Structural Reliability Assessment of Dual RC Buildings for Different Shear Wall Configuration

This study aims to develop the fragility curve of reinforced concrete buildings with different height based on dynamic analysis. There are 4 models of the moment-resisting concrete frame (MRCF) were used, which are 10, 15, 20, and 25-storey. Each of these frames was designed based on Eurocode 2. The SAP2000 program was used as the main analysis tool to obtain the limit state of MRCF. Then, an incremental dynamic analysis (IDA) was carried out with 7 ground motion records obtained from the Pacific Earthquake Engineering Research Center (PEER). The IDA curves were compared with the limit state of the MRCF, which is maximum allowable drift. The calculation of maximum allowable drift is based on the formula from the International Building Code (IBC, 2003). From the IDA results, 10-storey MRCF has better structural performance under the same ground motion as compared to other MRCF (10, 15, 20, and 25-storey). Fragility curves were developed by considering the results of IDA as parameters. Based on the results of the fragility curve, the MRCF that has the highest probability of exceeding the limit state is 25-storey MRCF. This is because 25-storey MRCF has the lowest PGA at 100% probability.KeywordsReinforced concreteIncremental dynamic analysisFragility curveGround motionsDrift limit

The seismic vulnerability of reinforced concrete (RC) buildings has prompted structural engineers to incorporate lateral load-resisting systems that enhance structural stability and performance. Among these, shear walls have proven to be highly effective in controlling lateral displacements and increasing energy dissipation. This study investigates the effect of shear walls on the seismic behavior of 3D RC buildings with different heights—10, 20, and 30 stories—through detailed finite element analysis using LUSAS FEA 14.03 software. A total of six models were analyzed: three without shear walls and three with shear walls symmetrically placed around the elevator core. Time-history analysis was conducted using the El Centro 1940 earthquake record over a 10-second interval. Peak displacement in the Y-direction was reduced from 0.1263 m to 0.0571 m in the 10-storey model (54.7% reduction), from 0.4666 m to 0.2669 m in the 20-storey model (42.7% reduction), and from 0.6466 m to 0.3033 m in the 30-storey model (53.1% reduction). Validation against ETABS software showed results within a 1.8–3% margin for displacement and modal frequencies. The Modal analysis further revealed that shear walls significantly influence dynamic characteristics by increasing stiffness and shifting critical mode participation to higher frequencies. For instance, in the 10-storey configuration, mass participation exceeding 90% occurred at Mode 5 without shear walls and at Mode 35 with shear walls. These findings confirm that shear walls substantially improve seismic performance and are essential for RC buildings in earthquake-prone regions

The superelastic shape memory alloy (SMA) rebar can significantly improve the seismic performance of reinforced concrete (RC) structures. This study was motivated from a blind prediction contest of a full-scale 7-storey RC shear wall building at the University of California, San Diego. A finite element (FE) analysis was conducted to investigate the seismic performance of RC shear wall with the application of SMA rebar. The SMA rebar was applied at the plastic hinge location of the shear wall only and the steel rebar was used for all other sections. The seismic performance of shear wall was evaluated by performing incremental dynamic analysis (IDA) using 13 ground motions. The seismic demand was recorded in terms of inter-storey drift ratio until the full collapse of the building. The safety of the wall was measured in terms of collapse margin ratio (CMR) explicitly considering the uncertainty. The results show that the SMA rebar significantly improved the performance of the shear wall building and yielded higher CMR as compared to the conventional RC building.

This paper focuses on seismic responses of a 30-story high-rise building with a dual lateral system of Reinforced Concrete (RC) core shear wall and steel moment frame. To assess the seismic performance of the building, a nonlinear finite element model is built by using the OpenSees software. This three-dimensional model is created by using the fiber-beams for members and multi-layer shell elements for RC core walls. The numerical simulation has been examined under the thirteen sets of strong ground motion records which are scaled with the design and maximum seismic levels, Design-Basis Earthquake (DBE) and Maximum Considered Earthquake (MCE) level hazards respectively. In consequence, the desirable performance of high-rise steel moment frame building with RC shear core consisting of coupling beams and rectangular shear walls is shown. The outcome of nonlinear time history analyses reports the acceptable seismic performance of tall buildings designed. Results showed that maximum inter-story drift is significantly lower than allowable drift. Also, the RC core wall absorbed almost two-third of the total shear forces from the base level to one-third of height. However, the shear values of the core wall were significantly reduced by increasing the height while the shear values of the steel moment frame stayed constant.

A high percentage of reinforced concrete (RC) buildings in Portugal were designed and built before the introduction of modern seismic codes. This research aims to assess the seismic capacity and vulnerability of RC buildings in the city of Lisbon. For that purpose, nonlinear static procedures have been used and fragility curves have been developed. These buildings are reaching the end of their nominal life. Therefore, ageing effects have been taken into account, as well as the presence of smooth rebar. To do so, a sensitivity analysis has been performed by considering the chloride-induced corrosion of the reinforcement steel rebar and the degradation of the concrete cover. To illustrate the effects of ageing and the procedure adopted for the seismic fragility assessment of old RC structures, three RC buildings with masonry infills have been selected as case studies. They were all built between 1960 and 1980, and they are representative of the current building stock in Lisbon. The seismic capacity of the buildings has been determined by means of nonlinear static analyses of three-dimensional numerical models. The N2 method and its extended version have been considered to determine the target displacement. The seismic safety of the buildings has been estimated in terms of the demand/capacity ratio for each vertical structural element (columns and walls) according to the bending and the shear failures. Then, a set of fragility curves has been developed for all buildings to represent the probability of RC elements reaching or exceeding the significant damage limit state. Results have shown that the concrete strength degradation has had more influence than reduction of the rebar diameter in the seismic capacity. When considering steel corrosion, it has been demonstrated that the corrosion rate has reduced the capacity more than the time of exposure. It can be concluded that ageing affects the seismic behaviour of RC structures, increasing the vulnerability of these buildings.

2 - Seismic vulnerability assessment of RC structures: research and practice at building level

Irregular multistorey buildings are prone to seismic forces due to torsional effects resulting from the eccentricity between the mass and stiffness centres. Shear walls are essential in multistorey buildings for improving structural behaviour when subjected to earthquake loads. The seismic response of buildings is highly sensitive to the placement and configuration of shear walls within the building infrastructure. This research focuses on optimising the location of shear walls in a T-shaped irregular reinforced concrete structure for better seismic resilience. The structural analysis is carried out, and the building is evaluated via the response spectrum as per the provisions of IS 1893:2016. This study examines various shear wall configurations to achieve optimised modal mass participation, thereby reducing dynamic irregularities and enhancing overall seismic performance. The impact of these optimised locations is assessed across various seismic zones in India, with a focus on critical response parameters, including lateral displacement, interstorey drift, storey shear, and base shear. The results reveal that strategically optimised shear wall placement significantly enhances seismic performance by reducing lateral drift and torsional effects. In this study, the shear wall configurations that resulted in higher modal participation factors and lower eccentricities between the centre of mass and the centre of stiffness demonstrated a superior seismic performance across all considered seismic zones.

En el presente trabajo se revisan las combinaciones de carga para el diseño de edificaciones que se establecen en el Reglamento de Construcciones del Distrito Federal (RCDF-2004) y sus Normas Técnicas Complementarias (NTC-2004). Se proponen nuevos factores de carga para que se especifiquen en la próxima versión del (RCDF). Se revisa la combinación de carga gravitacional (carga muerta más carga viva) y la combinación de carga por sismo (carga muerta, carga viva y carga por sismo). Se propone una metodología para establecer factores y combinaciones óptimos de carga que garanticen el mínimo costo total esperado durante la vida útil de la estructura y que la probabilidad de falla sea al menos igual a la implícita en el RCDF-2004. Para la estimación de la confiabilidad estructural se hace uso de las Redes Neuronales Artificiales.

Retrofitting is a technique wherein the damaged structure is strengthened to original design requirements. During 2001 Bhuj earthquake in Gujarat, India many open ground storey building damaged. So there is an urgent need for retrofitting of damaged buildings. This calls for techniques that are technically sound and economically feasible to upgrade deficient and damaged buildings. Also, Portland cement (PC) production is under critical review due to high carbon dioxide gas released to the atmosphere and Portland cement is also one among the most energy-intensive construction materials. So retrofitting of existing deficient building using eco-friendly material which could promise higher structural performance than the original building is required. The main contributions is development of retrofitting technique of seismically damaged building using Geopolymer concrete and Chevron steel bracing with passive energy dissipation devices. Experimental studies are carried out using the 4 m × 4 m tri-axial shake table test facility to evaluate the seismic performance of bare frame, Open ground storey building, X-plate retrofitted building, Shear wall retrofitted building. Two three storied half scale model buildings, one open ground storey (OGS) building and a bare frame building are tested for different earthquake inputs in the shake table. The acceleration spectrum of IS1893:2002, soft soil is used as seismic input for the above tests. The failure modes and crack pattern of buildings after the seismic test are analysed. The damaged OGS building after the shake table test is retrofitted. The local retrofitting of columns and beam-column joints in the ground storey is carried out using Geopolymer concrete. The global retrofitting of building is formulated with Chevron type steel bracing incorporating X-plate damper in the ground storey. Sweep sine tests on OGS building before and after retrofitting with X-shaped metallic damper is carried out. The natural frequencies and mode shapes of the models are evaluated. The retrofitted OGS building is again subjected to shake table test to the study the seismic performance under varying amplitude as per IS 1893:2002 ground motion. The same model buildings are analysed in SAP 2000 to predict the seismic performance of the retrofitted RC frames.An innovative technique of retrofitting the seismic damaged building using Geopolymer concrete and construction of shear wall is explored. Two Reinforced Concrete shear walls are constructed inside the open ground storey building as global retrofitting technique. Sweep sine test is carried out after retrofitting with shear wall. The fundamental frequency of open ground storey building increased from 3.75 Hz to 7.25 Hz due to the addition of shear wall. The pushover test on building is carried out. The pushover analysis is carried out to study the seismic response of reinforced concrete building with local and global retrofitting using SAP 2000 software. Comparison of experimental and analytical push over curves is plotted. A significant improvement in the strength and stiffness of the open ground storey building after retrofitting with shear wall is observed.

This paper examines the seismic behavior of CLT-steel hybrid walls at 6- and 10-story heights to increase seismic force resistance compared to conventional wooden walls. The ultra-strong shear walls proposed in this paper are called Framing Panel Shear Walls (FPSW), which are based on a robust articulated steel frame braced with CLT board panels and steel tendons. Timber structures are well-known for their ecological benefits, as well as their excellent seismic performance, mainly due to the high strength-to-weight ratio compared to steel and concrete ones, flexibility, and redundancy. However, in order to meet the requirements regarding the maximum inter-story drifts prescribed in seismic design codes, a challenging engineering problem emerges, because sufficiently resistant, rigid and ductile connections and lateral assemblies are not available for timber to meet both the technical and economical restrictions. Therefore, it is necessary to develop strong and cost-effective timber-based lateral systems, in order to become a real alternative to mid- and high-rises, especially in seismic countries. In this investigation, the dynamic response of cross-laminated timber (CLT) combined with hollow steel profiles has been investigated in shear wall configuration. After experimental work, research was also carried out into numerical modelling for simulating the cyclic behavior of a hybrid FPSW wall and the spectral modal analysis of buildings of 6- and a 10-stories with FPSW. A FPSW shear wall can double the capacity and stiffness.

A large number of existing reinforced concrete (RC) buildings have surpassed their anticipated service life and show signs of degradation due to aging; this degradation is a function of the construction practices adopted in the past as well as environmental conditions. This paper discusses seismic fragility and the risk assessment of RC structures, emphasizing the impact of corrosion due to concrete aging and the associated deterioration mechanisms. The literature on this topic is critically reviewed, and a methodology for studying the seismic fragility of deteriorated RC buildings is proposed. As a case study, a four-story RC building designed according to contemporary code provisions is examined. The investigation encompasses the derivation of fragility curves, considering critical parameters such as the corrosion rate, the initiation time, and the cover depth. The proposed approach enables the evaluation and quantification of the impact of corrosion mechanisms on the seismic performance of buildings.

The current study presents lateral load analysis of mid-rise reinforced concrete framed structures with two different lateral load resisting systems; shear walls and rigid marginal beams. The main objective here is to investigate the influence of the location of the system in the structure; i.e. arrangement of shear walls and level of the marginal beam. For that purpose, seismic fragility curves are used as an assessment tool for comparing the seismic performance of the studied structures in different situations. Incremental dynamic analysis was performed under ten ground motions to determine the yielding and collapse capacity of each building. Five performance levels were considered in the analysis. These performance levels are (i) operational, (ii) immediate occupancy, (iii) damage control, (iv) life safety and (v) collapse prevention. Fragility curves were developed for the structural models of the studied structures considering the previously mentioned performance levels. It was observed that arrangement of shear walls on the long direction of the structure has insignificant effects on its performance while interior shear walls provide the best behavior of the structure compared to exterior shear walls only and distributing shear walls internally and externally. The analysis outcomes also indicated that the presence of the rigid marginal beam in the lower storey gives more efficiency regarding to lateral loads resistance in the studied structure.

Influence of earthquake record truncation on fragility curves of RC frames with different damage indices

This study uses ETABS software’s sophisticated numerical modeling to investigate the seismic performance of multi-story reinforced concrete structures located in seismic zone 5. Three structural configurations, G+4, G+14, and G+24, with ground floor height 3.5 m & remaining floor height 3 m, were examined. Each was planned with four 5m spans in X & Y directions i.e. 20m x 20m square layout. Nonlinear direct integration time history analysis used in this study to assess dynamic structural reactions to seismic excitation. The study examined three different shear wall configurations: (1) Bare frame i.e. building without shear walls, (2) Building with shear walls at corner spans, and (3) Building with shear walls at the middle edges. Near field ground motion records from the Imperial Valley (IV) and Northridge (NR) earthquakes were used to generate seismic input, which included both parallel and normal elements. Important response parameters were measured to evaluate the impact of shear wall placement on seismic resilience, such as inter-story drift, and floor-wise displacement. In order to optimize structural design in high- seismic zones, the results provide important insights into the relative effectiveness of shear wall layouts in reducing seismic demands across structures of different heights.

Impact of climate change on the life cycle greenhouse gas emissions of cross-laminated timber and reinforced concrete buildings in China