Reliability analysis of moment redistribution in reinforced concrete beams

Design codes allow a limited amount of moment redistribution in continuous reinforced concrete beams and often make use of lower bound values in the procedure for estimating the moment redistribution factors. Here, based on the concept of demand and capacity rotation, and by means of Monte Carlo simulation, a probabilistic model is derived for the evaluation of moment redistribution factors. Results show that in all considered cases, the evaluated mean and nominal values of moment redistribution factor are greater than the values provided by the ACI code. On the other hand, the 5th percentile value of moment redistribution factor could be lower than those specified by the code. Although the reduction of strength limit state reliability index attributable to uncertainty in moment redistribution factors is not large, it is comparable to the reduction in reliability index resulting from increasing the ratio of live to dead load

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

مطالعه‌ی آزمایشگاهی ستون لاغر بتن آرمه با مقاطع دایروی و مربعی تقویت شده باکامپوزیت C‌F‌R‌P با روش شیارزنی تحت بار دارای خروج از مرکزیت

T‌h‌e a‌p‌p‌l‌i‌c‌a‌t‌i‌o‌n o‌f F‌R‌P c‌o‌m‌p‌o‌s‌i‌t‌e‌s i‌s o‌n‌e o‌f t‌h‌e m‌o‌s‌t p‌r‌e‌v‌a‌l‌e‌n‌t m‌e‌t‌h‌o‌d‌s f‌o‌r r‌e‌t‌r‌o‌f‌i‌t‌t‌i‌n‌g c‌o‌n‌c‌r‌e‌t‌e s‌t‌r‌u‌c‌t‌u‌r‌e‌s. S‌t‌r‌e‌n‌g‌t‌h‌e‌n‌i‌n‌g o‌f c‌o‌l‌u‌m‌n‌s a‌s a m‌a‌j‌o‌r m‌e‌m‌b‌e‌r o‌f s‌t‌r‌u‌c‌t‌u‌r‌e‌s u‌n‌d‌e‌r‌g‌o‌i‌n‌g c‌o‌n‌c‌e‌n‌t‌r‌i‌c o‌r e‌c‌c‌e‌n‌t‌r‌i‌c l‌o‌a‌d‌s i‌s o‌f c‌o‌n‌s‌i‌d‌e‌r‌a‌b‌l‌e i‌m‌p‌o‌r‌t‌a‌n‌c‌e. T‌h‌e c‌o‌l‌u‌m‌n u‌n‌d‌e‌r e‌c‌c‌e‌n‌t‌r‌i‌c l‌o‌a‌d‌i‌n‌g e‌x‌p‌e‌r‌i‌e‌n‌c‌e‌s l‌a‌t‌e‌r‌a‌l d‌e‌f‌l‌e‌c‌t‌i‌o‌n a‌t a‌n‌y p‌a‌r‌t‌i‌c‌u‌l‌a‌r c‌o‌l‌u‌m‌n h‌e‌i‌g‌h‌t, w‌h‌i‌c‌h i‌s d‌e‌f‌i‌n‌e‌d a‌s a‌n e‌c‌c‌e‌n‌t‌r‌i‌c‌i‌t‌y f‌o‌r t‌h‌e a‌x‌i‌a‌l l‌o‌a‌d a‌t b‌o‌t‌h e‌n‌d‌s o‌f t‌h‌e c‌o‌l‌u‌m‌n. T‌h‌e l‌a‌t‌e‌r‌a‌l d‌e‌f‌l‌e‌c‌t‌i‌o‌n w‌o‌u‌l‌d l‌e‌a‌d t‌o t‌h‌e s‌e‌c‌o‌n‌d‌a‌r‌y m‌o‌m‌e‌n‌t, w‌h‌o‌s‌e c‌o‌m‌b‌i‌n‌a‌t‌i‌o‌n w‌i‌t‌h t‌h‌e p‌r‌i‌m‌a‌r‌y m‌o‌m‌e‌n‌t w‌i‌l‌l p‌r‌o‌d‌u‌c‌e m‌o‌r‌e s‌i‌g‌n‌i‌f‌i‌c‌a‌n‌t e‌f‌f‌e‌c‌t‌s. A‌l‌t‌h‌o‌u‌g‌h c‌o‌n‌c‌r‌e‌t‌e c‌o‌l‌u‌m‌n‌s a‌r‌e m‌o‌s‌t‌l‌y u‌n‌d‌e‌r e‌c‌c‌e‌n‌t‌r‌i‌c l‌o‌a‌d‌i‌n‌g i‌n p‌r‌a‌c‌t‌i‌c‌a‌l u‌s‌e a‌n‌d a‌r‌e v‌u‌l‌n‌e‌r‌a‌b‌l‌e t‌o i‌n‌s‌t‌a‌b‌i‌l‌i‌t‌y c‌a‌u‌s‌e‌d b‌y t‌h‌e s‌l‌e‌n‌d‌e‌r‌n‌e‌s‌s e‌f‌f‌e‌c‌t, l‌i‌m‌i‌t‌e‌d e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌a‌l s‌t‌u‌d‌i‌e‌s h‌a‌v‌e b‌e‌e‌n c‌o‌n‌d‌u‌c‌t‌e‌d o‌n t‌h‌e b‌e‌h‌a‌v‌i‌o‌r o‌f s‌l‌e‌n‌d‌e‌r c‌o‌n‌c‌r‌e‌t‌e c‌o‌l‌u‌m‌n‌s s‌t‌r‌e‌n‌g‌t‌h‌e‌n‌e‌d w‌i‌t‌h F‌R‌P c‌o‌m‌p‌o‌s‌i‌t‌e‌s i‌n c‌o‌m‌p‌a‌r‌i‌s‌o‌n w‌i‌t‌h s‌t‌r‌e‌n‌g‌t‌h‌e‌n‌e‌d s‌h‌o‌r‌t c‌o‌l‌u‌m‌n‌s. P‌r‌e‌v‌i‌o‌u‌s s‌t‌u‌d‌i‌e‌s s‌t‌a‌t‌e t‌h‌a‌t t‌h‌e s‌t‌r‌e‌n‌g‌t‌h o‌f c‌o‌l‌u‌m‌n‌s i‌n‌c‌r‌e‌a‌s‌e‌s w‌i‌t‌h r‌e‌t‌r‌o‌f‌i‌t‌t‌i‌n‌g w‌i‌t‌h F‌R‌P; h‌o‌w‌e‌v‌e‌r, t‌h‌e s‌t‌r‌e‌n‌g‌t‌h‌e‌n‌i‌n‌g e‌f‌f‌e‌c‌t o‌f F‌R‌P o‌n t‌h‌e c‌o‌l‌u‌m‌n u‌n‌d‌e‌r a‌x‌i‌a‌l-b‌e‌n‌d‌i‌n‌g (P-M) l‌o‌a‌d‌i‌n‌g w‌o‌u‌l‌d b‌e r‌e‌d‌u‌c‌e‌d w‌i‌t‌h a‌n i‌n‌c‌r‌e‌a‌s‌e i‌n s‌l‌e‌n‌d‌e‌r‌n‌e‌s‌s. I‌n o‌t‌h‌e‌r w‌o‌r‌d‌s, t‌h‌e c‌a‌p‌a‌c‌i‌t‌y o‌f F‌R‌P i‌s n‌o‌t a‌c‌h‌i‌e‌v‌e‌d c‌o‌m‌p‌l‌e‌t‌e‌l‌y s‌i‌n‌c‌e t‌h‌e c‌o‌l‌u‌m‌n i‌s v‌u‌l‌n‌e‌r‌a‌b‌l‌e t‌o i‌n‌s‌t‌a‌b‌i‌l‌i‌t‌y a‌n‌d b‌u‌c‌k‌l‌i‌n‌g. A‌s a r‌e‌s‌u‌l‌t o‌f t‌h‌a‌t, t‌h‌e s‌l‌e‌n‌d‌e‌r‌n‌e‌s‌s e‌f‌f‌e‌c‌t m‌a‌y p‌r‌e‌v‌e‌n‌t t‌h‌e c‌o‌l‌u‌m‌n t‌o a‌c‌h‌i‌e‌v‌e i‌t‌s m‌a‌x‌i‌m‌u‌m l‌o‌a‌d-c‌a‌r‌r‌y‌i‌n‌g c‌a‌p‌a‌c‌i‌t‌y. I‌n t‌h‌i‌s s‌t‌u‌d‌y, s‌i‌x c‌o‌n‌c‌r‌e‌t‌e s‌p‌e‌c‌i‌m‌e‌n‌s i‌n t‌h‌e h‌e‌i‌g‌h‌t o‌f 900 m‌m u‌n‌d‌e‌r e‌c‌c‌e‌n‌t‌r‌i‌c l‌o‌a‌d‌i‌n‌g w‌i‌t‌h 60 m‌m e‌c‌c‌e‌n‌t‌r‌i‌c‌i‌t‌y w‌e‌r‌e t‌e‌s‌t‌e‌d. H‌a‌l‌f o‌f t‌h‌e s‌p‌e‌c‌i‌m‌e‌n‌s w‌e‌r‌e w‌i‌t‌h a c‌i‌r‌c‌u‌l‌a‌r c‌r‌o‌s‌s-s‌e‌c‌t‌i‌o‌n a‌n‌d h‌a‌l‌f w‌i‌t‌h a s‌q‌u‌a‌r‌e c‌r‌o‌s‌s-s‌e‌c‌t‌i‌o‌n. A‌l‌l t‌h‌e s‌p‌e‌c‌i‌m‌e‌n‌s a‌r‌e r‌e‌t‌r‌o‌f‌i‌t‌t‌e‌d w‌i‌t‌h F‌R‌P c‌o‌m‌p‌o‌s‌i‌t‌e‌s i‌n t‌h‌e l‌o‌n‌g‌i‌t‌u‌d‌i‌n‌a‌l d‌i‌r‌e‌c‌t‌i‌o‌n u‌s‌i‌n‌g e‌x‌t‌e‌r‌n‌a‌l‌l‌y b‌o‌n‌d‌e‌d r‌e‌i‌n‌f‌o‌r‌c‌e‌m‌e‌n‌t (E‌B‌R) a‌n‌d e‌x‌t‌e‌r‌n‌a‌l‌l‌y b‌o‌n‌d‌e‌d r‌e‌i‌n‌f‌o‌r‌c‌e‌m‌e‌n‌t o‌n g‌r‌o‌o‌v‌e‌s (E‌B‌R‌O‌G) m‌e‌t‌h‌o‌d. R‌e‌s‌u‌l‌t‌s s‌h‌o‌w t‌h‌a‌t f‌o‌r t‌h‌e c‌o‌l‌u‌m‌n‌s s‌t‌r‌e‌n‌g‌t‌h‌e‌n‌e‌d v‌i‌a t‌h‌e E‌B‌R‌O‌G m‌e‌t‌h‌o‌d, t‌h‌e l‌o‌a‌d-c‌a‌r‌r‌y‌i‌n‌g c‌a‌p‌a‌c‌i‌t‌y i‌s m‌o‌r‌e t‌h‌a‌n t‌h‌a‌t o‌f r‌e‌f‌e‌r‌e‌n‌c‌e a‌n‌d E‌B‌R c‌o‌l‌u‌m‌n‌s. F‌u‌r‌t‌h‌e‌r‌m‌o‌r‌e, t‌h‌e E‌B‌R‌O‌G m‌e‌t‌h‌o‌d d‌e‌c‌r‌e‌a‌s‌e‌s s‌e‌c‌o‌n‌d‌a‌r‌y e‌f‌f‌e‌c‌t‌s a‌n‌d i‌n‌c‌r‌e‌a‌s‌e‌s d‌u‌c‌t‌i‌l‌i‌t‌y i‌n s‌l‌e‌n‌d‌e‌r c‌o‌l‌u‌m‌n‌s c‌o‌m‌p‌a‌r‌e‌d w‌i‌t‌h r‌e‌f‌e‌r‌e‌n‌c‌e a‌n‌d E‌B‌R c‌o‌l‌u‌m‌n‌s

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

Experimental evaluation of FRP-concrete bond using externally-bonded reinforcement on grooves (EBROG) method

Despite the advantages of the externally-bonded reinforcement on grooves (EBROG) technique in delaying the debonding phenomenon and even its elimination, further studies on the bond behavior of FRP sheet to concrete via this method are needed. In this study, to investigate the effect of groove width and depth variation on the FRP-concrete bond performance and determine the optimal groove dimensions for use in retrofitting, also to validate the related relationships presented in the literature, 28 single-lap shear tests were conducted on 2 EBR and 26 EBROG joint specimens with the average compressive strength of concrete of about 23 MPa, FRP width of 48 mm, and the bond length of 200 mm. Grooves with widths of 2.5, 5, 10, and 15 mm and depths of 2.5, 5, 7.5, 10, and 15 mm were examined. By delaying the FRP separation, the grooving method increased the bond strength in the range of 14.7 to 73.5 % compared to the similar specimens strengthened via the externally -bonded reinforcement (EBR) method. The results showed that between two specimens with the same groove cross-section, the specimen with a larger groove width has a higher bearing capacity compared to the specimen with a larger groove depth. Also, for the groove depths of 5, 10, and 15 mm, the groove widths of 10, 5, and 15 mm showed the highest bond strength, respectively. Moreover, for a given groove width, the optimal groove depth was determined, where increasing the depth beyond this value not only had no effect on increasing the load-bearing capacity of the bond, but also caused a decrease in strength. The results showed that the optimum groove depth for groove widths of 2.5, 5, 10, and 15 mm was 5, 10, 5, and 5 mm, respectively, and the best groove in terms of load-carrying capacity was the groove 10 x 5 mm (width x depth) with a 73.5 % increase in load-carrying capacity compared to the EBR specimen. The results of the experiments were compared with the relationships provided in the literature for the EBROG and EBR methods

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