Petr Štěpánek

Optimized Design of Concrete Structures considering Environmental Aspects

This contribution describes a formulation of the optimized design of structures using the probability-based optimization method. The Monte Carlo simulation method, modified by the Latin Hypercube Sampling (LHS) method, was used for the calculation of the reliability of a designed structure. Efficient design procedures can achieve not only cost savings during construction (materials and energy), erection, servicing, maintenance, disassembly and material recycling but also a more favourable environmental impact. To find the best possible design for a structure an original optimization method was used. Therefore, the economical and ecological aspects (acquisition costs, CO2 and SO2 emissions and embodied energy associated with concrete member production) were taken into account in the objective function. A design example – a prestressed spun concrete pole made from reinforced concrete or alternatively from reinforced fibre concrete is presented.

Shear Resistance of Concrete Beams with FRP Grating as a Shear Reinforcement

This paper presents an experimental study on the shear behavior of concrete beams with fiber-reinforced (FRP) composite grating as shear reinforcement. Corrosion resistance and non-magnetic properties of FRP reinforcement allows its use in places where application of regular steel reinforcement would face difficulties. The use of FRP composites can increase the life span of constructions and reduce its maintenance costs. Shear stirrups are more susceptible to harsh conditions, due to their placement at the outer face of the reinforcement, and the use of FRP materials can lead to lower concrete cover thickness and therefore to a more effective design of an element. FRP reinforcements are highly anisotropic material with low strength in the direction perpendicular to the fibers. This causes the strength of a FRP stirrup to be limited by its strength in the bends (corners) of a stirrup. The tensile strength in the corner of the bent stirrup is around 40 to 60% of the strength of the straight bar. FRP grating doesn’t contain a bent section limiting its strength, but its behavior as a shear reinforcement is unknown. The paper contains the results of own experimental research on concrete beams with shear reinforcement made of FRP gratings done at the Faculty of Civil Engineering at the Brno University of Technology. Test specimen consisted of nine beams with different shear reinforcement ratios. Presented experimental data are then compared with the results of tests on beams with regular shear FRP stirrups found in literature.

Bond Behavior of FRP Bars in Concrete

This article deals with the bond of internal composite (FRP) reinforcement with different surface treatments. Bars with additional sand-coating exhibit different behavior due to different transmission of forces in relation to bars with ribbed surface. To compare the bond behavior of these types of reinforcement, an experimental program consisting of several sets of pull-out tests was designed. This test configuration was chosen primarily for simplicity, comparability with previously published results, and especially easy modification for assessment the effect of concrete cover thickness. The paper presents the results confirming the direct influence of the surface treatment and also the position of the reinforcement on the resulting bond behavior.

Stochastic Optimization of a Reinforced Concrete Elements Using Heuristic Algorithm

It is possible to see various applications of mathematical optimization in civil engineering (structural design, reconstruction of transportation networks etc.) Initially, deterministic approaches have been introduced to solve these problems. But despite their complexity, these approaches are insufficient to comprehend the probabilistic nature of said problems and thus provide only suboptimal solutions. Hence the effort comes to reconsider these deterministic approaches and deal with uncertainties involved in said problems in less straightforward way. The goal of the paper is to present the algorithm for stochastic optimization of design of steel-reinforced concrete cross-section. This algorithm is based on internal cycle of deterministic optimization using reduced gradient method and external cycle of stochastic optimization using regression analysis. Firstly, the deterministic problem is introduced and described. It is followed by the description of uncertainties, which are involved in the process, and stochastic reformulation of the problem. Then the algorithm itself is introduced and the paper ends with presentation of the results of performed calculations.

Assessment of Lightweight Concrete-to-Concrete Interface Shear Resistance

Different test setups were developed and standardized for the assessment of concrete–to–concrete interface shear resistance. One of the most frequently used is slant shear test, because of its simplicity, sensitivity to the surface roughness and the fact, that the effects of friction can be obtained.

Strut-and-Tie Model for Predicting the Punching Shear of Flat Slabs with Shear Reinforcement

The purpose of this paper is to describe a framework of the proposed method for predicting the punching shear of flat slabs with shear reinforcement. The proposed method is based on a strut-and-tie model. Current methods of predicting the punching shear strength of flat slabs could be divided into these categories: models based on empirical equations, physical models, analytical methods and finite element methods. Most of the current codes in force would be best described as empirical formulations. Physical model for prediction of punching shear is described in Model Code 2010. Proposed method for flat slabs with shear reinforcement is based mainly on a strut-and-tie model and therefore could be considered as an analytical method.For the purpose of demonstrating the effectiveness of the proposed method, the method is compared with some of the main methods currently in use, such as Eurocode EC2, American code ACI 318 and Model Code 2010. The comparison consists of results of more than 98 experiments of punching shear on the flat slabs with shear reinforcement, gathered from publications from all around the world.

Determination of Surface Roughness Parameters by Optical Profilometry and Sand Patch Test

In cases when two concrete parts are cast against in different times are not connected by dowels, main contributors to the resistance are cohesion and friction. Shear resistance of the interface is highly dependent on surface treatment and its roughness. In this paper, besides the review of available methods of surface roughness determination, the optical profilometry will be introduced and described. Optical profilometry represents non-contact and non-destructive method for characterizing surface topography. Furthermore, results obtained by abovementioned method will be compared with Sand Patch Test, in order to determine its usability and limitations.

A Method to Predict the Punching Shear Strength of Flat Slabs with Shear Reinforcement Using a Strut-and-Tie Model

The use of flat slabs in constructions due to its many functional and economic advantages is wide-spread. Behavior of flat slabs in shear and flexure is a fairly complex problem. Therefore, the punching shear failure belongs to one of the most critical aspects in the design of concrete buildings.The purpose of this paper is to describe a framework of the proposed method for predicting the punching shear of flat slabs with shear reinforcement. Most of the current codes in force are mainly based on empirical formulation. The proposed method is based on a strut-and-tie model and therefore could be considered as an analytical approach. For the purpose of demonstrating the effectiveness of the proposed method, the method is compared with some of the main methods currently in use, such as Eurocode EC2, ACI 318 and Model Code 2010. The comparison consists of results of more than 90 experiments on flat slabs with shear reinforcement, gathered from publications from all around the world.

The Strengthening of Reinforced Concrete Structures

The contribution deals with a method of strengthening reinforced concrete structures. It focuses on the use of non-bonded steel tendons for beams and plates. The strengthening of columns with the help of steel bandages is discussed too. The behaviour of the strengthened items is described, as well as the practical design issues involved. The article also provides information on practical experience gained during the application of the strengthening method.Other possible applications for the strengthening method are discussed, such as the use of materials based on FRP (fibre reinforced polymer), and especially those based on glass.

An Engineering Heat and Mass Transport Model Utilized for Concrete at Fire

Mathematical models which can sufficiently describe processes proceeding in concrete during fire play an important role when assessing a load bearing capacity of concrete structures. In this paper a coupled heat and mass transport model based on principles of conservation of mass and energy is presented. A 2D computational solver using FEM was created to find three unknowns – a temperature, an amount of free water and a magnitude of pore pressure in concrete cross section during rapid heating. These variables, mutually connected through state equation, are necessary not only for determination the load bearing capacity of concrete element but also for prediction of concrete spalling. A parametric study of numerical results influenced by material properties of concrete (e.g. permeability, thermal conductivity) and initial conditions (e.g. relative humidity, temperature) is introduced and discussed in the end.