Capacity Of Structural Elements Research Articles

Flexural behavior of corroded RC beams repaired with high performance cementitious mortar under cyclic loading

AbstractThe understanding of the cyclic performance of reinforced concrete (RC) elements is of vital importance in relation to the extent of the service life of buildings and infrastructures. Steel rebar corrosion plays a major role in this regard because it significantly affects the overall structural integrity, especially under cyclic loads, leading to reduced stiffness and load‐bearing capacity of structural elements. Cyclic condition has the potential to accelerate the corrosion‐induced cracking and spalling, the effectiveness of the bond strength between rebar and concrete, and also the ductility and energy dissipation characteristics of the structure. The primary objective of this study is to investigate the effectiveness of a high‐performance thixotropic repairing cementitious mortar in improving the fatigue behavior of RC elements through a multiscale experimental approach. First, at the material scale of concrete specimens, two different concrete classes together with the repairing one‐component, pre‐blended, thixotropic cementitious mortar, were tested under incremental cyclic condition. Based on the results obtained from material scale, four reinforced concrete beams were exposed to different levels of accelerated corrosion by means of the impressed current technique and, subsequently, repaired by bonding a layer of the thixotropic high‐performance mortar onto the tension side. Finally, beams were tested under incremental cyclic four‐point bending test to investigate the fatigue behavior in terms of crack onset, propagation and energy dissipation. The resulting cyclic properties and cracking behavior of the structural elements were related to the level of corrosion achieved through the accelerated test and the effectiveness of the structural repair mortar was proven. In terms of code compliance, the repairing mortar was able to fulfill the requirements of frequent and quasi‐permanent combination of loads, remaining below all the threshold values provided by the Italian NTC2018 and Eurocode.

Reinforcement method of reinforced concrete beam by using non-stressing strand

Many methods can be used in the repair of bridges or other structural buildings. The aim is to increase the existing capacity. In the reinforced concrete beam structure, capacity of structural elements can be carried out by reinforcement method. The research was done by experimental loading test in laboratory. The test objects are consisted of 2 (two) reinforced concrete beams: a normal beam without reinforcement (NB) and a reinforcement beam by using non-stressing srand (RB1). The dimensions of the beams are 150mm x 300mm x 3200 mm. All beams are loaded by static-monotonic load until collapses. From the results of the research, the first yield load for the NB beam and RB1 beam respectively are 22 kN and 29kN. The deformations that occur at the conditions are 9.5mm and 14mm respectively. The collapse occurring on the NB beam is the bending collapse, whereas in the RB1 beam is a bending- shear collapse.

Upgrading of the recording system of complex loading testing machine

The effectiveness of experimental studies of the mechanical properties of materials and the reliability of the results obtained are determined by the technical level of testing machines. The stress-strain state of the object is monitored using recording sensors. The reading accuracy for the existing CL unit is 8%. However, this accuracy appeared insufficient when studying the developed plastic deformations. The problem of insufficient accuracy is partially related to the outdated recording system of the experimental setup, both when taking the results of the experiments and when managing the experiment. Getting of the reliable data upon complex loading is necessary to identify the reserves of the bearing capacity of structural elements in conditions of multi-parameter loading. All the experiments on a CL testing machine were carried out at room temperature. An additional amplifier of the electric signal of the strain gauge sensor was introduced to improve the accuracy of the readings of the recording system. The results of modernizing the recording system of the CL testing machine intended for static isothermal tests of tubular specimens are presented. The testing machine provides testing of the samples under axial tensile force and torque.

Experimental Assessment of the Cyclic Behaviour of RC-DP Beam to Column Joints

ABSTRACT Corrosion represents one of the most important problems affecting the global behaviour of reinforced concrete (RC) buildings; in presence of aggressive environmental conditions reinforcing steel bars, as well as concrete, suffer from relevant modifications of the mechanical performance. Steel rebars show a high decrease of the deformation capacity, with reduction of the elongation to maximum load up to the 50% in case of TempCore® grades. This can cause unexpected brittle failures related to the premature achievement of ultimate rotation or, even worst, shear capacity of structural elements. To mitigate these problems, actual European standards for constructions foresee the adoption of specific precautions such as the increase of concrete strength class, of the concrete cover, of higher diameter; these tools allow to reduce the effects of corrosion without deleting the origin of the matter. During the last years, otherwise, another typology of reinforcing steel – characterized by a typical Dual-Phase (DP) microstructure – was developed with the aim of directly preventing corrosion initiation. Due to their microstructure, in which martensite is embedded in the ferrite matrix, Dual-Phase steels are less exposed to corrosion; on the other hand, being characterized by a not-defined yielding stress-strain plateau, specific rules need to be elaborated for their employment in civil applications. In the present paper, the experimental test campaign performed on reinforced concrete internal and external joints with Dual-Phase steel rebars is deeply described together with results’ critical discussion. The paper is preparatory for the elaboration of technical models to be used in the design of RC-DP structures.

Improving the Carrying Capacity of Structural Elements of Vehicles by the Corrosive Strength Criterion

The problems of improving the accuracy of the definition of resistance to corrosive fatigue of the shafts of transmission gears, which operate under the effect of atmospheric precipitation and under variable complex loading (joint cyclical bend and torsion), were considered. According to the results of fatigue tests, the equations of the families of fatigue lines for the probability interval of no-failure P(N) = 50–99.9% were derived. The dependences to determining the coefficients of strength and durability in a wide interval of multicycle fatigue are obtained. The nomogram of these coefficients for a probabilistic estimate of the carrying capacity of the shafts at N = 105–108 cycles is given.

Modeling of corrosion-mechanical behavior of multi-element metal structures of transport works in real-world conditions

The article is part of the author’s dissertation research. Multi-element metal structures are widely used in the construction of transport structures (metal spans, trusses of railway bridges, overpasses, etc.). During operation, such structures are subjected to the joint effect of loads, temperatures, and corrosive media. In accordance with this, the task of predicting the behavior of such structures seems to be relevant. It consists in the development of effective models oriented to the calculation of the bearing capacity of structural elements subjected to corrosive wear. The article discusses the most common corrosion damage to metal multi-element structures of transport facilities, the classification of corrosion processes according to the nature of the surface destruction, the main types of metal elements and bridge structures. The main parameters characterizing the corrosive wear of metal structures were determined. Ways to account for the effect of aggressive environment on metal structures, i.e. well-known mathematical models and work, in which attention is paid to the problem of corrosion, wear modeling. The process of identifying corrosion wear models (determining unknown model coefficients) is described. The system of equations for determining the coefficients of a mathematical model of corrosive wear is given. The values of the coefficients of the models used to predict the behavior of structures, with a different choice of an intermediate point are given. A statically indefinable flat five-element truss of arbitrary cross section, part of the rods of which works in tension and part in compression is considered. For this design solves the problem of assessing durability. To solve this problem, use the corrected Euler method. The obtained numerical values of the durability of trusses of five rods, depending on the lengths of the rods.

Влияние виброобработки на сопротивление усталости и демпфирующую способность конструктивных элементов с остаточными напряжениями

Влияние виброобработки на сопротивление усталости и демпфирующую способность конструктивных элементов с остаточными напряжениями

On the Carrying Capacity of Structural Elements

On the Carrying Capacity of Structural Elements

Numerical estimation of concrete beams reinforced with FRP bars

This paper introduces numerical investigation on mechanical performance of a concrete beam reinforced with Fibre Reinforced Polymer (FRP) bars, which can be competitive alternative to steel bars for enhancing concrete structures. The objective of this work is being identified as elaborating of reliable numerical model for predicting strength capacity of structural elements with implementation of Finite Element Analysis (FEA). The numerical model is based on experimental study prepared for the beams, which were reinforced with Basalt FRP (BFRP) bars and steel bars (for comparison). The results obtained for the beams reinforced with steel bars are found to be in close agreement with the experimental results. However, the beams reinforced with BFRP bars in experimental programme demonstrated higher bearing capacity than those reinforced with steel bars, which is not in a good convergence with numerical results. Authors did attempt to describe the reasons on achieving experimentally higher bearing capacity of beams reinforced with BFRP bars.

Strength Assessment of Structural Elements

Reinforced concrete structures, built in the last century, are reaching end of their life span and need strength assessment for their continuous safe use. Strength assessment is also required with increase in loads due to change in use or increasing weight of applied loading. Quite often people use finite element programs based on linear elastic theory to assess the carrying capacity of structural elements. However, the real behaviour of reinforced concrete structures in the vicinity of failure is plastic. In this paper, assessment methods based on nonlinear finite element (NLFE) method (using DIANA) and yield line theory (following the hodograph approach) are explained. In addition, new yield line mechanisms for flat slabs supported on non-rectangular column grid are introduced and compared with experimental observations and NLFE predictions. Based on comparison between the predictions by NLFE and Yield line theory conclusions are made.

PREDICTION OF DAMAGE IN R/C SHEAR PANELS SUBJECTED TO REVERSED CYCLIC LOADING

In this paper, the damage prediction of shear-dominated reinforced concrete (RC) elements subjected to reversed cyclic shear is presented using an existing damage model. The damage model is primarily based on the monotonic energy dissipating capacity of structural elements before and after the application of reversed cyclic loading. Therefore, it could be universally applicable to different types of structural members, includeing shear-dominated RC members. The applicability of the damage model to shear-dominated RC members is assessed using the results from reversed cyclic shear load tests conducted earlier on eleven RC panels. First, the monotonic energy dissipating capacities of the panels before and after the application of reversed cyclic loading are estimated and employed in the damage model. Next, a detailed comparison between the analytically predicted damage and the observed damage from the experimental tests of the panels is performed throughout the loading history. Subsequently, the effects of two important parameters, the orientation and the percentage of reinforcement, on the damage of such shear-dominated panels are studied. The research results demonstrated that the analytically predicted damage is in reasonably good agreement with the observed damage throughout the entire loading history. Furthermore, the orientation and percentage of reinforcement is found to have considerable effect on the extent of damage.

Modelling of residual stress field in spherical mandrelling process

Fatigue life of structural elements with bolt holes depends mainly on residual stress distribution law around these holes. Residual compressive circumferential normal stresses around the hole reduce operating stress magnitudes to minimum values for cyclic tension and this enhances fatigue life and load-carrying capacity of structures. The presence of residual stresses is a result of the manufacturing process. Residual stresses can also be induced deliberately around the holes by means of appropriate working with suitably chosen parameters. Quantitative knowledge of residual stresses is necessary to model the stress field after applying an external load to a structural element in order to assess static or dynamic strength, fatigue strength including. This paper presents a combined approach consisting of experimental and numerical modelling of residual circumferential normal stress distribution when forming holes in workpieces of medium carbon steel by spherical mandrelling (SM). Since the object of study is residual macrostresses (stresses of first type), a mechanical method of their determination has been employed. On the basis of experimental outcomes, a mathematical model has been built and it predicts mean integral value distribution of residual circumferential normal stresses. Since the range of the experimental technique employed is limited by the wall thickness of the bushing being worked, numerical modelling of residual stresses by means of FE simulation has been performed. The numerical results obtained allow this mathematical model to be applied to various wall thicknesses by introducing correction factors for the polynomial coefficients. At the same time, the adequacy of the proposed FE model can be evaluated only by the experimentally obtained mathematical model. The SM efficiency for enhancing the load-carrying capacity of structural elements with cylindrical holes subjected to tension has been proved by means of FE simulation.

The effect of high-frequency vibrations on the load bearing capacity of tubular models in complex states of stress

The article presents the results of investigations of the resistance to plastic deformation of specimens of steel 40Kh, alloy D16, and copper Ml loaded by a complex arrangement by high-frequency vibrations of different intensity, internal pressure, and subjected to torsion within a wide range of rates; this made it possible to evaluate the load bearing capacity of structural elements with the highest reliability.

Supporting capacity of structural elements with energy treatment of low-cycle fatigue

A method is suggested for estimating the supporting capacity of structural elements when in the capacity of a physical criterion of low-cycle fatigue the specific energy of elastoplastic deformation is selected as an integral characteristic of the stressed-strained state. In implementing this method relationships for determining the theoretical and effective coefficients of energy concentration and the relative gradient for the change in energy in a notch with elastoplastic deformation are obtained. Criteria are formulated for the similarity of equally critical mechanical states for a standard (smooth) specimen and a structural element. A procedure is developed for predicting a parameter for material sensitivity to energy concentration. The supporting capacity of structural elements made of high-strength steel with a V-shaped notch is studied with the aim of substantiating the suggested experimental method.

Tlastoplastic properties of multicomponent composites

Predicting the inelastic properties of materials with random discontinuities is one of the most important current developments in the mechanics of deformable solids. Modeling the macroscopic governing relations and calculating the effective characteristics of such media in many cases permits satisfactory estimation of the strain properties, limiting state, and load-carrying capacity of structural elements made of composites, powders, and other types of structural materials. The macroscopic behavior of multicomponent rigid-plastic and elastoplastic composites was examined in [I, 2] within the framework of flow theory. Here, we examine the use of the method of generalized singular approximation of the theory of random fields to describe small elastoplastic strains of composite materials with an arbitrary number of constituents. A similar problem was solved in a correlation approximation in [3, 4]. Let a micro-inhomogeneous medium occupying a volume V bounded by the surface S be composed of n different elastoplastic constituents connected to each other with ideal adhesion~ The governing relations for the material of each constituent are given by the equations

Evaluation of corrosion effects by investigation of the supporting capacity of structural elements damaged by corrosion

Evaluation of corrosion effects by investigation of the supporting capacity of structural elements damaged by corrosion

Bench for studying the carrying capacity of structural elements in high-temperature gas flows

Bench for studying the carrying capacity of structural elements in high-temperature gas flows

Investigation of the influence of corrosion on the durability of gas-turbine blades

The use of gas-turbine engines in sea-going vessels makes it necessary to estimate the load-carrying capacity of structural elements under the influence of corrosive seawater. This investigation is concerned with the influence of high-temperature gas corrosion on the durability of gas-turbine blades. The blade work-conditions are modeled on a special dynamic gas apparatus. The tests are carried out on actual nozzle vanes made of the chromium-nickel alloy EI-868 (0.09% C; 0.46% Si; 0.25% Mn; 25. 58% Cr; 0.52% Ti; 0.94% Mo; 14% W; 0.23% Al; 2.85% Fe; remainder Ni). The vanes are tested in products of combustion of kerosene in air (with and without seawater salts), the temperature of the gas stream being cyclically varied within the limits 1050 reversible reaction 700 degree C. It is found that, in the presence of seawater salts in the gas stream, the oxide films lose some of their protective power and become discontinuous, which promotes more intense oxidation, scale formation and crack growth.

Raising the load-carrying capacity of structural elements

Raising the load-carrying capacity of structural elements

The Weight-Rearing Capacity of Structural Elements in Femoral Necks

The Weight-Rearing Capacity of Structural Elements in Femoral Necks