RC Buildings Research Articles

Orientation and location of shear walls in RC buildings to control deflection and drifts

Orientation and location of shear walls in RC buildings to control deflection and drifts

The Amazing Mechanism of the Standing for 700years of the Tall Masonry Stone Tower of 32m in height on Manmade Sandy High Mound by Shallow Direct Foundation, Bayon Temple, Angkor, Cambodia

Soils and foundation of Bayon temple of Angkor Thom has been studied since 1994 by Japanese Government Team for Safeguarding Angkor (JSA). The main tower of Bayon of 32m in height from the base foundation mound consists of manmade fill of 14 m in thickness. The foundation was studied and found as a simple shallow direct foundation. This is just like a 10 story RC building standing upon thick manmade sand fill without such a deep foundation as piling. At present, such a structure based upon thick sandy fill shall lose the foundation stability in the dry season under the monsoon climate of South-eastern Asia. The amazing mechanism, standing for 700 years, has been identified as the unsaturated characteristics of well compacted silty sand.

Seismic behaviour of RC buildings in sloping ground

Seismic behaviour of RC buildings in sloping ground

SISMO-Fast: energy-based method for rapid seismic vulnerability assessment of industrial precast RC buildings

Single-storey precast RC buildings not originally designed to withstand seismic actions showed their vulnerability during the Emilia Earthquake events (2012). The legislation that followed this catastrophic event has highlighted the need to assess and raise their seismic performance, even if interventions are limited to the connections between structural elements. The need to evaluate the conditions of existing buildings and to compare the effectiveness of risk mitigation interventions has highlighted the importance to have rapid assessment tools to check seismic vulnerability. The procedure proposed below begins by considering a simplified energy approach and allows the quantification of the seismic vulnerability of a precast RC building using few significant parameters.The proposal, for this specific type of building, works by comparing the characteristics of a new structure, assumed to be like the one to be assessed and designed for the seismic action of the specific site, to the existing structure to be assessed. The seismic vulnerability is subsequently defined in terms of the percentage of deviation of the real structure from the ideal one. The quantification of the percentage of deviation, based on macro-parameters, is estimated in terms of the capacity to absorb and resist the seismic input, described through energy. The SISMO-Fast method is based on the evidence of damage mechanisms observed during the site survey performed after the 2012 Emilia earthquake and other recent seismic events. The procedure has been used, for rapid seismic vulnerability assessment of some industrial precast RC buildings in different seismic areas, providing always reliable results.

Seismic vulnerability assessment of RC frame structures subjected to seismic excitation: A review

Because of their unpredictable nature and high damage-causing ability, earthquakes pose a significant threat to buildings. As a result, loss of lives and significant loss of economy became a primary concern in many parts of the world. Damage to structures is one of the many reasons to examine their seismic behavior when subjected to seismic forces. The seismic vulnerability of a structure can also be defined as its vulnerability to damage caused by ground shaking of a certain intensity. A building fragility analysis is performed to assess its vulnerability. The analysis of structural fragility provides a better understanding of the response of structural and non-structural systems during seismic events. It also helps to reduce damage and the risk of loss of life. Fragility curves indicate the likelihood of failure when a building is subjected to earthquakes of varying magnitudes. This paper provides an overview of the studies published in the field of seismic vulnerability assessment of RC buildings using fragility curves. The adopted methods within the past studies were nonlinear static pushover analysis, nonlinear time history analysis, incremental dynamic analysis etc. This review study discusses the effects of aging, soil structure interaction, set back irregularities, effects of infill, effect of strong column and weak beam, soft story, construction quality etc. on the vulnerability of RC frame structures.

A SIMPLE EVALUATION OF THE WALL AND COLUMN WALL RATIOS OF LOW-RISE RC BUILDINGS BASED ON ENERGY BALANCE FOR CONTINUED USE AFTER EARTHQUAKES

This paper examines the wall and column wall ratios of low-rise RC buildings to determine wall and column wall ratios that would limit the degree of building damage to a level no greater than slight damage for the purpose of continued use of the building after a mainshock, foreshock, or aftershock. Based on the energy balance in seismic response, a simple evaluation formula was derived to calculate wall ratio to a strength that would allow walls to withstand a level of damage up to shear cracking after an earthquake. The applicability of this formula was confirmed by comparing the wall ratio of actual buildings based on earthquake damage surveys with the results of this evaluation formula. The results indicated standards for wall and column wall ratios that enable buildings to withstand being hit by one to three earthquakes of an extremely rare level, as described in the notice, and still sustain a level of damage below shear cracking.

SHEAR STRENGTH OF HIGH STRENGTH STEEL FIBER REINFORCED CONCRETE COLUMNS

At present, the highest high-rise RC building in Japan is over 200 meters high. All columns from the first to the 13th floor of the building are applied high strength steel fiber reinforced concrete columns （HSFRC）to control damage under huge earthquake loading. The high strength steel fiber reinforced concrete columns are contain 1.0% steel fiber by volume. It is the first time to apply much steel fiber for high strength concrete columns. Nevertheless, there is no established design equation for high-strength SFRC columns. Therefore, authors have conducted an experimental study of HSFRC columns since 2020. A total of 15 specimens were conducted. In this research, 13 specimens’ experimental data are used. The shear strength equation based on truss arch theory with the volume ratio of steel fibers as a variable factor is proposed as a design equation for high-strength steel fiber reinforced concrete columns.

Seismic vulnerability assessment of RC buildings at compartment scale: the use of CARTIS form

Large-scale seismic vulnerability assessment methods allow to classify the vulnerability of groups of buildings according to recurring parameters. The parameters necessary for the application of these methods may come from the adoption of survey forms. The 1st level CARTIS survey form collects the parameters of an area (town compartment) characterized by homogeneity among building types. The variation of the parameters within the same compartment may lead to the definition of several typological-structural groups of buildings, which can be characterized by different vulnerability. Therefore, the assessment of the seismic vulnerability of a compartment requires knowing the distribution of different typologies and their relative structural performance. In this work the vulnerability is evaluated at town compartment level starting from the vulnerability of the RC building typologies, by applying the RE.SIS.TO® method to the data collected from the 1st level CARTIS forms. In particular, a tree chart representation, characterized by variable number of branches depending on the different number of possible choices allowed by CARTIS form, is proposed for data organization of the typological-structural groups of buildings.

Seismic retrofit of a RC building using metallic yielding dampers: a case study

Many seismic dissipation devices have been proposed in the literature. However, their application in current practice is rather limited even for the general lack of simple and effective design procedures in the standard building codes. This paper presents an interesting application of metallic yielding dampers to a reinforced concrete school building in Italy. At first, the detailed investigations performed are described in detail, including geometrical, material, and soil surveys. Then, the results of the seismic performance assessment are discussed, and the structural deficiencies are highlighted. Finally, a design procedure is applied that allows an efficient design and dimensioning of dampers, and its effectiveness is demonstrated using the nonlinear response history analysis. The general design approach applied in the seismic retrofit project is illustrated. The construction phases, costs, and execution timing are described and discussed.

Shear devices coupling exoskeleton and existing RC buildings for seismic improvement

Usually, the works for seismic improvement do not allow the use of the building. The interruption of use in many cases is not allowed especially for buildings with strategic or public service functions. In recent years, an alternative approach to intervention has spread that allows operating exclusively outside the structure through the use of a technology called a structural exoskeleton. The exoskeleton in many cases consists of a bi-dimensional or three-dimensional truss steel structure. The goal of this technology is to transfer most part the seismic action to the external structure. This allows for avoiding reinforcements to the existing structure. for the building-exoskeleton system to be effective against seismic action, the exoskeleton must be sufficiently stiff and the coupling device between the two structures must not produce internal constraints and generate unwanted stresses for the existing structural elements. A critical aspect of the application of this technology is the transfer of the floor seismic forces from the existing structure to the exoskeleton. The present work illustrates the study of an innovative building-exoskeleton coupling device to transfer the seismic shear forces of the floor from the existing structure to the exoskeleton without generating in-plane and out-of-plane bending interactions. The study of the coupling device was carried out as part of the seismic improvement project of a real case study. The seismic improvement project involves the construction of external shear walls consisting of steel trusses. The results of nonlinear numerical analyses on the global models of the building-exoskeleton systems as well as the results of local numerical analyses of the coupling device are illustrated.

Seismic performance of a reinforced concrete building retrofitted with self-centering shape memory alloy braces

In recent years, a new generation of seismic lateral force resisting systems has been proposed that sustains little or no damage under severe earthquakes thus reducing the repair time and cost. This has stimulated the development of many types of self-centering (SC) earthquake-resistant systems even based on innovative materials. Among them, shape memory alloy (SMA) dampers have been proposed that use superelastic nitinol wires to dissipate energy and self-center the structure. Many studies have been dedicated to SMA-brace devices applied to steel moment frames. Only a few studies have employed these devices for the seismic retrofit of existing reinforced concrete buildings. Moreover, their applicability has been experimentally and numerically tested only on small scale brace-components, while applications to real RC buildings are still lacking. Finally, there is a general lack of reliable design procedures. This paper presents a study that investigates the seismic performance of a reinforced concrete building retrofitted with self-centering (SC) shape memory alloy (SMA) braces. A design procedure is applied that satisfies displacement-based performance criteria and allocates the damped braces over the height according to an optimal damper distribution rule. Finally, nonlinear response-history analyses are carried out to evaluate the effectiveness of both the self-centering retrofit solution and the design procedure. The results show the excellent recentering behavior of the SC-SMA braces together with their not negligible energy dissipation capacity.

TH Analyses and Simplified Approach for Precast RC Frames Retrofit with Dissipative Fuse Devices Sismocell

Precast RC structures are a typology of construction widely spread in Italy among industrial buildings, made of single-storey isostatic RC frames built, in past decades, without any connection between beams and columns. The Emilia Earthquake (2012) caused extensive damages in this kind of buildings that have a significant mass located at roof level and lack of connections between horizontal and vertical elements. The recent seismic events highlighted that the lack of connections is the main vulnerability of existing precast RC buildings and at the same time that large displacements are determined between beams and columns. In order to improve the seismic performance of precast RC buildings a cost-effective solution is to dissipate energy at roof level, avoiding at the same time any loss of support between elements. Dissipative fuse devices (Sismocell) placed at beam-column joints are able to dissipate energy and guarantee an effective connection between elements. To evaluate the improvement achieved with the use of Sismocell devices, non-linear time history analyses are usually performed, taking into account the plastic hinges at column base. This work aims to quantify the improvement that can be obtained using Sismocell devices, in terms of reduction of effect of actions in different typologies of structures, remaining in the range of elastic behavior of materials. The TH analyses have been performed on different frame configurations with different seismic input, comparing the behavior of models with hinged connections and connections equipped with dissipative fuse devices. In order to define the optimal force of plastic activation of Sismocell devices, different device sizes have been considered. The results have been analyzed in terms of reductions of shear and moment at base of the columns, with different scaling factor applied to seismic input. Finally, a proposal of a simplified approach based on linear analyses has been compared to TH results.

Seismic Response of Monolithic and Precast RC Building for Site-Specific Conditions

This paper investigates the seismic response of a rigid and flexible RC building by performing nonlinear time history analysis (NLTHA). In the present study, the numerical model of a 5-storey monolithic RC (MRC) and 5-storey precast RC (PRC) buildings are developed in SAP2000. The buildings are assumed to be situated in Assam and a real Silchar site from Assam is considered. For the NLTHA, six spectrum compatible time histories (SCTH) are considered. The first set comprises of 3 SCTH matched to the Indian seismic code design spectra (ISCDS) and the second set comprises of 3 SCTH matched to the site-specific elastic response spectra (SSERS). The NLTHA results show that the roof displacement of the MRC building is less as compared to the PRC building for all the considered cases. However, the response for both the structures for SSERS compatible time histories is more significant as compared to the ISCDS compatible time histories. It is interesting to note that when the energy dissipation in the structure is evaluated for ISCDS compatible time histories, the damage in PRC building is negligible as compared to MRC building. Moreover, for SSERS compatible time histories, the damage in both the buildings are comparable. The results show the importance of site-specific study and its response on the structure behavior.

Effect of Openings in Shear wall on Seismic Behaviour of RC Buildings

Shear walls along the exterior perimeter of buildings increase the efficiency of buildings to resist seismic forces. In some conditions, the locations of shear walls are very critical because of the demand of architectural openings like doors and windows in the exterior face of the buildings. The literature has revealed that stiffness and seismic response of the structure is affected by the size of openings and location of openings in shear walls. This paper demonstrates effect of static and dynamic actions on 15 storey RC building having shear walls with openings. 32 building models have been prepared in commercial software STAAD for various inline and staggered openings in shear walls. Seismic coefficient method and Response spectrum method are used for seismic analysis. The analysis is carried out for the seismic zones III and IV for hard and medium soil conditions. The paper compares the response of these building models having shear wall with and without openings on parameters of time period, base shear, storey displacement, storey drifts and surface stress distribution. Uniform stress distribution was observed in shear wall with staggered opening as compared to inline openings.

Retrofitting Solutions for Existing Open Ground Storey RC Buildings

In the last few decades with the increase in population and decrease in usable land, there has been an enormous rise in the construction of residential buildings with open ground storey (OGS) to facilitate vehicle parking. Such OGS are created by removing the infill walls in the first storey. However, during the past earthquakes many of such OGS buildings have suffered severe damage and sometimes complete collapse of the structure. This is because OGS buildings, in general, exhibit soft story irregularity. Although the design codes have recommended provisions to enhance the seismic capacity of the OGS buildings, such provisions are barely implemented during construction. In order to avoid casualties and economic losses, it is necessary to retrofit the existing OGS structures. In this work, an attempt is made to strengthen the OGS buildings using masonry infill walls and braces as the retrofitting solutions. The models are developed in Seismostruct and analysed using suitable analytical methods. The behaviour of OGS buildings with masonry and braces at selected locations is evaluated. Retrofitting solutions that provide enhanced seismic performance and maximum parking space are proposed.

Effect of Shear Wall Shape on Seismic Response of RC Building Frames

This paper presents the effect of shape of shear wall on seismic response of a nine-storey moment resisting RC frames using non-linear static (pushover) analysis. The moment resisting RC frame is rectangular in plan and shear walls are provided along the least lateral dimension of the building plan. Different shapes of the shear wall (e.g., S, B, C, H and E) have been used in the analysis. The building frame along with shear walls has been modelled using FEM software SAP2000 and seismic responses of the building frames with different shapes of shear wall has been measured in terms of pushover curve (performance point, storey drift, top displacement and base shear). It has been observed that maximum performance level of building frame occurred when the shear walls are provided with S-shape.

Seismic Evaluation of RC Building with Vertical Setbacks as per IS1893 (Part 1):2016

Earthquake forces are the least predictable and most devastating form of forces. These forces are not only responsible for loss of economy, property and material but possess a huge threat to lives of people as well. In past several years, severe damages to buildings and causalities have been witnessed due to these disastrous forces there by challenging the designing and construction authorities. Many buildings are designed with vertical setbacks due to architectural, functional or economic reasons wherein fewer stories in a building are wider than rest of the building. Such setbacks in buildings cause sudden jump in seismic forces at the level of discontinuity due to change in stiffness, mass and strength distribution along height. This might lead to torsion in the building under seismic forces. Structures incorporating vertical irregularities need to be studied for their behavioural aspects, identifying the weak links which might trigger the collapse. In the present study, effect of vertical geometric irregularities in a building is studied with respect to a regular building using equivalent static method and response spectrum method as per IS1893 (Part 1): 2016. The results obtained are compared in terms of displacements, storey drift, base shear, forces, modal time period, modal mass participation factor and % increase in structural members along with concrete quantity.

Comparative Study on Seismic Performance of Existing Building with and without Retrofitting Using Lateral Load Resisting Systems

Due to the lack of awareness and practice of implementing earthquake resistant structures in the past, a huge number of buildings today do not comply with the existing/updated seismic codes in India. This issue is predominant in existing residential buildings which involves a high probability of loss of lives. The increase in population and clustered city areas make code non-compliance dangerous and risky especially in the Northern and North Eastern regions which come under seismic zones IV and V. Retrofitting strategies are thus an important aspect of building and life safety. This study involved the seismic performance of an adapted existing residential building taken in the North-East region. The seismic response analysis of the RC building was studied in terms of peak responses (deflection). The performance of the building was based on response spectrum and time history analysis. The main objective of this study is to provide a comparison between the most commonly used retrofit strategies – shear wall, bracings and viscous dampers. The responses of the building with the mentioned strategies and their varied configurations were modelled and analysed through ETABS software. This study outlined the feasibility of each retrofit strategy based on the optimum configuration for deflection control and basic cost estimate.

Evaluation of Regional Demand Parameters for Design of Mid-high-rise Building Using Past Earthquake Records

Category of earthquake and distance from epicenter are the prime parameters that decide the demand on buildings for its engineering. As observed in past Bhuj earthquake of 2001 (7Mw), seventy buildings got severely damaged in Ahmedabad city which is located 250kms from the epicenter. Intensity index through observed damages fills the gap for the demand anticipations. Design of a building considering excitation frequency rather than just the zone factor is necessary to include effects of low frequency waves (e.g. Mexico-city). This paper shows the broad ways in which seismic demand can be obtained for performing PBD in Indian context. A mid-rise RC building is designed as per three standard code of practices (i.e. IS, ACI, EN) to provide seismic resistance. The anticipated demand levels are obtained using GMPEs (PEER), magnitude-intensity relations, micro-zonation study and NDMA hazard contours for 15 storey building in Ahmedabad. The highest capacity curve is for design using IS 1893 code and this building will survive earthquake having 0.22g PGA value. The magnitude-intensity-epicentral distance relation (Gutenberg et al, 1956) shows that the intensity of VII for Zone-III is not correct for Ahmedabad city and it shall be taken as VIII which is for Zone-IV (0.24g) as per zoning map of India. However, as per the micro-zonation study showing PGA of 0.18g for the city it can be said that building will survive the next earthquake of 7.0Mw in Bhuj. The damage to non-structural elements is evident from the NLTHA using matched response spectrum obtained using Uttarkashi and Chamoli earthquake records (COSMOS). It is suggested to use intensity-based response spectrum for design of mid-high-rise buildings in Ahmedabad city. Moreover, a local directive based on social and technology resilience shall be developed to provide design basis based on loss (%)-multiple hazard (PGA) matrix using the matching relations found in this paper. Design provisions and loss reduction strategy can only lead to sustainable infrastructure in cities planning for vertical development.

Seismic Response Analysis of Vertically Irregular RC Building with MR Dampers

Seismic hazard mitigation has become one of the emerging problems in structural engineering therefore; many researchers have been studied on seismic performance of reinforced concrete structures having vertically regular and irregular. It is noted that vertically irregular structures are more prone to hazards due to earthquake. The recent emerging trend is to use active, passive, semi-active controls that aid in keeping the responses of structures in permissible. The most dynamically varied semi-active damper is a Magneto-Rheological (MR) damper which is used in this study to control the seismic responses. In the present study, four different models with and without MR dampers of which three models are vertically irregular in height are subjected to four realistic ground motions. The governing equation of motion for various building models is solved numerically by Newmark’s step-by-step integration method. The dynamic behaviour of semiactive MR damper has been predicted by modified Bouc-Wen model. This study employed the Lyapunov direct approach as a control algorithm for stability analysis and design of MR controller. The responses of various building models are simulated through MATLABâcomputing software. The study observed that considerable reduction in seismic responses of models with MR dampers is obtained as compared to respective building models without control. It is also observed that responses of building models are influenced by the vertical irregularities in mass and stiffness of building models.