Concrete Frame Research Articles

Seismic Design and Risk Analyses of Safe-to-Fail Steel and RC Frames for Nuclear Facilities

Abstract In this article, the design and estimate of the collapse risk of safe-to-fail steel and reinforced concrete (RC) frames due to earthquakes were proposed. The frames are part of nuclear facility buildings, and their failures are to follow the safe-to-fail beam side-sway collapse mechanism. The safe-to-fail was dictated by allowing plastic hinges to form merely in beams and few in columns; no other failure but flexure was tolerated such as shear, local or lateraltorsional buckling. Two types of safe-to-fail frames were studied, one with special moment frame (SMF) and the other with ordinary moment frame (OMF). The design was elaborated, and the fragility-based collapse risks were estimated and compared. Nonlinear time history analyses were carried out to evaluate the structural performance. The analyses showed that the safe-to-fail OMF had lower collapse risk than the safe-to-fail SMF for both steel and concrete frames. The steel safe-to-fail OMF showed superior behaviours. Keywords: Safe-to-fail; concrete and steel frames; fragility; collapse risk; earthquake; time history analysis.

Development of an adaptive reliability analysis framework for reinforced concrete frame structures using uncertainty quantification

Development of an adaptive reliability analysis framework for reinforced concrete frame structures using uncertainty quantification

Multi-index evaluation on reinforcement programs for frame structures based on life cycle theory and time-varying reliability

Under the mandates of economic and environmental sustainability, the consideration of reinforcement engineering must extend beyond mere enhancement effects and short-term project costs. As a long-term engineering activity, reinforcement significantly impacts urban economies and environments. Although extensive research has evaluated the costs or environmental impacts of reinforcement engineering based on the whole life cycle theory, existing studies often focus on single indicators without adequately integrating them with other domains. Using a reinforced concrete frame structure as a case study, this paper develops a combined evaluation decision-making model integrating the Analytic Hierarchy Process for subjective assessment and an enhanced Rough Set method for objective evaluation. This model comprehensively assesses the seismic performance, economic costs, and environmental impacts of various reinforcement strategies. The results indicate that the combined strategy of enlarging column sections and carbon fiber reinforced polymer strengthening beams performs best in seismic performance, long-term economic benefits, and environmental impacts. Grounded in practical projects, this study adjusts the whole life cycle cost model to better align with engineering maintenance realities and introduces Rough Set theory to address deficiencies in objective indicator weighting. This research offers insights and guidance for leveraging information technology in resolving multi-criteria evaluation decision-making challenges in reinforcement engineering solutions.

Seismic behavior and resilience assessment of prefabricated beam–column joint with replaceable graded-yielding energy-dissipating connectors

Conventionally assembled monolithic concrete frame structures achieve structural ductility through beam-end failure, which results in structures that are difficult to repair after an earthquake. To improve the seismic and resilience performance, a prefabricated concrete beam–column joint with replaceable graded-yielding energy-dissipating connectors (RGECs) is introduced. The connectors assembled on the upper and lower sides of the beam end dissipate energy and transfer the beam-end load with the steel hinge device. By adjusting the design bearing-capacity coefficient of RGECs to precast beams, the plasticity and damage of the structure can be centered on the core energy-dissipation bending–shear components (BSCs) and buckling segment (BS) of the RGEC, and the structural function can be quickly recovered by replacing only the damaged RGECs after a seismic disaster. Moreover, compared to the conventional joints, the joint with RGEC can achieve target seismic-performance goals at different seismic-risk levels by designing BSCs and BS with graded yielding. Low-cyclic-loading tests were performed on seven full-scale beam–column joint specimens to investigate the effects of different core energy-dissipating member thicknesses, beam reinforcement ratios and loading protocols on the seismic behavior of the proposed joint. Subsequently, the damaged RGECs were replaced, and the structural-function resilience performance was evaluated in terms of the function-recovery efficiency and quality, indicated by the hysteresis response, strain development, and component energy dissipation. The experimental results proved that the beam–column joint exhibited excellent seismic performance and could realize graded-yielding energy dissipation. The damage to the specimens was concentrated in the RGECs, the key members (beams and columns) were in an elastic state, and the energy dissipation ratio of the RGEC was more than 97 %. This enables the rapid recovery of function after earthquakes. After replacing the RGEC, the hysteresis response, strain development, and component energy dissipation of the specimens were consistent with those of the initial specimens. Compared with the original specimen, the difference in each seismic index of the replaced specimen was less than 10 %. Additionally, the structural function recovered quickly, and the resilient performance was good.

Pre-relaxed cables for improving progressive collapse resistance of RC frame subassemblages considering slabs

A common method to improve the progressive collapse resistance of reinforced concrete (RC) frame structures is to increase the reinforcements in beams, which might result in the undesired failure mode of strong beam-weak column for the structures under earthquakes. To improve the progressive collapse resistance of the RC frame structures without affecting their seismic behaviors, a novel retrofit has been proposed using pre-relaxed cables. This study investigated the improvement of the pre-relaxed cables on the progressive collapse resistance of the RC frame structures considering the presence of the slabs subjected to the distributed loads. A quasi-static test was carried out on two one-quarter scaled 2 × 2-bay subassemblages, i.e., a beam-slab (BS) subassemblage and a beam-slab-cable (BS-cable) subassemblage. Experimental results found that the progressive collapse resistance and deformation capacity of the BS-cable subassemblage was 55 % and 260 % larger than those of the BS subassemblage, respectively. The resistance improvement mechanism of the BS-cable subassemblages was revealed, i.e., the tensile catenary action in the beams, tensile membrane action in the slabs, and tension action in the cables. The finite element (FE) models were then developed, validated against the experimental results, and used for parametric studies with the consideration of the cable diameter and cable original length. Numerical results found that there were two failure modes for the BS-cable subassemblages, i.e., beam failure mode and slab failure mode. The upper limit of the improvement of the progressive collapse resistance using the cables is critically related to the failure mode. For the beam failure mode, the increase in the cable diameter could improve the progressive collapse resistance until the slab failure mode occurred.

Experimental study on seismic performance of two-story two-bay. Precast concrete frame with UHPC-based connections

The UHPC-based connections, utilizing Ultra-high performance concrete (UHPC) to connect rebars within precast concrete structures, present the advantages of short splice length, simplified construction, and low cost due to the excellent bond property between UHPC and rebars. This investigation focuses on seismic performance of precast concrete frame (PCF) with UHPC-based connections. The UHPC-based connections were arranged strategically to the beam-column joints and column bases in PCF to connect longitudinal rebars of beams and columns, respectively. Two half-scale, two-story, two-bay reinforced concrete frames, including PCF and a monolithic concrete frame (MCF) for reference, were tested under cycle loading with axial compression ratios of 0.33 in the middle columns and 0.22 in the side columns. The results revealed that PCF exhibited a beam sway mechanism, with all beam hinges developed prior to column hinges, while MCF displayed a mixed sway mechanism, with part of beam hinges developed prior to column hinges. The hysteresis curves of the two frames were globally stable with minimal pinching, and PCF displayed greater energy dissipation compared to MCF. The load-carrying capacity of PCF was 9 % higher than that of MCF. The displacement ductility of PCF was 4.14, exceeding that of MCF by 10 %. The two frames showed similar laws of stiffness degradation. Overall, the precast concrete frame with the UHPC-based connections exhibited better seismic performance in comparison with the monolithic counterpart.

A generalized Timoshenko beam with embedded rotation discontinuity coupled with a 3D macroelement to assess the vulnerability of reinforced concrete frame structures

A generalized finite element beam with an embedded rotation discontinuity coupled with a 3D macroelement is proposed to assess, till complete failure (no stress transfer), the vulnerability of symmetrically reinforced concrete frame structures subjected to static (monotonic, cyclic) or dynamic loading. The beam follows the Timoshenko beam theory and its sectional behavior is described in terms of generalized forces and generalized strains. The beam response up to the peak is described by a macroelement, based on plasticity theory, that adopts a 3D failure criterion expressed in terms of axial force, shear force and bending moment. The Embedded Finite Element Method is then adopted to reproduce bending dominated failure, with a global cohesive model that links the cohesive moment to a rotational jump. The formulation allows for remedy of localization phenomena and significant reduction of the necessary computational time. The performance of the proposed simplified strategy is illustrated by comparison with experimental results.

Probabilistic evaluation of failure time of reinforced concrete frame in post‐earthquake fire scenario

AbstractThis paper aims at assessing the failure time of a 7‐story reinforced concrete (RC) frame in a post‐earthquake fire (PEF) event probabilistically. Cumulative distribution functions (CDF) of the studied frame's failure time in various seismic load intensities have been calculated and presented with the aid of Monte Carlo analysis. Seismic load intensity, failure time, and failure probability are three parameters that are correlated through probabilistic analysis. The effects of cracking, spalling, and residual deformations resulted from the seismic load are considered in the strength of structure against the fire load. Seismic load intensity, materials properties, gravity load, and geometry are considered as random variables and one probabilistic analysis has been carried out for each seismic load intensity. The results have illustrated that in low seismic load intensities, probabilistic values of failure time in a structure subjected to pure fire load are equal to the one exposed to PEF. With the increase of seismic load intensity, the effects of cracking, spalling, and residual deformations would lead to a decline in the strength of structural elements against PEF scenario. The failure time in 50% failure probability for Sa = 0.2 g, Sa = 1 g, and Sa = 2 g intensities has been calculated as 14,300, 12,200, and 5100 s, respectively. The analysis results have shown that in an unspecified seismic load intensity, the failure time of the 7‐story RC frame for the 50% occurrence probability is equal to 9750 s.

Seismic performance impacts of staircases in reinforced concrete frame structures under rarely occurred earthquake

Seismic performance impacts of staircases in reinforced concrete frame structures under rarely occurred earthquake

Predicting natural vibration period of concrete frame structures having masonry infill using machine learning techniques

The natural period of vibration is one of the most significant factors used in the seismic design of buildings. Although the building design codes and previous studies provide some empirical methods to compute the natural period of vibration (T), their marginal accuracy and inability to incorporate the effect of masonry infill on vibration period significantly limits their use. Thus, researchers are constantly trying to find new and accurate methods to calculate T of concrete structures. To this end, this study presents the novel approach to predict T of reinforced concrete framed buildings (RC buildings) using Multi Expression Programming (MEP), Extreme Gradient Boosting (XGB), and Gene Expression Programming (GEP) machine learning algorithms. For this purpose, an extensive dataset of 569 points was gathered from previously published studies and split into training and testing sets for training and testing the algorithms respectively by using several error evaluation metrices like coefficient of determination (R2), Root Mean Squared Error (RMSE), and Objective Function (OF) etc. The results of error evaluation showed that XGB is the most accurate algorithm having the least OF value of 0.012 compared to 0.037 of MEP and 0.048 of GEP. Additionally, several explanatory analyses like sensitivity and shapley analysis were conducted on the XGB model which showed that number of storeys and opening ratio are the most contributing variables to prediction period of vibration. Thus, the models developed in this study can be practically utilized for determining natural vibration period of reinforced concrete frames with masonry infill.

Seismic rehabilitation of RC frames with innovative precast U-shaped UHPC jackets: Experimental evaluation and computational simulation

The rehabilitation of post-earthquake reinforced concrete (RC) frames is crucial for both restoring structural integrity and enhancing seismic resilience against future seismic events. Ultra-high-performance concrete (UHPC) is distinguished by its exceptional strength, crack-control capabilities, ductility, and durability. Despite numerous studies on its use for structural retrofitting, its application in rehabilitating damaged RC frames remains limited. This study introduced a novel precast U-shaped UHPC jacket designed for the post-earthquake rehabilitation of RC frames. The jacketing method promotes composite action in rehabilitated members through lap splicing and dowel bars, complemented by cast-in-place connections using UHPC to minimize splice length and strengthen potential weak areas under external loads. The efficacy of this jacketing approach was rigorously evaluated through cyclic loading experiments on two RC frame specimens. Results indicated that the UHPC rehabilitation method not only recovered but significantly enhanced the seismic performance of the previously damaged frame, improving initial stiffness, yield strength, peak strength, displacement ductility, and energy dissipation capacity. However, the rehabilitated frame showed a reduced yield drift and increased residual displacement compared to the as-built frame. The experimental results also revealed the necessity of accounting for bond slip in structural rehabilitation analysis and design to prevent overestimating lateral stiffness. Furthermore, the study developed a computational model that incorporates flexure, bond slip, and shear responses, aiming to effectively simulate the load-displacement behavior of rehabilitated RC frames with reasonable accuracy.

Assessment, quantification and propagation of uncertainty in seismic life-cycle cost analysis

Seismic life-cycle cost analysis (SLCCA) is a comprehensive tool to estimate the expected lifetime economic losses due to seismic events in terms of present-day value and aids in lifetime investment planning and design decision-making. The state-of-the-art framework for SLCCA incorporates three essential components: seismic hazard analysis, seismic fragility curves and damage cost estimates. Due to different sources of uncertainty prevailing in each component, the SLCC estimates may vary substantially. However, most of the existing literature primarily focuses on the expected value of the SLCC, and uncertainties stemming from multiple sources are unaccounted for. To address this drawback, this study proposes a comprehensive approach to quantify and propagate multiple uncertainties and offers a visualization of the shape and nature of SLCC distribution. Furthermore, the application of the framework is demonstrated using a case study example of the reinforced concrete (RC) frame building. Results reveal that the SLCC distribution is multimodal due to multiple uncertainty sources and the expected SLCC values also shift significantly compared to the state-of-the-art approaches, highlighting the criticality of the uncertainty propagation. Lastly, a novel framework is proposed to rank uncertainty sources based on their relative influence that will aid stakeholders in informed decision-making under uncertainty.

Experimental evaluation of cyclic behavior of precast concrete frame with steel shear wall

AbstractThis study seeks to integrate steel shear walls with precast concrete systems into stable and resistant structures against lateral loads. It is desired to study the ductility factor, lateral strength, and behavior as well as the energy absorption of this integrated system compared to the precast concrete frame without a shear wall. For this purpose, two steel shear wall samples made of mild steel and galvanized steel plates are constructed within a precast concrete frame. The assembly is tested under a cyclic lateral load. The integrity of the connections of steel strips of the wall together, and the boundary of the wall to the frame, is observed to be excellent. The main failure mode is composed of the diagonal yielding of the steel wall. The system benefits from large hysteresis loops and no degradation because of any instability. The beam‐column connections remain almost intact even at large cycles of deformation. Moreover, a bare precast concrete frame is tested in the same way to compare the lateral behavior. The utilized ductile beam‐column connections are successful in retaining the integrity of the system until large drifts. However, the seismic design characteristics of the bare frame turn out to be inferior to the steel shear wall system. Results of the cyclic tests show that by proper design of the interior and exterior connections of the shear wall as well as the beam‐column connections, the steel shear wall system can largely increase the stiffness, ultimate strength, and energy dissipation capacity of a bare precast moment resisting reinforced concrete frame. On top of that, the system is able to retain its integrity up to lateral drifts over 2%.

Influence of the Vertical Load Bearing Status on the Seismic Performance of Weak-Joint-Type RC Frames Strengthened by the Wing Wall Installation Method

“Strong column–weak beam, strong joint–weak member” is a core concept for the seismic design of buildings. For existing reinforced concrete (RC) frame buildings that do not satisfy this concept, installing RC wing walls beside existing columns is a simple and effective method for strengthening both columns and joints to promote a beam-hinging mechanism. In this study, a numerical simulation method is used to analyze the seismic performance of weak-joint RC frames strengthened by additional wing walls considering the column axial force ratio and to determine whether to consider the secondary load as a variable. The results show that when the secondary load is not considered, i.e. existing columns do not bear a load during the strengthening process, the strength, stiffness and energy dissipation of the structure increase with increasing axial force ratio, but the ductility of the structure decreases. When the secondary load is considered, the strength and initial stiffness of the frame are the greatest when the column axial force ratio is 0.4. When the axial force ratio is less than 0.4, the secondary load has less influence on the strength, stiffness and energy consumption. When the axial force ratio is greater than 0.4, the secondary load has a significant impact on the seismic performance of the strengthened structure, and the strength, stiffness, energy consumption and ductility are significantly greater than those in the case in which the secondary load is not considered. Additionally, the larger the axial force ratio is, the more significant the difference is. It is revealed that in engineering seismic strengthening using the wing wall installation method, the influence of secondary load on seismic performance should not be ignored, especially when the axial force ratio is large.

Time history seismic response prediction of multiple homogeneous building structures using only one deep learning‐based Structure Temporal Fusion Network

AbstractStructural response prediction under earthquakes is crucial for evaluating the structural performance and subsequent functional restoration. Deep learning provides the potential to rapidly obtain the responses by skipping the time‐consuming nonlinear finite element analysis. However, a single deep learning network may only predict the time history responses of one specific structure, resulting in redundancy and resource waste when building multiple networks for modeling different structures. Thus, this study proposes a Structure Temporal Fusion Network (STFN) that can predict responses of various homogeneous structures using a single network. The key concept is that the seismic waves and the structural characteristics, such as story numbers, are fused together to predict diverse time history responses. Two numeric experiments are conducted, including predicting responses of ideal single‐degree‐of‐freedom (SDOF) structures and regular multistory reinforced concrete frames. Furthermore, a series of ablation analyses are carried out to validate the network architecture. The results indicate that STFN can predict nonlinear time history responses of different structures with mean square errors in the magnitude of and for two experiments, respectively. The solutions also highlight the importance of fusing static characteristics for the modeling of various structures with only one network. The STFN presents a promising solution for time history response prediction across multiple structures in regions.

Estimation of the Reduction Coefficient When Calculating the Seismic Resistance of a Reinforced Concrete Frame Building after a Fire

The consequences of destructive earthquakes show that the problem of analyzing the response of reinforced concrete frames under seismic loads after a fire is relevant. The calculation models used for individual elements and buildings as a whole must take into account the nonlinear properties of concrete and reinforcement. In the spectral calculation method, the nonlinear properties of materials are taken into account by introducing a reduction coefficient to the elastic spectrum. When determining the reduction coefficient, a common deformation criterion is based on the use of the plasticity coefficient. The seismic resistance of a three-span, five-story reinforced concrete frame under four different fire exposure options is considered. The residual strength and stiffness of frame elements after a fire is assessed by performing a thermal engineering calculation in the SOLIDWORKS software for a standard fire. For the central sections of the elements, the highest temperatures were obtained after heating—during the cooling stage. The reduction coefficient is estimated by performing a nonlinear static analysis of reinforced concrete frames in OpenSees and constructing load-bearing capacity curves. Fracture patterns and damage levels in plastic hinges are analyzed. Based on the numerical modeling of reinforced concrete frames after exposure to fire, it was revealed that the most dangerous scenario is the occurrence of a fire on the first floor of the building. Based on the obtained plasticity coefficients, reduction coefficients were determined in the range of 2.62 to 2.44. The influence of fire on the permissible damage coefficient of a reinforced concrete frame is assessed using the coefficient φK—the coefficient of additional damage after a fire, which is equal to the ratio of the reduction coefficients for the control and fire-damaged frames. Depending on the percentage of damaged structures on the first floor, the following values were obtained: 50% or less—φK = 1.09; 100%—φK = 1.17. The obtained coefficients are recommended to be used when assessing the seismic resistance of a reinforced concrete frame after a local fire.

Nonlinear modeling and time-history analysis of dry-assembled precast concrete frames with buckling-restrained braces

A combination of dry-assembled precast concrete frames and buckling-restrained braces (BRB) is a viable choice for achieving the full potential of building industrialization and promoting the popularization of precast structures in earthquake-prone zones. A recent study has tested the seismic performances of a dry-assembled precast concrete frame with BRBs (BRB-DPCFs) under cyclic quasi-static loading. To study the comparative seismic behaviors of BRB-DPCFs and the monolithic concrete frames with BRBs (BRB-MCFs) under ground motion records, buildings between 3 and 12 stories in height were designed based on GB50010-2016, Chinese code for design of concrete structures, and investigated numerically. This investigation includes two-dimensional nonlinear time-history analyses of BRB-MCFs and BRB-DPCFs under two seismic hazard levels. BRB-DPCF demonstrated a larger maximum story drift compared to BRB-MCF, while the maximum residual story drift of the former is negligible in comparison to the latter at a higher building height or under a higher seismic intensity. The two systems show similar drift concentration factors, which was observed irrespective of the hazard level and the specific height of the building.

Impact of irregular masonry infill walls on the seismic response of reinforced concrete frame buildings using linear dynamic analysis

This paper aimed to investigate the seismic response of reinforced concrete (RC) frame buildings using linear dynamic analysis. The study focused on the effects of irregular distributions of masonry infill walls both in elevation (soft story at different levels) and in horizontal (plan) distribution on seismic behavior. Seventeen models were analyzed, including infill frame models with soft stories, models with infill panels only in certain bays, and bare frame models. All models were analyzed using the linear response spectrum (RS) dynamic analysis method. Structural design typically focuses on peak response values, and response spectrum analysis examines the structure's behavior and performance through these peak values. The analysis results indicate that masonry infill walls significantly affect the building's fundamental time period, base shear, story shear, and inter-story drift.

Seismic Vulnerability Assessment of Self-Centering Prestressed Concrete Frames with and without Masonry Infill Walls: Experimental and Numerical Models

Seismic Vulnerability Assessment of Self-Centering Prestressed Concrete Frames with and without Masonry Infill Walls: Experimental and Numerical Models

A Comparative Analysis of Machine Learning Algorithms for Predicting Fundamental Periods in Reinforced Concrete Frame Buildings

A Comparative Analysis of Machine Learning Algorithms for Predicting Fundamental Periods in Reinforced Concrete Frame Buildings