International Journal of Civil Engineering
Volume:16 Issue: 1, Jan 2018

This paper investigates the seismic behavior of a wind turbine, including soil–structure interaction (SSI). A full-system finite-element model is introduced for dynamic analysis, including SSI. The model is based on the NREL 5 MW reference wind turbine that consists of a rotor blade system with three rotating blades, nacelle, and tower connected to a soil–foundation system. The proposed model is validated using the full-system natural frequencies of the reference wind turbine. In the soil foundation system, the foundation is modeled as a rigid gravity-based foundation with two DOFs and the SSI effect is considered using a cone model. Dynamic analyses are developed in frequency and time domains, and the model is subjected to earthquake excitation and wind loading for different soil types for parked and operational conditions. Transfer functions are obtained, and the modal frequencies of the soil foundation structure system are estimated. Results show that SSI plays an important role in the response of the wind turbine. We can conclude that for a parked wind turbine, the effect of SSI is beneficial while considering that SSI has a detrimental effect in the operational conditions of wind turbine. The participation of different input loads in total response of an operational wind turbine is also presented.

Increasing volumes of the international seaborne trade force liner shipping companies to improve efficiency of their operations to remain competitive. Many of liner shipping companies continue increasing size of their vessels, as larger vessels provide lower voyage costs per container due to their economies of scale. Larger vessels also allow liner shipping companies more efficiently share the demand with the alliance partners. Nowadays, many of liner shipping routes are served by vessels of different types (e.g., small, medium, large). However, the key assumption of studies on vessel scheduling, conducted to date, is homogeneous nature of the vessel fleet (i.e., all vessels in the fleet, serving a given liner shipping route, have the same technical characteristics). This study proposes a novel mathematical model for the vessel scheduling problem with heterogeneous fleet. The objective of a mixed integer non-linear model is to minimize the total vessel turnaround cost. Due to high non-linearity of the proposed mathematical model a non-linear optimization solver is used to solve it. Numerical experiments are performed to evaluate efficiency of the proposed solution approach and the novel methodology. Results demonstrate a computational efficiency of the adopted solution approach. Furthermore, vessel schedules are found to be more sensitive to introduction of larger vessels in the fleet as compared to increase in the unit bunker cost.

This study presents the results of an investigation aimed to study the behavior of reinforced walls constructing of permanent precast lightweight ferrocement hollow blocks. For this objective, an experimental program was carried out extensively, and a finite-element model with ANSYS14.5 was adopted. The experimental program constructed and tested of four walls having the dimensions of 840 × 650 × 250 mm consisting of six permanent precast lightweight ferrocement hollow blocks having the dimensions of 200 × 400 × 200 mm filled with the core material. The core material was investigated: one layer of welded steel mesh and mortar. Single, double, and three layers steel meshes were used to reinforce the plastering as a bonding layer forms, namely, welded steel mesh. Shear connections between the permanent precast hollow blocks and the core mortar were investigated, namely, the mechanical shear connector between the two surfaces. The test specimens were tested as a fixed wall under uniform load. The behaviors of the walls were compared. The experimental results emphasized that better cracks resistance, high serviceability and ultimate loads, and good energy absorption could be improved using the proposed walls which verify the validity of used the proposed model. There is a good agreement between theoretical and experimental ones. Out of this research, this study presents applications of using light weight ferrocement units in building construction of low-cost housing, which is very useful for developed and developing countries alike with great economic advantages.

The paper presents results of an experimental investigation carried out on the water permeation properties of self compacting concrete (SCC) containing fine recycled concrete aggregates (FRCA) and coarse recycled concrete aggregates (CRCA) as replacement of fine natural aggregates (FNA) and coarse natural aggregates (CNA), respectively. The replacement levels of CNA with CRCA were kept as 0, 50 and 100 %. For 50 and 100 % replacement of CNA with CRCA, 0, 25 and 50 % FRCA were used in place of FNA. In all the SCC mixes fly ash was used as partial replacement of Portland cement. Properties of fresh SCC were assessed using slump flow test, V-funnel test and L-box test. The water permeation properties of hardened SCC were investigated using initial surface absorption test, water permeability test and capillary suction test. The compressive strength of all the mixes was also determined. The results indicate that increasing the replacement level of CNA with CRCA has been observed to deteriorate the properties of SCC, whereas the replacement of FNA with FRCA up to 25 % has been found to improve the water permeation properties and compressive strength of SCC mixes up to some extent. Results of this investigation lend support to the use of recycled aggregates in SCC.

We present a new seismic intensity measure (IM) to reduce the dispersion in incremental dynamic analysis (IDA), which commonly use the elastic spectral acceleration as the IM. We propose using the inelastic spectral acceleration based on the principles of modal pushover analysis (MPA) as the seismic IM of ground motion. Unlike other methods of computing inelastic spectral acceleration, this new metric is calculated from the result of equivalent single degree-of-freedom (SDF) systems under the lateral force mode using the uncoupled modal response history analysis procedure. These equivalent SDF systems consider the constantly changing elastic–plastic hysteretic behaviour of the structure itself with different seismic intensities. The results indicate that the improved IDA method can more accurately estimate nonlinear structural responses in many intensity levels covering the entire range of structural responses—all the way from elastic behaviour to global dynamic instability. When the structure enters into the inelastic range, the seismic performance of the IDA’s dispersion using the inelastic spectral acceleration as the seismic IM is better than that using peak ground acceleration or elastic spectral acceleration.

This study provides a methodology to incorporate the dynamic bus stop simulation into a proposed static transit assignment model. It tries to combine the merits of the realism of dynamic models and the simplicity of static models in a single framework. An algorithm is developed to simulate any load profile of both passenger and bus arrivals. Then, the simulation results are used within the transit assignment process to allow a better line choice representation. A detailed illustrative example is given to validate the proposed assignment methodology performance. The resulted flows in some cases exceed lines capacity while conserving the static equilibrium principles. This capacity violation interprets the fact that some passengers may fail to board the first incoming bus of their desired line due to insufficient capacity. However, they wait until a vacant space is offered on the same line. In addition, a benchmark problem is solved to ease the comparison between the proposed methodology and the existing methodologies. It shows the methodology capability of incorporating different waiting time models to produce passengers’ flow on transit lines. It also indicates the importance of lines that might be neglected in other transit assignment models. This would highlight the methodology interpretation of passengers’ behavior in transit networks.

To obtain accurate finite-element (FE) models for structural health monitoring (SHM), effective modeling techniques are essential. This paper presents the process for establishing a 131-m large transmission tower’s SHM-oriented FE model. Incorporated procedures are appropriate modeling, manual tuning, model updating, and model validation. Through these works, a detailed realistic model that can reproduce all the experimental dynamic characteristics is obtained, and important conclusions about establishing SHM-oriented FE models for large steel pylon structures can be drawn accordingly: (1) it is necessary to model all the bar members using beam or truss elements of equivalent cross sections for local structural behavior exploration; (2) some components (e.g., ladders, steel plates, and rivets) are no influence on the structural overall stiffness, but their contributions to mass cannot be ignored in modeling; (3) the response surface (RS)-based FE model updating method is effective for complicated pylon models; (4) manual tunings are needed to ensure the quality of model updating.

Seismic risk assessment of unreinforced masonry (URM) buildings is an important process for seismic retrofit of essential facilities located in the central and southern United States (CSUS), as more than 30 % of facilities there are low-rise URM buildings. Although HAZUS, the current loss estimation package for natural hazards, provides a set of fragility curves for such structures as an essential tool for conducting seismic risk assessment, seismic performance level variation due to geometric characteristics is not explicitly considered. This study investigates the effect of geometric variation of low-rise URM structures on seismic fragility assessment. Utilizing URM building inventory information within the CSUS region, variables that describe the physical shape of URM structures are identified. A simplified composite spring model developed for URM structures is then utilized to monitor nonlinear seismic behavior. Finally, seismic fragility curves corresponding to various shape configurations of URM structures are developed and compared. The analysis confirms that the length of out-of-plane walls and the number of stories in URM buildings have significant effects on seismic risk. An increase in the wall length or the number of stories makes URM buildings more vulnerable. On the other hand, the perforation ratio does not significantly affect seismic performance. It is suggested that using a single set of fragility curves is not adequate for seismic risk assessment of low-rise URM buildings unless geometric variation is considered explicitly. In addition, comparing the fragility curves developed in this study with HAZUS data, it is clear that the seismic vulnerability of low-rise URM is underestimated in HAZUS for lower limit states and overestimated for higher limit states.

As a result of the large quantities of glass residues being generated, research is currently underway for efficient, economic and eco-friendly alternatives, among them the incorporation of recycled glass in mortar as a substitute for natural sand; this work has researched and studied recycled glass substitutions of 0, 15, 30, 60 and 100 %. A basic characterization of both sands was carried out with the aim of comparing both materials (granulometric profiles, density and absorption). Compressive and flexural strength were studied with regard to the mechanical behavior of the mortar in question; regarding deformation, the basic, drying and total shrinkage were determined. The results of the research show that the recycled glass sands are less dense than the standard sand used, and the latter has a higher absorption coefficient. With regard to compressive and flexural strength, the mortars with recycled glass reported lower resistance than the natural sand mortars, with the 15 % recycled glass combination being the closest to the natural mortar. On the other hand, in the case of deformation due to drying shrinkage (the most significant), the recycled mortars showed even more favorable results than the natural mortar; the 100 % glass content had the lowest shrinkage rate in the experimental phase. The study concludes that mortars with 15 % recycled sand may feasibly be used in applications with low mechanical requirements, with their low rates of shrinkage deformation being an additional advantage.

Ancient monuments have often sustained severe damage due to earthquakes. The examination of their dynamic behavior can reveal their vulnerability to different dynamic excitations. Ancient temples consisting of classical columns are of particular interest, due to their architectural features and complex geometry. The dynamic response of short free-standing classical columns is investigated in this study. Two small scale marble columns of the same size but with a different number of drums are subjected to harmonic, random and earthquake excitations. The effect of their geometrical features on their dynamic behavior is examined. Numerical models based on the finite element method can provide reasonable estimates of the dynamic response of classical columns but cannot predict all the attributes of their actual dynamic behavior.