Low-rise Reinforced Concrete Buildings Research Articles

The influence of torsion on acceleration demands in low-rise RC buildings

AbstractThis paper presents a study of acceleration demands in low-rise reinforced concrete (RC) buildings with torsion, evaluated by quantifying peak floor accelerations (PFAs) and floor response (acceleration) spectra (FRS). The study was performed with the aim to provide simple empirical formulas to quantify the amplification effects due to torsion, which can occur in most of the existing and new RC buildings. With this goal in mind, a set of eight archetype buildings was selected, characterized by an increasing floor eccentricity obtained by moving the centre of rigidity (CR) away from the centre of mass (CM). Numerical models of the proposed set of archetype RC buildings were considered in both linear elastic and nonlinear configurations. For the latter, the properties of models were widely varied, by systematically modifying parameters of plastic hinges, in order to obtain a sample of 1000 models. Non-structural components (NSCs) were considered linear elastic in all cases. To investigate acceleration demands, a set of forty Eurocode 8 spectrum-compatible ground motion records were used as input. For linear elastic building models, it was observed that the change of demands depends on the position of the NSC (in-plan and in-height), and on the distance between CR and CM. On the other hand, for nonlinear models, additional parameters must be considered, such as the building ductility (μ) and yielding force (Vy). New regression models were proposed for quantifying the observed differences in PFAs and FRS when torsion occurs. The efficiency of the proposed models was assessed by testing the new formulas on an existing case study building, as well as on the well-known SPEAR building.

Seismic performance evaluation and strengthening of RC beam-column joints adopted in Nepal

Beam-column joints are a crucial component of the reinforced concrete (RC) moment-resisting frame (MRF) as the behavior of the joints significantly influences the strength and ductility of the overall framing system. This study is performed to explore the seismic behavior of interior and exterior beam-column joints designed based on NBC 205:1994 (NBC1), NBC 205:2012 (NBC2), and the revised seismic design standard NBC 105:2020, defined as a well-designed joint (NBC3) which are the building standards used for designing low-rise RC buildings in Nepal and compares the results from the numerical simulations quantitatively. Three possible retrofit options (CFRP, steel and RC jacketing) were explored. Finally, retrofitting options were suggested for the joint of NBC1 and NBC2 with consideration of a well-designed joint (NBC3) as the currently required capacity of the joint based on the demand of revised seismic design standard NBC 105:2020.

A Machine-Learning-Based Seismic Vulnerability Assessment Approach for Low-Rise RC Buildings

ABSTRACT Seismic vulnerability evaluation of existing buildings is essential to minimize the destructive impacts of earthquakes. Rapid visual screening (RVS) methods are simple and effective vulnerability assessment techniques to help quickly identify high-risk buildings for more detailed evaluations. Among various RVS methods, the Hassan–Sozen priority index (PI) is one of the simplest methods that can be used for low-rise reinforced concrete (RC) buildings. The PI relates simple, easily attainable geometric features of a building including number of stories, floor area, column area, and wall area to damageability. However, the relationship is overly simplified, and there is no absolute basis for defining damage classification boundaries that can be used to interpret the PI. Furthermore, given the lack of seismic parameters as inputs, the PI only allows for a relative evaluation of buildings in a specific region. To address these issues and develop a more broadly applicable RVS method, this study first proposes an improved PI evaluation method using machine learning techniques to define damage classification boundaries. Then, a new generalized RVS method is proposed that considers the PI input features and earthquake intensity measures to predict damage states. Data from six post-earthquake damage surveys (Duzce (1999), Bingol (2003), Nepal (2015), Taiwan (2016), Ecuador (2016), and Pohang (2017)) are used to train and evaluate the classification models. Two earthquake intensity features, modified Mercalli intensity and peak ground acceleration, are introduced to develop a new earthquake intensity aware RVS. The results of the proposed methodologies show a considerable improvement from the original PI with no judgment needed to define the damage classification boundaries.

Retrofit of RC buildings using vertical shear links and hybrid connections

This study employs a retrofit system with a vertical shear link inside a steel frame to improve the structural behavior of an existing reinforced concrete (RC) frame. The steel frame is connected to the RC frame through a hybrid connection system. The hybrid connection not only provides a rigid, strong connection between the steel and RC frames but also increases the shear strength of RC columns and beams. It is referred to as a hybrid connection in light of such combined measures. The connection is composed of thin steel plates, bolts, and infilling grout. This study tested four one-bay one-story RC frames. One of the RC frames was the benchmark, while the three remaining RC frames were retrofitted under different schemes. The scale factor of the frames was set to 1/3 ∼ 1/4 to model a low-rise RC building. The experimental results of the retrofitted RC frames by vertical shear links demonstrated that the boundary steel frame played a key role in obtaining a stable hysteretic response. Moreover, the hybrid connection strongly withstood the shear force between the RC frame and the steel frame. A series of calculation approaches were proposed to find the lateral strength of retrofitted frames under different failure mechanisms. The calculated lateral strengths were observed to agree with the experimental results.

Progressive Collapse Evaluation of Low-Rise Reinforced Concrete Buildings Designed for Different Occupancy Classes

The study aims to investigate the progressive collapse behavior of low-rise reinforced concrete buildings designed for different occupancy classes. For this objective, two low-rise reinforced concrete framed buildings were designed independently according to the Turkish Seismic Code for Buildings by considering the Residential Occupancy Class and Government Buildings Occupancy Class. A nonlinear dynamic analysis method was employed to evaluate the progressive collapse response of the buildings by using the alternate path direct design approach of UFC 4-023-03 and GSA-2016 guidelines. Three-dimensional finite element models were created for the analyses, and fiber hinges were used to represent the nonlinear behavior of the load-bearing members. Three column loss scenarios were implemented independently. The analysis results show that the residual displacement of the residential building is higher than that of the government building in all column removal scenarios. Moreover, the damage conditions of the residential building are commonly worse than the government building for all column loss scenarios. It is deduced from the study that the buildings experienced the most severe local damage, disproportionate to the initial failure, under the inner column loss scenario

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.

Systematic strengthening scenarios for determination of most suitable retrofitting approach in a low-rise RC building

The aim of this study was to determine most suitable strengthening approach in a reinforced concrete (RC) building using numerical analyses. The entire process is illustrated using a case study for a five-story RC framed building. To determine the seismic performance level, numerical simulations were performed through pushover analysis. Then, a retrofitting approach is presented for the building that does not meet current regulations. Five different strengthening proposals were presented for the building to meet the current requirements. After the examination of the proposals, only one strengthening proposal was deemed the most suitable solution. This proposal includes addition of new shear walls to the building. In this proposal, lateral drifts are reduced and the torsional moment deformation effect is minimized. Also, inter-story drifts decreased and the shear force and moment capacities increased. This paper can be utilized by researchers and practitioners in retrofitting approaches for low-rise RC buildings which represent a significant proportion of the building stock.

Applicability of DDBD approach on low-rise RC buildings situated in Indian seismic regions

Design of reinforced concrete (RC) buildings with a direct-displacement-based design (DDBD) method has been used extensively for the last few decades around the world. As compared to force-based design (FBD) method, DDBD provides advantages in cost-reduction, construction timing, and better structural performance. This paper investigates the DDBD methodology for G + 3 storied RC buildings, having different structural configurations by varying bays in the longitudinal and transverse directions, but having the same total plan area. The selected case-study RC buildings are analysed via non-linear time history analysis considering seismicity of zone-V of Indian regions. A suite of different spectrum compatible ground motions is used. The seismic behaviour has been analysed in terms of base-shear ratio, ductility demand, displacement profiles and drift ratios. The results illustrate that the DDBD procedure proves to be useful in designing RC buildings situated in seismic regions of India and are competent enough to withstand lateral forces due to seismic excitations.

Impact of Revised Code NBC105 on Assessment and Design of Low Rise Reinforced Concrete Buildings in Nepal

Gorkha Earthquake in 2015 has impacted considerably in the design and construction of buildings in Nepal. Strength and Safety of life and constructions have become the prime concerns of the government and the public. Regulation is required to achieve the strength and safety in the constructions. Hence, a need for revision of building codes has been felt and Nepal Building Code, NBC105 has been revised. This paper presents the impact of the revised code on seismic load estimation for low rise reinforced concrete buildings. For the assessment of the impact linear and non- linear static and linear dynamic analysis of reinforced concrete residential buildings of two storey and four Storey has been taken subjected to Indian Standard Codes IS 1893: 2002, IS 1893:2016, Nepal Building Codes NBC 105: 1994 and NBC 105: 2020. The buildings were modeled and analyzed in SAP2000. The response of the buildings such as time period, base shear, drifts, and storey forces from the application of the four codes was compared. The comparison of the results shows that the structural response of the building under the revised NBC105:2020 is 60% to 65% higher compared to the previous code NBC105:1994.

A friction-based connection for retrofitting RC frames by steel braced frames

This paper presents a new connection for the installation of steel braced frames inside existing reinforced concrete (RC) frames. The proposed connection is called a “clamp-shaped connection” according to its action which is based on friction mechanism. In this connection, by inserting clamping forces on lateral faces of an existing RC beam, the required direct shear resistance between the existing RC frame and retrofitting steel braced frame is provided. The clamp-shaped connection mainly consists of high-strength grout, steel plates, high-strength bars, and clamp-shaped steel arms, that are majorly made and assembled in a manufactory. The benefit of the proposed technique is that it does not require any anchorage devices and minimizes disturbing retrofitting operations at a building site. In this study, four one-bay one-story RC frames are tested to verify the efficiency of the proposed clamp-shaped connection. The scale factor of the test specimens is 1/3 ~ 1/4, to model a low-rise RC building. One specimen is non-retrofitted, and three specimens are retrofitted by steel braced frames. The proposed clamp-shaped connection increases the direct shear resistance at the top of the installed steel braced frames. Simplified equations are proposed to estimate the direct shear resistance of the proposed connection. The experimental results confirm the accuracy of the suggested simplified calculations.

Evaluation of Seismic Vulnerability Indices for Low-Rise Reinforced Concrete Buildings Including Data from the 6 February 2016 Taiwan Earthquake

Communities need seismic vulnerability indices to identify which buildings are most susceptible to severe damage during earthquakes. To be of greatest value, these indices should be easy to use and should be vetted against data from previous earthquakes. To date, more than 800 reinforced concrete buildings have been surveyed after earthquakes for the purpose of evaluating a seismic vulnerability index proposed by Hassan and Sozen in 1997. This number includes 130 buildings surveyed after the 6 February 2016 earthquake in Taiwan. The data collected during these surveys consist of descriptions and photographs of damage, structural sketches, and measurements. Analyses of the data indicate that probability of severe damage and failure increases with decreasing column index and wall index (normalized measures of column and wall areas). They also suggest that the exact form of the threshold used to distinguish more vulnerable structures from less vulnerable structures is of little consequence in terms of the probable cost and benefits of the strengthening program this threshold may inform.

국내 기존 철근콘크리트 건물의 내진성능평가법 및 지진위험도 추정

본 연구의 목적은 국내 저층 RC 건물의 내진성능 평가법을 구축하는 것으로서, 국내 저층 RC 건물을 대상으로 내진진단법에 의해서 평가된 내진성능 평가결과를 기반으로 구조성능기본지표를 수정하여 국내 저층 RC 건물에 유효한 내진성능 평가법을 제안하였다. 내진진단법의 구조성능기본지표는 건물의 극한강도(C 지표) 및 연성능력(F 지표)에 의해서 평가한다. 국내에서 수행된 RC 기둥과 벽체의 실험결과를 바탕으로 국내 건물에 적합한 내진진단법의 휨극한강도 및 전단극한강도 평가식, 즉 C지표를 제한함과 동시에 전단여유도(전단내력과 휨내력의 비율)를 주로 이용하여 평가하는 F 지표도 제안하였다. 최종적으로 본 연구에서 제안한 국내 저층 RC 건물에 유효한 내진성능평가법을 이용하여 비내진상세를 가지는 14개 동 국내 저층 RC 건물을 대상으로 내진성능을 평가하였으며, 신뢰성 기반으로 국내 저층 RC 건물의 지진 피해율을 추정하였다. 그 결과 지진동 수준 0.1 g, 0.15 g, 0.2 g 및 0.23 g에 대해서 지진 피해율은 7 %, 27 %, 55 % 및 70 %로 추정되었다. 본 연구에서 수정 제안한 내진성 능평가법은 국내 비내진 상세를 가지는 저층 RC 건물의 내진 대책 수립을 위한 기본적인 기술로 효과적으로 활용가능 하다고 사료된다.

Seismic performance of an existing low-rise RC building considering the addition of a new storey

DOI: 10.7764/RDLC.18.3.459 In low-rise reinforced concrete (RC) buildings, structural design is generally performed considering the seismic effects as well as the vertical loads. However, there may be situations where the additional or unpredicted loads may be encountered during the service life of the buildings. The loads that are governed from a new storey addition during the service life is a good example for these additional loads. Since the reconstruction permits and building height limits specified by the authorities may vary in life-cycle of the structures, it is critical to decide the addition of a storey to an existing building considering the structural safety concerns. In this study, an existing low-rise RC building is modelled with an added storey (subsequently planned for construction), and numerical analyses are carried out considering the extra loads of this additional storey. The aim is to evaluate the seismic performance of the structure considering this unpredicted situation which was not taken into account in the original structural design. The suitability of the preliminary structural design project to the existing building was checked by the site investigations. The results of the numerical analysis were compared with the seismic code requirements, and the seismic performance level of the building is determined. The study is intended to be useful in determining the path to be followed for the determination of the seismic capacity if existing buildings are subjected to additional loads.

The Behaviours of the Brick-Masonry Infilled RC Frame Structure under Reversed Cyclic Lateral Loading

The experimental study for investigating the seismic responses of the Reinforced Concrete (RC) frame specimens is presented in this paper. Regarding this experimental, two one-bay and scaled-down specimens have been prepared and tested, i.e., RC bare frame and RC frame with brick masonry infill. The masonry infilled RC frame specimen was the RC frame which was infilled by the extracted brick masonry wall from the survive RC building in Padang city due to September 2007 Sumatra earthquake. These both of specimens, obviously, represent the typical low-rise RC building in West Sumatra, Indonesia. These specimens were tested to the constant vertical load, and lateral static reversed cyclic loading in the structural testing facilities. The lateral loading was applied incrementally and controlled by the drift angle of the specimens. The drift angle is the ratio between the lateral displacement of the top of the column and the column height of the specimen. The applied incremental lateral load and displacements at several points on the specimens were measured and recorded during the testing. The observation of the major cracks and its propagation were also conducted to identify the failure mechanism of the RC frame specimens. Comparison of the testing results for both of the specimens suggests that the masonry brick infill contributed to significantly increase the dissipating energy capacity, lateral strength, and stiffness of overall RC frames. On the other hand, unfortunately, the ductility performance of the brick masonry infilled RC frame specimen was decreasing. The presence of brick masonry infill in the RC frame seems to control the failure mechanism of the RC frame, reduces the deformation capacity of the boundary column, and alters the lateral and axial deformations of boundary columns.

Seismic Vulnerability Assessment of Low-Rise Reinforced Concrete Buildings Affected by the 2015 Gorkha, Nepal, Earthquake

Low-rise reinforced concrete (RC) frames with brick masonry infill walls up to five stories high have been used for housing construction in Nepal since the late 1980s. Many buildings of this type were damaged and/or collapsed in the 25 April 2015 Gorkha earthquake (M 7.8), even in areas characterized with moderate shaking intensity such as Kathmandu Valley. Due to inadequate design and/or construction of RC frame components, these buildings essentially behave like masonry shear wall structures with a shear-dominant failure mechanism. The paper presents the findings of a field survey of 98 RC buildings affected by the 2015 earthquake. The main objective of the study was to correlate the observed damage in the buildings using the modified European macroseismic scale (EMS)-98 and the wall index (defined as the wall area in the direction of shaking divided by the total building plan area above the level of interest). The results can be used to help establish recommendations regarding the required wall index for low-rise RC buildings in Nepal.

Seismic Demand for Low-Rise Reinforced Concrete Buildings of Islamabad–Rawalpindi Region (Pakistan)

Determination of appropriate seismic demand is important for deriving reliable seismic forces for use in structural design and vulnerability assessment. Demand can be defined by either probabilistic or deterministic approaches depending on the use of the assessment. The use of probabilistic or deterministic approaches depends on the level of the assessment since deterministic can mostly be used for single structures whereas probabilistic for city or country level assessment. This paper presents demand characterization which is based on results of existing seismic hazard studies and local tectonic features around Islamabad–Rawalpindi region (study region) in Pakistan. Existing seismic zoning maps and recent probabilistic seismic hazard studies are reviewed, and the findings are used to quantify and compare the demand for a typical low-rise reinforced concrete building. As another option, deterministic demand is defined through spectra using suitable attenuation relationship which is assessed and validated using the Kashmir earthquake and other similar earthquakes data. Deterministic spectra for study region are generated by considering the critical local tectonic features. Federal Emergency Management Agency (FEMA 356) approach is used for smoothening of deterministic spectra, and the new spectral corner periods are calculated.

Retrofitting of Low Rise Reinforced Concrete Building Using External Bolted Steel Plates Case Study: SPS Building, Jimbaran, Bali-indonesia

This paper presents the assessment results and structural retrofitting of SPS Building. The building is a three story reinforced concrete structure with a mezzanine floor for a storage. The building was an office building with a live load of 2.5kN/m2 and then the building function changes to be an industrial building with a live load of 10kN/m2. The existing concrete and rebars tensile strength, structural member dimensions and configuration were assessed before structural analysis and redesign were done using a commercial software. It is found that the average concrete strength is about 11MPa and most of existing structural members are less flexure and shear capacity. Therefore, an external flexure and shear strengthening using external bolted steel plates were applied to those members with grouting materials to fill the gaps between the steel plate and existing structural members. A strength evaluation using direct loading with a maximum water depth of 1000mm over an area of 60 m2 to represent the live load of 10kN/m2 was conducted to ensure the retrofitting method works well. The test results show that measured deflections of beams and slabs are still less than the maximum deflection limits. This indicates that the strengthening system using external bolted steel plates can improve the member capacity to support the new design loads.

An experimental study on the seismic performance of medium- to low-rise RC structures controlled by both shear and flexure

The lateral-force-resisting systems (LFRSs) of many medium- to low-rise reinforced concrete (RC) buildings are composed of members that may be vulnerable to pre-emptive shear failures, depending on whether their shear strengths are sufficient to develop their flexural strengths (hereafter referred to as dual LFRSs). Therefore, such buildings have a lateral strength associated with the strengths of components, and the component strengths may be governed by both shear and flexure. At present, there is no effective way of assessing the relationship of component strengths between the shear and flexure of a RC building having a dual LFRS. Several studies have investigated the seismic performance of RC buildings controlled by both shear and flexure, but the scope of these studies was very limited and they focused mainly on analytical research. In this study, a series of pseudo-static reversed cyclic loading tests was conducted in the laboratory to investigate seismic performance in terms of the structural non-linear behaviour and lateral-force-resisting mechanism at the ultimate state of a dual LFRS. The results of this research provide fundamental information for the proposal of hysteresis characteristics and a practical guideline for evaluating the seismic performance of medium- to low-rise RC buildings comprising members failing in both shear and flexure.

Seismic Damage Evaluation of Gravity Load Designed Low Rise RC Building Using Non-linear Static Method

In India, the 2001 Bhuj earthquake has given a serious warning to many existing reinforced concrete (RC) buildings. However, a considerable portion of the building stock of India is reinforced concrete buildings which are generally designed mainly for gravity loads only. Therefore, potential seismic evaluation of these buildings, especially in high seismic region, is very essential in order to implement any kind of seismic hazard mitigation strategy. Hence, the present study aims to evaluate the seismic vulnerability of low rise RC frame building which is designed for gravity load according to the Indian code. The non-linear static analysis is performed using SAP2000 (v16) to find the capacity curve of the building. Fragility analysis is used to develop the fragility curve for different damage grade based on HAZUS methodology. Damage probability matrices (DPM) are formed for two different seismic hazard levels i.e. for maximum considered earthquake and design basis earthquake depending on the performance point to compare the damage state for each hazard level. The result shows that the damage of considered building is vary from moderate to severe damage state to the corresponding different seismic hazard level.