سال:1389 | دوره: | شماره: |تعداد مقالات:10

Phosphogypsum is a by-product of phosphate fertilizer plants and chemical industries. As it is contaminated with the impurities that impair the strength development of calcined products, it can be used as partial replacement of cement. The present paper deals with the experimental investigation on compressive, tensile and flexural strength characteristics of partially cement replaced phosphogypsum concrete using 0%.,10%, 20%, 30% and 40% replacement with different water-binder ratios of 0040, 0.45, 0.50, 0.55, 0.60 and 0.65. The strength characteristics are studied by casting and testing a total of 450 specimens, which consists of 270 cubes, 90 cylinders and 90 beams for 7,28 and 90 days. It is shown that a part of Portland cement can be replaced with phosphogypsum to develop a good and hardened concrete to achieve economy; above 10% replacement of phosphogypsum in concrete lead to drastic reduction not only in the compressive strength but in the split-tensile strength also; the flexural strength decreases as width and number of cracks increases significantly at replacement above 10% of cement with phosphogypsum at different water binder ratios.

Polymer concretes (PC) were introduced to building and construction industry more than 50 years ago. Gradually, they became a suitable substitute for concrete .structures; however, their application was shortly diminished due to the higher costs. In this research a homemade cost-quality effective resin (unsaturated polyester) is used as binder in the polymer concrete production. Laboratory specimens made and evaluated for physical/mechanical tests. A comparative study was performed on the polymer concrete specimens, the ordinary Portland cement concrete (normal concrete) and the durable concrete specimens. It was found that the PC materials show much better physical/mechanical properties than the durable concretes.

The development of high strength concrete, higher grade steel, new construction techniques and advanced computational technique has resulted in the emergence of a new generation of tall structures that are flexible, low in damping, slender and light in weight. These types of flexible structures are very sensitive to dynamic wind loads and adversely affect the serviceability and occupant comfort. For a typical tall building, oscillations have been observed in the along wind and crosswind directions as well as in the tensional mode. To ensure the functional performance of tall flexible structures and to control the wind induced motion of the tall buildings, generally different design methods, various types of passive as well as active control devices and various types of aerodynamic modifications to the shape/geometry of the buildings are possible. This review paper presents an overview and a summary of past/recent work on various aerodynamic modifications to the shape of the buildings like comer cuts, chamfering of comers, rounding of comers, horizontal and vertical slots, dropping of comers, tapering etc. to reduce the wind excitation of tall flexible buildings and its application in some of the tall buildings across the world.

High strength concrete (HSC) provides high strength but lower ductility compared to normal strength concrete. This low ductility limits the benefit of using HSC in building safe structures. This means that a designer should be aware of limiting the amount of tensile reinforcement to prevent the brittle failure of concrete. Therefore the full potential of the use of steel reinforcement cannot be achieved. This paper presents a method to prevent the brittle failure of concrete beams. Five beams made of HSC were cast and tested. The cross section of the beams was 200x300 mm, with a length of 4 m and a clear span of 3.6 m subjected to four-point loading, with emphasis placed on the midspan deflection. The first beam served as a reference beam. The remaining beams had different tensile reinforcement and the confinement shapes were changed to gauge their effectiveness in improving the strength and ductility of the beams. The compressive strength of the concrete was 85 MPa and the tensile strength of the steel was 500 MPa and for the stirrups was 250 MPa. Results of testing the five beams proved that placing helixes with the right diameter and pitch in the compression zone of reinforced concrete beams improve their strength and ductility.

This paper is concerned with the study of the effect of combined horizontal and vertical accelerations on the seismic response of reinforced concrete structures. To achieve this objective, three reinforced concrete buildings representative of rigid, semi-rigid and flexible structures were analyzed in the nonlinear range using lumped mass and distributed mass models. The results obtained indicate that the inclusion of the vertical component has little effect on the storey drifts and base shears but can greatly influence the axial forces in the columns and the vertical displacements of girders.

A wind tunnel pressure measurements study was carried out to obtain the pressure distribution on a model (1:200) of an industrial structure with multi-segmental curved roof, under simulated open terrain conditions. The roof of the model was instrumented with pressure taps (area averaged) beneath and above the roof surfaces for both cases i.e., model with and without gable end walls. Pressure data were collected simultaneously beneath and above the roof surfaces of the model for various angles of wind incidence (q = 0° to 360° in steps of every 30°). In this paper, results pertaining to mean (C~pi C~pe) and standard deviation ( `Cpi,`Cpe) of internal and external pressure coefficients for flow direction from parallel (q = 0°) to perpendicular (q = 270°) to- the axis of the arch, for both cases are presented. The effect of gable end walls on Cpe and Cpe was also studied. Further, comparison of measured Cpe for flow direction q = 0° and 270° to the axis of the roof with the values given in various national/international codes of practice was also presented.

Results of an investigation conducted to evaluate the strength and flexure toughness of Hybrid Fibre Reinforced Concrete (HyFRC) containing different combinations of steel and polypropylene fibres are presented. An experimental programme was planned in which beam specimens of size 100 x 100 x 500 mm were tested under four point static flexural loading to obtain the flexural strength of HyFRC. In addition, cube specimens of size 150 x 150 x 150 mm were also tested to obtain its compressive strength. The specimens incorporated steel and polypropylene fibres in the mix proportions of 100-0%, 75-25%, 50-50%, 25-75% and 0-100% by volume at a total volume fraction of 1.0%. The flexural toughness parameters were obtained using procedure laid down in ASTM C-I018 C, JCI Method ASTM 1609/C 1609M and Post Crack Strength (PCS) Method. The results indicate that concrete containing a fibre combination of 75% steel fibres + 25% polypropylene fibbers can be adjudged as the most appropriate combination to be employed in HyFRC for compressive strength, flexural strength and flexural toughness.

Conventional methods of seismic rehabilitation with concrete shear walls or steel bracing are not considered suitable for some buildings as upgrades with these methods would have required expensive and time consuming foundation work. Supplemental damping in conjunction with appropriate stiffness offered an innovative and attractive solution for the seismic rehabilitation of such structures. This paper deals with the use of friction damper as a passive dissipative device in order to seismic retrofit of existing structures and discusses the design criteria and seismic analysis of a building. The structure is modeled using the finite element program Sap2000 and is analysed using both non-linear static pushover analysis and non-linear time history analysis.

Vibration monitoring of civil engineering structures has gained a lot of interest over the past few years, due to the relative ease of instrumentation and the development of new powerful. system identification techniques. The damage assessment consists of relating the dynamic characteristics to a damage pattern of the structures. This paper presents experimental results obtained within the framework of the development of a health monitoring system for civil engineering structures, based on the changes of dynamic characteristics. As a part of this research, Reinforced concrete beams subjected to cyclic loading to introduce damage. After each loading phase, an experimental modal analysis is performed on the beams with the impact hammer to obtain dynamic characteristics. Beams were excited with the impact hammer over a frequency range of interest 0-4000Hz. Frequency response functions (FRFs) were obtained using OROS Dynamic vibration analyzer. The FRFs were processed using NV Solutions modal analysis software to identify natural frequencies, Damping ratios and the corresponding mode shapes of the beams. A characteristic decrease of natural frequencies and an increase of structural damping were observed.

This study investigates the use of three different types of Epoxy Resin materialsviz., EXPACRETE SNE1, LAPOX B-47 and HARDENER K-46, and CONBEXTRA EP10, 65 & 120 for repairing the reinforced concrete beams. In this research, 6 standard size beams (150x230x1500mm) for M50 grade of concrete were distress in flexure by applying two points load by taking 90% of the ultimate load. Then, these distressed beams were repaired and retested up to ultimate failure load.The aim of this study is to determine the suitability of Epoxy Resin material type to be used in RCC beams for repairing and restoring good strength and for considering economical aspects. Hardened concrete specimens were tested for compression, and flexural test. The results of these experiments show that the beams repaired using Epoxy Resin material (EXPACRETE SNE1) gave higher increase in the ultimate load than other Epoxy Resin materials. The flexural strength increased significantly up to about 15 percent for concrete beams repaired with epoxy resin material (EXPACRETE SNE1) compared to other epoxy resin materials. Deflections were smaller in reinforced concrete beams with epoxy resin compared to conventional concrete beams. Compare to all the three types of epoxy resin materials used i.e. EXPACRETE SNE1 is cheaper than other two materials. Though reinforced concrete beams repaired with epoxy resins is costlier comparatively, it is cheaper than to reconstruct the structure.