Modelling the bond slip behaviour of FRP externally bonded to timber

Recent studies and applications have demonstrated that Fibre Reinforced Polymer (FRP) has become a mainstream technology for the strengthening and/ or rehabilitation of ageing and deteriorated structures. However, one of the main problems which limit the full utilisation of the FRP material strength is the premature failure due to debonding. This research study presents 1) a review of available FRP-to-timber and FRP-to-concrete bonded interface models, and 2) investigates factors affecting bond strength. A stepwise regression method has then been employed to evaluate the influence of potential factors on the bond strength. The proposed stepwise regression model is based on 195 experimental results of FRP-to-timber bonded interfaces. Results of this stepwise regression analysis are then assessed with results of pull-out tests and satisfactory comparisons are achieved between measured failure loads (R2=0.59) and the predicted loads (R2=0.71, P<0.0001)

Timber type effect on bond strength of frp externally bonded timber

© WCTE 2018 Committee. The performance of FRP composite bonded externally to timber is complex and limited attempts have been made to-date to investigate the bond behaviour of the FRP to timber interface. Furthermore, analytical solutions to determine the interface behaviour of FRP to timber have not been fully investigated and are not covered in current standards. This study investigates the influence of timber type and timber mechanical properties on the bond strength of FRP-to-timber joints. Two different types of timber (LVL and hardwood) have been used and results of experimental tests showed that with the increase of timber tensile strength and modulus of elasticity, the interfacial bond strength increases; however, the failure mode can be brittle. Specimens made from LVL exhibited more ductile behaviour failing gradually; while joints made from hardwood failed suddenly in a brittle manner. It was also observed that the local slip between FRP and timber was higher for joints fabricated from LVL compared to hardwood. Therefore, to achieve a satisfactory bonded joint, the effectiveness of timber mechanical properties is required to be accurately considered

Bond strength model for externally bonded FRP-to-timber interface

© 2018 Elsevier Ltd Despite the large number of studies on externally bonded elements using FRP composites, there is a significant knowledge gap to gain a comprehensive understanding of potential parameters such as bond width, bond length, material properties and geometries that influence bond strength. Behaviour of FRP bonded to concrete has been well investigated and there are a number of experimental and theoretical studies in this area; however, limited attempts have been made to investigate the bond behaviour of the FRP to timber interface. This paper reports an investigation on the behaviour of FRP externally bonded to timber. A novel theoretical model has been developed through stepwise regression analysis of 136 single shear FRP-to-timber joints. This has led to establishing a new predictive model for determination of the bond strength for FRP-to-timber joints. Results of this stepwise regression analysis are then assessed with results of experimental tests, and satisfactory comparisons have been achieved between ultimate applied loads and the predicted loads. Finally, a significant improvement in prediction of bond behaviour has been achieved when results of the proposed analytical model compared with the existing models from the literature, signifying the capability of the new models

Experimental and analytical investigation on CFRP strengthened glulam laminated timber beams: Full-scale experiments

© 2018 Elsevier Ltd Timber is one of the most appealing and aesthetic construction materials with excellent characteristics compared with other construction materials such as steel, concrete and clay bricks. It is one of the oldest sustainable construction materials and still continues to be a popular choice in modern infrastructure. In recent years, fibre reinforced polymers (FRP) has emerged to improve mechanical properties even further. In this study, results of experimental tests on strengthened glulam beams have been used to investigate potential parameters affecting flexural strength and ultimate load carrying capacity of glulam beams strengthened with externally bonded FRP sheets. Eight full-scale timber beams with and without FRP reinforcement were tested where the bonded length, width, and thickness of the FRP was varied for FRP strengthened beams. The test results pointed out that reduction of stress concentrations can enhance the mechanical performance of the strengthened beams. The ultimate load carrying capacity and flexural strength of reinforced beams improved significantly when bond length and bond width increased. Results of experiments showed that further increase in bond thickness predominantly improves stiffness and ductility of the strengthened timber beams which has a significant enhancement in ultimate deflection and serviceability limit state. An analytical model has been established to determine the ultimate flexural capacity of strengthened timber beam. Satisfactory correlation is achieved between measured and predicted flexural capacity, signifying the capability of the new models

Occurrence and diversity of Xanthomonas campestris pv. campestris in vegetable brassica fields in Nepal

Black rot caused by Xanthomonas campestris pv. campestris was found in 28 sampled cabbage fields in five major cabbage-growing districts in Nepal in 2001 and in four cauliflower fields in two districts and a leaf mustard seed bed in 2003. Pathogenic X. campestris pv. campestris strains were obtained from 39 cabbage plants, 4 cauliflower plants, and 1 leaf mustard plant with typical lesions. Repetitive DNA polymerase chain reaction-based fingerprinting (rep-PCR) using repetitive extragenic palindromic, enterobacterial repetitive intergenic consensus, and BOX primers was used to assess the genetic diversity. Strains were also race typed using a differential series of Brassica spp. Cabbage strains belonged to five races (races 1, 4, 5, 6, and 7), with races 4, 1, and 6 the most common. All cauliflower strains were race 4 and the leaf mustard strain was race 6. A dendrogram derived from the combined rep-PCR profiles showed that the Nepalese X. campestris pv. campestris strains clustered separately from other Xanthomonas spp. and pathovars. Race 1 strains clustered together and strains of races 4, 5, and 6 were each split into at least two clusters. The presence of different races and the genetic variability of the pathogen should be considered when resistant cultivars are bred and introduced into regions in Nepal to control black rot of brassicas

The feasibility of the Ages and Stages Questionnaire for the assessment of child development in a community setting in Nepal

Background: The Ages and Stages Questionnaire Third Edition (ASQ‐3) may be a feasible and cost‐effective tool to screen children's development in resource poor settings. We have assessed the feasibility of the ASQ‐3 “home procedure” when conducted by fieldworkers in a community‐based nutritional interventional trial on early child development in Nepal. Method: Six hundred children aged 6–11 months at risk of stunting were assessed by trained fieldworkers in their homes by the ASQ‐3. Three fieldworkers performed standardization exercises and were double scored with a gold standard during the study period. Intraclass correlations (ICCs) were calculated to measure the interrater agreement. The internal consistency was expressed by standardized Cronbach's alphas. The association between total ASQ score and gestation, low birth weight, and stunted children is presented to give an estimate of the construct validity of the tool. Result: Mean scores of the 600 Nepalese children were consistently lower than in the American norm sample. The ICCs from the standardization exercises were initially good to excellent but declined throughout the study period. The standardized alphas for the total score in the different age groups indicate good internal consistency but varied in the subscales. Children who were preterm, children with low birth weight, and children who were stunted scored substantially lower on the total ASQ score than those who were not. Conclusion: Although the ASQ‐3 “home procedure” is low at cost and easily accessible in a Nepalese context, the tool requires rigorous and stringent training to achieve acceptable interrater agreement. Further adjustment is required to achieve satisfactory internal consistency.acceptedVersio

Village Baseline Study: Site Analysis Report for Khulna - Morrelganj, Bangladesh

The Gabgachhia village is located in the coastal region of Bangladesh’s Khulna district. The population is rising and living with high levels of poverty and food insecurity. Local resources that are not critically strained from climate change and poor resource management are few, beyond mosques, roads and schools. The community has seen dramatic changes in resources, as early as 1990, which they attribute to increased population pressures and climate change impacts. Forests have been depleted, rivers are full of silt and lacking life, farmlands have low productivity due to rising salinity, flooding and inappropriate varieties, drinking water is insufficient to meet human, crop and animal needs, and infrastructure is weak and unable to withstand the environmen

The association of women's empowerment with stillbirths in Nepal.

INTRODUCTION: Globally, 2.6 million stillbirths occur each year. Empowering women can improve their overall reproductive health and help reduce stillbirths. Women empowerment has been defined as women's ability to make choices in economic decision-making, household and health care decision-making. In this paper, we aimed to evaluate if women's empowerment is associated with stillbirths. METHODS: Data from 2016 Nepal Demographic Health Surveys (NDHS) were analysed to evaluate the association between women's empowerment and stillbirths. Equiplots were generated to assess the distribution of stillbirths by wealth quintile, place of residence and level of maternal education using data from NHDS 1996, 2001, 2006, 2011 and 2016 data. For the association of women empowerment factors and stillbirths, univariate and multivariate analyses were conducted. RESULTS: A total of 88 stillbirths were reported during the survey. Univariate analysis showed age of mother, education of mother, age of husband, wealth index, head of household, decision on healthcare and decision on household purchases had significant association with stillbirths (p < 0.05). In multivariate analysis, only maternal age 35 years and above was significant (aOR 2.42; 1.22-4.80). Education of mother (aOR 1.48; 0.94-2.33), age of husband (aOR 1.54; 0.86-2.76), household head (aOR 1.51; 0.88-2.59), poor wealth index (aOR 1.62; 0.98-2.68), middle wealth index (aOR 1.37; 0.76-2.47), decision making for healthcare (aOR 1.36; 0.84-2.21) and household purchases (aOR 1.01; 0.61-1.66) had no any significant association with stillbirths. CONCLUSIONS: There are various factors linked with stillbirths. It is important to track stillbirths to improve health outcomes of mothers and newborn. Further studies are necessary to analyse women empowerment factors to understand the linkages between empowerment and stillbirths

Dynamics and drivers of land use and land cover changes in Bangladesh

Bangladesh has undergone dramatic land use and land cover changes (LULCC) in recent years, but no quantitative analysis of LULCC drivers at the national scale exists so far. Here, we quantified the drivers of major LULCC in combination with biophysical and socioeconomic observations at the sub-district level. We used Landsat satellite data to interpret LULCC from 2000 to 2010 and employed a Global SurfaceWater Dataset to account for the influences of water seasonality. The results suggest that major LULCC in Bangladesh occur between agricultural land and waterbodies and between forest and shrubland. Exclusion of seasonal waterbodies can improve the accuracy of our LULCC results and driver analysis. Although the gross gain and loss of agricultural land are large on the local scale, the net change (gross gain minus gross loss) at a country scale is almost negligible. Climate dynamics and extreme events and changes in urban and rural households were driving the changes from forest to shrubland in the southeast region. The conversion from agricultural land to standing waterbodies in the southwest region was mainly driven by urban household dynamics, population growth, distance to cities and major roads, and precipitation dynamics. This study, which is the first effort accounting for water seasonality and quantifying biophysical and socioeconomic drivers of LULCC at the national scale, provides a perspective on overall LULCC and underlying drivers over a decadal time scale and national spatial scale and can serve as a scientific basis for developing land policies in Bangladesh