Concrete Frame Research Articles

Seismic performance on PSPC beam - concrete encased CFST column frame with a built-in reduced beam section

The concrete-filled steel tubular (CFST) column is widely used to connect with a steel beam owing to the quick dry connection and acceptable seismic performance. Therefore, a partially steel-reinforced precast concrete (PSPC) beam with an embedded H-beam was developed to combine the merits of both the prefabrication in the precast concrete beam and the quick assembly in the steel beam. In this study, the developed beam was proposed to connect the concrete encased CFST column with a reduced beam section. A half-scaled frame substructure specimen with two floors and two bays was designed and tested under the cyclic loading to investigate the seismic performance. A series of seismic properties were analyzed, including the failure phenomena, hysteretic performance, stiffness degradation, and energy dissipation capacity. The dog-bone configuration was found to benefit the beam hinge failure mechanism and an acceptable deformation capacity (the ductility coefficient up to 2.77). The function of the H-beam contributed to stable energy absorption (the equivalent damping coefficient from 0.33 to 0.37). Finally, the proposed frame was compared with a reinforced concrete frame and a steel-reinforced concrete frame through numerical analysis. The partial steel-reinforced configuration had a positive influence on the bearing capacity, hysteretic performance, and safety storage. In addition, it could improve the cost-effectiveness with little decrease in the bearing capacity.

Isostatic and frictional energy dissipating connecting systems for UHPC curtain walls: Design and experimental validation

Ultra-high performance concrete (UHPC) curtain wall is a new type of non-structural building envelope component. Given its large size and high cost, rational connecting systems should be employed to prevent potential seismic damage and economic losses. In this study, two novel connecting systems, including an isostatic connecting system and a frictional energy dissipating connecting system, were proposed for reinforced concrete (RC) frame with UHPC curtain walls. The design methods for these two connecting system were provided first. Then, to evaluate the feasibility of the proposed connecting systems and the corresponding design methods, three 1/2-scale RC frame structures (i.e., one bare frame without curtain walls, one with isostatic curtain wall connecting system, and one with frictional energy dissipating curtain wall connecting system) were designed and fabricated for pseudo-static tests. The damage evolution, failure mode, strength, stiffness, and energy dissipation capacity of the three test substructures were assessed. The test results demonstrated that through reasonable design, independent rocking deformation of the curtain walls was achieved in both the isostatic and frictional energy dissipating connecting systems, allowing the curtain walls to remain free from damage even under an inter-story drift of 1/36, thus validating the reliability of the proposed connecting systems and design methods. Further, compared to the bare frame, curtain walls employing the isostatic connecting system exhibited a negligible effect on the seismic performance of the frame. On the contrary, curtain walls employing frictional energy dissipating connecting system effectively enhanced the strength and energy dissipation capacity of the frame, allowing dual damage control for both walls and frame. Consequently, the frictional energy dissipating connecting system is considered to be a more rational method for enhancing the seismic performance of buildings.

Development of self-centering and energy-dissipating dual-stage reinforced concrete rocking column-base system

Reinforced concrete (RC) frame is one of the most commonly adopted forms of building structure worldwide. However, server damages can develop in columns during earthquakes which often lead to the catastrophic collapse of the entire structure. In this paper, the novel dual-stage RC rocking column-base system with low-damage characteristics is proposed and tested. The system composes of the unbonded-buckling-restrained-brace (UBRBs) as the sacrificial energy-dissipation component and steel coat at column base to prevent concrete crushing. To prevent column overturning and base slippage while rocking, limiters and contact bars are used to establish the mechanism which limit the column uplift in an extreme earthquake and allow the column reinforcements to yield. Two column performance stages separated by the activation of limiter mechanism are established. In the first stage, the reinforcements of rocking column-base remain elastic while UBRBs yield to dissipate energy. In the second stage, the reinforcements of rocking column-base enter plasticity through the activation of limiter mechanism to dissipate additional energy and prevent column overturning. The hysteresis tests on UBRBs are performed which finds that the UBRBs with equilibrant triangle cross-section and no filling demonstrate stable hysteresis behavior and decent energy dissipation capacity. Experiments on the rocking column-base system demonstrated that the proposed system remains fully elastic at the drift of 0.18 %. Further, the system remains structurally intact at the drift of 2 % and its original performance can be rapidly restored through UBRB replacements. Immediately after 2 % drift, the limiter mechanism is activated and the entire system enters plastic state and dissipates significant energy. With the activation of the limiter mechanism, the bearing capacity of the rocking column-base increases sharply by almost 30 % as a result of column reinforcement yielding, demonstrating the characteristics of dual-stage performance. The system maintains higher levels of bearing capacity until 5 % drift then its peak capacity before the activation of limiter mechanism, indicating the significant ductility potential of the system. Additionally, the system shows reasonable capacity to self-center through axial load and gravity.

Experimental study on the post-fire seismic behavior of exterior beam-column joints in reinforced concrete frames

This study outlines the post-fire seismic behavior of reinforced concrete beam-column joints. Due to the lack of sufficient research data regarding the seismic vulnerability of exterior reinforced concrete beam-column joints after fire exposure, experimental investigations were carried out to assess variations in the seismic performance of these joints after experiencing high temperatures. In this way, five scaled beam-column joints were considered for examinations and were designed according to the seismic provisions of ordinary moment frames. One benchmark specimen was subjected to reverse cyclic loading at ambient temperature without prior fire exposure. Four others were exposed to the heating regimes with various target temperatures and then examined by reverse cyclic loading after cooling to the ambient temperature. Damage patterns were exhibited with substantial alterations from flexural beam-end hinging for the benchmark specimen to the shear ruptures for the fired specimens exposed to the high temperatures of 400°C, 600°C, and 800°C. The quantitative results indicated minor changes in the load-bearing capacity, ductility factor, and energy dissipation by the effect of the 200°C heating regime. On the other hand, other three heating regimes led to noticeable reductions of 16–62% in the load-bearing capacity, 25–65% in the cumulative energy dissipation, and 14–42% in the ductility factor by propagating diagonal cracks and developing shear ruptures inside the joint core. Trends in variations of investigated parameters were also discussed, and novel findings were presented in this regard. The results and observations in this study can be employed as the applicable data for retrofitting decisions of fired exterior beam-column joints in reinforced concrete ordinary moment frame buildings.

A dynamic strain prediction method for malfunction of sensors in buildings subjected to seismic loads using CWT and CNN.

Structural health monitoring (SHM) is a technique used to evaluate the safety of a structure based on the structural response. In the SHM, sensors may fail to measure the structural response, or data loss can occur during the data transmission and reception. In this regard, this paper proposes a method of predicting the strain response when a sensor installed in a structural member suffers a malfunction. To this end, a convolutional neural network (CNN) is introduced to predict the strain response. Time-history strain data for seismic loads measured in adjacent structural members are set as the input layer of the CNN, and continuous wavelet transform (CWT) results are additionally set in the input layer of the CNN to reflect the dynamic structural behavior during earthquakes in the CNN predictions. Time-history strain data for a member, the target of prediction, are set as the output layer of the CNN. Then, the trained CNN uses the time-history strain data of adjacent members with no sensor failure and the CWT result of the data to predict the strain response of a structural member with sensor failure. A numerical study on the seismic load of a single-span three-story steel moment frame and an experimental study on a single-span three-story reinforced concrete frame were carried out to verify the validity of the proposed method. This study presents a method of applying CWT data to the input layer of the CNN and discusses the effectiveness of CWT data for predicting the nonlinear response of a structural member with damaged sensors.

Simplified Gravity Load Collapse Dynamic Analysis of Old-Type Reinforced Concrete Frames

The results of shaking table tests from previous studies on a one-story, two-bay reinforced concrete frame—exhibiting both shear and axial failures—were compared with nonlinear dynamic analyses using simplified models intended to evaluate the collapse potential of older reinforced concrete structures. To replicate the nonlinear behavior of columns, whether shear-critical or primarily flexure-dominant, a one-component beam model was applied. This model features a linear elastic element connected in series to a rigid plastic, linearly hardening spring at each end, representing a concentrated plasticity component. To account for strength degradation through path-dependent plasticity, a negative slope model as degradation was implemented, linking points at both shear and axial failure. The shear failure points were determined through pushover analysis of shear-critical columns using Phaethon software. Although the simplified model provided a reasonable approximation of the overall frame response and lateral strength degradation, especially in terms of drift, its reduced computational demands led to some discrepancies between the calculated and measured shear forces and drifts during certain segments of the time-history response.

Theoretical and numerical modeling of a shallow foundation stiffness based on the theory of elastic half-space

Abstract The paper presents the derivation of equations for the calculation of the spring constants ky, kz, and kϕ and the spring coefficients βy, βz , and βϕ used in the modeling of a foundation with a rectangular base on elastic soil. All the equations were derived based on information provided in literature, for example, Barkan, Gorbunov-Possadov, and Whitman et al. To demonstrate the application of these equations in practice, two numerical models of a reinforced concrete frame structure that was built on soil were created using Abaqus FEA software. Model A represents a complex three-dimensional numerical model that consists of a reinforced concrete frame structure, which has a soil layer beneath it. Model B represents a simple three-dimensional numerical model consisting of a reinforced concrete frame structure, where the stiffness of the soil layer beneath the structure was modeled with vertical, horizontal, and rocking spring constants applied to the bottom of each foundation. Due to the nonlinear boundary condition used in the supports of the concrete frame model, such as contact and friction, all the involved loads were incorporated into a single load case, and a large displacement formulation was used in the analysis. The authors focused on the method of a simplified modeling of frame structures founded on soil. To conduct comparative analyses, two columns and two beams from each model were selected, from which the internal forces and displacements were compared. The findings of the comparative analysis are presented in tables and then discussed.

Experimental investigation on the seismic performance of reinforced concrete frames with decoupled masonry infills: considering in-plane and out-of-plane load interaction effects

AbstractMasonry infills are frequently employed as both outer and inner partitions in reinforced concrete (RC) frame structures due to their outstanding characteristics in terms of energy efficiency, fire resistance and sound isolation. However, common construction practice typically involves the mortar connection between masonry infills and RC frames. For this reason, the unforeseen frame-infill interaction takes part under seismic loading, which leads to severe and uncontrollable damage to masonry infills. This interaction also causes damage or even the collapse of the RC frames and thus of the whole structures. The poor performance of infilled RC frame structures in recent earthquake events is a strong motivation for the development of innovative engineering solutions, which aim to mitigate the detrimental effects of frame-infill interaction. This article introduces an innovative decoupling system founded on the concept of decoupling the RC frame from the masonry infill. The decoupling is achieved by inserting elastomeric material between the masonry infill and RC frame. The properly designed decoupling system allows infill activation only at high in-plane drifts. Simultaneously, it provides boundary conditions for seismic loads acting perpendicular to the infill plane. Firstly, the article explains the design of the masonry infill with the decoupling system and its installation. Afterwards, the results of small specimen tests carried out to determine the load-bearing capacity of the decoupling system are presented. Furthermore, the article discusses the findings of an extensive experimental campaign conducted on nine real-size RC frames with decoupled infills subjected to separate and combined in-plane and out-of-plane loadings. In addition to different loading types, various infill configurations are considered – solid infill, infill with centric window, and infill with centric door opening. Finally, the experimental results of RC frames with decoupled infills are compared with the experimental results of traditionally infilled RC frames, which were tested within the framework of the same project. The thorough evaluation and comparison of the experimental findings demonstrate the significant improvement of seismic performance of infilled RC frames if the decoupling system is applied.

Seismic capacity evaluation of corroded reinforced concrete frame structures

Seismic capacity evaluation of corroded reinforced concrete frame structures

Mainshock-aftershock building fragility methodology for community resilience modeling

This study introduces a methodology for developing fragility functions that enable the assessment of seismic vulnerability and resilience at the community level for buildings subjected to mainshock-aftershock sequences. To date, this has been assessed at a single structural level or through statistical combinatorial approaches. This paper provides a solution for a suite of archetypes including ductile and non-ductile reinforced concrete frames as well as woodframe buildings. The findings highlight the central role of aftershocks in exacerbating damage states and increasing economic losses, emphasizing the importance of including these events in accurate assessments of community resilience and seismic risk. The suite of archetypes is applied at the community level using the IN-CORE platform to quantify the effect of incorporating aftershocks into community-level seismic vulnerability analyses. The ability to accurately include the effect of aftershocks within community-level risk and resilience analyses will be key to planning for earthquakes.

Experimental investigation of progressive collapse resistance of bonded local prestressed concrete frame substructures

Bonded local prestressed concrete (BLPC) frames represent a structural form that combines long spans with prestressing and short spans without prestressing. Progressive collapse has become a focus of research in recent years, given the potential for severe consequences. BLPC frames exhibit distinct progressive collapse resistance compared to symmetrical structures due to their notable asymmetry. Therefore, this paper tested the behavior of two BLPC substructures and one unequal-span reinforced concrete (USRC) substructure against progressive collapse in the middle column removal scenario. The tests were conducted using displacement-controlled static loading, with the loading point situated at the top of the middle column. The test results demonstrate that the BLPC frame employs a two-stage mechanism to resist progressive collapse, comprising the beam-beam stage and the beam-link stage. Additionally, the frame exhibits a tri-fold failure mode. At the location of attachment of the short-span beam to the side column, the top rebars were found to be entirely fractured. At the junction of the reinforced and non-reinforced regions of longitudinal rebar in the long-span beam, a substantial crack developed, extending almost through. This indicates that the plastic hinge of the long-span beam appeared at the location where the longitudinal rebars were changed, rather than at the beam end. This paper also established a refined numerical model of the BLPC substructures based on LS-DYNA, and the modeling method was verified by comparison with the tests.

Machine learning – based approach for predicting pushover curves of low-rise reinforced concrete frame buildings

Reinforced Concrete (RC) frame buildings are prevalent worldwide due to their seismic performance and the broad availability of materials. Pushover analysis is regarded as one way to assess the seismic performance of these buildings, which is simple to interpret. The only downside of this method is that it requires developing nonlinear models, which can be time-consuming and computationally expensive. Recently, Machine Learning (ML) has emerged as an alternative to approximate the pushover response of RC frame buildings. However, there are still improvements in several areas, such as including relevant and easily obtainable parameters in structural design (e.g. reinforcement ratios), considering a wide range of building configurations, and comparing different ML techniques. This paper presents the development of two models based on Random Forest (RF) and Artificial Neural Network (ANN) to predict the pushover response of low-rise RC frame buildings, supported by a user-friendly graphical interface. First, a dataset of over 138000 Pushover analyses was performed on flexure-controlled RC frames ranging from two to five stories using OpenSeesPy, subsequently used to develop predictive ML models. These models are designed to offer a trilinear approximation of a building's Pushover curve, and they require input information that is available from the customary building design. The pushover predictions obtained with RF and ANN take 0.12 % and 3.05 % of the computing time compared to the OpensSeesPy nonlinear model. The proposed models demonstrate a high level of accuracy, with a coefficient of determination (R²) of over 0.88 and 0.81 in testing datasets for RF and ANN models, underscoring their potential to significantly streamline the seismic performance assessment process by providing quick Pushover curve estimations.

Retrofitting through the loss-Based Earthquake engineering

AbstractThe novelty of the research is the development of closed-from equations to assess the effective capacity of retrofitting interventions to reduce the seismic risk of existing buildings. The goal of the proposed procedure is to provide decision-making in the context of the Loss-Based Earthquake Engineering, whose purpose is the reduction of the seismic risk, which is herein computed through a monetary loss. The procedure consists of specifying performance targets (e.g. acceptable monetary losses, capital to invest, reduction of expected annual loss) and deriving engineering parameters, specifically the target fragility curves to achieve the established performance target. The identification of required fragility curves, in turn, allows to identify proper retrofitting interventions to mitigate the expected seismic loss. The method allows for estimating the maximum reduction of the annual average loss and the recommended capital to invest, accounting for the actual cost of the retrofitting alternatives and the nominal life of the building. In addition, it can be used to identify the payback period. With the aim of promoting the design procedure in the common practice, an existing reinforced concrete moment-resisting frame, retrofitted with three strengthening methods, is explored as case-study.

One novel block-type brace connector for retrofitting reinforced concrete frames

Buckling-restrained braces are widely utilized for retrofitting existing reinforced concrete frames. However, conventional plate-type brace connectors and joints often suffer damage from the additional forces exerted by buckling-restrained braces during earthquakes. This paper proposes a novel block-type brace connector to address this issue. The seismic performance of this new connector is evaluated through pseudo-dynamic and quasi-static tests. Pseudo-dynamic test results indicate that the reinforced concrete frame retrofitted with the new connectors demonstrates superior seismic performance compared to the frame without retrofitting. During a rare earthquake, the maximum inter-story drift ratios are 1/308 for the frame with new connectors and 1/84 for the frame without retrofitting. Quasi-static test results show that the new connectors shift the potential plastic hinges of the beam away from the gusset plate region by moving the post-installed anchorage position outward. The gusset plate of the conventional connector buckles at an inter-story drift ratio of 1/30, while that of the new connector avoids buckling due to the restraint from the concrete block. Overall, the new connector can mitigate the adverse effects of the additional forces from buckling-restrained braces and improve the seismic performance of the existing reinforced concrete frames.

Experimental evaluation of multi-story self-centering prestressed concrete frames with web friction devices under cyclic loading

The self-centering prestressed concrete (SCPC) frame with web friction devices is a novel resilient structural system capable of achieving minimal post-earthquake residual displacement. However, present research on its seismic performance under cyclic loading is primarily focused on single-story structures, with little consideration given to the influence of web friction device performance deterioration induced by variations in clamping force applied through bolts. Because of more complicated mechanical systems, multi-story structures' seismic performance may differ from that of single-story ones. Given this, this study performed a thorough investigation of the seismic performance of a multi-story SCPC frame through quasi-static tests. To further detect the variation in the performance of the web friction device during the test, clamping forces were monitored. The experimental results reveal that structural behavior may not scale linearly with structure size, while the multi-story frame exhibits notable displacement-dependent behavior. The lagging effect of the web friction device was observed, where the frame with lower clamping forces (or friction forces) demonstrates a higher energy-dissipating capacity under small drift levels. Simultaneously, higher energy-dissipating capacity is accompanied by greater residual displacement. Besides, higher post-tensioning (PT) forces provide better stability and more consistent clamping forces, whereas lower PT forces result in greater variability in bolt clamping. While limited cracking patterns were observed, the study notes concern about PT tendon anchorage abrasion. These findings offer crucial insights for optimizing SCPC frames across various structural sizes, underscoring the importance of a balanced design approach that considers energy dissipation, self-centering capabilities, and structural complexity.

Dynamic model identification of the medieval bell tower of Casertavacchia (Italy)

The structural safeguard of tangible cultural heritage, monuments in particular, needs a multi-disciplinary approach involving historical–critical analysis, survey, in-situ and laboratory testing to provide a comprehensive knowledge on the object under investigation and build a structural model representative of the current state of the monument. In this paper, this approach is applied to the case study of the bell tower of San Michele Arcangelo cathedral in Casertavecchia (Italy). The historical–critical analysis was fundamental to understand the evolution of the tower over the centuries. Material tests were complemented by ambient vibration testing (AVT) which allowed for a complete characterisation of frequencies and mode shapes for the bell towers. A further model identification procedure was carried out to exploit the amount of information gathered within the documental and experimental activities and set up a reasonably accurate numerical model. The activities described in this paper highlight (a) the importance of correctly representing all substructures present in the monument, possibly hidden and built in different historical periods; (b) the possibility offered by model identification procedures to separate identifiable from less significant parameters, as well as selecting the best model in terms of representation complexity; (c) the effect of soil-structure and structure-structure interaction on the modal behaviour of the monument. In particular, the identification analyses without considering the inner concrete frame are consistently characterised by higher values of ωf and ωMAC compared to the analogous analyses in which all substructures were included. The best fit with the dynamic data is obtained by introducing deformable structure-soil connection while the effect of lateral constraints is hardly captured by the utilised setup.

Seismic optimization design of reinforced concrete frames: uniform displacement criterion

Seismic optimization design of reinforced concrete frames: uniform displacement criterion

Review on Fragility Analysis of Building Structure in Seismic Prone Area

In general, using a steel bracing system is the most effective choice for enhancing the resistance of reinforced concrete frames to lateral loads. Steel bracing offers notable advantages over other methods, including greater strength and stiffness, cost-effectiveness, a smaller footprint, and minimal additional weight on existing structures. Both empirical and analytical fragility curves have been taken into account. Strengthening seismically deficient reinforced concrete frames with steel bracing systems is a practical solution for improving earthquake resilience. Nearly all structural analysis software, such as ETABS and SAP2000, supports linear and nonlinear static analysis for high-rise structures. Key parameters include fragility curves, the P-Δ effect, base shear, lateral displacement, axial force, and story drift, among others. The findings showed that bracing systems significantly reduce lateral displacement in frames. Fragility curves were developed based on peak ground acceleration (PGA) for various limit states—slight, moderate, major, and collapse-assuming a lognormal distribution. This study aims to develop analytical fragility curves for high-rise building structures.

Seismic performance of reinforced concrete building frames on sloping ground retrofitted with steel and reinforced concrete jacketing

Seismic performance of reinforced concrete building frames on sloping ground retrofitted with steel and reinforced concrete jacketing

Study on seismic performance of prestressed fabricated reinforced concrete frame structure assembled by steel sleeves

This paper introduces a novel type of prestressed fabricated reinforced concrete frame (PSFRC frame) structure, which utilizes steel sleeves for assembly. The PSFRC frame incorporates prestressed tendons, stiffened steel sleeves, and high-strength bolts, resulting in improved bearing capacity and assembly efficiency. To assess the seismic performance of the PSFRC frame joint, experimental tests were conducted on one reinforced concrete (RC) joint and two PSFRC frame joints under cyclic loading. Hysteresis analysis and elastic-plastic time-history analysis were also performed using a finite element model. The experimental results showed that the PSFRC edge joint reached a peak load of 89.30 kN, while the PSFRC middle joint exhibited a capacity of 169.95 kN, which was 58.87 % higher than that of the cast-in-place specimen XJ (107.87 kN). The hysteresis curves of the PSFRC joints demonstrated significant fullness, with the equivalent damping coefficient of the PSFRC joint being increased by 11.56 % compared to the RC joint. Additionally, a simulation method using ABAQUS software was proposed to investigate the seismic response of the integral structure of the PSFRC frame. Finite element models for both PSFRC and RC frames were established, and their seismic performance was analyzed under cyclic loading and the El Centro seismic wave. Various parameters including peak loading capacity, stiffness degradation, peak acceleration value, inter-storey drift ratio, and concrete damage value were considered. The finite element analysis results revealed that the load-carrying capacity of the PSFRC frame (435.33 kN) was approximately 30 % higher than that of the RC frame (386.48 kN). Furthermore, at the peak acceleration of 600 gal, the maximum inter-storey drift ratio of the first floor for the PSFRC frame was 1/58, which was below the limit value of 1/50. The plastic hinge position at the beam end of the PSFRC frame was further from the core area, aligning with seismic design objectives. This research provides valuable insights into the design of fabricated building structures and methods for analyzing seismic performance.