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Seismic strengthening for existing structures is a sustainable solution that is utilized to enhance building safety, reduce damages, and prevent failure in a future earthquake event. The choice of seismic strengthening techniques has to be accurate, efficient, and adjusted to make RC structures stronger in the building sector. Buckling-restrained brace (BRB) system is one of the successful strengthening strategies, that it is possible to utilize in both RC and steel structures. Therefore, this paper explores the possibility of employing buckling restrained braces in existing RC buildings and assesses the impact of different BRB bracing distributions and positions on seismic force resistance. In this work, a five-story RC building was considered, and to upgrade their performance seismic was modeled using four types of BRB systems, consisting of two types of bracing configurations with two arrangements: diagonal in the central bay, diagonal in the corner bays, chevron in the central bay, and chevron in the corner bays. To assess the efficiency of the four proposed BRB systems, firstly, the nonlinear static pushover method was conducted to investigate the lateral strength of structures. Secondly, a parametric study was undertaken using dynamic time history analysis to study various factors such as roof displacement, shear force, and roof acceleration of the original and strengthened models. The numerical study was executed using the Seismostruct software. The results and different performance levels were examined and compared. The obtained results indicate that the BRB and concrete structures can successfully work together to resist the reliability of strengthening RC structures. It was observed that the four prediction systems of the BRB models were excessively effective at upgrading the seismic resistance of the existing structure and provided significantly less damage, especially when using the chevron BRBs with the corner arrangement compared to the other models.

The pushover method is often used instead of the nonlinear time history (NTH) method for analyzing base-isolated structures due to its simplicity. However, pushover analysis cannot account for reversible earthquake effects on structural damage. An alternative fast method is the endurance time (ET) method, which has fewer limitations in considering the dynamic effects of earthquakes on structures. However, the accuracy of this method is questionable due to the inability to distinguish non-converged results of individual records. To clarify this question, this study investigates the application of the modified endurance time (MET) method, which is an enhanced version of the ET method under pounding. For this study, three base isolated special moment frames (SMFs) designed based on the design earthquake hazard level were analyzed under the earthquake hazard level with 2475-year return periods (EHL2475). The results of the MET and pushover methods were compared to each other with respect to the NTH analysis, which was considered the reference method. The results have indicated that the MET had less error than the pushover in predicting structural damage based on the maximum interstory drift ratio (IDR). In contrast to the pushover, the MET can predict nonstructural acceleration-sensitive element damage with errors of 12.3–20.8%.

Nonlinear static (pushover) analysis is an effective and simple tool for evaluating the seismic response of structures and offers an attractive choice for the performance-based design. As such, it has generally been used in modern design due to its practicality. However, the nonlinear plastic design method consumes extensive computational effort for practical structures under numerous load cases. Thus, an efficient element capturing the nonlinear behavior of a beam-column will be useful. In this paper, the authors propose a practical pushover analysis procedure using a single element per member for seismic design. As an improvement to previous research works, both P – Δ and P – δ effects as well as initial imperfections in global and member levels are considered. Therefore, the section capacity check without the assumption of effective length is adequate for present design and the conventional individual element design is avoided. The uncertainty of the buckling effects and effective length method can be eliminated and so a more economical design can be achieved. Two benchmark steel frames of three-storey and nine-storey in FEMA 440 were analyzed to illustrate the validity of the proposed method.

This paper investigates the combined effect of flexural and shear actions on the failure modes of the high strength reinforced concrete (HRC) members using the proposed algorithm for plastic hinge formation. The accuracy of the present procedure for the HRC columns was verified by comparing the results obtained with those of the cyclic loading tests performed in Japan. To evaluate the seismic performance of the HRC high-rise buildings, a seismic performance checklist for the HRC buildings was recommended. Based on the proposed algorithm for formation of plastic hinges, the seismic performance of HRC buildings based on the static pushover analysis is evaluated. From the results of the pushover analysis, a simplified lumped-mass stick model was developed, which is adopted to evaluate the seismic performance using the nonlinear time history analysis. For the purpose of illustration, the seismic performance of a high-rise building constructed with HRC was investigated by both the nonlinear pushover and nonlinear dynamic analyses using the proposed procedure and concepts. The results of this paper serve as a useful reference for the seismic design and evaluation of HRC high-rise structures.

A seismic design procedure for partially concrete-filled box-shaped steel columns is presented in this paper. To determine the ultimate state of such columns, concrete and steel segments are modelled using beam-column elements and a pushover analysis procedure is adopted. This is done by means of a new failure criterion based on the average strain of concrete and steel at critical regions. The proposed procedure is applicable to columns having thin- and thick-walled sections, which are longitudinally stiffened or not. An uniaxial constitutive relation recently developed is employed for concrete filled in the thick-walled unstiffened section columns. Modifications are introduced to this model for other types of columns. Subsequently, the strength and ductility predictions obtained using the present and previous procedures are compared with the corresponding experimental results. Comparisons show that the present procedure yields better predictions. It is revealed that the inclusion of the confinement effects and softening behaviour of concrete is important in the present kind of prediction procedures. Furthermore, an extensive parametric study is carried out to examine the effects of procedures and geometrical and material properties on capacity predictions.

The paper examines the requirements for inelastic static and dynamic analysis applied to earthquake design and assessment. Conventional pushover, with various load distributions, as well as advanced adaptive concepts are examined and compared to incremental dynamic analysis. Regions of applicability of each are discussed and suggestions on which method is better suited under a given set of conditions are qualitatively made. It is concluded that there will always be a class of structure-input motion pairs where inelastic dynamic analysis is necessary. Future developments should aim at reducing the regions where dynamic analysis is needed, hence static analysis may be used with confidence in other cases.

A five-storey steel frame incorporating dissipative knee elements is designed using the Eurocode 8 pushover analysis method. The non-linear analysis makes use of a novel knee element model capable of accurately simulating the bending and shear behaviour observed in full-scale tests. The performance of the structure is assessed using non-linear time-history analysis. This shows that the knee elements can be designed to yield under small earthquakes or early in a strong one (maximising their energy dissipation) while still being able to withstand a large event without collapse. Knee elements thus have the potential to give excellent seismic performance in steel framed structures. The time history analysis results are compared to those obtained with the three different pushover analysis methods (Eurocode 8, FEMA 356 and ATC 40). The FEMA 356 method, which includes a more accurate representation of the structure's significant post-yield stiffness, gave the closest agreement with the time history analyses, while the Eurocode 8 method gave rather conservative results and the ATC 40 method appears non-conservative for this type of structure.

The general trends of the inelastic behaviour of plan-asymmetric structures have been studied. Systems with structural elements in both orthogonal directions and bi-axial eccentricity were subjected to bi-directional excitation. Test examples include idealised single-storey and multi-storey models, and a three-storey building, for which test results are available. The response in terms of displacements was determined by nonlinear dynamic analyses. The main findings, limited to fairly regular and simple investigated buildings, are: (a) The amplification of displacements determined by elastic dynamic analysis can be used as a rough, and in the majority of cases conservative estimate in the inelastic range. (b) Any favourable torsional effect on the stiff side, which may arise from elastic analysis, may disappear in the inelastic range. These findings can be utilised in the approximate pushover-based seismic analysis of asymmetric buildings, e.g. in the N2 method. It is proposed that the results obtained by pushover analysis of a 3D structural model be combined with the results of a linear dynamic (spectral) analysis. The former results control the target displacements and the distribution of deformations along the height of the building, whereas the latter results define the torsional amplifications. The proposed approach is partly illustrated and evaluated by test examples.

In this paper, a methodology is suggested and tested for evaluating the relative performance of conventional and adaptive pushover methods for seismic response assessment. The basis of the evaluation procedure is a quantitative measure for the difference in response between these methods and inelastic dynamic analysis which is deemed to be the most accurate. Various structural levels of evaluation and different incremental representations for dynamic analysis are also suggested. This method is applied on a set of eight different reinforced concrete structural systems subjected to various strong motion records. Sample results are presented and discussed while the full results are presented alongside conclusions and recommendations, in a companion paper.

In this paper, the methodology for evaluation of conventional and adaptive pushover analysis presented in a companion paper is applied to a set of eight different reinforced concrete buildings, covering various levels of irregularity in plan and elevation, structural ductility and directional effects. An extensive series of pushover analysis results, monitored on various levels is presented and compared to inelastic dynamic analysis under various strong motion records, using a new quantitative measure. It is concluded that advanced (adaptive) pushover analysis often gives results superior to those from conventional pushover. However, the consistency of the improvement is unreliable. It is also emphasised that global response parameter comparisons often give an incomplete and sometimes even misleading impression of the performance.

A reliable estimate of the actual capacity and deformability of existing reinforced concrete buildings in earthquake prone areas is essential in pre- or post-earthquake interventions. This study is concerned with the evaluation of the structural overstrength, the global ductility and available behaviour factor of existing reinforced concrete buildings, designed and constructed according to past generations of earthquake resistant design codes. For the estimation of these global performance characteristics different failure criteria are incorporated in a methodology established to predict the failure mode of the buildings. As an application, a typical five-storey building of the 1960s, designed according to the prevailing design codes, is selected and analysed in the inelastic range. Both bare and infilled structural forms of this building are studied. For this structure, the plastic hinge rotation capacity is the critical failure criterion. The same structure, designed according to current design codes, is re-evaluated using the same methodology, in order to calibrate the procedure and to compare the static and dynamic inelastic performances of the two frames. The results indicate that existing buildings exhibit higher overstrength than their contemporary counterparts, but with much reduced ductility capacity. Perimeter infill walls correct for their lack of ductility by augmenting their stiffness and their overall lateral resistance. The methodology is subsequently applied to a larger inventory of typical existing buildings, as described in a companion publication.

The results of a parametric study are presented, concerned with the evaluation of the structural overstrength, the global ductility and the available behaviour factor of existing reinforced concrete (RC) buildings designed and constructed according to past generations of earthquake resistant design codes in Greece. For the estimation of these parameters, various failure criteria are incorporated in a methodology established to predict the failure mode of such buildings under planar response, as described in detail in a companion publication. A collection of 85 typical building forms is considered. The influence of various parameters is examined, such as the geometry of the structure (number of storeys, bay width etc.), the vertical irregularity, the contribution of the perimeter frame masonry infill walls, the period of construction, the design code and the seismic zone coefficient. The results from inelastic pushover analyses indicate that existing RC buildings exhibit higher overstrength than their contemporary counterparts, but with much reduced ductility capacity. The presence of perimeter infill walls increases considerably their stiffness and lateral resistance, while further reducing their ductility. Fully infilled frames exhibit generally good behaviour, while structures with an open floor exhibit the worst performance by creating a soft storey. Shear failure becomes critical in the buildings with partial height infills. It is also critical for buildings with isolated shear wall cores at the elevator shaft. Out of five different forms of irregularity considered in this study, buildings with column discontinuities in the ground storey exhibit the worst performance. Furthermore, buildings located in the higher seismicity zone are more vulnerable, since the increase of their lateral resistance and ductility capacity is disproportional to the increase in seismic demand.

This paper summarises the first phase of the fragility analyses of generic (representative) buildings in the area of Memphis, Tennessee, USA. The study was conducted at Cornell University as a part of the project Loss Assessment of Memphis Buildings (LAMB) for the National Center for Earthquake Engineering Research (NCEER). In this study, the fragility analyses focus on low-rise Lightly Reinforced Concrete (LRC) frame buildings with and without infill walls. The obtained fragility curves are compared with those of ATC-13 for different facility classes. Based on the obtained fragility curves, it is concluded that adding masonry infill walls to low-rise LRC frame buildings significantly reduces the likelihood of seismic damage.

Structures designed according to earlier codes with inadequate seismic provisions have not performed satisfactorily during recent earthquakes. The seismic performance of an existing three-storey reinforced concrete building designed according to the 1963 ACI 318-63 is evaluated and compared to the performance of a similar frame designed according to current code provisions. Non-linear static and dynamic analyses of the reinforced concrete frames are conducted. In this study, a probabilistic approach is adopted where a large number of artificially generated ground motion records is used as input motion to the structure. The results of the analysis indicated the probability of various degrees of damage to be expected when the existing frame is subjected to different ground motion levels. This information is useful in the design of the required rehabilitation scheme to provide an identified level of protection.

This study is focused on the effects of the new standard of the building design under seismic loading in Thailand (DPT 1302-52) on cost estimates and the seismic performance of nine-story reinforced concrete apartment buildings with various ductility in moderate seismic zone and a gravity load designed (GLD) building. Both the nonlinear static pushover and nonlinear dynamic analyses are applied. Comparisons of performance point (PF) evaluation of studied frames are investigated by three different methods, namely, capacity spectrum method (CSM), inelastic demand diagram method (IDDM), and nonlinear time history analysis (NTHA) method. Five selected ground motion records are investigated in the analyses. In order to examine the influence of design ductility classes, the seismic forces on moment resisting frame buildings are defined according to the new standard of the building design under seismic loading in Thailand with ductility from 8, 5, and 3, corresponding to special ductile frame (SDF), intermediate ductile frame (IDF), and ordinary ductile frames (ODF), respectively. For the cost estimates, ODF is the most expensive among ODF, IDF, and SDF. Costs of SDF and IDF in Chiang Mai are quite similar. The results show that SDF is more ductile than that of ODF, however, the strength of SDF is less than ODF. The results indicate that all frames including GLD are able to withstand a design earthquake. The study also found that the average ductilities at the failure state for SDF, IDF, ODF, and GLD are 1.45, 1.42, 1.28, and 1.17, respectively. The average PGAs at the failure state for SDF, IDF, ODF, and GLD are 0.85 g, 0.83 g, 0.63 g, and 0.35 g, respectively when these buildings have the volumetric ratio of horizontal confinement within joint panel greater than 0.003. Moreover, at the failure state of GLD with volumetric ratio of horizontal confinement within joint panel less than 0.003, the average PGA is only 0.17 g which is lower than the design earthquake of PGA of 0.39 g in the draft DPT. The SDF and IDF are the two best options in consideration of cost and seismic performance.

Uttarakhand in the foothills of Himalayas is considered to be one of the most tectonically active regions of northern India as it had experienced several destructive earthquakes such as Pithoragarh (1980), Uttarkashi (1991), Chamoli (1999) and Gopeshwar (2005). The state of Uttar Pradesh (now Uttarakhand) being the center of activity during British regime is having numerous historical brick masonry structures such as churches, missionaries, hospitals, administrative building and educational institutions required to be safeguarded against catastrophic future earthquakes. One such building: Forest Research Institute Dehradun which suffered extensive damages during the Uttarkashi earthquake has been considered for seismic vulnerability assessment and achieving a generalized retrofitting strategy for the region which can be extrapolated globally. Structural assessment by non-linear static analysis has been carried out for FRP retrofitted and an un-retrofitted building using FEM. Different types of FRP has been modeled numerically as wrapped around the piers of huge brick masonry structure and analyzed under site specific earthquake loading which reported in an improved performance of strengthened structure.

The objective of this study is to propose a framework for evaluating the seismic fragility of bridge systems analytically taking into account correlations between component behaviors. To include coupled effects of component behaviors on system behavior, the second-order reliability approach is adopted. The damage states of the combined fragility are proposed based on system behavior characteristics obtained by pushover analyses. The characteristics of the combined fragility information of two bridge models are illustrated using probabilistic seismic demand analysis based on the time history analysis results from several earthquake excitations. The fragility curves obtained from the second-order reliability model are compared with the first-order reliability model. It is shown that the proposed framework can provide more detailed fragility information rather than only providing bounds of system fragility as in the first-order reliability-based approach.

Concrete filled tube (CFT) columns combine steel and concrete in one member, which results in a member that has the beneficial qualities of both materials. A developed monotonic stress-strain relation for confined concrete is modified for the analysis of steel tube walled section columns. The influence of steel tube on the lateral response of CFT columns is studied based on the fiber analysis method; particularly, the enhancement of the ultimate compressive strain of concrete, the increase in curvature ductility capacity based on moment-curvature relationship and yield load-displacement are investigated. Inelastic dynamic analyses of CFT columns using two ground motions recorded are conducted to evaluate the seismic performance of CFT columns. The results indicate that using CFT columns provides adequate protection against the damage potential of the ground motions and shows the enhancement of seismic capacity of structures.

Most materials used in civil engineering are sensitive to strain rate. Therefore, strain rate effects should be considered in seismic analysis. Pushover analysis is a static method that deals with dynamic problems. How to consider strain rate effects in the method rationally needs research. The theory and approach of pushover analysis considering strain rate effects are presented in the paper. The process of pushover analysis can be regarded as a 1/4 cycle, and the duration of a 1/4 cycle can be estimated approximately. Using average strain rate, performing pushover analysis for the structure twice, strain rate effects can be considered rationally. According to the procedure presented in the peper, a four-story reinforced concrete frame structure is analysed. The result shows that the capacity of the structure increases after considering strain rate effects.