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.     

Floor Spectra of Inelastic RC Frame Buildings Considering Ground Motion Characteristics

A range of reinforced concrete frame buildings with different levels of inelasticity as well as periods of vibration is analyzed to study the floor response. The derived floor acceleration response spectra are normalized by peak ground acceleration, peak floor acceleration, and ground response spectrum. The normalization with respect to ground response spectrum leads to the lowest coefficients of variation. Based on this observation as well as previous studies, an amplification function is proposed that can be used to develop design floor spectra from the ground motion spectrum, considering the building’s dynamic characteristics and level of inelasticity.     

Simplified Seismic Sidesway Collapse Capacity-Based Evaluation and Design of Frame Buildings with Linear Viscous Dampers

This article describes a simplified procedure for estimating the seismic sidesway collapse capacity of frame building structures incorporating linear viscous dampers. The proposed procedure is based on a robust database of seismic peak displacement responses of viscously damped nonlinear single-degree-of-freedom systems for various seismic intensities and uses nonlinear static (pushover) analysis without the need for nonlinear time history dynamic analysis. The proposed procedure is assessed by comparing its collapse capacity predictions on 272 different building models with those obtained from incremental dynamic analyses. A straightforward collapse capacity-based design procedure is also introduced for structures without extreme soft story irregularities.     

Nonlinear Static Procedure for Multi-Story Asymmetric Frame Buildings Considering Bi-Directional Excitation

The present article focuses on a nonlinear static procedure (NSP) for a multi-story asymmetric frame building with regular elevation subjected to bi-directional ground motion. In this procedure, two simplified models—an equivalent single-story model and an equivalent single-degree-of-freedom (SDOF) model—are used to predict the peak response of multi-story asymmetric buildings. The peak response is predicted through pushover analysis of an equivalent single-story model considering the effect of bi-directional excitations and an estimation of the nonlinear response of equivalent SDOF models. The predicted results are compared with the nonlinear dynamic analysis results, and satisfactory predictions can be obtained by the proposed procedure.     

Developing Direct Displacement-Based Procedures for Simplified Loss Assessment in Performance-Based Earthquake Engineering

Various loss assessment methodologies have been proposed and developed over the past decades to provide risk assessment on a regional scale. There is an increasing need, however, to provide engineers with practical tools for building-specific loss assessment. Recently, progress has been made towards probabilistic loss models such as the PEER framework. However, as comprehensive probabilistic methodologies could be too complex for practicing engineers, this article presents a simplified probabilistic loss assessment methodology that builds on a direct displacement-based framework. The methodology is tested via examination of two RC frame buildings and encouragingly shows similar results to the PEER methodology.     

Fuzzy-Sliding-Mode Supervisory Control of a Seismic Shake Table with Variable Payload for Robust and Precise Acceleration Tracking

Precise tracking of the earthquake acceleration profile in the presence of uncertainties is a challenge for the shake table control design. Design and implementation of a fuzzy-sliding-mode super- visory controller for an electric seismic shake table with variable payload is addressed in this paper. The proposed controller contains two layers including a proportional–integral loop and a fuzzy-sliding-mode supervisory controller. The controller is then implemented in the shake table and its performance is evaluated. The test results reveal successful performance of the proposed controller at robust tracking of some harmonic and seismic excitations in the presence of parametric uncertainties.     

Fast Nonlinear Analysis of Traditional Chinese Timber-Frame Building with Dou-Gon

ABSTRACT

This article presents a study of the applicability of fast nonlinear analytical (FNA) models in predicting the global response of Chinese traditional timber-frame building with Dou-Gon under seismic excitation. Efforts are made to overcome challenges in establishing simplified calculation models, and the corresponding dynamic equations are derived considering the mechanical behavior of sliding column root, mortise-tenon joint and Dou-Gon (bracket sets). Furthermore, nonlinear time-history analysis is conducted under different seismic excitations. Through a verification study, a good correspondence is obtained with previous shake-table test results. Seismic response analysis is also conducted to investigate the energy dissipation of column root sliding, mortise-tenon joint, and Dou-Gon. Subsequently, peak responses of column root and roof under increased values of peak ground acceleration (PGA) are also analyzed. And then, seismic isolation ability and damping characteristics of the model are discussed.     

STRUCTURAL RESPONSE AND DAMAGE ASSESSMENT BY ENHANCED UNCOUPLED MODAL RESPONSE HISTORY ANALYSIS

The Uncoupled Modal Response History Analysis (UMRHA) method developed by Chopra et al. is modified in this paper to estimate damage to welded moment-resisting connections in a steel frame (MRSF) subjected to earthquake ground motions. The behaviour of these connections is modelled by a moment-rotation relationship that accounts for the cracking of the beam flange-to-column flange groove weld. The behaviour of the frame is approximated by a sequence of single-degree-of-freedom (SDOF) models for the first three modes to allow for the contribution of higher modes of vibration. The dynamic properties of these SDOF systems are determined by nonlinear static pushover analyses of the building frame. Because of the significant drop in connection strength caused by beam-to-column weld cracking, the pushover procedure uses a changing rather than invariant distribution of horizontal loads, while the structural responses are calculated from shapes that are based on the displaced shape of the frame after damage occurs. The accuracy of the method is demonstrated by a comparison with the results of a nonlinear time history analysis of the frame. This method can be used for rapid assessment of seismic damage or damage potential and to identify buildings requiring more detailed investigation.     

Seismic Response of Base-Isolated Benchmark Building with Variable Sliding Isolators

The seismic response of base-isolated benchmark building with variable sliding isolators like variable friction pendulum system (VFPS), variable frequency pendulum isolator (VFPI), and variable curvature friction pendulum system (VCFPS), along with conventional friction pendulum system (FPS), was studied under the seven earthquakes. The earthquakes are applied bi-directionally in the horizontal plane ignoring vertical ground motion component. The shear type base-isolated benchmark building is modeled as three-dimensional linear elastic structure having three degrees of freedom at each floor level. Time domain dynamic analysis of the benchmark building was carried out with the help of constant average acceleration Newmark-Beta method and nonlinear isolation forces was taken care by fourth-order Runge-Kutta method. The base-isolated benchmark building is investigated for uniform isolation and hybrid isolation in combination with laminated rubber bearings through the performance criteria and time history response of important structural response parameters like floor accelerations, base displacement, etc. It is observed that variable sliding isolators performed better than conventional FPS due to their varying characteristic properties which enable them to alter the isolator forces depending upon their isolator displacements thus improves the performance of the structure. The VFPS efficiently controls large isolator displacements and VFPI and VCFPS improve super structural response on the cost of isolator displacement. It is also observed that the hybrid isolation is relatively better in comparison to the uniform isolation for the benchmark building.     

The Numerical Study of Base-Isolated Buildings Under Near-Field and Far-Field Earthquakes

The behavior of base-isolated building frame is investigated with the help of a numerical study for far-field and near-field earthquakes with directivity and fling-step effects. Both design-level and extreme-level earthquakes are considered. Selected response parameters are peak floor displacement, acceleration, base shear, and isolator displacement. Inelastic behavior of base-isolated structure during the earthquake is investigated performing nonlinear time history analysis of a ten-story building frame. This study shows that base isolation is not effective for near-field earthquakes. Even for design-level earthquake, the frame gets significantly into inelastic range for earthquakes with fling-step effect.     

CODE PROVISIONS AND ANALYTICAL MODELLING FOR THE IN-PLANE FLEXIBILITY OF FLOOR DIAPHRAGMS IN BUILDING STRUCTURES

In this paper a review of the provisions of some modern seismic codes for the analytical modelling of the floor diaphragm action is made and a methodology using simplified 2-D finite elements models for monolithic floors is suggested, taking into consideration the in-plane flexibility of them. The simplified models use the coarsest discretisation mesh possible, simply taking into account all the connection points of the vertical structural elements on the diaphragm of each storey. The efficiency of the proposed simplified F.E. models is tested with comparative response-spectrum dynamic analyses of various building structures with different plan shapes, according to EuroCode 8 [EC8, 1994]. The simplified models provided excellent results for the dynamic characteristics of the entire building and the stress state of the framing substructure and a fair estimation for the in-plane stresses of the floor diaphragms.     

Inelastic Displacement Ratios for Nonstructural Components Subjected to Floor Accelerations

This paper describes a study on the characterization of the Inelastic Displacement Ratios (IDRs) of inelastic acceleration-sensitive nonstructural components subjected to floor accelerations obtained from the linear analysis of multistory building structures under far-field ground accelerations. Several building models having different structural systems and a number of stories were considered. IDRs were obtained from the displacement response of elastic and inelastic single-degree-of-freedom systems subjected to floor accelerations. Similarities and differences between floor acceleration IDRs and ground acceleration IDRs were identified, and efforts were made to explain the differences. Finally, a predicting equation for floor acceleration IDRs is proposed and validated.     

Direct Acceleration Feedback Control of Shake Tables with Force Stabilization

This study presents a new strategy for shake table control that uses direct acceleration feedback without need for displacement feedback. To ensure stability against table drift, force feedback is incorporated. The proposed control strategy was experimentally validated using the shake table at the Johns Hopkins University. Experimental results showed that the proposed control strategy produced more accurate acceleration tracking than conventional displacement-controlled strategies. This article provides the control architecture, details of the controller design, and experimental results. Furthermore, the impact of input errors in shake table testing on the structural response is also discussed.     

Analytical Modeling of Horizontally Curved Steel Girder Highway Bridges for Seismic Analysis

This article introduces a generic modeling approach that is suitable for static and dynamic analysis, and response assessment of highway bridges with varying levels of irregularities. The proposed approach and modeling recommendations are based on grillage modeling rules that allows explicit representation of various types of details and components. The validity and accuracy of the proposed approach is demonstrated against three-dimensional finite element models as well as experimentally recorded response various benchmark bridges. While achieving remarkable accuracy, the required analysis time was also reduced up to 80%, making the proposed approach suitable for computationally intensive studies.     

Seismic Performance Assessment of Steel Frames with Shape Memory Alloy Connections. Part I — Analysis and Seismic Demands

This article is the first of two companion articles that evaluate the seismic performance of steel moment-resisting frames with innovative beam-to-column connections that incorporate shape memory alloys (SMAs) to dissipate energy and provide recentering effectively during large earthquakes. Two types of SMA elements are considered: (1) superelastic SMA elements with recentering capability and (2) martensitic SMA elements with high energy dissipation capacity. This article describes the fundamental engineering characteristics of these SMA connections, their modeling in connections for nonlinear dynamic finite element analysis of building frames, and the validation of these connection models using data from full-scale experimental tests that were performed in previous research at Georgia Institute of Technology. Using three- and nine-story partially restrained (PR) moment frames selected as case studies from the SAC Phase II Project, nonlinear time history analyses of frames with and without SMA connections were conducted using suites of ground acceleration records. The beneficial effects of SMA connections on peak and residual deformation demands are quantified and discussed.     

Dynamical Assessment of the Work Conditions of Reinforcement Tie-Rods in Historical Masonry Structures

Tie-rods are essential structural elements, which have been employed for centuries in masonry historical buildings, either during the construction or in successive strengthening interventions, with the aim of containing dangerous horizontal actions. The actual work conditions of these tie-rods, which are strongly influenced by their load history, are difficult to be quantified theoretically, and an effective method for their measure is of great importance in order to ensure the efficiency of these elements during the time and the stability of the entire building. Common measurements are often carried out adopting models based upon significant simplifications, like, for example, hinges at the extremities. These assumptions, rarely represent the real work conditions for anchorages. In this work, a non-destructive testing method is presented, based upon sophisticated dynamical models that can take into consideration many of the circumstances neglected by the simplified models. Four case studies are extensively described, trying to embrace the most common situations in term of peculiar features of the building, structural configuration, and load history. The discussion of the results yields the safety margin of the rod with respect to the material failure and provides important indications about the overall stability of the whole building.     

Simulation of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (IV): Macro and Micro FEM Based Approaches

ABSTRACT

This article presents a study on the out-of-plane response of two masonry structures without box behavior tested in a shaking table. Two numerical approaches were defined for the evaluation, namely macro-modeling and simplified micro-modeling. As a first step of this study, static nonlinear analyses were performed for the macro models in order to assess the out-of-plane response of masonry structures due to incremental loading. For these analyses, mesh size and material model dependency was discussed. Subsequently, dynamic nonlinear analyses with time integration were carried out, aiming at evaluating the collapse mechanism and at comparing it to the experimental response. Finally, nonlinear static and dynamic analyses were also performed for the simplified micro models. It was observed that these numerical techniques correctly simulate the in-plane response. The collapse mechanism of the stone masonry model is in good agreement with the experimental response. However, there are some inconsistencies regarding the out-of-plane behavior of the brick masonry model, which required further validation.     

Analytical Collapse Study of Lightly Confined Reinforced Concrete Frames Subjected to Northridge Earthquake Ground Motions

Review of older non seismically detailed reinforced concrete building collapses shows that most collapses are triggered by failures in columns, beam-column joints, and slab-column connections. Using data from laboratory studies, failure models have previously been developed to estimate loading conditions that correspond to failure of column components. These failure models have been incorporated in nonlinear dynamic analysis software, enabling complete dynamic simulations of building response including component failure and the progression of collapse. A reinforced concrete frame analytical model incorporating column shear and axial failure elements was subjected to a suite of near-fault ground motions recorded during the 1994 Northridge earthquake. The results of this study show sensitivity of the frame response to ground motions recorded from the same earthquake, at sites of close proximity, and with similar soil conditions. This suggests that the variability of ground motion from site to site (so-called intra-event variability) plays an important role in determining which buildings will collapse in a given earthquake.     

Performance-Based Vulnerability Assessment of Multi-Story Reinforced Concrete Structures Exposed to Pre- and Post-Earthquake Fire

Post-earthquake fire can potentially bring about much more damage than the earthquake itself. Performing a vulnerability assessment for a structure that has already sustained damage in an earthquake and is then exposed to fire is therefore of importance. This paper describes a performance-based investigation in which applied loads to a structure are appropriately quantified. To do so, a sequential structural analysis is performed on the Life Safety performance level of a three-story reinforced concrete frame selected from a building. For the analysis to be more realistic, the slab is also included in the frame analysis through the concept of effective length. The frame is first subjected to an earthquake load with the PGA of 0.30 g followed by a fire analysis, using the ISO834 fire curve and the iBMB fire curve. The time needed for the structure weakened by the earthquake to collapse under fire is then calculated. As a benchmark, fire-only analysis is also performed for the undamaged frame. Moreover, the effect of thermal spalling is considered in the slabs. The selected frame is evaluated under various failure criteria such as load capacity, displacement, and rate of displacement. The results show that no failure is observed when the frame is exposed to fire alone, either when using the ISO curve or the iBMB curve under various failure criteria. It is also shown that while the PEF resistance based on load capacity criteria under the ISO curve is around 120 minutes, it reduces to about 95 min under the iBMB curve. However, considering the rate of deflection failure criteria, the PEF resistance is around 103 min and 75 min under the ISO and the iBMB curves, respectively. It is then concluded that in the PEF analysis, the iBMB curve is more compatible with the concept of performance-based design than the ISO curve is.     

SEISMIC RESPONSE OF REINFORCED CONCRETE FRAMES INFILLED WITH WEAKLY REINFORCED MASONRY PANELS

The research work presented in this paper is related to the seismic response of RC frames infilled with weak masonry panels, as it is traditional in many seismic prone countries in southern Europe. More specifically, the benefits derived from the insertion of a light reinforcement, in the mortar layers or in the external plaster, are studied in some detail.

Tests have been performed on different types of single bay, single storey, infilled frames to investigate the in-plane response at different earthquake intensity levels and the out-of-plane strength as a function of the in-plane damage. A series of parametric simulations have then been performed, calibrating the models used in the test results, to evaluate the effects of the different panels characteristics on the response of whole buildings, with different infill patterns. Both in-plane and the out-of-plane response have been considered. The results are described in terms of peak ground acceleration required to induce given limit states of serviceability or damage relatively far from the collapse of the structure, which is governed by the RC frame design more than by the infill panels properties.