Reinforced Concrete Buildings Research Articles

Development of Seismic Fragility Functions for Reinforced Concrete Buildings Using Damage-Sensitive Features Based on Wavelet Theory

In this study, wavelet-based damage-sensitive features are employed to derive the seismic fragility functions/curves for reinforced concrete moment-resisting frames. Two different wavelet transform functions, namely, Bior3.3 and Morlet mother wavelet families, were applied to absolute acceleration time histories of building frames to extract the wavelet-based and refined wavelet-based damage-sensitive features (i.e., DSF and rDSF). The accuracy of seismic assessments and certainty in predicting structural behavior strongly depend on the specific optimal intensity measures selected, reliability of wavelet-based damage-sensitive features, and some such intensity measures as PGA, PGV, PGD, Sa, and Sdi as the conventionally utilized measures to detect the damage state of a structure. These measures were examined against their statistical properties of efficiency, practicality, proficiency, coefficient of determination, and sufficiency to select the appropriate optimal intensity measures, which were then used to drive the fragility curves disclosing the failure or other damage states of interest. For the purposes of this study, three different concrete moment-resisting frames with four-, eight-, and twelve-story building frames were adopted for implementing the proposed approach. The findings demonstrate that the wavelet-based damage-sensitive features (DSFs/rDSF) simultaneously satisfy all the statistical properties cited above. This is evidenced by the low variance and dispersions observed in the frame damage state predictions by the fragility functions derived from the wavelet-based DSF when compared with those derived from the classical fragility analyses such as spectral acceleration at the first mode period of the structure. A final aspect of the study concerns the superior performance and efficiency of the fragility curves derived by the Bior3.3 wavelet-based DSF over those derived from Morlet wavelet-based DSF.

Investigation of the Causes of Soft-Storey and Weak-Storey Formations in Low- and Mid-Rise RC Buildings in Türkiye

This study investigates the causes of soft-storey and weak-storey formations in low- and mid-rise RC (Reinforced Concrete) buildings in Türkiye. In the first phase of the study, 96 model buildings were designated for the examination of soft-storey irregularity when the ground floors are used for commercial purposes and the upper floors for residential use. The ground floor heights that would cause soft-storey irregularity in each of the selected buildings were determined according to the formulas given in the Türkiye Building Earthquake Code (TBEC) and the American Society of Civil Engineers Standard (ASCE). It was found that the ground floor heights obtained according to ASCE are usable in practice, whereas those obtained according to the TBEC, particularly for buildings over three storeys, are excessively high for practical use. This indicates that, even if the buildings in Türkiye are designed with very high ground floor heights, they do not have soft-storey irregularities, according to the TBEC, but soft-storey formation may occur in these buildings due to the high ground floor height as a result of the effects of earthquakes. Instead of the soft-storey irregularity coefficient limit value (nki > 2) found in the TBEC, this study proposes a new limit value to prevent the design of buildings with very high ground floors. In the second phase of the study, for the purpose of examining weak-storey irregularity, 105 model buildings differing in their infill wall layout, number of spans, span length, and number of storeys were selected. The weak-storey irregularity coefficients of each of these models were determined according to the TBEC. The results of the study revealed that buildings with no infill walls in one direction or with infill walls in only one of the exterior axes in one direction have a high risk of having weak storeys.

Evaluation on Effective Dimensions of Base Isolators Applied at Existing RC Building due to Earthquakes

This study investigates the structural performance of High Damper Rubber Bearings (HDRB) as base isolators in reinforced concrete (RC) buildings subjected to seismic loads. Given the potential for damage or collapse in RC buildings during earthquakes, the utilization of base isolators offers a promising solution to mitigate seismic risks. Finite element analysis was employed to assess the displacement efficiency of different HDRB configurations, focusing on the SMP 5 Muhammadiyah building in Surabaya as a case study. Results indicate that HDRB type HH090X6R exhibits superior performance, achieving displacement efficiencies of 90.56% in the x-direction and 95.87% in the y-direction. These findings underscore the importance of selecting optimal base isolator configurations to enhance the seismic resilience of RC structures. The study's implications extend to seismic retrofitting and structural design practices, offering valuable insights for improving the seismic performance of existing buildings and bolstering community resilience to earthquakes.

Relationships for Evaluating the Seismic Resilience Index of Reinforced Concrete Buildings Built Up with FRP Lying on Different Soil Types under Near-Field Earthquakes

Relationships for Evaluating the Seismic Resilience Index of Reinforced Concrete Buildings Built Up with FRP Lying on Different Soil Types under Near-Field Earthquakes

Failure mechanism and landslide fragility of reinforced concrete buildings considering uncertain flow properties

ABSTRACT This study examines the failure mechanism and landslide fragility of regular and irregular reinforced concrete (RC) buildings under flow-type landslides. Efficient intensity measures to evaluate landslide fragility of regular flat land buildings and irregular buildings, having step-back and split foundation configurations, are proposed. Further, a methodology is proposed to consider the uncertain flow properties in the investigation of failure mechanisms and landslide fragility. Uncertainty in landslide properties is considered based on some database of past landslide events and laboratory experiments conducted on the soil samples collected from four landslide-active sites in the Mandi district in Himachal Pradesh, India. Overturning moment (hv) is found to be the efficient as well as most proficient intensity measure (IM), among several other IMs for landslide fragility assessment of regular and irregular RC buildings. Further, it is concluded that the landslide performance of RC buildings is directly related to the seismic design level of the building. Moreover, the buildings with step-back configuration are found to be more vulnerable than their split foundation counterparts. Furthermore, structural deficiency of the short columns, typically observed in the considered building configurations, under landslide loading is highlighted and design recommendations are presented for improvements.

Elastic Analysis of the Influence of Masonry on the Soil-Structure Interaction of a Reinforced Concrete Building

Elastic Analysis of the Influence of Masonry on the Soil-Structure Interaction of a Reinforced Concrete Building

Lateral Load Response of Reinforced Concrete Buildings Constructed on Clay Soil with Weak Zones

Lateral Load Response of Reinforced Concrete Buildings Constructed on Clay Soil with Weak Zones

Seismic analysis of RC building with plan irregularity in Baghdad/Iraq to obtain the optimal behavior

Abstract A study was conducted for four-story reinforced concrete (RC) structure existing in Baghdad-Iraq (residential building) to evaluate the accuracy and reliability of the equivalent lateral force procedure (ELFP) analysis and the response spectrum model (RSA) according to Iraqi seismic code (ISC 2016) for designing and analyzing irregular buildings. The building was classified as an irregular in plan according to American Society of Civil Engineers (ASCE 7-16). The seismic behavior of the building was investigated by verifying many parameters: the ratio of shear demand to shear strength on the columns ( V V / V n {V}_{n} ), internal force (bending moment, shear force, and axial force) for beams and columns, and the inter-story drift ratio (IDR) obtained from the (ELFP and RSA); then, the results were compared with the nonlinear static procedure (NSP) and the nonlinear dynamic procedure (NDP) according to ASCE 7-16. Also, this study investigated the effects of the higher modes in the plan (roof plan displacement). From the results, it can be concluded that ELFP and RSA are not a suitable analysis for asymmetric structures and should use appropriate methods such as the NSP and NDP.

Modal-based fragility analysis of high-rise tubular structures: A methodology for vulnerability assessment

This study addresses the limitations of current vulnerability assessment processes for tall buildings, which fail to incorporate the effects of higher modes and the resulting structural vulnerability to seismic hazards. Additionally, the extensive computational resources required for assessing tubular high-rise buildings make vulnerability assessments almost impossible. This study proposes a new methodology for assessing the modal-based structural vulnerability of high-rise reinforced concrete (RC) tubular buildings by incorporating nonlinear response and reducing computational effort. The proposed methodology discreetly develops the vulnerability information of each structural vibrational mode separately using nonlinear time history analysis rather than the linear Modal Response Spectrum Analysis (MRSA). The methodology includes steps for establishing vulnerability information for high-rise tubular buildings, and a case study of a 55-story RC building with core wall is presented to demonstrate the methodology. The vibrational modes of the building were decoupled and analyzed separately using single degree of freedom (SDOF) systems, and fragility curves were developed for three different limit states using various intensity measures. The obtained fragility relationships were compared with the curves of another structure of similar class. The results indicated good compatibility and significance of incorporating higher vibrational modes in assessment of structural vulnerability, thus, proposed methodology can be extended to any structural configuration of tubular buildings.

Seismic behaviour of Exterior RC beam-column joints repaired and strengthened using post-tensioned metal straps

Exterior beam-column joints are the most vulnerable part of substandard reinforced concrete (RC) buildings and are often the first to be damaged during earthquakes. This article presents an experimental and numerical investigation into the behaviour of exterior RC beam-column joints repaired and strengthened using Post-Tensioned Metal Straps (PTMS) for active confinement. The study focused on full-scale beam-column joints with an inadequate core zone detailing, thus emulating the deficiencies found in existing substandard RC buildings. Initially, four “bare” joints were subjected to cyclic tests to induce substantial damage within the core zone. Subsequently, the damaged core of the joints was repaired and recast with new concrete, and PTMS were applied to strengthen the joints, followed by another round of cyclic testing. The experimental findings were compared with predictions generated through established models from existing literature. The results revealed that ASCE/SEI 41–17 guidelines accurately predict the shear capacity of the bare joints. It is shown that recasting the core with new concrete significantly increased the joint’s shear capacity by up to 42% compared their bare counterparts. The use of PTMS strengthening further enhanced the capacity by up to 25%. A “scissors model” was employed for numerical simulations of both bare and PTMS-strengthened joints using DRAIN-2DX, which proved effective at predicting their nonlinear load-displacement envelope response. This article contributes towards the development of new cost-effective post-earthquake strengthening techniques for beam-column joints, with the potential to reduce the vulnerability of substandard RC buildings in developing countries.

Field Reconnaissance and Earthquake Vulnerability of the RC Buildings in Adıyaman during 2023 Türkiye Earthquakes

The 6th February 2023 Pazarcık and Elbistan earthquakes (Mw = 7.7 and Mw = 7.6) caused great destruction in many cities and were the disaster of the century for Türkiye. The greatest destruction was caused in the provinces of Hatay, Kahramanmaraş, and Adıyaman during these earthquakes, which were independent of each other and occurred on the same day. Information about earthquakes and strong ground motion records is given within the scope of this study. Reinforced concrete (RC) structures which constitute a large part of the urban building stock in the earthquake region were exposed to structural damage at different levels. The structural damage in the RC structures in the city center, Gölbaşı, and Kahta districts of the province of Adıyaman was evaluated within the scope of earthquake and civil engineering after field investigations. Insufficient RC, low-strength concrete reinforcement problems, RC frame failure, heavy overhang, short columns, soft story, and pounding effect are the main causes of the earthquake damage. The presence of these factors that reduce the earthquake resistance of RC structures increased the damage level. In addition, the fact that the earthquakes occurred nine hours apart and the continuation of aftershocks during that period negatively affected the damage levels. It has been observed that structures that receive the necessary engineering services during the construction and project phases ensure the safety of life and property, even if the structure is slightly damaged. In this study, we also tried to reveal whether the target displacements were satisfactorily represented by numerical analysis for a sample RC structure.

Multiple performance objective design for a sliding isolator with variable curvature

Thanks to its variable mechanical properties, the sliding isolator with variable curvature (SIVC) has recently attracted significant attention in seismic isolation research. Nevertheless, designing an SIVC is a challenging task, as it usually involves more design parameters than a conventional sliding isolator. To expedite the application of SIVCs, this study proposes a systematic design method that enables SIVCs to achieve multiple performance objectives corresponding to dual earthquake levels. The method comprises linear and nonlinear design stages. During the linear design stage, the linearized isolator parameters that comply with the design-basis-earthquake (DBE) and maximum-considered-earthquake (MCE) seismic demands specified in a design code are determined. Subsequently, in the nonlinear design stage, the isolator geometric parameters are determined based on the linearized parameters. While the linear design procedure is generic and applicable to all types of SIVCs, the derived formulas for determining the isolator geometric parameters in the nonlinear design stage are tailored for the polynomial friction pendulum isolator (PFPI). Finally, the proposed method is demonstrated by implementing a PFPI design for a 5-story reinforced-concrete (RC) building. The effectiveness of the proposed design method is validated through dynamic analysis of a hysteretic structural model representing the RC building with two different types of PFPIs subjected to 23 spectrum-compatible ground motions. The results demonstrate that, despite their different mechanical features, both types of PFPIs can accomplish the “preset” DBE and MCE design objectives. Additionally, the simulated results highlight the advantages of using different types of PFPIs.

Influence of the Plan Structural Symmetry on the Non-Linear Seismic Response of Framed Reinforced Concrete Buildings

Seismic-resistant design incorporates measures to ensure that structures perform adequately under specific limit states, focusing on seismic forces derived from both the equivalent static and spectral modal methods. This study examined buildings on slopes in densely built urban areas, a common scenario in Latin American cities with high seismic risks. The adjustment of high-rise buildings to sloping terrains induces structural asymmetry, leading to plan and elevation irregularities that significantly impact their seismic response. This paper explores the asymmetry in medium-height reinforced concrete frame buildings on variable inclines (0°, 15°, 30°, and 45°) and its effect on their nonlinear response, assessed via displacements, rotations, and damage. Synthetic accelerograms matched with Chile’s high seismic hazard design spectrum, scaled for different performance states and seismic records from the Chilean subduction zone, were applied. The findings highlight structural asymmetry’s role in influencing nonlinear response parameters such as ductility, transient interstory drifts, and roof rotations, and uncover element demand distributions surpassing conventional analysis and in earthquake-resistant design expectations.

Empirical Fragility Analysis of Haitian Reinforced Concrete and Masonry Buildings

This study develops empirical fragility curves for concrete and masonry buildings in Haiti, utilizing data from the 2021 earthquake. A dataset of 3527 buildings from the StEER database, encompassing a diverse range of building types, is used. These buildings types include reinforced concrete structures with masonry infills, confined masonry buildings, reinforced masonry bearing walls, and unreinforced masonry bearing walls. Shakemaps from the USGS are utilized to assess the earthquake’s intensity at each building, with the peak ground acceleration (PGA) as the intensity measure. Damage is classified into five distinct states: no damage, minor, moderate, severe, and partial or total collapse. For each of these states, the corresponding probabilities of exceedance are calculated, and log-normal cumulative distribution functions were fitted to those data to produce empirical fragility curves. The results show a notable similarity in performance among the four types, each having high probability of failure even under low-intensity earthquakes. Total fragility curves (including all four building types) are developed subsequently and they are convolved to the probabilistic seismic hazard map of Haiti to assess the seismic risk. This includes estimating the annual probability of partial/total collapse and the probability of partial/total collapse in the event of 475-year and 2475-year earthquakes. The results indicate a significant risk, with up to 64% probability of collapse in certain areas for the 2475-year earthquake and a probability of collapse of 15% for a 475-year earthquake. These findings underscore the critical vulnerability of Haiti’s buildings to seismic events and the urgent need for their retrofit.

Green Structural Retrofitting Materials for Fire-Damaged Reinforced Concrete Buildings: Advances in Sustainable Repair of Distressed Buildings

Green Structural Retrofitting Materials for Fire-Damaged Reinforced Concrete Buildings: Advances in Sustainable Repair of Distressed Buildings

Evaluating Seismic Performance in Reinforced Concrete Buildings with Complex Shear Walls: A Focus on a Residential Case in Chile

This study employs a non-linear static analysis, known as pushover analysis, to explore the flexural-compressive behavior of complex shear walls within a reinforced concrete (R.C.) structure, adhering to contemporary design standards in Chile. The primary objective is to assess the initiation of damage as the building approaches the limit states outlined in Achisina’s seminal “Performance Based Seismic Design” framework. To achieve this, a sophisticated fiber model, accounting for the confined behavior of concrete derived from the structural elements’ detailing, has been uniformly integrated across the building’s entire height. Furthermore, the analysis incorporates a rigid diaphragm to simulate the R.C. slab’s response accurately. The study implements the N2 method, adjusting for seismic demands in an acceleration-displacement format, which leverages the displacement spectrum defined by Supreme Decree 61, a legislative response to the 8.8 Mw Maule earthquake in 2010. The findings reveal that the analyzed structure meets the immediate occupancy performance level with drifts nearing 5‰ in the symmetrical Y direction. This outcome aligns with prior assessments of Chilean R.C. wall buildings. However, in the asymmetric X direction, the structure exhibits a higher degree of structural damage, aligning with a life safety performance level. This differentiation underscores the critical need for nuanced understanding and modeling of structural behavior under seismic loads, contributing to the ongoing refinement of seismic design practices and standards.

Assessment of Different Methods for Enhancing Progressive Collapse Resistance of Irregular Reinforced Concrete Buildings Using Pushdown Analysis

AbstractEnsuring structures meet rigorous structural requirements is paramount in mitigating progressive collapse risk. In this comprehensive investigation, we scrutinize the impact of four distinct mitigation techniques on the propensity for progressive collapse in a six-story building featuring irregular structural attributes. The study adheres to the concrete building construction code ACI 318-14 and evaluates methods that include: (a) reinforcing the reinforced concrete (RC) slab with high-performance fiber-reinforced cementitious composites (HPFRCCs), (b) enhancing the RC slab with carbon fiber-reinforced polymers (CFRPs), (c) incorporating steel plate shear wall (SPSW) within specific columns, and (d) introducing an innovative approach named as the steel belt strip (SBS). In the context of 10 independent column loss scenarios conducted on the first floor, the nonlinear dynamic analysis reveals that HPFRCC effectively reduces vertical displacement under the removed column by up to 99.89% in certain scenarios. Meanwhile, the use of CFRP layers leads to reductions of up to 95% in vertical displacement, but with variations in effectiveness across scenarios. Notably, the SBS technique demonstrates remarkable potential by reducing vertical displacement by 97%, 89%, and 25.9% in different scenarios. This reduction, in conjunction with the mitigation of axial load on adjacent columns, makes the SBS a standout performer. Moreover, pushdown analysis indicates that, with the employment of these mitigation methods, the maximum loading factor can be increased up to 2.14 times in specific scenarios, significantly enhancing the structure’s resistance to progressive collapse. This pioneering research not only bolsters the resilience of irregular RC buildings but also holds profound implications for industry standards, risk assessment, and construction technology innovation.

Reliability-based conformity control method for chloride diffusivity of coastal reinforced concrete buildings

Chloride diffusivity significantly affects the durability of coastal reinforced concrete (RC) buildings, and is one of the major concerns in practice. However, its design and conformity control are commonly based on “deem-to-satisfy” methodology, and consequently it's difficult to evaluate the building's durability performance. In this paper, a reliability-based conformity control method for diffusivity is proposed to eliminate the gap. First, the existing empirical method and semi-empirical method are reviewed, and their drawbacks are addressed according to the reliability assessment. Then, based on the statistical acceptance sampling theory and the engineering practice of Hong Kong-Zhuhai-Macau sea-link project, the reliability-based method for diffusivity is proposed, which can be applied in the construction of coastal RC buildings. In this method, effects of local environmental conditions (e.g., temperature and humidity) on chloride diffusivity are considered, and the relation between diffusion coefficient for design (Da0) and for conformity control (Dnssm) is suggested accordingly. Finally, the conformity control for the concrete's chloride diffusivity of an accessory RC building in the Shantou Harbor is taken as the example, and the schemes by empirical method, semi-empirical method and reliability-based method respectively are established. Their acceptable quality level (AQL) and limiting quality level (LQL), probabilities of acceptance and outcomes in terms of durability reliability are evaluated and compared. It is found that the reliability-based method can offer the schemes that is consistent with the design target, and reject most of the nonconforming lots without harming the producers' benefits.

A Comparative Study of Fragility Model for RC Girder Bridges and Buildings

Field surveys and data on the earthquake reveal that RC (reinforced concrete) bridges and buildings have been widely found in engineering structures, with abundant samples at disposal. By taking actual seismically damaged samples in the Wenchuan Earthquake happened in 2008 as examples, the paper established probability models for fragility matrix within Intensity VH-X/XI for the said two engineering structures based on EMS-98, MSK-81 and CSIS-08, and analyzed the comparative models for failure ratio and exceedance probability curves defined by these three scales. The paper, according to these analytical findings, proposed relevant measures and methods for improving the earthquake resistance of RC bridges.

Convolutional Neural Network Approach for Vibration-Based Damage State Prediction in a Reinforced Concrete Building

Convolutional Neural Network Approach for Vibration-Based Damage State Prediction in a Reinforced Concrete Building