high-strength steel wires are positioned inside the empty molds and stretched with a high tensile force, which is maintained constant. After the concrete has been placed and allowed to harden, the tension is released. As the wires contract, they put the structure in a state of compression because the stress is transmitted to the concrete via the concrete-wire bond that is formed. 

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