Experimental Analysis of Bolted Steel Beam-to-Column Connections: Component Identification

In this paper, the results of an experimental program dealing with the ultimate behavior of bolted beam-to-column connections under cyclic actions are presented. The design criteria adopted for tested specimens are discussed in detail, aiming to point out how the ultimate behavior can be governed by properly strengthening the components for which yielding has to be prevented. To this scope, the component approach is adopted as a design tool for component hierarchy criteria. The aim of the paper is the investigation of the actual possibility of extending the component approach to the prediction of the cyclic response of beam-to-column joints. To this scope, the attention has been focused on the possibility to evaluate the overall energy dissipation capacity starting from the energy dissipation of the single joint components, provided that they are properly identified and their cyclic behavior is properly measured.     

NONLINEAR ANALYSIS OF REINFORCED CONCRETE SHEAR WALL UNDER EARTHQUAKE LOADING

A constitutive model for predicting the cyclic response of reinforced concrete structures is proposed. The model adopts the concept of a smeared crack approach with orthogonal fixed cracks and assumes a plane stress condition. Predictions of the model are compared firstly with existing experimental data on shear walls which were tested under monotonic and cyclic loading. The same model is then used in the finite element analysis of a complete shear wall structure which was tested under a large number of cyclic load reversals due to earthquake loading at NUPEC's Tadotsu Engineering Laboratory. Two different finite element approaches were used, namely a two-dimensional and a three-dimensional representation of the test specimen. The ability of the concrete model to -reproduce the most important characteristics of the dynamic behaviour of this type of structural element was evaluated by comparison with available experimental data. The numerical results showed good correlation between the predicted and the actual response, global as well as local response being reasonable close to the experimental one.     

Predictive Tri-Linear Benchmark Curve for In-Plane Behavior of Adobe Walls

In the present study, numerical simulations are conducted to estimate the in-plane response of adobe walls subjected to pseudo-static cyclic loading based on the finite element code ABAQUS. The simplified micro-modeling approach is adopted and an interface model reported in ABAQUS material library is applied as material model for zero-thickness interface elements. The comparison between obtained results and field test data results in good agreement. Parametric studies are carried out to evaluate the effectiveness of independent parameters changes on response of adobe walls. It is noted that mechanical properties of joints and adobe units play an active role on in-plane behavior of walls. A tri-linear benchmark curve is proposed to predict the response of aforementioned walls. In this regard, a statistical study is performed to derive the predictive tri-linear benchmark curve. The regressive analysis on 59 numerical models resulted in proposing predictive models. Finally, by comparing tri-linear curves obtained from the regressive analysis, numerical analysis, and experimental study, appropriate accuracy of theoretical model can be found.     

Estimating the Seismic Performance of CFRP-Retrofitted RC Beam-Column Connections Using Fiber-Section Analysis

Over the past two decades, many experimental techniques have been developed to improve the efficiency of the externally-bonded fiber-reinforced polymers (FRPs) in order to improve the structural performance of reinforced concrete (RC) beam-column connections. Numerical analysis is also being used as a cost-effective tool to predict the experimental results and to further investigate the parameters that are beyond the scope and capacity of experimental tests. In this study, at first, a fiber-section modeling approach is developed for estimating the seismic behavior of RC beam-column connections before and after application of FRP retrofits. The accuracy of the analysis results were validated against a series of the available experimental data under both monotonic and cyclic loadings. It was pointed out that the proposed model can predict the strength and displacement of un-retrofitted and FRP-retrofitted RC beam-column connections up to the failure points. The verified model was then used to perform a parametric study pertaining to the effect of longitudinal reinforcement ratio on the efficiency of the adopted FRP retrofitting technique to improve the structural behavior of RC beam-column connections.     

Hysteretic Model for Flexure-shear Critical Reinforced Concrete Columns

A model for predicting the cyclic lateral load-deformation response of flexure-shear critical reinforced concrete (RC) columns subjected to combined axial load and cyclic shear is proposed. Strength deterioration in the primary curve due to the effect of shear after yielding is considered by a modification coefficient. Rules for unloading and reloading branches of the hysteretic curve are obtained from regression analysis of test results. Unloading stiffness is fitted as a function of displacement ductility and secant stiffness of the point with maximum displacement in the primary curve. Pinching is simulated by changing the slope of reloading branch. Path-based cyclic strength deterioration is incorporated in the proposed model. In the expression of cyclic strength deterioration, the effects of aspect ratio and axial-load ratio are considered. Comparison between the predicted cyclic response and experimental results indicates that the proposed model can predict the observed hysteretic response of flexure-shear critical RC columns well.     

COUPLED P-Y T-Z ANALYSIS OF SINGLE PILES IN COHESIONLESS SOIL UNDER VERTICAL AND/OR HORIZONTAL GROUND MOTION

Various approaches are currently used for the analysis of piles under vertical and lateral loading. Among these, the beam-on-a-nonlinear Winkler foundation (BNWF) approach using published P-y, T-z and Q-z curves is widely used in practice. In this approach, the P-y and T-z responses are generally uncoupled from each other. The objective of this paper is to investigate the influence that the coupling of the P-y and T-z responses has.on the cyclic and dynamic response of piles in cohesionless soil. A cyclic model is first developed and a parametric study is conducted to investigate the effect the initial confining pressure, angle of wall friction and effective vertical stiffness have on the lateral cyclic hysteretic response. A dynamic model is then developed, and used to study the response of a single pile in cohesionless soil under horizontal and/or vertical ground motion. Results from the parametric study showed that the three parameters did not have a significant influence on the lateral cyclic hysteretic response. Under horizontal and/or vertical ground motion, the horizontal ground motion was observed to dominate the inertial interaction response, and significantly affected both the horizontal and vertical displacement response, mainly due to second-order P-Δ and gapping effects.     

Beam-Column Joint Model for Nonlinear Analysis of Non-Seismically Detailed Reinforced Concrete Frame

An efficient and simplified plane beam-column joint model that can describe the strength deterioration, stiffness degradation, and pinching effect was developed for the nonlinear analysis of non-seismically detailed reinforced concrete frames. The proposed beam-column joint model is a super-element consisting of eight spring components and one panel zone component, representing the bond-slip mechanism of the longitudinal reinforcement and the shear deformation mechanism of the joint concrete core region, respectively. In order to represent the dynamic response at the system level, the elastic constitutive law is applied to the eight connector springs, while the Bouc-Wen-Baber-Noori (BWBN) model is adopted to describe the hysteretic behavior of the panel zone component. For the implementation of the finite element analysis, the algorithmically consistent tangent of the BWBN model is derived as a uni-axial constitutive model, while the initial stiffness of the panel zone component is determined by the concrete compression strut assumption. The accuracy and efficiency of the proposed beam-column joint model were calibrated at both the component and structural levels by comparing the simulated results with the experimental data for non-seismically detailed joint sub-assemblages and a reinforced concrete plane frame.     

Seismic behavior of two Portuguese adobe buildings: part II —numerical modeling and fragility assessment

Considering the likely unfavorable behavior under seismic action of adobe construction, this article aims at providing a seismic fragility characterization of two adobe Portuguese traditional buildings, using numerical models calibrated over experimental results. The study of such two case-study buildings in the region of Aveiro contributes to the understanding of the seismic fragility of adobe construction in the region in general. The buildings were numerically modeled to estimate their structural behavior under seismic loading using adobe material properties that were calibrated based on the experimental results of a cyclic in-plane test of a full-scale double-Tshaped adobe wall. The method chosen to characterize adobe masonry and model its nonlinear behavior followed a total strain crack-based macro-modeling (TSCM) approach, whereas pushover analysis was carried out to reproduce the pseudo-static experimental test in order to enable a refined calibration of adobe masonry mechanical properties. Fragility functions were then derived, based on the above-mentioned numerical models, using nonlinear static analysis, bringing further insight on the seismic fragility of traditional Portuguese adobe construction.     

On-line Model Updating in Hybrid Simulation Tests

Hybrid simulation has emerged as a relatively accurate and efficient tool for the evaluation of structural response under earthquake loading. In conventional hybrid simulation the response of a few critical components is obtained by testing while the numerical module is assumed to follow an analytical idealization. Where there is a much larger number of analytical components compared to the experimental parts, the overall response may be dominated by the idealized parts hence the value of hybrid simulation is diminished. It is proposed to modify the material constitutive relationship of the numerical model during the test, based on the data obtained from the physically tested component. An approach based on genetic algorithms is utilized as an optimization tool to identify the constitutive relationship parameters used in updating the numerical model. The proposed model updating approach is verified through two analytical examples of steel and reinforced concrete frames. The results show the effectiveness of the updating process in minimizing the errors, compared to the assumed exact solution.     

Analysis of Carbon Fiber Sheet-Retrofitted RC Bridge Columns Under Lateral Cyclic Loading

In recent years, the use of carbon fiber sheet (CFS) to provide lateral confinement for enhanced ductility and strength of reinforced concrete bridge columns has been increasing. While the monotonic behavior of CFS-confined concrete has been studied extensively, its cyclic response has not been fully understood. Most of the available studies are experimental investigations, hence there is a need to develop an analytical model to simulate the experimental results. Analysis of the hysteretic behavior of CFS-retrofitted circular columns is presented in this article using the fiber element that is based on cyclic constitutive models of longitudinal reinforcement and concrete confined by both CFS and tie reinforcement. The analysis was verified based on available cyclic test data and the analysis provides good agreement with the experimental results. Results show that flexural strength and ductility of columns wrapped with CFS increases as CFS ratio increases. However, as tie reinforcement ratio increases, there is no much difference on the hysteretic response for low tie reinforcement ratios. Using the fiber element analysis, the effect of CFS retrofit on the seismic response of a 7.5 m tall prototype pier built in the 1970s to 1980s is also clarified.     

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.     

Constant and Variable Amplitude Cyclic Behavior of Welded Steel Beam-to-Column Connections

This article presents a study on welded beam-to-column joints of moment-resisting steel frames. The main features of the joint specimens are summarised, in order to identify key parameters influencing the joint response as well as their low-cycle fatigue endurance. The cyclic behavior and the low-cycle fatigue strength of the connections were initially assessed by cyclic quasi-static testing, carried out at the Technical University of Milan. Analysis of the results has been carried out in order to verify the validity of a linear damage accumulation model combined with a low-cycle fatigue approach based on S-N lines concept. Moreover, a criterion to predict the type of failure and a procedure of appraising the fatigue endurance are presented and their validity proved by the results of variable amplitude tests.     

Experimental and Numerical Seismic Response of a 65 kW Wind Turbine

A full-scale shake table test is conducted to assess the seismic response characteristics of a 23 m high wind turbine. Details of the experimental setup and the recorded dynamic response are presented. Based on the test results, two calibrated beam-column finite element models are developed and their characteristics compared. The first model consists of a vertical column of elements with a lumped mass at the top that accounts for the nacelle and the rotor. Additional beam-column elements are included in the second model to explicitly represent the geometric configuration of the nacelle and the rotor. For the tested turbine, the experimental and numerical results show that the beam-column models provide useful insights. Using this approach, the effect of first-mode viscous damping on seismic response is studied, with observed experimental values in the range of 0.5–1.0% and widely varying literature counterparts of 0.5–5.0%. Depending on the employed base seismic excitation, damping may have a significant influence, reinforcing the importance of more accurate assessments of this parameter in future studies. The experimental and modeling results also support earlier observations related to the significance of higher modes, particularly for the current generation of taller turbines. Finally, based on the outcomes of this study, a number of additional experimental research directions are discussed.     

Quantitative basin modeling: present state and future developments towards predictability

A critique review of the state of quantitative basin modeling is presented. Over the last 15 years, a number of models are proposed to advance our understanding of basin evolution. However, as of present, most basin models are two dimensional (2‐D) and subject to significant simplifications such as depth‐ or effective stress‐dependent porosity, no stress calculations, isotropic fracture permeability, etc. In this paper, promising areas for future development are identified. The use of extensive data sets to calibrate basin models requires a comprehensive reaction, transport, mechanical (RTM) model in order to generate the synthetic response. An automated approach to integrate comprehensive basin modeling and seismic, well‐log and other type of data is suggested. The approach takes advantage of comprehensive RTM basin modeling to complete an algorithm based on information theory that places basin modeling on a rigorous foundation. Incompleteness in a model can self‐consistently be compensated for by an increase in the amount of observed data used. The method can be used to calibrate the transport, mechanical, or other laws underlying the model. As the procedure is fully automated, the predictions can be continuously updated as new observed data become available. Finally, the procedure makes it possible to augment the model itself as new processes are added in a way that is dictated by the available data. In summary, the automated data/model integration places basin simulation in a novel context of informatics that allows for data to be used to minimize and assess risk in the prediction of reservoir location and characteristics.     

Application of In-Test Model Updating to Earthquake Structural Assessment

Analytical methods are frequently utilized for structural assessment due to their simplicity and cost-effectiveness. However, modeling of material inelasticity and geometric nonlinearity under reversed inelastic deformations is still very challenging and its accuracy is difficult to quantify. On the other hand, realistic experimental assessment is costly, time-consuming, and impractical for large or spatially extended structures. Hybrid simulation has been developed as an approach that combines the realism of experimental techniques with the economy of analytical tools. In hybrid simulation, the structural is divided into several modules such that the critical components are tested in the laboratory, while the rest of the structure is simulated numerically. The equations of motion solved in the computer enable the integration of the analytical and experimental components at each time increment. The objective of this article is to apply a newly developed identification and model updating scheme to acquire the material constitutive relationship from the physically tested specimen during the analysis to two complex hybrid simulation case studies. The identification scheme is developed and verified in a companion article, while the two experiments presented in this article are selected such that they address different structural engineering applications. First, a beam-column steel connection with heat treated beam section is analyzed. Afterwards, the response of a multi-bay concrete bridge is investigated. The results of these two examples demonstrate the effectiveness of model updating to improve the numerical model response as compared to the conventional hybrid simulation approaches.     

Testing of Superelastic Recentering Pre-Strained Braces for Seismic Resistant Design

Over the past decade, the use of shape memory alloys (SMAs) in passive control devices has been explored. Nevertheless, some aspects in regards to the cyclic behavior of SMAs and the effect of pre-straining need to be clarified. In this study, small-scale shake table tests have been performed to explore the effectiveness of SMA bracing systems as compared to steel bracing systems. The reduced-scale experimental results imply that SMAs used in braces are more effective in controlling the response of a steel frame compared with a traditional bracing system. A finite element model (FEM) of the frame is developed in order to compare the analytical results with the shake table tests. Further, the effect of pre-straining the SMA braces is evaluated through both experimental and analytical studies. The results show that pre-straining improves the performance of the frame compared to the nonpre-strained case. However, as the level of pre-straining increases above approximately 1.0% to 1.5%, the benefits of pre-straining decrease compared with low-to-moderate pre-strain levels.     

Bayesian Updating of Seismic Demand Models and Fragility Estimates for Reinforced Concrete Bridges with Two-Column Bents

Probabilistic models have been developed in a previous study by the authors to estimate the seismic deformation demands on structural components of reinforced concrete (RC) bridges with two-column bents. However, such models should be updated to reflect the latest laboratory of field data. Using a Bayesian approach, this article updates a currently available probabilistic model for the deformation demands of columns in bridges with two-column RC bents. The updated model incorporates information from newly available experimental data from shake table tests conducted based on a record of the 1994 Northridge Earthquake for a structural system with three bents with two columns per bent. The updated model is more accurate than the previous one in predicting the deformation demand of bridges with two-column RC bents and reduces the statistical uncertainty due to the addition of new data. As an application, fragility estimates for an example bridge are computed using the updated model both at the component (column) and system (bridge) levels.     

Simulation of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (VI): Discrete Element Approach

ABSTRACT

Although many experimental tests and numerical models are available in the literature, the numerical simulation of the seismic response of existing masonry buildings is still a challenging problem. While the nonlinear behavior of masonry structures is reasonably predictable when the out-of-plane behavior can be considered inhibited, when the in-plane and out-of-plane responses coexist and interact, simplified models seem unable to provide reliable numerical predictions. In this article, taking advantage of the experimental tests carried out in a shaking table on two masonry prototypes at LNEC, a macro-element approach is applied for the numerical simulations of their nonlinear response. The adopted approach allows simulating the nonlinear behavior of masonry structures considering the in-plane and out-of-plane responses. Since it is based on a simple mechanical scheme, explicitly oriented to representing the main failure mechanisms of masonry, its computational cost is greatly reduced with respect to rigorous solutions, namely nonlinear FEM approaches. Two modeling strategies are adopted, namely a regular mesh independent from the real texture of the prototypes and a detailed one coherent with the units disposal. The numerical results are discussed and the correlation between the nonlinear static analyses and the dynamic response is provided.     

SEISMIC REHABILITATION OF SHORT RECTANGULAR RC COLUMNS

Non-ductile response of structural elements, particularly columns, has been the cause of numerous documented failures during earthquakes. The objective of this experimental study was to evaluate the non-linear behaviour of non-ductile reinforced concrete short columns under lateral cyclic deformations and to evaluate rehabilitation schemes. Three reinforced concrete short columns were tested under cyclic lateral loads and constant axial load. The behaviour and effectiveness of different rehabilitation systems using carbon fibre reinforced polymers (CFRP) were investigated. Two different techniques to improve concrete confinement were used in the two rehabilitated specimens. It was found that it is possible to eliminate the non-ductile modes of failure of short column using anchored CFRP wraps. In addition, an analytical model to predict the confining effect and the total shear resistance of rectangular reinforced concrete columns with anchored fibre wraps was introduced. The confinement model is an extension to an available model for concrete confined by steel reinforcement. The model was used to predict the shear capacity of the tested specimens and has shown good results.     

Simplified Macro-Model for Infill Masonry Panels

In structural analyses, masonry infill walls are commonly considered to be non structural elements. However, the response of reinforced concrete buildings to earthquake loads can be substantially affected by the influence of infill walls. In this article, an improved numerical model for the simulation of the behavior of masonry infill walls subjected to earthquake loads is proposed and analyzed. First, the proposed model is presented. This is an upgrading of the equivalent bi-diagonal compression strut model, commonly used for the nonlinear behavior of infill masonry panels subjected to cyclic loads. Second, the main results of the calibration analyses obtained with two series of experimental tests are presented and discussed: one on a single frame with one story and one bay tested at the LNEC Laboratory; and the second, on a full-scale four story and three-bay frame tested at the ELSA laboratory.