Steel Grid Research Articles

Influence of corrosion on reliability-based design of steel grid MSE walls

Design for internal limit states of steel grid reinforcement in mechanically stabilized earth (MSE) walls must provide for loss of steel thickness due to corrosion. The paper combines key features of zinc and steel corrosion models used in North American practice with corrosion rate statistics reported in the literature for the zinc coating on buried galvanized steel strips and for steel rebar. Examples of loss of strength and pullout capacity of steel grid elements constructed with different member diameters and up to 120 years after construction are presented in probabilistic terms. Results of reliability-based analysis for the tensile strength and pullout limit state at design lives of 75 and 120 years are demonstrated for a typical wall under operational conditions using tensile load and resistance models in combination with non-aggressive soils recommended in North American design codes. The results of calculations show that for the wall example the influence of different zinc cover thickness on probability of tensile failure of longitudinal members is detectable at the end of design life. However, the typical minimum specified zinc thickness of 0.086 mm recommended in North American practice is likely sufficient to keep probabilities of failure to 1% or less (i.e., reliability index of 2.33 or greater). The influence of a range of initial zinc thickness reported in the literature on probability of pullout failure of the same steel grid elements was found to be negligible.

钢网架结构吊装就位后围护结构连接件的焊接研究

钢网架结构吊装就位后围护结构连接件的焊接研究

In-plane stiffening and strengthening of timber floors for the improvement of seismic behaviour of URM buildings

The seismic vulnerability of URM buildings is strongly influenced by the strength and stiffness of timber floors. In this work, a steel strengthening solution is proposed to improve the in-plane stiffness of timber floors. The solution consists of placing underneath the wooden floors a steel grid of thin plates and angles at the perimeter to connect to the walls of the existing building. The connections between steel elements were done with screws. The strengthening solution proposed was numerically modelled in SAP 2000 and experimentally checked. A cyclic shear test was carried out on a real scale timber floor strengthened with the steel structure proposed. This test allowed the evaluation of the failure mode, force-displacement diagrams, and of various behavioural parameters such as floor resistance and in-plane stiffness. The experimental cyclic test showed that the strengthened timber floor considerably increased the floor resistance and in-plane stiffness. A proposal to model the stiffening solution is offered.

Excessive coverage effect (over peening) in the blasting operation of aluminum alloy “AA 7475-T7351” with steel shot

ABSTRACT Aluminum and its alloys are widely used in the aeronautics industry due to its high lightness and ductility, and it can add other elements, thus changing its characteristics. Fatigue is the major cause of failure of metal materials due to the dynamic and oscillating stresses of the finished materials. The objective of this work is to evaluate the effect of Shot Peening with coverage percentages 1blasting, 3 blasting and 10 blasting in fatigue life of aluminum alloy AA 7475-T351. Shot Peening is a cold surface treatment used to increase fatigue life of the alloy by inducing residual stresses of compression on the surface of the part. In the Shot Peening process, spherical steel grids of type S230 were used, in which the specimens were subjected to 1blasting, 3 blasting and 10 blasting coverage in two stress levels (42 Ksi and 50 Ksi). The results presented in the fatigue tests and electron scanning (SEM) showed the increase in the mechanical properties of all the samples, and those exposed to 1 blasting and 3 blasting presented better results.

Numerical modeling of nonlinear dynamic and static compression of the metal mesh

Simulation of elastoplastic compression of a symmetric fragment of a bundle of woven steel grids was carried out. The simulation was carried out under static and dynamic loading modes in ANSYS and ANSYS LS-DYNA computing systems. A porous mesh package is formed by overlaying the layers on top of each other while maintaining the directions of wires. Such a packet has a quasiperiodic structure; therefore, a certain symmetric fragment can be distinguished. The compression was carried out by a pair of absolutely rigid plates moving symmetrically towards each other. In the calculations, a multilinear plasticity model with isotropic hardening was used. The diagram of static deformation of the material was used which was obtained experimentally. The calculations were carried out according to the algorithm of a perfect symmetric contact of bodies without friction and with friction. The dynamic loading of a fragment of the mesh packet was carried out at a constant speed. The characteristics of the pulse and the loading rate correspond to those observed in previous experimental studies. The dynamic strain diagram was assumed to be similar to a static one with an increased yield strength. Calculations showed that in all loading modes there is a high level of internal stresses, and complex inhomogeneous stress-strain state. We investigated two factors that could cause differences in the behavior of the curves of deformation of a porous medium - the finite length of the acting pulse and the differences in the dynamic and static compression diagrams of the initial mesh material. The main influence on the dynamic behavior of a fragment of a porous packet of a steel mesh is exerted by the dynamic properties of the wire material. The strain curves of the porous fragment qualitatively change in accordance with the behavior observed in static and dynamic experiments. The final duration of the loading pulse and the friction between the wires for this type of mesh do not have a significant effect. The numerical dependences of the relative area of the normal and lateral through sections of the symmetric fragment of the grid packet on the compression deformation are obtained.

On the bending behaviour and the failure mechanisms of grid-reinforced aluminium foam cylinders by using an experimental/numerical approach

Metal foams are attracting interest in both aerospace and automotive industries due to their intriguing properties such as high stiffness coupled with low specific weight, good absorbing energy capabilities and flame resistance. To date, many researchers are trying to develop innovative solutions for the improvement of the mechanical properties of metal foams keeping the light-weight condition, with the scope to extend their potential application field. In this scenario, an advanced solution was here proposed; in particular, an innovative manufacturing process was presented for the production of steel grid–reinforced closed-cell aluminium foam cylinders in one single step by using the powder compact melting technique. The bending properties of plain, as well as reinforced, foam systems were experimentally tested and extensively discussed. An original finite element model was developed and validated for the analysis of the bending behaviour and the synergistic action of each component constituting the hybrid system, with a special focus on the failure mechanisms occurring under specified load conditions. The outcomes showed an increase of the mechanical properties of the reinforced systems due to the action of the light-weight mesh grid reinforcement that delays the failure of the structure. The solution proposed shows promises of being a useful method to expand the industrial applications of metal foams.

Investigation of electrophoretic deposition as a method for coating complex shaped steel parts in solid oxide cell stacks

Electrophoretic deposition (EPD) is a promising method for coating complex shaped interconnects and contact components for solid oxide fuel cells and electrolyzers. In this work, we employ a combination of finite element modelling and experiments to assess the effect of substrate curvature on the fabrication of a Mn1.5Co1.5O4 coating by EPD. The coating is deposited on steel substrates machined to create a well-defined curvature and on a Crofer 22 H steel grid. We find that post-deposition sintering of the coated steel substrate may lead to crack formation in concave surfaces, while a defect-free coating is achieved at convex surfaces. The formation of cracks is found to depend on a complex interplay between the coating thickness, the sintering procedure, and the substrate curvature radius. Oxidation testing in air at 750 °C showed that the Mn1.5Co1.5O4 coating reduced the oxidation rate of the Crofer 22 H steel grid. Sintering the coating by a two-step reduction and re-oxidation procedure resulted in a more protective coating showing a greater tendency for crack healing compared to sintering the coating in air only.

Optimal seismic retrofitting techniques for URM school buildings located in the southwestern Iberian peninsula.

This paper aims to study different seismic retrofitting techniques to test the reduction of the seismic vulnerability of unreinforced masonry buildings. Three techniques have been considered in a case study: adding steel or carbon fibre reinforced polymer grids in the walls and steel encirclements in the openings. The performance-based method has been used to that purpose. Nonlinear static analyses have been performed to obtain the capacity and fragility curves, the performance point and the damage level states. Moreover, an analysis of the cost-benefit ratio has been carried out. Results have shown that the three techniques have produced considerable improvements. The addition of encirclements has reduced the deformation resulting in a slight increase of the structure’s stiffness. Adding steel grids has produced the maximum peak strength increase while adding polymer grids has produced the largest ultimate displacements. Adding encirclement has had the best cost-benefit ratio.

Experimental Investigation on the Quasi-Static Tensile Capacity of Engineered Cementitious Composites Reinforced with Steel Grid and Fibers.

An engineered cementitious composite (ECC) was reinforced with a steel grid and fibers to improve its tensile strength and ductility. A series of tensile tests have been carried out to investigate the quasi-static tensile capacity of the reinforced ECC. The quasi-static tensile capacities of reinforced ECCs with different numbers of steel-grid layers, types of fibers (Polyvinyl alcohol (PVA) fiber, KEVLAR fiber, and polyethylene (PE) fiber), and volume fractions of fibers have been tested and compared. It is indicated by the test results that: (1) On the whole, the steel grid-PVA fiber and steel grid-KEVLAR fiber reinforced ECCs have high tensile strength and considerable energy dissipation performance, while the steel grid-PE fiber reinforced ECC exhibits excellent ductility. (2) The ultimate tensile strength of the reinforced ECC can be improved by the addition of steel grids. The maximal peak tensile stress increase is about 50–95% or 140–190% by adding one layer or two layers of steel grid, respectively. (3) The ultimate tensile strength of the reinforced ECC can be enhanced with the increase of fiber volume fraction. For a certain kind of fiber, a volume fraction between 1.5% and 2% grants the reinforced ECC the best tensile strength. Near the ultimate loading point, the reinforced ECC exhibits strain hardening behavior, and its peak tensile stress increases considerably. The energy dissipation performance of the reinforced ECC can also be remarkably enhanced by such an increase in fiber volume fraction. (4) The ductility of the steel grid-PVA fiber reinforced ECC can be improved by the addition of steel grids and the increase of fiber volume fraction. The ductility of the steel grid-KEVLAR fiber reinforced ECC can be improved by the addition of steel grids alone. The ductility and energy dissipation performance of the steel grid-PE fiber reinforced ECC can be improved with the increase of fiber volume fraction alone. A mechanical model for the quasi-static initial and ultimate tensile strength of the steel grid-fiber reinforced ECC is proposed. The model is validated by the test data from the quasi-static tension experiments on the steel grid-PE fiber reinforced ECC.

Influence of Alkaline Environments on the Mechanical Properties of FRCM/CRM and their Materials

Fabric Reinforced Mortar (FRCM) used as Externally Bonded Reinforcements (EBR), provide a sustainable solution for retrofitting and repair of existing masonry structures. They are commonly made by fibrous meshes embedded in a cementitious/hydraulic lime matrix. This technique represents a valid alternative to the well-known FRP (Fiber Reinforced Polymer) composites, which show some limitations in heritage masonry applications. In this scenario, a new system known as CRM (Composite Reinforced Mortar) has been developed in the last years. In this system, a pre-cured FRP grid is utilized as internal reinforcement in a mortar layer. The system reproduces the traditional technique of reinforced plaster, where the steel grid is substituted by a non-metallic one. In masonry applications high compatibility with the substrate, sustainability and removability are commonly required in heritage construction. These goals are not easily achieved by using fibers immersed into a polymeric resin. Moreover, the inorganic matrix ensures the transpiration of substrates and consequently a higher durability of the whole strengthened system is expected. On the other hand, the recent use of these new materials in civil engineering needs appropriate design guidelines. The proposed paper focuses attention on the initial results of a large experimental study on the durability of FRCM/CRM systems and their single components (dry glass fibers, resin, pre-cured FRP grid and mortar). In particular, the influence of three alkaline environments solutions was studied. Exposure conditions were stressed by increasing the temperature of the three aqueous solutions. The mechanical retention of tensile properties was measured by performing direct tensile tests after different exposure times.

FINEX® as an environmentally sustainable ironmaking process

ABSTRACTFINEX® is an alternative ironmaking process to the blast furnace route. As the core facilities in Pohang Steel Works, two commercial FINEX® plants have already produced over 25 million tons of hot metal. For more than 10 years of operation and continual improvements, including an energy recovery system, binders for coal briquettes as well as the steel grid system in FBR (Fluidized-Bed Reactor), such a substantial improvement have been achieved on the overall cost and environmental footprint. The potential for large-scale CO2 removal system working as carbon capture and utilization in the process further enhances the environmental potential of the process. In this paper, the brief history and overall process of the FINEX® were introduced especially focusing on the key technologies.

Adhesion of steel and fiberglass meshes with concrete

Introduction. To prevent the formation of cracks and destruction of masonry structures they are reinforced with meshes at the stage of construction. Compatibility of the reinforcing material and the main body of the structure is an important parameter for the efficient operation of the structure. The article examines the amount of adhesion of fiberglass and steel mesh elements with sand concrete, which is the binding of bricks. Materials and methods. Reinforced beams are tested for bending. Samples of beams consist of two halves connected by a rod in a stretched zone and uncoupled by a hinge in a compressed zone. Elements of steel and fiberglass grids with limited anchorage zones in concrete act as reinforcement. The values of rod slippage in concrete were fixed by a dial gauge. Results. According to the results of the test, the slipping forces of the rods were obtained and the cohesive stresses of the elements of steel and fiberglass grids with concrete were calculated, and diagrams were drawn. The value of adhesion with concrete fiberglass rods was greater compared with the adhesion of steel rods for all values of slip. Conclusions. Fiberglass meshes have a number of drawbacks to steel meshes, however, a large number of positive characteristics of fiberglass meshes, including adhesion with concrete, make them competitive with steel, and in many cases more preferable for use in structures. Keywords: coupling reinforcement with concrete, adhesion, brickwork, reinforcement of structures, masonry mesh, composite materials, steel mesh, composite mesh, innovation in construction/

In-plane shear capacity of tuff masonry walls with traditional and innovative Composite Reinforced Mortars (CRM)

Abstract The effectiveness of reinforced plasters and Composite Reinforced Mortars (CRM) for increasing the in-plane shear capacity of masonry walls was investigated on a series of 32 single-leaf tuff masonry panels subjected to diagonal compression tests. Six specimens were used as control and two specimens were strengthened with reinforced plaster (steel grid 100 × 100 mm and cementitious matrix) with a thickness of 40 mm. The remaining specimens were strengthened with two different fibre reinforced lime-based mortars, characterized by different cement content ratios, and coupled with three different grids (steel grid 100 × 100 mm, GFRP grid 30 × 30 mm and GFRP grid 40 × 40 mm). Both single-sided and double-sided strengthening configurations were adopted for all strengthening solutions, to investigate the reduction in strengthening effectiveness in case of single-sided applications. The results showed that strengthening in single-sided configuration increased the shear capacity from 42% to 85% with respect to the unreinforced masonry panels (URM) average shear capacity. Conversely, strengthening in double-sided configuration led to a shear capacity increase from 138% up to 288%. Based on experimental results, reducing the matrix cement content ratios in strengthened system led to a reduction in shear capacity and energy dissipation, independently from the grid properties. Furthermore, specimens strengthened with GFRP 40 × 40 grid, although characterized by a large spacing with respect to GFRP 30 × 30, achieved an increase in the shear capacity and energy dissipation greater than other strengthened specimens clearly evidencing that the grid spacing and the interlock between grid and micro-fibres embedded in the mortar are crucial aspects for the strengthening system effectiveness.

Research on evaluation method of soil corrosive property to grounding grid in transformer substation

In the paper, a nine-index evaluation method of soil corrosive property to grounding grid is established based on analysis of soil physical and chemical properties in 120 transformer substation test stations, inspection of index corrosion condition about soil corrosion to buried metals as well as the test results of influence of soil temperature, water content, pH value, chlorine ion content, sulfate ion content and other factors on metal corrosion. The method is simple and practical, comprehensive influence factors are considered, the accuracy is high, thereby providing scientific basis for surveying and designing newly-established transformer substations, and monitoring corrosion of transformer substation grounding grid in operation. Two factors of air capacity and regional annual average temperature are included into the evaluation method for the first time in China, and the evaluation method of galvanized steel and copper grounding grid is proposed for the first time according to the nine-index evaluation method determined in the paper.

Variant Concept of Elevation of a Steel Grid Tower

The article presents the stages of analysis of an existing steel structure of a 35m-high lattice tower, located in a woodland. The assessment of the condition of the tower’s structural elements and connections was made in the aspect of plans for its elevation, in order to install an observation camera warning against fire hazard. The tower up to 30 m was made of five segments with a square section, with decreasing width from 4.86 m to 2.05 m. The last segment, 5m high, was made as a cuboid. Truss walls and horizontal truss membranes were used. Technical platforms were installed inside the shaft. Rolled sections of St3S steel with a yield point fd = 215 MPa were used as structural elements. The tower was erected on concrete spot footing. Static and strength analyses of the existing structure were carried out, taking into account the actual condition of materials and connections in the aspect of the planned modernization. The influence of wind gusts and the load from ice were taken into account. The user planned to install an observation camera on an additional mast with a height of 12 m. Initially, the concept of an additional construction made of Ø60.3 × 4 mm steel pipe set in a steel sleeve fastened to the bridge plates was adopted. The support tube was stabilized with four steel stay rope with diameter of 5 mm, fixed to the corners of the platform at 35m. As a result of the conducted calculations, it was justified that the adopted concept is inappropriate due to the fact that the limit values of horizontal displacement of the end of the mast, also unacceptable due to excessive vibrations of the image from the observation camera, would have been exceeded. Therefore, another concept was developed, in which a 12 m mast would be made with an aluminium lattice construction. In the horizontal section, the mast would have the shape of an equilateral triangle with a side length of 450 mm (420 mm in the axes). The mast branches would be made of RO35x2 round tubes, and the gratings would be made of rectangular, full profiles with a 20 x 10 mm cross section. The mast would consist of three latticed segments with a length of 4.0 m. The stays would be made of Ø5 mm steel ropes. Mast with sliding support would be stabilized with lashings, mounted on three levels. In order to obtain a proper tilting of the lashings in relation to the vertical axis of the mast, it is planned to use additional horizontal expansion elements made of square profiles RK80x5, located at the level of the highest platform. As a result of the calculations carried out, it was shown that a construction designed as presented would meet the conditions of limit states defined in the current standards of fire safety. The work was summarized by providing user guidelines for ensuring the durability of the modernized structure in the anticipated period of usage.

Refined safety assessment of steel grid structures with crooked tubular members

Abstract For grid structures, damages of structural members such as crookedness significantly affect the overall structural safety. Traditional assessment methods can hardly evaluate the impact of crooked members in existing grid structures accurately due to difficulties lying in crookedness measurement and residual load-bearing capacity analysis. In this paper, a new method of refined model adjustment and structural assessment with crooked tubular members of steel grid roofs taken into consideration is proposed, while the crooked measurement is conducted with an image-based 3D measurement method for the first time. Firstly, the original shape of crooked members is recovered using image-based 3D measurement method. Secondly, the measured deformation of the crooked members is adjusted from the load status at the time of measurement to the zero-load status in two ways. Finally, the FE model of the entire grid structure, together with the adjusted crooked tubular members is adopted in the residual load-bearing capacity analysis considering both geometric nonlinearity and material nonlinearity. A large span steel grid roof structure containing four crooked tubular members is utilized for the illustration and validation of the proposed methodology. The proposed method inventively offers a new direction for refined assessment of existing grid structures with crooked members and provides significant potential for practical implementation.

Lessons from the seismic behavior of a steel grid roof structure heavily damaged in Lushan earthquake

The seismic behavior of a school gymnasium, whose steel grid roof was heavily damaged during the Mw6.6 Lushan earthquake in 2013, is simulated through nonlinear dynamic analysis. The simulated damage is compared with field observations to validate the numerical model, based on which a parametric study was performed to provide insight into the failure process and damage patterns of steel grids. The results suggest that the grid damage is strongly related to roof-substructure interactions. These include not only the substructure’s amplification of the vibration, but the uncoordinated displacement of the substructure’s columns which support the grid also play an equally important role. In particular, the latter effect may significantly alter the internal force distribution in the steel grid and lead to unexpected buckling of members that are proportioned as tension-only members. While such interactions are generally not accounted for in the design practice for grid structures in China, similar seismic damage may be expected for other existing grid roofs in future earthquakes. As is also demonstrated in this study, seismic isolation of the roof is a promising solution to protect grid roof structures by mitigating the detrimental effects of roof-substructure interactions.

Combination of potential nanomaterials for intermediate temperature oxygen membranes on the base of δ-Bi2O3/Ag

The new architecture of IT thin oxygen membranes on a flexible support made of stainless steel grid is proposed. This membrane is designed to realize clean coal energy with combustion of pulverized low ranked solid fuels in oxygen enriched atmosphere using purified flue gases as a sweep gas. Multilayer membrane with thickness about 40 μm is consist of metal grid with deposited protected layer and filled by porous agglomerates of e-conducting perovskite, dense selective layer on the base of multilevel nanocermet δ-Bi2O3/Ag, protected porous layer and supported Pd/Pt-catalyst layer. Mechanochemical ceramic method is the main approach to designing of nanomaterials with interpenetrating and core-shell microstructures. Compatible combination of materials and operations is determined for creating oxygen membranes with operating temperature 500-550 °C. The best combination of materials successfully passed the degradation test at 500 °C for 500 hours.

Experimental Studies on Shear Resistance Performances for the Shear key of H Shape Steel Spatial Grid Roofs

Abstract In this paper, a new type of structure was introduced. The spatial steel grid structure was composed of the top layer, lower layer H-shaped steel ribs and square steel tubes. The shear key is the key part of the structure.Based on the real dimensions of a practical prototype,two sets of full-scale shear key specimens were made, one of which has vertical stiffening ribs. The loading tests of two groups of specimens were carried out to simulate cases under pure shears and the experimental results were compared with the simulations from the finite element analysis. The effects of vertical stiffeners on failure modes, ultimate loads, strength-yield ratio and ductility of shear key were studied through experiments. By parametric analyses in the present article, relations of the stiffening plates width and thickness was recommended.

A Heuristic Approach to Identify the Steel Grid Direction of R/C Slabs Using the Yield‐Line Method for Analysis

In the last few years, nonregular reinforced concrete (R/C) slabs have become more popular in buildings and bridges due to architectural or functional requirements. In these cases, an optimum design method to obtain the ultimate load capacity and the minimum reinforcement amount should be used. For simple R/C slabs, the yield‐line method is extensively used in engineering practice. In addition to strength, the “true” failure mechanism is also obtained by identifying the parameters that define it and minimizing the collapse load. Unfortunately, when the mechanism is too complicated to be described or defined by several parameters (e.g., in slabs with complicated geometry), the method becomes more difficult because the system of nonlinear equations becomes harder to solve through traditional methods. In this case, an efficient and robust algorithm becomes necessary. In this paper, a structural analysis of R/C slabs is performed by using the yield‐line method in association with a zero‐th order optimization algorithm (the sequential simplex method) to avoid calculating gradients as well as any derivatives. The constraints that often limit these parameters are taken into account through the exterior penalty function method, leading to a successful solution of the problem. Considering that the direction of each yield‐line is sought by minimizing the ultimate load and finding the parameters defining the collapse mechanism, another parameter concerned with the direction of an orthotropic reinforcement grid is introduced. In this way, the number of unknown parameters increases, but aside from obtaining the ultimate load and the parameters defining the collapse mechanism, the solution also finds both best and worst reinforcement orientations.