Seismic evaluation of R/C framed building using shear failure model

Prediction of nonlinear shear hinge parameters in RC members is difficult because it involves a number of parameters like shear capacity, shear displacement, shear stiffness. As shear failure are brittle in nature, designer must ensure that shear failure can never occur. Designer has to design the sections such that flexural failure (ductile mode of failure) precedes the shear failure. Also design code does not permit shear failure. However, past earthquakes reveal that majority of the reinforced concrete (RC) structures failed due to shear. Indian construction practice does not guaranty safety against shear. Therefore accurate modelling of shear failure is almost certain for seismic evaluation of RC framed building. A thorough literature review does not reveal any information about the nonlinear modelling of RC sections in Shear. The current industry practice is to do nonlinear analysis for flexure only. Therefore, the primary objective of the present work is to develop nonlinear force-deformation model for reinforced concrete section for shear and demonstrate the importance of modelling shear hinge in seismic evaluation of RC framed building. From the existing literature it is found that equations given in Indian Standard IS-456: 2000 and American Standard ACI-318: 2008 represent good estimate of ultimate strength. However, FEMA-356 recommends ignoring concrete contribution in shear strength calculation for ductile beam under earthquake loading. No clarity is found regarding yield strength from the literature. Priestley et al. (1996) is reported to be most effective for calculating shear displacement at yield whereas model proposed by Park and Paulay (1975) is most effective in predicting the ultimate shear displacements for beams and columns. Combining these models shear hinge properties can be calculated. To demonstrate the importance of modelling shear hinges, an existing RC framed building is selected. Two building models, one with shear hinge and other without shear hinges, are analysed using nonlinear static (pushover) analysis. This study found that modelling shear hinges is necessary to correctly evaluate strength and ductility of the building. When analysis ignores shear failure model it overestimates the base shear and roof displacement capacity of the building. The results obtained here show that the presence of shear hinge can correctly reveal the non-ductile failure mode of the building

Variability of mechanical properties of cellular lightweight concrete infill and its effect on seismic safety

Cellular lightweight concrete (CLC) block masonry has gained popularity in the masonry market with the growing demand in the modern construction industry due to its various advantages, including a positive impact on the environment. Subsequently, the detailed characterization of its vital engineering properties should be studied for the development of the mathematical model, analysis, evaluation, and design of structures made of CLC block masonry. The present study investigates the variability in two important strength properties of CLC block masonry and proposes the most appropriate models for their statistical distribution to support probability-based structural analysis and design. This study shows that the assumption of a normal distribution in the absence of an appropriate uncertainty model can result in an inaccurate estimate of the seismic risk of an RC frame building infilled with CLC block masonry. The paper further assesses the seismic safety of a typical RC framed building infilled with CLC block masonry in relation to traditional brick masonry, considering the proposed uncertainty model. Although CLC block masonry results in a higher seismic risk compared with traditional brick masonry, it can be used as an infill material in high seismic areas because it results in a probability of failure within the acceptable limit

Studies on Vertically Irregular RC Infilled Frame Buildings

A regular building is defined as a building with uniformly distributed mass, stiffness, strength and structural form. When one or more of these properties is non-uniformly distributed, either individually or in combination with other properties in the vertical direction, the building is referred to as being vertically irregular. There are many examples of the failure of such buildings in past earthquakes due to non-uniform distribution of structural properties. Major international codes including ASCE/SEI 7 (2016) recognize five different classes of vertical irregularity in multi-storeyed buildings that need special design considerations. Most inter-national design codes either prohibit construction or recommend alternative seismic analysis and design of vertically irregular buildings depending on the degree of irregularity and site hazard. Force-based quantities such as mass, stiffness, and strength or geometrical quantities such as plan dimensions are used by design codes as measures (irregularity indicators) for assessing the degree of vertical irregularity present in buildings. Previous literature have proposed different methodologies to quantify the vertical irregularity of buildings in terms of their elastic mode properties. However, the definition of vertical irregularity of buildings mentioned in the codes and standards appears to be not supported by their associated seismic risk. Present study reviews the existing provisions of quantifying vertical irregularity in the context of seismic risk and found that all the vertically irregular buildings listed in the design codes do not pose higher seismic risk. Seismic risks of these buildings are evaluated in terms of fragility function, drift hazard, probability of failure and design confidence level. A concept of ‘vulnerability indicator’ in RC moment resisting vertically irregular framed buildings is proposed to replace the existing ‘irregularity indicator’. A good correlation between the proposed indicator and associated seismic risk is observed for different types of vertically irregular buildings. The design codes recommend five different irregularity quantifier, one for each of the five categories of vertically irregular building. If there is no correlation between ‘irregularity measures’ and ‘seismic safety’ exists the purpose of estimating ‘irregularity measures’ is lost. Therefore, a direct performance indicator of seismic risk is essential for the design code to impose special design requirement in place of presently used indirect irregularity indicator. This study also concludes that vertical geometric irregular buildings exhibit seismic risks lower than even a reference regular building and can be excluded from the list of special design group of building codes. Vertically irregular infill framed buildings are conventionally built with burnt clay brick masonry. However, with growing environmental concern for conservation of natural resources and disposal of waste, fly ash bricks, Autoclaved Aerated Concrete (AAC) and Cellular Lightweight Concrete (CLC) blocks are emerging as a substitute to burnt clay bricks for the construction of masonry infill. AAC and CLC blocks have been widely used as infilled masonry all over the world as a potential infill material due to various advantages. A study on the effect of such modern infill materials in the seismic performance of the vertically irregular building can be useful to ensure the safety of such buildings. However, the variability of mechanical properties related to the modern infill masonry materials are not readily available unlike the conventional building material like steel, concrete, clay and fly ash bricks. For this purpose, an extensive experimental programme was carried out to determine various physical and mechanical properties of AAC and CLC block masonry and best-fit probability distribution models are proposed. Higher order analyses such as XRD and field emission scanning electron microscope (FESEM) are conducted to understand the morphological and microstructural differences in block unit leading to variation in its properties. The proposed probability distributions are used to study performance of typical vertically irregular buildings made of modern infill masonry. The seismic risk of a vertically irregular building with AAC and CLC infill is found to be lower than that with conventional infill materials like clay and fly ash bricks. Although clay and fly ash brick masonry have higher strength and stiffness properties, the lightweight properties may be attributed to the lower seismic risk of buildings with AAC and CLC block masonry. This study concludes that the use of modern lightweight infill materials can improve the building performance in seismically active areas

Sensitivity and Reliability Analysis of Masonry Infilled Frames

The seismic performance of buildings with irregular distribution of mass, stiffness and strength along the height may be significantly different from that of regular buildings with masonry infill. Masonry infilled reinforced concrete (RC) frames are very common structural forms used for multi-storey building construction. These structures are found to perform better in past earthquakes owing to additional strength, stiffness and energy dissipation in the infill walls. The seismic performance of a building depends on the variation of material, structural and geometrical properties. The sensitivity of these properties affects the seismic response of the building. The main objective of the sensitivity analysis is to found out the most sensitive parameter that affects the response of the building. This paper presents a sensitivity analysis by considering 5% and 95% probability value of random variable in the infills characteristics, trying to obtain a reasonable range of results representing a wide number of possible situations that can be met in practice by using pushover analysis. The results show that the strength-related variation values of concrete and masonry, with the exception of tensile strength of the concrete, have shown a significant effect on the structural performance and that this effect increases with the progress of damage condition for the concrete. The seismic risk assessments of the selected frames are expressed in terms of reliability index

A comparison of the performance of SWAT and artificial intelligence models for monthly rainfall–runoff analysis in the Peddavagu River Basin, India

Rainfall–runoff (R–R) analysis is essential for sustainable water resource management. In the present study focusing on the Peddavagu River Basin, various modelling approaches were explored, including the widely used Soil and Water Assessment Tool (SWAT) model, as well as seven artificial intelligence (AI) models. The AI models consisted of seven data-driven models, namely support vector regression, artificial neural network, multiple linear regression, Extreme Gradient Boosting (XGBoost) regression, k-nearest neighbour regression, and random forest regression, along with one deep learning model called long short-term memory (LSTM). To evaluate the performance of these models, a calibration period from 1990 to 2005 and a validation period from 2006 to 2010 were considered. The evaluation metrics used were R2 (coefficient of determination) and NSE (Nash–Sutcliffe Efficiency). The study's findings revealed that all eight models yielded generally acceptable results for modelling the R–R process in the Peddavagu River Basin. Specifically, the LSTM demonstrated very good performance in simulating R–R during both the calibration period (R2 is 0.88 and NSE is 0.88) and the validation period (R2 is 0.88 and NSE is 0.85). In conclusion, the study highlighted the growing trend of adopting AI techniques, particularly the LSTM model, for R–R analysis. HIGHLIGHTS The study used SWAT and seven AI models for the Peddavagu River Basin.; LSTM performed well in simulating R–R during calibration (R2 is 0.88 and NSE is 0.88) and validation (R2 is 0.88 and NSE is 0.85).; These models are valuable for sustainable water management in the Peddavagu River Basin.