Civil and Environmental Engineering

The adsorption and treatment of organic contaminants using activated carbon from waste Nigerian bamboo was investigated. Waste Nigerian bamboo was carbonized at 400 o C-500 o C and activated with acid at 800 o C to produce granular activated carbon (GAC). Adsorption of organics from the refinery waste on the activated carbon produced was examined at 28 o C. The experimental batch equilibrium data was correlated by Freundlich and Langmuir isotherms. The adsorption data fitted well into the Freundlich isotherm. Breakthrough time of about 1.5 hours was observed for the fixed bed adsorption process. The organic concentration expressed as chemical oxygen demand (COD) was reduced from an initial value of 378 mg/l to 142 mg/l for the first hour, 143 mg/l for the second hour, 152 mg/l for the third and fourth hours, and 156 mg/l for the final hour., which also compare favorably with the refinery effluent specification of 150 mg/l Results from the study shows that waste Nigerian bamboo can be converted into high capacity adsorbent and used for the remediation of polluted industrial waste waters. @ JASEM

Abstract The classical first-passage reliability problem for linear elastic single-degree-of-freedom (SDOF) oscillators subjected to stationary and nonstationary Gaussian excitations is explored. Several analytical approximations are available in the literature for this problem: the Poisson, classical Vanmarcke, and modified Vanmarcke approximations. These analytical approximations are widely used because of their simplicity and their lower computational cost compared with simulation techniques. However, little is known about ...

This paper analyzes the dynamic behaviour of continuous bridges with transverse abutment restraint. These are a particular class of multi-span bridges whose transverse motion is restrained at the abutments.The transverse dynamic behaviour of these partially-restrained bridges is described by a model consisting of a two-dimensional simply-supported beam with intermediate visco-elastic restraints. A minimal set of characteristic problem parameters that completely describe the dynamic response is initially identified and an analytical solution is developed for particular configurations. The influence of these characteristic parameters on the properties of the dynamic systems are analyzed by considering the undamped and the damped free vibrations separately.Successively, in order to cover more general and complex configurations of realistic bridges, an extension of the definition of the characteristic parameters is proposed. The results obtained considering selected case studies are finally presented. Copyright © 2011 John Wiley & Sons, Ltd.

This paper uses a fully probabilistic approach to investigate the seismic response of multispan continuous bridges with dissipative piers and a steel���concrete composite (SCC) deck, the motion of which is transversally restrained at the abutments. This bridge typology is characterized by complex dual load path behavior in the transverse direction, with multiple failure modes involving both the deck and the piers. Proper assessment of the seismic vulnerability of these structural systems must rigorously take into account all pertinent ...

ABSTRACT Multi-span steel-concrete composite (SCC) bridges are very sensitive to earthquake loading. Extensive damage may occur not only in the substructures (piers), which are expected to yield, but also in the other components (e.g., deck, abutments) involved in carrying the seismic loads. Current seismic codes allow the design of regular bridges by means of linear elastic analysis based on inelastic design spectra. In bridges with superstructure transverse motion restrained at the abutments, a dual load path behavior is observed. The sequential yielding of the piers can lead to a substantial change in the stiffness distribution. Thus, force distributions and displacement demand can significantly differ from linear elastic analysis predictions. The objectives of this study are assessing the influence of piers-deck stiffness ratio and of soilstructure interaction effects on the seismic behavior of continuous SCC bridges with dual load path, and evaluating the suitability of linear elastic analysis in predicting the actual seismic behavior of these bridges. Parametric analysis results are presented and discussed for a common bridge typology. The response dependence on the parameters is studied by nonlinear multi-record incremental dynamic analysis (IDA). Comparisons are made with linear time history analysis results. The results presented suggest that simplified linear elastic analysis based on inelastic design spectra could produce very inaccurate estimates of the structural behavior of SCC bridges with dual load path.

Seismic isolation is a commonly used technique for protecting new and existing bridges. It usually consists of introducing isolation bearings between the superstructure and the substructures in order to decouple their motion and reduce the force demand due to the earthquake action. This paper deals with partially restrained seismically isolated continuous bridges, which are a particular class of isolated bridges whose transverse motion is restrained at the abutments.In this study a method is proposed for the preliminary design of these systems, which can be applied to both new and existing bridges. The dynamic problem is described in a variational form in order to obtain a simplified solution based on a pre-fixed transverse deformed shape of the deck. The objective of the design procedure is to control the internal actions on the piers by means of an appropriate configuration of the isolation bearings. Simple formulas for estimating the forces transmitted to the abutments and the superstructure transverse curvature demand are also derived, which account for the contribution of higher modes of vibration.Validation studies are undertaken for different bridge configurations, in order to assess the ability of the simplified method to control the force demand at the piers.

Earthquake ground motion excitation can induce pounding in adjacent buildings with inadequate separation distance. The corresponding risk is particularly relevant in densely inhabited metropolitan areas, due to the usually limited separation distance between adjacent buildings.Existing procedures to determine a minimum separation distance needed to avoid seismic pounding are based on approximations of the peak relative horizontal displacement between adjacent buildings, and are characterized by unknown safety levels. The present study proposes a probabilistic performance-based procedure for assessing the mean annual frequency of pounding between adjacent buildings. An efficient combination of analytical and simulation techniques is defined for the calculation of the pounding risk under the assumptions of linear elastic behavior for the buildings and of non-stationary Gaussian input ground motion.The proposed methodology is illustrated by estimating the probability of pounding between linear single-degree-of-freedom systems with deterministic and uncertain properties. Furthermore, the capabilities of the proposed method are demonstrated by assessing the effectiveness of the use of viscous dampers, according to different retrofit schemes, in reducing the pounding probability of adjacent buildings modeled as linear elastic multi-degree-of-freedom systems. The results obtained based on the proposed methodology are validated against purely numerical simulation results.► A probabilistic performance-based assessment of seismic pounding risk is proposed. ► Accurate risk estimates are obtained using analytical hazard functions. ► Analytical risk estimates are more accurate for well spaced building natural periods. ► Model parameter uncertainty significantly affects the pounding risk. ► Use of viscous dampers can dramatically reduce the risk of seismic pounding.

The paper illustrates a probabilistic methodology for assessing the vulnerability of existing reinforced concrete (RC) buildings with limited ductility capacity retrofitted by means of dissipative braces. The aim is to highlight the most important parameters controlling the capacity of these coupled systems and specific aspects concerning the response uncertainties. The proposed methodology is based on the use of local engineering demand parameters for monitoring the seismic response and on the development of component and system fragility curves before and after the retrofit. In the first part of the paper, the methodology is illustrated by highlighting its advantages with respect to the existing approaches. Then, its capability and effectiveness are tested by considering a benchmark two-dimensional RC frame designed for gravity-loads only. The frame is retrofitted by introducing elasto-plastic dissipative braces designed for different levels of base shear capacity. The obtained results show the effectiveness of the methodology in describing the changes in the response and in the failure modalities before and after the retrofit, for different retrofit levels. Moreover, the retrofit effectiveness is evaluated by introducing proper synthetic parameters describing the fragility curves and by stressing the importance of employing local engineering demand parameters (EDPs) rather than global EDPs in the seismic risk evaluation of coupled systems consisting in low-ductility RC frames and dissipative braces. Copyright © 2012 John Wiley & Sons, Ltd.

Abstract. This paper introduces an innovative reliability-based methodology for the seismic assessment of viscous/visco-elastic dissipative devices in single and/or coupled buildings. The general approach proposed in this study is specialized to the case of linear elastic systems in order to take advantage of an existing analytical technique for estimating the buildings' structural response statistics.

ABSTRACT The present study proposes a probabilistic performance-based procedure for assessing the mean annual frequency of pounding corresponding to a given value of the separation distance between adjacent buildings. The methodology is consistent with and can be easily incorporated into modern performance-based earthquake engineering frameworks.

SUMMARY: This paper proposes an analytical model and formulation for predicting the seismic response of isolated bridges with abutment transverse restraint. These are a particular class of multi-span continuous bridges in which isolation bearings are provided only between the piers top and the deck whereas seismic stoppers restrain the transverse motion of the deck at the abutments.

Una importante tappa di avvicinamento verso l'implementazione e la standardizzazione dell'approccio “performance-oriented” alla progettazione ed analisi strutturale è stata recentemente compiuta con la formalizzazione delle cosiddette procedure di prima generazione nei moderni codici anti-sismici Vision 2000 (SEAOC, 1995), FEMA 273 and FEMA 356 (1996) and ATC-40 (1996), Eurocode 8 (ECS 2005) and Norme Tecniche 2008).

ABSTRACT: The performance of multi-span steel-concrete composite bridges in recent seismic events has shown that these structures are very sensitive to earthquake loading. Extensive damage may occur not only in the substructures, which are expected to yield, but also in the components of the superstructure involved in transferring the seismic loads.

SUMMARY: The paper illustrates a probabilistic methodology for assessing the vulnerability of low-ductility reinforced concrete (RC) buildings retrofitted by dissipative braces. The aim is to highlight the most important parameters controlling the capacity of these systems and specific aspects concerning the response uncertainties.