An experimental study of cathodic protection for chloride contaminated reinforced concrete

Cathodic protection (CP) is being increasingly used on reinforced concrete structures to protect steel reinforcing bars from corrosion in aggressive conditions. Due to the complexity of environmental conditions, the design specifications in national and international standards are still open to discussion to achieve both sufficient and efficient protection for reinforced concrete structures in engineering practices. This paper reports an experimental research to investigate the influence of chloride content on concrete resistivity, rebar corrosion rate and the performance of CP operation using different current densities. It aims to understand the correlation between the chloride content and concrete resistivity together with the CP current requirement, and to investigate the precision of the CP design criteria in standards

Seismic response of steel frames with knee braces

The use of steel bracing systems for upgrading seismically insufficient structures is a feasible solution by enhancing the global stiffness and strength of such structures. Moreover, steel bracing systems have relatively low cost and easy construction phases. For this purpose, several configurations of steel bracing systems can be applied for upgrading the seismic behavior of the structures. The most frequently utilized systems comprise concentrically-braced frames, eccentrically-braced frames, and knee-brace frames [1]. In the last few decades, the seismic behavior and design of new steel structures with knee bracing systems has been studied extensively due to its efficiency as an earthquake resisting system [2-8]. Indeed, the structures with knee bracing can be designed to be stiff enough to control structural and nonstructural damage, and ductile enough to prevent sudden collapse. In order to achieve these purposes, the lateral stiffness is provided by the brace elements and ductility by the knee elements through the formation of plastic behavior for dissipation of the energy under earthquakes. In the current study, apart from the studies in the literature, the effectiveness of using different types of knee bracing systems, such as chevron, cross and diagonal knee bracing systems for enhancing the seismic response of the existing steel moment resisting frame systems were comparatively examined through nonlinear time history analysis

Rotation capacity and overstrength of steel beams: evaluation of prediction models

The ductility is the structure’s ability to sustain large deformations in plastic range without considerable loss of strength. The design concept based on the ductility properties of structures is the principle method to assure for an appropriate structural behavior against strong ground motions. The capacity to predict required and available ductility under severe loads is a key-point in earthquake design. The actual progress in this problem is given by the possibility to prove the ductility of the structure at the same level as for rigidity and strength. Unfortunately, in present design specifications, there are only vague provisions relating to the evaluation of the structure ductility, mainly based on cross-section classes. However, the actual ductility is affected by the properties of full member [1]. In this regard, the knowledge of the rotation capacity and flexural ultimate resistance of the steel member is of prime importance for an appropriate application of hierarchy criteria in seismic design of structures [2]. In this paper, a critical review of the existing prediction models for the rotation capacity and flexural overstrength factor for the steel members with a wide range of cross-section typologies is presented. Moreover, the description of rotation capacity and overstrength factor in current design codes is discussed comparatively

Seismic Upgrading of Steel Moment-Resisting Frames by Means of Friction Devices

In recent decades, several passive energy dissipation systems have been conceived in order to minimize the damage in structural and non-structural components of either new or existing buildings. In this study, the use of friction damped tension-compression diagonal braces for seismic upgrading of a steel moment resisting frames is investigated. To this aim, nonlinear time history analyses have been carried out on a set of representative frames with and without friction damped braces. In the nonlinear time history analyses, two sets of natural accelerograms compatible with seismic hazard levels of 10% and 2% probability of exceedance in 50 years have been considered. Under these records, the structural response has been comparatively investigated in terms of the maximum inter-storey drift ratio, maximum storey acceleration, residual drift ratio and displacement demand for the friction device. The results clearly highlighted that the application of friction damped braces allows reducing the damages to the main structural elements, thus significantly improving the seismic behaviour of the frame

Analytical prediction of available rotation capacity of cold-formed rectangular and square hollow section beams

In this paper, a soft-computing based study aimed to estimate the available rotation capacity of cold-formed rectangular and square hollow section (RHS-SHS) steel beams is described and novel mathematical models based on neural network (NN) and genetic expression programming (GEP) are proposed. In order to develop the proposed formulations, a wide experimental database obtained from available studies in the literature has been considered. The data used in the NN and GEP models are arranged in a format of eight input parameters covering both geometrical and mechanical properties such as width, depth and wall thickness of cross section, inside corner radius, yield stress, ratio of modulus of elasticity to hardening modulus, ratio of the strain under initial hardening to yield strain and shear length. The accuracy of the proposed formulations is verified against the experimental data and the rates of efficiency and performance are compared with those provided by analytical semi-empirical formulation developed by some of the Authors in a previous study. The proposed prediction models proved that the NN and GEP methods have strong potential for predicting available rotation capacity of cold-formed RHS-SHS steel beams

Prediction of the flexural overstrength factor for steel beams using artificial neural network

The flexural behaviour of steel beams significantly affects the structural performance of the steel frame structures. In particular, the flexural overstrength (namely the ratio between the maximum bending moment and the plastic bending strength) that steel beams may experience is the key parameter affecting the seismic design of non-dissipative members in moment resisting frames. The aim of this study is to present a new formulation of flexural overstrength factor for steel beams by means of artificial neural network (NN). To achieve this purpose, a total of 141 experimental data samples from available literature have been collected in order to cover different cross-sectional typologies, namely I-H sections, rectangular and square hollow sections (RHS-SHS). Thus, two different data sets for I-H and RHS-SHS steel beams were formed. Nine critical prediction parameters were selected for the former while eight parameters were considered for the latter. These input variables used for the development of the prediction models are representative of the geometric properties of the sections, the mechanical properties of the material and the shear length of the steel beams. The prediction performance of the proposed NN model was also compared with the results obtained using an existing formulation derived from the gene expression modeling. The analysis of the results indicated that the proposed formulation provided a more reliable and accurate prediction capability of beam overstrength