ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING)
Year:2013 | Volume:14 | Issue:6|Papers Count:11

In this study, the pozzolanic activity of pyrogenic nanosilicas with different specific surface areas (90m2/g, 200m2/g and 300m2/g) and aggregation states in lime and cement pastes and their effects on cement hydration have been investigated and compared to the influences of silica fume. The results show very rapid pozzolanic activity for the pyrogenic nanosilicas compared to silica fume and the rate increases with increasing specific surface area of nanosilicas. The large differences in the initial aggregate sizes of nanosilicas appear not to influence their pozzolanic activity. Nanosilicas accelerate cement hydration at early ages, however; at later ages, progress in cement hydration is reduced.

Geopolymer, an inorganic alumina silicate polymer is synthesized predominantly from silicon and aluminum materials or from by product materials like fly ash. The application of geopolymer technology substantially reduces the CO2 emissions by the cement industries and utilizes the solid waste materials such as fly ash. The fresh geopolymer mortar has stiff consistency and high viscosity. Further, the chemical reaction is fast. To evaluate the performance of geopolymer bricks, the tests namely Compressive Strength, Split Tensile Strength and Flexural strength are conducted. The objective of present investigation is to improve the quality of geopolymer mortar through special treatments and study the property, particularly the acid resistance. The durability tests such as water absorption test and acid resistance test (HCl and H2SO4) are also conducted. The main focus of the investigation is on optimum utility of the available fly ash and minimizing the water absorption and attaining high compressive strength.

This research aims to evaluate seismic behavior of moment frames (MF) and eccentrically braced frames (EBF), two common systems in most of the steel codes, due to far-field and near-field ground motions and to propose practical technique for acquiring demand distributions. Much intensive amounts and distinct patterns of demand are recognized according to near-field records. Also, the results demonstrate distinctive dissimilarities in demand distributions, their rate of changes and intensities and different higher mode participation patterns in MF and EFF systems. In addition, calculated R factors and these parameters in ASCE and UBC codes were compared thoroughly in this study.

In this paper using the eigenvalues and eigenvectors of symmetric and asymmetric of tridiagonal matrices with infinite dimension, inverse of these matrices are found. Moreover numerical method of finite difference is used for numerical modeling of engineering problems. Many engineering problems modeled by numerical methods result in solution of linear systems. Many of these linear systems are in tri-diagonal form. The inverse of this kinds of matrices have many applications. In this paper, response of linear and nonlinear structures resulting from different types of arbitrary dynamics and statics analyses are presented. The method of this paper provides closed form solutions for the analysis of structures under different static and seismic loadings.

This study has an objective to assess the utilization of grains epoxy polystyrene, or better known as Styrofoam that have light density, to serve as a partial substitution of sand in concrete materials. On the use of 5% EPS concrete compressive strength characteristics obtained amounted to 18.69 MPa (down approximately 20.9% of the normal mixture). While the use of 10% EPS, decrease concrete compressive strength of 21.67% ie 18.51 MPa. Modulus of elasticity of concrete decrease with the addition of the percentage of EPS, the use of EPS up to 40% decrease modulus of elasticity to be 16.219 MPa (down around 21%). The relationship between the modulus of elasticity (E), Specific Gravity (wc), compressive strength (f|/c) and the percentage of EPS (p) can be expressed in an empirical equation as follows: E=(wc)1,5·0,05·exp(-0,23·p)· Öf|c.

Spatially uniform ground motion is an assumption that is often made for structural analyses of arch dams. However, it has been recognized for many years that the ground motion is non-uniform due to large distances between the supports of structures such as bridges and dams. In this paper, a comprehensive investigation on the seismic response of dam-reservoir-foundation systems subjected to spatially varying ground motions is represented. Monte Carlo simulation approach is utilized for generating spatially non-uniform ground motions. A high arch dam is selected as numerical example to investigate nonlinear seismic behaviour of the coupled system. Reservoir is modelled as compressible material and the foundation is supposed to be mass-less medium. Seismic responses of the dam due to incoherency and wave passage are investigated. According to the results, the non-uniform input produces a response that is substantially different from the response produced with uniform input and can increases the structural response of the system.

In this paper it is attempted to study seismic responses of adjacent buildings subjected to earthquake induced pounding and to clarify pounding effects for various separation gaps. An analytical model of adjacent buildings resting on a half-space is provided whilst the buildings are connected by visco-elastic contact force model. Results show that with same separation gap, adjacent buildings with structure-soil-structure interaction (SSSI) are more likely to pound together than buildings with fixed-based (FB) condition. Also, building condition gets worse due to pounding because the seismic responses of buildings are unfavourably increased and the condition becomes more critical if the separation gap becomes narrower.

To improve the understanding of soil-pile interaction under horizontal dynamic loads and seismic events, a parametric centrifugal study was undertaken. Flexible piles with pile caps of different masses and instrumented with 20 strain gauges on the length of the pile were used for this purpose. The piles were impacted and the resulting displacement and  acceleration for different levels of force were measured. The equation of the movement of abeam equivalent to the pile under dynamic loading has been established and all the terms of this equation was determined using the experimental results. The term of inertia was divided into two parts, one related to the mass of the pile and the other related to the mass of the associated soil. The contribution of each term to the equation at different period (or time of) of vibration was illustrated. Distribution versus time of the displacements and the reactions of the soil at any depth were deduced from the profiles of the bending moments by a double integration and a double derivation respectively. Then the dynamic P-y curves or loops were constructed based on these results. The procedures of experimental tests and P-y curves construction are explained and a comparison between static and dynamic P-y curves is also indicated.

The use of recycled coarse aggregate (RCA) is replacing the natural coarse aggregate (NCA) in the concrete construction and has become popular to answer many environmental problems caused by the large volumes of construction and demolition waste (CADW). This paper presents the experimental results of mechanical properties of RCA concrete and compared with NCA concrete. Recycled coarse aggregate was obtained from crushed laboratory concrete specimens. Three grades of concrete M 20, M 25 and M 30 were produced with 50% and 75% of RCA. RCA concrete has compressive strength comparable to NCA concrete. RCA concrete has low modulus of elasticity compared to NCA concrete. This is mainly due to the attached mortar on the surface of RCA and highly angular nature of RCA leads to poor quality of coarse aggregate. In rapid chloride permeability test (RCPT), the chloride penetrating rate is “moderate” for the grade of concrete. From the results, it can be concluded that RCA can be recommended as structural concrete.

Steel-concrete composite construction has gained wide acceptance world wide as an alternative to pure steel and pure concrete construction. However, this system is a relatively new concept for the construction industry in Bangladesh. Reinforced concrete members are used in the framing system for most of the buildings since this is the most convenient & economic system for low-rise buildings. However, for medium to high-rise buildings this type of structure is no longer economic because of increased dead load, less stiffness, span restriction and hazardous formwork. Steel-concrete composite frame system can provide an effective and economic solution to most of these problems in medium to high-rise buildings. An attempt has been made in this study to explore the cost effectiveness of composite construction for medium to high-rise buildings in Bangladesh. A cost versus number of story curve shows that for low-rise buildings RCC frame system is cheaper than composite system. However, for buildings with number of stories greater than 15, composite construction becomes economic than RCC construction.

As the using of reinforced concrete shells structures with opening have many advantages that they permit to cover large area without using intermediate supports. They have light weights and require minimum amounts of material that it is required small thicknesses comparing to their spans. This investigation is carried out to study the efficiency of repair and strengthening of elliptical parablooid reinforced concrete shells, which loaded by four concentrated loads at the center of the opening. An experimental program of several different techniques in repair and strengthening is executed. The materials, which are considered for strengthening, are; Glass fiber reinforced polymers GFRP at different position of the shell bottom surface, steel strip and external tie. The initial and failure loads as well as the crack propagation for the tested shells at different loading stages, deflections and failure load for repaired and shells are recorded. A non-linear computer program based on finite element techniques is used to study the behavior of these types of shells. Geometric and materials nonlinearities are considered in the analysis. The efficiency and accuracy of computer program are verified by comparing the program results with those obtained experimentally for the control shell with opening and strengthened shells.