ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING)
Year:2010 | Volume:11 | Issue:2|Papers Count:9

Engineering structures such as bridges, tunnels, dams or towers are beginning to approach their service lifetime. To give an example, more than 20,000 bridges in Germany currently require immediate rehabilitation; similar situations apply in other countries. Thus, efficient and cost-effective structural health monitoring systems are needed to ensure serviceability and structural safety through permanent monitoring and reliable safety assessment. Backed by the recent advances in engineering technologies and computing methods, structural health monitoring has the potential to accurately identify damages and deteriorations of structures at an early stage, resulting in significantly reduced repair and maintenance costs. In this paper, the design, implementation and evaluation of a novel generation of intelligent, self-managing structural health monitoring systems is presented, introducing a prototype called "autonomous monitoring system based on software agents" (AMBOS). It provides autonomous controls, executes relevant monitoring processes in real-time and supports the involved human experts in a pro-active fashion.

In this paper the results of an experimental study of the effect of freeze and thaw cycles on the bond between repair materials and concrete substrate is presented. The work was aimed at studying the effect of various factors such as initial curing periods and surface preparation method on bond strength. Old concrete samples were made based on BS6319, Part 4 standard. Smooth as-sawn and acid etching methods were used for preparation of concrete substrate surface. Ordinary concrete with cement type II and concrete containing microsilica were used as repair materials. Repaired samples were subjected to 10 to 100 freeze and thaw cycles based on ASTM C666. The bond between repair materials and concrete substrate was evaluated based on slant shear test method (BS, 1984). The obtained results are tabulated and presented in this paper.

The dynamic stability is studied for thin-walled structural elements with variable stiffness subjected to periodically alternating axial force in this paper. Here, the variation stiffuess means that it changes with periodically alternating axial force as for nonlinear geometry stiffuess matrix of thin-walled member. Damping is considered and the governing equations are expressed in terms of a system of two second-order differential equations of the Mathieu type, with periodic coefficients. MATLAB package is used to determine the stability boundary. Numerical example is presented for the dynamic stability boundary of a simply supported beam with I-shaped cross section. Comparison is made with finite element analysis. Considered damping, some conclusions are drawn out: Excited zone of thin-walled member is continuous, the dynamic instability is highly dominant in the first region while the second and third instability regions are of much less practical importance; The larger the ratio of damp, the less the dynamic instability region; The larger the ratio of damp, the more time dependent components of the load wanted, absorption of damping is commonly of no effect to prevent parametrically excited vibration from dynamic instability; Parametrically excited vibration considering damping is much more different from damped forced vibration in nature.

This study has carried out seismic hazard analysis and Peak Ground Acceleration (PGA) in different regions of Arak City located in Markazi province of Iran. Historical and instrumental earthquakes data sets from 4 B.C. to 2007 were used, and seismic sources up to 200km-radius surrounding Arak City were considered in modeling. In addition, seism city parameters were calculated by kijko (2000), and three Attenuation relationships were used with Logic Tree method. Analysis was conducted for 17 x 12 grid points over Arak region and province area with SEISRISK III (1987) software. Results were shown by PGA maps for four hazard levels.

The use of high strength concrete (HSC) has been studied for many years in developed and developing countries. Although, HSC has a few disadvantages, it has many advantages. The concrete with compressive strength (CS) levels in the range of 50 to 100 MPa, is called HSC. The most important property of HSC is 28-day CS as a criterion. Sometimes due to time limitations and construction project problems, estimation of 28- day CS based on 7-day CS can be useful. Based on many experimental tests and analysis of the results, three sets of equations are determined with ANN and Regression techniques are compared and the best is recommended.

In this paper, application of rectified square steel jackets for improving the hysteretic behavior of reinforced concrete column has been investigated. Deficient performance of square steel jacket due to out of plane bulging in cross section under moderate and severe earthquake excitations and having an advantage of taking less space after retrofitting, strengthening of square steel jacket in potential plastic hinge regions can be useful means for achieving appropriate performance of this type of steel jacket. In the present study, all of the analyses have been undertaken using ANSYS (version 10.0). In order to verify the accuracy and validity of the finite element modeling, the numerical results, obtained from nonlinear finite element analyses, have been compared with the available experimental data. Having verified the finite element modeling, a deficient RC column designed according to pre-1971 codes was selected and eleven specimens with different states of retrofitting details were used for reinforcement of square steel jacket in potential plastic hinge regions. Also, the effects of increase in thickness of plate stiffeners, geometric shape of stiffeners and stiffened length of column have been investigated. The results of analyses indicate that energy dissipation and shear strength at rectified steel jacketed specimens significantly are improved by increasing the thickness of steel plate stiffeners until achieving maximum flexural strength of cross section and also stiffened height of column. However, geometric shape of stiffeners does not have a drastic effect on the hysteretic behavior of retrofitted column.

Influence of adding finely crushed dune sand Sd to cement, on the physical-mechanical performances results primarily from two effects: a physical-chemical and a chemical effect. On one hand it modifies the hydration process of cement as well as the structuring of hydrated products, on the other hand, it reacts on the cementing medium and develops new hydrated products. These effects act simultaneously and in a complementary way on the final performance of cementing materials.In order to better understand the gain in strength of the premixed cement OPC of the finely crushed dune sand, the microstructural aspect has been examined. Mixtures of Sdlime pastes present a hydraulic setting which is due to the formation of a CSH phase. The latter is semi-crystallized. The study of mixtures Sd-lime paste is thus a simplified approach of that of the mixtures Sd-OPC in which the main reaction is the fixation, by the Sd, of lime coming from the hydration of C3S in the form of CSH.

Conservation of natural resources and rapid urbanization has prompted growing demand for natural aggregate by construction industry. This demand is compounded by considerable decline in the availability of good quality natural aggregate and enormous increase in the quantities of demolished concrete. The alternative materials to cement in terms of fly ash and other pozzolanic materials were evolved, popular alternative material to coarse aggregate are being explored. Recycled aggregate is one such alternative and the present research work is a step forward in developing the design parameters using stress block parameters. The objective of present investigation is to develop stress - block parameters for the design of reinforced recycled aggregate concrete members. To arrive at the objectives defined above, a comprehensive experimental programme was undertaken. The influence of replacement ratio, (Rr) the ratio of recycled coarse aggregate to total coarse aggregate (Rr=RCA/TCA) on mechanical properties of recycled aggregate concrete was studied. The scope of the investigation programme is defined to generate stress strain test data of concrete, viz; M15, M20, M25, M30, and M35 and five replacement ratios, viz; 0, 0.5, 0.75, 0.85, and 1.0 were considered. A total of 150 cylinder specimens' were cast for the stressstrain characteristics of hardened concrete.

The fracture of High Performance Concrete (HPC) occurs in a. very explosive manner without previously exhibiting any cracking pattern as a warning. By using special fibre cocktails, (combinations of steel and polypropylene fibres) the explosive failure behaviour of High Performance Concrete (HPC) may be avoided. With the variation of cocktail composition different seismic performance of the material could be adjusted. An experimental programme has been carried out to compare the behaviour of high performance concrete and cocktail fibre reinforced high performance concrete beam column joint under reversed cyclic loading. HPC mix has been designed to obtain a concrete grade of M 60.The mix was designed based on modified ACI 211 method suggested by M.S. Shetty [1]. Five numbers of exterior beam-column joints modeled to one fourth of a prototype of a building [10], designed according to Bureau of Indian Standards were cast and tested under reversed cyclic loading. The first specimen was made with high strength concrete and designed as per IS 456:2000 [16] and reinforced accordingly without considering the seismic requirement. The second specimen was made with high strength concrete and reinforcements in the beam column joint portion was detailed according to IS 13920-1993 [17], for seismic requirements. The remaining three specimens were similar to the first one but various combinations of cocktail fibre concrete in the joint region (constant %(1.5) of steel fibre and 0 to 0.4% of polypropylene fibre) were used. The cocktail fiber combinations of 1.5% of steel fibre and 0.2% of polypropylene fibre have best performance considering the strength, energy dissipation capacity, and ductility factor. Results indicate that the addition of polypropylene fibre to the steel fibre is optimum for a percentage of 0.2, which have more energy absorbing capacity, less joint rotation, more shear strength, more curvature ductility factor and less reinforcement strain.