Four measures to reduce the amount of steel in the construction of the project

The design and construction of construction steel works in the premise of quality assurance, such as reasonable design, reasonable processing and preparation of materials, reasonable substitution, the use of reasonable construction methods, and actively promote the use of new technologies, new techniques, can reduce the amount of reinforcing steel in the entire project, reduce project costs, improve economic efficiency.

Currently, in the structural design of construction projects, taking into account the calculation, construction of simple and construction conditions of the limitations of the components of the reinforcement of the existence of "more than not less than a large do not use the small" phenomenon, such as high column reinforcement, according to the column of each part of the force calculation of the column root with a number of large-diameter rebar, and gradually reduce the number of bars and narrow the diameter of the rebar, and gradually reduce the number of roots and the diameter of the rebar. The number of roots and reduce the diameter of reinforcement, in order to reduce the amount of reinforcement, but some of the current design is only calculated at the root of the column reinforcement, regardless of how high the column, how the force, from the bottom of the column to the top of the unified reinforcement, according to statistics, 10% to 20% of the reinforcement in the column is more than one, such as an elevator shaft frame column, the use of a different diameter of the steel bar butt welding after the new process, from the bottom of the column reinforcement ?32 to start, upward gradual transformation of the? 25, ?22, ?20, ?18, than the unchanged reinforcement and tied design less than 30% of the amount of rebar. Again, in some rigid beams, ring beams, beams in different locations of the reinforcement, can also be done accordingly, can save a certain amount of steel.

Although the use of computerized CAD calculation of multi-storey frame can be exempted from a large number of manual calculations to speed up the speed of the drawing, but through the design of a number of multi-storey frame project found that the multi-storey frame of the computer still needs to be manually adjusted, some beams, columns, the final reinforcement with experienced construction personnel to determine, can save some of the reinforcement.

Drawing designers according to textbook recommendations for beams, columns, cross-section size of the value of the range, combined with their own experience first of all the size of the components of the initial determination of a size, at this time, attention must be paid to as far as possible to make the column of the linear stiffness ic and the beam of the linear stiffness of the ratio of the value of the Ib is greater than 1, this is in order to realize the action of the rare earthquakes, so that the beam end of the formation of a plastic hinge, the end of the column can still be in the inelastic state without working. Yield, but the nodes are still in the elastic phase of the purpose of the work, that is, "strong columns and weak beams and strong nodes", the preliminary determination of the size of the input computer for trial calculation, generally can be obtained as follows two kinds of results:

(1), part of the beams and columns are only for the construction of reinforcing bars, than when, according to the electric calculations show that the beam of the width of the crack and the column of the axial compression ratio Size appropriate to reduce the beam, column section size, and reinforcing steel and then trial calculation.

(2), part of the beam shows super reinforcement or crack width greater than 0.3mm, part of the column axial compression ratio exceeds the limit or the reinforcement rate is too large (trial calculation can be controlled column reinforcement rate is not greater than 3%), at this time, you can appropriately reduce the reinforcement, amplify most of the cross-section size and then trial calculations, the author suggests that: for the framework of the beam, the longitudinal tensile reinforcement reinforcement of the more appropriate to take 0.4% ~ 1.5%, for the framework of the column, all longitudinal reinforcing steel bar of the more appropriate to take 0.4% to 1.5%, for the framework of the column, all longitudinal reinforcing steel bar of the more suitable for the framework, and then trial calculations. For the frame column, all the longitudinal force reinforcement reinforcement rate of 1% to 3% is more appropriate, so that the steel content is more economical.

Reasonable processing and preparation of materials using low-strength steel can save materials. In ordinary reinforced concrete structure using low strength steel and not using high strength steel, because the use of high strength steel can not play its own material strength, can only be used as a low strength steel to use, and thus also lost the significance of the use of high-strength steel, can not achieve the purpose of saving steel, but instead of causing a waste of both the ultimate tensile strain difference is very large, when the concrete cracks the ultimate tensile strain For: (0.1 ~ 0.15) × 10-3, and the concrete is about to appear cracks in the reinforcement stress is only 20 ~ 30N/mm2, even in the use of the maximum crack width allowed to appear [Wmax] = 0.2 ~ 0.3mm of the components, the stress of the steel bar is only 150 ~ 250N/mm2, which shows that the use of high-strength reinforcing bars did not achieve the purpose of saving steel bars.

At present, some construction units due to the difficulty of feeding, and by the limitations of the processing conditions and other reasons, in the processing of reinforcing steel batching methods and reasonable materials, there are some drawbacks, if the use of reasonable processing and batching methods, first of all, according to the level of reinforcing steel, specification classification, different diameters of reinforcing steel are long cold drawn, and then calculated, reasonable materials, materials, using the first after the first long, the rest of the head of the pre-buried iron under the Material procedures, can reduce the loss rate of steel within 1%, the utilization rate increased by about 2%, such as I once constructed a training building in the city, non-prestressed steel bars all by cold drawing after the reasonable material, that is, the long line of coiled round steel bar by 3% of the cold-drawing rate of cold-drawing to achieve the best use of material, achieved good results, more than 700 tons of rebar volume of construction is completed, the site is basically no short waste, and save steel 9 tons. More than a ton.

Construction site, such as sufficient materials, in the components allow and the density of steel is small, such as the consideration of Ⅲ level of steel instead of Ⅱ level of steel, Ⅱ level of steel instead of Ⅰ level of steel, such as the strength of the replacement program. Can save the amount of reinforcing steel, such as a commercial and residential building in the construction of the project by the design institute agreed to use this replacement program to save more than 7 tons of reinforcing steel.

Improve the strength grade of concrete can reduce the anchorage length of steel, in order to ensure that reinforced concrete structures work reliably, longitudinal stress steel must be extended into the full use of its tensile strength according to the calculation of the stress section a certain length, in order to use this length of the bond to anchor the steel in the concrete, the anchorage length ln is to determine the longitudinal reinforcement of the cut-off length of the extension of the steel and concrete bond strength between steel and a number of factors. There are many factors affecting the bond strength between the steel bar and the concrete, including the concrete strength, the surface characteristics of the steel bar, the ratio of the thickness of the protective layer of the steel bar to the diameter of the steel bar, etc. When the type of reinforcing steel and the thickness of the protective layer has been determined, then the main factor determining the bond strength is the concrete strength level, the reduction of the concrete strength level will reduce the bond strength between the steel bar and the concrete, which is necessary to increase the anchorage length of the steel bar. Length.

Concrete strength grade on the full use of reinforcing steel strength anchorage length ln the impact of the full use of tensile strength of reinforcing steel, such as reinforced concrete cantilever beam upper longitudinal force steel, extending into the support of the minimum anchorage length ln, when the concrete strength grade from C20 to C30, grade Ⅰ reinforcing bar to be reduced from 30d to 20d, grade Ⅱ reinforcing bar to be reduced from 40d to 30d, the strength grade of concrete can be reduced by the increase in concrete strength grade, the anchorage length of the reinforcing bar. Concrete strength grade can be reduced by the anchorage length, so that save steel, tensile strength underutilized steel, such as reinforced concrete simply supported beams of the lower longitudinal force reinforcement, because the beam simply supported end of the positive section of the moment M = 0, according to the requirements of the positive section of the bending capacity, longitudinal reinforcement can be appropriate to extend into the support, but under the action of the main tensile stress, if there is no increase in concrete strength, that is, near the support along the support to begin to Appear oblique cracks, then the longitudinal reinforcement intersected with the cracks by the tensile force increased significantly, then the longitudinal reinforcement in the support at the anchorage length does not uniformly can not be reduced and also appear particularly important, from the above analysis fully explains, improve the strength of the concrete grade does not uniformly can save some of the reinforcing steel, but also improve the performance of the component.

At present, some design units in order to make the support easy to locate and set up in the foundation, beams in the bar welding piece, lengthening column bars, plate wall bars to the bottom of the foundation, so that there will be a certain amount of rebar just for the construction of the temporary positioning support and waste, if you set up a temporary bracket instead of the welding piece, you can save rebar, such as coal-fired power plant engineering in the construction of a large boiler foundation, the use of setting up temporary brackets, instead of steel welding piece support positioning.

Column bars are mostly large diameter steel, according to the design specification, the length of the column bars inserted into the foundation as long as to meet the anchorage length on the line, but in order to facilitate the construction of the positioning support, regardless of the depth of the foundation, there are 20% to 40% of the column bars inserted into the floor resulting in a waste of steel in order to save this part of the reinforcement, a commercial building in a number of projects using a small diameter steel with columns of large diameter steel bars. Reinforcement bars and columns of large diameter steel butt welding method to meet the construction of support positioning requirements, in a few foundations of the column root reinforcing steel construction less than 5t of reinforcing steel.