Three-dimensional Reinforced Concrete Research Articles

Predicting Main Characteristics of Reinforced Concrete Buildings Using Machine Learning

This paper presents a comprehensive study of five machine learning (ML) algorithms for predicting key characteristics of Reinforced Concrete (RC) structural systems. A novel dataset, ModRes, consisting of 9723 examples derived from modal and response spectrum analyses on masonry-infilled three-dimensional RC buildings, was created for ML applications. The primary objective is to develop an ML model using five distinct algorithms from the literature, capable of concurrently predicting torsional irregularity, modal participating mass ratio (MPMR), and the fundamental period in a 3D environment, while accounting for the influence of infill walls. Additionally, the study aims to determine the applicability of pushover analysis (POA) without the need for extensive numerical modeling and analysis. This approach optimizes the preliminary design process with minimal computational effort, providing valuable insights into dynamic and torsional responses during seismic events. The Categorical Boosting algorithm demonstrated outstanding performance, achieving R2 values of 0.977 for torsional irregularity, 0.997 for the fundamental period, and 0.923 for MPMR on the test dataset. It also successfully predicted POA applicability with an error rate of only 1.36%. This study highlights the practical application of ML algorithms, underscoring their effectiveness in structural engineering.

Failure Probability-Based Optimal Seismic Design of Reinforced Concrete Structures Using Genetic Algorithms

Artificial intelligence (AI) has enabled several optimization techniques for structural design, including machine learning, evolutionary algorithms, as in the case of genetic algorithms, reinforced learning, deep learning, etc. Although the use of AI for weight optimization in steel and concrete buildings has been extensively studied in recent decades, multi-objective optimization for reinforced concrete (RC) and steel buildings remains challenging due to the difficulty in establishing independent objective functions and obtaining Pareto fronts. The well-known Non-Dominated Sorting Genetic Algorithm II (NSGA-II) is an efficient genetic algorithm approach for multi-objective optimization. In this work, the NSGA-II approach is considered for the multi-objective structural optimization of three-dimensional RC buildings subjected to earthquakes. For the objective of this study, two function objectives are considered: minimizing total cost and the probability of structural failure, which are obtained via several nonlinear seismic analyses of the RC buildings. Beams and columns’ cross-sectional dimensions are selected as design variables, and the Mexican Building Code (MBC) specifications are imposed as design constraints. Pareto fronts are obtained for two RC-framed buildings located in Mexico City (soft soil sites), which demonstrate the efficiency and accuracy of NSGA-II for structural optimization.

Experimental Study on 3D RC Frame Structures with VE Energy Dissipation Braces Using STM32-Matlab-OpenSees Hybrid Test Platform

This study aims to reveal the control mechanism of viscoelastic (VE) energy dissipation braces with strong mechanical nonlinear characteristics on the seismic response of reinforced concrete (RC) frame structures. Firstly, a new STM32-Matlab-OpenSees joint hybrid test platform is developed by introducing OpenSees, which is convenient for structural modeling and fast for structural calculation. The overall architecture and operation of the hybrid test platform are comprehensively analyzed. Then, a series of simulated seismic hybrid tests on three-dimensional (3D) RC frame structures with VE energy dissipation braces under different seismic waves are successfully carried out. Lastly, the hybrid test results of this structure system at different working conditions are compared and analyzed comprehensively. The research results show that the developed platform breaks the boundary limitation that OpenSees relies on the framework software OpenFresco and can only be connected to specific control systems in the hybrid test. Thus, it greatly expands the application scope of flexible configuration controller and actuator categories for the hybrid test platform, and it also provides a good reference value for the establishment and implementation of similar hybrid test platforms. Under the action of various seismic waves, VE energy dissipation braces has good universality for the shock absorption of RC frame structures. The damping control effect and energy dissipation efficiency of VE energy dissipation braces are significantly different under various seismic waves. In the design of RC frame structures with VE energy dispersion braces, it is very necessary to conduct the seismic analysis of the structures under multiple ground motions with wide frequency domain. The additional position of VE energy dissipation braces should be an important analysis indicators in the optimization design of the structures.

Effects of modeling assumptions on prediction of seismic demands of a single-story RC structure

This study investigates the seismic response of a single-story reinforced concrete (RC) structure subjected to strong ground motions. Effects of modeling assumptions used to idealize the reinforcement slip in beam-column joints and column footing are studied. For this purpose, the numerical model of a single-story, single-bay, three-dimensional asymmetric RC structure, tested on a shake table and its symmetric version, is analyzed. Two modeling approaches are considered to show the significance of rotation associated with the reinforcement slip. Bidirectional nonlinear time-history analyses are conducted using symmetric and asymmetric 3D models. In these analyses, 30 pairs of near-field ground motions, selected and scaled to match the target spectrum, are used. The findings indicate that the neglection of reinforcement slip in numerical model may result in an underestimation of almost 50% in story drift ratio demands.

Influence of masonry infills on blast response of earthquake-resistant reinforced concrete buildings

The present study investigates the influence of masonry infill strength on the blast performance of earthquake-resistant reinforced concrete (RC) buildings under surface burst. These buildings, having three-dimensional RC moment resisting frames, are designed to withstand different levels of seismic demand. The masonry infills are modelled as an equivalent diagonal strut using a macro-modelling approach to account for its in-plane strength and stiffness. The blast-induced loads are directly applied as nodal loads on the exposed beam-column joints, and nonlinear time history analyses are then performed to obtain the various response quantities such as top floor displacement, interstory drift ratio, and base shear. The comparative matrices of various response quantities are developed to examine the effect of infill’s nonlinearity. Further, the influence of the infill strength and seismic design level of the considered buildings is probabilistically assessed by developing the blast fragility curves using an uncoupled approach. It is observed that the consideration of infill’s nonlinearity influences the blast response up to a certain scaled distance only. Moreover, increasing the infill strength does not necessarily enhance the blast performance; however, designing the building to higher seismic demand results in improved blast performance. In addition, proper insight into seismic design level and infill strength of any RC building is required prior to plan and design them with suitable blast-mitigation measures.

Matrix equations models for nonlinear dynamic analysis of two-dimensional and three-dimensional RC structures with lateral load resisting cantilever elements

In control engineering and structural dynamics, mathematical models such as the state-space representation, equation of motion, and the phase plane are matrix equations describing the system equilibrium. This paper develops novel matrix equations models for linear/nonlinear dynamic analysis of reinforced concrete (RC) buildings with cantilever elements lateral load resisting systems (e.g., RC shear wall, RC core). The models offer a new approach for introducing two-dimensional and three-dimensional cantilever structures to control the theory’s state-space representation and structural dynamics’ equation of motion. The development primarily addresses the stiffness and mass matrices. The proposed displacement-related stiffness matrix of cantilever elements satisfies the necessary conditions of symmetricity and elemental boundary conditions. The nonlinear matrix structural analysis employs a smooth hysteretic model for deteriorating inelastic structures, referring to the relation between the bending moment and the bending curvature through the bending stiffness. The parameters controlling the cyclic behavior regard a composite RC cross section subject to gravitational load and bending simultaneously. The paper includes four examples that exemplify the practical utilization of the matrix equations models in analyzing two-dimensional and three-dimensional structures of linearly elastic and inelastic properties. The four examples demonstrated the idealized applicability of the matrix equations models for modal analysis, pushover analysis, and inelastic earthquake response analysis.

Influence of Masonry Infill on Seismic Design Factors of Reinforced-Concrete Buildings

Infill walls are the most common separator panels in typical reinforced-concrete (RC) frame structures. It is crucial to investigate the influence of the infill walls on the earthquake behavior of RC frames. The load resistance of infill materials was often not taken into account in the designing phase, whereas the infill walls have significant contributions to the structural behavior under lateral and vertical loadings. A three-dimensional 4-story RC building is designed, and in order to make a realistic model, different infill walls configurations were taken into account with the openings in the infill. Four different models were created for structural analysis for infill wall effects, namely, full RC infilled frame (Model I), corner infill at ground story RC infilled frame (Model II), open ground story RC infilled frame (Model III), and bare RC frame (Model IV). Static adaptive pushover analysis has been performed for all structural models by using the SeismoStruct software. The double strut nonlinear cyclic model was used for modeling the infill walls. In this study, three different compressive strengths of infill walls are taken into consideration, and the effects on seismic design factors (namely, the response reduction factor, the ductility, the overstrength factor, and the deflection factor) are calculated. The obtained values of the response reduction factor (R) are compared with the given values in the BIS code. The results show that the R factors of all RC infilled frames are decreased when the compressive strength of the masonry infill reduces. However, the R values of bare frames are less than the corresponding values recommended in the BIS code. It is worth noting that the National Earthquake Hazards Reduction Program (NEHRP) provisions underestimate the deflection factors of the reinforced-concrete (RC) frames according to the evaluated deflection factors of the herein studied RC frames.

Probabilistic framework for failure investigation of reinforced concrete wall panel under dynamic blast loads

Over the last decade, excessive devastations caused by extreme events, such as blast loading have raised significant concern on the performance of civil structural systems. Despite realizing the importance of inherent risk associated with this phenomenon, most of the studies neglected the effects of uncertainties associated with the system, wherein the design approaches have been entirely on deterministic scale. Hence, it is deemed important to identify the complexities in the system, and in this regard, a probabilistic framework is proposed which utilizes the effects of uncertainties in the system to compute the failure probabilities of a reinforced concrete (RC) structural member under extreme blast loading. The structural member adopted here is a three-dimensional (3-D) RC wall panel, which is modeled considering material and geometric nonlinearity, and the subsequent analysis is carried out under surface-burst and free airburst scenarios. High strain rate effect induced in the RC wall is modeled using available standard dynamic increase factors (DIFs) for concrete and steel. Uncertainty in the system is assumed in material capacity (strength), mechanical loads, and dynamic blast loads considering a certain mean and standard deviation. Responses are obtained in terms of deflection, stresses, and strains at center of the wall. Limit state of failure and the respective threshold limiting values are obtained from the United States Department of Defense manual, PDC-TR 06-08 (2008). Finally, first-order sensitivity analysis is conducted to show the extent of uncertainties in input parameters affecting the output response quantities. It is concluded that the uncertainty induced in the system has significant influence in the response of the wall panels under blast loading scenarios. Moreover, based on the sensitivity analysis performed, charge weight, standoff distance, and strength of concrete material are suggested to be crucial parameters for design of blast-resistant structures. To conclude, based on the currently considered scenario of intensity of blast, exposure type, and performance level required by the user, it is recommended to use wall panels of sizes more than 100 mm in civil structures, especially 125 mm to counter the effects of extreme blast loadings.

Member and structural fragility of reinforced concrete structure under fire

Purpose Despite recognizing the significance of risk-based frameworks in fire safety engineering, the usual approach in structural fire design is largely member/component level, wherein effect of uncertainties influencing the fire resistance of structures are not explicitly considered. In this context, a probabilistic framework is presented to investigate the vulnerability of a reinforced concrete (RC) members and structure under fire loading scenario. Design/methodology/approach The RC structures exposed to fire are modeled in a finite element (FE) platform incorporating material and geometric nonlinearity, in which the transient thermo-mechanical analysis is carried out by suitably incorporating the temperature variation of thermal and mechanical properties of both concrete and steel rebar. The stochasticity in the system is considered in structural resistance, thermal and fire model parameters, and the subsequent fragility curves are developed considering threshold limit state of deflection. Findings The fire resistance of RC structure is reported to be significantly lower in comparison to the RC members, thereby illustrating the current prescriptive design approaches based on studies of structural member behavior to be crucial from a safety and reliability point of view. Practical implications The framework developed for the vulnerability assessment of RC structures under fire hazard through FE analysis can be effectively used to estimate the structural fire resistance for other similar structure to enhance safety and reliability of structures under such extreme threats. Originality/value The paper proposes a novel methodology for vulnerability assessment of three-dimensional RC structures under fire hazard through FE analysis and provides comparison of the structural fragility with fragility developed for structural members. Moreover, the research emphasizes to assume 3D behavior of the structure rather than the approximate 2D behavior.

Assessment of three-dimensional RC moment-resisting frames under repeated earthquakes

Earthquakes are one of the major unavoidable natural disasters. These are characterized by the recorded ground motion data at a particular location. In any real earthquake event, shaking repeatedly occur several times within a few hours or days. In view of lack of time between the occurrences of tremors, the rehabilitation of the structure often becomes impractical, and the structural damages get accumulated. Hence, it is imperative to assess the behavior of reinforced concrete (RC) buildings under repeated earthquakes to prevent a disaster. The current practices of earthquake-resistant design utilize only a single strongest earthquake input in the form of a response spectrum, corresponding to the seismic code of practice at the site location. Hence, this investigation is primarily focused on vulnerability assessment of three-dimensional RC building frames conformed to the Indian standard codes of practice under bi-directional single and repeated ground motions. Incremental dynamic analysis is carried out to assess the inelastic behavior of the structure in terms of maximum horizontal displacement, residual displacement, and maximum inter-story drift ratio for particular spectral accelerations. The results obtained in this investigation conclude that the collapse capacity of RC building under repeated earthquakes reduces significantly compared to that of the most severe single earthquake. This emphasizes the need to account for repeated earthquake forces during the design phase in order to build a seismic resilient structure.

Fire fragility of reinforced concrete panels under transverse out-of-plane and compressive in-plane loads

This article focuses on investigating vulnerability of fire-exposed reinforced concrete (RC) panels under transverse out-of-plane and compressive in-plane loads following a probabilistic methodology. The three-dimensional (3-D) RC panels are modeled by considering material and geometric nonlinearity and subsequent transient thermo-mechanical analysis is conducted for single-side exposure to fire loading. Uncertainties in the system are considered in structural capacity (material strength), heat transfer-, and fire model to study the stochastic thermo-mechanical response of the RC panels. The stochastic responses are studied in terms of central deflection, distribution of temperature, and variation in stresses and strains developed at the exposed and unexposed faces of the RC panels. It is concluded that the system uncertainty has significant influence on the duration of fire resistance of the RC panels under the considered thermo-mechanical loadings. The RC panels under the transverse out-of-plane loading exposed to fire are relatively more vulnerable as compared to the panels under the compressive in-plane loading. Moreover, the thicknesses of the RC panels have significant influence in determining the fire rating. Finally, it is recommended to use RC panels of at least 125 mm thickness irrespective of functionality if the desired code-specified fire rating is to be achieved.

Fatigue Stress-Life Model of RC Beams Based on an Accelerated Fatigue Method

Several standard fatigue testing methods are used to determine the fatigue stress-life prediction model (S-N curve) and the endurance limit of Reinforced Concrete (RC) beams, including the application of constant cyclic tension-tension loads at different stress or strain ranges. The standard fatigue testing methods are time-consuming and expensive to perform, as a large number of specimens is needed to obtain valid results. The purpose of this paper is to examine a fatigue stress-life predication model of RC beams that are developed with an accelerated fatigue approach. This approach is based on the hypothesis of linear accumulative damage of the Palmgren–Miner rule, whereby the applied cyclic load range is linearly increased with respect to the number of cycles until the specimen fails. A three-dimensional RC beam was modeled and validated using ANSYS software. Numerical simulations were performed for the RC beam under linearly increased cyclic loading with different initial loading conditions. A fatigue stress-life model was developed that was based on the analyzed data of three specimens. The accelerated fatigue approach has a higher rate of damage accumulations than the standard testing approach. All of the analyzed specimens failed due to an unstable cracking of concrete. The developed fatigue stress-life model fits the upper 95% prediction band of RC beams that were tested under constant amplitude cyclic loading.

Assessment of dynamic increase factor for progressive collapse analysis of RC structures

Abstract Assessment of a building vulnerability against progressive collapse using Nonlinear Dynamic (NLD) analysis has greater accuracy compared to other methods. Yet, the relevant standards and design guidelines allows the use of Linear Static (LS) analysis and Nonlinear Static (NLS) analysis to assess the progressive collapse risks of buildings. To approximately account for the dynamic effects due to sudden element removal, two different dynamic amplification factors namely, the Load Increase Factor (LIF) and the Dynamic Increase Factor (DIF) in linear and nonlinear static analyses, respectively are suggested. The DIF formulation of the current design guidelines of progressive collapse is relied on the material properties of the affected structural members. In this study, the effect of available structural capacity on DIF value in the Reinforced Concrete (RC) structures is investigated and on this basis a new empirical DIF formula is proposed. For this purpose, several three-dimensional RC building structures with different span lengths and number of stories are designed that have different levels of seismic resistance and implemented to derive the new DIF empirical formula. One of the advantages of the proposed formulae is the possibility of predicting stress and deformation in the RC structures' members after column removal.

Evaluation of Structural Robustness against Column Loss: Methodology and Application to RC Frame Buildings.

A computational methodology is presented for evaluating structural robustness against column loss. The methodology is illustrated through application to reinforced concrete (RC) frame buildings, using a reduced-order modeling approach for three-dimensional RC framing systems that includes the floor slabs. Comparisons with high-fidelity finite-element model results are presented to verify the approach. Pushdown analyses of prototype buildings under column loss scenarios are performed using the reduced-order modeling approach, and an energy-based procedure is employed to account for the dynamic effects associated with sudden column loss. Results obtained using the energy-based approach are found to be in good agreement with results from direct dynamic analysis of sudden column loss. A metric for structural robustness is proposed, calculated by normalizing the ultimate capacities of the structural system under sudden column loss by the applicable service-level gravity loading and by evaluating the minimum value of this normalized ultimate capacity over all column removal scenarios. The procedure is applied to two prototype 10-story RC buildings, one employing intermediate moment frames (IMFs) and the other employing special moment frames (SMFs). The SMF building, with its more stringent seismic design and detailing, is found to have greater robustness.

Development of CSMM-based shell element for reinforced concrete structures

Reinforced concrete shell structures have been widely used in a variety of modern engineering applications. It is found from earthquake reconnaissance that reinforced concrete (RC) shell structures, such as nuclear containments, cooling towers, roof domes, shear walls, etc., are the key elements in resisting earthquake disturbances. This paper presents the development of a finite element analysis (FEA) program, SCS-3D, to predict the inelastic behavior of RC shell structures. In the program, a Cyclic Softened Membrane Model (CSMM)-based shell element is developed based on the degenerated shell theory with a layered approach and taking into account the CSMM developed at the University of Houston. To form the FEA program, the constitutive relation modules and the analysis procedure were implemented into a finite element program development framework, OpenSees developed at UC Berkeley. Several large-scale structural tests were employed to validate the developed FEA program, including RC panels subjected to a combination of shear and bending, three-dimensional RC shear wall and cylindrical RC tanks subjected to reversed cyclic loading.

Seismic performance evaluation of a three-dimensional unsymmetrical reinforced concrete building

Reinforced concrete (RC) structures require advanced analysis techniques for better estimation of their seismic responses, especially in the case of exhibiting complex three-dimensional coupling of torsional and flexural behaviors. This study focuses on validating a numerical approach for evaluating the seismic response of a three-dimensional unsymmetrical RC structure through the participation in the SMART 2013 international benchmark program. The benchmark program provides material properties, detailed drawings of the RC structure, and input ground motions for the seismic response evaluation. In this study, nonlinear constitutive models of concrete and rebar were formed and local tests were conducted to verify the constitutive models in finite element analysis. Elastic calibration of the finite element model of the SMART 2013 RC structure was performed by comparing numerical and experimental results in modal and linear time history analyses. Using the calibrated model, nonlinear earthquake analysis and seismic fragility analysis were performed to estimate the behavior and vulnerability of the RC structure with various ground motions.

Deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion

A three-dimensional reinforced concrete (RC) deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion is presented in this study. The finite element formulation accounts for both material and geometrical nonlinearity. Damage modelling considers uniform and pitting corrosion and includes the reduction of cross-sectional area of corroded bars, the reduction of ductility of reinforcing steel and the deterioration of concrete strength due to splitting cracks, delamination and spalling of the concrete cover. The beam finite element is validated with reference to the results of experimental tests carried out on RC beams with corroded reinforcement. The application potentialities of the proposed formulation are shown through the finite element analysis of a statically indeterminate RC beam and a three-dimensional RC arch bridge under different damage scenarios and corrosion penetration levels. The results indicate that the design for durability of concrete structures exposed to corrosion needs to rely on structural analysis methods capable to account for the global effects of local damage phenomena on the overall system performance.

Experimental study and numerical simulation of the damage mode of a square reinforced concrete slab under close-in explosion

Terrorist attacks using improvised explosive devices on reinforced concrete buildings generate a rapid release of energy in the form of shock waves. Therefore, analyzing the damage mode and damage mechanism of structures for different blast loadings is important. The current study investigates the behavior of one-way square reinforced concrete (RC) slabs subjected to a blast load through experiments and numerical simulations. The experiments are conducted using four 1000mm×1000mm×40mm slabs under close-in blast loading. The blast loads are generated by the detonations of 0.2–0.55kg trinitrotoluene explosive located at a 0.4m standoff above the slabs. Different damage levels and modes are observed. Numerical simulation studies of the concrete damage under various blast loadings are also conducted. A three-dimensional solid model, including explosive, air, and RC slab with separated concrete and reinforcing bars, is created to simulate the experiments. The sophisticated concrete and reinforcing bar material models, considering the strain rate effects and the appropriate coupling at the air–solid interface, are applied to simulate the dynamic response of RC slab. The erosion technique is adopted to simulate the damage process. Comparison of the numerical results with experimental data shows a favorable agreement. Based on the experimental and numerical results, the damage criteria are established for different levels of damage. With the increase of the explosive charge, the failure mode of RC slab is shown to gradually change from overall flexure to localized punching failure.

Strengthening of reinforced concrete structures with external steel shear walls

The strengthening of reinforced concrete (RC) structures with external steel shear walls was investigated in this study. The proposed technique allows the strengthening of in-service RC structures in parallel to reducing the construction costs and leading to faster and more workable solutions. The experimental program includes three-dimensional RC models, which exhibited some of the structural deficiencies commonly encountered in existing RC structures. The related tests were conducted under the imposed reversed cyclic lateral sway. Accordingly, performance of the proposed strengthening technique is found to be adequate for improving the seismic capacity of existing RC structures. Additionally, base shear capacity and stiffness of the strengthened model were significantly improved.

Effects of Variation of Axial Load and Bidirectional Loading on Seismic Performance of GFRP Retrofitted Reinforced Concrete Exterior Beam-Column Joints

Most of the experimental studies available in literature on the seismic assessment and retrofit of existing, poorly detailed, reinforced concrete (RC) beam-column joints, typical of pre-1970s construction practice, have concentrated on the two-dimensional (2D) response, using unidirectional cyclic loading testing protocol and constant axial load. Even more limited information is available on the performance of exterior (corner) three-dimensional (3D) RC beam-column joints with substandard detailing subjected to bidirectional loading regime. In this study, the results of a comprehensive experimental program is presented, aiming to show the effects of varying axial and bidirectional loading on the seismic performance of deficient exterior RC beam-column joints before and after retrofit. Ten exterior beam-column joint subassemblies are tested, including four as-built specimens and six retrofitted specimens using externally bonded glass fiber-reinforced polymer (GFRP) sheets. Test results are herein presented...