Economy Analysis Of Roof Beam On The Basis Of The Intensity Grade Of Concrete

There are much papers studied about the armored concrete roof beam economy, most papers suppose the price of unit volume of the concrete is Ck, the price of unit volume of the reinforcing bar is Cg, and the calculation formula obtained. From the calculate formulae of straight section of roof beam of square-section of single muscle, the grade fc of the concrete intensity is the important factor of influencing roof beam fabrication costs. And the construction project fabrication costs have dynamic characteristics, the pricing of main material, reinforcing bar and concrete of the roof beam of armored concrete, should accord with the actual conditions, so, we should analyze the economy of the roof beam from the dynamic angle.Reinforcing bar and concrete can be valuated according to two ways of valuating currently by norm and valuating according to their information prices of material. The concrete valuating by norm can be divided into two kinds of pricing ways of according to the concrete price on-the-spot and according to the sand, stone, cement. This paper has separately calculated the unit price of reinforcing bar and concrete with the budget software, and analyzed the unit price of the reinforcing bar. It is cheaper that the unit price of reinforcing bar of diameter 18-25 whorl steel.Armored concrete roof beam fabrication costs expression formula can simplify for reinforcing bar fabrication costs and concrete costs. From the calculate formulae of straight section of roof beam of square-section, the areas of reinforcing bar can be expressed in concrete axis compression strength. We can find out the relations between unit prices of concrete and concrete axis compression strengths with SPSS software. In this way, there is only one variable, the concrete axis compression strength, in the expression formula of the fabrication costs of roof beam. The derivative is greater than 0 that the fabrication costs expression formula of the roof beam towards fc of two steps, so the figure of the fabrication costs of roof beam are concave. This has offered theoretical foundation for optimization design of the roof beam, optimization steps are:The first step, calculate the unit prices of the reinforcing bar and concrete of various intensity grade according to the regulations of the current fabrication costs.The second step, confirm the minimum intensity grade of the concrete of the structure requirement according to " structural design specification of concrete " or other regulations. calculate the longitudinal sectional areas of drawing reinforcing bar with PKPM software.The third, increase one grade of concrete intensity, calculate the longitudinal sectional areas of drawing reinforcing bar. If improving the concrete rank can make the fabrication costs of roof beam reduce, repeat the third step and continue optimizing, otherwise, the last step intensity grade of concrete was optimum.With the improvement of the intensity grade of concrete, the axis tensile strength of the concrete increases, what the oblique section of roof beam bears increasing cuts strength. It is the goal of building structural economy that increase to resist ability of cutting roof beam and utilize performance of material fully without increasing the fabrication costs of roof beam by improving the intensity grade of concrete.