Asian journal of civil engineering
Volume:15 Issue: 6, Dec 2014

The main objective of the current study is to utilize the capabilities of recently developed meta-heuristic algorithms for structural cost optimization of a one-way reinforced concrete ribbed slab simply supported at both ends. Two of these new and simple optimization algorithms, known as colliding bodies optimization (CBO) and democratic particle swarm optimization (DPSO), and a renowned optimization algorithm, PSO, are presented to solve cost optimization of a concrete ribbed slab. Although PSO is a very well-known and commonly used optimization algorithm, democratic PSO is an improved version of particle swarm optimization method. In DPSO the emphasis is placed upon improving the premature convergence phenomenon which is believed to be one of defects of the original PSO. CBO utilizes simple formulation to find optimum values and does not need any internal parameter. Performance of these algorithms is compared with harmony search. The results illustrate the power of the CBO and effectiveness of improvements of DPSO method in the present optimization problem.

The uncertain nature of future ground motions is leading to development of probabilistic structural damage estimation procedures. Fragility curves are useful tools for showing the probability of structural damage due to earthquakes as a function of ground motion indices. The contribution of this study is to develop the fragility curves for mid-rise RC frames designed according to the Iranian Seismic Design Code. These structures constitute the most vulnerable construction type in Iran well as several other countries prone to earthquakes. Sample 4, 6 and 8 story buildings were designed according to the Iranian seismic code. Incremental nonlinear dynamic analyses were performed for these sample buildings using ten near-fault ground motions to determine the maximum inter-story drift ratio. Based on those ratio fragility curves were developed in terms of peak ground acceleration for immediate occupancy and life safety damage levels with lognormal distribution assumption. The results show that sample frame structures do not satisfy performance objectives of Standard No. 2800.

In this study, uniform hazard spectra assessment is performed for the city of Shiraz and eight graphs are prepared to indicate the probabilistic estimate of spectral ordinates over bedrock in this area. For this assessment; first, earthquake catalogue and main active faults in a radius of 200 km are gathered and processed and then seismicity parameters are obtained by Kijko and Tavakoli methods, after that the results are introduced to the computer program of seismic hazard analysis «SEISRISK III» by three attenuation relationships and eventually the outputs are combined by logic tree method. The isospectrums are calculated in two levels of hazard in four soil types; which are needed for retrofit of building in Seismic Rehabilitation Code for Existing Buildings in Iran. The Results show that the recommended SA and what is achieved in this study for the return periods of 475 and 2475 years, are same together in maximum and mean amounts, respectively.

A time integration scheme is proposed for dynamic analysis of linear elastic problems. This method assumes higher order variation of the acceleration at each time step. Two variable parameters are used to increase the stability and accuracy of the method. In the proposed method, second order accuracy and unconditionally stable method is achieved for all values of the assumed parameters with and without numerical damping. Moreover, the proposed method controls numerical dissipation in the higher modes. Finally, the numerical results of the proposed method are compared with two classical methods; namely the average acceleration and the Wilson- methods.

This paper presents the test results of three precast and one monolithic connection in moment-resisting concrete frame subjected to constant axial compression and lateral reversed cyclic loads. The precast specimens had cast-in-place concrete connections with different details, namely straight spliced (PC1), U-shaped (PC2), and U-shaped with steel plate (PC3).The results for Hysteresis loops, strength, damping, energy dissipation and ductility are presented. Comparisons of performance parameters revealed that the behavior of PC1 was more similar to monolithic Specimen and it can be used in high seismic zones. The other two precast connections are recommended to be used in moderate seismic regions.

Configuration processing’ is a branch of knowledge that deals with the concepts andsoftware necessary for generation and processing of geometric configurations. ‘Formexalgebra’ and its programming language ‘Formian’ provide a convenient environment forconfiguration processing of all kinds. Architects and structural engineers working withstructural forms are among experts in many different disciplines that benefit fromconfiguration processing concepts and tools.The objective of the present work is to explore the capabilities of a particularconfiguration processing concept that is referred to as ‘novation’. The concept ofnovation is implemented as a ‘function’ in Formian. This function is an effectiveconfiguration processing tool. In particular, the function provides a powerful conceptualaid for creation of freeform configurations. In this paper, the emphasis is on the practical considerations and guidance forprocessing of forms, rather than involvement in details of the mathematical theory. Thepaper contains many examples providing an overall view of the capabilities of thenovation function.In using the concept of novation for processing of configurations, the following mainparameters are used for the control of the operation:(1) The overall guide for the formation of the configuration is provided byspecification of movements of points on or around a given configuration. The novationfunction will then cause the configuration to be shaped in ‘conformity’ (harmony) withthe specified movements (relocations). For example, the simple grid of Sketch (a),below, can be formed into the shape of Sketch (b) by specifying the relocations indicatedby the arrows.(2) There are a number of choices for the way in which conformity, in the context ofnovation, may be interpreted. This choice of the ‘interpretation of conformity’ is a keyparameter in creating the required shape. For example, a change of the style ofconformity for Sketch (b) will change the configuration of the grid into Sketch (c).

This article presents a realistic analogy, with practical applications, between green trees and manmade moment frames under similar loading conditions. The paper also introduces a new facet of bioinspiration which attempts to benefit from some of the natural design strategies involved in the structural performance of trees, rather than utilizing them as raw materials. The paper suggests that bioinspiration can help transfer and improve basic design concepts from trees to moment frames under seismic as well as gravity loading scenarios. For instance, it has been shown that earthquake resistant systems can best be realized by performing design led analysis rather than investigating analytic results and that structural design should be performance based rather than instruction oriented computations. In other words, it is preferable for earthquake resistant structures to be designed in accordance with observed rather than expected behavior, i.e., desirable response characteristics should be induced rather than investigated. These features constitute the core of the recently developed performance control (PC) methodology that aims at rational design of engineering structures under both service as well as extreme loading conditions. In the interim a number of new design formulae have also been introduced. Two examples have been provided to demonstrate the applications of the conceptual design similarities between green trees and earthquake resisting moment frames.

Energy-based methods for structural damage detection have been widely investigated in the last decade. In this paper, the energy balance concept used in these methods is proposed for integrated design of the steel frames equipped with added damper. The proposed procedure is based on the assumption that all of input energy is dissipated by added damper and plastic work done by structural elements (beams and columns). The required damping coefficient and cross sectional area of elements are determined by equating the total dissipated energy (energy capacity) to the input energy (energy demand) such that the target displacement does not exceed maximum displacement and uniform drift is reached. The total dissipated energy (energy capacity) is considered to be the sum of the energy dissipated by added damper and the hysteretic energy damped out by plastic work in structural elements. The proposed method is evaluated by numerical simulations. The method is applied for integrated design of two moment frames with added dampers. In both cases, push over analysis for behavior of the frames indicate that while the structural elements are reduced in size (compared to conventional design), the designed frames with added dampers have a good performance by developing plastic hinges in all beams.

The present study investigated the effect of fine aggregate characteristics namely individual size, grade and type on the Compressive, split tensile and flexure strengths of concrete mixes. Two types, river sand/ Natural sand and Foundry sand four single sizes namely 4.75mm, 2.36mm, 1.18 mm, 0.600 mm, were considered to prepare M20 and M40 concretes in the present research work. The suitability of Foundry sand (FS) to replace river sand in concrete production was addressed in this study. Slump test was performed on fresh concrete to evaluate workability while compressive, indirect tensile strength, flexure strength and Sorptivity tests were performed on hardened concrete. Strength and sorptivity characteristics measured optimal Values with mixes prepared using 0.6mm fine aggregate and concrete with foundry sand exhibited superior performance. Ultrasonic Pulse velocity (UPV) test was also conducted to assess the quality of concrete. The overall test results revealed that foundry sand can be utilized in concrete mixtures as a good substitute of natural sand. In addition to conservation of river sand, a better and meritorious way of disposing wastes is using Foundry sand in concrete production to our advantage.