Selection of ground motion prediction equations for probabilistic seismic hazard analysis based on an improved fuzzy logic

The fuzzy logic method has been used widely in civil and earthquake engineering, but there is no comprehensive point of view for utilizing fuzzy approach in order to obtain ground motion prediction equations (GMPEs) for probabilistic seismic hazard analysis (PSHA). Hence, fuzzy magnitude–distance method as a new approach for choosing GMPEs in the process of PSHA, is developed in this research through the selection of the ruling peak ground acceleration (PGA) of each common cell (the combined cell of earthquake intensity and site to source distance). The presented method reduces the need for engineering judgments in seismic analysis based on a newly developed benchmark. It enables designers to not only determine the range of acceptable fuzzy results but also introduces a concept which ensures the selection of initial well-suited GMPEs for the analysis

An Iterative Two-step Lagrangian-based Method for Evaluation of Structural Reliability Index

In structural reliability analysis, Hasofer-Lind and Rackwitz-Fiessler (HL-RF) method is a widely used approximation method for evaluating the reliability index. However, by increasing the nonlinearity or complexity in the limit state function of a structure, HL-RF may get in trouble for convergence. This paper represents an iterative algorithm that tries to minimize the Lagrange function, associated with the reliability problem. In each iteration of this method, two steps are followed, to satisfy the minimization condition and the existing constraint. In the first step, a movement for minimization in a descent direction is followed. In the second step, another search direction contributes to approach limit state surface, and therefore the next iteration can start from the vicinity of the surface. Employing Lagrange reliability function and limit state function simultaneously in the proposed two-step Lagrangian-based method (TSLB) can help to control the numerical instability in highly nonlinear problems. The accuracy and robustness of the proposed algorithm are shown in illustrative examples of the literature

Classification of Precast Concrete Segments Damages during Production and Transportation in Mechanized Shield Tunnels of Iran

Precast concrete segments used in shield tunnel linings are prone to damage in many situations. These damages can occur at different stages such as fabrication in segment factory, transportation to tunneling site, during tunneling process, and at serviceability stage. The aim of the present article is to study the damages inflicted on concrete segments during production and transportation, and to present a new classification of these damages throughout the two stages.  The developed classification is based on field observations and examinations of major subway and water conveyance mechanized shield tunnels of Iran, located in Tehran, Tabriz, Mashhad, Kermanshah (Nosood) and Isfahan (Golab). The quality of tunnel lining suffers from what, as a direct consequence of any damage to concrete segments, during production and transportation, which will be also discussed in this article. For further investigation, more than 250 concrete segments from Tehran subway line 3 and 350 segments of concrete segments from Tehran subway line 7 were selected and studied for a statistical analysis of chipping and crack, consecutively.  Absence of preventive measures to limit segment damages in precast segment factories is one of the main reasons for increased number of damaged concrete segments, and as a result, increased costs of tunnel construction at later stages. In this paper, production phase damages and factors contributing to these damages are studied. According to the findings of the study, the human (operator) error was the most important cause for chipping, and, time-dependent behavior of concrete was the essential reason in crack of precast segments. Eventually, final section of the article presents practical solutions for reduction of damages during fabrication and transportation of concrete segments

Simulation of the Behavior of Corrosion Damaged Reinforced Concrete Beams with/without CFRP Retrofit

Harsh environmental conditions along with aggressive chemical agents are known as one of the main reasons behind damages observed in reinforced concrete members. Corrosion of reinforcement worldwide is one of the leading causes of damages occurred in reinforced concrete over the lifespan. There are many critical energy and transportation infrastructures located on coastal regions exposed to high humidity and chloride content where they are highly prone to reinforcement corrosion. This calls for retrofit methods, which safeguard not only the strength but also the durability of corrosion deteriorated reinforced concrete structures. Carbon fiber polymers considering their mechanical and chemical properties are recognized as one of the main retrofit techniques. In this study, the influence of different levels of corrosion on the structural behavior of reinforced concrete beams is studied. ABAQUS software package is employed to simulate the nonlinear behavior of reinforced concrete beams with tensile reinforcements and stir-ups corrosion degrees of 20% and 40%. The structural behavior of original damaged specimen as well as the same specimen strengthen with carbon fiber reinforced polymer (CFRP) is studied. The purpose of the retrofit is compensate for the loss of shear and flexural capacity of the member due to corrosion. Different variants for the arrangement of CFRP strips are studied and compared. The result of the current research further uncaps the efficiency of fiber polymers to secure strength and durability of corrosion damaged reinforced concrete members

Time-dependent Seismic Performance Assessment of Corroded Reinforced Concrete Frames

In this study, effects of reinforcement corrosion such as reinforcement cross section reduction, steel yield strength and concrete compressive strength reduction on RC member capacity decrease are studied. Next, a two-dimensional reinforced concrete moment resistant frame is modeled to evaluate the effects of moderate and severe intensity corrosion on moment-curvature behavior of elements and structure seismic response under nonlinear analysis. Structure capacity curves in push-over analysis and failure curves resulted from IDA for both the structure without and with corrosion are obtained and the effects of reinforcement’s corrosion on the reinforced concrete frame seismic performance are determined through comparing the results. The results revealed that in terms of amount, place and type of corrosion in the reinforced concrete frame, value of the reduction resisting moment of elements is different. Furthermore, the outcomes of nonlinear analyses showed that the capacity of structure is reduced and its seismic performance level is changed as a result of corrosion

Nonlinear finite element analysis of normal and high strength concrete structures

This thesis presents a new hypoelasticity model which was implemented in nonlinear finite formulation to analyze normal and high strength reinforced concrete structures under both monotonically increasing and reversed cyclic loadings. The model includes a new hypoelasticity constitutive relationship utilizing the rotations of material axis through subsequent iterations, employment of both fixed and rotating crack models, compressive strength degradation in post-cracking regime, new uniaxial stress-strain relationships for concrete under monotonically increasing and reversed cyclic loadings, accounting for mesh sensitivity, and utilizing the tensile strength degradation due to extensive internal microcracking of the concrete. The model can account for high nonlinearity of the stress-strain behaviour of concrete in the pre-peak regime, the softening behaviour of concrete in the post-peak regime, the stiffness degradation caused by the extension of microcracks during subsequent unloadings and reloadings and the irrecoverable volume dilatation at high levels of compressive load.The effect of element size on different behavioural aspects of reinforced concrete elements including the load-displacement and load-strain characteristics, crack pattern and ultimate load are discussed along with a comparison with the experimental data where available. Various analyses indicated that the length of the descending branch of the tensile stress-strain curve of concrete defined by the value of the ultimate tensile strain, $varepsilon sb{ rm tu}$, has a significant effect on the computed results. If the value of $varepsilon sb{ rm tu}$ is adjusted appropriately according to the element size, it can help eliminate the mesh sensitivity drawback. To adjust an appropriate value for $varepsilon sb{ rm tu}$, two models have been used: (a) crack band model, as a function of the fracture energy, mesh size and tensile strength of concrete, and (b) a new proposed model as a function of only the element size. The analytical results obtained using the different models are compared with the experimental results; the proposed model gives good agreement. The proposed formula is very simple and can be used for both square and non-square elements.The effect of steel reinforcement details on the general behaviour of the structure and its mode of failure, the criterion for using the rotating crack model versus the fixed crack model, and the importance of compressive strength degradation in the post-crack regime are established using detailed analysis of five shear panels tested by Vecchio and Collins (1982). The effect of a sudden drop of the stress after the tensile strength of concrete has been exceeded on the load-deflection response, the ductility ratio and the crack pattern for two high strength concrete beams are also examined. Further analyses of a squat shear wall and a shear panel are carried out to examine the reliability of the computer program HODA developed in this study for analysis of concrete structures under both monotonic and reversed cyclic loads.Complete response of three structural walls in a low-rise building is studied under monotonically increasing loads until failure using the nonlinear finite elements program HODA. The influence of the tension-stiffening, steel strain-hardening on the load-deflection response and the ultimate load are studied for the case of the rectangular wall. The influence of smeared steel idealization and bar elements idealization on the wall response are also investigated. The ultimate loads of walls are compared with the values calculated using the current CSA Standard CAN3-A23.3-M84. (Abstract shortened by UMI.

Estimation of Corrosion Occurrence in RC Structure Using Reliability Based PSO Optimization

In this study, meta-heuristic approach of two types of Particle Swarm Optimization (PSO) method is used to calculate corrosion occurrence probability, due to chloride ions penetration and carbonation. The models' eciency is verified by comparing with available examples in technical literature and results of Monte Carlo analysis. According to the analyzes performed, using different probabilistic distributions regardless of probabilistic moments based on real distribution, lead to diverse results. In addition, influence of each eective parameter on corrosion occurrence varies by changing other parameters and by time The eect of concrete cover (d) reduces at corrosion initiation and the corrosion threshold (Cth) slightly increases over time. Almost, the concrete cover is the most important factor, and the corrosion threshold is also the least important factor. The influence of chloride concentration amount at surface (Cs) increases over time, in a way that, it becomes the most important parameter in low-quality concretes after several years. Thus, the precise amount of Cs is of great importance in exact estimation of corrosion and durability design

Evaluation of Advanced Nonlinear Static Procedure

Having very simplicity, nonlinear static procedures (NSPs) are the most popular tools for estimation of structural capacity. These approaches construct a graphic display of the overall structural response via a pushover curve. The overall response of the system provides a direct simulation of the building as single degree of freedom (SDOF) system that simplifies the design and evaluation of the structure. In this research, the first step in any nonlinear static analysis or in other words perform a pushover analysis has been studied. Applied lateral load to the structural model not only affects the overall responses of the structure through structural capacity curve, but also directly affects the local responses of the structure. In order to evaluate these lateral loads, steel buckling restrained braced frame structures are examined by advanced modal pushovers. Next, the results of these pushover analyses will be compared with nonlinear time history analysis as the most accurate method. Finally, the most efficient method in this particular structure is introduced. The analysis conducted in these structures shows that the lateral load pattern based on story shears offers a good prediction of the maximum response of the concentrically buckling restrained braced frame buildings

Reinforced concrete columns strengthened with near-surface mounted and hybrid FRP under compression with or without eccentricity: Experimental study and finite element modeling

The utilization of FRP in strengthening of reinforced concrete (RC) columns has garnered significant attention in the past two decades. Researchers have proposed the use of near-surface mounted (NSM) FRP bars with (hybrid) or without FRP jackets alongside the conventional approach of column strengthening through jacketing particularly in the presence of load eccentricity. In the realm of static loading scenarios, a significant focus has been directed toward the evaluation of the NSM, jacketing, and hybrid methodologies, while comparatively less attention has been given to the impact of various parameters on the capacity. In this article, a total of 22 RC column specimens with medium slenderness were tested under axial compressive loads with or without eccentricity to study the effect of the parameters the number and type of NSM FRP bar, the number of layers and type of FRP jacket, and the groove size for FRP bar mounting. The experimental results reveal the beneficial effects of using FRP jackets, increasing their layers and groove dimensions, and augmenting the number of NSM FRP bars on column capacity and ductility up to 36% and 197% respectively. Additionally, an accurate Finite element model has been developed and role of corbel in eccentricity application is investigated. The results showed that the corbel is not capable of transmitting the desired eccentricity