ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING)
Year:2008 | Volume:9 | Issue:2|Papers Count:8

The influence of high temperature on microstructure and mechanical properties of cement paste is vital to characterize fire resistance. Some experimental investigations on the microstructure and compressive strength of pre-heated metakaolin-silica fume blended cement pastes are presented in this paper. The aim of this investigation is to study the effect of substitution of metakaolin (MK) by silica fume (SF) on thermal stability of Portland cement-MK blended pastes. The kaolinte was thermally activated at 850°C for 2 hours. The cement pastes were prepared using standard water of consistency. The pastes were kept in moulds at 20oC and 100% relative humidity for 24 hours and then hydrated for 28 days under water. The hydrated pastes were exposed for 2 hours to temperature 200, 400, 600 nd 800oC. The pre-heated specimens were tested for compressive strength, thermal stability, and microstructure and phase composition. The thermal shock resistance was performed on cement pastes after hydration. The results of investigation showed that the compressive strength of pre-heated blended cement increases with temperature up to 400oC and then, it decreases as the pre-heated temperatures increase up to 800oC. The replacement of Portland cement, PC, by 15% MK and 15% SF in cement pastes increases the thermal shock resistance by about 20 times than control.

Applying elastic methods in the design of steel moment resisting frames (SMRF) and not recognizing the redistribution of moments in the inelastic range, do not guarantee a suitable seismic behavior in earthquakes. In order to be able to predict and control the inelastic behavior under seismic loading and to determine the corresponding load factor, the design of SMRF is studied in this paper. Classic concepts of plastic analysis and genetic algorithms are combined to arrive at an optimal proportioning of the frame members. Various examples, along with studies on the parameters of the employed genetic algorithm are also presented within this work.

This article presents a research program on a structure representing a seven-story residential building tested on the shaking table in the NEES [6]. The building was designed using a displacement based capacity approach for a site in Los Angeles resulting design lateral force. The structure is composed of 2 main perpendicular walls connected by slotted connections. The numerical calculations have been made up to failure of the specimen, at the local but also at the global level, using multi-fiber beams. Constitutive laws are based on damage mechanics and plasticity to describe cracking of concrete and the plastic behavior of steel. It is shown that the model is able to describe the global behavior of the structure and qualitatively the distribution of damage at the base of the specimen.

Modal analysis is a process of describing a structure in terms of its natural characteristics which are the frequency, damping and mode shapes-its dynamic properties [1]. The change of modal characteristics directly provides an indication of structural condition based on changes in frequencies and mode shapes of vibration. This paper presents results of an experimental modal analysis of beams made with different materials such as Steel, Brass, Copper and Aluminum. The beams were excited using an impact hammer excitation technique over the frequency range of interest, 0–2000 Hz. Frequency response functions (FRFs) were obtained using OROS vibration analyzer. The FRFs were processed using NV Solutions modal analysis package to identify natural frequencies, Damping and the corresponding mode shapes of the beams.

The idea of using steel plate shear wall as a lateral load resisting system in design and retrofit of structures has attracted the attention of researchers and designers for more than three decades. In this research, the ductility of thin steel plate shear walls are studied based on ATC-24 protocol and Popov’s definition. Two three-story unstiffened steel plate shear walls were tested under cyclic loading. In these tests shear walls had rigid and simple beamto-column connections. For the plate of panels, low strength steel and for the boundary frame high strength steel were used. In addition, some other valid tests on steel plate shear walls with different configurations, which were done in the world also, were considered. The results obtained from all of the tests show that the ductility factor in thin steel plate shear walls according to ATC-24 protocol and Popov's definitions can be assumed about 6.5 and 13, respectively.

Concrete incorporating steel fibers poses difficulty in mixing, transporting, placing and compacting that may lead to voids in hardened concrete. The determination of fresh fiber reinforced concrete properties is therefore, important for satisfactory performance in hardened state. The present experimental study investigates effect of three fiber properties volume fraction of fiber, aspect ratio of fiber and diameter of fiber- on the rheological properties of high performance concrete with a parallel plate rheometer. The test result shows that yield stress and plastic viscosity are adversely affected by all the three parameters. Fiber volume concentration has the highest effect on the measured rheological parameters whereas fiber diameter has the least effect.

Expert system technology provides a new opportunity for organising and systematising the available knowledge and experience in the structural selection domain. Computerisation, in general, and expert system technology, in particular, can provide assistance for the engineers by giving much greater access to information, knowledge and expertise and by processing this information. This paper presents an interactive expert system called Structural Selection Expert System (SSE) that assists engineers and designers in the choice of the most appropriate structural system for a particular function to meet proposed criteria. It can be used as a teaching aid for architecture, civil engineering and structural design students.The paper explains why the selection of suitable structures for a particular function was considered appropriate for an expert system, then the knowledge acquisition techniques are described. The different tools used to develop expert systems are briefly discussed with emphasis on the implementation methodology and tools adopted in the research. The advantages of implementing the SSE using object-oriented development and Kappa-PC are presented. Knowledge representation in the SSE and the techniques adopted to represent the structural systems knowledge is discussed. The inference mechanism in the SSE is described in some detail, followed by hardware requirements for the system.

In this paper formulation and solution technique using Simulated Annealing for optimizing the moment capacity of steel fiber reinforced concrete beams, with random orientated steel fibers, is presented along with identification of design variables, objective function and constraints. Steel fibers form an expensive constituent of steel fiber concrete and therefore it is important to determine ways and means of using these fibers in a judicial way with care consistent with economy for achieving the desired benefits. The most important factors which influence the ultimate load carrying capacity of FRC are the volume percentage of the fibers, their aspect ratios and bond characteristics. Hence an attempt has been made to analyze the effective contribution of fibers to bending of reinforced fiber concrete beams. Equations are derived to predict the ultimate strength in flexure of SFRC beam with uniformly dispersed and randomly oriented steel fibers. Predicted strengths using the derived expressions have been compared with the experimental data. A reasonable agreement (within the range of ±20 percent!) was evident with different types of steel fibers, aspect ratio, and material characteristics. A computer coding has been developed based on the formulations and the influence of various parameters on the ultimate flexural strength is discussed. A computer algorithm that conducts a random search in the space of four variables-beam width, beam depth, fiber content and aspect ratio-to yield an optimum solution for a given objective function (ultimate moment (Mu)) is presented. The outlined methods provide a simple and effective tool to assess the optimum flexural strength of steel fiber reinforced concrete beams. Using the results obtained the influence of various parameters on the ultimate strength are discussed. Particular attentions are given to the construction practice as well as the reduction of searching space. It has been shown that within a reasonable and finite number of searching the developed algorithm is able to yield optimum solutions for the given objective function.