Optimal strengthening by steel truss arches in prestressed girder bridges

This work focuses on the proposal and the evaluation of a new consolidation system for prestressed reinforced concrete (PRC) beams of girder bridges. The system consists of two arch-shaped steel trusses placed alongside the lateral faces of the beam to beconsolidated. The arches develop longitudinally along the entire span of the beam and in elevation using the available height of the PRC cross section. The consolidation system is characterized by its own external constraints, independent from those serving the pre-existing element. The efficiency of the system with respect to parameters variability is described also focusing on the ratio between the load discharged by the consolidation system and the total applied load. Referring to a case study, the consolidation of a PRC beam is presented adopting the proposed system with respect to the usually adopted external prestressing technique. The cross sections properties of the steel arch shaped trusses are defined by means of a structural optimization process using a genetic algorithm, identifying the minimum steel consumption. Finally, a preliminary cost-benefit analysis is performed for the proposed solution for a comparison with other commonly adopted techniques.

STUDY ON FORCE MECHANISM OF CABLE-TRUSS FRAME AND JUMPED LAYOUT OF ANNULAR CROSSED CABLE-TRUSS STRUCTURE

A new type of cable-strut tension structure named Annular Crossed Cable-truss Structure(ACCTS) comprises a series of planar cable-truss frames crossed each other. To investigate the force mechanism of ACCTS, a cable-truss frame model with 2-bar and 6-cable has been developed, and its initial stiffness formula has been derived as well. The model is further simplified to make it is upper and lower vector heights equal, and then the initial stiffness formula and the critical slack load formula are further deduced. Based on ANSYS software and cable-truss frame with a span of 60m, the influences of the number of struts and position of jumped layout on the cable-truss frame are studied. According to the former 60m span cable-truss frame's research results, the jumped layout of ACCTS with a span of 100m is studied. The static and dynamic performances of two schemes, the optimal jumped layout scheme and the original scheme, are systematically studied. It is shown that the number of struts would be about 6~8 for the planar cable-truss frame and the optimal order of jumped layout is strut 6-7→strut 4-5→strut 2-3. The optimal order of jumped layout of ACCTS agrees with that of the cable-truss frame, verifying the feasibility of conclusions. In the condition of no variation in the original structure's static and dynamic performance, the optimal scheme of the jumped layout will lower the steel consumption and enhance the buckling loads. Moreover, it also simplifies structure for easy construction.

Structural form and experimental research of truss arch bridge with multi-point elastic constraints

With the increase of the arch bridge span, the mechanical properties of arch bridges will decrease rapidly. In order to solve this problem, triangular net is set between the arch rib and girder to form a kind of truss arch bridge in which arch rib acts as top chord, girder acts as lower chord, triangular net acts as web member, and hangers provide elastic restrains at several points. The triangle stability of the truss can improve linear stiffness of arch rib and girder, which will thus improve the mechanical properties of arch bridges. A test bridge with a span of 50 m was built to prove the superiority of the truss arch bridge with multi-point elastic constraints (MTAB). Structural stresses and displacements were obtained through dead load experiments, and the mechanical properties of the structure were calculated through the finite element (FE) software. It is turned out that, compared with the conventional through arch bridge (CTAB), the mechanical performance of the MTAB is greatly improved. The test values of structural stresses and displacements match calculation values well. Moreover, with the same steel consumption, the more layers of the triangular net, the better the mechanical properties of the structure.

ANALYSIS OF CALCULATION REGULATION METHODS IN STEEL COMBINED TRUSSES

The article is devoted to the calculated regulation of the stress deformation state (SDS) of combined steel trusses, which allows to reduce the efforts in some sections of the structure by increasing the efforts in other and design evenly stressed structures as the most rational systems. It is shown that the calculated method of SDS regulation makes it possible to reduce steel consumption by up to 34%. Four methods of calculated SDS regulation are proposed. The advantages of combined structures are given: the concentration of materials and the possibility of designing them as low-element. As shown in the example, for the quantitative criterion of quality it is possible to use rationally the maximum potential energy of deformation. Dependences for calculation of the maximum potential energy of compressed stretched, and compressed-bent elements of rod-bearing steel structures are given.

THEORETICAL JUSTIFICATION OF INCREASING THE EFFICIENCY OF REINFORCEMENT OF FLEXIBLE CELLULAR CONCRETE STRUCTURES

Aerated concrete is actively used in energy efficient construction, mainly as a masonry material for vertical load-bearing structures. At the same time, the creation of a closed thermal contour of the building, which is the basis of modern energy saving requirements, is rational by the use of aerated concrete in load-bearing horizontal structures that require reinforcement. Traditionally bar reinforcement is ineffective in aerated concrete due to low specific adhesion at the contact of the reinforcement with concrete and significantly less than that of heavy concrete, the distribution capacity of concrete around a rod, which evenly transforms concrete stress to bar extension, the consequence of which is the significant bar understress while pulling it in concrete. The authors’ research in the field of rationalization of reinforcing elements that are effective in cellular concrete, aimed at increasing the contact surface of the reinforcing element with concrete while maintaining the original steel consumption, makes it possible to recommend tape reinforcement for use in reinforced aerated concrete structures. Punched steel tapes equal to the bar reinforcement of the cross-sectional area, but having developed lateral surface, provide an increase in the adhesion strength of the reinforcement and preventing its pulling. The article presents the results of a numerical study of stress-strain state in reinforced aerated concrete beam with rectangular section, reinforced with the proposed tape reinforcement in comparison with traditional bar reinforcement

INFLUENCE OF SPATIAL ORIENTATION OF FRAME BUILDINGS ON METAL CAPACITY OF STEEL COLUMNS

The calculated values of wind pressure are identified without taking into account changes in wind speed and pressure from different directions. Current load standards in Ukraine allow taking into account the decreasing coefficients of wind direction if there is sufficient statistical justification and when the objects are located on open flat terrain. The purpose of this work is to identify possible effect of considering the orientation of frame buildings and corresponding coefficients of the wind direction when designing steel columns of one-story frame buildings. By analyzing design and calculated parameters of one-story industrial and civil buildings, possible limits of their change were established, and a plan for the experimental design of columns from broad-flanged rolling H-beams was developed and implemented. A dependence was obtained and described by analytical expression that allow forecasting steel consumption for the columns of single-aisle one-story buildings, taking into account their height, total load from roof and active component of wind pressure. Based on the results of earlier studies, the characteristic values of wind pressure and generalized wind direction coefficients were established for each of 25 regions of Ukraine. For most part of the territory of Ukraine, minimum wind loads are realized when wind directions are north-south or north-east-south-west. Generalized wind direction coefficients, together with the formula for the forecasting mass of columns, made it possible to identify possible savings in steel on the columns of one-story buildings taking into account spatial orientation of buildings. On average, throughout the territory of Ukraine, metal consumption of rolling columns decreases by 4.2%, and in some cases, depending on the region, wind direction and building height, it can decrease to 17.5%. Significant influence of the underlying surface and surrounding buildings on the nature of the wind flow allows wind direction coefficients to be taken into account only when calculating the frames of buildings located in an open flat area, under conditions that their values are statistically substantiated using the results of wind observations at nearest meteorological stations.

Mathematical model of steel consumption minimization considering the two-stage billets cutting

Purpose. To achieve a decrease in energy and resource costs in the multi-stage production of rolled products within a given plan through the development of appropriate mathware. Methodology. The multi-stage problem mathware for producing rolling steel products is developed on the basis of system approach applying fundamental principles of the optimization and operation research theory. Realization of the developed mathematical model allows discovering such a strategy of using steel during the whole manufacturing process, which minimizes not only the steel waste at the moment of its casting in a mold, but also the offcuts in the process of cutting the obtained ingots into the billets. Findings. A mathematical task model is built to minimize the amount of steel for producing a certain order of size of one cast volume only. The developed model specifies the possibility to pre-evaluate the billet optimal size, based on the necessary cutting along the final product length, appropriate for the certain billet form of section, and ingot weight limits. Originality. A mathematical model is provided for the optimal metal distribution process when implementing the plan of manufacturing rolling products. The model, in contrast to the existing ones, shifts the emphasis on forming the optimal ingot weight, which has a pre-calculated optimal cutting plan. Practical value. The use of the developed mathematical optimization model (minimizing the amount of steel for producing a certain order) as part of an automated decision support system for management of rolling production will reduce the number of cutting machine changeover and minimize resources use and stock balance.

Erection of solid columns of one-storey industrial buildings with bridge cranes made of high-strength sandy concrete and its economic efficiency

The use of high-strength sandy concrete (HSSC) is an alternative to high-strength crushed stone. Its use is profitable for those regions of Russia in which crushed stone is an imported building material. Thus, crushed stone is supplied to the Republic of Tatarstan (RT) from the Ural, and the local reserves of sand are significant. Authors presented the results of studies to determine the economic efficiency of solid columns’ erection in one-story industrial buildings with bridge cranes according to the 1.424.1-5 series from HSSC of HSSC60 and HSSC80 classes in comparison with heavy concrete of B20...B80 classes. Studies have shown that in relation to Kazan, the use of HSSC of HSSC60 and HSSC80 classes in comparison with heavy concrete of B20...B40 classes, depending on the size of the span, column spacing, floor height and lifting capacity of cranes, can reduce steel consumption by 43.2…71.5 %. At the same time, the total cost of materials (steel and concrete) when using heavy concrete of B20...B40 classes is 1.7 %...38.1 % lower than with HSSC60 and HSSC80. This is due to the sharp rise in the cost of concrete in the Russian market in the third quarter of 2002 and continuing to the present (second quarter of 2021). When recalculated before the indicated price increase, the use of HSSC60 and HSSC80 in comparison with heavy concrete of B20…B40 classes gives a decrease in the total cost of materials by 1.9...34.5 %. The results obtained are novel because in the scientific and technical literature there is no information about the design of these columns from the HSSC.

An Integrated CRITIC-MARCOS Technique for Analysing the Performance of Steel Industry

Steel has played critical role in the expansionist ambition of successful aristocrats and laying the foundation of enviable empires. Modern economies are built on strong infrastructure, communication, and transport networks. Industries, like automobiles, consumer durables, real estate, cannot be imagined without steel. Its synonymy with growth of an economy can be gauged by the fact that matrices, like per capital steel consumption and its contribution to the GDP, are considered as parameters of economic development. It is one of the most tracked industries by the investors, analysts, and financial institutions. In this chapter, a novel multi-criteria decision-making tool while integrating measurement alternatives and ranking according to compromise solution (MARCOS) and criteria importance through intercriteria correlation (CRITIC) methods is developed for evaluation of steel organisations which are constituents of BSE 200 index. The results derived from the implementation of integrated MARCOS-CRITIC model aid diverse stakeholders in making informed investment decisions.