Concrete Frame Research Articles

Experimental study and seismic assessment on base isolated precast concrete frame structure with box connectors

The precast construction method offers fast and environmentally friendly solutions for sustainable development in construction. Various connection methods, including wet and dry, have been proposed to enhance assembly convenience. However, challenges remain in achieving complete assembly and considering disassembly processes, hindering post-earthquake restoration. This study introduces a precast RC structure system with easily assembled joints that facilitate disassembly. To enhance the structural system's adaptability to regions with high seismic intensity, rubber-bearing base isolation technology is employed to optimize its seismic performance. Shaking table tests were conducted to evaluate the structure system's dynamic response and seismic performance. Test results indicate that the isolation layer significantly decreases the acceleration response, inter-story drift ratios, floor shear forces, and strain of reinforcements. The isolation structure has a high probability of entering operational and immediate occupancy states during rare earthquakes. The deformation of the isolation bearings has a decisive impact on the overall seismic fragility of the isolation structure system.

Novel outrigger element utilizing thin steel plates as infill to concrete frames in concrete high‐rise buildings

AbstractRapid population growth and the need for sustainable land use have led to a remarkable increase in the construction of tall buildings. To accommodate the increasing need for floor space, high‐rise structural systems are being developed aiming to improve building performance against lateral loads. This paper introduces a novel steel‐infilled Reinforced Concrete Frame (SP‐RCF) outrigger and compares its structural performance against other systems, such as the Concrete Wall‐infilled Reinforced Concrete Frame and the Steel Truss‐infilled Reinforced Concrete Frame. A geometrically and materially non‐linear analysis was applied to these systems and validated through existing experimental and analytical data. Subsequently, a case study on a prototype tall building was conducted. The results indicate that the SP‐RCF outrigger shows superior performance compared to the other systems in terms of ultimate strength, stiffness, and ductility; demonstrating its potential to enhance the structural integrity of high‐rise buildings.

Experimental and numerical study on flexural performance of ultra-high performance concrete frame beams reinforced with steel-FRP composite bars

This paper presents the bending tests of four ultra-high performance concrete (UHPC) frame beams and one normal strength concrete (NSC) frame beam, all reinforced with steel-FRP composite bars (SFCBs). A comprehensive analysis was carried out, encompassing evaluation of the failure mode, crack propagation, bearing capacity, deformation, strain response, and plastic rotational capacity of the frame beams. Investigating the effects of concrete type, reinforcement type, and beam-end reinforcement ratio on the flexural performance of the frame beams was a key aspect of this study. A three-dimensional finite element (FE) model of the frame beam was established and rigorously verified. The developed model enabled a detailed parametric analysis involving the steel ratio, the yield strength of the inner core steel bar, the elastic modulus of the FRP, and the ultimate tensile strength of the SFCB. The results indicated a consistent failure mode of all frame beams: crushing of concrete at the beam-end, initiating a sequence of plastic hinge occurrence starting at the beam-end and then progressing to mid-span. The substitution of normal strength concrete with UHPC significantly enhanced various aspects of the frame beams, including the flexural capacity, deformation, ductility, ultimate energy dissipation, and plastic rotational capacity, while inhibiting the generation and expansion of cracks. Notably, the plastic rotation angle of SFCB-UHPC frame beams was 4.9 times greater than those of steel-UHPC frame beams, emphasizing the effectiveness of SFCB in enhancing the beam-end plastic rotational capacity. A decrease in the beam-end reinforcement ratio significantly reduced the flexural capacity, ultimate energy dissipation, and beam-end plastic rotational capacity, while improving ductility. Additionally, the study established a formula for calculating the equivalent plastic hinge length, utilizing the relative compressive zone height and effective section height of the beam-end controlling section as variables, which demonstrated good alignment between predicted and experimental results.

Seismic Behavior of Precast Prestressed Concrete Frame with Hinge-Relocated Mortise–Tenon Connections

To satisfy the easy-construction demands of precast concrete (PCa) frames after an earthquake, a PCa frame with mortise–tenon (MT) connections is proposed in this paper. MT connections are secured solely through the binding force of unbonded prestressed tendons without grouting for easy construction. The design and construction of the joint are detailed. During an earthquake, the hinge system of the connection allows for slight rotational movements. Finite element analysis was employed to assess the joint’s hysteresis behavior, revealing a three-stage earthquake response mechanism: closing, hinge relocation, and self-centering. Based on the hysteresis performance of the beam and column in the precast prestressed concrete (PCaPC) frame, a seismic response model for PCaPC buildings was established.

Experimental evaluation of damage state and failure propagation of infilled frames under the opening effect

In this study, four frame specimens were tested: two with concentric window and door openings in the infills, and two with eccentric window and door openings. The serviceability limit of the infilled state was determined by evaluating the structural behaviour of infilled reinforced concrete frames with openings. The results indicate that frames with centrally located openings exhibit a reduction in lateral load capacity. The damage characteristics are influenced more by the location of the opening than by its percentage. When the opening is positioned closer to the edge of the masonry panel, the structural performance improves. Initial cracking occurs at a lateral drift of 0.2%, while crushing of the masonry panel occurs at approximately 2%. In frames with centrally located openings, the segment near the loaded column is more prone to damage, whereas the segment farther from the loaded column shows increased vulnerability.

Research on column overdesign factor of reinforced concrete frame structures in the 2022 Ms 6.8 Luding earthquake

The strong column-weak beam failure mode of reinforced concrete (RC) frame structures is one of the most important targets of structural seismic design and is primarily realized by a reasonable column overdesign factor (COF). However, most RC frame structures in previous earthquakes were often subjected to strong beam-weak column failure modes. To address this issue, the RC frame with a strong column-weak beam failure mode and a typical strong beam-weak column RC frame in the 2022 Ms 6.8 Luding earthquake were intensively studied in this study. The differences between the two failure modes of the RC frame structure were comparatively analyzed at both the overall structure and member levels. A numerical simulation was conducted to obtain the structural response under actual ground motion. Finally, a probabilistic analysis method was adopted to process the COF data of the RC frame joints. The results indicate that the structural safety redundancy of the RC frame with the undesired failure mode cannot be fully utilized, whereas the RC frame with the strong column-weak beam failure mode allows more structural members to participate in the energy dissipation through a complex redistribution mechanism of internal forces. Damage to the infill wall further mitigates the degree of damage to the main structure and reduces the risk of soft-story failure. The COF of the actual RC frame structure shows a non-uniform distribution, and it is recommended that the COF be higher than 1.5 for the seismic design of the structure following the Chinese code.

Comparative Analysis of the Impact of Vertical Irregularities on Reinforced Concrete Moment-Resisting Frame Structures According to Eurocode 8

Comparative Analysis of the Impact of Vertical Irregularities on Reinforced Concrete Moment-Resisting Frame Structures According to Eurocode 8

Localizing structural damage based on auto-regressive with exogenous input model parameters and residuals using a support vector machine based learning approach

Machine learning algorithms operating in an unsupervised fashion has emerged as promising tools for detecting structural damage in an automated fashion. Its essence relies on selecting appropriate features to train the model using the reference data set collected from the healthy structure and employing the trained model to identify outlier conditions representing the damaged state. In this paper, the coefficients and the residuals of the autoregressive model with exogenous input created using only the measured output signals are extracted as damage features. These features obtained at the baseline state for each sensor cluster are then utilized to train the one class support vector machine, an unsupervised classifier generating a decision function using only patterns belonging to this baseline state. Structural damage, once detected by the trained machine, a damage index based on comparison of the residuals between the trained class and the outlier state is implemented for localizing damage. The two-step damage assessment framework is first implemented on an eight degree-of-freedom numerical model with the effects of measurement noise integrated. Subsequently, vibration data collected from a one-story one-bay reinforced concrete frame inflicted with progressive levels of damage have been utilized to verify the accuracy and robustness of the proposed methodology.

Machine learning-based approach for assessing the seismic vulnerability of reinforced concrete frame buildings

Recent artificial intelligence (AI) advancements have significantly impacted the field of structural engineering by offering new solutions to enhance safety, efficiency, and cost-effectiveness in the design, construction, and maintenance of infrastructure and urban areas. This study has investigated a machine learning-based approach to estimate the seismic vulnerability of reinforced concrete (RC) building frames. The study utilized a probabilistic technique to assess the simulation of a 4-story RC building frame in the face of epistemic uncertainty. Data was collected using the Monte-Carlo approach, which created a machine learning (ML) model for predicting structural damage. The problem was formulated as both a regression-based and a classification-based model. An artificial neural network (ANN) feed-forward network architecture model was used to solve the classification problems. The optimal number of neurons in the hidden layer was determined to produce the best estimation model. Three different models were combined for the regression model, including LASSO regression, random forest, and gradient boosting, by implementing the stacking generalization. The investigation results indicate that the stacked predicted model exhibits less variance than other ML models. The classification and regression-based algorithms can forecast damage states with a high degree of accuracy, ranging from 87 to 95 percent. In conclusion, the study has demonstrated the effectiveness of machine learning techniques for predicting the seismic vulnerability of RC building frames. With the continued advancement of AI and big data, these methods will likely play a crucial role in the structural engineering field.

A Machine Learning-Based Framework for Estimating Fragility Parameters in RC/MR Frames Considering Seismic, Structural, and Site Attributes

ABSTRACT This study investigates applying machine learning (ML) algorithms to estimate seismic fragility curves of reinforced concrete moment-resisting frames. The goal is to achieve computationally efficient estimations while maintaining accuracy compared to traditional methods. Various multi-classification algorithms are explored for this purpose. A greedy search method identifies key fragility features (structure period, soil shear wave velocity, ground motion intensity). Analysis shows that the decision tree method strikes an optimal balance between accuracy and speed. ML-based fragility curves closely align with analytical results, with area ratios under 10%, mean absolute error (MAE) below 0.06, and root mean square error (RMSE) below 0.082.

RESULTS OF THE TECHNICAL INSPECTION OF A MULTI-STORY RESIDENTIAL BUILDING DAMAGED AS A RESULT OF A ROCKET IMPACT

The article presents the results of the examination of the technical condition of part of the construction structures of the building damaged as a result of a missile strike, the determination of the characteristics and classification of their defects and damage, the provision of conclusions and recommendations regarding the correction of the life cycle and further safe and reliable operation of the building. As part of the study, the object of the survey was a monolithic 22-story residential building with a basement (ATP) floor and a complex configuration in plan. The structural scheme of the complex is a monolithic reinforced concrete frame with stiffening cores. The stability and rigidity of the frame is ensured by diaphragms of stiffness in the form of reinforced concrete walls, elevator-stair nodes and rigid nodes connecting pylons and horizontal disks of monolithic reinforced concrete floor slabs. During the examination, visual and instrumental methods of research were performed. Before the field work, measures were taken to collect design and archival information about the research object. Instrumental studies to determine the actual concrete strength of reinforced concrete frame elements and to determine the diameter, protective layer and pitch of the working rods of the reinforcing frames of the load-bearing elements were carried out by non-destructive methods. The calculation model of the spatial scheme of the structure of the frame of the residential building, taking into account the damage, was made in the subsystem (PS) "COMPOSITION" of the software complex (PC) "MONOMAH CAD". The result of the survey is conclusions and recommendations, which indicate the specifics of damage and types of defects, destruction and debris in various structural elements that were discovered during the survey. The general technical condition of the residential building is classified as emergency. As for the recommendations, two options for carrying out repair and restoration works were provided. The first option is to restore the plan-elevation position of the building, the design marks of vertical and horizontal structures and the unloading of overloaded structures, to be performed with the help of an automatic hydraulic complex. The second option is the arrangement of temporary strengthening of emergency structures with the help of a metal space frame, without restoring the planned height position of the residential building.

RESEARCH OF THE METHODS OF STRENGTHENING REINFORCED CONCRETE COLUMNS DURING THE RECONSTRUCTION OF INDUSTRIAL BUILDINGS

Over the past two years, Ukraine has noted significant losses of the state's residential and non-residential stock as destroyed or partially damaged. Damaged or destroyed buildings must be restored, reconstructed and dismantled and new ones erected in their place.Industrial facilities suffered significant destruction. In addition, the condition of the structures of many old enterprises is extremely unsatisfactory.Currently, only in Kyiv, about 30% of the city's territory is industrial territory.Depending on the level of reconstruction of the object, it is possible to perform certain structural and enclosing elements. Any intervention in the structural elements of buildings must be preceded by an examination of both the building as a whole and these structures themselves.Repair, dismantling or strengthening of frame structures are among the typical types of work during the reconstruction of industrial facilities. The vast majority of old industrial buildings in our country have a reinforced concrete frame, especially the buildings that were erected in the 60s of the 20th century and in later periods. These are those buildings whose structural condition still allows for reconstruction or repair in order to continue their intended use. Buildings of an earlier stage, as a rule, are subject to reconstruction (if they are monuments of culture and architecture) or dismantling.The article investigates various methods of reinforcing reinforced concrete columns, which are key structural elements of industrial buildings, during their reconstruction. The technological and organic features of reinforcement are presented. The destabilizing factors that affect the efficiency of work are systematized. Modern technologies are studied, including changing the structural scheme, increasing the cross section, injecting into the body of the structure and external gluing of metal reinforcing structures.The effectiveness of each method is analyzed, which allows to assess their advantages and disadvantages, costs and duration of the reconstruction process. In particular, attention is focused on methods that increase the bearing capacity and durability of structures without significant interference with the overall structural scheme of the building.The results of the study allow us to identify optimal solutions for different types of industrial buildings, which helps engineers and designers ensure the sustainability and safety of reconstructed facilities.

Theoretical model of ultimate shear capacity and flexural capacity design method of boundary elements for reinforced concrete frames with steel plate shear walls

AbstractThe steel plate shear walls (SPSWs) have been proven effective in reinforced concrete frames (RCFs) as a lateral force‐resistant structure. Despite of advancements, accurately predicting the ultimate shear capacity of RCFs with SPSWs remains challenging using current simplified models. Additionally, the flexural capacity design procedure for the boundary elements (beams and columns) in previous studies of RCF‐SPSWs involved intricate iterative procedures, hindering its widespread implementation. To address the two issues, this paper investigates the pushover responses and the plate‐frame interaction (PFI) of an RCF‐SPSWs system using theoretical and numerical methods. There are three main contributions. First, a theoretical model of ultimate shear capacity for RCF‐SPSWs is proposed, which can also be used to predict shear contributions of boundary frames in RCF‐SPSWs. Calculation errors for ultimate shear capacity of RCF‐SPSWs and shear contribution from the boundary frame are only 3.7% and 6.7% respectively, which are reduced dramatically compared with the traditional model. A simplified schematic diagram for the global collapse mechanism (uniform distribution of plastic hinges within a structure) of RCF‐SPSWs is developed to facilitate the calculation of internal work and reaction forces. Secondly, a flexural capacity design method for the boundary elements to avoid in‐span plastic hinges is proposed. The proposed method enables the achievement of direct estimation of the flexural demands that could trigger a global collapse mechanism, all without intricate iterative procedures. The applicability of current assumptions for the design of steel boundary frame in RCF‐SPSWs system is discussed, and engineering suggestions are provided to ensure safer and more economic designs. Comparison results confirmed the applicability of the proposed design method, which can be adopted to achieve the global collapse mechanism for RCF‐SPSW system. Thirdly, impacts of yielding panel actions on the flexural capacity of boundary elements of RCF‐SPSWs are clarified. Comparison results demonstrated that adding SPSWs to an RCF alters the axial force on boundary elements and significantly impacts the flexural capacity. A design suggestion is made to emphasize the importance of avoiding the balanced failure of boundary elements. The proposed theoretical model can be used to economize the cross‐section of boundary elements in RCF‐SPSWs system under seismic loads due to accurate prediction of their shear contribution; the proposed flexural capacity design method can achieve a global collapse mechanism, and thus the structural safety and energy dissipation capacity are improved; moreover, the building design efficiency is also improved due to avoidance of intricate iterative procedures.

Experimental study on acoustic emission damage in precast reinforced concrete interior joints containing disc springs

To address the inferior performance of precast reinforced concrete beam-column joints compared to cast-in-place joints during earthquakes, this study designed a precast concrete frame beam-column interior joint incorporating disc springs. The disc springs, installed based on grouted sleeve connections, aimed to enhance structural ductility and mitigate seismic forces on the joints. Five joints, including one cast-in-place joint, two ordinary precast joints, and two precast joints with disc springs, were tested quasi-statically and monitored using acoustic emission technology. The precast joints had axial compression ratios of 0.2 and 0.4. Parameters such as energy, count, and b-value from acoustic emission monitoring were analyzed. The Gaussian mixture model was employed for the clustering analysis of RA-AF parameters, and a damage model was developed to evaluate performance differences among the joints in the quasi-static tests. The results indicate that precast joints with the same axial compression ratio can achieve performance similar to cast-in-place joints, with more rapid damage development at higher axial compression ratios. Installing disc springs decelerates damage progression in the later stages of loading, maintaining joint integrity for a certain period even after reaching maximum load, thereby demonstrating improved ductility. At higher axial compression ratios, the b-value curve of joints with disc springs more closely resembles that of ordinary joints. Disc springs' positive effect is more pronounced in clustering analysis and damage models, such as their lower proportion of shear fractures.

Retrofit of damaged reinforced concrete frame by autoclaved aerated concrete blocks infill wall: Experimental validation and strength estimation

This study introduces a novel approach for the global retrofitting of seismic performance in destructively damaged reinforced concrete (RC) frames through the application of autoclaved aerated concrete (AAC) blocks infill walls to enhance both structural strength and stiffness. Three full-scale RC frames are designed and fabricated, comprising an intact bare frame, a damaged frame strengthened by carbon fiber-reinforced polymer (CFRP), and a damaged frame retrofitted with the same CFRP and AAC blocks infill walls. To verify the cyclic behaviors and working principle of the retrofitted system, the two frames undergo a pre-damage scenario with a maximum inter-story drift ratio (MIDR) of 2.52%, and then both specimens are retrofitted. Afterward, a pseudo-static cyclic test is conducted on three specimens, with a MIDR of 3.36%. The test data is analyzed and discussed in terms of hysteretic responses, secant stiffness, displacement ductility, and energy dissipation capacity. The findings indicate a significant improvement in the lateral strength and stiffness of the seismic-damaged frame through the implementation of AAC blocks infill walls, demonstrating performance comparable to the intact RC frame. Also, the slight local crushing of AAC blocks and their interaction with mortar joints effectively dissipates a considerable amount of input energy, thereby reducing the energy dissipation demands on retrofitted structural components. Moreover, the theoretical deduction of the lateral strength of the retrofitted RC frames is presented. The errors between the predicted and test results fall within 5%, suggesting that the analytical outcomes can reasonably predict the lateral strength of the specimens.

Predicting embodied carbon reduction by evaluating building shape parameters in preliminary design through the Dom-ino system

ABSTRACT Adopting carbon-efficient building shapes has significant potential to reduce embodied carbon emissions (ECEs). Early-stage design decisions play a crucial role in this process, yet current methods lack predictive models for ECEs based on building shape parameters. This study addresses this gap by utilizing the Dom-ino system, which includes concrete and steel framing, to develop a method for estimating ECEs. The study analyzes the influence of building shape parameters, such as plan aspect ratio and number of floors, on ECEs and fits equations to the results to establish predictive models. Our findings indicate that these parameters significantly impact ECEs, and the study delves into the mechanisms by which they affect structural components and material usage. The developed method provides architects with a tool to evaluate and optimize building designs for lower carbon impact during the early stages of design. This approach supports a swift and environmentally conscious design process, enhancing the ability to predict and reduce ECEs in architectural projects.

Seismic Performance Analysis of the Internal Joint in the New Demountable Fabricated Concrete Frame with Prestressed Mortise–Tenon Connections

This paper proposed a novel demountable fabricated joint in frame, which is connected by the prestressed and mortise–tenon connection. The prefabricated components of the demountable structures are designed to be reused, and the joint presented in this paper will promote the sustainable application of prefabricated components in future. The damage process and damage pattern of the internal joints under the horizontal load were analyzed using the refined numerical analysis model based on ABAQUS 6.14. Parametric analyses were conducted simultaneously for five parameters: axial compression ratio, the area and effective initial stress of unbonded prestressed strands (UPSs), the local reinforcement ratio in the core zone of the demountable joint, and the friction coefficient between the interface of concrete. The results showed that the demountable joint exhibits excellent energy dissipation potential under horizontal loads, but the damage was concentrated in the core zone. The deformation of the joint mainly consisted of the self-deformation of the prefabricated components, including bending, bearing and shear, as well as the relative slip deformation between the prefabricated components. The axial compression ratio has a more significant effect on the hysteresis performance compared to the areas of the UPSs and the reinforcement ratio. The initial effective stress of the UPS and the friction coefficient have relatively minor influence on the hysteretic performance of the joint. Finally, this paper recommends the design parameter values (axial compression ratio should not exceed 0.4, area of unbonded prestressed reinforcement should be not lower than Asn=0.02 and not higher than Asn=0.1, the initial stress of the UPS takes the value of 0.75fpu) and outlines optimization measures.

Seismic Performance of Reinforced Concrete Frames on Sloped Ground Using Non-Linear Static Pushover Analysis

Nepal, renowned for its majestic Himalayan Ranges, is also highly vulnerable to seismic activity. Buildings on hill slopes often endure more significant damage during earthquakes than those on flat terrain. Traditional seismic analyses of buildings typically employ linear-static and dynamic methods, which might not fully represent the building's behavior under actual seismic conditions. This research addresses this gap by assessing the seismic performance of buildings on hill slopes using non-linear static analysis techniques. Specifically, the study evaluates the seismic response of 5-story buildings with stepback and stepback-setback configurations on slopes of 15°, 30°, and 45°. This evaluation is conducted through non-linear static analysis, also known as Pushover Analysis, using ETABSv20 software. Key performance metrics analyzed include the building's period, topstorey displacement, and base shear. The findings reveal that buildings with stepbacksetback configurations demonstrate superior seismic performance on the sloping ground compared to those with stepback configurations. This study underscores the importance of employing non-linear analysis methods to better understand and improve seismic resilience in hilly terrains.

The fiber hinge model for unbonded post‐tensioned beam‐column connections

AbstractThe precast concrete frame with unbonded post‐tensioned beam‐column connections (UPBC) has been emphasized in recent years for it is capable of sustaining a design‐basis earthquake with minor damage. The fiber hinge model (FHM), which is a simple and effective approach, is proposed in this paper for the simulation of UPBC. In the FHM, the mild steels and prestressed tendons crossing the interface are integrated into one element. The mechanism and behavior of the FHM are presented in this paper. The proposed model, which is developed in OpenSees, has been validated by tests, and the FHM is able to accurately describe the shift of compressive center induced by the opening of the interface between the precast beam and column, as well as “beam elongation effects.”

Column-to-beam flexural strength ratio for rigorous strong-column–weak-beam design for steel–concrete composite frames

This study addresses the limited research and unclear principles surrounding the strong-column–weak-beam (S-C–W-B) criterion in steel–concrete composite frames, a critical aspect of structural engineering. Despite its widespread application in steel frames, the S-C–W-B criterion's adaptation to steel-concrete composite frames remains underexplored. The research aims to clarify and establish consistent guidelines for preventing column hinge formation at the joint, a key concern in S-C–W-B design. Beginning by analysing the definitions of ultimate flexural strength and flexural yielding strength of a section, essential components of the S-C–W-B criterion, the minimum column-to-beam flexural strength ratio (ηc, min) required for a robust S-C–W-B design was deduced. The methodology involves a novel parametric analysis using a fibre beam–column model. This model is used to derive a closed-form equation for ηc, min, which was then verified through time-history analysis using the finite-element software MSC.Marc. The findings indicate that the established ηc, min provides a stringent, nonetheless, reliable criterion for S-C–W-B design in steel-concrete composite frames. This research not only bridges a significant gap in existing structural engineering knowledge but also proposes a practical approach for safer and more efficient design in real-world applications.