the floors of buildings. Also, A588 steel is often preferred for bridge members in view of its greater durability.

Columns. The relative material cost for two columns of different steels designed to carry the same load may be expressed as

where Fc1 and Fc2 are the column buckling stresses for the two members. This relationship is similar to that given for tension members, except that buckling stress is used instead of yield stress in computing the relative price-strength ratios. Buckling stresses can be calculated from basic column-strength criteria. (T. Y. Galambos, Structural Stability Research Council Guide to Design Criteria for Metal Structures, John Wiley & Sons, Inc., New York.) In general, the buckling stress is considered equal to the yield stress at a slenderness ratio L/r of zero and decreases to the classical Euler value with increasing L/r.

Relative price-strength ratios for A572 grade 50 and other steels, at L/r values from zero to 120 are shown graphically in Fig. 1.3. As before, A36 steel is the base. Therefore, ratios less than 1.00 indicate a material cost lower than that of A36 steel. The figure shows that for L/r from zero to about 100, A572 grade 50 steel is more economical than A36 steel. Thus the former is frequently used for columns in building construction, particularly in the lower stories, where slenderness ratios are smaller than in the upper stories.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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