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The values of structural response modification factor R are fundamentally critical in the specification of design seismic action for buildings. However, there are significant differences in the values of R in the codes or standards in different countries. In this paper, 15 reinforced concrete (RC) frames with 3-story, 5- story, 8-story, 10- story, and 12-story for design basic earthquake acceleration 0.05 g, 0.10 g, and 0.20 g are designed using the R≈3 implicit in the current Chinese codes. The accuracy of finite element models is verified via data from the shaking table test. A Demand-Capacity-Factor Method (DCFM) is used to evaluate R. The results show that the RC frames designed using the R≈3 and redesigned using the R≈6 can all meet the expected safety goals-against collapse under major earthquakes. The R≈3 implicit in the current Chinese codes are relatively conservative and the seismic influence coefficient curves under minor earthquakes should be improved.

A new external retrofitting sub-structure is proposed, namely, self-centering precast bolt-connected steel-plate reinforced concrete buckling-restrained-brace-frame (SC-PBSPC BRBF). Based on the 3D...

Nonstructural components (NSCs) are parts, elements, and subsystems that are not part of the primary load-bearing system of building structures but are subject to seismic loading. Damage to NSCs may disrupt the functionality of buildings and result in significant economic losses, injuries, and casualties. In past decades, extensive studies have been conducted on the seismic performance and seismic design methods of NSCs. As the input for the seismic design of NSCs, floor response spectra (FRS) have attracted the attention of researchers worldwide. This paper presents a state-of-the-art review of FRS. Different methods for generating FRS are summarized and compared with those in current seismic design codes. A detailed review of the parameters influencing the FRS is presented. These parameters include the characteristics of ground motion excitation, supporting building and NSCs. The floor acceleration response and the FRS obtained from experimental studies and field observations during earthquakes are also discussed. Three RC frames are used in a case study to compare the peak floor acceleration (PFA) and FRS calculated from time history analyses (THA) with that generated using current seismic design codes and different methods in the literature. Major knowledge gaps are identified, including uncertainties associated with developing FRS, FRS generation methods for different types of buildings, the need for comprehensive studies on absolute acceleration, relative velocity, and relative displacement FRS, and the calibration of FRS by field observations during earthquakes.

This paper investigates the influence of perforated masonry walls on the progressive collapse resistance of multi-story reinforced concrete (RC) structures. In this study, bare and infill-wall RC frames are studied by considering column failure at corner and exterior locations. Infill-wall panels are simulated by using equivalent compression struts and their provision of alternate load paths under the removal of a critical load-bearing element is examined. Linear static, nonlinear static, and nonlinear dynamic analyses are conducted by following the General Service Administration (GSA) guidelines. The analysis results show that the infill walls are beneficial in the redistribution of loads after the failure of the column and the collapse resistance of the RC building is increased. Empirical dynamic amplification factors (DAF) are also calculated in the sequel and the factor instructed in the GSA guidelines is judged by comparing with these computed dynamic factors. The results show that the DAF of 2, recommended by the GSA guidelines, is conservative and the presence of infill walls does not significantly affect the value of DAF.

Seismic performance evaluation of non-seismically detailed reinforced concrete buildings requires proper analytical modeling approaches for beam-column joints which are most vulnerable parts. This study investigates the influence of beam column joint modeling assumptions on performance evaluation of non-ductile RC buildings. Numerical simulation model includes truss-based elements for beam-column connections and fiber-based elements for beams and columns. Two-dimensional four- and six- story reinforced concrete frames of an existing RC building are designed and analyzed by conducting incremental dynamic analyses. Column chord rotations and corresponding strains are compared with code provisions for performance assessment of non-ductile RC frames., Seismicperformance evaluation of non-seismically detailed reinforced concretebuildings requires proper analytical modeling approaches for beam-column jointswhich are most vulnerable parts. This study investigates the influence of beamcolumn joint modeling assumptions on performance evaluation of non-ductile RCbuildings. Numerical simulation model includes truss-based elements for beam-columnconnections and fiber-based elements for beams and columns. Two-dimensionalfour- and six- story reinforced concrete frames of an existing RC building aredesigned and analyzed by conducting incremental dynamic analyses. Column chordrotations and corresponding strains are compared with code provisions forperformance assessment of non-ductile RC frames.

In this article, the effect of mainshock-aftershock sequences on the seismic performance of ordinary reinforced concrete frames (ORCFs) retrofitted by fiber reinforced polymers (FRPs) is studied. Various mainshock damage levels are used to precede aftershocks that are incrementally scaled to drive the studied structures into the collapse state. The mainshock damage is represented by the maximum inter-story drift (MID) parameter, and aftershock scaling is performed following incremental dynamic analysis (IDA) procedure. The derived collapse capacities are evaluated to study the effect of the mainshock and the retrofit action. The obtained results indicate that while the retrofit program is effective in elevating the collapse capacities of the structures, the capacity reductions caused by various mainshock damage levels in the studied structures are independent of the structures strength and ductility capacities. Rather, these capacity reductions were attributed to structures’ inherent plastic behavior mechanisms, including concrete cracking and reinforcement yielding.

In this paper, based on the RC frame structure of an industrial building, the finite element model of the structure is developed, according to the Chinese code for seismic design of buildings [9]. Considering the lack of seismic performance, the buckling restrained brace (BRB) is adopted for seismic retrofitting, and various configurations of buckling restrained support are considered for reinforcement. The elastic response spectrum analysis (RSA) and direct integration nonlinear time history analyses (NL-TH) are carried out for the frame structure before and after reinforcement using ETABS finite element software. From the joints displacement, inter-story displacement, inter-story shear force, acceleration, energy dissipation, and other aspects of the seismic response of the strengthened structure and the non-strengthened structure, the comparison has been made. The effect of buckling restrained support and common support on the existing building structure is verified through analytical modeling. After reinforcement, there is a 40%, 39.3%, 40%, 36.4%, and 38.3% reduction in the first period of vibration after the building is strengthened by inverted BRB, V BRB, two-story BRB, single BRB, and ordinary steel braces, respectively. Strengthening of the structure by buckling restrained braces and ordinary steel braces both decrease the original building displacement by more than 50% from the first to the fourth floor. Under severe earthquakes, the use of BRB reduced the column shear by 46.6%; similarly, the incorporation of ordinary steel braces reduced the column shear by 4.72%. It is concluded that using buckling restrained braces will increase the vertical stiffness of the structure to a very high extent.

In this study is investigated the performance of different glass fibre-reinforced polymer strengthening schemes on infilled reinforced concrete (RC) frames. The main objective was to limit the dama...

This paper presents experimental and analytical investigations of infilled reinforced concrete (RC) frames with steel corrugated shear walls. In the experimental study, two 1/3-scale, one-bay, two-storey specimens were constructed and tested under cyclic load reversals. One specimen was bare, for comparison. Properties affecting seismic performance, such as strength and stiffness of the two specimens, were investigated. However, owing to the inherent complexity of the infilled RC frame and the unique features of the steel corrugated shear walls, the experimental investigation was not sufficient to fully explain the influence of several parameters. Therefore, an analytical investigation based on finite-element models using ANSYS was conducted. Validation of the finite-element models against the experimental results showed good agreement. Critical parameters influencing the behaviour of steel corrugated shear walls, such as thickness and orientation of corrugated sheets, were varied, and the effects on seismic behaviour discussed.

This paper presents an experimental study about the development of a sustainable and multifunctional composite sandwich panel for the rehabilitation of reinforced concrete (RC) buildings from the 1960s to the mid-1980s. For this purpose, the cyclic behaviour of representative RC frames was assessed by performing in-plane quasi-static cyclic tests on three different specimens: (i) a bare RC frame (individual behaviour of the frame); (ii) an RC frame with masonry infill wall (representative of target buildings); and (iii) an RC frame strengthened with an innovative sandwich panel formed by outer wythes in recycled steel fibre reinforced micro-concrete and polystyrene core layer. The results show that, in comparison with the traditional masonry infill wall solution, the proposed rehabilitation solution significantly improved the cyclic performance of the RC frame, reaching higher levels of load carrying capacity (395% vs. 349% increase) and energy dissipation (700% vs. 524% increase). Moreover, the sandwich panel has maintained its structural integrity with low level of damage in its internal load-bearing layer for high values of lateral drift (up to 2.1%)., The first author wishes to acknowledge the financial support provided by the Portuguese Foundation for Science and Technology (FCT) and the Eco-Construction and Rehabilitation (EcoCoRe) Doctoral Program through the research grant PD/BD/52657/2014. The authors would like to thank the collaboration and support of the following companies for supplying/producing different components: (i) Twincon (RSF); (ii) Tecnipor (RC-frames); (iii) CiviTest (sandwich panel prototype); (iv) BVT–Rausch and PreConTech (functional GFRP connectors); (v) Sch¨ock Bauteile GmbH (structural GFRP connectors); (vi) Hilti (mechanical and adhesive anchoring systems); and (vii) Danosa/Eurofoam (extruded polystyrene plates). The authors also wish to thank the Structural Laboratory from University of Minho.

Equivalent single-degree-of-freedom (ESDOF) models are widely used to evaluate the collapse capacity of multistory structures, and their rationality is very important because it greatly affects the...

Shake-table tests conducted on three as-built and six haunch-strengthened two-story RC frames were analyzed to develop damage scale; suggest roof drift and base shear coefficient for various perfor...

Research efforts are still required for modelling the seismic behaviour of infilled frames, especially for existing buildings, generally characterised by shear failures. This work discusses the experimental seismic behaviour and the related modelling of four conforming (compliant with modern seismic codes) and non-conforming (gravity-loads-designed) Reinforced Concrete (RC) frames with and without infills (with hollow-clay bricks). The experimental results are analysed, showing that non-conforming frames exhibited shear failures involving the infill panel and the RC columns/joints. A proposed modelling approach able to reproduce these shear failures is carried out, providing support towards more reliable numerical simulations of RC buildings.

This paper discusses on the efficiency of partial replacements of fine aggregate (sand) by waste crumb rubber for improving the deformability and structural ductility of the reinforced concrete (RC) frame and thus resisting progressive collapse. This research experimentally tested the behaviour of four RC frames at one-third-scale under the middle column removal scenario. For comparison, two frames were prepared for 0% crumb rubber as the controlled specimens. The remaining frames were prepared for 20% crumb rubber replacements by volume for sand. The mechanical properties, failure mode, the crack pattern, the load-displacement behaviour, and structural ductility are analysing herein for normal and RuC frames. Results indicated that there was enhanced in structural ductility induced by the addition of crumb rubber in conventional concrete. Meanwhile, the RuC frames showed more deflection than the NC frames. Therefore, RuC is an eco-friendly building material that can be used for enhancing the ductility of RC elements as a new design strategy for preventing progressive collapse.

Improper execution of modern code-designed structures in many developing countries have resulted in significant deficient building stock; low strength of concrete, reduced reinforcement, inappropriate detailing of beam-column members, and lack of lateral ties in joint panels. Observations based on earthquake-induced damages and experimental studies conducted on such buildings have revealed significant vulnerability of beam-column joints of bare moment-resisting frame structures. Shake table tests were conducted on selected three 1 : 4 reduced-scale three-story reinforced concrete (RC) moment-resisting frames, including one bare RC frame and two masonry-infilled RC frames, having relatively lower bay width-to-height ratio. The models were tested under multilevels of seismic excitations using natural acceleration time history of 1994 Northridge and also free vibration tests, to acquire the models’ dynamic characteristics, i.e., frequencies and elastic viscous damping, and seismic response parameters, i.e., roof displacement, interstory drift and interstory shear, and seismic response curves, in order to understand the role of masonry infill in the selected frames under moderate seismic actions. The inclusion of masonry infill avoided joint shear hinging of the frame. Additionally, the infill provided energy dissipation to the structure through masonry sliding over multiple cracks. This enabled the structure to control seismic displacement demand and resist relatively higher ground motions, yet limiting structural damages.

The conventional reinforced concrete Moment Resisting Frames (MRFs) have suffered from soft story failure during major earthquake events. A novel system of steel Energy-Dissipative Rocking Column (EDRC) is proposed to mitigate seismic responses of MRFs. Pseudo-dynamic tests are conducted on large-scale two-story and two-bay reinforced concrete frames, with and without EDRC, respectively. The post-earthquake behavior of these two systems is also compared through quasi-static cyclic tests. The experimental results show that the presence of EDRC can effectively mitigate the maximum value, residual value and inhomogeneous distribution of inter-story drifts, and thus prevent the soft story failure of MRFs. It is found that the maximum and residual inter-story drift of combined MRF and EDRC systems is reduced by 26.0% and 82.0%, respectively, compared to pure MRFs. The inhomogeneous degree of inter-story drifts can be reduced by 25.0% and 11.0%, respectively, in the pseudo-dynamic and quasi-static tests.

Purpose Columns are structural elements that are predominantly subjected to compressive forces and moments that are to be transferred from the super-structure to the sub-structure. The geometrical shape of a column is a significant factor to be considered. The paper aims to discuss this issue. Design/methodology/approach Pushover analysis is carried out, to study the behavior of RC frames with rectangular and specially shaped columns for the same building layout. Findings Reduction of 27.3 percent in base shear, 67.4 percent in spectral displacement, 66.5 percent reduction in storey displacement, 70.22 percent in storey drift and 0.315 percent reduction in storey shear is observed. Practical implications Special shaped RC columns can effectively enhance the structural behavior of high rise structures under seismic excitation in comparison to those with regular shaped RC columns. Originality/value Applications of special shaped columns in structures have showed a great deal of reduction in displacement and shear forces developed due to seismic activity, for the same area of concrete and steel as in rectangular columns.

Due to inadequate lateral stiffness and insufficient structural redundancy, many single-span reinforced concrete (RC) frames were highly damaged or collapsed in previous earthquakes. This paper presents an experimental study on seismic performance of rehabilitated single-span RC frames. Four frames were strengthened using various retrofitting strategies and one non-retrofitted frame served as the reference specimen. All these frames were fabricated and tested under cyclic loadings. The failure modes, hysteretic behavior, skeleton curve, energy dissipation, strength and stiffness degradation of each frame were evaluated. The validity of different strengthening methods for improving frames’ failure mechanisms and seismic performances was verified. Test results indicated that strength, stiffness, as well as many seismic characteristics of the strengthened frames were improved substantially.

Performance of infill walls in reinforced concrete (RC) frames is generally questionable under the combined action of in-plane and out-of-plane seismic demands. Despite the vast number of tests investigating the behavior of brick masonry infill walls in RC frames, past research is limited for infill walls made of Autoclaved Aerated Concrete (AAC) blocks. In the first part of the study, six single-bay single-story half-scaled RC frames were tested under the action of in-plane cyclic displacement excursions and/or out-of-plane pressure. It was found that the presence of out-of-plane pressure can significantly reduce the deformation capacity of RC framed AAC infill walls. Afterwards, a new innovative system is proposed to protect the infill walls from in-plane induced forces while providing out-of-plane support. Sliding connectors placed inside the AAC blocks were used to isolate the infill wall from earthquake-induced frame deformations, while providing out-of-plane support. In order to test the beneficial effect of the proposed system, three additional tests were conducted. The proposed system managed to reach in-plane deformation demand of 2% without cracking and preserving its out-of-plane stability.

The analysis of the behaviour of masonry infills under out-of-plane (OOP) and in-plane (IP) loading is paramount to correctly assess the seismic performance of reinforced concrete (RC) frames. A very important issue about this topic is certainly the IP/OOP interaction, namely the analysis of how the IP damage, which affects infills during earthquakes, can influence their OOP behaviour (and vice-versa). Some studies about this topic were developed in the last years; nevertheless, only a dozen of tests currently exists in the literature to experimentally explore this key issue. This work first presents an experimental campaign carried out on square infill walls in RC frames to investigate about the OOP behaviour of the masonry infills, and about the IP/OOP interaction. On the whole, four specimens have been tested under OOP monotonic loading. Three of them have been first damaged under cyclic IP actions, with different extent; the remaining one, used as a reference, was tested under OOP loading only. The experimental campaign is described in detail in terms of specimens’ characteristics, material properties, adopted setup and instrumentation layout. The experimental results are analysed in terms of IP and OOP force-displacement responses, vertical arch strength contribution evolutions, and damage state evolutions, and compared with prediction proposals from the literature. Then, the influence of the infill aspect ratio (width (w)-to-height (h) ratio) on the IP/OOP interaction is investigated by means of the comparison between data presented herein (collected on infills with w/h = 1) and a companion experimental campaign previously performed on nominally identical infills except that for the aspect ratio of the specimens (in that case, higher than the unit). It has been observed that under given IP drift levels, square infills presented lower IP damage levels with respect to rectangular infills (with w/h > 1), thus generally producing a less pronounced detrimental effect of the IP imposed drift on the OOP strength. Nevertheless, none of the predictions from literature takes into account the role of the aspect ratio on the IP/OOP interaction, generally resulting in conservative predictions, to be improved in future works.

In this paper, a new technique is proposed for retrofitting low-rise soft-first-story reinforced concrete buildings. The proposed retrofitting technique is called “Thick Hybrid Wall”. In this method, channel-shaped steel plates jacket boundary RC columns of a bare frame. The steel plates are extended to the bay of the frame through the additional steel plates connected together with the help of bolts. Then, additional concrete is cast in the provided steel formworks. To verify the efficiency of the proposed technique, one non-retrofitted specimen and four retrofitted specimens were tested under cyclic horizontal loading and constant axial forces. The observed experimental results determined that the thick hybrid walls not only increase the lateral strength and stiffness of the frames, but also considerably improve the lateral ductility. In addition to obtaining superior structural performance, the proposed method provides ease in construction at a building site, and minimizes the vibration, noise, and concrete dust of the retrofitting operation. The proposed method has the potential of significant reduction in construction costs of retrofitting existing buildings.

The shear capacity of masonry-infilled reinforced concrete (RC) frames is determined experimentally by testing of five 2/3 scale, one story, one bay infilled RC frame specimens with varying degrees of separation between upper and lower portions of the masonry infill panel. The main premise of this experimental study was to find the contribution of masonry panel in global resistance of infilled RC frames versus shear force. Based on the experimental results, a new method is proposed for the determination of the shear resistance and the contribution of the masonry infill panel is derived. Comparisons of experimental and analytical results show that the proposed method for evaluating the shear resistance of the masonry panels offers a promising approach for the design of infilled RC frames. Furthermore, the results of this study indicate that the shear resistance of masonry panel in infilled RC frames is strongly influenced by the stiffness and lateral resistance of the RC frame.

A precast prestressed concrete frame system with mild press joints is introduced for the seismic retrofit of existing reinforced concrete frames. Cyclic loading tests are conducted on precast prestressed concrete and cast-in-situ reinforced concrete frame subassemblies to investigate the hysteretic behavior and damage characteristics of the frames. The test results demonstrate the damage-tolerance of precast frames in terms of well-controlled cracking and minimized residual drift compared to monolithic RC frames. A simplified numerical model is introduced to simulate the hysteretic behavior of mild press joints. The dynamic seismic response of a prototype building retrofitted by the proposed method is evaluated by numerical analysis. Two retrofit plans with different attached precast frames are compared. The results suggest that a partial retrofit of certain lower stories, which has been a common practice in Japan, may create drift concentration in the upper stories of a building.

A set of 4-, 8-, 12-, and 15-storied reinforced concrete moment resisting frames were analysed and designed by direct displacement-based design method and performance-based plastic design method. The design spectra of Indian Standard IS 1893:2016 have been used for the calculation of base shear after its proper synchronization with respect to both the methods. The seismic performance evaluation was done by nonlinear static pushover analysis, and the parameters of comparison were (a) pushover curves, (b) storey drifts and (c) response reduction factor. Results show satisfactory performance of both the methods in terms of capacity and deformation. The response reduction factor values obtained for both approaches are greater than the IS 1893:2016-specified value which indicate the enhanced ductility for both methods.

Freeze-thaw of concrete is significantly responsible for serious damage to RC buildings, which may result in premature failure with little warning. Therefore, it is necessary to consider the effect...

This study focused on characteristic cases of recently tested real-scale RC framed wall infilled structures with innovative seismic protection through polyurethane joints (PUFJ) or polyurethane-impregnated fiber grids (FRPU). The frames revealed a highly ductile response while preventing infill collapse. Herein, suitable 3D pseudo-dynamic FE models were developed in order to reproduce the experimental results. The advanced Explicit Dynamics framework may help reveal the unique features of the considered interventions. Externally applied double-sided FRPU jackets on OrthoBlock infills may maintain an adequate bond with the surrounding RC frame as well as with the brick infill substrate at up to a 3.6% drift. In a weak four-column RC structure, the OrthoBlock infills with PUFJ seismic joints may increase the initial stiffness remarkably, increase the base shear by three times (compared with the bare structure) and maintain a high horizontal drift of 3.7%. After this phase, the structure may receive FRPU retrofitting, reveal the redistribution of stress over broad infill regions, including predamaged parts, and still develop a higher initial stiffness and base shear (compared with the bare RC). The realization of a desirable ductile behavior of infilled frames through PUFJ of only 20 mm thickness, as well as through FRPU jacketing, may remarkably broaden the alternatives in seismic protection against the collapse of structures.

Previous earthquakes have shown that for structures that experience a significant ground motion with only minor damage, there is a likelihood of severe damage or complete collapse during th...

Reinforced concrete (RC) frame structures with open first stories and masonry infill walls at the upper stories are very common in seismic areas. Under strong earthquakes, most of the energy dissipation demand imposed by the earthquake concentrates in the first story, and this eventually leads the building to collapse. A very efficient and cost-effective solution for the seismic upgrading of this type of structure consists of installing hysteretic dampers in the first story. This paper investigates the response of RC soft-story frames retrofitted with hysteretic dampers subjected to near-fault ground motions in terms of maximum displacements and lateral seismic forces and compares them with those obtained by far-field earthquakes. It is found that for similar levels of total seismic input energy, the maximum displacements in the first story caused by near-fault earthquakes are about 1.3 times larger than those under far-field earthquakes, while the maximum inter-story drift in the upper stories and the distribution and values of the lateral forces are scarcely affected. It is concluded that the maximum displacements can be easily predicted from the energy balance of the structure by using appropriate values for the parameter that reflects the influence of the impulsivity of the ground motion: the so-called equivalent number of cycles.

The natural landscape in China exposes many existing RC buildings to aggressive environments. Such exposure can lead to deterioration in structural performance with regard to resisting events such as earthquakes. Corrosion of embedded reinforcement is one of the most common mechanisms by which such structural degradation occurs. There has been increasing attention in recent years toward seismic resilience in communities and their constituent construction; however, to date, studies have neglected the effect of natural aging. This study aims to examine the effect of reinforcement corrosion on the seismic resilience of RC frames that are designed according to Chinese seismic design codes. A total of twenty RC frames are used to represent design and construction that is typical of coastal China, with consideration given to various seismic fortification levels and elevation arrangements. Seismic fragility relationships are developed for case frames under varying levels of reinforcement corrosion, i.e., corrosion rates are increased from 5% to 15%. Subsequently, the seismic resilience levels of uncorroded and corroded RC frames are compared using a normalized loss factor. It was found that the loss of resilience of the corroded frames is greater than that of their uncorroded counterparts. At the Rare Earthquake hazard level, the corrosion-induced increase in loss of resilience can be more than 200%, showing the significant effect of reinforcement corrosion on structural resilience under the influence of earthquakes. Supported by: National Natural Science Foundation of China under Grant No. 51778198, and the Natural Science Foundation for Excellent Young Scientists of Heilongjiang Province under Grant No.YQ2020E023.

The 2017 New Zealand Society for Earthquake Engineering (NZSEE) guidelines for seismic assessment of buildings recommends using Simple Lateral Mechanism Analysis (SLaMA) before implementing numerical analyses. The method and the NZSEE guidelines have been enhanced from the 2006 version, resulting into an efficient procedure, balancing simplicity and accuracy. This paper presents a numerical study, initiated as part of the development of the SLaMA-2017 method, to investigate the accuracy of the analytical approach via comparison with numerical 2D-pushover on 40 RC frames. SLaMA is effective in capturing the plastic mechanism of the frames, including global or soft-story mechanisms. Further-yet-simple refinements of the procedure are suggested.

In the world, many existing buildings with RC framed structure are extremely vulnerable, as they were designed to sustain gravity loads only, or to resist seismic actions lower than those expected today. Since a complete renewal of the existing building heritage is not possible, the seismic assessment of existing structures has gained importance in recent years to identify the structural deficiencies and design the most appropriate retrofit interventions. This paper proposes a multimodal adaptive nonlinear static method of analysis named overDamped Displacement Adaptive Procedure (D-DAP). This method has been developed from the combination of the approaches adopted by Pinho et al. and Lenza et al. In addition, the D-DAP explicitly considers the increase of the energy dissipation due the cumulated damage in the structure by updating the value of equivalent viscous damping ratio according to a new damping law properly calibrated for RC frames with and without infill panels.

Lateral stiffness provided by infill walls to the building structures is generally neglected in designs. Infill walls, which are only included in the calculations as dead loads, significantly affect the lateral resistance, stiffness and energy dissipation of the frames. Both the studies in the literature and the infill wall damages observed after the earthquake support the existence of these unforeseen effects in the design. It is an important problem to reflect the infill wall effects to the site application as designed. In this study, the solution to isolate the infill walls from the load-carrying frames is adopted. Three different flexible connection elements designed in this context were examined experimentally and numerically, their in-plane behavior was compared with bare and traditionally infilled frames. As a result of the study, it was observed that the frames with flexible connections behaved close to the bare frame in the initial drifts, unlike the fully infilled frame behavior, which significantly lost its lateral resistance in the initial drifts, and continued its lateral resistance without any damage until further drifts. It is thought that the flexible connections will be an important development in terms of compatibility of design and site applications.

This research investigated the changes in vibration characteristics of a simple reinforced concrete (RC) frame subjected to incremental cyclic pushover testing as a basis for detection, quantification, and localization of damage in RC frames using vibration data obtained before and after a seismic event. A half-scale one-story one-bay plane frame was subjected to progressive damage through cyclic lateral loading to incrementally increasing drift ratios. Ambient and impact vibration tests were performed at each increment of drift ratio, and modal analyses of the acceleration responses obtained at seven locations on the frame were carried out with the acceleration responses measured at seven different locations on the frame to track changes in the dynamic characteristics. Linear degradation of the lowest two vibration frequencies was identified with increasing drift ratio, which was regarded as a promising result towards detection and quantification of damage. For localization, a flexibility-based damage localization procedure, the damage locating vector (DLV) approach, was explored. Localization results mostly agreed with the observed damage, and the approach was found to have potential for use in prioritizing the suspected damage locations in the structure for detailed inspections.

This paper evaluates the effect of construction quality defects on the seismic vulnerability of reinforced concrete (RC) frames. The variability in the construction quality of material properties and structural detailing is considered to assess the effect on the seismic behavior of RC frames. Concrete strength and yield strength of the reinforcement are selected as uncertain variables for the material properties, while the variabilities in the longitudinal reinforcement ratio and the volumetric ratio of transverse reinforcement are employed for structural detailing. Taking into account the selected construction quality uncertainties, the sensitivity analysis of the seismic vulnerability of the RC frames is performed and the impact of significant parameters is assessed at the global and local levels. This extensive analytical study reveals that the seismic vulnerability of the selected RC frame is particularly sensitive to concrete strength and the volumetric ratio of transverse reinforcement.

This paper presents a study on a retrofit technique for masonry infilled reinforced concrete (RC) frames. The proposed retrofit technique involves the addition of reinforcing steel bars into epoxy-filled pre-cut grooves on the surface of infill walls. The feasibility of the developed technique is initially investigated experimentally through pull-out tests conducted on near-surface mounted (NSM) reinforcing steel bars. The experimental results are used to augment an existing nonlinear finite element modeling approach used to simulate the response of RC frames with the retrofitted infill panels and to calibrate the numerical models developed. The nonlinear finite element models employ smeared-crack and zero-thickness cohesive-crack interface elements to model the RC members and masonry infills, while nonlinear truss elements are used to model the reinforcing steel bars. The modeling scheme is used to numerically simulate the performance of one- and two-bay infilled RC frames with a variety of reinforcing steel retrofit configurations under lateral loads. The results indicate that the retrofit solution can improve the deformation capacity of existing infilled frames, and its effectiveness depends on the orientation and the distribution of the NSM reinforcement steel bars that are added to the infill panels.

This study is devoted to experimentally investigate the seismic behaviour of reinforced concrete (RC) wide beam–column joints equipped with a steel jacketing seismic strengthening solution. To this end, three identical full-scale specimens have been tested under cyclic loading, one in the as-built condition and two after the application of the strengthening solutions. Details of selected solutions are described in the paper along with the experimental results which confirm how the application of simple and feasible steel interventions can effectively improve the seismic capacity of wide beam–column connections in RC frames, especially in terms of lateral load carrying capacity and energy dissipation.

In the present study, the behaviour of infilled RC frames under earthquake loading is investigated numerically, and the influence of three different concrete material models on the in-plane behaviour of infilled RC frames is evaluated using the finite element analysis (FEA). For this reason, the efficiency of infilled walls is examined on full scale models. Finite element analysis results show that mathematical model of concrete may change behaviour of infilled RC frames. The post-peak behaviour is especially influenced.

Lateral load behavior of reinforced concrete (RC) frames infilled with fly-ash brick masonry having various sizes of central openings was investigated experimentally. Results showed that th...

Within the European FP7 Project “INSYSME”, a new seismic-resistant clay masonry infill system was conceived with the purpose of controlling damage in the masonry and reducing detrimental effects of the panel-frame interaction, through a combined use of sliding joints inserted in the masonry and deformable joints at the wall-frame interface. Although the idea behind the proposed solution stems from principles already implemented in the past, the originality of this work lies in the innovative development of the materials and of the construction details of the components. In order to assess the seismic performance of this new system, in-plane cyclic tests on one-storey one-bay RC frames with two different infill configurations (one solid and one with a central opening) have been performed within the framework of a wider experimental campaign and are discussed here. These in-plane test results have proved the ability of the proposed solution in limiting the level of damage along with the attainment of a wide margin towards the life safety requirements in comparison with traditional infill systems. Although design and construction optimization of the solution still needs to be further implemented, the results of the in-plane tests appear very promising about its use as an efficient seismic resistant non-structural component in RC buildings.

When existing Reinforced Concrete (RC) framed structures are strengthened with Precast Concrete (PC) wall panels, a special connection is required that can accommodate the time-dependent deformation of the RC frame when using PC members made of the same size and resist a large shear force. In this study, we propose a connection that can solve both of these issues through overlapping anchors. The purpose of this study is to investigate and analyze the shear resistance of the overlapped anchor connections between the PC panel and the RC elements in modeling tests. A total of ten full-scale specimens of anchored connection models were constructed and push-out tested. Two anchor groups were installed in three concrete segments and overlapped in the connection of the specimens. The tested average shear strength of the overlapped anchored connections was 109% of the calculated values according to the American anchor design code. The results of this study show that the new anchored connection model can be analyzed using the American anchor design code. Therefore, we can predict the effect of the proposed connection, and it is expected that the design safety and construction practicability of the infill method will be improved using these connections.

One of the common method for retrofitting RC frames is to use steel braces. The majority of reported research related to steel bracing of RC frames have highlighted the positive effects of bracing such as improving structural performance, increasing shear capacity, reducing displacements and decreasing drifts. Very little is reported on the possible side effects of the technique on the RC members, particularly those of columns. This papers aims at evaluating, through time history analyses, the behaviour of RC columns before and after retrofitting with steel X-bracing and examining possible complications, increased demands and side effects of such a retrofitting method. The effects on the level of column shear and axial force, as well as, column performance level and low cycle fatigue life are investigated. As a general conclusion, it is found that retrofitting low-rise RC frames with steel X bracing is beneficial to the performance of frame columns in almost every aspect; however, for mid to high-rise frames, the adverse effects of retrofitting, particularly on columns attached to the bracing system, are considerable and should be taken into consideration and if needed, local strengthening of columns should simultaneously be undertaken.

Steel bracing may be used to enhance the seismic strength of RC frames. Concentric steel bracing generally reduces ductility, which is a key component of seismic design. To overcome the problem, ductile steel brace-RC frame systems are therefore usually introduced in the form of eccentric braces. In the present study, the Off-Diagonal Bracing System (ODBS), which works as a concentric type of bracing, is investigated. In this paper the response of ODBS elements to cyclic loading is first explored and compared with those of other types of bracing such as X-bracing and inverted-V bracing systems. The time history analysis responses and cyclic hysteresis responses of a number of lowrise to mid-rise RC frames retrofitted with different types of bracing systems are then evaluated and compared. It is shown that under seismic excitation, a much reduced base shear is experienced by frames retrofitted with ODBS compared to other bracing systems. The results of time history and cyclic hysteresis response analyses also indicate a far greater energy dissipation capacity and ductility for the ODBS compared to other bracing systems. It is also concluded that ODBS performs best in lowrise frames. The out-of-plane buckling response of the ODBS is also investigated, and it is shown that a double-plated central connection can control such an adverse response.

In recent years, a novel type of hybrid coupled wall (HCW), which consists of reinforced concrete (RC) wall piers and replaceable steel coupling beams (RSCBs), has been proposed for enhancing the seismic resilience of high-rise buildings. This paper presents the assessment of the seismic performance of an 11-story building located in a highly seismic area and designed per modern Chinese codes. The building adopts the frame-shear wall interacting system. For comparison, two cases are considered: one using the novel hybrid coupled walls and another using conventional RC coupled walls (RCW). The dynamic response of the buildings under high intensities of ground motion shaking is obtained from nonlinear dynamic analysis in OpenSees. The seismic performance, expressed in terms of repair cost and time, is assessed based on the FEMA P-58 method. The results indicate that most of the damage is concentrated in the coupling beams and nonstructural components. The use of novel HCWs instead of conventional RCWs results in maximum interstory drifts up to 24.5% lower in the HCW building than the RCW building when subjected to a maximum considered earthquake (MCE) intensity. Novel HCWs result in a reduction of 50.8% and 60.5% in the median building repair cost and time, respectively, under MCE, due to less damage to coupling beams and RC frames and easy replacement of RSCBs after a damaging earthquake. It is also noted that HCWs have limited influence on the peak floor accelerations, and thus the repair cost and time for acceleration-sensitive non-structural components are similar for both the HCW building and the RCW building.

The strengthening of damaged concrete structures using new cementitious composites such as high-performance fiber-reinforced cementitious composites (HPFRCC) with proper strain hardening behavior under cyclic loads is a suitable solution for economic utilization of RC structures. In this paper, the technique and results of strengthening the damaged and undamaged frames with HPFRCC composite thin layer subjected to lateral and gravity loads are presented. Experimental program includes four frames, one unstrengthened and undamaged frame as reference, one strengthened undamaged frame, and two strengthened partially damaged (with initial 55 and 75 percentage of ultimate load), and they were tested under both vertical and lateral loads. The results indicated that the ductility of two strengthened frames with initial 55, 75% damage of the maximum load and the undamaged strengthened frame was up to 110, 60, and 121% more than that of reference frame, respectively. The yielding loads of the tension bars at the strengthened damaged and undamaged specimens had been significantly increased up to 42%, and ultimate loads of the undamaged and two damaged frames (55, 75%) were increased up to 38 and 35, 16% compared to the reference frame; energy absorption in three same frames was 2.37, 2.75, 1.83 times of that of unstrengthened reference frame.

Three reinforced concrete (RC) structures of the same height (3000 mm) but with different span lengths (4500, 6000 and 7500 mm) were subjected to nine different natural fire curves when different opening ratios (0·02–0·20) were applied. All the cases aimed to meet a 60 min fire resistance rating (FRR) based on the standard ISO 834 fire curve. Structural fire analyses showed that there was no collapse during the heating phase, confirming that all the cases were able to meet the required FRR. However, the results also showed that the possibility of structural failure during the decay phase increased with increases in span length and opening ratio. Furthermore, the results showed that structures with larger span lengths were more susceptible to collapse during the cooling phase than structures with shorter span lengths. The results of this study can be used as guidance to determine the FRR of structures with different opening ratios, thus providing more information about structural performance prior to a fire event.

The response modification factor (R-factor) of reinforced concrete (RC) moment resisting frames (MRFs) designed with adequate ductility in accordance with the Egyptian code is evaluated. Static pushover and earthquake time history analyses are employed to determine the actual R-factors of nine RC-MRFs with different geometric configurations. The geometric configuration parameters considered include the number of stories, the number of bays, the bay-width and the story height. The results obtained in this study indicate that the R-factor value decreases with the increase in the frame height and that the changes in the number and span of bays have a minor effect on the R-factor. The R-factors calculated by earthquake analysis are generally smaller than the corresponding values calculated by static pushover loading. The R-factors calculated for the frames considered in this study vary from 6.18 to 9.85 in case of static analysis and from 5.43 to 8.43 in case of earthquake analysis. The minimum limit of the calculated R-factors is smaller than the R-factor of seven specified by the Egyptian code for the design of RC-MRFs with adequate ductility.

Friction-based dampers can be considered as one of the suitable passive control systems for seismic strengthening and rehabilitation of existing substandard structures due to their high adjustability and good energy dissipation capability. One of the main issues in the design of these systems is to obtain the magnitude of the maximum slip force and the distribution of slip forces along the height of the building. In this study, a practical performance-based optimisation methodology is developed for seismic design of RC frame buildings with friction energy dissipation devices, which allows for an accurate solution at low computational cost. The proposed method aims at distributing the slip loads of the friction dampers to achieve a uniform distribution of damage along the height of the building. The efficiency of the method is evaluated through the optimum design of five different low to high-rise RC frames equipped with friction wall dampers under six natural and six synthetic spectrum-compatible earthquakes. Sensitivity analyses are performed to assess the reliability of the method using different initial height-wise slip load distributions, convergence parameters and earthquake records. The results indicate that optimum frames exhibit less maximum inter-storey drift (up to 43%) and global damage index (up to 75%), compared to uniform slip load distribution. The method is then developed to obtain the optimum design solution for a set of earthquakes representing a design spectrum. It is shown that the proposed method can provide an efficient tool for optimum seismic design of RC structures with friction energy dissipation devices for practical purposes.

Artificial neural networks, ANNs, can predict the behavior of systems that have common main features. When the problem under consideration contains groups that involve different main features, different ANNs are needed to predict the behavior of each group separately. In this paper, the efficiency of a single ANN to predict the lateral behavior of two-span structures representing a mix of low-, medium- and high-rise buildings in Egypt was investigated. All buildings were first analyzed using nonlinear pushover analysis to obtain their capacity curves, failure loads and displacements. Obtained data were used for training different ANN models. The results indicated the efficiency of a single ANN to predict the behavior of a mix of all buildings under investigation with a confidence level of 99%. The successful network was further utilized to obtain another set of data that were merged with the original data and used to develop a design neural network. The obtained network showed a very good capability to predict design variables which can be a good tool for engineering practitioners.

Unreinforced masonry infill walls are widely used as non-structural partitions in RC frames. The effects of infills on the structural responses are often ignored in the design process since they are generally considered as expendable elements. However, recent studies have shown that not only shear damage can be inflicted to the columns braced by the infill walls, but also that the structural stability can be jeopardised by the fall-off of the infills. This paper presents the development of new detailing methods for the infill walls, which features slit panels, isolation gaps between the infills and columns, and anchorage of the infills. The proposed detailing methods were tested and verified experimentally using shake-table tests on five 1/3-scale infilled RC frame specimens with different combinations of the features stated above. The design and construction of the shake-table test specimens have taken into account the similitude requirements. The test results indicate that the proposed detailing method effectively reduced the undesirable interaction between column and infill walls. And the use of proper anchorage could prevent the fall off of infills from the bounding frame. Furthermore, the specimens with slit infill walls displayed better seismic performances, which could be attributed to the rocking behaviour of the sub-panels with increased aspect ratios.