Experimental and numerical investigations on the seismic behavior of bridge piers with vertical unbonded prestressing strands

In the performance-based seismic bridge design, piers are expected to undergo large inelastic deformations during severe earthquakes, which in turn can result in large residual drift and concrete crack in the bridge piers. In this paper, longitudinal unbonded prestressing strands are used to minimize residual drift and residual concrete crack width in reinforced concrete (RC) bridge piers. Seven pier specimens were designed and tested quasi-statically and the numerical simulations were carried out. The effectiveness of using vertical unbonded prestressing strands to mitigate the residual drift and concrete crack width of RC bridge piers are examined and discussed in detail. It is found that the residual drift and residual concrete crack width of the piers can be reduced significantly by using the prestressing strands. Moreover, the strands can increase the lateral strength of the piers while have little influence on the ductility capacity of the piers. The hysteretic curves, residual drifts and strand stress of the piers predicted by the numerical model agree well with the testing data and can be used to assess the cyclic behavior of the piers

Impacts of climate change on plant diseases – opinions and trends

There has been a remarkable scientific output on the topic of how climate change is likely to affect plant diseases in the coming decades. This review addresses the need for review of this burgeoning literature by summarizing opinions of previous reviews and trends in recent studies on the impacts of climate change on plant health. Sudden Oak Death is used as an introductory case study: Californian forests could become even more susceptible to this emerging plant disease, if spring precipitations will be accompanied by warmer temperatures, although climate shifts may also affect the current synchronicity between host cambium activity and pathogen colonization rate. A summary of observed and predicted climate changes, as well as of direct effects of climate change on pathosystems, is provided. Prediction and management of climate change effects on plant health are complicated by indirect effects and the interactions with global change drivers. Uncertainty in models of plant disease development under climate change calls for a diversity of management strategies, from more participatory approaches to interdisciplinary science. Involvement of stakeholders and scientists from outside plant pathology shows the importance of trade-offs, for example in the land-sharing vs. sparing debate. Further research is needed on climate change and plant health in mountain, boreal, Mediterranean and tropical regions, with multiple climate change factors and scenarios (including our responses to it, e.g. the assisted migration of plants), in relation to endophytes, viruses and mycorrhiza, using long-term and large-scale datasets and considering various plant disease control methods

Static and dynamic behaviours of railway prestressed concrete sleepers with longitudinal through hole

As the crosstie beam in railway track systems, the prestressed concrete sleepers (or railroad ties) are principally designed in order to carry wheel loads from the rails to the ground. Their design takes into account static and dynamic loading conditions. It is evident that prestressed concrete has played a significant role as to maintain the high endurance of the sleepers under low to moderate repeated impact loads. In spite of the most common use of the prestressed concrete sleepers in railway tracks, there have always been many demands from rail engineers to improve serviceability and functionality of concrete sleepers. For example, signalling, fibre optic, equipment cables are often damaged either by ballast corners or by tamping machine. There has been a need to re-design concrete sleeper to cater cables internally so that they would not experience detrimental or harsh environments. Accordingly, this study will investigate the effects of through hole or longitudinal hole on static and dynamic behaviours of concrete sleepers under rail shock loading. The modified compression field theory for ultimate strength design of concrete sleepers will be highlighted in this study. The outcome of this study will enable the new design and calculation methods for prestressed concrete sleepers with holes and web opening that practically benefits civil, track and structural engineers in railway industry

Algorithmically imposed thermodynamic compliance for material models in mechanical simulations using the AIM method

Thermodynamic irreversibility can be imposed on empirical material behaviour by using an appropriate algorithm which takes the path-dependence of the degradation process into account. This new algorithm, Algorithmically Imposed Mechanics (AIM), for algorithmically irreversible mechanics, is described, and the convergence and unicity of the solutions obtained are proven. AIM is applicable to a range of mechanical behaviour and is demonstrated to work in conjunction with non-local damage with rotating cracks as well as a mixed plastic and damage behaviour

Shear behavior of concrete beams reinforced exclusively with longitudinal glass fiber reinforced polymer bars: Analytical model

A design approach based on the simplified modified compression field theory, but with the advantage of not requiring an iterative procedure, is proposed for evaluating the shear capacity of beams without including shear reinforcement. This model is capable of simulating beams flexurally reinforced with steel and fiber reinforced polymer (FRP) systems. To appraise the predictive performance of the proposed model, a database (DB) composed of 215 reinforced concrete beams without shear reinforcement is set. By applying the model to this DB, an average value for V-exp./V-ana. of 1.05 with a COV of 24% is obtained, where V-exp. and V-ana. are the shear capacity registered experimentally and obtained with the model, respectively. By applying the approach proposed by ACI Building Code to the DB, average and COV values of 0.91 and 42% are determined, revealing the higher predictive performance of the proposed model. This was even higher in the beams flexurally reinforced with FRP systems, since the proposed model conducted to average and the COV values of 1.0 and 22%, while 0.76 and 32% were obtained with the ACI approach. When proposed model was applied to the beams tested in the experimental program carried out, an average and COV values of 1.02 and 5.23% were determined.The second author wishes to acknowledge the grant SFRH/BSAB/114302/2016 provided by FCT. The support of the FCT through the project PTDC/ECM-EST/1882/2014 is acknowledged.info:eu-repo/semantics/publishedVersio