Reinforced Concrete Building Structures Research Articles

Experimental investigation on rehabilitation effectiveness of ductile RC beams with various seismic damage levels using dynamic and static-cyclic loading protocols

With respect to the seismic damage of a ductile reinforced concrete (RC) beam in an RC building structure with seismic design, since the functionality of the building must be recovered, the maximum strength and ductility of the member must be restored by repair or retrofit. Therefore, this work focuses on the effectiveness of the selected repair and retrofit methods in rehabilitating a ductile RC beam with a specified damage level. For this purpose, eight RC beam specimens are designed based on the seismic design requirements in ACI 318-19 to investigate their mechanical properties using the test. In the experiment, loading protocol tests of two types - traditional static-cyclic loading protocol and earthquake-then-cyclic loading protocol—are conducted to quantify the effectiveness of rehabilitation of the RC beam specimens with the selected repair or retrofit methods. The repair and retrofit methods include surface treatment, epoxy low-pressure injection, epoxy resin mortar coating, rebar planting and steel plate retrofitting. Finally, the test results related to the development of strength, stiffness and cracking are used to quantify the effectiveness of rehabilitation of the ductile RC beams with various seismic damage levels using the selected repair or retrofit methods.

Damage-Controlling Seismic Design of Low- and Mid-Rise RC Buildings Considering Mainshock-Aftershock Sequences

Recently, the modified equivalent linearization method (MELM) is used to estimate the maximum deformation response for a structure under a near-fault or far-fault earthquake. However, most works in which the equivalent linearization method is used consider only one earthquake event. When a reinforced concrete (RC) building structure is damaged by a mainshock, which is the main seismic event of an earthquake, its stiffness and strength are reduced by concrete cracking and rebar yielding and then its period is longer in the sequent seismic events or so-called aftershock. Therefore, for seismic design of low- and mid-rise RC building structures, this work is aim to propose a simplified method that can be used to quantify the damage that is subjected to an MSAS sequence in a near-fault or far-fault earthquake using MELM. Additionally, a formula that can be used to do the damage-controlling seismic design considering an MSAS sequence is also suggested.

Topologically preoptimized ground structure (TPOGS) for the optimization of 3D RC buildings

As an optimization that starts from a randomly selected structure generally does not guarantee reasonable optimality, the use of a systemic approach, named the ground structure, is widely accepted in steel-made truss and frame structural design. However, in the case of reinforced concrete (RC) structural optimization, because of the orthogonal orientation of structural members, randomly chosen or architect-sketched framing is used. Such a one-time fixed layout trend, in addition to its lack of a systemic approach, does not necessarily guarantee optimality. In this study, an approach for generating a candidate ground structure to be used for cost or weight minimization of 3D RC building structures with included slabs is developed. A multiobjective function at the floor optimization stage and a single objective function at the frame optimization stage are considered. A particle swarm optimization (PSO) method is employed for selecting the optimal ground structure. This method enables generating a simple, yet potential, real-world representation of topologically preoptimized ground structure while both structural and main architectural requirements are considered. This is supported by a case study for different floor domain sizes.

Seismic Capacity Estimation for Composite Multi-storeyed RC buildings

Seismic hazard happens to be one of the most devastative natural hazards to be faced by mankind. In view of urbanization and knowledge gained from past natural hazards, several urban cities have seen a transformation in building their habitats. These range from regular, irregular multistoried Reinforced Concrete (RC) buildings to several composite multi storeyed RC buildings due to certain inherent functional benefits (viz., ventilation, parking space, ease of construction etc.,). The existing seismic code regulations provided by BIS (Bureau of Indian Standards) do not specify any approach to arrive at appropriate design seismic forces and capacity for composite multi storeyed buildings. Therefore, it is imminent to assess the structural behaviour of these multistoried composite RC buildings under earthquake forces at the site location to provide a safe and functional configuration. Hence an attempt has been made in this study to analytically compare regular and composite RC building models having similar Plan and Height. The multistoried RC building configurations considered in this study comprises of regular RC building as well as RC building frame coupled with steel joists at certain locations to represent a composite structural system. These models are further analyzed to arrive at inherent nonlinear seismic capacity, ductility and design seismic forces necessary to be considered during design of RC building structure. Hence, a typical hypothetical G+5 regular and composite multistoried buildings were modelled and analysed using the nonlinear static (pushover analysis) approach. The outcomes of these analyses clearly portrays the variation in dynamic characteristics of the building frames represented in terms of its time period, inelastic capacity and response reduction factor (R). Moreover, the present study emphasizes to analytically evaluate the design seismic forces necessary for earthquake resistant design of composite buildings in any urban environment albeit the changes in structural configurations.

Vision‐based seismic damage detection and residual capacity assessment for an RC shaking table test structure

AbstractIn this paper, the existing postearthquake performance assessment framework for reinforced concrete (RC) building structures is improved by adding a new feature of the computer vision‐based damage detection. In this framework, visible seismic damage is classified and quantified from photographs of damaged RC components using the developed deep convolutional network (CNN) Damage‐Net of semantic segmentation, and then the mechanical property degradation factors of components determined from the detected damage states are used to update the numerical model. Pushover analysis of the updated model assesses the residual capacity of the damaged structure. Large‐scale shaking table tests of a three‐story RC building structure, which was heavily instrumented with sensors and recorded with a large volume of photographs, were used as a case study to demonstrate the improved postearthquake performance assessment framework. The vision‐based approach accurately detected multicategory seismic damage of the test structure and effectively estimated the residual crack widths and angles under various lighting, image acquisition, and surface conditions. The updated model, which incorporated the mechanical property degradation of the damaged components, provided accurate estimate on the fundamental vibrational frequencies of the damaged structure after various levels of seismic motion shaking, which matched well with the system identification results. Using the mechanical property reduction factor values recommended by FEMA 306 & Chiu et al., pushover analysis of the updated models provided residual capacity curves that reasonably captured the measured hysteretic responses of the structure. In addition, the damage states of components as estimated by the vision‐based methods were also compared with the measured plastic hinge rotation data. The successful implementation of the vision‐based assessment in this test case indicates its potential for application in the postearthquake evaluation of buildings.

Dynamic behavior and retrofitting of RC frame building under vehicular bomb explosion

Although the terrorist explosion attacks on critical buildings caused by the Vehicle-Borne Improvised Explosive Device (VBIED) are low-probability events, the blast-induced progressive collapse of buildings generally lead to the catastrophic consequences of the events. Through the high-fidelity hybrid finite element (FE) model and numerical simulations, this work aims to get a deep insight into the progressive collapse behavior of high-rise reinforced concrete (RC) frame buildings under blast loadings induced by VBIED, as well as the feasibility of two blast-resistant external retrofitting measures, i.e., fiber reinforced polymer (FRP) and steel plate (SP). Firstly, the applicability of the hybrid FE modelling approach, element types and size, material models and parameters, as well as numerical algorithms, i.e., multi-material Arbitrary Lagrangian-Eulerian (MM-ALE) and Fluid-Structure Interaction (FSI), are fully validated by comparing with the explosion tests on 1/4-scale bare and prototype FRP/SP-retrofitted RC frame structures, respectively. Then, a twelve-story RC frame building is designed following the Chinese regulations, and the corresponding hybrid FE model is established. The failure modes and progressive collapse process of building under the explosions of cargo vans bomb (equivalent TNT of 1814 kg) specified by Federal Emergency Management Agency are numerically examined. Furthermore, the effectiveness of FRP/SP-retrofitted frame columns is assessed quantitatively. It derives that, the SP-retrofitted building is not collapsed for both the scaled distance of 1.0 and 0.55 m/kg1/3; by retrofitting FRP warps, the collapse of entire buildings can be prevented with the scaled distance of 1.0 m/kg1/3, while the progressive collapse of the retrofitted building occurs with a scaled distance of 0.55 m/kg1/3. The present work could provide helpful references for the blast-resistant evaluation, design and retrofitting of the as- and newly-built RC building structures.

Preliminary seismic assessment for low-rise reinforced concrete buildings including corrosion-induced deterioration

The main purpose of this work is to develop a preliminary seismic assessment method for corroded low-rise reinforced concrete (RC) building structures. Additionally, the proposed method can be combined with the existing evaluation method of durability, which is used to determine the deterioration degrees of corroded RC members. In order to quantify the effect of corrosion on the ultimate shear strength of a corroded RC column, this work uses experimental data concerning corroded RC column members to verify models for predicting the mechanical behavior of a corroded RC member. Furthermore, based on the database of low-rise RC building structures in Taiwan, this work also proposes strength reduction factors for use in estimating the ultimate shear strength of corroded RC columns in a preliminary seismic assessment. Finally, this work takes two school buildings as in the case study to demonstrate the procedure for making a preliminary seismic assessment of corroded low-rise RC building structures.

Post-earthquake preliminary seismic assessment method for low-rise RC buildings in Taiwan

After the 1999 Chi-Chi Earthquake in Taiwan, to improve the safety of a huge number of low-rise reinforced concrete (RC) buildings, including typical RC school buildings and street houses, preliminary seismic assessments were conducted to pre-screen for seismic capacity. The main purpose of this work is to modify the existing preliminary seismic assessment method to make it applicable to earthquake-damaged low-rise RC building structures. In this work, reduction factors of strength, stiffness and energy dissipation, which are based on experimental data in past research, are used to modify the nonlinear plastic hinges of damaged RC column members with various damage levels. Additionally, the behavior of modified nonlinear plastic hinges is verified using experimental data. To develop a method of preliminary seismic assessment for a damaged low-rise RC building structure, the reduction factors of shear strength per unit area are suggested using the modified nonlinear plastic hinges of the damaged RC column members. Furthermore, the effect of the stiffness reduction on the development curve of strength of an RC column member is also considered in determining the reduction factors of shear strength per unit area for the preliminary seismic assessment. Finally, in a case study of ten real damaged low-rise RC building structures, in addition to the strength reduction factors, a post-earthquake preliminary seismic assessment method is thus proposed and verified using the detailed seismic assessment method.

A decision-making model for supporting selection of green building materials

The manufacture and use of building materials result in numerous environmental concerns in the construction industry. Green building materials (GBMs) are environmentally friendly compared to their traditional counterparts. However, identifying the criteria for selecting GBMs and assessing their sustainability have been challenging. In this study, the Analytic Hierarchy Process (AHP) technique was used to decide between selecting steel building structure and reinforced concrete (RC) building structure as an alternative. In the first phase, the criteria for selecting GBMs were identified through literature review, experts’ opinions, and questionnaire survey. In the second phase, the purposive sampling technique was used to select experts and professionals in materials selection to compare the different GBMs criteria and also, to compare and weight the provided alternatives. The findings of this study identified that 29 criteria were ranked using a scatter plot of means and standard deviation scores. Besides, the results indicated that RC building structure, with a weight value of 0.5225, was a better alternative to steel building structure. Additionally, the results show that the environmental and economic criteria are more important than the social criteria. This study, therefore, developed a decision-making model for helping stakeholders to select materials required to achieve sustainable buildings.

Estimation of Seismic Damage Induced by Near- and Far-Fault Earthquakes Using Modified Equivalent Linearization Method of Mid-Rise RC Buildings

For the seismic design of a mid-rise reinforced concrete (RC) building considering the damage control, the main purpose of this work is to propose a simplified method that can be used to estimate the damage index or damage state induced by the near-fault and far-fault earthquakes. In addition to the maximum deformation response, the hysteretic energy dissipation induced the earthquakes is also considered in the damage index quantification based on the modified equivalent linearization method (MELM). Based on the damage index model in terms of the maximum deformation response and hysteretic energy dissipation under an earthquake, this work provides a convenient method by which an engineer can determine the damage-controlling minimal ductility requirement to ensure that the damage index remains under a specified value. For a mid-rise RC building structure, an engineer can also apply the simplified formula proposed in this work to obtain the damage-controlling yielding strength for a specified ductility capacity.

Optimization of RC Structures in Terms of Cost and Environmental Impact—Case Study

Reinforced concrete (RC) structures represent one of the most widespread building systems around the world. This paper deals with the optimization of load-bearing RC structures in terms of cost and environmental impact. The results of the optimization are the dimensions and reinforcement of structural elements for which the total construction costs and environmental impacts are the lowest. Six variants of RC building structures were designed and analyzed in a case study. The construction cost was evaluated on the basis of the national pricing system. The life cycle assessment (LCA) characterization model according to the ReCiPe methodology version 1.08 was used to assess environmental impacts. The main motivation of this article was to show the possibilities of the multi-criteria optimization of a load-bearing structure, not only from a structural point of view but also from economic and environmental points of view. The presented conclusions correspond to this specific construction of the RC structure used in the case study and may not be generalized. Nevertheless, they point to certain trends and patterns that can also be used in the design of other reinforced concrete structures. The method used in this case study could be applied to the analysis of other structures using specific datasets for cost and environmental impact evaluation.

Robustness of RC building structures with infill masonry walls: Tests on a purpose-built structure

Structural robustness is a significant property towards improving resilience of buildings, i.e. enhance their ability to withstand and recover from extreme events which often can cause local damage and progressive collapse. It is widely accepted that robustness depends on the capacity of the structure to activate alternative load paths (ALPs) after the failure of load-bearing elements, e.g. columns. Early evidence during World War II showed that progressive collapse of some buildings was avoided by the presence of masonry infill walls. Subsequent studies focused on this effect for cases of sudden column removal although most of these studies were analytical, numerical and only looked at internal columns which are generally less vulnerable to accidental events compared to corner and edge columns. The aim of this study was to analyse how infill walls can improve the robustness of reinforced concrete (RC) buildings in corner columns failure scenarios. A purpose-built 3D two-storey full-scale RC building structure with infill masonry walls was tested. The contribution of masonry infill walls was analysed in terms of: (i) load redistribution, (ii) ALPs, and (iii) Dynamic Amplification Factors (DAFs) to be applied in linear-static analyses. The test was highly monitored by 38 strain gauges, 38 LVDTs and 2 accelerometers to register the vertical and lateral response. The results showed that masonry infill walls had a significant influence on the structural response and activated the predominant ALPs at very small deflections.

Seismic assessment of existing gravity load-designed RC framed building: a case study from Warangal, India

Most of the existing reinforced concrete (RC) buildings in India are either designed before the existence of seismic design codes or without proper provisions to resist lateral loads. These structures generally possess low strength and limited ductility, thereby always prone to global failure and are a primary reason for causalities during an earthquake. Hence, seismic evaluation of these structures and strengthening, if necessary, is essential to prevent a disaster during its serviceable lifetime. In this investigation, a four-storied (G+3) RC building structure in Warangal city, Telangana State, India, has been selected as a case study. Furthermore, the structure is to be extended vertically by two stories above the existing configuration. The structural and material inputs to the analytical model are updated from visual inspection and nondestructive tests, followed by an analytical study. From the analytical study, the seismic capacity of the existing gravity load-designed structure itself is found to be inadequate for seismic requirements. Since the structure is to be extended vertically, the existing building needs to be strengthened appropriately to withstand additional loads and remain functional throughout its lifetime. The outcome of the seismic analysis is checked for conformity using demand and capacity requirement of the structural components of the six-storied (G+5) structure. This behavior mimics the current scenario of existing RC buildings in this locality, which needs to be appropriately strengthened. It has been observed from the analysis that the RC building was vulnerable to the seismic forces and needed retrofitting to remain functional during its service life.

Optimal seismic retrofit method for reinforced concrete columns with wing walls

Seismic retrofit of reinforced concrete (RC) columns using wing walls can be used to improve the shear and flexural strength of the column through a relatively simple process. However, the feasibility and efficiency of the seismic retrofitting of RC frames with wing walls heavily depends on the selection of number of columns to be retrofitted, the cross-sectional dimensions of wing walls, and the quantity of re-bars of the wing wall. In this study, an optimal seismic retrofit design method is proposed to minimize not only the initial retrofit cost but also the earthquake-induced damage expected during the life cycle of the building. The seismic performance of structures before and after the application of the retrofit has been verified with the comparison of four response parameters: pushover curves, the inter-storey drift ratios, the energy dissipation capacities, and failure modes. The proposed retrofit method is applied to seismic retrofit of a six-storey RC building example and an actual RC building structure in use. For the retrofit of actual building structure, with an initial retrofit weight of 70.85 kN, which corresponds to 1.85% of the weight of the non-retrofitted building, the energy dissipation capacity was increase by 3.02 times and the life cycle cost (LCC) of the retrofit was reduced to 69.47% of the required LCC for the non-retrofitted building. In addition, it has been confirmed that no storey collapse occurred in collapse prevention level, which indicates the most severe failure mechanism of a structure due to an earthquake.

Seismic evaluation of ordinary RC buildings retrofitted with externally bonded FRPs using a reliability-based approach

Despite the extensive literature on reinforced concrete (RC) members retrofitted with fiber-reinforced polymer (FRP) composites, few studies have employed a reliability-based approach to evaluate the seismic performance of RC buildings in terms of their collapse capacity and ductility. In this study, the performance of a poorly-confined RC building structure is investigated for different FRP retrofitting schemes using different configurations and combinations of wrapping and flange-bonded FRPs, as two well-established techniques. A nonlinear pushover analysis is then implemented with a computational reliability analysis based on Latin Hypercube Sampling (LHS) to determine the collapse capacity and ductility of the case-study structure. The variations in material properties and applied loads are examined using a rational probabilistic procedure. The results demonstrate the effectiveness of the reliability approach as it is capable of providing reliable and accurate comparisons between the retrofitting schemes implemented. In addition, the failure modes of the original and retrofitted frames are scrutinized for a more detailed study. It was found that the failure mode of the case-study building is remarkably dependent on the variations of both the input parameters and the adopted retrofitting scheme.

Reliability-based constant-damage ductility demand spectra of mid-rise RC building structures using modified equivalent linearization method

In the displacement-based seismic design and evaluation, the equivalent linearization method is one of the approximation methods to estimate the maximum displacement response of a single-degree-of-freedom (SDOF) system. Based on the past research conducted by Okano & Miyamoto and the seismic design code in Taiwan, this work proposes modified equivalent linearization method (MELM) of a SDOF system for a mid-rise reinforced concrete (RC) building structure. By considering a modification factor suggested by the equivalent linear method proposed by Okano and Miyamoto and performing the nonlinear regression analysis, the accuracy of the proposed method can be improved. A total of 348 ground motions recorded on the various earthquakes are used to calculate error statistics of MELM. Additionally, a closed-form formula for the constant-damage ductility demand spectrum (CDDDS) that corresponds to a specified reliability is suggested in this work.

A new index to evaluate exposure and potential damage to RC building structures in coastal areas

Exposure to an aggressive marine atmosphere can seriously harm reinforced concrete (RC) structures and affects a building's service life. In particular, buildings close to the sea are at high risk of suffering damage, mainly due to the effects of chloride. The scientific and technical communities are interested in studying new parameters related to building degradation, including “exposure to aggressive environments” in order to predict a building's service life and schedule maintenance and monitoring systems. This paper proposes a marine exposure index aimed at quantifying potential risks and damage to RC building structures. The definition of the index includes three synergistically related techniques: i) the Analytic Hierarchy Processes to analyze the complexity of the problem and the parameters involved in marine exposure; ii) a state-of-the-art technique to evaluate the degree of building degradation; iii) an optimization calibration procedure by setting a Mathematical Programming problem. The resulting index can be extensively and fruitfully applied by researchers and practitioners in order to assess the building's exposure to an aggressive marine atmosphere. Architects and engineers could apply the proposed index in any phase of the building process, from the project to the maintenance and management phases. The effectiveness of the proposal was tested in a survey of 1816 buildings on the Valencia coast (Spain).

Increase of Temperature and Fire Resistance for Reinforced-Concrete Structures by Surface Treatment with Protective Coating

The normative documents of Ukraine (DBN V.1.1.7 ̶ 2016) [1] establish that the limit of fire resistance of reinforced-concrete building structures is determined by the calculation method or by fire tests, and shall be at least 45 minutes. Taking into account the modern construction technologies, namely, the reduction of the section of the main building reinforced-concrete structures, it is expedient to use fire-retardant coatings to provide the necessary fire resistance limit.

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.

Exposure of RC building structures to the marine environment of the Valencia coast

As the marine atmosphere is very harmful to reinforced concrete (RC) structures, buildings situated close to the sea are at a high risk of suffering damage. Such is the case for many of the buildings near the coast in Valencia (Spain). Most of these buildings were built between 1968 and 2007, and nowadays their RC structures are seriously damaged. This paper describes the condition of 1816 buildings that were inspected in 14 towns along the Valencia coast. From these inspections, there have been identified the main factors which are the most significant in the damage of these RC structures by the aggressive marine conditions. These factors include environmental characteristics, urban parameters, and the construction system of the buildings.