Post‐earthquake fire resistance of CFRP strengthened reinforced concrete structures

Post‐earthquake fire (PEF) presents a high risk to buildings that have been partially damaged in a prior earthquake, particularly in urban areas. As most standards and criteria ignore the possibility of fire after earthquake, buildings are not adequately designed for that possibility, and thus, PEF is a high‐risk load needed to be scrutinized further, codified and become part of a routine design. An investigation based on sequential analysis inspired by FEMA356 is performed here on two RC frames, of three and five stories, at the Life Safety performance level and designed to the ACI 318‐08 code, after they have been subjected to a spectral peak ground acceleration of 0.35 g. A fire analysis of the weakened structures follows, from which the time it takes for the damaged structures to collapse is determined. As a point of reference, the fire resistance is also determined for undamaged structures and before the occurrence of earthquake. The results show that structures previously damaged by the earthquake and exposed to PEF are considerably more vulnerable than those that have not been damaged previously. A method using carbon fiber‐reinforced polymer as a means of relocation of plastic hinges away from the column faces towards the beams is introduced as a function of the time required for fire extinguishment or evacuation. This is carried out to increase the structural load‐carrying capacity, thus reducing the potential damage for the anticipated earthquake and thereby improve the PEF resistance. The results show a considerable improvement in the PEF resistance of the frames. While the investigation and the proposition relate to a certain class of structures (ordinary buildings, intermediate RC structures, three and five stories) and the results can therefore be applied only to the cases investigated, it is hoped that this study paves the way for further research into this very important phenomenon and leads to an eventual revision of codes. Copyright © 2013 John Wiley & Sons, Ltd.     

Two Novel Adaptive Transmission Schemes in a Decode-and-Forward Relaying Network

Wireless Personal Communications - Adaptive transmission in a cooperative network with a half-duplex relay operating in decode-and-forward mode is considered. The main purpose of the paper is...     

A simplified method for collapse capacity assessment of moment-resisting frame and shear wall structural systems

A simplified methodology for predicting the median and dispersion of collapse capacity of moment-resisting frame and shear wall structural systems subjected to seismic excitations is proposed. The method is based on nonlinear static (pushover) analysis. Simple mathematical models denoted as “generic structures” are utilized to model moment-resisting frames and shear walls. After examining a wide range of structural parameters of the generic structures, a comprehensive database of collapse fragilities and pushover curves (using ASCE 7-05 lateral load pattern) are generated. Based on the obtained pushover curves, closed-form equations for estimation of median and dispersion of building collapse fragility curves are developed using multivariate regression analysis. Comparing the estimates of the median collapse capacity calculated from the closed-form equations with the actual collapse capacities determined from nonlinear response-history analysis indicates that the simplified methodology is reliable. The effectiveness of this methodology for predicting the median collapse capacity of frame and wall structures is further demonstrated with two case studies of structural systems designed based on current seismic provisions.     

Optimal design of double-layer barrel vaults using genetic and pattern search algorithms and optimized neural network as surrogate model

This paper presents a combined method based on optimized neural networks and optimization algorithms to solve structural optimization problems. The main idea is to utilize an optimized artificial neural network (OANN) as a surrogate model to reduce the number of computations for structural analysis. First, the OANN is trained appropriately. Subsequently, the main optimization problem is solved using the OANN and a population-based algorithm. The algorithms considered in this step are the arithmetic optimization algorithm (AOA) and genetic algorithm (GA). Finally, the abovementioned problem is solved using the optimal point obtained from the previous step and the pattern search (PS) algorithm. To evaluate the performance of the proposed method, two numerical examples are considered. In the first example, the performance of two algorithms, OANN + AOA + PS and OANN + GA + PS, is investigated. Using the GA reduces the elapsed time by approximately 50% compared with using the AOA. Results show that both the OANN + GA + PS and OANN + AOA + PS algorithms perform well in solving structural optimization problems and achieve the same optimal design. However, the OANN + GA + PS algorithm requires significantly fewer function evaluations to achieve the same accuracy as the OANN + AOA + PS algorithm.     

Performance evaluation of different types of steel moment resisting frames subjected to strong ground motion through incremental dynamic analysis

Comparative studies on seismic performance for various types of steel moment resisting frames subjected to near field and far field earthquakes are performed through Incremental dynamic analysis (IDA) method in this study. Near field earthquake has a pulse like effects on the structures. It imports immediate force in very short duration to buildings. Therefore, destructive effects of surge energy are not negligible. Four intensity indices are used, namely, peak acceleration (PGA), spectral acceleration at the structure??s first-mode period (S_a(T₁, 5%)), spectral acceleration at the structure??s nth effective-mode period (S_a(T_n, 5%)) and the Spectral velocity at the structure??s first-mode period (S_v(T₁, 5%)). Numerical results illustrate that the intensity measure parameters related to ground velocity and the higher mode-related parameters present better correlation with the seismic responses of near source ground motion for given systems. The higher mode-related parameters are more suitable for tall systems subjected to near field earthquakes. Moreover, the chosen parameters S_a(T_n, 5%) and S_v(T₁, 5%) of near-fault impulsive ground motions enhance the performance of intensity measure of corresponding conventional parameters, i.e. S_a(T₁, 5%). A comparison for the special and intermediate steel moment resisting frames is made as regard to performance using IDA method. A more efficient performance is observed for the special moment resisting frames compare to intermediate ones.     

Nitrate removal using different carbon substrates in a laboratory model

Agricultural fields have been frequently identified as major contributors of nitrate leaching into surface and ground waters. Tile drains can act as direct pathways, transferring leached nitrate to surface water. Bioreactor filters are useful for the removal of nitrate from drainage waters; however, these filters require an external carbon supply to sustain denitrification. In this study, four organic carbon sources including wood, barley straw, rice husks, and date palm leaf, were used to enhance denitrification and the effects of water velocity and influent nitrate concentration on the nitrate removal were evaluated. Cumulative nitrate removal was highest for the date palm leaf treatments and was lowest for the wood treatments. The effects were in decreasing order for date palm leaf, barley straw, rice husks, and wood, respectively. The performance of the biofilters improved with increasing influent nitrate concentration and decreasing water velocity, allowing for high nitrate removal rates to be achieved. The results showed that all of the treatments had reduced the effluent nitrate concentrations below the USEPA maximum contaminant level for drinking water of 45 mg L(-1) nitrate at the end of the study.     

Risk-Based Design of Flood Control Systems Considering Multiple Dependent Uncertainties

Due to random behavior of flood events and inaccuracies in measurements, design, analysis, and operation of flood control systems are subjected to several uncertainties. An important aspect in developing stochastic models for evaluating and analyzing more than one uncertainty is the dependence or independence of them. In flood control projects, hydrologic, hydraulic, geotechnical, and economic uncertainties are important considerations. In this paper, a stochastic Monte-Carlo simulation – optimization modeling approach is described for risk-based design of flood control levees (as a common structural flood control measure): considering multiple dependent uncertainties. It has been applied to the Leaf River reach in Hattiesburg, Mississippi for testing and evaluation of modeling results. Unlike a deterministic model that yields just one set of values for system dimensions, the stochastic model solution gives a range of values for each of them. One of the major reasons for limited field application of uncertainty analysis is difficulties in performing the modeling results in real world contexts. For closing the gap between theory and reality, design charts are developed in this study. This helps decision makers in identifying design values with desired and accepted risks.     

A Novel Statistical Technique for the Estimation of DC Stability in Higher-Order Σ-Δ A/D Converters

The existing techniques available for the statistical estimation of the dc input signal stability in general-order Σ-Δ analog-to-digital (A/D) converters are based on the assumption that the constituent quantizer input signal has a Gaussian distribution. However, empirical investigations reveal that this assumption holds adequately true only for the special case of conventional first-order Σ-Δ A/D converters. This paper presents an alternative technique for the accurate estimation of the dc input signal stability for higher-order Σ-Δ A/D converters. This estimation technique is based on the practical assumption that the constituent quantizer operates in its overload-free region, permitting the characterization of the quantizer output signal digit-pattern for the determination of the statistical moments of the corresponding quantizer input signal. The resulting statistical moments are subsequently incorporated in a Gram-Charlier series for an accurate quasi-linear modeling of the quantizer. A typical application example is given to demonstrate the accuracy of the proposed statistical technique for predicting the existence of multiple regions of instability and stability in the Σ-Δ A/D converter operation, and particularly for predicting the point where the A/D converter operation becomes unstable.     

Effect of waste EVA and waste CR on high temperature performance of bitumen

In this study, waste polymer ethylene vinyl acetate (EVA) in three levels 3%, 5%, and 7% and waste crumb rubber in three levels 2%, 4%, and 6% as modifiers of bitumen 85/100 of Iran refinery have been used. After conducting a classical test involving softening point and penetration degree, the use of these polymers improves the classic properties of bitumen, and then in order to evaluate high temperature treatment of modified bitumen and its comparison with high temperature treatment of base bitumen, it is recognized that the combination of above additives improves the performance properties of base bitumen at high temperature.