97 publications from this institution
Deterioration due to corrosion becomes a more serious problem when future earthquakes with unpredicted intensity and time are considered. Therefore, the prediction of performance levels of corroded reinforced concrete structures is important to prevent serious premature damage. In this study, a corroded, 50-year-old high school building was analyzed by considering corrosion effects and is presented here as a case study. The relevant data obtained from the structure were used to predict its performance level for different time periods by combining two major effects of corrosion. Deformation due to bond-slip relationships and loss in cross-sectional areas of reinforcement bars were examined as a function of corrosion rate for five corrosion levels. Plastic hinges were defined as a consequence of corrosion effects, and they were used to perform nonlinear push-over analyses. Incremental dynamic analysis was then performed for 20 individual earthquake ground motion records to predict the structure’s time-dependent performance levels as a function of corrosion rate. Results showed that corrosion had a serious effect on the performance levels of the school building considered in this study by decreasing bond strength.
Effects of crusher dust content in aggregate on properties of fresh and hardened concrete are not very well known. On the other hand, it is known that short discrete fibers delay the propagation of microcracks and improve some properties of concrete. In this research, the effect of crusher dust replacement levels of fine aggregate and hooked-end steel fibers with different aspect ratios and different volumes on some properties of concrete was investigated. All mixes were tested for compressive and splitting tensile strength, water penetration, flexural toughness energy and impact energy. Relations such as compressive strength/splitting tensile strength/water penetration depth/flexural toughness energy/impact energy-dust replacement level-fiber reinforcement index were also determined.
Compressive strength and modulus of elasticity of concrete are two important properties involved in the design of reinforced concrete members and sections. The main objective of this investigation was to investigate the effect of fiber aspect ratio (1/d) and fiber volume on the compressive strength and modulus of elasticity of fiber reinforced concrete (FRC), and to study the relationship between compressive strength and modulus of elasticity of FRC. in this investigation, 19 fiber reinforced concrete mixes were produced by adding three different hooked-end steel fibers of aspect ratio of 60, 75, and 83 and also six different volumes of fibers namely 0.5, 1.0, 1.25, 1.5, 1.75, and 2.0 % by volume of concrete were added for each aspect ratio. As a result, good relationships between compressive strength of FRC and the fiber reinforcement index (FRI = Vr .1/d) between modulus of elasticity and FRI, and between compressive strength and modulus of elasticity of FRC were obtained.
This study provides the experimental and statistical modeling in order to increase the performance of ultra high performance concrete (UHPC) within reducing the cement consumption. Also showing the effect of waste glass powder and nano silica fume on mechanical, rheological, and shrinkage properties. For this purpose, a fraction of binder was added with the range of 0–5% of nano-silica fume and fraction of Portland cement were substituted with 0–20% of waste glass powder, the maximum particle size of 63 μm. The mechanical properties were obtained by testing on 28 days compressive strength. The rheological property found by doing the flow test. Numbers and randomization orders of experiments were designed by central composite face-centered (CFC) and modeled by response surface methodology (RSM). The validity of models was controlled by analysis of variance (ANOVA). The study showed adding nano-silica and waste glass powder and especially their interaction improved the properties of UHPC.
This paper presents the results of an investigation on the effect of Portland cement replaced by fly ash or granulated blast-furnace slag on the concrete strength at different curing temperatures. Compressive strength results are analysed according to the hyperbolic strength-age function by introducing a power indexn. The regression analysis is done considering different n values andt o (final setting times) values.
Usually, a material of higher strength does not necessarily indicate in a higher structural performance. While a higher energy absorbing material usually expresses higher structural performance when failure happens. This study aims at finding the relation between 28-days compressive strength and Compression toughness factor of Ultra High Performance Concrete (UHPC) using varying range of five variables which include; Steel Fiber, Silica fume (SF), Cement 42.5, Superplasticizer (SP), and water to cemetiotious ratio (w/c) by Design of Experiments (DOE) methodology. The results shows the significant relationship between the Compression toughness factor and 28 days compressive strength of UHPC. The model is valid for the mixes made with 1.0 sand, 0.15-0.30 silica fume amount, 0.70-1.30 cement amount, 0.10- 0.20 steel fiber, 0.04- 0.08 superplasticizer (all values are by aggregate weight mass) and 0.18- 0.32 water to cementitious ratio.
Abstract Discarding of old rubber tires is indeed a very serious environmental problem all over the world represented by a high risk for uncontrolled fires and other environmental and health hazards. It was estimated that every year about one billion tires get to the end of their life span. Recently, the construction industry has taken up the challenge to incorporate recycled materials in concrete mixtures by means aggregate replacement. Nowadays, many researches are focused on investigating rubberized concrete as a structural material due to its enhanced properties such as ductility, energy dissipation and damping ratio. Previous studies have suggested the use of fine rubber particles rather than coarse ones when high strength concrete is targeted despite the fact that using coarse ones provide enhanced energy dissipation, damping ratio and vibration behavior. This study is intended to address the effects of utilizing significant amount of well graded fine and coarse rubber aggregates on the properties of high strength concrete. On the basis of the investigations some mechanical, durability and dynamic tests will be conducted on concrete with different rubber replacement percentages. The results of the experimental works have shown that it is possible to develop high strength concrete when well graded fine and coarse rubber particles is used to replace 25% percent of the natural aggregates. Furthermore, the vibration behavior of the concrete mixture was improved considerably when high content of rubber aggregates was added into concrete.
An experimental investigation was carried out to evaluate the seismic behaviour of 200 × 200 mm2 reinforced-concrete columns with an embedded drain pipe subjected to monotonic and reversed cyclic loading. Nine full-scale specimens were prepared, including two control specimens without an embedded pipe and seven specimens with a pipe embedded in the column core. Among the latter seven columns, two were highly confined using 8 mm dia. ties with 80 mm spacing, while a 200 mm spacing was used in the other columns. The test results indicated that the pipe adversely affected the column's load-carrying capacity, load–displacement response and ductility. The extent of the adverse effect was found to depend on the level of axial load, the degree of confinement and the distance of the pipe exit from the column base. Due to local stress concentration, some local damage was observed in the vicinity of the pipe exit, but the provision of high confinement in the pipe exit region significantly improved the overall behaviour of the column under reversed cyclic loading.
No abstract is provided for this article.
This paper aims to model the effects of five different variables which includes: cement content (C), the steel fiber amount (F), the silica fume amount (SF), the superplasticizer (SP), the silica fume amount (SF), and the water to cementitious ratio (w/c) on 28 days flexural toughness of Ultra High Performance Concrete (UHPC) as well as, a study on the variable interactions and correlations by using analyze of variance (ANOVA) and response surface methodology (RSM). The variables were compared by fine aggregate mass. The model will be valid for the mixes with 0.18 to 0.32 w/c ratio, 4 to 8 percent steel fiber, 7 to 13 percent cement, 15 to 30 percent silica fume, and 4 to 8 percent superplasticizer by fine aggregate mass.
One of the effective vibration control systems used for structures is the semi active tuned mass damper (STMD), which is popular since it is reliable and simple. STMD characteristics in the design for piled foundations are usually obtained by modelling the foundation raft only to incorporate the soil structure interaction (SSI). However, as it proposed in the recent studies the role of SSI and simulation of piled raft in the analyses proved to be very important in the determination of the STMD parameters. Hence, in this study, efficiency of STMD with respect to the control of seismic response of the structure, is studied by considering the soil-pile-structure interaction (SPSI). Nonlinear time history analysis is applied for a three-layered soil profile including pile foundations by using the well-known substructure (spring) model under two different ground motion records. In order to increase the accuracy of the results, soil profile with piles and building structure with STMD are considered all at once in a single model under the action of seismic loading, named as direct method. P-Y curves which are suggested by American Petroleum Institute (API) are used in the spring method for simulating soil-pile-structure interaction. The results showed that, adjusting the STMD characterizations on piled structures without considering the soil-pile-structure interaction may result to ineffective control of the seismic vibration and in the worst case may lead to amplification of the vibration of buildings.
