An experimental and analytical investigation of reinforced concrete beam-column joints strengthened with a range of CFRP schemes applied only to the beam

This paper investigates the experimental and analytical behaviour of beam-column joints that are subjected to a combination of torque, flexural and direct shear forces, where different Carbon Fibre Polymer (CFRP) strengthening wraps have been applied only to the beam. These wrapping schemes have previously been determined by the research community as an effective method of enhancing the torsional capacities of simply supported reinforced concrete beams. In this investigation, four 3/4-scale exterior beam-column joints were subjected to combined monotonic loading; three different beam wrapping schemes were employed to strengthen the beam region of the joint. The paper suggests a series of rational formulae, based on the space truss mechanism, which can be used to evaluate the joint shear demand of the beams wrapped in these various ways. Further, an iterative model, based on the average stress-strain method, has been introduced to predict joint strength. The proposed analytical approaches show good agreement with the experimental results. The experimental outcomes along with the adopted analytical methods reflect the consistent influence of the wrapping ratio, the interaction between the combined forces, the concrete strut capacity and the fibre orientation on the joint forces, the failure mode and the distortion levels. A large rise in the strut force resulting from shear stresses generated from this combination of forces is demonstrated and leads to a sudden-brittle failure. Likewise, increases in the beams’ main steel rebar strains are identified at the column face, again influenced by the load interactions and the wrapping systems used

Global age-sex-specific mortality, life expectancy, and population estimates in 204 countries and territories and 811 subnational locations, 1950–2021, and the impact of the COVID-19 pandemic: a comprehensive demographic analysis for the Global Burden of Disease Study 2021

Background Estimates of demographic metrics are crucial to assess levels and trends of population health outcomes. The profound impact of the COVID-19 pandemic on populations worldwide has underscored the need for timely estimates to understand this unprecedented event within the context of long-term population health trends. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 provides new demographic estimates for 204 countries and territories and 811 additional subnational locations from 1950 to 2021, with a particular emphasis on changes in mortality and life expectancy that occurred during the 2020–21 COVID-19 pandemic period. Methods 22 223 data sources from vital registration, sample registration, surveys, censuses, and other sources were used to estimate mortality, with a subset of these sources used exclusively to estimate excess mortality due to the COVID-19 pandemic. 2026 data sources were used for population estimation. Additional sources were used to estimate migration; the effects of the HIV epidemic; and demographic discontinuities due to conflicts, famines, natural disasters, and pandemics, which are used as inputs for estimating mortality and population. Spatiotemporal Gaussian process regression (ST-GPR) was used to generate under-5 mortality rates, which synthesised 30 763 location-years of vital registration and sample registration data, 1365 surveys and censuses, and 80 other sources. ST-GPR was also used to estimate adult mortality (between ages 15 and 59 years) based on information from 31 642 location-years of vital registration and sample registration data, 355 surveys and censuses, and 24 other sources. Estimates of child and adult mortality rates were then used to generate life tables with a relational model life table system. For countries with large HIV epidemics, life tables were adjusted using independent estimates of HIV-specific mortality generated via an epidemiological analysis of HIV prevalence surveys, antenatal clinic serosurveillance, and other data sources. Excess mortality due to the COVID-19 pandemic in 2020 and 2021 was determined by subtracting observed all-cause mortality (adjusted for late registration and mortality anomalies) from the mortality expected in the absence of the pandemic. Expected mortality was calculated based on historical trends using an ensemble of models. In location-years where all-cause mortality data were unavailable, we estimated excess mortality rates using a regression model with covariates pertaining to the pandemic. Population size was computed using a Bayesian hierarchical cohort component model. Life expectancy was calculated using age-specific mortality rates and standard demographic methods. Uncertainty intervals (UIs) were calculated for every metric using the 25th and 975th ordered values from a 1000-draw posterior distribution. Findings Global all-cause mortality followed two distinct patterns over the study period: age-standardised mortality rates declined between 1950 and 2019 (a 62·8% [95% UI 60·5–65·1] decline), and increased during the COVID-19 pandemic period (2020–21; 5·1% [0·9–9·6] increase). In contrast with the overall reverse in mortality trends during the pandemic period, child mortality continued to decline, with 4·66 million (3·98–5·50) global deaths in children younger than 5 years in 2021 compared with 5·21 million (4·50–6·01) in 2019. An estimated 131 million (126–137) people died globally from all causes in 2020 and 2021 combined, of which 15·9 million (14·7–17·2) were due to the COVID-19 pandemic (measured by excess mortality, which includes deaths directly due to SARS-CoV-2 infection and those indirectly due to other social, economic, or behavioural changes associated with the pandemic). Excess mortality rates exceeded 150 deaths per 100 000 population during at least one year of the pandemic in 80 countries and territories, whereas 20 nations had a negative excess mortality rate in 2020 or 2021, indicating that all-cause mortality in these countries was lower during the pandemic than expected based on historical trends. Between 1950 and 2021, global life expectancy at birth increased by 22·7 years (20·8–24·8), from 49·0 years (46·7–51·3) to 71·7 years (70·9–72·5). Global life expectancy at birth declined by 1·6 years (1·0–2·2) between 2019 and 2021, reversing historical trends. An increase in life expectancy was only observed in 32 (15·7%) of 204 countries and territories between 2019 and 2021. The global population reached 7·89 billion (7·67–8·13) people in 2021, by which time 56 of 204 countries and territories had peaked and subsequently populations have declined. The largest proportion of population growth between 2020 and 2021 was in sub-Saharan Africa (39·5% [28·4–52·7]) and south Asia (26·3% [9·0–44·7]). From 2000 to 2021, the ratio of the population aged 65 years and older to the population aged younger than 15 years increased in 188 (92·2%) of 204 nations. Interpretation Global adult mortality rates markedly increased during the COVID-19 pandemic in 2020 and 2021, reversing past decreasing trends, while child mortality rates continued to decline, albeit more slowly than in earlier years. Although COVID-19 had a substantial impact on many demographic indicators during the first 2 years of the pandemic, overall global health progress over the 72 years evaluated has been profound, with considerable improvements in mortality and life expectancy. Additionally, we observed a deceleration of global population growth since 2017, despite steady or increasing growth in lower-income countries, combined with a continued global shift of population age structures towards older ages. These demographic changes will likely present future challenges to health systems, economies, and societies. The comprehensive demographic estimates reported here will enable researchers, policy makers, health practitioners, and other key stakeholders to better understand and address the profound changes that have occurred in the global health landscape following the first 2 years of the COVID-19 pandemic, and longer-term trends beyond the pandemic

Analytical assessment of CFRP retrofitted reinforced-concrete buildings subjected to near-fault ground motions

Application of externally bonded fiber-reinforced polymers (FRPs) in the form of composite sheets has received a great deal of attention in the last two decades. However, their efficiency in improving the seismic performance of reinforced concrete (RC) structures subjected to near-fault ground motions has not yet been scrutinized in detail. Seismic motions near the fault rupture can be characterized by a large long-period velocity pulse at the beginning of the earthquake, causing severe damage or even collapse of code-compliant buildings. Although seismic design codes cannot adequately address the effect of these impulsive ground motions on structures, retrofitting of many important buildings located in regions near the active faults is high priority. Towards this, a numerical investigation is conducted in this study on the seismic retrofitting of existing RC building structures under near-fault ground motions using carbon FRP (CFRP) sheets. As the case study, an 8-story RC moment resisting frame was selected to represent the midrise buildings. Aimed at improving the lateral strength of the structure, CFRP retrofits were applied to the top and bottom (flange) sides of the beams and columns in the regions prone to inelastic behavior during the strong ground motion. Seismic responses of the original and retrofitted structures were evaluated using nonlinear time-history analysis performed under a set of near-fault ground motions possessing directivity pulses. The results were compared in terms of distribution of maximum interstory drifts and plastic deformations at beams and columns. It was shown that the adopted retrofitting scheme can substantially improve the seismic behavior of existing code-compliant RC structures subjected to impulsive seismic motions

Numerical investigation on the behavior of FRP-retrofitted RC exterior beam-column joints under cyclic loads

This paper reports on the capability of nonlinear quasi-static finite element modeling in simulating the hysteretic behavior of FRP-retrofitted reinforced concrete (RC) exterior beam-column joints under cyclic loads. For the purposes of our investigation, three concrete beam-tocolumn joint specimens (un-strengthened and FRP-strengthened) were selected. The ANSYS finite element software was used for modeling RC exterior joints. The specimens were loaded using a step-by-step load increment procedure to simulate the cyclic loading regime employed in testing. Additionally, an automatically reforming stiffness matrix strategy was used to simulate the actual seismic performance of the RC members after cracking, steel yielding, and concrete crushing during the push and pull loading cycles. The results show that the hysteretic simulation is satisfactory for both un-strengthened and FRP-strengthened specimens. Furthermore, when FRP strengthening is employed, strengthened beam-column joints exhibit a better structural performance than the un-strengthened specimens

Evaluating the behavior and bond properties of FRP spike anchors under confined conditions and elevated temperature

The use of fiber-reinforced polymer (FRP) anchors in combination with the conventional externally bonded reinforcement (EBR) installation technique is an effective method to prevent or postpone the debonding of FRP sheets. However, their behavior under confined conditions and elevated temperatures is still unknown. In such a framework, in the first phase, the current research aims to assess pullout test results for single FRP anchors with dowels ranging from 50 to 75 mm in confined and unconfined conditions. To achieve this goal, three concrete slabs with the dimension of 1550 × 1250 × 250 mm3 were cast. Experimental results showed that the bond strength of FRP anchors in confined conditions increased by about 50% compared to the unconfined conditions. Additionally, a comparison was made between the experimental results and the literature models. In the second phase, eleven pullout tests were conducted on the cylindrical specimens with the dimension of 150 × 200 mm2 (diameter × height) under confined conditions and elevated temperatures by considering different sustained load levels.The results showed as the temperature increases and FRP anchor is constantly loaded, it fails in a shorter time before the adhesive reaches its glass transition. Finally, a bond strength vs. temperature model was developed for FRP anchors in confined conditions and high temperatures

Numerical Investigation on the Behavior of FRP-Retrofitted RC Exterior Beam-Column Joints under Cyclic Loads

This paper reports on the capability of nonlinear quasi-static finite element modeling in simulating the hysteretic behavior of FRP-retrofitted reinforced concrete (RC) exterior beam column joints under cyclic loads. For the purposes of our investigation, three concrete beam to column joint specimens (un-strengthened and FRP-strengthened) were selected. The ANSYS finite element software was used for modeling RC exterior joints. The specimens were loaded using a step by step increment procedure to simulate the cyclic loading regime employed in testing. Additionally, an automatically reforming stiffness matrix strategy was used to simulate the actual seismic performance of the RC members after cracking, steel yielding, and concrete crushing during the push and pull loading cycles. The results show that the hysteretic simulation is satisfactory for both un-strengthened and FRP-strengthened specimens. Furthermore, when FRP strengthening is employed, strengthened beam column joints exhibit a better structural performance than the un-strengthened specimens