Uncertainty quantification and seismic fragility of base-isolated liquid storage tanks using response surface models

Seismic response of base-isolated liquid storage tank is represented using response surface model (RSM) to consider the uncertainty in the isolator parameters. The effectiveness of RSM to represent the probability distributions of the peak seismic response quantities of the base-isolated liquid storage tank is studied in the framework of Monte Carlo (MC) simulation. Broad and slender configurations of the tanks isolated by lead–rubber bearing (New Zealand – NZ system) characterized with non-linear force-deformation behavior is considered in the present study. The influence of the uncertain isolator parameters on the seismic response of the base-isolated liquid storage tanks is investigated. Subsequently, seismic fragility of the base-isolated liquid storage tanks is evaluated using the RSM based MC simulation. The RSM estimates the non-linear seismic response of the base-isolated liquid storage tanks with sufficient accuracy. It is observed that the uncertainties in the isolator parameters significantly influence the peak response quantities of the base-isolated liquid storage tanks. The effectiveness of the base isolation technique, in terms of the reduced probability of failure, is observed by comparing the fragility curves for the fixed-base and base-isolated liquid storage tanks. It is also observed that increase in the isolation time period decreases the probability of failure for the base-isolated liquid storage tanks. It is concluded that the peak ground acceleration (PGA) of the earthquake ground motion can be included in the RSM to reduce the computational efforts for seismic fragility analysis.     

Street level urban design qualities for walkability: Combining 2D and 3D GIS measures

Much of the physical activity and built environment literature has focused on composite walkability indices based on the D variables– design, density, diversity, destination accessibility, and distance to transit. This literature, however, has largely ignored the microscale streetscape features that affect the pedestrian experience. Five street level urban design qualities were recently identified and defined for quantitative measures although these measures are mostly through subjective field observation. View related features such as long sight line and proportion of sky have not yet been objectively measured due to the limitation of data and method. This study uses both 2D and 3D GIS to objectively measure street level urban design qualities in Buffalo, New York and tests their correlation with observed pedestrian counts and Walk Scores. Our results showed that 3D GIS helped to generate objective measures on view related features. These objective measures can help us better understand the influence of street level urban design features on walkability for designing and planning healthy cities.     

Research on the energy-saving and revenue sharing strategy of ESCOs under the uncertainty of the value of Energy Performance Contracting Projects

Under the uncertainty of the value of Energy Performance Contracting Projects (EPCPs), this paper develops a revenue-sharing bargaining model between an Energy Service Company (ESCO) and an Energy-Using Organization (EU). Based on the model the paper analyzes the impacts of energy prices, risk-adjusted discount rates and accidents on the ESCO’s bargaining strategies. The research shows that the greater the probability of adverse circumstances is, the higher is the revenue share (of the EU), and the more disadvantageous is the ESCO’s position in the game. Furthermore, we design a forecast–commitment contract between an ESCO and an EU and analyze the optimal product’s energy savings commitment strategy of the ESCO to cope with uncertain energy savings and contract risk. The research illustrates that by introducing penalties and commitments, the contract can eliminate the impact of the uncertain energy savings on the contract execution to a certain extent; when the EU takes a greater commitment risk, the ESCO is willing to provide a higher commitment, thus enhancing the strategy value of the bilateral relationship and reducing the contract risk. Finally, the policy recommendations about improving shared savings contract standard, third-party energy savings measurement and verification mechanism and arbitration mechanism of EPCs are provided.     

Simulating RC beams with unbonded FRP and steel prestressing tendons

A partial interaction based analysis to simulate the behaviour of RC beams with prestressed unbonded tendons is proposed. Unlike bonded reinforcement, the strain developed in unbonded reinforcing tendons under bending is uniform along the length of the member and is thus member dependant. Conventional analysis techniques incorporate correction factors and empirical components in defining the strain developed in both the unbonded and bonded reinforcement. Being semi-empirical, the post-cracking analysis cannot directly simulate the effects of tension-stiffening on the untensioned bonded reinforcement. Accordingly, this paper presents a segmental moment–rotation approach for simulating the behaviour of RC beams with unbonded prestressed reinforcement, such that the mechanics of the approach removes the reliance on empiricisms in defining the reinforcement and unbonded tendon behaviour. Validated against experimental results, the approach is shown to accommodate concrete creep, shrinkage and reinforcement relaxation, thus enabling prestressing losses to be quantified.     

Strength properties of steel slag stabilized mixes

A new type of low-strength concrete made with steel slag and gravel was investigated in this report. Increasing the amount of cement or steel slag in the mix increased the maximum dry density and optimum moisture content of the concrete. Additionally, the compressive and indirect tensile strength of the concrete increased with curing age. The strength of mixes with low cement contents increased with the slag content, while that of mixes with higher cement contents decreased with slag content. Finally, the average indirect tensile strength for all mixes as a percentage of compressive strength was ∼14%.     

Study on splitting failure in rock masses by simulation test,site monitoring and energy model

To study the phenomenon of splitting failure in the rock mass adjacent to an underground hydro-power station excavation in a region of high initial stresses, both laboratory simulation tests and site monitoring were undertaken. Concurrent with the excavation design and monitoring, an energy dissipation model was formulated. Back analysis was performed on the monitored site data obtained during excavation and construction. For study in the laboratory, large specimens were designed using rock-like materials. Using a true triaxial state test condition, one side of the specimen was unloaded to model the exposed cavern wall of the excavation. In the experimental model, rock splitting failure was observed. During the excavation (construction site), monitoring instruments were installed in boreholes in the cavern wall. Sliding micrometer, electrical resistivity tomography equipment and a borehole TV camera were employed to monitor the effects of the excavation. Back analysis using the deformation of the surrounding rock mass was carried out. The deformation and the depth of the splitting area in the surrounding rock mass after final excavation were predicted using the energy dissipation model and also by an alternate prediction formula for the splitting depth previously proposed by the authors. The correlation of measurements and predicted results was reasonably good.     

Pore pressure and consolidation of saturated silty clay induced by progressively heating/cooling

The thermal pore pressure and consolidation of a saturated silty clay are experimentally studied. The specimen was heated progressively from the room temperature of 25 °C to 85 °C (T = 25 °C → 35 °C → 45 °C … → 85 °C), and then cooled from 85 °C to 25 °C (T = 85 °C → 75 °C → 65 °C … → 25 °C), with (case 1) or without (case 2) drainage between temperature stages at four confining pressures (50, 100, 150 and 200 kPa, respectively). It shows that during the undrained heating/cooling, the pore pressure reaches a peak at the time when the specimen is heated to the required temperature and then decreases slightly, and it declines to a minimum at the time when the specimen is cooled to the required temperature and then increases slightly. Such phenomenon can be attributed to the adjustment of soil structure induced by the interaction of solid grains with pore water. On the other hand, during the drained heating/cooling, the maximum pore pressure increases with the increase of temperature stages, and the normalized negative pore pressures show a decreasing trend with the decrease of temperature stages. This appears to be especially obvious as the applied confining pressures decrease. It is also observed that consolidation volumetric strains during the isothermal drainage increase significantly with the increase of temperature stage, and the reduction in the volumetric strains due to absorption after cooling shows a decreasing trend with the decrease of temperature stage.     

Mechanical properties of laminated bamboo strips from Gigantochloa Scortechinii/polyester composites

In this study, the mechanical properties of culm fiber composites with various thicknesses from the inner through the outer layer of bamboo strips were investigated. This study utilized a specific type of bamboo species named Gigantochloa Scortechinii (Buluh Semantan), which was collected from the Bukit Larang village in Melaka, Malaysia. In these experiments, unsaturated polyester (UP) and bamboo fiber (BF) strips were prepared through the hand lay-up technique using 3 mm thick aluminum mould. The composite bamboo strips were prepared in 1.5–2.5 mm thicknesses. The weight of the inner, middle and outer bamboo parts varied from a minimum of 0.742 g to a maximum of 2.600 g. The specimens were then characterized using several techniques including tensile, flexural, hardness, and impact tests. The results indicated that the properties of the middle part of the bamboo strips improve as the bamboo strip thickness increases due to the incorporation of unsaturated polyesters. However, the hardness properties increase for the outer layer of the laminate. These findings suggest that bamboo strips, based on unsaturated polyesters, yield excellent mechanical properties and are a viable alternative to composite-based reinforcing fibers.     

Mechanical behaviour of FRP adhesive joints: A theoretical model

In this paper a mathematical model for studying the equilibrium problem of adhesive joints between FRP adherents is presented. In particular, double and single-lap joints, both in the case of normal and shear/flexure stresses are considered. The problem is non linear due to the cohesive constitutive law adopted for modeling the interface. On the contrary, the adherents are supposed to be indefinitely linear elastic.The possibility to uncouple the problem of shear/flexure from the extensional one, as well as disregard the mutual effects between the normal and tangential stresses acting at the joint interfaces is also assumed. As highlighted in literature, this hypothesis allows results which are sufficiently correct from a technical perspective when the mechanical characteristics of the adherents are almost the same, as supposed in the present paper. Within such a framework it is possible to trace back the examined equilibrium problems to those of simpler auxiliary structural schemes. A simple and efficient iterative procedure for solving the aforementioned problems is also proposed.