Reinforced Concrete Frame Structures Research Articles

Progressive collapse fragility of substandard and earthquake-resistant precast RC buildings

Several natural and man-made disasters have highlighted that precast reinforced concrete (RC) buildings often have insufficient levels of structural robustness, which is the last line of defence under extreme events. Even though robustness studies were originated by the progressive collapse of the Ronan Point precast RC building in 1968, such a structural feature of disaster resilience has been partially investigated in case of precast RC buildings to date. In this study, a precast RC frame structure representative of low-rise commercial buildings is analysed under different column loss scenarios, which can produce the partial or total collapse of the structural system. Two building classes are considered, namely, buildings designed only to gravity loads and buildings designed for earthquake resistance. Structural robustness is probabilistically assessed through a fragility analysis procedure, using three-dimensional fibre-based finite element models with nonlinear links simulating connections, large-displacement incremental dynamic analysis, and multiple performance limit states for damage assessment. The output of the study is threefold: (i) a detailed assessment of the effects of column loss on precast RC frame buildings, quantifying the major role of structural detailing and beam-column connections; (ii) a fragility-informed evaluation of beneficial effects of seismic detailing on structural robustness, which can drive designers in retrofitting of existing precast RC buildings and decision-makers towards prioritization-related issues; and (iii) the generation of typological fragility curves for progressive collapse risk assessment in both single- and multi-hazard environments. Progressive collapse fragility curves can be convolved with more classical fragility models describing the failure of single components (under, e.g., flow-type landslide impact, vehicle collision or blast) and hazard, to assess systemic structural risk.

Reliability analysis of reinforced concrete structure against progressive collapse

New reliability computation framework is proposed based on polynomial chaos expansion method and used to investigate the reliability of four typical configurations of reinforced concrete (RC) frame structures under progressive collapse. The analytical model of considered structures was generated using displacement-based fiber elements to simulate frame structural components and an appropriate macro model to simulate masonry infills and subjected to pushdown analysis to assess the anti-collapse capacity of the structures. The reliability and failure mode of frame structures under different column-loss scenario are obtained from the analyses. Finally, based on PCE-based computation, sensitivity analyses are conducted. The effect of uncertain parameter on the progressive collapse resistance of RC frames are discussed. Results shows the failure probabilities of RC frame structure range from 0.0162 to 0.1373. The reliability of frame structures under side column-loss scenario is lower than the other conditions.

Research on Dynamic Characteristics of Joint of RC Frame Structure with NES

The NES (nonlinear energy sink) is a new type of nonlinear tuned mass damper that is connected to the shock-absorbing main structure through strong nonlinear stiffness and viscous damping. The vibrational energy in the main structure is transferred to the NES oscillator by means of target energy transfer. A shaking table test of a 1:4 scaled RC (Reinforced Concrete) frame structure model with a new type of NES shock absorber was conducted to study the damping effect of the NES shock absorber, especially for the influence of joint strength and deformation. The NES used in this experiment has a relatively large nonlinear stiffness and a wide vibration absorption frequency band. The variation of reinforcement strains, node failure mode, and structural natural frequency of 1 story and two-layer joints of the model frame structure with NES were studied. The test results showed that NES could effectively reduce the strains of longitudinal reinforcement and stirrup in beams and columns and delay the plastic hinge development at the bottom and the top of the column. The frame model with NES installed has failures at the beam ends and shear failures at the nodes, realizing the seismic mechanism of solid columns and weak beams. Compared with ordinary seismic structures, the NES can effectively reduce the shear stress of concrete at the joints and alleviate the shear failure of joints. The final failure of the NES shock absorbing structure was the yielding of the steel bars at the bottom of the column and the crushing of the concrete at the foot of the column, and the connection between the column foot and the backplane became loose simultaneously. The decreasing rate of the vibration frequency declined due to the NES with varied broadband absorbing capability. It can be seen that the NES shock absorber not only has a good effect on reducing the seismic response of the structure, but more importantly, the damage of the structural nodes is greatly reduced, and therefore, the seismic capacity of the structure improved.

Structural response of RC frame under surface curvature and differential settlement in mining areas

Ground subsidence caused by coal mining can lead to various forms of surface deformation, which endanger the safety of the buildings. To assess the influence of the surface curvature of the mining area on the dynamic performance and damage of surface buildings, the reinforced concrete (RC) frame structures with various differential settlement types are investigated using SAP2000 software. These structures' structural vibration property and damage characteristics are analyzed separately through the modal analysis method, theoretical derivation, and nonlinear static analysis. The result shows that the RC frame structure's natural vibration property and damage degree in the subsidence area vary with negative and positive surface curvature and should not be treated equally. The impact of surface curvatures in mining areas on natural vibration property is the change of structural mass distribution and the stiffness degradation caused by structural damage. The damage caused by the differential settlement will inevitably degrade the seismic performance of the structures located in the subsidence area.

Fast damage assessment of seismic-damaged structures based on response deduction and energy dissipation ratio

Considering the difference of cumulative deformation energy between the elastic-plastic state and the ideal elastic state, a structural damage assessment method based on the generalized elastic–plastic energy dissipation ratio (GEPEDR) is proposed. To solve the problem that the actual structure dynamic response in the ideal elastic state is difficult to predict, a method to deduce the dynamic response in the ideal elastic state according to Kalman filter is proposed. Based on the above research, the overall damage and interlayer damage assessment methods of seismic-damaged structures are presented. The nonlinear finite element analysis of reinforced concrete (RC) frame structures and the shaking table test of the 12-story RC frame structure are taken as examples for verification. The results show that the GEPEDR method can realize damage assessment based on only seismic signals and structural responses and reveal the dynamic evolution process of structural overall damage and the distribution of weak story.

Lateral load behaviour of Glass Fibre Reinforced Gypsum walls supported on Reinforced Concrete frames

Glass Fibre Reinforced Gypsum (GFRG) panel is a light-weight load-bearing hollow building panel, used as structural elements (walls, slabs etc.) with Reinforced Concrete (RC) filled inside the cavities. In GFRG construction, usually all the load bearing walls start from the foundation itself. But the ever-growing issue of land scarcity compels the housing sector to have the provision of parking space at the ground storey of the building. This will require the GFRG walls to be supported on an RC frame structure with columns, beams and slabs. The columns of such a structure can potentially cause a brittle mode of failure under the action of seismic forces, owing to the development of plastic hinges resulting in storey mechanism. The behaviour of such structures under combined gravity and lateral loads (monotonic and cyclic) was evaluated in the present study through quasi-static testing of two full scale specimens. The failure of the specimen under lateral loading was characterised by the failure of wall panel, with extensive crack formation before the yielding of frame members. The test results demonstrated the feasibility of designing GFRG wall on RC frame system without leading to brittle collapse mechanisms.

The Influence of the Flexural Strength Ratio of Columns to Beams on the Collapse Capacity of RC Frame Structures

Reinforced concrete (RC) frames are designed based on the strong column-weak beam (SCWB) philosophy to reduce structural damage and collapse during earthquakes. The SCWB design philosophy is ensured by the required minimum flexural strength ratio of columns to beams (FSRCB) in the seismic code. Quantifying the relationship between the FSRCB and the collapse capacity of the frames may facilitate the efficient assessment of the seismic performance of the existing or newly designed RC frames. This paper investigates the influence of different FSRCBs on the collapse capacity of three- and nine-story RC frames designed according to Chinese seismic codes. The results show that the collapse capacities of the RC frames can be efficiently improved by increasing the FSRCB, and the collapse capacities of frames with FSRCB = 2.0 are improved by approximately 1.6–2.0 times compared with those of the frames with FSRCB = 1.2. Compared with the middle- or high-rise (nine-story) frames, it is more efficient to improve the collapse capacity for low-rise (three-story) frames by increasing the value of CBFSR. The logarithmic standard deviation of the collapse capacity of the RC frames designed according to the Chinese seismic codes ranges from 0.5–0.9, which is larger than the proposed maximum logarithmic standard deviation (0.4) in FEMA P695.

Performance-based seismic design of RC frame structure with energy dissipative cladding panel connection system using equivalent energy design procedure

Recently, a high-performance reinforced concrete (RC) frame structure with an energy dissipative cladding panel connection system (EDCPCS) was proposed. It creatively uses the relative deformation between the main structure and the cladding panel through U-shaped steel dampers (USDs) to dissipate plastic energy and control the damage to the RC frame. To realize a performance-based seismic design of this novel structure, performance objectives of the entire structure, USDs, and the frame structure under four earthquake levels were recommended. Subsequently, an equivalent energy design procedure (EEDP) was developed to realize the four-level performance objectives, and a calculation method for the critical design parameters (i.e., energy modification factors) was recommended. To validate the reliability of EEDP, an eight-story structure was designed, and nonlinear time history analyses were conducted under four earthquake levels. The critical seismic responses of the overall structure, energy dissipation characteristics of the USDs, and damage characteristics of the main structure were evaluated. The results indicate that the expected performance was successfully achieved using this method, thus validating the feasibility and reliability of this method. This study provides a practical design method for RC frame structures with EDCPCS.

Issues Regarding the Appropriateness of Using Precast Reinforced Concrete Frame Structures Compared to Monolithic Reinforced Concrete Frame Structures, in Office Buildings and Residential Buildings

Abstract Given the current context at national and European level in terms of reducing skilled labour force in constructions, as well as the high level of density and traffic in large cities, there is an increasing emphasis on the possibility of shortening the duration of building the structural frames on site, reducing the number of workers or even reducing the level of noise pollution. Thus, the introduction of precast technologies in the case of office buildings and residential buildings, with multi-storey frame structure, is becoming an increasingly pressing and topical issue. The purpose of this paper is to enable structural engineers, architects and potential investors to consciously choose the type of optimal structure, taking into account a number of technical and economic aspects. In this sense, in order to highlight the main advantages and disadvantages of using multi-storey precast reinforced concrete frame structures, a comparative case study will be carried out between a precast frame structure and a monolithic frame structure, respectively.

Analytical Study Regarding the Seismic Response of a Moment-Resisting (MR) Reinforced Concrete (RC) Frame System with Reduced Cross Sections of the RC Beams

In the last few decades, a series of earthquakes were recorded which pointed out several deficiencies regarding the ductile seismic response of MR RC frame structures. Thus, the research problem centres around the failure mechanisms registered by the structures, which differ from the general notions of seismic response commonly found in current design standards and norms regarding seismic actions. In these conditions, in the present paper—by using comparative methods—the analytical validation of the solution of plastic hinge concentration and seismic energy dissipation in the marginal beam areas is proposed. Therefore, the RC beam sections were reduced (weakened) in the marginal areas which exhibit a plastic deformation potential, as well as in the corner areas of concrete slabs with vertical rectangular holes. The significant outcomes of this research imply the partial “guiding” of plastic hinges in the zones adjacent to beam ends. Furthermore, a reduction of both the negative effects of horizontal rigidization of the beams and the cracking and plastic deformation effects of beam-column frame joints was observed. With these technical implications, a complex mechanism of plastic deformation of MR RC frame models is registered in which all lateral elements (including RC columns) participate in the dissipation of seismic energy, without the occurrence of the “weak storey” mechanism for any of the analytical RC frame models. Furthermore, it is possible to observe the partial formation of the global plastic mechanism “Strong Columns—Weak Beams” (SCWB) for some of the structural models. Finally, the analytically studied innovative element regarding the improvement of the seismic response of pure MR RC frame structures is successfully validated.

Direct Displacement Based Design for Reinforced Concrete Framed Structures with Seismic Isolation

Direct displacement-based design is a nonlinear static procedure and has to check the suitability of the method against different types of ground motions namely far field, near field forward directivity and near field fling step. The method is applied for the buildings supported on a fixed base and hysteretic isolation bearings. Seismic isolators are provided between the foundation and the superstructure to minimize the influence of ground motion on the superstructure. The method is applied for four, eight and twelve storey reinforced concrete frame structures equipped with and without seismic isolators. Lead rubber bearing is used as seismic isolators. An equivalent damping ratio, derived from the particular characteristics of buildings supported on isolation bearings, is suggested. The energy dissipation mechanism in the isolators controls the displacement of the structure within acceptable limits at the level of the isolator. The results were validated with nonlinear time history analysis and were found to be in good agreement with the Direct displacement-based design methodology for far field ground motions. The performance of the building was measured for interstorey drift ratio, time period, acceleration of top floor, base shear, isolator displacement. This is an attempt to link the direct displacement-based design of the reinforced concrete building with seismic isolators subjected to the far field, near field forward directivity, near field fling step ground motions.

Method for Ranking Pulse-like Ground Motions According to Damage Potential for Reinforced Concrete Frame Structures

To rank the pulse-like ground motions based on the damage potential to different structures, the internal relationship between the damage potential of pulse-like ground motions and engineering demand parameters (EDPs) is analyzed in this paper. First, a total of 240 pulse-like ground motions from the NGA-West2 database and 16 intensity measures (IMs) are selected. Moreover, four reinforced concrete frame structures with significantly different natural vibration periods are established for dynamic analysis. Second, the efficiency and sufficiency of the IMs of ground motion are analyzed, and the IMs that can be used to efficiently and sufficiently evaluate the EDPs are obtained. Then, based on the calculation results, the principal component analysis (PCA) method is employed to obtain a comprehensive IM for characterizing the damage potential of pulse-like ground motions for specific building structures and EDPs. Finally, the pulse-like ground motions are ranked based on the selected IM and the comprehensive IM for four structures and three EDPs. The results imply that the proposed method can be used to efficiently and sufficiently characterize the damage potential of pulse-like ground motions for building structures.

Post-Earthquake Fire Assessment of Reinforced Concrete Frame Structures

Earthquakes can cause several catastrophic events and the consequences of fires in urban areas can be even worse than the consequences of the earthquake itself. Several numerical models were developed with SAFIR—software that models the behaviour of structures subject to fire for reinforced concrete (RC) frames to study their post-earthquake fire behaviour. First, a calibration was performed to validate the modelling strategy. Subsequently, two different frame typologies were considered, and a parametric study was carried out considering as the main variables the location and configuration of the damage caused by the earthquake and the location of the fire within the structure. The results show that the damaged RC frames have a lower fire resistance when compared with the undamaged frames. It was observed that the difference in time until collapse between an undamaged frame and a heavily damaged frame can be higher than 2 h. This observation is particularly relevant since, after a large earthquake, the rescue teams are generally overloaded, and consequently the response times are higher than that. This, combined with the reduction of the fire resistance of the reinforced concrete elements caused by the earthquake, can lead to increased severity and ultimately to the losses.

Research on Seismic Design Method for Reinforced Concrete Frame Structure

In this paper, the losses caused by earthquake and the damage brought to engineering structures are firstly introduced. Then, the types of seismic damage of such structures are introduced with reinforced concrete frame structure as an example. Next, the seismic design methods of structures in domestic and foreign codes are summarized, mainly including seismic measures and seismic structural measures, and the types and applications of seismic shock absorption technology are further introduced. Finally, the effectiveness of the seismic shock absorption technology is verified by using the passive control method as an example.

Residual Seismic Performance of Fire-Damaged Reinforced Concrete Frame Structure with Metallic Yielding Dampers

Residual Seismic Performance of Fire-Damaged Reinforced Concrete Frame Structure with Metallic Yielding Dampers

Seismic damage detection of an instrumented RC frame structure with deconvolution interferometry

This manuscript identifies the variation of the dynamic characteristics of an instrumented reinforced concrete (RC) frame structure, which is damaged by the 1999 Chi-Chi earthquake. The records from four earthquake events, including three moderate events before 1999 and the significant Chi-Chi earthquake, are collected and used in this study. The deconvolution interferometry is used to identify the shear wave velocity and damping ratio in the building, and the transfer function is used to identify the fundamental frequency of the building. The results indicate that the identified dynamic characteristics of the building under the three earthquakes before 1999 share similar values, indicating that there is no damage induced by these events. However, after the 1999 Chi-Chi earthquake, the shear wave velocity is decreased with the level from 30% to 40%, and fundamental frequency is decreased with the level from 41% to 55%. Meanwhile, the damping ratio is increased by this earthquake with the level from 58% to 91%, indicating that there is clear damage occurred in the building. Moreover, the comparison of the shear wave velocity profile with the height of the building indicates that the damage occurred in the lower part of the building, meaning that deconvolution interferometry can be used to identify the damage location once the sensors are enough in the building. • The seismic damage of a building is detected with deconvolution interferometry. • Shear wave velocity is decreased by Chi-Chi earthquake with the level of 30%–40%. • Fundamental frequency is decreased by Chi-Chi earthquake with the level of 41%–55%. • Damping ratio is increased by Chi-Chi earthquake with the level from 58% to 91%. • Damage location in the building can be identified by deconvolution interferometry.

Unbiased simplified seismic fragility estimation of non-ductile infilled RC structures

Infilled reinforced concrete (RC) buildings represent a prevalent taxonomy class in the Mediterranean region. Many were constructed before proper seismic provisions and detailing were enforced meaning they typically possess non-ductile failure mechanisms. Therefore, their simple but adequate seismic fragility estimation remains a challenge for the research community and practitioners. Moreover, their performance quantification can typically require characterisation via detailed numerical models that capture salient behaviour features, which involves extensive non-linear dynamic analyses with large computational burden. In this regard, an unbiased seismic fragility estimation methodology for the simplified assessment of infilled RC frame structures is described for both collapsing and non-collapsing scenarios. Its development is using extensive cloud analyses carried out with a large set of oscillators representative of the infilled RC frame's structural behaviour to permit the well-established pushover-based methods to be adopted in practice. The result is a novel set of empirical relationships relating the seismic behaviour of these typologies to their pushover curve parameters to allow practitioners to perform an accurate risk assessment and verification in an expedited manner. The choice of average spectral acceleration as the intensity measure used to characterise the fragility parameters for these relationships is shown to present notable advantages in reducing bias compared with other existing approaches. The results are validated via comparison with a detailed hazard-consistent assessment of case studies from a database of three-dimensional archetype building models. These were also developed here to capture the temporal evolution of building codes and architectural features of the building class in Italy.

Shear-Flexure-Interaction Frame Element Inclusion of Bond-Slip Effect for Seismic Analysis of Non-Ductile RC Columns

T his paper demonstrates the effect of bond-interfaces slip on the shear responses within the non-ductile reinforced concrete (RC) columns. Those columns were conducted as the flexure-shear critical members, which were commonly found in the existing RC frame structures constructed before the regulation of recent seismic codes. To represent the behaviors of those columns, the proposed model is developed within the framework of the forced-based formulation under the Timoshenko beam kinematic assumption. The axial-flexure interaction of the RC frame element is considered through the fiber-section model while the shear action couples to the flexural action through the UCSD shear-strength model within the shear constitutive model. Finally, one simulation is employed to verify the model performance to predict complex behaviors of the non-ductile RC columns for seismic analysis and to discuss the effect of bond-interfaces slip on those responses. From the results, it confirms that the proposed model is simple but accurate. Furthermore, the model can well represent several salient features of the non-ductile RC columns such as the shear-flexure interaction effect, the strength degradation in shear due to the increasing curvature ductility demand, the gradual spread inelasticity, and the weakened shear responses due to the bond-slip effect. The predicted maximum shear force is well corresponding to the value obtained from the experiment with an error of about 0.83% while the error obtained from the frame model without the bond-slip effect is about 2.58%.

Seismic performance of reinforced concrete beams under freeze-thaw cycles

Previous studies have shown that freeze-thaw cycle (FTC) action in severe cold environments is a durability issue that seriously threatens the seismic performance of concrete members. However, research on the seismic resistance of reinforced concrete (RC) beams under FTC action is still scarce. This paper presents an experimental study of six undamaged and frost-damaged RC beams subjected to a low-cycle reciprocating load. The paper aims to investigate the influences of FTC number and concrete strength on the seismic resistance of damaged beams. The paper reports on frost damage at different levels, cyclic damage process, hysteresis response, strength, ductility, shear deformation, and energy dissipation. The test results demonstrate that as the FTCs rose, the width and number of frost-heave cracks on the surface of the beam gradually increased. Moreover, frost action had a significant negative effect on strength, deformation, and energy dissipation, especially when the beams were highly frost-damaged. Further, the shear deformation and shear component to whole deformation gradually increased. Based on the experimental results, a time-dependent evaluation model is proposed to estimate the residual capacity of key elements of RC frame structures in severe cold climates, taking into account the effects of FTCs, concrete strength, and uneven distribution of freeze-thaw damage.

Estimation of Aleatory Randomness by Sa(T1)-Based Intensity Measures in Fragility Analysis of Reinforced Concrete Frame Structures

Based on the multiple stripes analysis method, an investigation of the estimation of aleatory randomness by Sa(T1)-based intensity measures (IMs) in the fragility analysis is carried out for two typical low- and medium-rise reinforced concrete (RC) frame structures with 4 and 8 stories, respectively. The sensitivity of the aleatory randomness estimated in fragility curves to various Sa(T1)-based IMs is analyzed at three damage limit states, i.e., immediate occupancy, life safety, and collapse prevention. In addition, the effect of characterization methods of bidirectional ground motion intensity on the record-to-record variability is investigated. It is found that the damage limit state of the structure has an important influence on the applicability of the ground motion IM. The Sa(T1)-based IMs, considering the effect of softened period, can maintain lower record-to-record variability in the three limit states, and the Sa(T1)-based IMs, considering the effect of higher modes, do not show their advantage over Sa(T1). Furthermore, the optimal multiplier C and exponent α in the dual-parameter ground motion IM are proposed to obtain a lower record-to-record variability in the fragility analysis of different damage limit state. Finally, the improved dual-parameter ground motion IM is applied in the risk assessment of the 8-story frame structure.