The paper presents the description of structure and the selected problems of the technical condition, as well as the strength analysis of the thin-walled reinforced concrete shell which has been making a covering of the main hall of the Gdynia Seaport Building through the last 80 years. The rectangle projection of four single curvature shells of the dome was shaped out of mutual perpendicular intersection of two cylindrical shells.
The analysis of the state of stress and deformations was carried out using the special model worked out in MES considering the combination of loads, the thermal ones included. For the long lasting loads (the deadweight of the dome), the computed results of static quantities were confronted with analytical results obtained according to F. Dischinger’s method. This method had been applied by the DYWIDAG Company in Berlin and its branch in Katowice (Poland) who designed the Gdynia Dome.
The computational analysis and the assessment of the technical state, along with laboratory pH tests of concrete, made it possible to carry out the overall evaluation of durability and safety of operation of the Gdynia Seaport Dome through the next decades.
Statistical conformity criteria for the compressive strength of concrete are a matter of debate. The criteria can have prejudicial effects on construction quality and reliability. Hence, the usefulness of statistical criteria for the small sample size n = 3 is questioned. These defects can cause a reduction in the quality of produced concrete and, consequently, too much risk for the recipient (investor). For this reason, the influence of conformity control on the value of the reliability index of concrete and reinforced concrete has been determined. The authors limited their consideration to the recommended standards PN-EN 206-1, PN-EN 1992 and ISO 2394 method of reliability index, which belongs to the analytical methods FORM (First Order Reliability Method). It assumes that the random variables are defined by two parameters of the normal distribution or an equivalent normal: the mean and the standard deviation. The impact of conformity control for n = 3 for concrete structures, designed according to the Eurocode 1992, for which the compressive strength of concrete is the capacity dominant parameter (sensitivity factor of dominating resistance parameter according to the FORM is 0.8), has been determined by evaluation of the reliability index.
Reinforced concrete composite slab consists of a thin prefabricated slab in which span reinforcement is located and of concrete joined with the slab, with such concrete being laid on site.
The existence of a joint of two concretes in such floors is interpreted as introducing a contact layer into a monolithic slab. In the paper parameters of two models are estimated. The first is a model of a contact layer and the second is a model of a composite slab with a single degree of freedom. The models consider that the contact has elastic properties and inelastic properties causing energy dissipation. Experimental investigations are discussed further based on which the parameters values of the contact layer model were determined.
Delamination was experienced for the slabs characterised by low contact layer stiffness after applying a maximum load. In addition, the strains of a contact layer having low stiffness are accompanied by lower energy dissipation than of a layer with high stiffness.
The smaller stiffness of composite floors, as compared to monolithic floors, occurs as a consequence of the existence of a joint. Such decrease for a composite slab is interpreted in the model with a single degree of freedom as the serial connection of stiffness of a monolithic slab and an element considering the existence of a contact layer.
The stiffness of an element considering the existence of a contact layer decreases along with a load, and the elements corresponding to the higher stiffness of the contact layer are characterised by higher energy dissipation.
The aforementioned results of the investigations confirm the assumptions of the contact layer model and a composite slab model with a single degree of freedom. The findings made represent a basis for establishing a method of evaluating the condition of a joint in composite slabs according to statistical investigations.
This study aims to evaluate the efficiency of strengthening reinforced concrete beams using some valid strengthening materials and techniques. Using concrete layer, reinforced concrete layer and steel plates are investigated in this research. Experiments on strengthening beam samples of dimensions 100x150x1100 mm are performed. Samples are divided in to three groups. Group “A” is strengthened using 2 cm thickness concrete layer only (two types). Group “B” is strengthened using 2 cm thickness concrete layer reinforced with meshes (steel and plastic). Group “C” is strengthened using steel plates. The initial cracking load, ultimate load and crack pattern of tested beams are illustrated. The experimental results show that for group A and B, the ultimate strength, stiffness, ductility, and failure mode of RC beams, with the same thickness strengthening layer applied, will be affected by the mesh type, type of concrete layer. While for group C, these parameters affected by the fixation technique and adhesion type.
This paper presents the possibility to apply numerical simulation in static analysis of reinforcedconcrete structure strengthened with carbon fibre reinforced polymer composite strips (CFRP).Reinforced concrete beams, with strengthening in form values CFRP made of carbon fibres andepoxy resin, featuring various width, as well as non-strengthened bent beams, were analysed. Thesimply supported beams arranged in a free support scheme were subjected to two concentratedforces within full range of loading (until collapse). The numerical analysis was performed throughapplication of the Finite Elements Method (FEM), and the calculation model applied took intoaccount the geometric and physical nonlinearity. The problem was solved by application of thequasi-staticstrategy method of calculations using ABAQUS software. While analysing the results,we focused on the run of changes in structure displacement and development of material damage,up to the point of destruction of the beam.
The present study has been taken up to emphasize the role of the hybridization process for optimizing a given reinforced concrete (RC) frame. Although various primary techniques have been hybrid in the past with varying degree of success, the effect of hybridization of enhanced versions of standard optimization techniques has found little attention. The focus of the current study is to see if it is possible to maintain and carry the positive effects of enhanced versions of two different techniques while using their hybrid algorithms. For this purpose, enhanced versions of standard particle swarm optimization (PSO) and a standard gravitational search algorithm (GSA), were considered for optimizing an RC frame. The enhanced version of PSO involves its democratization by considering all good and bad experiences of the particles, whereas the enhanced version of the GSA is made self-adaptive by considering a specific range for certain parameters, like the gravitational constant and a set of agents with the best fitness values. The optimization process, being iterative in nature, has been coded in C++. The analysis and design procedure is based on the specifications of Indian codes. Two distinct advantages of enhanced versions of standard PSO and GSA, namely, better capability to escape from local optima and a faster convergence rate, have been tested for the hybrid algorithm. The entire formulation for optimal cost design of a frame includes the cost of beams and columns. The variables of each element of structural frame have been considered as continuous and rounded off appropriately to consider practical limitations. An example has also been considered to emphasize the validity of this optimum design procedure.
A continuous contact layer exists between the top and bottom layer of concrete composite reinforced floors. The contact layer is characterised by linear elasticity and frictional properties. In this paper a model of single degree of freedom of composite floor is determined. The model assumes that the restoring forces and the non-conservative internal friction forces dissipating energy are produced within the contact layer. A hysteresis loop is created in the process of static loading and unloading of the model, with the energy absorption coefficient being defined on this basis. The value of the coefficient is rising along with the growing stiffness of the composite.
A critical damping ratio is a parameter describing free decaying vibration caused by non-conservative internal friction forces in the contact layer and in the bottom and top layer. The value of the ratio in the defined model is rising along with the lowering stiffness of the element representing contact layer.
The findings resulting from the theoretical analyses carried out, including the experimental tests, are the basis for the established methods of determining the concrete layer state for reinforced concrete floors. The method is based on energy dissipation in the contact layer.
In the recent years a tendency for design of increasingly slender structures with the use of high performance concrete has been observed. Moreover, the use of high performance concrete in tunnel structures, subject to high loads with possibility of extreme loads occurrence such as fire, has an increasing significance. Presented studies aimed at improving high performance concrete properties in high temperature conditions (close to fire conditions) by aeration process, and determining high temperature impact on the concretes features related to their durability. In this paper it has been proven that it is possible to obtain high performance concretes resistant to high temperatures, and additionally that modification of the concrete mix with aerating additive does not result in deterioration of concrete properties when subject to water impact in various form.
Recently, textile reinforced concrete (TRC) has been intensively studied for strengthening reinforced concrete (RC) and masonry structures. This study is to experimentally explore the effectiveness of application of carbon TRC to strengthen RC beam in flexure and shear. Concerning the cracks formation, failure modes, ultimate strength and overall stiffness, the performance of the strengthened beams compared to the control beams were evaluated from two groups of tests. The test results confirm that the TRC layers significantly enhance both shear and flexural capacity of RC beams in cracking, yielding and ultimate loads. All of the tested specimens were also modelled using ABAQUS/CAE software, in order to validate the experimental results. The numerical results show that the simulation models have good adaptability and high accuracy.
The paper presents a 3D model and simulations of corroding reinforcement bars in a concrete element. Electric potential distributions are calculated in the concrete matrix and on its surface for two rebars arrangements with one or three active (anodic) sites to assess the reliability and identify possible problems when standard test measurements for corrosion assessment in concrete structures are used and conclusion on the corrosion state is inferred. The values of the potential strongly depend on a concrete layer thickness and beyond the threshold of 5-7 cm it is hardly possible to detect the number of active sites on the rebar. Also conductivity – which is not constant in real world constructions – is an important factor. Thus without estimation of the state of concrete it is difficult to draw reliable conclusions on the corroding activity from shear potential measurements on the surface.
Paper presents the issue related to the selection of slab formwork taking into account the criteria that are currently the most important The in the process of the construction project execution. The analysis included selected, modern system solutions, which significantly accelerate the tempo of reinforced concrete works and, as a consequence, increase the effectiveness of the construction project execution. The innovative system of drop heads, which the analysed slab formwork is equipped with, is offered by various formwork producers. The offered solutions, however, differ not only in the construction of the drophead itself, but also in the arrangement and variety of other system elements, as well as the scheme of their operation, which may ultimately significantly affect the effectiveness of their application. For that reason, the choice of formwork for specific buildings should be made from among carefully analysed several variants of the wide market offer. The paper presents the results of analysis and evaluation of formwork systems with dropheads according to the proposed methodology, including multi-criteria analysis.
This paper presents probabilistic assessment of load-bearing capacity and reliability for different STM of beams loaded with a torsional and bending moment. Three beams having different reinforcement arrangement obtained on the basis of STM but the same overall geometry and loading pattern were analysed. Stochastic modelling of this beams were performed in order to assess probabilistic load-bearing capacity. In the analysis, the random character of input data - concrete and steel was assumed. During the randomization of variables the Monte Carlo simulation with the reduce the number of simulations the Latin Hypercube Sampling (LHS) method was applied. The use of simulation methods allows for approximation of implicit response functions for complex in description and non-linear reinforced concrete structures. On the basis of the analyses and examples presented in the paper, it has been shown that the adoption of different ST models determines the different reliability of the analysed systems and elements.
The scope of the paper is to investigate analytically and determine experimentally the shear resistance of low height reinforced precast concrete lintels. The chosen procedures included in national and international standards applied for the design of structural concrete elements to an estimation of shear behaviour of reinforced concrete elements are described. The characteristic and designed shear strength of precast concrete lintels are determined and compared with experimentally obtained results. The shear resistance for precast concrete lintels was determined by laboratory tests according to a European standard. The assessment of the in-situ compressive strength of concrete in precast concrete lintel is specified. The designed compressive strength class is confirmed. The real reinforcement distribution is verified to assess the wide scatter of experimentally obtained failure forces. A short literature outlook of the papers concerning investigations on lintels and shear resistance of concrete is given also. The paper can provide scientists, engineers, and designers a theoretical and experimental basis in the field of precast concrete lintels shear resistance.
This paper outlines a method of determining the deformation and strength parameters for a hypothetical, homogeneous, substitute material which approximates the properties of heterogeneous materials in reinforced concrete elements. The model of the substitute material creates a concrete reference model, in which the static - strength - deformation parameters were modified on the basis of the homogenizing function with the homogenization coefficient assumed as the effective reinforcement ratio of the reinforced concrete structural elements. The results of the comparative analysis of the numerical models using the hypothetical substitute material with experimental results for statically loaded beams and deep beams taken from the literature are presented.
Reinforced concrete is one of the most widely used structural components about which much scientific research has been conducted; however, some of its characteristics still require further research. The main focus of this study is the effect of direct fire on the shear transfer strength of concrete. It was investigated under several parameters including concrete strength, number of stirrup legs (the steel area across the shear plane), and fire duration. The experimental program involved the testing of two sets (groups) of specimens (12 specimens each) with different concrete strengths. Each set contained specimens of two or four stirrup legs exposed to direct fire from one side (the fire was in an open area to simulate a real-life event) for a duration of one, two, and three hours. The results of the comparison showed the importance of using high-performance concrete (instead of increasing the number of stirrup legs) to resist shear stress for the purpose of safety. A significant reduction in shear strength occurred due to the deterioration of the concrete cover after three hours of direct fire exposure.
The level of degradation of reinforced concrete bridges was evaluated based on the in-situ measurements performed on five reinforced concrete bridges under service located in the Czech Republic. The combined effect of carbonation and chlorides with respect to the corrosion of steel reinforcement, namely the pH and the amount of water-soluble chlorides, were evaluated on drilled core samples of concrete. Based on these parameters, the ratio between the concentrations of Cl– and OH, which indicates the ability of concrete to protect reinforcement, was calculated. All the data were statistically summarized and the relationships among them were provided. The main goal of this study is to evaluate the non-proportional effect of the amount of chlorides per mass of concrete on the risk of corrosion initiation and to localize the “critical” locations in the bridges that are the most affected by the degradation effects.